Analytical Approach for Performance of Wireless Sensor Networks

Transcription

1 International Journal of Electronics and Computer Science Engineering 1877 Available Online at ISSN Analytical Approach for Performance of Wireless Sensor Networks Prof. Satish K Shah 1, Ms Sonal J. Rane 2, Ms Dharmishtha D. Vishwakarma 3 1,2,3 Department of Electrical Engineering Faculty of Tech. & Engg., M.S.Univeristy of Baroda, Vadodara, Gujarat, India Satishkshah_2005@yahoo.com 1,sonu4sona@yahoo.com 2,a1dharmu@yahoo.co.in 3 Abstract- Wireless Sensor Networks (WSN) have been noticed and researched in recent years. WSNs have inherent and unique characteristics compared with traditional networks. It consists of light-weight, low power and small size sensor nodes (SNs). They have ability to monitor, calculate and communicate wirelessly. Sensor nodes should send their collected data to a determined node called Sink. The sink processes data and performs appropriate actions. Nodes using routing protocol determine a path for sending data to sink. Sensor nodes have a limited transmission range, and their processing and storage capabilities as well as their energy resources are also limited. Routing protocols for wireless sensor networks have to ensure reliable multi-hop communication under these conditions. In this paper, we provide an accurate simulation model with respect to the specifications of IEEE standard. We simulated and analyzed two different scenarios, where we examined the topological features and performance of the IEEE standard using OPNET simulator. We compared the two possible topologies (Mesh and Tree) to each other. The comparative results have been reported for the performance metrics like: Number of hopes, End to End Delay and Load of network. Keywords Wireless Sensor Network, OPNET, Number of hopes, Load, Routing Protocols I. INTRODUCTION Wireless Sensor Networks (WSNs)[1,2] are expected to be the nerve system of our future network world, sensing, processing and transmitting useful and timely information to be used in some monitoring and actuating capabilities. In all these activities, communication plays a central role. Recently IEEE approved [3] standard defining the Medium Access Control sub layer (MAC) and the physical layer (PHY) for low-rate, Wireless Personal Area Networks (LR-WPAN). IEEE devices typically operate in limited personal operating space. The objective of this paper is to analyze the performance of various network topologies of IEEE WPAN. The novelty of the work resides in the evaluation of key performance parameters that can be influenced by the topology. The performance has been analyzed through extensive simulations to capture the behavior of some key performance parameters. These investigations are usable to configure IEEE WPAN [4] to select a suitable topology. The organization of the paper is as follows: Section 1 gives brief introduction of WSN and objectives of this paper. Section 2 and 3 constitute the description of Routing Protocols, IEEE Protocol Standard. Section 4 constitutes system description. Section 5 shows the results and discussions derived from the simulation carried out on different topological scenarios of WSN using OPNET. Finally Section 6 concludes the paper.

2 1878 II. ROUTING PROTOCOLS Routing protocols [5] in WSNs vary depending on the application and network architecture. Used sensors are small, inexpensive, intelligent, and disposable, they can be deployed in large numbers in areas where there is no human access, disaster areas, battlefields etc. Sensor networks have high requirements on the routing protocol due to the high node density and the limited hardware resources. Scalability represents an important issue in WSNs since the nodes have to solve the problem of routing table explosion [6]. Beside the problem of scalability, routing protocols have to deal with a large number of other challenges which arise from the characteristics of WSNs. The topology of the network changes frequently which represents a challenging problem for the routing protocol design since the sensor nodes are also very limited in their computational power and memory. Moreover, the available bandwidth of the low-power transceivers and the high node density of WSNs have to be taken into account when designing a routing protocol. Wireless sensor networks are formed by small devices communicating over wireless links without using a fixed networked infrastructure. Because of limited transmission range, communication between any two devices requires collaborating intermediate forwarding network nodes, i.e. devices act as routers and end systems at the same time. Communication between any two nodes may be trivially based on simply flooding the entire network. However, more elaborate routing algorithms are essential for the applicability of such wireless networks, since energy has to be conserved in low powered devices and wireless communication always leads to increased energy consumption. Even through, there are many routing protocols for WSN, there is still a great need for new protocols that can prolong the lifetime of the network and can be easily implemented in the nodes using the currently technology, and also can be used for networks with different size. WSN routing protocols based on a network structure can be classified as flat and hierarchical protocols. Flat routing protocols distribute information as needed to any router that can be reached or receive information. No effort is made to organize the network or its traffic, only to discover the best route hop by hop to a destination by any path. Hierarchical routing protocols often group together by function into a hierarchy. A hierarchical protocol allows an administrator to make best use of his fast powerful routers as backbone routers, and the slower, lower powered routers may be used for access purposes. Flat protocols are more effective for using than hierarchical WSN protocols, due to the fact that they are scalable and simple Scalability of flat protocols is because each node participates equally in routing tasks, and that the node requires only information about its neighbors. The simplicity is because flat routing networks provide simple routing, without much overhead, and no need for complex algorithms. The primary goal of routing protocols which are designed for WSNs is to maintain energy efficient and reliable paths between different nodes in the network without generating a lot of overhead. Note that sustaining a route from a source to a destination may consume more bandwidth than is required to support the data traffic flow. In order to optimize the communication, it is important to know the characteristics of the traffic in advance. III. IEEE STANDARD The IEEE [7] Full Function Devices (FFD) has three different operation modes: The Personal Area Network (PAN) Coordinator: the principal controller of the PAN. This device identifies its own network as well as its configurations, to which other devices may be associated. This device is referred to as the Coordinator (C). The Coordinator: provides synchronization services through the transmission of beacons. This device should be associated to a PAN Coordinator and does not create its own network. This device is referred to as the Router (R). The End Device: a device which does not implement the previous functionalities and should associate with a C or R before interacting with the network. This device is referred to as the End Device (ED).

