Wireless Ad Hoc and Sensor Networks

Distributed Power Control and Rate Adaptation 277TABLE 6.3Energy Efficiency (kb/J)Protocol 0.5 Mbps 1.2 Mbps 4 MbpsRBAR 196.73 217.77 233.65DP 670.58 780.05 803.58RBAR for all the traffic rates because it intelligently selects the rate basedon channel state and congestion. Here the higher throughput observedfor the proposed protocol is the result of rate adaptation and not dueto DPC which clearly shows that the channel state has to be consideredduring rate selection. Moreover, when observing energy-efficiency inFigure 6.19, the proposed protocol can transmit up to three times moredata for the same amount of energy consumed, because of the inclusionof DPC.Figure 6.20 displays the drop rate at the intermediate node. The numberof dropped packets increases for the RBAR as traffic increases, whereasfor the proposed protocol, this rate is constantly low because, in theproposed rate adaptation scheme, the buffer occupancy of the receivingnode is fed back to the transmitter. This information is used at thetransmitting node to delay transmissions, thus preventing packet dropsand retransmissions, whereas the RBAR transmits constantly dropping300Network throughput250Throughput (Kbps)20015010050The proposed protocolRBAR00 200 400 600 800 1000 1200 1400Per-flow rate (Kbps)FIGURE 6.18Throughput for varying per flow rate.