Wireless Ad Hoc and Sensor Networks

350 Wireless Ad Hoc and Sensor Networks6Totaldata transmitted (cluster topology)12 clusters, 8 sensors per cluster, duration 20sTotaldata (Mbits)5432106 8 10 12 14 16 18 20Per-flow rate (Kbps)DPC + sleep modeDPC802.11FIGURE 7.24Total data transmitted for varying per flow rates.In terms of total data transmitted, the DPC without and with sleep modeachieve better results as shown in Figure 7.24. For both, DPC without andwith sleep mode, the amount of transmitted data decreases with anincrease in per flow rates. This indicates that the network is congested;hence, the utilization decreases. At low per flow rates, the sleep mode isnot as beneficial; hence, low throughput whereas for moderate to highflow rates, sleep mode provides a reasonable throughput compared toother methods. Figure 7.25 presents the energy efficiency of each protocolwhere the DPC with sleep mode performs better than DPC without sleepmode and 802.11 protocols. This will extend lifetime of the sensors andthe network.Example 7.6.2: Twenty-Cluster Sensor Network ResultsTo simulate significant traffic, a 20-cluster topology is used. Similar to the12-cluster case, the DPC with sleep mode achieves lower contention time.Also, from Figure 7.26 and Figure 7.27, with total data transmitted andtotal data transmitted per joule, the DPC without and with sleep modeoutperform 802.11. Additionally, DPC with sleep mode is able to increasethroughput and energy efficiency as the traffic increases. However, ingeneral, the 20-cluster network is able to transmit less data than a smallernetwork due to heavy congestion and presence of a bottleneck linkbecause the entire traffic is directed to one node — BS.