Mainfi~1

ADVANCED CELL PLANNING Submitted By – MD. ASHRAFUL KABIR CHAPTER-1 INTRODUCTION 1.1 GLOBAL SYSTEM FOR MOBILE COMMUNICATION In 1982, the Nordic PIT sent a proposal to Conference Europeans des Posts et Telecommunications (CEPT) to specify a common European telecommunication service at 9QO MHz. A Global System for Mobile Communication (GSM) standardization group was established to formulate the specifications for this pan-European mobile cellular radio system. During 1982 through 1985, discussions centered around whether to build an analog or a digital system. Then 1985, GSM decided to develop a digital system. In 1986, companies participated in a field test in Paris to determine whether a narrowband or broadband solution should be employed. By May 1987, the narrowband Time Division Multiple Access (TDMA) solution was chosen. Concurrently, operators in 13 countries (two operators in the United Kingdom) signed the Memorandum of Understanding (GSM) which committed to fulfilling GSM specifications and delivering a GSM system by July 1, 1991. This opened a large new market. In 1989 the ownership of GSM standard was shifted to ETSI (European Telecommunications Standard Institute). ETSI has members from 54 countries inside and outside Europe, and represents administrations, network operators, manufacturers, service providers, research bodies and users.

The next step in the GSM evolution was the specification of the Personal Communication Network (PCN) for the 1800 MHz frequency range. This was named the Digital Cellular System (DCS) 1800.

The Personal Communication Services (PCS) 1900 for the 1900 MHz frequency range were also established for use in the Americas. GSM 400 is intended as a replacement of analog system around 450 MHz (NMT 450). GPRS (General Packet Radio Services) is an extension of the GSM architecture.

Packet data traffic runs on a new backbone IP network and is separate from the existing GSM core network that is used mainly for speech. GPRS was introduced in 2001. EDGE is a new modulation method enabling higher data bit rates introduced in R9.

Table 1-1: Frequency bands for the different GSM-based networks.

Network Type Frequency Band UL/DL GSM 800 GSM 900 GSM 1800 GSM 1900

824 - 849 / 869 - 894 MHz (880) 890 - 915 / (925) 935 - 960 MHz 1710- 1785 / 1805- 1880MHz 1850- 1910/1930- 1990MHz

1.2 NETWORK HARDWARE Every cellular system has hardware that is specific to it and each piece of hardware has a specific function. The major systems in the network are:

1

Figure: 1-1: GSM Based System Model OPERATION AND SUPPORT SYSTEM (OSS) For GSM system administration, the OSS supports the network operation by providing: • •

Cellular network administration Network operation and support.

SWITCHING SYSTEM (SS) The figure below shows the main components of the switching system. The Following is a brief description of each of these components.

Figure- 1-2: Switching System Mobile Services Switching Center (MSC) The MSC is responsible for the setup, routing, and supervision of calls to and from mobile subscribers. Other functions are also implemented in the MSC, such as authentication. The MSC is built on an AXE- 10 platform.

2

Visitor Location Register (VLR) The VLR is may be integrated with the MSC. This is referred to as the MSC/VLR. The VLR contains non-permanent information about the mobile subscribers visiting the MSC/VLR service area, for example, the current location area of the MS. Gateway MSC (GMSC) The GMSC supports the function for routing incoming calls to the MSC, where the mobile subscriber is currently registered. It is normally integrated in the same nods as the MSC/VLR. Home Location Register (HLR) In GSM, each operator has a database that holds information about the subscribers belonging to the specific Public Land Mobile Network (PLMN). This database can be implemented in one or more HLRs. Two examples of information, stored in the database, are the location (MSC/VLR service area) of the subscribers and the services requested. The HLR is built on an AXE- 10 platform.

A Authentication Center (A UC) For security reasons, speech, data, and signaling are ciphered, and the subscription is authenticated at access. The AUC provides authentication and encryption parameters required for subscriber verification and to ensure call confidentially.

Equipment Identity Register (EIR) In GSM, there is a distinction between subscription and mobile equipment. As mentioned above, the AUC checks the subscription at access. The EIR checks the mobile equipment to prevent a stolen or non-type-approved MS from being used.

Inter-Working Location Register (ILR) Around the world, there are markets demands for roaming capabilities with GSM. The ILR is the node that forwards roaming information between cellular networks using different operating standards. This currently exists only in the GSM 1900 network.

Short Message Service - Gateway MSC (SMS-GMSC) A Short Message Service Gateway MSC (SMS-GMSC) is capable of receiving a short message from a Service Center (SC), interrogating a HLR for routing information and message waiting data, and delivering the short message to the MSC of the recipient MS. Short Message Service - Inter- Working MSC (SMS-IWMSC) A Short Message Service Inter-Working MSC (SMS-IWMSC) is capable of receiving a mobile originated short message from the MSC or an ALERT message from the HLR and submitting the message to the recipient Service Center (SC).

3

Data Transmission Interface (DTI) DTI- consists of both hardware and software- provides an interface to various networks for circuit switched data communication. Through the DTI, users can alternate between speech and data during the same call. Its main function includes a modem and fax adapter pool and the ability to perform rate adaptation. It was earlier implemented as the GSM Inter- Working Unit (GIWU).

BASE STATION SYSTEM (BSS) The Base Station System (BSS) comprises two major components. These are: • Base Station Controller (BSC) and TRanscoder Controller (TRC) • Radio Base Station (RBS) or Base Transceiver Station (BTS)

Figure 1-3: Base Station System Base Station Controller (BSC) The Base Station Controller (BSC) is the central point of the BSS. The BSC can manage entire radio network and performs the following functions: • • • • • •

Radio network management Handling of the mobile station connection and handover Transcoding and rate adaptation Traffic concentration Transmission management of the BTSs Remote control of the BTSs

The Transcoding and rate adaptation function can be separated from the rest of the BSC and physically located together with the MSC. This will save on transmission resources between MSC and BSC.

4

Radio Base Station (RBS) /Base Transceiver Station (BTS): The Radio Base Station (RBS) or Base Transceiver Station (BTS) includes all radio and transmission interface equipments needed in one cell. Each BTS operates at one or several pairs of frequencies.

One frequency is used to transmit signals to the mobile stations and one to receive signals from the mobile stations (frequency division duplex). For this reason, at least one transmitter and one receiver is needed.

1.3 CELLULAR TECHNOLOGY Today's wireless communication systems are based on a composite wireless and wired system as shown in Figure 1.4, where the wireless segment of the communication system is shown as a cluster of seven hexagonal cells. This is a widely used cell plan, also known as the N = 7 frequency plan in which all the available channels are evenly distributed among seven cells. Each cell is essentially a radio communication center where a mobile subscriber establishes a call with a land telephone through the Mobile Telephone Exchange (MTX) and the Public Switching Telephone Network (PSTN).

This composite platform enables us to communicate with anyone at any time from any where within the service area. The MTX and PSTN are essentially multiple access points serving as system intelligence. It is this technology that has reached all walks of life, bringing communities and businesses

Figure 1-4: Basic elements of cellular communication system. closer than ever before. Designing, implementing, and maintaining this complex network is challenging task that falls under several engineering disciplines such as RF propagation, antenna engineering, frequency planning, traffic engineering, and cell site provisioning. A good compromise between theory and practice is the essence of this communication system.

5

1.4 CELLULAR FREQUENCY BANDS Due to the rapid growth of cellular traffic in recent years, it was necessary for the federal regulatory authority to allocate new frequency bands. As a result, rapid technological growth took place. A brief description of these technologies and the supporting frequency bands are giver in the following subsections.

10'8Hz Radio Wave Microwav Infrared Visible Ultra Gamma Cosmic e Ray Light Violet 10<Hz

s

10 Hz

10" Hz

10" Hz

ls

10 Hz

x-ray 10<6Hz

10" Hz

Figure 1-5: Electromagnetic spectrum.

Table 1.2: Communication Sub-bands Frequency Very Low Frequency (VLF) Low Frequency (LF) Medium Frequency (MF) High Frequency (HF) Very High Frequency (VHF) Ultra High Frequency (UHF) Super High Frequency (SHF) Extra High Frequency (EHF)

Range 3 to 30 KHz 30 to 300 KHz 300 to 3000 KHz 3 to 30 MHz 30 to 300 MHz 300 to 3000 MHz 3 to 30 GHz 30 to 300 GHz

1.4.1 North American AMPS and TDMA Bands In 1974, the Federal Communication Commission (FCC) allocated a 40 MHz band, known as the NonExpanded Spectrum (NES), in the 800- 900 MHz range for cellulat application. The AMPS (Advanced Mobile Phone System) standard, introduced in 1979 was subsequently adopted by the FCC. Licenses to operate these frequencies were issuec in 1982 for wireline (Band B) and non-wireline (Band A) markets. Because of the rapu growth of cellular traffic, an additional 10 MHz band, known as the Expanded Spectrun (ES), was allocated. Cellular telephony provides full-duplex communications, whicl requires simultaneous transmission in both directions: 1. Forward Path or Downlink 2. Reverse Path or Uplink A 45 MHz guard-band is provided to avoid interference between Tx/Rx channels i shown in Figure 1.6

The Available frequency bands are further divided into several sub-bands. Each band occupies 12.5 MHz, of which 10 MHz is NES and 2.5 MHz is ES. Being a multiple access technique, these bands are divided into several channels of 30 kHz each, and each channel is assigned to a subscriber. This arrangement provides 10 MHz/ 30 kHz = 333 channels per band in the NES and 2.5 MHz/ 30 kHz = 83 channels per band in the ES. The total number of channels per band is therefore 333 +83 = 416 in each band. Among them, 21 channels are used as control channels, which are used for channel

6

assignment, paging, messaging, etc. The remaining 395 channels are used as voice channels for conversations.

Figure 1-6: Cellular band allocation.

With the advent of AMPS, which is based on Frequency Division Multiple Access (FDMA), rapid technological growth took place. In the 1990s, additional communication standards were proposed for cellular, such as Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA).

1.4.2 North American CDMA Bands The North American CDMA standard (IS-95) was introduced in 1994. It is based on the Spread Spectrum (SS) technique in which multiple users have access to the same band. This is accomplished by assigning a unique orthogonal code (Walsh code) to each user. The spreading is also accomplished by means of the same code. This code is generated from apseudonoise (PN) sequence whose chip rate (switching rate) is many times that of the input binary data. The chip rate of the PN sequence was chosen to be approximately 1.25 MHz to derive 10 different frequency bands from the existing 12.5 MHz cellular carrier (A or B). Each of these bands can support 64 Walsh codes. CDMA air-link is based on a forward link and a reverse link, separated by 45 MHz. This is similar to AMPS and TDMA. The forward link is comprised of four different link protocols: 1. A pilot channel 2. A paging channel 3. A sync channel and 4. A traffic channel.

7

The reverse link is based on two different protocols: 1. An access channel 2. A traffic channel.

It has been claimed that CDMA cellular will outperform the existing TDMA cellular. At present, CDMA trials are being carried out by several operators in North America.

1.4.3 North American PCS Bands The North American Personal Communication Services (PCS) standard was introduced in 1994. Six different bands are designated for Major Trading Areas (MTAs) and Basic Trading Areas (BTAs). All MTAs are allocated a 15 MHz band, whereas all BTAs are allocated 5 MHz bands for a total of 60 MHz bands. This is also a full-duplex system having a 20 MHz band gap. This band gap is allocated to unlicensed operators for voice and data at 10 MHz each.

1.5 SALIENT FEATURES OF CELLULAR RADIO 1.5.1 Mobility Mobility is one of the major features of cellular communication system. It implies that a cellular call, originating from anywhere, any time within the service area, would be able to maintain the same call without service interruption, while in motion. This is attributed to the built-in-hand-off mechanism, which is a process of changing the carrier frequency. Its primary purpose is to assign a new frequency while a mobile moves into a new cell. This is accomplished by setting a hand-off threshold; that is, if the received signal level is too low and reaches a predefined threshold, the system controller - namely the mobile switching center provides a stronger free channel (frequency) from an adjacent cell. This process continues cell to cell as long as the mobile is in the coverage area, maintains the call, and is also in motion.

1.5.2 Capacity Channel capacity is measured by the available voice channels per cell, translated into Erlangs.

Because there are 21 control channels, the number of voice channels is 333 - 21 = 312 in the NES and 416 - 21 = 395 in the ES. The channel capacity per cell or per cluster in a seven cell plan can be evaluated as: NES channel capacity = 312 / 7 = 44 voice channel per cell = 35 Erlangs / cell @ 2% GOS = 35 * 7 = 245 Erlangs / cluster @ 2% GOS = 7350 subscribers (@ 30 subs / Erlangs typical) Similarly with ES, the channel capacity becomes ES channel capacity = 395 / 7= 56 channels per cell = 46 Erlangs / cell @ 2% GOS = 46 * 7 = 322 Erlangs/cluster @ 2% GOS = 9660 subscribers (@ 30 subs / Erlangs typical)

8

Assuming 10 square miles/cell in a rural area, a cluster of seven cells translates into 7,350 subscriber /7,000 square miles in the NES and 9,660 subscriber 77,000 square miles in the ES. 1.5.3 Frequency Reuse Because there are a limited number of channels, these channel groups are reused at regular distance intervals. This is an important engineering task that requires a good compromise between capacity and performance.

Figure 1-7: The N=7 frequency reuse plan.

The mechanism that governs this process is called frequency planning. Several frequency planning techniques are available today. One of the most widely used frequency planning technique is the N=7 frequency plan. In this plan, all the available channels are divided into 21 frequency group, numbered 1 to 21. These frequency groups are then evenly distributed among seven cells, three groups per cell as shown in finger 1.7. This group (cluster) of 7 cells is then reused along with the associated frequency groups according to figurel.7, where the original cluster is surrounded by six additional clusters. A 7-cell cluster is further surrounded by 12 clusters (not shown). In this manner, a given service area can be covered by clusters of cells with frequency ruse, thus providing mobility and capacity. However, with the advent of subscriber growth, the existing frequency plans do not provide adequate service due to limitations such as co-channel interference and capacity. Therefore, a mechanism is needed to enhance cellular performance and capacity.

9

1.5.4 Roaming There are many cellular operators within the same city, using different switches, radios, and cell site equipments. But a subscriber is registered to one operator only. As a result, an agreement between these operators is needed to provide services to any subscriber irrespective of a call's origin. This is accomplished by means of a separate link between various switches, which is established by the IS 41 link protocol (figure 1.8). A mobile moving out of its own territory and establishing a call from a foreign territory is known as a roamer and the process itself is known as roaming. Roaming enhances mobility.

Figure 1-8: Illustration of roaming. A mobile from a host system moving into a foreign system is designated as a roamer. Communication can take place if there is a link (IS-41) between mobile switches.

1.5.5 Data Transmission Data transmission over the analog cellular channel is a new feature in today's cellular communication systems. This is attributed to the recent introduction of Cellular Digital Packet Data (CDPD). It is based on the existing cellular networks and uses an unused AMPS channel from a given frequency set in a cell site. Numerous services can be performed and received over the CDPD channel, including fax transmission, computer data transmission, stock exchange portfolio access, news wire service access, commodity price list access, travel information, and many more services that currently rely on e-mail. The CDPD channel is composed of a Forward CDPD (FOCDPD) channel and a Reverse CDPD (RECDPD) channel over which data transmission takes place between the base station and the mobile. Data transmission is based on encoding 47 data bits into a (63, 47) ReedSolomon code, which can correct as high as (63-47)/2=8 errors. This encoded word (block) is then transmitted by means of GMSK modulation at 19.2 Kbps. In GMSK modulation, the power spectral

10

density is such that more than 90% energy is retained within a transmission band-width of 19.2*1.2=23kHz, which is sufficient for the available 30-kHz channel spacing. As a result, adjacent channel interference is greatly reduced and is expected to be lower than TDMA. On the receiving side, the RF signal is demodulated, decoded and finally the original data are recovered.

11

Chapter-2 FREQUENCY GUIDELINES 2.1 INTRODUCTION The GSM systems are required to operate in the following frequency bands, with a carrier spacing of 200 kHz: Table 2-1: Frequency band of GSM 800 MS transmit, Base receive Base transmit, MS receive

824-849MHz 869-894MHz

Table 2-2: Frequency band of GSM 900 (values in parentheses refer to E- GSM) MS transmit, Base receive Base transmit, MS receive

(880) 890-9 15 MHz (925) 935-960 MHz

Table 2-3: Frequency band of GSM 1800 MS transmit, Base receive Base transmit, MS receive

1710-1785 MHz 1805- 1880 MHz

Table 2-4: Frequency band of GSM 1900 MS transmit, Base receive Base transmit, MS receive

1850-1910 MHz 1930- 1990 MHz

2.2 EQUIPMENT CHARACTERISTICS In this section, the Equipment characteristic references are taken from ERICSSION RBS 2000 series.

In the GSM specifications reference, sensitivity levels are mentioned. The BTSs, as well as the MSs, must meet some predefined performance values in terms of FER, BER, and RBER, defined in the GSM specifications. The actual sensitivity level is defined as the input level for which the performance is met, and should be less than a specified limit, called the reference sensitivity level. It should be noted that these sensitivity figures may change, for example, at high temperatures (exceeding 30째C) and in hilly terrain.