3 IV. SYSTEM DESCRIPTION IEEE [8] supports three types of topologies: Star, Mesh and Tree that can be considered as a special case of Mesh topology. A. Creating a Tree Topology To create a tree topology in a single personal area network (PAN), place one coordinator node and the desired number of router and end devices in the workspace. With the default attribute settings, each router can accommodate about two end devices. On each device, set the Network Parameters attribute to Default Tree Network. If you want greater control over the characteristics of the tree topology (such as the number of children, routers, or depth) expand the Network Parameters to specify these parameters. B. Creating a Mesh T opology To create a mesh topology in a single PAN, place one coordinator node and the desired number of end devices in the workspace. On each device, confirm that the Network Parameters attribute is set to Default Mesh Network. In this section, the WSN networks performances are evaluated and analyzed using OPNET simulation. The OPNET is used for developing its sophisticated graphical user interface. This version of simulation model supports point to point, star, ring, mesh and cluster topologies where communication is established between devices, called inside the model end devices and a single central controller called PAN coordinator. Each device operating in the network has a unique IP address. V. SIMULATIONSETUP AND RESULTS Many Performance metrics can be considered for the performance evaluation for the routing protocol of the wireless sensor network some of the performance metrics that considered in this paper are as follows. Number of hopes: The number of hops is the number of times a packet travels from the source through the intermediate nodes to reach the destination. End to End Delay (ETE): This statistics represents the total delay occurs for the transmitted packet from source to the destination. Throughput: Throughput is the average number of bits or packets successfully received or transmitted by the receiver or transmitter channel per second. Load per PAN: This statistics represents the total load (in bits/sec) for a particular PAN submitted to MAC by all higher layers in all WPAN nodes of the network. PAN Affiliation for Coordinator: This represents time that the node joins a network. C. SCENARIO 1 Tree Routing and Mesh Routing networks are designed and both are identical networks only difference is to configure PAN of Tree Routing with Default tree Network and PAN in Mesh Routing with Default Mesh Network. The same network tree structure forms in each case. The majority of the nodes have been configured with Random traffic; however Router 1 has been explicitly configured to send traffic to Router 3. The PAN in the Tree Routing scenario has been configured as a Default Tree Network. Application traffic will be routed to the destination along the parent-child links of the network tree. The PAN in the Mesh Routing scenario has been configured as a Default Mesh Network. After mesh routes have been established (a few seconds after network formation), application traffic will be routed through the shortest possible route using any of the router or coordinator presents in the network. End devices do not participate in mesh routing, therefore they must still route traffic through their parent node.

4 1880 Figure 1 shows that the number of hops taken by Router 1to reaches its destination. This statistic for Tree Routing is of red line and for Mesh Routing is of blue line. Note that both lines begin at two hops, but the Mesh Routing line quickly changes to one hop for the remainder of the simulation. In Figure 2, the red line indicates ETE Delay for the Tree Routing scenario while the blue line indicates ETE Delay for Mesh Routing. The ETE Delay for Mesh Routing is lower due to the mesh routing process finding more efficient routes than tree based routing for some of the traffic. For some nodes, the tree based route will be the most efficient route, resulting in only a minor overall improvement in ETE Delay. Figure 1. Figure 1 Number of Hopes (Tree, Mesh) Figure 2. Figure 2 End to end delay In Figure 3 the red line indicates ETE Delay for Router 1 in the Tree Routing scenario while the blue line indicates ETE Delay for Router 1 in Mesh Routing. The ETE Delay in Mesh Routing is lower due to the mesh routing process finding more efficient route than tree based routing (1 hop vs. 2 hops). The red line in Figure 4 is the total load for the Tree Routing scenario while the blue line is total load for Mesh Routing. The load for Mesh Routing is lower due to fewer hops for application traffic resulting in less overall traffic seen at the MAC layer. Also note that is a very small spike in load for Mesh Routing near the beginning of the simulation that is not seen for Tree Routing. This is due to the routing messages being broadcast at that time. Figure 3. End to end delay for Router 1 Figure 4. Load per PAN

