Performance Enhancement of Multiple Cell Users using Coordinated Multipoint in LTE

IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 04, 2016 | ISSN (online): 2321-0613

Performance Enhancement of Multiple Cell Users using Coordinated Multipoint in LTE Zeel G. Bhatt1 Prof. Anil K. Sisodia2 1 M.E. Student 2Professor 1,2 Department of Communication System Engineering 1,2 L. J. Institute of Engineering and Technology, Gujarat Technological University, Ahmedabad, Gujarat Abstract— LTE (Long Term Evolution) was started as a project by telecommunication body known as 3GPP. Main goal of LTE is to provide high data rate, low latency, packet optimized radio access technology and supporting flexible bandwidth. LTE is important because it will bring up to 50 times performance improvement and much better spectral efficiency to cellular networks, but due to one frequency reuse factor in LTE there is a high interference between the cells. So to enhance the performance CoMP (Coordinated Multipoint) is used. We can also use different types of decoding technique or receiver to get better performance of LTE. Key words: LTE, CoMP I. INTRODUCTION LTE is basically started as a project by 3 rd generation partnership project to fulfill all the requirement for today’s explosive intranet growth. It is name of technology standard for cellular network beyond 3G. LTE uses MIMO (Multiple input Multiple Output) and OFDM (Orthogonal Frequency division Multiplexing) technology both. LTE uses OFDMA (Orthogonal Frequencies division Multiple Access) in its downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) in its uplink. It supports flexible bandwidth operation upto 20MHz. it provides peak data rate upto 300 Mb/s for downlink and 75Mb/s for uplink. LTE provides TDD and FDD at same platform. It provides low latency to connect to the network. LTE also provides seamless connection to existing network like GSM, CDMA. It support 4x4 antenna configuration for transmission as well as for reception. These all parameters are supported bt early version of Long Term Evolution that is known as LTE Release 8. To fulfill the requirements of IMT-A (International Mobile Telecommunications), there is a new version called LTE Release 10 or LTE-A (Long Term Evolution Advanced). LTE-A supports flexible bandwidth up to 100MHz via Carrier Aggregation. It supports upto 8x8 antenna configurations in uplink and downlink. It uses Coordinated Multipoint for performance enhancement. It provides peak data rate of 1GB/s for downlink and 500Mb/s for uplink. With the use of Coordinated Multipoint technique, which is basically coordination between different base station performance in terms of Bit Error Rate (BER), throughput, data rate will increase.

Fig. 2: LTE time-frequency resource grid As can be seen in the Figure 1 and 2 LTE frame is of 10 millisecond (msec) duration which is divided into 10 Subframes of 1msec duration. Each Subframe is further divided into two slots each has a length of 0.5msec. Each slot comprise either 6 or 7 OFDM symbols depending upon normal or extended cyclic prefix that is used.

A PRB is the smallest unit that Base Station can allocate to the user. Subcarrier Bandwidth and PRBs Bandwidths are 15 KHz and 180 KHz respectively for all system Bandwidths.

A Resource Element is the smallest physical Resource and it consists of one subcarrier during one OFDM symbol. A group of Resource Element s are referred as physical Resource Blocks i.e. PRBs. A PRB has a seven OFDM symbols having duration of one time slot 0.5ms and 12 subcarriers having a Bandwidth of 180 KHz (15 KHz * 12 = 180 KHz), so each Resource Block in the case of normal cyclic prefix has of 84 Resource Element s (12 Subcarrier * 7 OFDM Symbols = 84 Resource Element s) whereas in the case of extended cyclic prefix.

Resource Block has 72 Resource Elements (12 Subcarrier * 6 OFDM Symbols = 72 Resource Element)

II. LTE FRAME STRUCTURE

Fig. 1: LTE Time Domain Structure

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Performance Enhancement of Multiple Cell Users using Coordinated Multipoint in LTE (IJSRD/Vol. 4/Issue 04/2016/200)

III. LTE ARCHITECTURE

V. MAXIMUM LIKELIHOOD DECODING ML will compares the Euclidian distance of received symbol with transmitted symbol. Those with minimum Euclidian distance will accept as a correct received symbol.

This will give better results than ZF-SIC. ML tries to find x which minimizes, J = |Y − Hx|2 VI. COORDINATED MULTIPOINT

Fig. 3: LTE Physical Layer Architecture The figure shown above is considered for simulation in this paper. Precoding is used that is spatial multiplexing scheme in wich channel gain is multiplied with each symbol that is transmitted by antenna. FEC (forward Error Coorection) is basically channel coding technique to detect & correct error.

Signal mapping maps the output of channel coding to the particular symbol according to symbol mapping technique.

IFFT and Cyclic prefix is basically OFDM block that is used in LTE as a modulation scheme.