12

RBS2000 RBS 2000 is the second generation of Ericsson BTSs for GSM. For RBS 2101, 2102, and 2202, functional units, as for example, combiners are included in a Combining and Distribution Unit (CDU).

There are three different CDU types, A, C+, and D, all with different characteristics. When selecting CDU type, there are three different alternatives.

•

Maximum Range (CDU-A): It is designed to maximize the output power and can be used together with a Tower Mounted Amplifier (TMA).With this alternative, up to 2 TRUs can be connected to one antenna (using a cross polarized antenna) in a cell, but are configurable to up to 6 TRUs (having three antennas per cell).

•

Standard (CDU-C+): It is contains a hybrid combiner, which allows 4 TRUs to be connected to one antenna (using a cross polarized antenna) in a cell, but is configurable for up to 12 TRUs (having three antennas per cell). There are two versions, one for Standard GSM (900/1800/1900) and one for Extended GSM (900 only).

•

High capacity (CDU-D): It contains a filter combiner, which makes it possible to connect up to 12 TRUs to one antenna (using a cross polarized antenna) in a cell. Using filter combiners, it is not possible to perform synthesizer frequency hopping, only base band hopping.

There is another alternative, Smart Range, which allows a CDU -A and CDU-C+ to be combined in the same cell. This solution combines high coverage with high capacity, up to 6 TRUs per cell can be connected using 2 antennas.

For RBS 2206 and RBS 2106 there exist two different types of CDUs, F and G, both with different characteristics and the possibility to be used together with TMA. Both types of CDUs make it possible to support 3*4 configurations in one cabinet. The antennas referred to are cross-polarized: •

CDU-F. It contains a filter combiner, which makes it possible to connect up to 12 TRXs to one antenna in a cell. It is not possible to perform synthesizer frequency hopping, only base band hopping.

•

CDU-G. With CDU-G the RBS 2206 can be configured in two modes: capacity mode or coverage mode. In capacity mode up to 12 TRXs can be connected to 3 antennas in a cell. It supports both synthesizer hopping and base band hopping.

Increased coverage with CDU-G can be achieved on RBS 2206 and 2106 by use of Transmitter Coherent Combining (TCC). This features increase the EiRP with 2.5 dB compared to the output power of a coverage configuration. A prerequisite of TCC is that the dTRU hybrid combiner is used.

When TCC is used, the gain should be added to the link budget. Software Power Boost can be used to improve the downlink output power for RBS 2000 and, thus, achieve better coverage. A prerequisite is that CDU-A, CDU C+ or CDU G is used and that each cell is equipped with 2 TRUs for this carrier. Separate TX antennas are used or the 2 transmitters. TX- diversity is used to obtain a downlink diversity gain of 3 dB, which should be added to the link budget. The RBS 2106 and 2206 is a macro base station supporting up to 12 TRUs per cabinet, which can be configured for one, two or three sector cell. The micro base station RBS 2302 is not equipped with a CDU. Three RBS 2302 can be connected to build up to six TRUs per cell (note: BTS 7.1 required). Software Power Boost can also be used together with RBS 2302. The RBS 2401 is the first dedicated pico radio base station, designed for indoor applications. It is equipped with 2 TRXs.

13

The outdoor power, sensitivity, and minimum carrier separation of the RBS 2000 series are listed in Table 2-5, Table 2-6, and Table 2-7.

Table: 2-5: Outdoor power, Sensitivity, and Minimum Carrier Separation of RBS 2000 (GSM 900) CDU/RBS Output Power [dBm] Sensibility [dBm] Minimum Carrier Separation [kHz] A 44.5 -no1 4003 C2 41.0 -no1 4003 1 c+ 41.0 -no 400J C+(E-GSM) 40.5 -109.5 4003 D (E-GSM) 42.0 -no 600 F 42.5/43.06 -no1 400/6006 G 42.5/43.07 -no1 400 RBS 2302 33.0 -107 400 4 RBS 2401 19.0 -100 400 Table: 2-6: Output power, Sensitivity, and Minimum Carrier Separation of RBS 2000 (GSM 1800) CDU/RBS

Output Power [dBm]

Sensitivity [dBm]

A C2 C+ D F G RBS 2302 RBS 2401

43.5 40 40 41 41.0/42.06'8 41.0/44.5â&#x201E;˘ 33 224

-no1 -no1 -no1 -no1 -no1 -110' -106 -100

Minimum Carrier Separation [kHz] 4003 4003 4003 1000 400/8006 400 4003 400

Table: 2-7: Output power, Sensitivity, and Minimum Carrier Separation of RBS 2000 (GSM 1900) CDU/RBS Output Power [dBm] Sensitivity w/o TMA Minimum Carrier [dBm] Separation [kHz] A 43.5 -111.51'/N/A 4003 C2 40 -111. 51'110 4003 1 C+ 40 -111. 5 '110 4003 G 41.0/44.5 -111. 51'110 400 RBS 2302 33 N/A/-106 400 4 RBS 2401 22 N/A/-100 400 1 With TMA, the sensitivity is -111.5 dBm. This sensitivity figure applies for antenna feeders with up to 4 dB loss. If the loss between the TMA and the BTS exceeds 4 dB, the sensitivity is decreased.

2

CDU-C is today replaced by CDU-C+

3

The CDU can, from a radio performance perspective, handle 200 kHz carrier separation, but bursts may then be lost, due to low C/A. From a system point of view, the consequences of going below 400 kHz are not fully investigated. Problems with, for example, standing wave alarms may occur.

Thus, it is recommended to keep a 400 kHz carrier separation.

14

4

Since the two TRXs are combined inside the cabinet, the output stated is obtained on both antenna connectors and contain the signal from both TRXs. 5

These sensitivity figures apply for antenna feeders with up to 4 dB loss. If the loss between the TMA and the BTS exceeds 4 dB, the sensitivity is decreased.

6

If 400 kHz carrier separation is used the output power is 42.5 dBm (GSM 900)741.0 dBm (GSM 1800).

7

0utput power is 42.0dBm (GSM 800/GSM 900)741.0 dBm (GSM 1800) if hybrid combiner is used in the dTRU. 8

0utput power is 41 dBm if hybrid combiner is used in RBS 2106.

2.3 CELL COVERAGE When planning a system it is not sufficient to use this sensitivity level as a planning criterion. Various margins must be added to obtain the desired coverage. In this section, these margins are discussed, and the planning criteria used in different types of environments are presented. Furthermore, the principles of how to perform coverage acceptance tests are described.

2.3.1 DEFINITIONS Required Signal Strength: Margins must be added to the sensitivity level of an MS to compensate for Rayleigh fading, interference and body loss. The obtained signal strength is what is required to perform a phone call in a real- life situation and will be referred to as SS req. SSreq is independent of the environment.

SSreq = MSsens +RFmarg +IFmarg + BL Where, MSSens = MS sensitivity RF marg = Rayleigh fading margin IF marg = Interference margin BL = Body loss

15

Design level Extra margins must be added to the SS req to handle the log- normal fading, as well as, different types of penetration losses. These margins depend on the environment and on the desired area coverage.

The obtained signal strength is what should be used when planning the system and it will be referred to as the design level (SSdesign). This signal strength is the value that should be obtained on the cell border when planning with prediction tools, such as TEAMS Cell planner.

The design level can be calculated from: SSdesign SSdesign SSdesign

= SSreq + LNFmarg (o) MS outdoor = SSreq + LNFmarg (o) + CPL MS in-car = SSreq + LNFmarg (0+1) + BPLmean MS indoor Where, LNFmarg (o) = Outdoor log-normal fading margin.

LNFmarg (o+i) = Outdoor + indoor log- normal fading margin.

CPL = Car penetration loss BPLmean = Mean building penetration loss

2.3.2 MARGINS Rayleigh Fading Rayleigh Fading is due to multi-path interference and occurs especially in urban environments where there is high probability of blocked sight between transmitter and receiver. The distance between two adjacent fading dips is approximately A/2. The required sensitivity performance of GSM in terms of FER, BER, or RBER2 is specified for each type of channel and at different fading models (called channel models). The channel models reflect different types of propagation environment and different MS speeds. The sensitivity is measured under simulated Rayleigh Fading conditions for all the different channel models and the sensitivity is defined as the level where the required quality performance is achieved. In a noise limited environment, the sensitivity is the level, listed previously.

This would mean that Rayleigh Fading is already taken into consideration in the sensitivity definition.

However the GSM standard allows worse quality for slow MSs (3 km/h) than for fast moving MSs. The sensitivity performance under fading conditions corresponding to an MS speed of 50 km/h (called TU 50), is in accordance with good speech quality, while the sensitivity performance at 3 km/h (TU 3) does not correspond to acceptable speech quality. TU means Typical Urban. In order to obtain good speech quality even for slow mobiles, an extra margin (RF marg) is recommended when planning. From experience, 3dB margin seems adequate. In a frequency hopping system, the Rayleigh Fading dips are leveled out and there should be no need for a Rayleigh Fading margin. But since a Broadcast control Channel (BCCH) never hops, the Rayleigh Fading margin is recommended in cell coverage estimations, regardless of using frequency hopping or not. Also, antenna diversity reduces the effect of Rayleigh Fading, but in a different way than frequency hopping. Therefore diversity gained is still relevant in frequency hopping systems.

Note: For simplicity, the diversity gain figure is considered independent of frequency hopping and MS speed distribution.

16

Log-Normal Fading The signal strength value computed by wave propagation algorithms can be considered the mean value of the signal strength in a small area with a size, determined by the resolution and accuracy of the model. Assumed that fast fading is removed, the local mean value of the signal strength fluctuates in a way local mean is dB, compared to the predicted mean, has an almost normal distribution. Therefore, this variation is called log-normal fading. The received signal strength is a random process, and it is only possible to estimate the probability that the received signal strength exceeds a certain threshold. In the result from a prediction (for example, with TEMS Cell Planner), 50% of the locations (for example, at the cell borders) can be considered to have a signal strength that exceeds the predicted value. In order to plan for a probability of more than 50% of signal strength above the threshold, a log-normal fading margin (LNF marg) is added to the threshold during the design process.

Jakes's Formula A common way to calculate LNF marg is to use Jakes's Formula. In Jakes's Formula, simple radial path loss dependence (I/Rn) is assumed to calculate the percentage of area within an omni-cell with a signal strength that exceeds a certain threshold. The threshold is related to the percentage of locations at the cell border that have a signal that exceeds the same threshold. The border coverage corresponding to a desired area coverage, is strength in the MS. The margin in dB (LNF marg) to go from the original 50% coverage at the cell border to the given border percentage can be calculated.

Simulation of Log-Normal Fading Margin in a Multi-Cell Environment A disadvantage of Jakes's Formula is that it does not take the effect of many servers into account.

The presence of many servers at the cell borders reduces the required log-normal margin. This is because the fading patterns of the different servers are fairy independent. If the signal from one server fades down below the sensitivity level a neighboring cell can fill out the gap and rescue the connection. In order to find the log-normal fading margins in a multi-cell environment, simulations have been performed.

The prerequisites for the simulations are: • 3 sectored sites • Correlation of log-normal fading between one MS and different BSs is 0.5 • Log-normal fading correlation distance is 28.85 m • The time to perform a handover is 0.5 s The propagation environment is modeled with the Okumura Hata formula as follows: Lpath = A + 10 a logd [dB] where A = 15.3 and a = 3.76 d [m].

Five different environments (OLNF = 6, 8, 10, 12, 14) have been studied. The used handover hysteresis in the simulations is 3 dB. In order to find the required value of LNFmarg: 1. Chose the corresponding to the fading environment in question.

2. On the X-axis, find the log-normal fading margin for the desired area coverage (Y-axis).

17

Log-Normal Fading Margin Below the size of the log-normal fading margin is given for different types of fading environments and area coverage. The values originate from the simulations described above. A multi-cell environment with a handover hysteresis of 3dB is assumed.

Table 2-8: tog-Normal Fading Margin (LNF marg) in dB for Different Environments

ﾏキNF (dB)

Coverage [%] 75

85

90

95

98

6 8 10 12 14

-3.7 -3.4 -3.1 -3.1 -3.2

-1.2 -0.2 0.7 1.3 1.8

0.5 1.8 3.2 4.2 5.1

3.0 4.9 6.8 8.4 9.9

5.5 8.1 10.7 13.1 15.3

Interference The plain receiver sensitivity depends on the required carrier to noise ratio (C/N). When frequencies are reused, the received carrier power must be large enough to combat both noise and interference, that means C/(N +1) must exceed the receiver threshold. In order to get an accurate coverage prediction in a busy system, an interference margin (IF marg) is defined. The interference margin depends on the frequency reuse, the traffic load, the desired percentage of area coverage, and whether the uplink or the downlink is considered. Frequency hopping, dynamic power control and, particularly, DTX reduce the interference level. In a normal system, an interference margin of 2 dB is recommended.

Body Loss The human body affects the MS performance in a number of ways, compared to a freestanding mobile phone: 窶｢ The head absorbs energy 窶｢ The antenna efficiency of some MSs may be reduced 窶｢ Other effects may be a change of the lobe direction and the polarization. These effects can be neglected in the link budget since: - no mobile antenna gain is used - X- Polarized antennas are standard equipment today. In this case, the polarization loss is included in the downlink link budget. In the uplink, both polarizations can be received.

The body loss is less for higher frequencies than for lower. The body loss recommended by ETSI is 3dB. For 850/900 MHz, a need for a somewhat higher margin has been indicated.5 dB is the Ericsson recommendation.

Car Penetration Loss When an MS is situated in a car without an external antenna, an extra margin must be added to cope with the penetration loss of the car. This extra margin is approximately 6 dB. 2.3.3 DESIGN LEVELS In this section, the design levels (SS design) are calculated for outdoor, in-car, and indoor coverage for GSM 800/GSM 900 (the difference for GSM 1800/1900 is the body loss). This signal strength is calculated as the sum of the required signal strength (SS req) and various margins (See equations 2, 3, and 4). In this section, the value of SS,cq has been taken to be: SSreq =

MSSens + RFmaig + IFmarg + BL = -104 + 3 + 2 + 5 = -94 dBm

18

Outdoor and In-Car Coverage The design levels for outdoor and in-car coverage are calculated according to: SSdesign= SSreq + LNFmarg (0) SSdesign=

MS outdoor

SSreq+ LNF'marg (0)

MS in-car

Where, LNFmarg (o) is the log-normal fading margin that is needed to handle the outdoor log-normal fading.

This fading will be represented by its standard deviation OLNF (0) and depends on the area type.

Typical values of QLNF(O) are presented in Table 2-9.

Table 2-9: Typical Values of the Standard Deviation of the Outdoor Log-Normal Fading for Different Area Types.

Area Type Dense Urban Urban Suburban Rural

<*LNF(O) [dB] 10 8 6 6

In Table 2-10, the design levels SSdesign, for different area types and coverage requirements are calculated. The values are calculated for GSM 800 / GSM 900. Values for GSM 1800 / GSM 1900 are 2 dB lower body loss. The value of LNF marg (0> is calculated according to simulations, which includes the multi-server gain. A hysteresis value of 3 dB between the cells has been used.

19

Table 2-10: Design Levels for Various Area Types and Coverage Requirements (GSM 800/GSM 900).

A car penetration loss (CPL) of 6 dB has been used Area Type

Coverage

SSreq (dBm)

LNF marg(o) SSdesign [dB] Outdoor [dBm]

Dense Urban CLNF(O)= 10 dB

75 85 90 95 98

-94 -94 -94 -94 -94

-3.1 0.7 3.2 6.8 10.7

-97.1 -93.3 -90.8 -87.2 -83.3

SSdesign in-car [dBm] -91.1 -87.3 -84.8 -81.2 -77.3

75 85 90 95 98 75 85 90 95 98

-94 -94 -94 -94 -94 -94 -94 -94 -94 -94

-3.4 -0.2 1.8 4.9 8.1 -3.7 -1.2 0.5 3 5.5

-97.4 -94.2 -92.2 -89.1 -85.9 -97.7 -95.2 -93.5 -91 -88.5

-91.4 -88.2 -86.2 -83.1 -79.9 -91.7 -89.2 -87.5 -85 -82.5

Urban ﾏキNF(0) = 10 dB

Suburban + Rural OLNF(O) = 6 dB

Indoor Coverage Indoor coverage is the percentage of the ground floors of all the buildings in the area where the signal strength is above the required signal level of the mobiles (SS req).

Building Penetration Loss Building penetration loss is defined as the difference between the average signal strength, immediately outside the building, and the average signal strength over the ground floor of the building. The building penetration loss for different buildings is log-normally distributed with a standard deviation of CBPL- Variations of the loss over the ground floor could be described by a stochastic variable, which is log-normally distributed with a zero mean value and a standard deviation of af|00r. In this chapter, CBPL and Ofioor are lumped together by adding the two, as were they standard deviations in two independent log-normally distributed processes. The resulting standard deviation, or OLNF(i), could be calculated as square root of the sum of the squares.

General Indoor coverage concerns calculation of a required margin to achieve a certain indoor coverage in a fairly large area; large compared to the average macro cell size. It is assumed that it is the macro cells in the area that provide the major part of the indoor coverage. Hotspot micro cells in the area will of course improve on the indoor coverage. The guidelines, in this chapter regarding indoor coverage are not applicable to the case where the area of interest basically is covered by contiguous micro cells and where micro cells are only used as umbrella cells. It is common knowledge that the building penetration loss to floors higher up in the building in general decreases. This effect is

20

known as height gain. This is actually an effect of the building penetration loss definition and not of the building structure.

