Wireless Ad Hoc and Sensor Networks

252 Wireless Ad Hoc and Sensor NetworksContention (Msec)Contention for random topology100 nodes, 50 flows, duration 50s1801601401201008060402000 5 10 15 20 25 30 35 40 45 50Per-flow rate (Kbps)802.11 DPCFIGURE 6.8Contention time.the proposed protocol, the maximum throughput and energy-efficiencyis achieved at the higher per flow rate (10 and 5 kbps, respectively),because the proposed protocol achieves higher channel utilization whencompared to the 802.11 protocol.The average contention time is presented in Figure 6.8. The proposedprotocol yields lower contention time for the per flow rate (up to 30 kbps),because of higher channel utilization and shorter interval between packettransmissions, than in the case of the 802.11. As per flow rate increasesfurther, the contention time increases for the proposed protocol. Thisneutralizes the advantage of higher channel utilization in the proposedprotocol. Consequently, both protocols achieve similar contention time forper flow rates above 30 kbps.The simulations in random topology were repeated for constant a perflow rate of 10 kbps with varying packet size. The energy efficiency ispresented in Figure 6.9. As expected, the energy efficiency increases withpacket size. The MAC protocol introduces constant bit OH for everypacket transmitted; thus, for the same rate, the OH decreases as the packetsize increases. In consequence, a higher channel capacity is utilized fortransmission of bigger user data packets. Additionally, the DPC protocoloutperforms the 802.11 scheme for all packet sizes, which conforms theprevious results that are displayed in Figure 6.10.