ZF-SIC (Zero Forcing Successive Intereference Cancellation) receiver or decoding scheme is used for MIMO decoding.

Multiple base station cooperation is very attracting approach now a day for better user experience. So coordinated Multipoint (CoMP) is used by LTE. CoMP is a process of coordinating and combining signals from multiple antennas and hence we will get better system coverage, cell-edge throughput, system efficiency and interference suppression.

It can be classified into coordinated scheduling/ beamforming

IV. ZF-SIC (ZERO FORCING SUCCESSIVE INTERFERENCE CANCELLATION) Zero forcing is a spatial Signal Processing by which the multiple antenna transmitter can null multiuser interference signals in wireless communication.

Suppose we have 2x2 antenna, In the 1st time slot, received signal on 1st receive antenna, The received signal on 2nd antenna is Where, y1, y2 are the received symbol on 1st and 2nd antenna. h11 is channel from 1st transmit antenna to 1st receive antenna, h12 is a channel from 2nd transmit antenna to 1st receive antenna, h21 is a channel from 1st transmit antenna to 2nd receive antenna, h22 is a channel from 2nd transmit antenna to 1st receive antenna. x1 and x2 are transmitted symbol from 1st & 2nd transmit antenna.

Equation can be written as So, y= Hx+n and to solve for x, ZF for meeting this constrain WH=I is given by,

Fig. 4: CoMP Joint Transmission VII. SIMULATION PARAMETERS AND RESULTS A. Parameters: Parameters Value Antenna configuration 2x2,3x3,4x4 Cellular layout 7 cell layout System bandwidth 20 MHz Channel Rayleigh fading Signal mapping QPSK No. of subcarrier 600 Subcarrier bandwidth 15kHz Macro eNB Tx power 46dBm No. of RBs used 100 Macro intersite distance 500m frequency 2.14GHz UE noise density -174 MIMO decoding ZF-SIC,ML Pathloss model 148.1+ 37.6log10(R) Table 1: Parameter B. Result:

ZF-SIC which is a non-linear scheme for further cancellation using ZF approach, the receiver can obtained estimate of two transmitted symbol x1, x2.

Suppose we take 1 estimated symbol, for example estimate of x2 and substract its effect from y1,y2 then, After this, we apply Maximal Ratio Combining (MRC) Fig. 5: BER Comparision of OFDM and MIMO-OFDM (LTE)

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Performance Enhancement of Multiple Cell Users using Coordinated Multipoint in LTE (IJSRD/Vol. 4/Issue 04/2016/200) 6

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UE Distance VS Throughput

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Fig. 6: cellular layout & user distribution

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Fig. 11: Throughput comparison for CoMP & non-CoMP case VIII. CONCLUSION  

By using ZF-SIC and ML receiver, Performance of LTE is improved With the use of CoMP technique in LTE, BER and Throughput is increased than normal transmission.

REFERENCES

Fig. 7: BER comparision of ZF and ML for 2x2 antenna.

Fig. 8: BER comparision of ZF-SIC and ML for 3x3 antenna

Fig. 9: BER comparision of ZF-SIC and ML for 4x4 antenna UE SNR VS BER

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Papers [1] Kazi Mohammed saidul Huq,Shahid Mumtaz,Jonathan Rodriguez, “Investigation on Energy Efficiency in HetNet CoMP Architecture” IEE ICC ,vol 18, pp.11121117, July 2014 [2] Pallavi Chawla, Bhasker Gupta, “BER Analysis Of Single/Multi-User LTE and LTE-A System” International Advance Computing Conference (IACC), 2014 IEEE Pages 262-266 [3] Mr. Shreedhar A. Joshi, Dr Rukmini T.S., Dr Mahesh H.M., “Error Rate Analysis Of The V-BLAST MIMO Channels Using Interference Cancellation Detectors” International Conference on Signal Processing, Communication, Computing and Networking Technologies (ICSCCN), 2011 IEEE [4] Gaurav Nigam, Paolo Minero, Martin Haenggi,“Coordinated Multipoint in Hetegenerous Network: A Stochastic Geometry Approach” Globecom Workshop, 2013 IEEE, Pages 145-150.

[5] Atsushi Nagate, Sho Nabatame, Daigo Ogata, Kenji Hoshino, and Teruya Fujii, “Field Experiment Of CoMP Joint Transmission Over X2 Interface For LTEAdvanced” 2013 IEEE. [6] Husam Aldin Elfadil, Mohammed Adil Ibrahim Ali, Mohammed Abas, “Performance Evalution of Joint Processing Coordinated Multipoint Transmission in LTE Network”, 2015 IEEE, 978-1-4673-7869-7 Books [7] Introduction to MIMO communication by Jerry R. Hampton

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Fig. 10: BER comparision for CoMP & non-CoMP transmission

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