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Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

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330 <strong>Wireless</strong> <strong>Ad</strong> <strong>Hoc</strong> <strong>and</strong> <strong>Sensor</strong> <strong>Networks</strong>32ADFSDFS802.111Delay variation (sec)0−1−2−3−4 0 20 40 60 80 100 120PacketsFIGURE 7.13Delay variations.Figure 7.13. It can be observed that ADFS results in minimal delay variations,whereas those of DFS <strong>and</strong> IEEE 802.11 are relatively high. Hugedelay variations can adversely affect the QoS of the network.To evaluate the performance of the proposed algorithm, the networkwith 32 nodes was simulated with different flow rates, such as 200, 250,300, 350, 400, <strong>and</strong> 500 kbps per flow. Figure 7.14 presents the throughput/weight ratios of 4 r<strong>and</strong>omly selected flows (4, 10, 12, <strong>and</strong> 26), for the ADFS,DFS, <strong>and</strong> IEEE 802.11 protocols with different flow rates. The channel getscongested around 300 kbps per flow rate, after which the fairness of theprotocols is evaluated. Observe that using ADFS <strong>and</strong> DFS protocols, thefour flows get equal throughput/weight ratios after 300 kbps per flow,whereas the throughput/weight ratios of the flows using IEEE 802.11 keepvarying. Although both ADFS <strong>and</strong> DFS result in fair allocation of b<strong>and</strong>width,notice that the ADFS results in better throughput per flow. The FIof the network is calculated using Equation 7.83. Figure 7.15 presents thefairness indices of the network with different per-flow rates. The fairnessindices of the ADFS <strong>and</strong> DFS protocols are close to one, showing fairallocation of b<strong>and</strong>width, while those of 802.11 keep decreasing withincrease in per flow rates.The contention time for a packet is calculated as the time from whenthe packet is received by the MAC layer for transmission, to the timewhen it receives a successful CTS message to transmit the packet.

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