Indoor Design Level The indoor design level is calculated according to: SS'design=

SSreq + LNF marg (0+1) + BPLmean

MS Indoor

Where the sum of BPL mean and LNFmarg (o+i) can be seen as the indoor margin. BPL mean is the mean value of the building penetration loss and LNF marg(o+i) is the margin that is required to handle the total log-normal fading which are composed of both the outdoor log-normal fading (OLNF(O)) and the indoor log-normal fading (OLNF(J))- The total standard deviation of the log-normal fading is given by : ﾏキNF(0+1)

=

(ﾏキNF(0)2 + ﾏキNF(1)2)

In table 2-11 some values of BPL mean, CLNF (Q) ar|d SLNF (i) are presented. Note that the characteristics of different urban, suburban etc. environments can differ quite a lot over the world. Thus the values in table 2-11 must be treated with restraint. They should be considered as a reasonable approximation when no other information is obtained. Rural areas are not considered in table 2-11, since these are usually not designed for indoor coverage.

Table 2-11: Some Typical Values of Buildings Penetration Loss and Log-Normal Fading for Different Area Types BPLmean [dB] OLNF(O) [dB] ^LNF(i) [dB| LNFmarg(o+i) [dBl Dense urban 18 10 9 14 Urban 18 8 9 12 Suburban 12 6 8 10 In table 2-12, the design levels required to obtain 75%, 85%, 90%, 95%, and 99% indoor coverage are given.

The parameters for the building penetration and the log-normal fading are taken to be those presented in Table 2-11.

The log-normal fading margins are given by the simulations described earlier. A multi cell environment has been assumed with a hysteresis value of 3 dB.

21

Table 2-12: Indoor Design Level for Various Area Types and Coverage Requirements (GSM 800/GSM 900).

Area Type

Dense Urban CLNF(0+1) = 14 dB

Urban 0LNF(0+1) = 12 dB

Suburban ﾏキNF(0+l) = 10 dB

Coverage [%]

SSreq [dBm]

LNFmarg(o1) [dB]

BPLmean [dB]

SSdesign 1Hdoor[dBml

75

-94

-3.2

18

-79.2

85 90 95 98 75 85 90 95 98 75 85 90 95 98

-94 -94 -94 -94 -94 -94 -94 -94 -94 -94 -94 -94 -94 -94

1.8 5.1 9.9 15.3 -3.1 1.3 4.2 8.4 13.1 -3.1 0.7 3.2 6.8 10.7

18 18 18 18 18 18 18 18 18 12 12 12 12 12

-74.2 -70.9 -66.1 -60.7 -79.1 -74.7 -71.8 -67.6 -62.9 -85.1 -81.3 -78.8 -75.2 -71.3

2.4 CELL PLANNING 2.4.1 WAVE PROPAGATION MODELS FOR ESTIMATION When roughly estimating the cell coverage, without respect to specific terrain features in the area, a fairly simple propagation algorithm can be used. That means the diffraction loss, due to "knife edge" and "spherical earth" is ignored. A simple empirical model, based on the original Okumura-Hata algorithm can be used. The equation below describes the propagation loss Lp. Lp = A - 13.82 loghr + (44.9-6.55 loghr) logd -a (hM) [dB] Where

A A

= 146.2(800) 146.8(900) 153.8(1800) 154.3(1900) urban area = 136.4(800) 136.9(900) 146.2(1800) 146.9(1900) Suburban and semi open areas A = 127.1(800) 127.5(900) 134.1(1800) 134.6(1900) rural areas A = -117.9(800) 118.3(900) 124.3(1800) 124.8(1900) open areas hB = base station antenna height [m] d = distance from transmitter [km] hM = mobile station antenna height [m] a (hM) = 3.2 (log 11.75 hM)2 -4.97.

22

For small cells in an urban environment, the cell range is typically less than 1 km, and in that case the Okumura-Hata algorithm is not valid. The COST 231-Walfish-lkegami model gives a better approximation for the cell radius in urban environments. The path loss according to this model is: Lb = K + 381ogd-log(ha-17) Where K:

142.4 for 850 MHz 143.2 for 900 MHz 153.2 for 1800MHz 154.1 for 1900MHz

According to Walfisg-lkegami, the cell range then becomes: d = 10", where a = [Lpathmax -K + 180 log (hB - 17)]/ 38 2.4.2 POWER BUDGET Path balance implies that the coverage of the downlink is equal to the coverage of the uplink. The power budget shows whether the uplink or the downlink is the weak link. When the downlink is stronger, the EiRP used in the prediction should be based on the balanced BTS output power. When the uplink is stronger, the maximum BTS output is used instead. Practice indicates that it is advantageous to have a somewhat higher base EiRP (2-3 dB) than the one strictly calculated from power balance considerations. This is because the diversity gain sometimes exceeds 3.5 dB. In the calculations below the antenna gain in the MS and the MS feeder loss are both zero and therefore omitted. It is also assumed that the antenna gain and the feeder loss are the same for the transmitter and the receiver side on the BTS. Following abbreviations are used: PinMS = Received power in MS MSsens = Sensitivity MS PinBTS = Received power in BTS BTSSens = Sensitivity BTS PoutMS = MS maximum transmitted power PoutBTS = BTS transmitted power Poutbai = BTS balanced transmitted power LfBTS = Feeder and jumper loss at BTS Ldutbal = External duplex loss at BTS LTMA = Duplex loss at TMA LslantBTS= Slant polarization (+- 45°) downlink loss Lp = Path loss between MS and BTS GaBTS =Antenna gain in BTS GdBTS = Diversity gain in BTS D = MSsensâ&#x20AC;&#x201D;BTSsens

23

Downlink Budget: Downlink (DL) is the direction from the BTS to the MS. The downlink budget gives the power level, received in the MS. Uplink Budget: Uplink (UL) is the direction from the MS to the BTS. The uplink budget gives the power level, received in the base station.

2.4.3 POWER BALANCE Power Balance without TMA The formula for the received power in MS (PinMs) for the downlink (DL) is as follows: DL:

PinMs = Pouters - (LduplBTs) - LfBTs + GaBTs - (Lslanters) - Lp The formula for PinBTs for uplink (UL) is as follows: UL: PinBTS = PoutMs - Lp +GaBTs +GdBTS - LfBTS - (LduplBTs) PinBis is referenced to RX ref. point and Pout Brs is referenced to TX ref. point. The duplex loss should only be taken into account if an external duplexer is used. The slant loss should only be taken into account if cross polarized antennas are used.

Assuming that the path loss is reciprocal, i.e. Lp upimk =Lpd0wniink. Then Poutsrs = PoutMs +GdBTs + (LslantBTs) + PinMs - PinBTs A balanced system is obtained when PinMs = Pin Brs - Ds where Ds = MSsens - BTSsens.

To calculate the BTS output power which makes the system balanced for a certain Ms power class, the following formula is used.

Poutbal = PouMS = (LslantBTs) +Ds The corresponding EiRP is given by: EiRP = (LduplBTs) -LfBTs +GaBrs - (LslantBTs) Example without TMA In table 2-13, the balanced BTS output power at TX Reference Point (GSM 900) for RBS 2000 equipped with CDU-A, and (+- 45째) polarized antenna is calculated.

T/ble 2-13: Balanced BTS Output Power at TX Reference Point (GSM 900).

PoutMs [dBm] GdBTS [dBm] Lslanteis [dBm] Ds [dBm] Poutbai [dBm]

MS Class 4 33 3.5 1 -104-(-110)=6 43.5

MS class 5 29 3.5 1 -104-(-110)=6 39.5

24

Power Balance with at the Antenna The formula for PinMs downlink (DL) is as follows: DL:

PinMs =

Pouters - LfBTs -(Lduplers) + GaBTs - LTMA -(Lslanteis) -Lp

The formula for PinBrs downlink (DL) is as follows: UL:

Piners = PoutMs -Lp + Gaers + GdBTs Assuming the path loss is reciprocal, that is, Lp upiink =LpdOWniink then :

Pouters = PoutMs + GdBTs + LfBTs + LTMA +(LduplBrs) + (LslantBTs) + PinMs - PinBTs A balanced system is obtained when PinMs - PinBrs +Ds. Where Ds = MSsens -BTSsensTo calculate the BTS output power which makes the system balanced for a certain Ms power class the following formula is used: PoutBai=PoutMs + GdBTs + LfBTs + (LduplBTs) + (Lslantsrs) - Ds Where the difference between the BTS and MS receiver sensitivity is referred to as Ds = MSSens The corresponding EiRP is given by: EiRP = Poutbai - LfBTs -(LduplBTs) +GaBTs -(LslantBis) Example with TMA: In table 2-14 Balanced BTS Output Power at TX Reference point (GSM 900), the balanced BTS output power for RBS 2000 equipped with CDU-A, TMA, and ( +- 45째) polarized antenna is calculated. No software power boost is used.

Table 2-14: Balanced BTS Output Power at TX Reference Point (GSM 900).

PoutMs [dBm] Gdeis [dBm] Lfers [dBml Ldup!BTS [dBm] LTMA [dBm] LslantBTs [dBm] Ds [dBm] Routbai [dBm]

MS Class 4 33 3.5 3 0.3 1 -104-(-l 11.5) =7.5 48.3*

MS Class 5 29 3.5 3 0.3 1 -104-(-l 11.5) =7.5 44.3

*The maximum output power for RBS 2000 equipped with CDU-A is 44.5 dBm, thus, in this example, the uplink will become stronger than the downlink.

25

2.4.4 CELL SIZE The maximum allowed path loss (Lp) can be calculated from the downlink power budget: Lp = EiRP - SSdesjgn Once the maximum allowed path loss has been calculated, the corresponding cell size can be determined by using the wave propagation model in the previous sections.

Table 2-14 and Table 2-15 show the calculated cell range, d, for 95% area coverage and for the macro cell case for GSM 900.

The allowed path loss, Lpathmax- Corresponds to outdoor path loss for power balance according to the handheld class 4 MS in the example with TMA. Table 2-15: Assumptions of Cell Sizes, Calculated in the tables below: EIRP Design Level SSdesiRn Height of MS (HM) Height of BTS Antenna (HB)

56.7 dBm Sector (17 dBi Antenna, X polarized) 52. 2 dBi omni (1 1 dBi Antenna, Ver polarized) See Table 2-27 and 2-29 1.5m 30m

Table 2-16: Cell Sizes of a Sector Cell, 95% Area Coverage (GSM 900 MS Class

Area

Outdoor Lp [dB] d[km] In-Car Lp [dB] d[km]

Indoor d[km]

Class 4 33 dBm (2W) Y

Urban Suburban Rural Open area

145.8 147.7 147.7 147.7

124.3 131.9 131.9 131.9

3.7 7.9 14.6 26.6

139.8 141.7 141.7 141.7

2.5 5.4 9.9 J8.0

Lp

[dB]

0.9 2.8 5.2 9.5

Table 2-17: Cell Sizes of an Omni Cell, 95% Area Coverage (GSM 90' MS Class Class 4 33 dBm (2W) \f

Area

Outdoor Lp [dB d[km]

In-Car Lp [dB d[km]

Urban Suburban Rural Open area

141.3 142.3 143.2 143.2

135.3 137.2 137.2 137.2

2.8 5.7 10.9 19.9

1.9 4.0 7.3 13.4

Indoor d[km| 119.8 127.4 127.4 127.4

Lp

|dB

0.7 2.1 3.9 7.1

When determining the cell range for small cells in urban, environments, the Walfish-Ikegami model is recommended. 95% coverage area is considered and the allowed path loss, Lp athmax, corresponds to outdoor path loss, for power balance according to the handheld class 4 MS in the example with TMA. The following assumptions are made:

26

Table 2-18 : Assumptions of the Cell Size for a Small Cell, 95% Indoor Coverage in an Urban Environment (GSM 900).

EIRP Design Level SSDesign Height of MS (HM) Height of BTS Antenna (HB)

56.7 dBm Sector (17 dBi Antena, X potarized) -68 dBm, See Table 2-29 1.5 m 22m

2.5 SIMULATED LOG-NORMAL FADING MARGIN Hysteresis = 3dB Log normal fading correlation, one MS to different BSs = 0.5 Prorogation = 15.3 + 37.6 log(d) Handover dealy = 0.5 s

Figure 2-1: LNF margins [dB].

2.6 FREQUENCY PLANNING Frequency planning is a means to optimize spectrum usage, enhance channel capacity, and reduce interference. The use of a spectrum and licenses to operate radio transmitters is controlled by a number of regulatory authorities: â&#x20AC;˘ Federal Communications Commission (FCC) for commercial carriers;

27

• National Telecommunications and Information Administration (NTIA) for government systems; • Military Communications and Electronics (MCEB) for military systems; • Consultative Committee for International Radio (CCIR) for issues and recommendations on radio channel assignment. They do not have regulatory power but their recommendations are usually adopted worldwide.

The FCC provides licenses to operate cellular communication systems over a given band of frequencies. Because cellular communication is a multiple- access system, operators have to comply with the regulations. Compliance requires proper frequency planning and spectrum control and also involves channel numbering, channel grouping into subsets, cell planning, and channel assignment. A frequency plan must ensure adequate channel isolation to avid energy slipover between channels, so that adjacent channel interference is reduced to a minimum. Moreover, an adequate repeat distance should be provided to an extent where co-channel interference is acceptable, but a high channel capacity is maintained. Frequency planning is an important task in cellular communications for system planning, installation, performance analysis, capacity analysis, etc.

2.6.1 TRANSMITTING / RECEIVING CHANNEL PAIRING Cellular communication is a full-duplex system in which each band is divided into two equal halves: one-half is for forward channels (base to mobile communication) and the other half is for the reverse channels (mobile to base communication). A 45- MHz guard-band is provided to avoid interference between Tx/Rx channels.

2.6.2 FREQUENCY BAND ALLOCATION AND CHANNEL NUMBERING Frequency planning for cellular communications begins with the available frequency band allocated by the regulating authority. Each band occupies 12.5MHz, of which 10MHz is in the non-expanded spectrum (NES) and 2.5 MHz is in the expanded spectrum (ES). With 30-kHz channel spacing, this arrangement provides 10 MHz/30kHz - 333 channel per band in the NES and 2.5 MHz/30kHz = 83 channels per band in the ES. The total number of channels per band is therefore 333 + 83 =416 in each band. Among them, 21 channels are used as control channels, and the remaining 395 channels are used as voice channels. Note that the control channels are used for channel assignment, paging, messaging, etc.

28

Table 2-19: Channel Numbers System Type A" ES A NES B NES A' ES B' ES Base transmitting frequency Base receiving frequency

BW (MHz) 1 10 10 1.5 2.5

No. of Channels 33 333 333 50 83

= (0.03N + 870) MHz (NES) = 0.03(N - 1023) + 870 MHz (ES) = 0.03N + 825MHz (NES) = 0.03(N - 1023) + 825 MHz (ES)

Where N is the channel number (N=l,2,.. ..,1023). Thus by knowing the channel number, the associated pair of frequencies can be obtained from (7.1) and (7.2).

2.6.3 CHANNEL GROPING AND REUSE PLAN Cellular communication is a multiple- access system in which several non interfering channels are combined to form a channel group and assigned to a cell site. Because the number of channel is limited, these channel groups are reused at a regular distance. This is an important engineering task because it determines system capacity and performance. Several frequency reuse techniques are available and are generally known as frequency planning or channel assignment techniques. Some of the most widely used frequency planning techniques are as follows: N = 7 frequency reuse plan N = 9 frequency reuse plan N = 4 frequency reuse plan N = 3 frequency reuse plan.

The N=3 and N=9 frequency plans are relatively unknown. However, since the advent of TDMA techniques, these frequency plans are becoming popular among cellular industries for enhancing channel capacity

29

CHATER-3 SITE SURVEY INTRODUCTION In the implementation of a cellular network, the site survey can be considered one of the most critical stages towards the implementation process. At this stage, it will fulfill or spoil the overall goal of the project. Therefore, great care is taken to ensure that, conducting site surveys will meet the desired network goals. Falling short at this stage may mean having to go through the whole process again, and that is costly. The material that is used in this book is partly based on documents written by experienced surveyors, some of whom have been involved in big projects concerning Ericsson's GSM system implementation, and partly on experiences from the Philippines.

3.1 SITE SURVEY CONSIDERATIONS The site survey may be considered an ordinary routine task that should be performed during the implementation process of a cellular network. Conducting successful site surveys, however, requires an extensive knowledge. Someone who wishes to conduct a site survey must have a thorough understanding of the system to be implemented, and should know how the system functions. This draws particular attention to the aspects of radio wave propagation, air interface, equipment configurations and functionalities, antenna systems and structural regulations, only to mention a few. Other considerations may include aspects, such as, knowledge of the use of the planning tool (TEAMS Cell Planner), familiarity with the place, multi-lingual- which is an advantage, and some coordination skills. To perform a successful site survey, experienced surveyors are needed to make sure that the sites to be installed will be placed in the correct locations in order to function satisfactorily. The survey stage does not allow for mistake. Mistakes will incur delays, thus, making the project more costly.

