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IJEEE, Vol. 1, Spl. Issue 1 (March 2014)

e-ISSN: 1694-2310 | p-ISSN: 1694-2426

Optimization of Transmission Schemes in Energy-Constrained Wireless Sensor Networks 1

Vivek Rana, 2Jaspal Singh, 3Leena Mahajan

1,2

Rayat Institute of Engineering & Information Technology,Railmajra, Punjab, India.

3 Indo Global college of Engineering, Abhipur,Distt. Mohali,Punjab,India 2 1 ranavivek01@gmail.com, jaspal_116@yahoo.co.in, 3leenamahajan1997@gmail.com

Abstract- This paper reviews medium access control (MAC) in wireless sensor network (WSN),and different management methods to save energy.MAC protocol controls how sensors access a shared radio channel to communicate with neighbours. This paper discusses design trade-offs with an emphasis on energy efficiency, latency, fairness and throughput. One mechanism used to reduce energy expenditure is to periodically turn off the radio receivers of the sensor nodes in a coordinated manner. SMAC may require some nodes to follow multiple sleep schedules causing them to wake up mmore often than other nodes. A typical node in WSN consists of one or more sensors, embedded processors, moderate amount of memories and transmitter/receiver circuitry. These sensors are battery powered and recharging of these nodes is very expensive and normally not possible. The proposed modification in MAC protocol solves the energy inefficiency caused by idle listening, control packet, overhead, and overhearing taking nodes latency into consideration based on network traffic. The modified version improves the energy efficiency, latency and the throughput and hence increases the life span of a wireless sensor network. Simulation experiments have been performed to demonstrate the effectiveness of the proposed approach. This protocol has been simulated in Qualnet 5.0.

A WSN generally consists of a host or “gateway” that communicates with a number of wireless sensors via a radio link. Data is collected at the wireless sensor node, compressed, and communicated to the gateway directly or, if required, uses other wireless sensor nodes to forward data to the gateway. The gateway then ensures that the data is input into the system. The main function of a wireless sensor network (WSN) is to collect data from environment and send it to a reporting site where the data can be observed and analyzed Each wireless sensor is considered a node and presents wireless communication capability, along with a certain level of intelligence for signal processing and networking data. Depending on the type of application, each node can have a specific address. Figure 1 represents a generic block diagram of a node. It usually comprises a sensing unit, a microcontroller to process data, and a RF block for the wireless connection. Depending on the network definition, the RF block can function as a simple transmitter or transceiver (TX/RX). When designing the nodes, it is very important to pay attention to the current consumption as well as the processing capability. The microcontroller’s memory is very dependent of the software stack used.

Keywords- Wireless Sensor Network, Medium Access Control, Energy Efficiency , latency, throughput, fairness.

I. Introduction A wireless sensor network (WSN) of spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location. The more modern networks are bi-directional, also enabling control of sensor activity. The development of wireless sensor networks was motivated by military applications such as battle field surveillance; today such networks are used in many industrial and consumer applications, such as industrial process monitoring and control, machine health monitoring, and so on.

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Fig.1: Generic block diagram of a node of a WSN.

Wireless Sensor Networks (WSNs) are an important new class of networked system.

Dealing with both scale and density is hard enough in ideal environments. Unfortunately, we don’t have the luxury of ideal environments with sensor networks. Because sensor networks are intended to monitor the physical world, they must often be deployed in natural and uncontrolled environments. No longer can we assume the carefully controlled temperature, abundant power, and human

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monitoring of server rooms and data centers. Instead, wireless sensor networks must be designed to operate while no external power is connected, unattended, irregularly connected (radios may be turned off for significant periods of time to conserve power), and uncontrolled environment [1].

MAC protocols have a significant effect on the function of WSN. MAC protocol, which builds bottom infrastructure in sensor network systems, decides how to use wireless channel and allocate limited wireless communication resources for sensor nodes. MAC protocol, one of the key network protocols that ensure effective communication in sensor network, is in the bottom part of the sensor network protocol and has a great impact on the performance of sensor network [6].

II. RELATED WORK A. Proposed S-MAC Protocol Design Challenges It is necessary to establish communication links between nodes because a great number of sensor nodes are distributed to the medium in Wireless Sensor Networks. For this reason, MAC protocol has two aims in WSNs. The first is to build a sensor network infrastructure. The second is to share the communication medium in a fair and efficient way [8].

Attributes that should be taken into consideration in the design of MAC protocol are listed on below : Energy efficiency: Energy efficiency is the most important issue when designing a new MAC protocol in WSNs because the network’s lifetime is determined by the nodes’ energy.

Latency: The elapsed time for sending a MAC-layer data packet successfully is called “Latency”.