5 Figure 5 shows the throughput for the tree and mesh topologies respectively. It shows that the maximum throughput is achieved in Tree topology and Mesh topology has the low throughput. The reason for this is because Tree topology is communicating on the basis of the PAN coordinators and R which are more efficient as compared to the end devices. Also in Tree topology total load of the network is divided among the local PAN and Rs as a result of which lesser collisions and lesser packet drops takes place as a result of which the throughput is maximum in case of Tree topology. Figure 5. Throughput Figure 6(a) and 6(b) shows the tree structure and mesh route from Router 1. The tree structure in this scenario is identical to the previous one. Also note that the tree path from Router 1 to Router 3 passes through the Coordinator. In Mesh Network, the mesh route goes directly to Router 3. Figure 6. Tree structure Figure 7. Mesh Route

6 1882 D. SCENARIO I1 This Figure 7 scenario studies the behavior of a network when the coordinator fails. The network contains two coordinators and 24 routers and end devices. Each router and end device in the scenario has its PAN ID set to Auto- Assigned. The coordinators have their PAN ID's set to 1 and 2 respectively. A portion of the remaining nodes should join each of the two coordinators (any given node may join either coordinator). Figure 8. Snapshot of the Network when Coordinator Fails Two minutes into the simulation, the first coordinator fails. It will remain failed until four minutes, when it will recover and re-establish a network. At eight minutes, the second coordinator will fail. It will remain failed until ten minutes. The expected behavior is approximately half the nodes to join each of the two coordinators at initialization. When the first coordinator fails, the nodes joined to that PAN should leave and join the second coordinator. When the second coordinator fails, all the nodes should join the first coordinator. Figure 8 shows Global MAC load for PAN. The blue line in figure 7 is the first coordinator (PAN 1) while the red is the second coordinator (PAN 2). Initially, both PANs have more or less equivalent loads (PAN 1's is greater due to a few more nodes joining that network). After 2 minutes, PAN 1's load drops to zero while PAN 2's load increases. Note that these numbers remain constant even after the first coordinator recovers at 4 minutes. When the second coordinator fails after eight minutes, PAN1's load increases and PAN 2's falls to zero at that time. Figure 9 shows the PAN affiliation for coordinator and coordinator_0 in the network. From these two graphs you can see that during the their failed periods the coordinators have a PAN ID of -1, which is the code indicating they are not currently joined to the network.

7 Figure 9. Load per PAN Figure 10. PAN Affiliation Figure 10 shows the global Output report derived from the simulation. From the Number of Nodes column in the three tables presented here, we can see that initially 15 nodes are joined to PAN 1 while 11 are joined to PAN 2 (roughly half each, with an acceptable variation due to randomness). After the first failure, 25 nodes are joined to PAN 2 while only one (the coordinator itself) is joined to PAN 1. After the second failure, the reverse is true. Figure 11. Global Output Report at simulation time 360, 60,720 VI.CONCLUSION This project focuses set of simulation experiments performed in OPNET simulator. To examine topological features of WSNs, simulation and investigation of two scenarios is taken. In first scenario, comparison of the two possible topologies (Mesh and Tree) to each other and the statistics for end-to-end delay, number of hops and global throughput, load is considered. In the second scenario, the Tree topology with two coordinators is carried out and observed situation when one coordinator fails for some time period where considered statistics are load, pan affiliation and output report. The fifteen nodes (one C, six Rs and eight EDs) in each topology were identical. From the simulation results we can conclude that the end-to-end delay and load of the Tree topology is higher compared to mesh topology. The throughput is high in the Tree topology, and low in a Mesh topology. In the second part of the simulation study, the Tree topology with two coordinator scenario is examined and observed the situation when one coordinator fails for

8 1884 some time period. The expected behavior is approximately half the nodes to join each of the two coordinators at initialization. When the first coordinator fails, the nodes joined to that PAN should leave and join the second coordinator. When the second coordinator fails, all the nodes should join the first coordinator. Our future work will be associated with the study of energy efficiency and reliability of all these topologies separately, i.e. emphasis will be placed on developing protocols that would continue the battery life, as well as access to the source code of the network and the application layers. VII. REFERENCE [1] Akyildiz, I. F., Su, Sankarasubramaniam, W. Y. and Cayirci, E. Wireless sensor networks: A survey, Computer Networks (Elsevier), vol. 38, pp ,2002. [2] I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, A survey on sensor networks, IEEE Communications Magazine, vol. 40, pp , August [3] Jurcik, P.; Koubaa, A.; Alves, M.; Tovar, E.; Hanzalek, Z.; A Simulation Model for the IEEE protocol: Delay/Throughput Evaluation of GTS Mechanism, Analysis, and Simulation of Computer and Telecommunication Systems, MASCOTS '07. 15th International Symposium, Oct [4] IEEE OPNET Simulation Model, [5] Kemal Akkaya and Mohamed Younis. A survey on routing protocols for wireless sensor networks. Ad hoc [6] Networks, 3(3): , May [7] Al-Karaki, J. N. and Kamal, A. E. Routing techniques in Wireless Sensor Networks: A survey, Department of Electrical and Computer Engineering Iowa State University, Ames, Iowa [8] Francesca Cuomo; Emanuele Cipollone; Anna Abbagnale; Performance analysis of IEEE wireless sensor networks: An insight into the topology formation process, Comput. Netw. (2009). Doi: /j.commet [9] Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (LR-WPANs), IEEE SA Standards Board Std , 2006.