3.2 INSTRUMENTS FOR SITE SURVEYS Only a few instruments are needed to perform a site survey, but in case something unexpected happens, the surveyor should be prepared. Therefore, when packing the equipment, bear in mind that the surveyor must be able to move freely. Checklist of survey equipment: • Camera (Film and batteries) / Video camera • GPS (with correct map datum setting) • Maps • Compass • Inclinometer • 10 or 50 meter tape measure • Site survey document • Computer • Binoculars • Office materials • Safety equipment -Mast climbing equipment • Gloves • TEAMS Cell Planner prediction plots (if available)

30

Compass This is the surveyor's most important tool. The compass indicates the bearing of a certain direction in relation to a particular point. Normally, the tip of the pointer is directed to the magnetic north. As the compass is moved, the compass scale rotates around the fixed reference marker to indicate the bearing. To use this tool is quite uncomplicated. However, care must be taken when using the compass to be able to accurately define a direction. The pointer of the compass is made of a material that is magnetic and must, therefore, be kept away from metallic structures (such as towers, metal water tanks, etc.) in the immediate vicinity, when taking a direction or bearing.

3.2.1 METHODS OF TAKING ANTENNA DIRECTION Back Azimuth If clearance of metallic structures is not possible, the back azimuth technique can be used. First, determine the opposite or counter bearings of the antenna bearings using equations 1 or 2.Move the compass around the proposed site to a clear area, approximately 50 m away from the site, until the counter bearings are found. Take note of the clear areas as reference points and mark them on the map or sketch. Example, if the antenna bearing is 0 or 360 degrees, the counter bearing should be 180 degrees. It is simply done by adding or subtracting the antenna bearing by 180 degrees.

Counter bearing = antenna bearing (value is 180 deg.) + 180 Counter bearing = antenna bearing (value is 180 deg.) - 180

Equation 1 Equation 2

This technique generally requires two people, one on the site and one who moves around with the compass and takes the readings.

Using landmarks One of the most accurate methods to determine antenna directions is to use an appropriate location map that shows roads and buildings, since it is not dependent on magnetic deviation. An alternative is to mark the antenna directions on the map using an angle- measuring tool, such as a protractor to help determine landmarks (buildings, towers, roads, open fields, etc.), for reference purposes. When on site, this will facilitate the location of the antenna directions using the reference landmarks, mentioned above. The compass can be used to further check the antenna directions. 90°.

900 Technique From the figure below, take the reading of direction X by sighting through the back of the antennas using the compass. Assume that all antennas are oriented in the same direction, and add or subtract the reading of direction X by 90°. The result should, eventually, be the direction of the antennas. This technique is usually applied to check the direction of already installed antennas. The acceptable error for the antenna directions must be within ± 5°.

31

3.2.2 POSITIONING Map Datum Map datum is a mathematical description of the earth, or part of the earth that is necessary to correctly assign real-world coordinates to points on a map or a chart. Since each datum is based on different assumptions and measurements, a position calculated in one datum, can differ by 600 meters or more from the same position calculated in another datum. Therefore, it is very important to set the GPS equipment to the correct map datum. The map datum used, should be the same as the one used for the digitized map in TEMS Cell Planner. Also, note if the paper map has a different map datum.

GPS Instruments GPS stands for Global Positioning System. The GPS instrument receives information from signals sent from satellites. In order to get accurate coordinates for a location (usually termed as position fix or waypoint), the GPS must be placed in an unobstructed location to sight as many satellites as possible. At least four satellites must be obtained to get accurate readings, provided that the correct map datum is set in the GPS. In addition to a fix, the GPS usually provides information that is needed for navigating. GPS features differ and it may be favorable to have a GPS with features for the functionalities that are required concerning site surveys. A full-featured GPS is not necessarily the best unit for site survey. Features, such as battery saver, very user-friendly, route tracking capability, large waypoint log, vast map datum database, multiple coordinate system, and time-and-date stamp are some of the basic functionalities needed. These things are usually defined in the GPS manual.

The manual also describes the operation of the GPS in further detail. In wide-scale surveying, where more than one team performs surveys, it is recommended to have only one type of GPS equipment.

Site hunters should have the same GPS type as the survey teams. This sets standard results and prevents confusions in later site verifications.

3.2.3 GPS PROCEDURES Waypoint List Before performing site surveys, make sure that all nominal coordinates of the sites to be visited are logged into the waypoint list with their corresponding site names or IDs. Once on site, this will facilitate the procedure of determining if the site is off grid or not, simply by comparing the logged nominal coordinates to the actual coordinates. Likewise, take readings of site coordinates for sites that are rejected. The saved coordinates can be used for future site verifications.

Waypoint Tracking -nominal In some GPSs, it is possible to track down the location of the nominal site. This function is recommended for site hunters to enable them to get as close as possible to the nominal site. It is simple done by logging in the nominal coordinates of a site in the waypoint list and the actual waypoint will automatically be set as the moving waypoint. The two waypoints (nominal and moving) must be displayed on the appropriate page or screen. Some GPSs, however, may not have the said screen. Track back by moving the GPS around until the moving waypoint is very close to the nominal waypoint, as will be shown on the screen. The scale on the screen can be changed to zoom in or zoom out to see the distance between the waypoints. Other techniques can also be used for tracking. Furthermore, getting close to the nominal site can also be achieved using an appropriate

32

map. The nominal site can be marked on the map then find a building structure close to the nominal location.

Batteries If a number of sites are to be visited on the same day, be sure to activate the battery saver function of the GPS, or, even batter, to bring extra batteries. Normally, the battery level is indicated on the GPS's display to provide information about the batteries. Make sure that the batteries are always fully charged. Insufficiently charged batteries tend to cause inaccurate reading of coordinates from the satellites.

Camerd The camera is used to take photos of the sites to be surveyed. The photos will present the surroundings of the site, exact locations of the antennas and BTS cabinets, immediate obstructions, site ID, and outlook of the building. When conducting site surveys, it's important to bring a sufficient supply of films and batteries. A handy, quality, and auto-focus camera is preferable for site surveys because it does not require complex operation and focusing. Using a digital camera is preferable, since pictures taken on site can be interfaced directly into the computer as files. The picture files can be easily included as attachments to the reports and can be sent via e-mail to the main office.

Panoramic View In site surveys, it is absolutely necessary to take a panoramic view of the site. The panoramic view shows the clutter type in the surrounding environment, including existing and upcoming obstructions. This also pictures the actual situation of the site for the benefit of other planners and decision-makers who have not visited the site. Additionally, it shows the antenna directions. This can be done by inserting corresponding markings, such as sticking fingers or pointing the compass as superimposed in the photos. North should always be identified in the panoramic view. This is usually done by tilting the camera vertically when taking the north direction and tilting it back horizontally for the rest of the view. An additional method is to point a compass towards north and take a picture that includes the compass. Normally, it only takes 9 to 10 shots for a complete panoramic view, which means that an auto-focus camera has a normal capture angle of 36 to 40 degrees. However, there are cases where taking a panoramic view at a single point is not possible. This make taking photos a bit complicated and it may take more shots to complete a panoramic view. Video Camera ^\ \ A video camera is an excellent tool to use for site surveys. The video camera can provide better and more accurate information about the site, since the surveyor can orally describe the site while recording the surrounding environment, antenna locations, RBS location, buildings, etc.

Measuring Tape This tool is used to measure distances or heights. It can be used independently, or together with the clinometer for height measurements. When used independently, height measurements can be performed by stretching out the tape from the top of the building

33

down to the ground. The length of the tape must exceed the building height. If not, use it together with the clinometer.

Clinometer A clinometer is a more convenient tool for measuring heights. Measurements can be performed on the ground, or near the base of a structure. Height measurements can be performed by a combination of distance and angle measurements, coupled with trigonometric calculation. The methods used are as follows: • Establish an exact distance, for example, 20 meters, from the base of the structure or building outwards to a clear space using a measuring tape.

• Stand at the end of the tape -20 meters from the base of the building.

• Hold the clinometer in front of your right eye. With both eyes open, project the view upwards at the topmost or apex of the building. Take the reading of the angle on the eye piece of the clinometers.

• Calculate the building height using the formula.

Calculation: Where,

Building Height = ha + d tan α

Equation 3

h2 = height of surveyor's eye level, in meters a α = angle read from the clinometer, in degrees d = established distance using measuring tape, in meters In case the ground is sloping or irregular, the following method can be applied: A sloping terrain introduces errors on the horizontal measurement and this must be considered for accurate results. The error is insignificant for most purposes at small ground slope angles, but increases progressively as the angle p increases. The height can be calculated using equation 4, assuming the slope angle is insignificant. .

Hs = d (tan (p - tan β)

Equation 4

Where, Hs d ϕ β

= height of structure, in meters = distance, measured from the structure base, in meters = angle, measured at the apex of the structure, in degrees = angle, measured at the structure base, in degrees

This method can also be applied if the structure to be measured is a tower on top of a building. The angle, P, will then be the measured angle at the top or apex of the building.

If the surveyor's location is above the base of the structure, the structure height can be determined by applying equation 5.

34

Building height = d cos Îą [tan 6 + tan p ] Where, d =

Equation 5

distance, measured from the base of the building, in meters Ď&#x192;= slope angle, in degrees θ= angle, measured at the apex of the building, in degrees p= angle, measured at the base of the building, in degrees h2= height of the surveyor's eye level, in meters

3.3 PRE-SITE SURVEY PROCEDURES Responsibility Matrix Some time of responsibility matrix must be understood by everyone who is involved in the survey process. The matrix clearly defines the responsibilities to be performed by the vendor and the customer. It also defines who is responsible for what. It may happen that the survey team has different members each time the survey is conducted. In that case, a copy of the organizational structure, or layout, must be provided for each new member who joins the survey team. This provides information as to where the new member should position himself in the organization.

Together with the assigned responsibilities for each team member, there should be a coordination system that defines the agreed process flow for the duration of the survey. The process flow will avoid repetition of activities, already performed by a team. Normally, the intention is to survey a site only once, especially if there are a large number of sites to be surveyed.

Site Hunting The vendor or the customer, depending on the agreement, stipulated in the contract performs site hunting. Site hunting must be done with care and precision.

Search Ring It is vital for the quality of the system to maintain the grid. Thus, site hunters should find a site location as close to the nominal location as possible. Practical guidelines recommend maximum offgrid. Tolerances of up to 15% of the site-to-site distance for analog systems, and 20% for GSM systems. For GSM, this means that, for a grid type of 1.5 kilometers in an urban area, the proposed site location is allowed to be off-grid up to maximum of 300 meters. It should be noted that the considered grid type is the site-to-site distance of the network, planned for the future. This means that, if the network will expand in the future, there is no risk of relocating the sites, since distances between the sites are well catered for from the very start. In practice, the search ring radius is normally set to 100 meters for urban areas, and 200 meters for suburban and rural areas. In place where site acquisition is difficult, the maximum tolerances, mentioned earlier, may be applied.

Search rings can be conveniently generated in the TEAMS Cell Planner and can be printed out to serve as a guide, if needed. If there is a limitation to the number of frequencies in the network, search rings must be kept as small as possible. This is very important, since a tighter re-use will be applied in the future, which will require shorter site-to-site distances. It should be emphasized that a site must cover the area it is

35

intended to cover, no more-no less. If, however, unfavorable circumstances cause a site to be too much off-grid, appropriate measures must be undertaken to minimize the effects of interference, which may lead to capacity constraints. It requires creativity to deal with this situation; new antenna directions, proposed antenna tilts or antenna beam widths may be considered.

Building Selection In places where building heights are approximately the same, the best choice for the site is as close to the nominal site location as possible. For other areas, where building heights differ, the choice is made considering antenna heights, antenna directions, upcoming obstructions, leasing contracts, equipment delivery access, and installation, etc. For propagation purposes, the selected building must be high enough to allow clearance for the antennas of immediate obstacles in the vicinity.

However, the antenna height should not deviate too much from the nominal height.

Site Candidates It may occur that there are several suitable site candidates within the search ring. When selecting the best site candidate, these issues should be considered: • Distance from the nominal site, (as close as possible) • Strategic location to fulfill coverage objectives.

• Better leasing contract offered.

• Clear of present and upcoming obstructions.

• Ease of equipment and antenna installations.

• Easy access for installation equipment (crane, trucks, etc.)

Fresnel Zone When on the roof, check for clearance in places where the antennas should be installed. Upcoming obstructions must be considered. Antennas should be installed at the edges of the roof to keep the first Fresnel zone free, if possible. The problem arises when the roof is too wide, since longer cables are needed to connect the antennas to the BTS. If the antennas are to be installed on the roof, the tables below give the recommended height above the roof. The following values apply to directional antennas only.

Table 3-1: Antenna height above roof for 900 MHz. Distance (D) to obstacle edge.

Height (h) above roof (obstacle) 0-lm 0.5m l-10m 2m 10-30m 3m >30m 3.5m

36

Table 3-2: Antenna height above roof for 1800/1900 MHz. (D) 0-2m 2- 10m >10m

(h) 0.5m 1m 2m

These values are valid, regardless of antenna tilt. Use 2m as minimum height, if there is risk that people may walk past the antenna. Other considerations, such as antenna isolation, diversity, and co-location are discussed in the Antenna configuration guidelines. As a general rule, antennas must be free from obstacles up to 100 meters horizontally, and 5 meters below the antennas (for 900 MHz). According to the guidelines, it is also important to keep the cell sector free from obstacles. A safety margin of 15째 should be added on both sides of the sector borderlines, relative to the -3 dB points, and it should be kept free from obstacles to reduce risk of shadowing effects and bean distortion, due to reflections.

Transportation and Accommodation This section involves preparing cash advances, ordering plane tickets, making hotel reservations, etc. support personnel, such as secretaries or coordinators can handle these items. However, it is the responsibility of the teams to follow up these issues.

3.4 SITE SURVEY PRODUCERS General The following discussions will be based on the RF site Survey From for a complete survey procedure.

The term survey form will often be used in placed of RF site Survey From, for simplification purposes.

3.4.1 BASIC PREPARATIONS Site List Usually, the list of sites to be surveyed is provided in advance. At least one day prior to the actual site survey. It is recommended always to check the immediate vicinity of the sites to be surveyed on the TWMS Cell Planner plots and maps to get knowledge of the intended coverage of the sites. If a site is rejected, it is easier to identify the location of the alternative site and still maintain its purpose.

Survey Materials Prepare all materials and instruments that will be needed. It may occur that climbing a tower or penthouse is required and the instruments should be easy to reach. A clipboard may be needed in windy areas.

37

Site Prior to making the site survey, it is recommended to fill out known data on the survey form, such as Site Name, Site Number, and Site Address. Keep the survey forms in strict order. This saves time.

Surveyor Similarly, fill in the Name of the Surveyor and the Date on the survey form. If there are several surveyors, include their names.

Position Once on site, switch on the GPS for a couple of minutes and then take reading of the site coordinates on the GPS and check if it is on-grid or off-grid. This is done by comparing the nominal coordinates to the read coordinates.

It is emphasized that the GPS must be set to the correct map datum when faking the paper Map coordinates and TEMS Cell Planner coordinates. For off-grid conditions, evaluate the site location, if it is immediately outside or too far from the search ring. If it is immediately outside the search ring, take the GPS coordinates and address proceed to the next site. The visited site could still be considered. If negotiation of site acquisition is a great issue within the area. There are cases where the customer wants an immediate decision whether to reject or approve the site location.

Remember always to check TEMS Cell Planner plots and maps to help facilitate decision making. To confirm the exactness of the site coordinates, take, at least, two coordinate samples of each site.

The samples must be labeled to enable identification of the proper nominal coordinates in the GPS waypoint list. Complete the survey form for Map and TEMS Cell Planner coordinates, Grid type, off grid, and mark the position of the site on the map.

Coverage/Capacity Assess the surroundings of the site and determine the degree of importance concerning coverage and capacity of each sector. The degree of importance is rated from 1 to 5, where 1 is least important and 5 most important. This data will be used for more extensive planning to balance traffic requirements and coverage ranges. Fill in the corresponding data under coverage and capacity on the survey form. This will be used as guidelines by the project manager for prioritizing the site rollout.

Radio Frequency Investigation (RFI) The surveyor should also consider existing radio transmitters that may cause interference to the system. If interference is expected, RFI measurements should e performed to confirm if it is "safe" to put up a site in the proposed location. An example of a possible interfere may be a nearby AMPS site, located along the direction of the antenna.

Height Perform height measurements using methods, previously described. Indicate whether the construction measured is a building, tower, or mast. If there is an additional construction (tower or mast) on top of the building, measure the height, as well. Information on construction heights is vital, since it will guide the cell planner when considering antenna heights to be used in-the future.

Fill in the necessary height data on the survey form.

38

3.4.2 ANTENNA PROPOSALS Antenna Height Compare the proposed antenna heights with the nominal antenna height. According to specifications, the maximum deviation allowed for antenna heights in relation to the nominal or predicted height is 15%. An example: if the nominal antenna height is 35 meters, a variation of up to 40.25 meters for the proposed height is allowed. If the proposed antenna height is shorter than the nominal height, a tower or pole is considered to reach the nominal height. Otherwise, another site location should be chosen. The antenna height must be distinguished from the height described earlier, in that, the antenna height may vary, depending on where on the building or tower it will be installed, whereas "height" simply refers to the building and/or tower height. The antenna height is measured above the mean ground level, see Figure below.