Throughput: The ratio of the messages served by communication systems is called “Throughput”.

Robustness: Robustness is composed of the attributes including reliability, usability, and durability. It shows the protocol’s degree of resistance to errors and false information.

Scalability: Capability of communication system regardless of the number of sensor nodes performing a transaction and the size of the network is called “Scalability”.

Stability: The ability of communication system to handle the issue of traffic congestion in the medium that changes constantly is called “Stability”. A stable MAC protocol should handle sudden loads that can exceed maximum channel capacity.

Fairness: Bandwidth is limited in most of WSNs applications, but the base station must receive data equally from all the nodes. Channel capacity should be fairly shared among the nodes without reducing the efficiency of the network.

The main goal in our S- MAC protocol design is to reduce energy consumption, while supporting good scalability, fairness and collision avoidance. Our protocol tries to reduce energy consumption from all the sources that we have identified to cause energy waste. To achieve the www.ijeee-apm.com

design goal, we have developed the S-MAC that consists of three major components: periodic listen and sleep, collision and overhearing avoidance, and message passing. A modification of the protocol is then proposed to eliminate the need for some nodes to stay awake longer than the other nodes. The modified version improves the energy efficiency, latency, fairness and the throughput and hence increases the life span of a wireless sensor network.

Wireless sensor networks use battery-operated computing and sensing devices [3]. We expect sensor networks to be deployed in an ad hoc fashion, with nodes remaining largely inactive for long time, but becoming suddenly active when something is detected. These characteristics of sensor networks and applications motivate a MAC that is different from traditional wireless MACs such as IEEE 802.11 in several ways [2, 4]: energy conservation and selfconfiguration are primary goals, while per-node fairness and latency are less important. S-MAC uses a few novel techniques to reduce energy consumption and support selfconfiguration. It enables low-duty-cycle operation in a multi-hop network. Nodes form virtual clusters based on common sleep schedules to reduce control overhead and enable traffic-adaptive wake-up. S-MAC uses in-channel signaling to avoid overhearing unnecessary traffic. Finally, S-MAC applies message passing to reduce contention latency for applications that require in-network data processing.

B. S-MAC Protocol S-MAC [9] is a CSMA –based MAC protocol designed with a modified IEEE 802.11. Its primary goal is power consumption. S-MAC supports message transition so that large-sized packets can be sent more efficiently. The innovations in this protocol are periodical listening, reducing collision, preventing unintentional receiving, and message transition. Nodes generally sleep instead of continuously listening to the medium. Listening and sleeping times are stable and periodic. There should be a strict synchronization so that the nodes can move together.

The timing diagram of S-MAC is shown in Figure 2.

Fig. 2. Timing diagram of S-MAC

The Sensor MAC (S-MAC) protocol was introduced in [5] to solve the energy consumption related problems of idle listening, collisions, and overhearing in WSNs using only one transceiver. S-MAC considers that nodes do not need to be awake all the time given the low sensing event and transmission rates. S-MAC [3] reduces the idle listening problem by turning the radio off and on periodically. Nodes are synchronized to go to sleep and wake up at the same time. In order to address the issue of synchronization over multi-hop networks, nodes broadcast their schedules to all its neighbors. This is performed sending a small SYNC frame with the node schedule periodically. S-MAC divides time in two parts: the active (listening) part and the inactive (sleeping) part. The active part is divided at the same time in two time slots. During the first time slot, nodes are expected to send their SYNC frames to synchronize their schedules. The second time slot is for data transmission in which the S-MAC protocol transmits all frames that were queued up during the inactive part. In order to send SYNC International Journal of Electrical & Electronics Engineering

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frames over the first time slot or RTS–CTS–DATA–ACK frames over the second time slot, nodes obtain access to the media utilizing the same contention mechanism included in IEEE 802.11, which avoids the hidden terminal problem and does a very good job avoiding collisions too. However, nodes using the IEEE 802.11 protocol waste a considerable amount of energy listening and decoding frames not intended for them [4]. In order to address this problem, SMAC allows nodes to go to sleep after they hear RTS or CTS frames. During the sleeping time, a node turns off its radio to preserve energy.

exist. Nodes A, B and C follow one schedule (schedule 1); and nodes X, Y and Z follow another schedule (schedule 2).

The circle around a node indicates the communication range of the node. When M starts, during its initial listening spanning a synchronization period, it receives sync frames corresponding to both the schedules. M will then adopt one of the schedules (e.g. schedule 2) as its own, and announce this schedule in its sync frames. However, it will also have to wake up during the listen time of the other schedule.

Thus M has higher duty cycle, and consumes more energy.

