Wireless Ad Hoc and Sensor Networks

34 Wireless Ad Hoc and Sensor NetworksReceiver1. RTS2. CTS3. DATA4. ACKTransmitterFIGURE 1.5IEEE 802.11 signaling for addressed messages.path loss, fading, and interference cause variations in the received SIR.Such variations also cause variations in the bit error rate (BER), becausethe lower the SIR or SNR, the more difficult it is for the receiver to decodethe received signal. Hence, SIR is an important metric, which needs to bemaintained even when there are fluctuations in the wireless network.The block diagram representation of the DPC is illustrated in Figure 1.6.The receiver (as shown in the block diagram), after receiving the signal fromthe transmitter, measures the SIR value and compares it against therequired target SIR threshold. The difference between the desired and thereceived signal SIR is sent to the power update block, which then calculatesthe optimal power level with which the transmitter has to send thenext packet to maintain the required SIR. This power level is sent asfeedback to the transmitter, which then transmits with the power level asrequested by the receiver during the next packet transmission.Chapter 5 and Chapter 6, respectively, present DPC schemes for cellularand ad hoc networks, which satisfy the stringent requirements placed bythe wireless networking environment. Outage probability, total powerconsumed, and rate of convergence of the new links seeking admissioninto the network are taken as metrics to evaluate the proposed DPCscheme’s performance and to compare various power control schemes. Infact, a few DPC schemes (Dontula and Jagannathan 2004) have beenproposed in the past. Convergence of these schemes has not been provenChannel with uncertaintiesTransmitter TPC commandP iFeedback∗ Transmitter powerRadio channelInterferenceReceiverPower updateIEEE 802.11Target SIRMeasured SIRFIGURE 1.6Block diagram representation of DPC.