Antenna Direction Analyze the immediate vicinity for coverage purposes. As far as possible, maintain the nominal antenna directions, as planned. However, the nominal directions may not, necessarily, be the best direction to fulfill the coverage objectives. The RF engineer must determine the proposed antenna directions and configurations considering the following items: • Are there immediate or upcoming obstacles along the nominal antenna directions, such as buildings or hills?

• Need the antennas be redirected to cover roads or more populated areas, instead of open areas or water?

• Is an omni or a two-sectored site sufficient to provide coverage and traffic?

• Is it more reasonable to use broader beam width antennas than narrow beam width antennas?

There may exist additional outstanding issues, whereby antenna directions or configurations must be changed.

Antenna Type (beam width, gain, diversity) Normally, antenna types are already laid down in the plan. However, it may be necessary to change antenna type to fulfill the site objectives. The decision is affected by considering antenna characteristics, such as beam width, gain, and diversity type. The surveyor must determine the said characteristics to meet the requirements of the site and its intended coverage. For example urban areas may use the typical 65° antennas, whereas long roads may employ 30° high-gain antennas to provide long range coverage. In areas where the grid is not uniform, a wider beam width antenna should be considered (that is, 105-120° antenna).

Likewise, a check of the antenna space, if space diversity is applied. According to the guidelines, the horizontal separation for diversity in the 900 MHz band is 4 to 6 meters, and 2 to 3 meters in the 1800/1900 MHz band. A wider separation would be better still. For road sites, the use of a space diversity antenna beam width. On the other hand, if the antennas used are of the polarization diversity type, the antenna space is no problem.

39

Meanwhile, tall building in urban areas may require wider vertical beam width antennas to cover as many building floors as possible. As the sites are unknown at the initial design, an approximation of antenna types can be made: 80% of all sector sites should have 65% antennas, 5% should have 30° antennas, and 15% should have 105° antennas.

Antenna Tilt If a network is in its initial stage, antenna tilt is, usually, not recommended. The intention of the network is to provide coverage, initially. However, if the antenna height is too high from the nominal point of view-for high sites, antenna tilt may be recommended. Proposals concerning antenna tilt should be expressed in millimeters for the sake of the installation team and in degrees considering the data input into TEAMS Cell Planer. For areas with an established grid, antenna tilt is recommended. A general rule is to point the center of the antenna lobe towards the theoretical cell border, that is, 2/3 of site-to-site distance, and then to add 2 dB, this result in increased signal strength within the cell and improved C/I. The tilt also tends to "widen" the horizontal beam width of the antenna. This effect is due to ground reflections of the signal. If excessive tilt is needed, evaluate lowering the antennas in combination with the tilt.

Feeder Information on the feeder length is needed to be able to make accurate predictions. It is to be noted that the EIRP of a site, located on top of a building or on the ground will differ significantly.

Therefore, it is important to estimate the feeder length to make sure that the feeder loss is within the tolerable value. As a recommendation, the actual feeder loss must not be higher than 0.5dB from the loss, considered in the TEAMS Cell Planner. For practical purposes, the feeder length may vary up to 10 meters. Fill in the Feeder type, Attenuation, and Approximate feeder lengths on the form.

Photos As mentioned earlier, make sure to take photos of the following: • Building and building entrance (from the street) • 360-degree panoramic view • RBS location • Antenna locations • Antenna directions (usually included in the panoramic view) • Tower (if existing) • Site ID, date and time, written on a sheet of paper Complete the form accordingly, as each item is concluded during the process.

Obstacles Look out for nearby obstacles in the surroundings, which may, possibly, affect the propagation of the signal from the antenna. Take approximate measurements of distance and height applying methods, previously described. The bearing or direction can be taken using the compass.

Complete the survey form with impending obstacles.

40

Comments and Sketches Before leaving the site, make sure all data is gathered and recorded on the survey document. Fill in comments at the bottom of the document to be used as basis by the RND responsible and point out all vital issues. Rejected sites should be commented, as well, indicating the reasons for rejection. To support the photos, make a sketch of the top of the building indicating north, antenna directions, main roads near the building, obstructions (buildings, hills, towers) and clutters around the vicinity.

It is favorable to draw the sketch at the back of the survey form to avoid mixing up forms and sketches.

Survey Reports As a recommendation, it is a good practice to conclude and submit survey reports at the end of each day to the RND responsible for the immediate processing. Also, if possible, develop photos the same day and attach to the reports. If survey teams are far from the main office, completed reports may be sent via fax or through other mediums.

Project Database Information regarding the surveyed sites must be organized and properly compiled. All material should be kept in one single room to which survey team members and cell planners have access.

Likewise, a database of the proposed sites should be established in a master computer, indicating the status of each site. Information in the database must be updated each time a site status is changed. The progress of the project should be possible to track from the database.

3.5 PARAMETERS 3.5.1 GENERAL When a cell is added, or changed, in a cellular system, the cell planner has to produce a document for the cell containing data (the parameters). These documents are called the ^|Cell design data (CDD). The data from all such documents is then converted into a data /transcript tape and loaded in the BSC. For a description of all parameters, with maximum, minimum and default settings please refer to the Cell Design Data document (CDD). The parameters are divided into Site Data, Cell Data.

Locating Data, Idle Mode Behavior Data, Neighboring Cell Data, and Hardware Characteristics Data.

3.5.2 SITE DATA The common site data is the same for all cells in a site.

RSITE The parameter RSITE stands for Radio site. It is the identity of the radio site where the transceiver group (TG) is located. MSC NAME identifies the MSC, to which the cell belongs. MSC NAME is only information, and is not stored in the MSC or the BSC. BSC identifies the BSC, to which the cell is connected. This parameter is only present as information, and is not stored in the BSC. Site name is the name of the site. Site name is stored neither in the MSC nor in the BSC, but is useful information that can help you geographically identify the site. Use a name that gibes an easy explanation of the geographic location of the site, so that everyone familiar with the area knows where the site is.

3.5.3 TCELL DATA CELL Cell stands for cell name, it is recommended to use the name of the site plus one more character to identify the cell within the site. Usually, numbers (1,2, 3...) or letters (A, B, C...) are used to identify the antenna pointing direction of the cell. Use a reference direction for the network, for example, zero degrees true north. The cell whose antenna direction is closest to this reference when counting clockwise should be assigned the letter A (or number 1).

41

CGI CGI stands for Cell Global Identity and is the global identity of the cell in the whole system. It is composed of four different parameters:  MCC. Mobile Country Code  MNC, Mobile Network Code. Identifies the PLMN, that is, the operator.  LAC, Location Area Code. Identifies the location area.  CI, the Cell Identity within the location area.

42

The CGI is sent to the MS as part of the system information massage. The combination MCC - MNC LAC is also known as the Location Area Identity (LAI).

BSIC BSIC stands for Base Station Identity Code. The BSIC is composed of two entities: -NCC, Network Color Code. (NCC=0..7) -BCC, Base Station Color Code. (BCC=0..7) NCC is used to discriminate cells in two different PLMNs that use the same frequency, see Figure.

These PLMNs with the same frequencies are in different countries, since the PLMNs in one country use different parts of the frequency band. The NCC assignment must be decided by agreements between operators and countries. The operators may use more than one NCC value, as long as they only use their agreed value in the border areas. BCC is used for protection against co-channel interference within the PLMN. The MS reports the BCC value so that the BSC can distinguish among different cells transmitting on the same frequency. If frequency reuse clusters are used, it is recommended that all BTSs in a cluster use the same BCC, and that an adjacent cluster should use another BCC. If clusters are not used, great care must be taken when planning BCC. BSIC is defined per cell and is sent on the SCH (on the BCCH carrier).

BCCHNO The frequency carrying the BCCH (Broadcast Control Channel) in a cell is defined by the Absolute Radio Frequency Channel Number, ARFCN, with the parameter BCCHNO. The defined ARPCN must be unique within the cell.

BSPWRB Base station output power in dBm for the BCCH RF channel number. The BTS can transmit with different power levels on the frequency that carries the BCCH and on the frequencies that do not carry it. The power is specified at the power amplifier (PA) output, that is, immediately after the transmitter unit and before the combiner.

MBCCHNO MBCCHNO is the BCCH allocation (that is, it indicates to the MS the frequencies that must be monitored and measured in idle, active or both modes). They are sent to MSs in the system information message, on the BCCH channel in idle mode and on the SACCH in busy mode.

Up to 32 BCCH carriers can be defined by specifying their ARFCN. The measurement reports from the MS are sent to the BSC on the SACCH, indicating the signal strength and quality of the serving link, and the signal strength frequency, and BSIC from the six BTSs with the strongest signal strength. Only measurement from neighboring cells that meet the requirement that their BCCHs have a frequency as indicated by MBCCHNO, and an NCC as indicated

by NCCPERM, are valid. To be allowed to perform a hand over to any of the measured cells , it is also necessary to

43

define the measured cell as a neighbor to the serving cell. Up to 64 different cells can be defined as neighbors.

LISTTYPE The parameter LISTTYPE identifies which type of list the chosen frequencies are located on. When the MS is in IDLE or ACTIVE mode, it measures on the frequencies of the corresponding list.

If LISTTYPE is not specified, both lists are affected.

BSPWRT Base Station output power in dBm for the non-BCCH RF channel numbers.

CHGR The CHGR parameter stands for Channel Group Number. A cell is divided into one or several channel groups that contain all physical channels on an arbitrary number of frequencies. Channel groups are connected to a Transceiver Group (TG). Channel groups can be used for controlling the properties of the assigned frequencies (for example, to set frequency hopping on and off). Cells with a sub cell structure must have, at least, one channel group defined in each sub cell. A cell without a sub cell structure is given CHGR = 0 by default. However, a cell planned with a sub cell structure as overlaid under laid sub cell is given CHGR = 0 by default for the under laid sub cell.

3.5.4 LOCATING DATA BSPWR BSPWR is the BTS output power on the BCCH frequency. BSPWR is defined at the reference point, used in the locating algorithm.

MSRXMIN Minimum required signal strength received at the MS in a given cell to consider the cell as a possible candidate for handover.

MSRXMIN takes a positive value that represents the corresponding negative value in calculations.

BSRXMIN Minimum required signal strength received at the BTS at the reference point, to consider the cell as a possible candidate for handover.

BSRXMIN takes a positive value that represents the corresponding negative value in calculations.

44

MSRXSUFF Sufficient signal strength received at the MS to consider the cell selectable for further ranking, according to the magnitude of the path loss.

MSRXSUFF takes a positive value that represents the corresponding negative value in calculations.

BSRXSUFF Sufficient signal strength received at the BTS, at the reference point, to consider the cell selectable for further ranking, according to the magnitude of the path loss.

BSRXSUFF takes a positive value that represents the corresponding negative value in calculations.

BSTXPWR BSTXPWR is the BTS output power on all frequencies other than the BCCH frequency.

BSTXPWR is defined at the reference point, used in the locating algorithm.

SSEVALSD Signal strength filter for speech /data The filters for down and uplink signal strength in the serving cell and downlink signal strength from neighboring cells are selected by SSEVALSD for the channel mode speech/data.

QEVALSD Quality filter for speech/data.

The filters for quality in down and uplink in the serving cell are selected by QEVALSD for the channel mode speech/data.

SSEVALSI Signal strength filter for signaling only.

The filters for down and uplink signal strength in the serving cell and downlink signal strength from neighboring cells are selected by SSEVALSI for the channel mode signaling only.

QEVALSI Quality filter for signaling only.

The filters for quality in down and uplink in the serving cell are selected by QEVALSI for the channel mode signaling only.

SSLENSD Length of signal strength filter for speech/data.

SSLENSD should be specified only when SSEVALSD is in the range 6 to 9.

45

QLENSD Length of quality filter for speech/data.

QLENSD should be specified only when QEVALSD is in the range 6 to 9.

SSLENSI Length of signal strength filter for signaling only.

SSLENSI should be specified only when SSEVALSI is in the range 6 to 9.

QLENSI Length of quality filter for signaling only.

QLENSI should be specified only when QEVALSI is in the range 6 to 9.

3.5.5 NEIGHBORING CELL RELATION DATA All neighbor relations should be defined. It is possible to define up to 64 neighbors for each cell.

CELLR The CELLR parameter is the Related cell designation. The identity of the neighboring cell for which the set of parameters should be applied is set by means of CELLR. The name of the neighboring cell, as defined by the parameter cell in its corresponding CDD, must be specified here. All cell relations are mutual, unless explicitly specified. Offset parameters have antisymmetric relations, and hysteresis parameters have symmetric relations. If the neighboring cell belongs to another BSC then this must be specified explicitly by means of CTYPE. -EXT The neighboring cell is external.

-omitted the neighboring cell is internal.

RELATION is only specified when the relation is one way. This means that offset and hysteresis parameters are only defined in one direction. RELATION is always set to single for external cells, that is, neighboring cells that belong to another BSC. CS Co-site, indicates if a cell shares the same, site as its neighbor.

46

3.5.5.1 PARAMETERS FOR NEIGHBORING CELL RELATIONS These parameters must also be defined for neighboring cell relations: BQOFFSET AWOFFSET CAND TRHYST KHYST LHYST TROFFSET KOFFSET LOFFSET HIHYST LOHYST HYSTSEP OFFSET

(parameters valid for Ericsson 1 locating algorithm)

(parameters valid for Ericsson 3 locating algorithm)

KHYST KHYST is the hysteresis for cell borders defined by the signal strength criterion. It is defined as a cellto-cell relation, that is, in each cell it can be defined individually for each neighbor that has been defined for that cell. KHYST is a symmetrical relation parameter, that is, the same value applies for both directions of the cell-to-cell relation.

LHYST EHYST is the hysteresis for cell borders defined by the path loss criterion. It is defined as a cell-to-cell relation, that is, in each cell it can be defined individually for each neighbor that has been defined for that cell. EHYST is a symmetrical relation parameter, that is, the same value applies for both directions of the cell-to-cell relation.

TRHYST Signal strength hysteresis for a K-and E-cell border segment.

KOFFSET Signal strength offset when evaluating K-cells.

LOFFSET Path loss offset when evaluating E-cells.

TROFFSET Signal strength offset for a K-and E- cell border segment.

HIHYST Signal strength hysteresis when evaluating high signal strength cells.

LOHYST Signal strength hysteresis when evaluating low signal strength cells.

47

HYSTSEP Signal strength separator that specifies whether the serving cell is currently a low or a high signal strength cell.

HYSTSEP takes a positive value which represents the corresponding negative value in calculations.

OFFSET Signal strength offset.

3.5.5.5 EXTERNAL NEIGHBORING CELL DATA For external cells additional parameters need to be defined, since the cells are defined in a different BSC. These are CGI, BSIC, BCCHNO, MISSNM, EXTPEN, SCHO, BSPWR, BSTXPWR, MSTXPWR, BSRXMIN, MSRXMIN, BSRXSUFF, MSRXSUFF, AW, HCSBAND, HCSBANDHYST, HCSBANDTHR, LAYER, LAYERHIST, LAYERTHR, PSSTEMP, and PTIMTEMP. 3.5.6 IDLE MODE BEHAVIOR - CELL DATA ACCMIN Minimum received signal level in dBm at the MS for permission to access the system.

CCHPWR Maximum transceiver power level an MS may use when accessing on a control channel.

CRH Cell reselection hysteresis. Receiving signal strength (rxlev) hysteresis for required cell re-selection over location area border.

NCCPERM PLMN (NCC) Permitted.

Defines the allowed NCCs (Network Color Code) on the BCCH carriers for which the MS is permitted to send measurement reports.

CB Cell Bar Access Defines whether the cell is barred for access or not.

No The cell not barred for access.

Yes The cell is barred for access.

CBQ Cell Bar Qualify HIGH: The cell has high priority.

LOW: The cell has low priority.

48

ACC Access Control Class Defines which access classes that are barred. Up to 16 access classes can be defined.

Class 10 defines emergency call in the cell.

0 to 9 Access Classes that are Barred.

10 Emergency call not allowed for MSs belonging to classes 0 to 9.

11 to 15 Access Classes That Are Barred.

MAXRET Maximum retransmissions.

Defines maximum number of retransmissions an MS may perform when accessing the system on RACK. TX TX-integer.

Defines the number of timeslots over which the MS may spread transmission when accessing the system.

ATT Attached- detach allowed.

NO MSs in the cell are not allowed to apply IMSI attach and detach. YES apply IMSI attach and detach.

MSs in the cell should

T3212 T3212 time-out value.

Defines the time out value that controls the location updating procedure, that is, when notifying the availability of the MS to the network.

CRO Cell Reselection Offset, (for phase 2 MSs).

Defines an offset to encourage or discourage MSs to select the cell while it is camping on another cell, that is, perform a cell reselection.

TO Temporary Offset, (for phase 2 MSs) Defines a negative offset applied to CRO. PT Penalty Time, (for phase 2 MSs) Defines duration for which TO is applied.

