Wireless Ad Hoc and Sensor Networks

Distributed Power Control and Rate Adaptation 2818000Data dropped at intermediate nodeDrop rate (Kbps)7000600050004000300020001000PDPModified RBAR00 200 400 600 800 1000 1200 1400Per-flow rate (Kbps)FIGURE 6.24Number of packets dropped at the intermediate node for varying per flow rate.scheme is able to increase the effective throughput more than RBAR,because the PDP prevents packet drops at the intermediate node asdepicted in Figure 6.24, by limiting incoming flow using the feedbacksignal. The traffic emitted from sources is reduced as the queue utilizationat the router increases, thus preventing buffer overflows. On the otherhand, the modified RBAR with burst enabled cannot control the incomingtraffic and, as a result, the packets are dropped at the intermediate node,and the end-to-end throughput suffers. An improvement of throughputup to 96% is observed for the proposed scheme, when compared with themodified RBAR protocol.The buffer overflow in the case of modified RBAR protocol is shown inFigure 6.24 in terms of dropped packets at the intermediate nodes. Theproposed PDP scheme eliminates any queue-related packet drops at theintermediate node regardless of the generated traffic, because it can preciselycontrol the incoming flow by specifying a maximum number ofadmissible packets.Figure 6.25 illustrates the energy efficiency (amount of data transmittedper joule of consumed energy) of the protocols. The proposed schemeoutperforms the modified RBAR for all values of per flow rate, because thePDP reduces transmission power when possible, whereas the RBAR alwaystransmits with maximum power. Additionally, the PDP avoids buffer overflowthus preventing retransmissions, which, in turn, increases energy