2. Sleep delay Sleep delay introduce extra end to end delay called sleep delay [3]. Sleep delay increases communication latency in multihop networks, as intermediate nodes on a route do not necessarily share a common schedule. In a nutshell, the difficulty is to make a trade off between sleep delay and optimal active periods.

Fig.3: S-MAC frame

D. Proposed Modification in S-MAC C. Problems with S-MAC The following two problems have been identified in SMAC [3] protocol with multiple schedules.

1. Longer listen period 2. Sleep delay 1. Longer listen period While choosing and maintaining the listen and sleep schedule some nodes may have to keep wake during the listen time of more than one schedule [3]. This happens, for example, if a node,

(A): Before

In this section we propose a modification of the S-MAC protocol. The following features were included in the SMAC design:  RTS/CTS for hidden terminal problem.  Both virtual and physical carrier sense.  Back off and retry.  RTS/CTS/ACK.  Broadcast packets are sent directly without using  The RTS/CTS reserves the medium for the entire message.ACK is used for immediate error recovery.  Node goes to sleep when its neighbor is communicating with another node. Each node follows a periodic listen/sleep schedule.  At boot up time each node listens for a fixed Sync period and then tries to send out a sync packet. It suppresses sending out of sync packet if it happens to receive a sync packet from a neighbor and follows the neighbor's schedule.  A node can choose its own schedule instead of following others, the schedule start time is user configurable.  Neighbor Discovery: in order to prevent that two neighbors cannot find each other due to following complete different schedules, each node periodically listen for a whole period of the SYNCPERIOD.  Duty cycle is user configurable.

III. RESULT AND DISCUSSION

(B): After Fig.4: Sleep schedule before and after node M join the network

When it starts up, finds some of its neighbors following one schedules and the rest following another. The nodes following a shared schedule are said to form a virtual cluster. Figure 4 shows an example of this situation. Before node M starts up, two isolated virtual clusters of nodes International Journal of Electrical & Electronics Engineering

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The objective of this discussion is to compare the S-MAC and the modified proposed S-MAC protocol in terms of energy efficiency, latency, fairness, security and throughput. We need to have set of protocols to perform successful communication among different nodes. There are more steps for design a MAC protocol. First, researchers have to decide that in which application do they use this protocol. Because there are more priority such as energy efficiency, latency, fairness, throughput, security. If your first priority is energy efficiency, you can neglect to www.ijeee-apm.com

A. Measurement of Energy Consumption We measured the energy consumption in the ten-hop network. In each test, the source node sends a fixed amount of data, 20 messages of 100-bytes each. Figure 5 shows that S-MAC with periodic sleep consumes much more energy over MAC without sleep, but the proposed MAC achieves better energy efficiency than the S-MAC protocol.

No Sleep

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Average latency

14 No Sleep

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S-MAC

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Mod S-MAC

6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 11 Number Of Hops

FIG.6 (A): Average Message Latency under the lowest traffic load

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S-MAC

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12

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0 1 2 3Number 4 5 6Of7Hops 8 9 10 11

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FIG. 6(B): Average Message Latency under the highest traffic load

C. Measurement of Throughput

10 5 0 0 1 2 3 4 5 6 7 8 9 10 11 Message Inter- Arrival Time (S) FIG.5: Energy Consumption

B. Measurement of Average Message Latency Since S-MAC makes the trade-off of latency for energy savings, we expect that it can have longer latency under both the high and low traffic loads due to the periodic sleep on each node as shown in figure 6(A) and figure 6(B). We consider two extreme traffic conditions, the lowest traffic load and highest traffic load. Under the lowest traffic load, the second message is generated on the source node after the first one is received by the sink. To do this, a coordinating node is placed near the sink. When it hears that the sink receives the message, it signals the source directly by sending at the highest power. In this traffic load, there is no queuing delay on each node. Compared with the MAC without sleep, the extra delay is only caused by the periodic sleep on each node. Under the highest traffic load, all messages are generated and queued on the source node at the same time. So there is a maximum queuing delay on each node including the source node. The latency of the www.ijeee-apm.com

Just as S-MAC may increase latency, it may also reduce the throughput. Therefore we next evaluate throughput in the same 10-hop network. We first consider throughput for the highest traffic load, which is the same as that when measuring the latency in the highest traffic load. It delivers the maximum possible number of bytes of data in a unit time. The results in figure 5 show that for S-MAC as well as for proposed S-MAC, throughput drops as the number of hops increases, due to the RTS/CTS contention in the multihop network.

90 80 70 60 50 40 30 20 10 0

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proposed MAC protocol is nearly equal to that of MAC without periodic sleep but still it doesn’t reach the shortest latency.