49

3.5.7 THARDWARE CHARACTERISTICS TG The parameter TG is the transceiver group identity. A TG includes all radio equipment connected to one transmission antenna, and serves one cell or a part of a cell. Each TG must be given a unique value of TG within a BSC. It is recommended to start with TG = 0 and then increase TG one step at a time. A TG is connected to a cell via one or several channel groups. A TG can support a maximum of 16 channel groups. If the BTS is an RBS 200 multi cell, or belongs to RBS 2000 series, a TG can support channel groups in more than one cell, that is, one TG can serve all cells (maximum 3) at the site.

TG 0: Cell Al, Cell A2, Cell A3, Each TG can contain up to: RBS 200 RBS 2101 RBS 2102 RBS 2202 RBS 2103 RBS 2301 RBS 2302

MC 7 TRXs 4TRUs 12TRUs 12TRUs 12TRUs 2 TRUs 2 TRUs

It is recommended to define one TG per site, if not more TRXs /TRUs than those specified above are required.

If the BTS is an RBS 200, or an RBS 205 a TG can only support channel groups belonging to the same cell, that is, each cell must be served by a TG of its own: TG0: CellAl TG 1: CellA2 TG2: CellA3 Each TG can contain up to: RBS 200: RBS 205:

16 TRXs 16 TRXs

It is recommended to define one TG per site if not more TRXs /TRUs than those specified above are required.

50

CHAPTER-4 INDOOR CELL PLANNING INTRODUCTION An indoor system can be built for different reasons. If the coverage is poor from cells outside the building, leading to bad quality, a solution can be to build an indoor system. Buildings generating a high traffic load, such as conference centers and airports, may need indoor systems to take care of the traffic. A different application is the business indoor system with the aim to complement or replace the fixed telephony network. The aim of indoor cell planning is, as for "traditional" cell planning, to plan for good coverage and capacity, and at the same time interfere as little as possible.

The focus is on antenna and RBS- systems, RF design, and antenna configuration, but also frequency planning and capacity issues are described. The tools for indoor cell planning, TEMS Light, and TEMS Transmitter, are also described with focus on how to use them in the planning process.

4.1 CAPACITY DIMENSIONING When dimensioning the capacity of an indoor cell, its application must be considered. Two different categories of indoor cells can be identified: 1. Public indoor cells. Indoor cells which cover public buildings, such as shopping centers and airport terminals.

2. Business indoor cells. Indoor cells which cover areas, such as offices. In some applications the coverage, capacity and quality demands in business indoor cells may be considerably higher than those in public indoor cells, and the GoS must be very low.

Diving One Cell into Several Cells A way to increase the capacity is to divide the cell in a "one cell building" into several cells. This should only be considered if the building is large and the traffic demand is high. The cell should be divided into, at least, three cells to allow frequency re-use in the building, and the division should preferably be vertically performed. A horizontal split should be avoided, at least for frequency reuse, but may be necessary in low and long buildings. The cell size of the divided cell constitutes the re-use distance. The recommended dividing distance is around four floors, depending on the leakage between the co-channel cells.

4.2 ANTENNA AND RBS SYSTEMS- OVERVIEW When designing an indoor system, the ambition is (note that this is not a requirement) to get an antenna network which is as symmetric as possible to provide each single antenna within the system with the same output power. It is desirable to place the RBS somewhere in the middle of the building to minimize the feeder distance of the antennas. A preparation for any future extension of the indoor system, both from a coverage point of view and from a capacity point of view, should always be considered before installation. The RF- link budget should be calculated so that there is a possibility to add

51

power splitters, hybrid couplers, etc. to the antenna system in case of further extension of the antenna network. Although the intention, at the planning of an indoor system, may be to operate on a GSM frequency single-band, it is more favorable to prepare the antenna network for multi-band.

The higher investment cost of multi-band equipment is marginal, compared to what it would cost, in the future, to replace the single-band equipment with multi-band equipment. In an indoor cell, the downlink is usually the most critical link in the air-interface. This means that there is no need for using uplink diversity in an indoor system, or to use amplifiers for improving the uplink signal.

4.2.1 ANTENNA SYSTEMS Antennas The antenna configurations for indoor applications can be divided into four categories: • Integrated antennas, that is, antennas integrated in the base station.

• Distributed antennas using a coax feeder network.

• Leaking cable.

• Distributed antennas using a fiber-optical feeder network.

A single antenna is here considered to be a special case of distributed antennas.

There are several types of antennas that are suitable for indoor applications. The two most commonly used antenna types are • The directional antenna (figure 4.1) and • The omni-directional antenna (figure 4.2)

Figure 4-1: Directional Antennas.

Two commonly used types of omni-directional antennas are the so-called "Mexican hat" antenna and the so-called "rod" or "tubular mast" antenna, refer to Figure 4.2. Both antenna types are attached to the ceiling where they are difficult to spot among other equipment, such as smoke detectors. Comparing these two antenna types, the "Mexican hat" is to be preferred, since it has a more stable construction than the "tubular mast".

52

Figure 4-2: Omni-Directional Antennas The "Mexican hat" is usually mounted without a jumper cable. The feeder is bent down into a drilled hole through the ceiling and is connected to the antenna. Once the antenna has been connected to the feeder, it is attached to the ceiling.

Integrated Antennas An indoor area which can be covered from one location, for example, open premises, and where it is possible to have the RBS mounted on a wall, is a suitable application for RBS 2302 using the integrated antennas. Examples if applications are, for example, sports arenas and railway stations.

Antennas Distributed via a Coax Feeder Network Antennas distributed via a coax feeder network, is the configuration having the widest application range. This can be explained by the attractive features of the configuration: • Low cost.

• Flexibility in the design when shaping the coverage area: - Power distribution can be controlled by using unequally distributed power splitters.

- Additional antennas are inexpensive and easy to add.

• Robust and well-proven technique: - No active devices in the antenna system requiring local power supply or supervision.

Coaxial Cable The most suitable dimensions of coaxial feeders for indoor systems are listed (including typical feeder loss values) in table 7-1.The N- connector is suitable for all the listed coaxial cables, except for the 7/8" coaxial cable. The 7/8" coaxial cable, which is hard to install due to its inflexibility, should be used together with 7/16 connectors.

53

Table 4-1: Typical Feeder Loss Values.

Feeder Type

Feeder Loss, dB/100m 800-900 MHz

Comments 1800- 1900 MHz

CF %"

13.5

20.5

LCF 3/8" ½ Super flex

10 11

14.5 16.5

LCF 1/2" LCF 7/8"

7 4

10.5 6.2

Suitable to use between hybrid couplers, etc.

Conceivable, but not recommended for indoor applications.

4.2.2 POWER SPLITTERS Power splitters are used for splitting up the antenna feeder network. There are two types of power splitters: 1. Equally distributed The equally distributed power splitters divide the power equally over the output ports, which means that a two-way power splitter has an attenuation of 3 dB, a three-way power splitter 5 dB, etc.

2. Unequally distributed The unequally distributed power splitters distribute the power unequally over the output ports. This type of power splitter is suitable in, for example, high buildings with small floor areas or tunnels.

Leaking Cable Leaking cable may be an alternative to distributed antennas in some applications, such as car or train tunnels. Leaking cable is also conceivable in indoor applications. Compared to distributed antennas (coaxial), leaking cable is generally a more expensive alternative both in terms of equipment and installation costs.

There are two types of losses associated with leaking cable: 1. Longitudinal loss The longitudinal loss is the analog of ordinary feeder loss. For a leaking cable, it is somewhat higher than for a normal coaxial cable, due to the intentional leakage.

2. Coupling loss The coupling loss is the average difference between the signal level in the cable and the power received by a dipole antenna at a certain distance, usually six meters, from the cable. Some typical values of longitudinal and coupling loss are given in table 4-2.

54

Table 4-2: Typical Longitudinal and Coupling Loss Values for Leaking Cables.

Cable Type %' 3/8" 1/2" 7/8"

Longitudinal Loss, dB/100m 800-900MHz 1800- 1900MHz 23-32 32-52 12-14 18-21 9.5-11 13-18 5.5-6 8-11

Coupling Loss, dB 800-900MHz 69 68 68 69

1800- 1900MHz 71 74 73 72

Antennas Distributed Via a Fiber-Optical Network There are different solutions based on fiber-optics that can be used for indoor systems. The main purpose is to overcome losses in long coaxial feeder cables. One disadvantage of using a fiber-optical network is that each antenna terminal requires local power supply and alarm handling. An additional fiber-optical antenna requires the installation of two additional transmitter/receiver-fibers all the way from the optical interface unit to the location of the antenna. Ordinary antennas may, however, be connected to the external antenna terminal on the fiber-optical antenna.

4.3 RF DESIGN Link Budget The link budget of an indoor cell can be determined in a way similar to the link budget of macro cells.

Required Signal Strength To be able to perform a call in a real-life situation some margins must be added to the MS sensitivity level to compensate for Rayleigh fading, interference, and body loss. This obtained signal strength will be referred to as SSreq and can be expressed as: SSreq = MSS + RFmarg +BL Where MSens = MS sensitivity (-104dBm) RFmarg = Rayleigh fading margin (3 dB no frequency hopping, 0 dB frequency hopping) IFmarg = Interference margin BL = Body loss (5 dB MHz, 3dB 1800/1900MHz) Design Level In the design phase, an extra margin must be added to SS req to handle the log-normal fading. The obtained signal strength should be used when planning the system according to the Keenan-Motley model and will be referred to as the design level, SSd es.

Where,

SSdes = SSreq + LNFmarg LNFmarg = The indoor log normal fading (5 dB can be used as an estimate).

55

BTS Output Power The required BTS output power can be calculated by adding the losses in the antenna network to the design level. That is: "outers Where, PoutBTS = SSdes +Lp - Ga + Lf + Lps + L, Where PoutBTS = Lp Ga Lf Lps Lc

BTS output power at the antenna connector. = Path loss from antenna to MS at the cell border. = BTS antenna gain, MS antenna gain assumed to be 0 dB. = Feeder loss = Loss in power splitters. = Loss in external combiners, duplexers, diplexers, etc.

Note that the loss in the CDUs is not part of L c, since the reference point for the BTS output power is at the antenna connector.

Design Levels In areas with a high interference level, the required interference margin must be higher, and in areas with low interference it must be lower. The question is only how high and how low. To avoid the complex matter of measuring the level of interference and from this data calculate SS des, a simplified design procedure is proposed. The idea is that by studying the surrounding radio environment it should be possible to classify the level of interference in the cell as low, medium, or high and from this classification determine what the required signal strength should be. In table 4-3, the proposed values of SSdes are given for each of the mentioned interference levels. Note that these values must be regarded as rules of thumb.

Table 4-3: design levels and required signal strengths in areas of different interference.

Level of interference Low Medium High

Design level (SSdes) -85 dBm -75 dBm -65 dBm

Required level (SSreq) -90 dBm -80 dBm -70 dBm

The cell should be designed so that SS des is obtained at at the cell border when designing the cells according to the Keenan-Motley model. In the verification measurements, it is, of course, not necessary to measure SSdes- In that case, SSreq is sufficient, since the log-normal fading dips are included in the measurements.

4.4 ANTENNA CONFIGURATION When the requirements for the received signal strength and coverage are defined, an antenna configuration must be chosen. Coverage measurements are time consuming and should be used, primarily, to decide if a nominal configuration provides the anticipated coverage. It becomes more and more important to plan for reduced interference towards neighboring cells. The requirement for low interference towards other cells implies that:

56

â&#x20AC;˘ â&#x20AC;˘

Several antennas should be used. This lowers the necessary output power at each antenna.

It is, furthermore, not expensive to add antennas to a distributed antenna system.

In general, do not place antennas close to windows.

Work Flow 1. The purpose of this process is to create an antenna plan which works "on paper". An antenna plan includes antenna locations and types, as well as design of the feeder network.

2. Some antenna locations may be unsuitable from an implementation point of view and may have to be adjusted. If major changes are needed, the creation of a new nominal antenna plan is required.

3. Since predictions inside buildings contain uncertainties, such as wall losses, it is necessary to control the actual coverage from the nominal antenna.

4. When the nominal antenna plan has been decided, the system is implemented.

Nominal Antenna Plan A nominal cell plan is made in two steps: 1. Studies of different indoor configurations with the desired performance regarding public or business, as well as studies of interference situation and building types. The aim is to develop a knowledge of indoor antenna configurations.

2. Path loss estimations. This can be done with paper and pen.

4.4.1 ANTENNA CONFIGURATION, EXAMPLES Single Antenna in an Office Building: Requirements The required signal strength is -65 dBm to obtain a sufficient C/I. The signal strength requirement is derived from the fact that the building is tall, compared to the surrounding buildings and that the frequencies are very tightly reused in the area, giving high interference in the building.

Solution An omni-directional antenna is placed in the middle of the area that should be covered. The antenna is fed with 30 dBm, the maximum power with the coax net and base station used.

57

Result Floors six and seven are fully covered, but floor five is not covered in the shaded areas. The cell borders are not possible to control. The cell extends several floors outside the desired area. The signal strength also varies significantly in the cell, and is very high close to the antenna (approximately -25 dBm).

Conclusion 1. Equipment and installation costs are slightly lower than for a distributed antenna system.

2. There may be difficulties in obtaining coverage.

3. The higher interference towards other cells may prevent tight re-use.

4. The cell borders may be difficult to control.

Distributed Antenna System in an Office Building: Another solution to provide coverage of the three floors is to use several antennas.

Requirements The same as in the preceding example.

Solution A distributed antenna system consisting of eleven antennas, both directional and omnidirectional antennas. The power fed into the antennas is 6 dBm. No antennas are mounted in rooms next to outer walls.

Result Full coverage. Evenly distributed signal strength and a low amount of radiated power to the surroundings.

Conclusion A distributed antenna system can be used to control the cell borders, giving high coverage and lower interference than one single antenna. This is especially desired in business applications where buildings tend to be tall and excellent quality is required. It is especially important to use many antennas and low EIRP high up in a building with line-of-sight to other cells. This decreases the risk of interfering other cells.

Coverage predictions: In the same way that the Okumura-Hata model has been developed semi-empirically for macro cell coverage predictions, the Keenan-Motley model has been developed for indoor wave propagation predictions. This model has been accepted by COST 231, and contains a 3D term. The following are rough estimates of wall loss parameters that can be used: â&#x20AC;˘ 2 dB for plaster board walls in office buildings, etc. â&#x20AC;˘ 5 dB for reinforced concrete walls in stairwells and car parks.

58

Antennas and/or BTS + feeder network are distributed by the user and the program quickly calculates the signal strength. The model underestimates the signal strength in certain locations.

This may be seen in rooms at the end of corridors, far from an antenna. The underestimation of the signal strength is due to the fact that the model assumes that the signal passes through several walls, whereas, in reality, it is reflected and diffracted along the corridor. This leads to a higher signal strength than is expected in these locations.

Manual Estimate of Path Loss In a simplified form the Keenan-Motley model can be written in the following way for 900MHz. L = 31.5 + 201og(d) + Nw W Where, L is the path loss between isotropic antennas (dB) d is the transmitter-receiver separation (m) Nw is the number of walls passed by the direct ray.

W is the wall attenuation factor (dB).

The free space path loss increases by 6 dB for 1800 MHz in the equation above, a figure that can be used for 1900 MHz, as well. The total wall loss is given by counting the number of walls between the antenna and the estimated location and multiplying this figure by the wall attenuation factor. A more elaborate model also considers floor loss, as well as an additional distance dependent loss, due to diffraction, scattering, obstructive objects, and destructive interference, which is added after a breakpoint distance.

4.4.2 DISTRIBUTED ANTENNA CONFIGURATION FOR INDOOR CELLS If a building with low traffic concentration is to be planned as one single cell, the antennas should be positioned so that the distribution of the signal strength within the cell becomes as even as possible.

When the "several-cell" configuration is used for a building, there should be enough distance to separate co-channel cells. This distance comprises approximately four floors. The antennas can, with this re-use distance, still be placed in a zigzag fashion to get a distribution of the signal strength that is as even as possible. However, placing antennas on top of each other may facilitate the planning and installation. For buildings that are divided into several cells with very tight re-use (one or two floors' separation) the same antenna positions on co-channel cells are recommended to get the most favorable C/I. such tight re-use is, however, not recommended for business indoor systems.

Horizontal re-use of cells within buildings is not recommended.

RF Electromagnetic Exposure Measurements and calculations of the RF exposure levels from omni-directional and directional indoor Pico cell antennas have been performed at Ericsson, both at 900 and 1800 MHz. the tests were performed at the maximum output power possible and at a distance of 5 cm from the surface of the antenna unit, in the direction of the maximum

59

emission. This corresponds to worst case exposure conditions. The results have shown that the exposure levels are below the general public and occupational RF safety standards, for example, those published by WHO, IRPA/ICNIRP, CENELEC, IEEE/ANSI, and FCC. Therefore, there is no need for any special RF exposure safety instructions for these antennas. Installation and maintenance people can work close to the antennas in operation without any risk of RF exposure exceeding the safety limits. It is, however, always advisable to place the antennas so that people cannot easily touch them or stay close to them, which could affect their performance. A discretely placed antenna also reduces the risk of unnecessary public concern about the RF exposure.

