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Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

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376 <strong>Wireless</strong> <strong>Ad</strong> <strong>Hoc</strong> <strong>and</strong> <strong>Sensor</strong> <strong>Networks</strong>The average delay of the packets (E2E) is chosen as one of the metricsto evaluate the performance of the protocols. Moreover, the networkthroughput is affected by the decisions of the routing protocol, <strong>and</strong> thereexists a trade-off between the average delay <strong>and</strong> the network throughput.Therefore, in an attempt to minimize the average delay, the OEDR protocolmight result in lower network throughput. However, the ratio of throughputto delay (throughput/average delay) is proven to be a more concisemetric that can be used to compare different protocols, according to Jain(1991).The third metric is the energy-delay product, <strong>and</strong> it is calculated as(total energy used/number of packets received at the destinations) timesthe average delay. Because the OEDR protocol aims at finding the optimalpath with respect to the energy-delay cost of the links, instead of theshortest hops path (like in OLSR), in some cases, it can result in routeswith higher number of hops compared to other routing protocols. Thiscould slightly increase the energy consumption for packet delivery thoughminimizing the overall delay. Therefore, the energy-delay product wouldserve as a more precise metric to compare the performance of differentrouting protocols. The average contention time for a packet at an ad hocnode is calculated as the time interval elapsed between the packet beingready for transmission at the MAC layer to the time when it receives asuccessful CTS message to transmit the packet. The two simulationscenarios are presented next.Example 8.5.1: Varying Node MobilityA network of 100 nodes, r<strong>and</strong>omly distributed in an area of 2000 × 2000 mis simulated by varying the node mobility between 20 <strong>and</strong> 100 km/h, alongwith the following parameters: simulation time is 100 sec, maximum numberof flows is 50, location of the nodes <strong>and</strong> the flows are generated r<strong>and</strong>omly,channel b<strong>and</strong>width is 1 Mbps, “two-ray ground” propagation model with a“path-loss exponent” of 4.0 is used, initial energy of each node is 10 J, flowrate is 41 kbps, packet size is 512 B, <strong>and</strong> the queue limit is 50 packets.According to Figure 8.9, the average E2E delays using the OEDR protocolare much smaller than the delays using the OLSR <strong>and</strong> AODV protocols,because the proposed OEDR protocol considers the transmission delay ofthe links in the cost function while computing the routes between the source<strong>and</strong> destination. Also, observe that the average packet delays tend toincrease with an increase in node mobility. With the movement of nodes,links get broken (<strong>and</strong> created) more frequently as the nodes enter <strong>and</strong> leavethe transmission range of other nodes. Therefore, the routes have to berecomputed dynamically to reflect the changes in network topology.According to Figure 8.10, the throughput/delay values of the OEDRprotocol are always higher than those of OLSR <strong>and</strong> AODV protocols,

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