Wireless Ad Hoc and Sensor Networks

Distributed Power Control and Rate Adaptation 245NAV (G)(with pulses)EIFS EIFS EIFS EIFS EIFS EIFS EIFSTx powerMaxDPC levelRTSCTSDATAACKTimeFIGURE 6.4Periodic increase in power during frame transmission.6.5.2 Protocol DesignIn the proposed protocol, only the initial RTS-CTS frames for a new linkhave to be transmitted using the maximum power defined for the network.Subsequently, all frames, including RTS-CTS-DATA-ACK frames,will use the power calculated according to the proposed DPC scheme.The MAC header needs to be changed to allow power information to besent between the communicating nodes.In other words, the MAC frames have to embed the power informationthat is used for the current packet, as well as for any subsequentresponse. This process repeats for all transmissions occurring betweenany two nodes A and B resulting in an increase in overhead, whichcould cause a decrease in throughput. However, an increase inthroughput observed because of better channel utilization overcomesthe penalty introduced by the additional overhead. Moreover, thisoverhead can be further reduced by using discrete power levels. Consequently,the number of bits necessary for storing the power value inthe header will decrease, thus reducing the overhead. Additionally,these fields can be defined as an option in the frame header by usinga one-bit flag.Whenever the power level changes, this flag will be set indicating thereceiving node to calculate its transmitter power for the subsequent transmission.Otherwise, the flag will be cleared and the node will continue touse its previous value.Because a lower power is selected for transmission of the MAC frames,during severe fading, certain frames will be unsuccessfully decodedbecause of poor reception and they will be dropped. It is important tonote that predicting the channel during severe fading conditions is quitedifficult and impossible. To mitigate this problem, the proposed protocol