Survey The nominal configuration may not be suitable for the building. Reasons for this can be that the suggested locations are too close to where people sit, that there are obstacles deteriorating the radiation pattern or that there are problems mounting the antennas at these locations. Note that the landlord often has an opinion about the antenna locations. Ensure that these locations are accepted before final installation. This will save unnecessary work. It is also necessary to consider the effect of non-optimal antenna locations. See to it that the antennas are not placed in positions where the cable running will be difficult, for example, with a concrete wall between the antenna location and the cable ladder. Note that omni-directional antennas are ceiling mounted and directional antennas are wall mounted.

Coverage Measurements Coverage measurements are performed to verify the antenna configuration so that it provides a sufficient coverage. The antenna locations that are determined are then tested one or several at a time. A test transmitter is connected to the antenna and the signal strength is measured with a mobile receiver.

Transmitter Equipment For the generation of test signals, it is suitable to use one or several TEMS Transmitters. The TEMS Transmitter is a small unit that transmits in the GSM downlink band. The output power is adjustable between 20 and 27 dBm (GSM 900/1900), or 22 and 27 dBm (GSM1800). Using two optional attenuators the output power can be varied between 2 and 27 dBm (GSM 900/1900), or 4 and 27 dBm (GSM 1800). A complete editable BCCH is transmitted whereas the other 7 time slots contain an un-modulated carrier.

Receiver Equipment The recommended receiver is TEMS Light equipment. This is a TEMS mobile connected to a small pen-operated PC. The TEMS light program is a reduced version of the standard TEMS PC software, but with the possibility to log fix points by marking with the pen on a scanned map. The information in the log files is displayed on the scanned map as color marks, associated to a window with more information about each mark. If TEMS Light is not available, the standard TEMS equipment or a TMR can be used. A faster coverage verification can be made using TEMS pocket. This is a test mobile with some TEMS functions available on the mobile display. TEMS pocket cannot be operated from a computer. Areas where the signal may be weak are checked by locking TEMS

60

pocket to the used ARFCN and BSIC and by reading off the signal on the display. In addition, there is an audible warning for low signal.

4.5 FREQUENCY PLANNING Here, it is assumed that the public indoor cells use the same frequency band as the outdoor cells (macro cells and micro cells), if not stated otherwise. It is also possible that indoor cells may have a dedicated frequency band. This facilitates frequency planning. Business indoor cells should be planned in the same way as public indoor cells. A separate band is recommended later on for quality and capacity reasons, for easy frequency planning and O & M handling, especially, if a tight MRP is applied for the macro cells. If only one cell is used within a building, no frequency plan is needed for that cell other than the consideration taken for outdoor cells. When a building is divided into more than one cell, co-channels should be planned as far apart as possible.

4.5.1 PLANNING RULES WITH RE-USE OF OUTDOOR FREQUENCIES Frequency planning is performed manually, selecting suitable frequencies by studying the operator's frequency plan.

• Exclude frequencies of neighboring cells which are likely to significantly interfere with the indoor system and their adjacent frequencies.

• From the remaining frequencies, choose those that, most likely, will not to cause any interference. The BCCH frequencies should be the least disturbed of these. Hop on several frequencies to smooth out the interference.

The following needs to be considered if there are too few acceptable frequencies: • • •

Increase the signal strength for indoor cells Allocate the dedicated frequencies for indoor cells. Start with frequencies for the BCCH. Redesign the frequency plan.

4.5.2 PLANNING RULES WITH DEDICATED FREQUENCIES Dedicated frequencies for public indoor environments are useful when there are several indoor systems at a rather low height in the building, that is, mostly shopping malls and subway stations. In this case, it is recommended to use a group of 4-6 frequencies and reuse them in all buildings. The important issue is that, at least, one best server outdoor cell must geographically separate the public indoor cells. Dedicated frequencies for business indoor should be considered when several of high buildings in a close area will be planned. The need for dedicated indoor cells when one cell is needed is rather low and the general method of re-using outdoor frequencies should be applied.

61

4.5.3 TALL BUILDINGS AND SKYSCRAPERS The business indoor cells are, very often, located in tall buildings. One way to plan is to use the standard method, described above, for the lower part of the building and to use the dedicated frequencies for the upper parts of the building. This provides good quality even for tall buildings.

There need to be several tall buildings with indoor systems if, the dedicated frequencies for an indoor approach should be spectrum efficient.

4.6 TRAFFIC CRONTROL In many situations, it is necessary to control the traffic flow in the indoor cell. For example, it is often desired to direct the traffic from the nearby macro cells to the indoor cell, and make it stay there, in order to off-load the macro cell. Another requirement may be that only certain subscribers should be allowed to access the cell. This can be achieved by appropriate use of the radio network features: Hierarchical cell structures, idle mode offsets, and Differential channel allocation.

4.7 STUDY CASE A building (that is, the Ericsson training center in Kista, Sweden) consists of four floors, each approximately 70 meters long and 18 meters. All indoor areas in this building have poor coverage from the serving cell outside the building. Indoor walls have a loss of 5 dB per wall. Floors/ceilings between two floors attenuate 25 dB. Outer walls have an attenuation of 18 dB. 4.8 DESIGN CRITERIA Coverage Good coverage, SSdesign > -85 dBm.

Capacity The capacity demand is 200 subscribers, with a traffic of 30 mE/subscriber during busy hour.

The grade of service is 2% System Balance Balance towards the most common class of MS. Hardware BTS, antennas, cables, etc. in accordance with the data, previously given, in this chapter.

Task Make the design, based on the information previously provided. Present a block diagram, signal level diagram, material list, and floor plans with their material positions marked.

62

Chapter-5 NETWORK EXPANSION 5.1 INTRODU Capacity demands for GSM systems increase. In order to meet these demands, operators look for cost-effective alternatives that both support the continued improvement of the network quality and enhance the services that are provided. With the GSM systems, Ericsson is able to offer an extremely attractive way to a multiple increase in radio network capacity, in a very spectrum and cost-efficient way. The concept is based on tight frequency reuse, multi band operation, and micro cells. The benefits, derived from frequency hopping, are utilized to achieve a tighter frequency plan. A tighter frequency reuse allows for more transceivers per cell and/ or making frequency available for a very spectrum-efficient micro cell implementation. Adaptive Multi beam Antennas is a new technique that substantially increases the gain from tighter frequency reuse. It can increase the capacity of up to 250%, compared to the tightest reuse, possible today. Operators with access to both the 900 MHZ and the 1800 MHz frequency bands can implement a multi band functionality, and will, thus, achieve a seamless service between the bands. In the near future, many operators will have to face the challenge of introducing GPRS/EDGE services into their networks. In the first phase, no particular consideration is required concerning the radio network, due to similar interference, robustness of speech, and GPRS phase one, whereas the second phase of GPRS, especially EDGE, will need special consideration to achieve the highest possible data rates. Here, the network improvements, offered

by The Way Forward, will be of invaluable assistance to the operator, since it allows for the successful introduction of high speed data services.

5.2 CELL SPLIT It is evident that a smaller cell size increases the traffic capacity. However, a smaller cell size means more sites and higher costs of the infrastructure. Obviously, it is preferable not to work with unnecessarily small cell sizes. What is needed is a method that matches cell sizes to the capacity requirements. The system is started using a large cell size; however, when the system capacity needs to be expanded, the cell size is decreased to meet the new requirements. This normally also calls for using different cell sizes in different areas. This method is called cell split.

Example: Initially, the largest possible cell size is used, considering coverage range. The next step is to introduce three cells per site using the original sites and feeding the cells from the corners. This represents a cell split of 1 to 3. Now, the number of sites is still the same, but the number of cells is three times as many. The next step is to do a cell split of, for example, 1 to 4. The old sites are still used in the new cell plan, but additional sites are required. Cell split 1 to 3 requires three times as many cells. After the split, the capacity is three times higher per area unit, and the cell area is three times smaller. The antenna directions on the site that exited before the split must be changed by 30 degrees. Cell split 1 to 4 requires four times as many sites. After the split, the capacity is four times higher per area unit, and the cell area is four times smaller. There is no need to change the antenna directions in a 1: 4 cell split.

63

5.3 FINAL TRAFFIC CAPACITY After having undertaken the different steps of cellular system design, it is time calculate the capacity of a typical cellular configuration. Assuming that a cell radius 14 km is used initially, in an eight cell cluster of omni cell (step 0) and then introdi Sectorization (step la). Since a 24 reuse is not common for digital cellular systems, immediately introduce a tighter (12) reuse pattern (step Ib). This is followed by t successive one to four (1:4) cell splits (2 and 3). Assume that 24 carriers are available: Estimating the traffic capacity per cell and km 2, and assuming a GOS_o_f 2% and 20i per subscriber, table 8-1 is obtained.

Step

Cell Radius

N

Channels per Cell

Cell Area

Subs./ Cell

D:o/kn2

0 La Lb 2 3

14km 8km 8km 4.6km 2km

8 24 12 12 12

22 7 14 14 14

510km2 166km2 166km2 55km2 14km2

745 145 410 410 410

1.5 0.9 2.5 7.5 29

As is shown in the table, the capacity is decreased after Sectorization. This is due to t lower Trunking efficiency when there are less channels per cell. This is a necessary st to be able to proceed with the subsequent stages of cell splits. In the following 1:4 ce splits, the capacity per km 2 increases four times per cell-split.

5.4 IMPLEMENTATION Starting with a theoretical cell plan, site locations are now adjusted to conform to what physically possible and convenient as regards, for example, existing buildings or towei In this context, it is also wise to check the surroundings of the location for potential inter-modulating transmitters belonging to other radio networks. In practice, it is n uncommon that two or even more alternative site locations exist at this stage. It essential that both C/A and C/I are predicted for each cell, using the selected sites ai considering the aforementioned factors.

5.5 HIGH CAPACITY SOLUTIONS 5.5.1 CAPACITY OPTIONS Operators have, traditionally, built smaller and smaller cells to increase the network capacity.

However, after a satisfactory indoor coverage has been achieved, further economical and a radio network performance aspect. Expansion of the macro cell network is usually costly and frequently faces difficulties concerning site acquisition. Our approach is, therefore, that an

operator should maximize the capacity of the existing GSM infrastructure before investing in now sites.

Main Way Forward Tighter Frequency Reuse

64

By using frequency hopping, Ericsson quality based dynamic power control and discontinuous transmission, innovative frequency allocation techniques, such as MRP -Multiple Reuse Pattern and FLP - Fractional Load Planning, can be implemented. These enable very tight frequency reuse patterns, allowing more transceivers per cell. The MRP uses base band frequency hopping, which means that the number of transceivers in a cell is equal to the number of frequencies. Each transceiver has its own frequency reuse pattern, which is successively tightened. An advantage of the MRP is that the BCCH carrier can be include in the hopping sequence and a reuse of 12 frequencies can be sufficient for the transceiver, configured as a BCCH. The other transceivers in the cell transmit only on the TCH and can have a tighter reuse. An example of an MRP frequency allocation with four transceivers using 31 frequencies is 12/9/6/4, the average reuse is 5. 75.

A network with 1/3 or 1/1 frequency reuse is characterized by using random synthesizer hopping in combination with fractional loading. These means that the number of transceivers, per cell, is smaller than the number of hopping frequencies. Several hopping frequencies per cell is possible, if a tight frequency reuse is applied, for example 1/3. In addition, the interference variation becomes larger, since the interfering cells are closer now. These two effects increase the gain from frequency hopping. The network can cope with this very tight reuse, since each frequency is only used a fraction of the time. Severe interference hits are rare, due to the hoping and the channel coding, and interleaving schemes can, thereby, limit the bit errors in the received frames. It is vital to limit the traffic load and just fractionally load the frequencies, that is, keep the number of TRXs smaller than the number of hopping frequencies, or else the network quality will degrade. For this reason, a frequency load measure is used to measure the interference level of 1/3 networks. The frequency load is defined as the average traffic load, per cell, divided by the number of hopping traffic channels per cell (that is, the number of hopping frequencies multiplied by the number of time slots). This measure can be written as:

FRQLoad=

Erlang cell 8 * (# FRQCell )

The frequency load reflects how much time a frequency is being transmitted. Sometimes, the frequency load is referred to as the fractional load. Another commonly used measure is the hardware load, defined as the average number of TRXs per cell divided by the number of hopping frequencies per cell. This measure is similar to the frequency load and the hardware load can be expressed as: HWLoad=

TRX cell FRQCell

65

However, the hardware load does not consider the Trunking efficiency. The same hardware load results in different served traffic loads, depending on the number of frequencies and thereby, different frequency loads. The most common FLP patterns are 1/1, where all cells in an area use the same TCH frequencies, and 1/3, where every third cell uses the same TCH frequencies. For both patterns, the result is much simpler frequency planning, compared to MRP. Another advantage of the FLP is that, when adding transceivers no frequency re-planning is necessary. The reuse is automatically tightened when new transceivers are taken into service. In a network where FLP is used, the BCCH carriers is generally non-hopping, and careful planning is needed to ensure good speech quality. In many networks, a reuse of around 15 is common for non-hopping carriers. It is also possible to have the BCCH carrier include in the hopping sequence using what is called a BCCH carrier CO filler. The drawback of CO fillers is that they require an extra transceiver that does not carry any traffic and they are, therefore, seldom used.

Applying tighter frequency reuse, enables a cost-efficient and fast alternative to increase the capacity when the existing network is becoming congested. It does not require additional spectrum, new mobiles, or new sites. Simply, an expansion of the transceivers in the existing cells is needed.

This option alone, allows an operator that already has a well planned and optimized system with an average frequency reuse of about 12-14 to more than double the capacity of his network. At a later stage, this can also be introduced in a dual band network, to increase the capacity of the new band.

For areas with a very high capacity need, tighter frequency reuse combined with other methods, provide a very spectrum efficient way forward to virtually unlimited capacity. The dedicated micro cell frequencies required can be made available by applying a tighter reuse on the macro cells. By also using frequency hopping, that is, synthesized frequency hopping over many frequencies, in the micro cells, it is possible to keep the number of frequencies, required exclusively for the micro cells to a minimum.

Adaptive Multi Beam Antennas Adaptive Multi Beam Antennas is a new and revolutionary technique to achieve high capacity. It is based on the principle to use a multi beam antenna and dynamically transmit and receive only on the beam that is best suited for a specific mobile. This, dramatically, reduces the interference in the network allowing for a much tighter frequency reuse. All tight frequency reuse methods show significant capacity increase. However, the best results are achieved when applying the FLP with 1/1 reuse. Adaptive Multi Beam Antennas cab increase the capacity with up to 250%, compared to the tightest frequency reuse possible today. While, in every cell that is converted to Adaptive Multi Beam Antennas, the full capacity potential can be exploited, also many surrounding cells can be expanded with additional transceivers. By installing Adaptive Multi Beam Antennas in less than 20% of the macro cells in one area, the macro cell network capacity in that area can be doubled. Adaptive Multi Beam Antennas are most cost-efficient until up to, approximately, 20-25% of the cells in an area have been converted. Since even more cells are converted, the network capacity will continue to increase until all cells use Adaptive Multi Beam Antennas. At that stage, the capacity will have more than tripled in a 1/1 reuse network, whereas in an MRP network, the capacity will have more than doubled. Today, plans exist only to manufacture Adaptive Multi Beam Antennas for the 900 MHZ band. Availability on other frequency bands is, of course, dependent on market needs.

66

Dual Band Operation By making additional frequencies available to the GSM operator, who uses the 1800 MHz band, additional capacity can be seamlessly achieved by using dual band mobiles, dual band functionality, and efficient traffic management features in the networks. For many operators, this is the solution to future problems with congestion in the GSM 900 band. For today's 1800 operators the same functionality can solve future coverage issues. The capacity potential of the dual band network is, of course, dependent on the amount of frequencies available in the two bands, but also on the penetration of the dual band mobile terminals. Almost all terminals sold today are dual band. It is clear that a significant portion of dual band mobile stations is needed and that further growth depends on an increasing population of such mobile stations. Ways to stimulate the uptake of dual band terminals may be required; if a fast capacity increase is needed. However, the long-term aspect should not be critical, since the majority of all new mobile terminals today support dual band.

Micro Cells The introduction of micro cells, that is, cells with antennas below the rooftops, thus providing a more contained cell, is the next logical step in the process of building higher capacity. Micro cells are, usually, introduced into a network to take care of traffic hot spots, quickly providing offload for congested macro cells, since more and more micro cells are deployed, a contiguous micro cell layer will involve. The profitability from hot spot micro cells in dependent on finding the precise location.

To assist in this task, Ericsson has developed the Hot Spot Finder, which is a tool that helps operators locate the precise position of a traffic hot spot. This makes it possible to measure the actual minimum traffic level that a micro cell, in this place, will carry. In effect, the Hot Spot Finder can guarantee a profitable hot spot micro cell introduction. It should be noted that micro cells, very often, provide additional coverage, thus increasing the traffic uptake in an area. It may, therefore, be motivated to introduce micro cells in an area that does not have a congested macro network.

5.5.2 COMPLEMENTARY CAPACITY ENHANCING OPTIONS In-building Systems As the network matures, more and more subscribers start making calls from indoor locations and it makes sense to start deploying in-building systems. In-building systems also provide a significant quality improvement in situation with difficult interference indoor, such as top floors in high-rise buildings. Designed to provide capacity and quality in indoor locations, such as shopping malls, airports, and train stations, in-building systems provide operators with new traffic and revenues.