Average Latency (S)

more security. Because, each work for security causes that consumption and delay. Otherwise, if you develop a protocol which will be use in military or healthcare applications, you have to provide security requirements. In order to meet the application level security requirements, the individual nodes must be capable of performing complex encrypting and authentication algorithms. Long mechanism of encryption and decryption should not be kept as they consume more energy. In WSNs, energy efficiency is the main task. After measuring the effect of the parameters like power, lifetime of sensor network, memory, security and type of radio communication on different protocols, it can be concluded that these evaluation parameters should be kept in mind while designing MAC protocol. Simulation results of the WSN models are presented under varying network load conditions followed by performance comparisons and analysis.

Mod S-MAC

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1 Message 2 3 Inter-Arrival 4 5 6 7Period 8 9(S) 10 11

FIG.7: Throughput over 10-hops under varying traffic loads.

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IV. FUTURE SCOPE OF WORK During this work we realized that the MAC protocols for the wireless sensor networks are a hard and extensive area.

Although modification in S-MAC protocol has been proposed, there is possible future work for system performance optimization. Therefore, some of the planned work has to be rationalized away for future work. We see clear paths for future work:  Verification through implementation and extensive simulations.  Formal descriptions to address other type of MAC protocols and extension of components.  Cross layer optimization is an area that needs to be explored more extensively.

REFERENCES [1] Akyildiz, I.F. ; Su, W. ; Sankarasubramaniam, Y. ;Cayirci, E. (2002) “A survey on sensor networks”, IEEE Communications Magazine 40.8 (2002) 102-114.

[2] Brenner, Pablo. (1996) “A Technical Tutorial on the IEEE 802.11Protocol”, Breezecom Wireless Communications, July 1996.

[3] Cui, S. ; Goldsmith A. J., and Bahai A., “Energy-constrained modulation optimization,” IEEE Trans. Wireless Commun., vol. 4, no. 5, pp. 2349–2360, Sep. 2005.

[4] Ghosh, S.; Veeraraghavan, P.; Singh, S.; Zhang, L. (2009) “Performance of a Wireless Sensor Network MAC Protocol with a Global Sleep Schedule” International Journal of Multimedia and Ubiquitous Engineering Vol. 4, No. 2, April, 2009 [5] IEEE Standard 802.11. (1999) “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”, 1999.

[6] Kodialam, M and Nandagopal T., “Characterizing achievable rates in ulti-hop wireless networks: The joint routing and scheduling problem,” in Proc. ACM MobiCom’03, Sep. 2003, pp. 42–54.

[7] Labrador, M. A.; Wightman, P. M. (2009) “Topology Control in Wireless Sensor Networks” Springer, USA. [8]Pottie, G. and Kaiser, W. “Wireless sensor networks,” Communication.

ACM, vol. 43, no. 5, pp. 51–58, 2000.

[9] Ye, W.; Heidemann, J. ; Estrin, D. (2002) “An Energy-Efficient MAC Protocol for Wireless Sensor Networks”, Twenty-First Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM) 3 (2002) 1567-1576.

Jaspal Singh graduated in Electronics & Communication Engineering from Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib, Punjab.

He has received his M-Tech degree in Electronics & Communication Engineering from Thapar Institute of Engineering and Technology, Patiala, Punjab. He is working as Associate Professor and HOD in ECE department in Rayat Institute of Engineering and Technology, Railmajra, Punjab. He is a life member of ISTE. His active research interests include intelligent sensor network, wireless sensor network, Optical wireless communication, Wireless communication & network, microwave engineering, semiconductor devices Leena Mahajan graduated in Electronics & Communication Engineering from Institute of Electronics and Telecommunication Engineering , New Delhi. She has received her M-Tech degree in Electronics & Communication Engineering from Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib, Punjab. She has a very rich experience of 13 years in Telecom sector. She has served many organizations like Himachal Futuristic Communications Limited, Chambaghat, Himachal Pradesh, India, Punjab Communications Limited, Mohali, Punjab, India. Presently she is working as Assistant Professor in Indo Global College of Engineering, Abhipur, Punjab,India.

She is a corporate life member of IETE. She is guiding many thesis of M Tech students. She has published many national and international papers on WSN and Managememt . Her active research interests include intelligent sensor network, wireless sensor network, Optical wireless communication, Wireless communication network & switching devices. .

AUTHORS Vivek Rana graduated in Electronics & Communication Engineering from Rayat Institute Of Information and Technology, Railmajra, Punjab. Now he is a student of M-Tech in Electronics & Communication Engineering in Rayat institute of information and Technology Railmajra, Punjab. His active research interests include wireless sensor network, Wireless communication, computer networking & semiconductor devices.

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