People tend to make more and longer telephone calls in indoor networks, where the coverage and quality is satisfactory.

Dynamic Overlaid/Under laid sub cells A concept that is designed to enhance the gain from tighter frequency reuse is Dynamic Overlaid/Under laid Sub cells. It is based on the idea to use certain frequencies close to the cell center, and, thereby, allow a tighter reuse of these frequencies. The drawback is

67

that it is necessary to divide the available bandwidth into two parts, hence reducing the number of frequencies available for each sub cell layer.

Cell Load Sharing Cell load sharing provides the possibility to increase the capacity by distributing the traffic load from busy cells to less busy neighboring cells, as the traffic distribution is often uneven in a real system.

An average radio network capacity increase of 10% is achieved, simply by increasing the utilization rate of the existing hardware.

Half Rate Half rate could, theoretically, more than double the capacity of a network, but, in practice, this in not the case. The reduced quality for Half Rate requires higher interference margins in the cell planning process, thus reducing the frequency reuse possible to apply. In addition, the capacity increase is dependent on the penetration of dual rate mobiles, which are yet not available in large volumes. On top of that, the operator needs to consider the impact that the reduced speech quality has on the subscriber perception of the network quality. However, when combined with Dynamic Half rate Allocation, half rate can be used as a last resource to handle temporary traffic peaks.

Consequently, cells can be dimensioned for a higher average traffic level.

5.6 CAPACITY POTENTIAL To be able to make the right choice concerning an increase in the capacity of the network, it is important to consider the capacity potential of each option. It describes that the relative capacity gain from the different options, one by one, compared to a reference network with a frequency allocation of 7.5 MHz at 900 MHz. the network has a macro cell site-to-site distance of 700 m, which is used to meet the high requirements for satisfactory indoor coverage. Additionally, it is a common distance in many dense urban networks today. It needs to be pointed out that the maximum capacity in the dual band case is dependent on the amount of additional 1800 spectrum the operator has access to, as well as the frequency reuse that is employed on the 1800 frequencies.

5.7 COST The actual cost of each alternative is market dependent, for example, costs of cell sites (acquisition, site preparation, and rental) and transmission vary between different markets. To provide an understanding of the difference in costs of the alternatives, a case study, for a reasonably representative market, has been developed. The case study shows the cost of doubling the capacity in a mature macro cell network using the main alternatives, except Adaptive Multi Beam Antennas.

The case study is based on a cost model, including HW cost, basic SW, installation cost, site cost, site rental, electricity and maintenance cost for RBSs, BSCs and transmission. The investments have been evenly distributed over five years, whereas the annual cost is assumed to be the same

68

every year. The net present value of the five different scenarios has been calculated and is presented in the chart. The scenario is based on typical costs in a city, and the operator has access to 7.5 MHz spectrum. The scenario shows that the tighter frequency reuse option is the most cost-effective option. It requires only an additional 35% cost in order to double the BSS network capacity, closely followed by the dual band case. Prerequisites are cell site (co-sitting with GSM 900 cell sites), transmission, and BSC infrastructure-sharing. The reason for the high cost in the small macro cell case are the high site investment costs, that is, macro cell site acquisition, civil work, and site preparation. The conclusion is that capacity enhancing techniques that allow for a maximum use of the existing infrastructure are preferred. The BTS sites represent a major part of the operator costs of the network, and by reusing the same BTS sites, large savings can be made. In addition to site sharing, infrastructure sharing (that is, HLR, MSC, BSC, and transmission) helps reduce the costs and speeds up deployment for the operator.

5.8 TIME FOR IMPLEMENTATION It is very important to understand how fast the various options can be deployed to increase the network capacity. In today's highly competitive environment, the operator cannot afford to refuse new customers due to radio network congestion. Increasing the capacity by applying tighter frequency reuse is widely used today. This is the fastest alternative to achieve increased capacity, since it mainly involves adding transceivers to existing cells and applying advanced frequency planning techniques. Here, the FLP is especially worth mentioning, due to the simple frequency allocation schemes involved, both FLP implementation and transceiver expansion is extremely fast.

Adaptive multi beam antennas are fast and easy to implement. These are implemented by replacing the RBS equipment for the cell in question. The existing site equipment, such as power supply, cooling, and battery backup can be reused. Dual band networks can be built in a very cost-efficient way with the Ericsson GSM system. The fastest way to implement dual band is by utilizing the possibility to share infrastructure, in the form of a common BSC, dual band sites and common transmission solutions. The high capacity BSS nodes, available from Ericsson, offer a unique potential in this respect, compared to equipment from any other system vendor. If the dual band terminal penetration is not high enough it may be necessary to stimulate the uptake, if a fast capacity increase is required.

The speed of the capacity rollout with micro cells is facilitated by small and easily placed base stations, such as the micro base station RBS 2302. Micro cells are a commonly used method for capacity increase. Implementing .in-building systems need not take long and be a tedious task. In fact, many turnkey in-building systems, delivered by Ericsson, have been up and running within four weeks from placing the order. The availability of small dedicated indoor RBSs, such as the RBS 2401 further simplifies deployment of GSM coverage in indoor locations. Half rate, together with the feature dynamic half rate allocation is easily deployed, since it is simply a matter of activating software features. The big hurdle with half rate lies instead in acquiring a high enough penetration of half rate capable mobile phones. Activating cell load sharing is simply a matter of setting the right parameters in the BSC; hence this is, by far, the fastest alternative to get higher capacity.

69

5.9 WAY FORWARD TO CAPACITY 5.9.1 CONSIDERATION BEFORE STARTING THE WAY FORWARD Build a Solid Foundation A well-built macro cell network has all the requirements to derive the benefits from the different options of the way forward. Macro cells are mainly built to achieve the general goals of indoor coverage. In most networks, this is achieved if the site-to-site distance comprises around 700 m.

Factors, such as city structure, placing of macro cells, and antenna tilting govern the required site-tosite distance. Operational networks with site-to-site distances of around 250 meters do exist. Careful cell planning and optimization are needed in networks with very short macro cell site-to-site distance, to gain benefits from the very tight frequency reuse schemes.

Choosing the Right Tighter Frequency Reuse Method There are two types of frequency planning methods available for frequency hopping networks, MKPMultiple Reuse Pattern and FLF'-Fractional Load Planning. The MRP utilizes base band frequency hopping and it can, therefore, be used with all types of combiners. The FLP, on the other hand, is based on synthesizer frequency hopping and can not be used with filter combiners. The use of hybrid combiners results in more antennas for large transceiver configurations. An alternative is to use multiple combining steps, but since half the power is lost in each step, this may cause coverage problems.

Based on the characteristics of each method, the following guidelines can be derived. In an Existing Network: 1. If filter combiners are used in the network, and the operator does not wish to replace them, the MRP is the only choice.

2. In a network with only hybrid combiners and/or "over the air combining" is used (that is, CDU-A), the FLP is the obvious choice, due to easy frequency planning. When choosing which type of FLP to use, the following should be considered: a) In narrow frequency band networks (<-7.5 MHz) an FLP with 1/1 reuse is the obvious choice, due to its excellent capacity ability. For instance, in a 7.5 MHz network 1/1 yields -20% more capacity than the MRP or 1/3, and the smaller the frequency band gets the greater the gain with 1/1 will be. The main reason for this gain is the larger number of frequencies per cell that is giver by 1/1. b) In networks with large frequency bands (>-7.5 MHz) the capacity advantage of 1/1 becomes smaller and smaller. Here, the FLP with 1/3 reuse is the primary choice, since it is easier to adapt to the local variations in a network than 1/1. In areas, where more capacity is required, a combination of 1/3 and 1/1 in an overlaid/under laid sub cell structure can be used.

70

In a New Network: 1.

In narrow frequency band networks (<-7.5 MHz), the FLT with 1/1 reuse is still the obvious choice, due to the same reasons as for the existing network above.

2.

For networks with large frequency bands (>-7.5 MHz) other considerations than those concerning capacity need to be made. The advantages of the FLP is still simple frequency planning and, to a certain degree, capacity, especially together with the overlaid/under laid sub cell feature. However, since the FLP is limited to hybrid combiners or "over the air combining", one dual polarized antenna can support a maximum of four transceivers per cell with today's RBS products. The MRP supports filter combiners and need only one dual polarized antenna for up to twelve transceivers per cell. Concerning large configurations this means that more antennas are required when the FLP is used. From these facts the following can be deduced: a) If the number of antennas is not an issue, use the FLP as described above, for an existing network, together with hybrid combiners. b) If the number of antennas is a problem and multiple combining steps are possible, use the FLP, as described above, for an existing network together with hybrid combiners. c) If the number of antennas is a problem and multiple combining steps are not feasible, use the MRP and filter combiners.

5.9.2 GOING ALONG THE WAY FORWARD Step 1 : Applying Tighter Frequency Reuse The first action to take for an operator who wishes to implement a tighter frequency reuse is to allocate a separate band for the macro cell BCCH frequencies. The separate BCCH band is recommended, since it allows the operator to control the level of interference on the BCCH carriers.

This is important for the handover and idle mode cell selection performance. The remaining spectrum can be used for the TCH carriers. These carriers can, in a first step, be planned for an equivalent average 8-9 TCH frequency reuse using the Ericsson MRP technique or the Ericsson FLP technique and by applying quality based power control and frequency hopping.

Step 2: The different options in step 2 can be introduced simultaneously, depending on the frequency availability, traffic distribution, and site accessibility of the micro cells.

Introducing Dual Band Functionality Operators with access to frequencies in both bands should introduce dual band operation into their networks. When some 900 cells start to be congested, co-located 1800 cells are

71

added to those sites. As the traffic increases, more and more 1800 cells are added to offload the 900 cells. Eventually, a situation where all (possible) 900 sites have become dual band sites will be reached. Some dedicated single band 1800 cells will probably also be needed. When the traffic level in the 1800 cells becomes sufficiently high, a tighter frequency reuse should also be applied in the 1800 cells. If the operator's original band is the 1800 band, the opposite applies. An operator who has access to both bands from the start should begin building out his 900 band, since this procedure requires fewer sites to achieve coverage.

Introducing Hot Spot Micro Cells When a hot spot has been found using the Hot Spot Finder, a micro RBS can provide fast relief for a congested macro cell. Hot spot micro cells have a short payback time, since they carry a high traffic load. With RBS 2302, micro cells are fast to decoy and thanks to its small size and distance looks it is easy to find suitable site locations. Hot spot micro cells can be introduced by borrowing frequencies from the macro cells. To ease the frequency planning and implementation of these micro cells, a few frequencies can be made available by a further tightened reuse on the TCH carriers in the macro network to facilitate the tighter frequency reuse, random frequency hopping, quality based power control, and DTX (both directions) are needed.

Introducing Adaptive Multi Beam Antennas Identify the main congested cells where the frequency reuse cannot be tightened further. Start by migrating these cells to Adaptive Multi Beam Antennas, at the same time, its neighboring cells can be expanded with additional transceivers, if the reduced interference level allows it.

Building Contiguous Micro Cell Networks Apply an even tighter TCH reuse in the macro network, to make dedicated micro cell carriers available, as the micro cell network grows. An allocation of 5 to 8 carriers is generally sufficient for a contiguous micro cell network with two transceivers per micro cell. This is made possible by employing the synthesized frequency hopping capabilities of RBS 2302 in the micro cells.

Deploying in Building Systems When indoor location with high enough traffic levels can be identified, it is justifiable to deploy an in-building system to cater for this traffic, thereby offloading the macro cell network. Experience shows that well-placed indoor cells tend to attract planned. When there are many in-building systems in an area, it is a wise choice to allocate dedicated frequencies for these indoor cells.

The Foreseeable Capacity Demand Can Be Satisfied In the 7.5 MHz, a well-optimized macro cell network is developed into a dual band, multi layer network. The available capacity enhancing options are combined, step by

72

step, to form a network that can handle very high traffic levels. The capacity is increased by a factor of 16, thus supporting about 85,000 subscribers/km 2 assuming 20mE per subscriber in a massmarket scenario. Generally, there are always several operators of the cellular systems in each market. Therefore, it is evident that there is no capacity limit. Further capacity increase in hot spots is possible by implementing more micro cells or indoor cells. It has also been shown that it is possible to further increase the capacity by building even smaller macro cells through careful cell planning and site selection.

MS Aspects Frequency hopping and related features that facilitate a tight frequency reuse have been used in many networks for a number of years. Tighter frequency reuse has become a common technique to achieve higher capacity. This implies that problems that were identified on early versions of different manufacturers GSM terminals have been solved. Solutions to some problems have, where possible and justified, been implemented in the Ericsson GSM system. We believe that other remaining problems have been considered negligible by the operators and the faulty terminals have either been upgraded or have disappeared from the market.

73

CONCLUSION AND REMARKS

After finishing our field work, research, study and discussion with telecom experts, we can now come to a conclusion that the quality of service may depend on various factors which can influence the objective of the mobile operator companies in many ways. In the case of an existing cell, the traffic capacity may not be sufficient due to many reasons in the future. Because, the population density may highly be increased due to newly established high rise buildings, industries etc. and the base station will not be able to handle huge subscribers more than its capacity. As a result, the cellular communication system of that area may break down.

To overcome such problems, Advanced Cell Planning is required for more system stability and reliability. While planning a new cell, the theoretical concept of Advanced cell planning covers all the matters to get the optimum performance of cell sites.

We have found the following outstanding advantages of Advanced cell Planning: 1.

2.

3.

4.

5.

6.

The entire system performance is highly increased Future extension does not influence the system performance The system becomes more reliable and stable It reduces further planning and implementation costs Traffic signal jam does not occur on a festival or emergency situation Eventually the mobility is enhanced.

APPENDIX -1 ABBREVIATIONS A Abis Abis Interface between BSC - BTS ACCH Associate Control CHannel AMPS Advanced Mobile Phone Service AMSS Aeronautical Mobile Satellite System ARFCN Absolute Radio Frequency Channel Number AuC Authentication Center B BCC BCCH BS

-

BTS Color Code Broadcast Control Channel Base Station

74

BSC BSIC BSMAP BSS BSSAP BTS

Base Station Controller Base Transceiver Station Identity Code BSC Mobile Application Part Base Station Subsystem BSS Mobile Application Part Base Transceiver Station

C CBCH CCCH CCH CDMA CEPT CGI

Cell Broadcast Channel Common Control Channel Control CHannel Code Division Multiple Access European Post & Telecom Conference Cell Global Identification

D DCCH DCS DTAP DTMF

Dedicated Control CHannel Digital Cellular System (1800) Direct Transfer Application Part Dual Tone Multi - Frequency

E EIR

-

Equipment Identity Register

F FDMA

-

Frequency Division Multiple Access

G GMSC GSK GSM H HLR

Gateway Mobile Services Switching Center Gaussian filtered Minimum Shift Keying Global System for Mobile Communication -

Home Location Register

I ID IMEI IMSI ISDN

-

Identification International Mobile Equipment Identity International Mobile Subscriber Identity Integrated Switched Digital Network

K Kc Ki

-

Cipher Key Identification Key

M MAP MoU MS MSC

-

Mobile Application Part Memorandum of Understanding Mobile Station Mobile Services Switching Center

N

75

NMC NSS

-

Network Management Center Network and Switching Subsystem

O OMC OSS

-

Operation & Maintenance Center Operation Sub- System

P PIN PLMN PSTN

-

Personal Identification Number Public Land Mobile Network Public Switched Telephone Network

R RCP RFC(H) -

Radio Control Point Radio Frequency CHannel

S SIM SMS SS7

-

Subscriber Identity Module Short Message Service (CCITT) N*7 Signaling System

V VLR VMSC

-

Visitors Location Register Visited MSC

76

REFERANCES [1]

Lee, William C. Y., "Mobile Cellular Telecommunications Systems, " New York: McGraw-Hill Book Company, 1989.

[2]

Smith, David R., "Digital Transmission Systems," New York: Van NostrandReinhold Company, 1985.

[3]

Faruque, Saleh, "A Journey into the Realm of Wireless Communication," An internal RF engineering course, Northern Telecom, Brampton, Ontario, Canada, 1993.

[4]

Faruque, Saleh, "Cellular Mobile Systems Engineering, "Norwood, MA: Artech House, 1996.

[5]

Ericsson, "GSM Cell Planning Principles - 2, " Ericsson Radio Systems, 2002.

[6]

Mehrotram, Asha, "Cellular Radio, Analog and Digital Systems, " Norwood, MA: Artech House, 1994.

[7]

Faruque, Saleh, "Cellular Control Channel Performance in Noise, Interference and Fading, "Proc. IEEE Int. Conf. Selected Topics in Wireless Communications, IEEE, 1992, pp. 328 - 331.

[8]

Mehrotram, Asha, "Cellular Radio Performance Engineering, " Norwood, MA: Artech House, 1994.

[9]

Kraus, J. D., "Antennas, " New York: McGraw-Hill Book Company, 1950.

[10]

Xia, H. H. et al., "Radio Propagation Characteristics for Line of Sight Microcellular and Personal Communications," IEEE Trans. on Antennas and Propagation, Vol. 41, No. 10, October 1993, pp. 1439 - 1447.

77