Wireless Ad Hoc and Sensor Networks

Distributed Power Control and Rate Adaptation 2917060SNR (dB)Power (dBm)50Power (dB)/SNR (dBm)403020100−10−200 20 40 60 80 100 120 140 160 180 200PacketsFIGURE 6.32Receiver SNR and transmitter power level corresponding to channel uncertainties.for the receiver is set at 40 dB. Figure 6.31 demonstrates the performanceof the DAPC. In red, the SNR at the receiver is plotted. In blue, the outputpower of the transmitter is plotted (Figure 6.32). The receiver SNR waskept very close to the target SNR. We can clearly see that at packet number65, the receiver starts moving close to the transmitter, resulting in a reductionin the power level. At the 180th packet, the radio had been movedback to its original location, and the output power for the transmitter hasincreased to provide required SNR. This experiment shows that the DAPCaccurately estimates the channel loss g ii in a noninterfered environment.6.11.4 Slowly Varying InterferenceIn this experiment, a paired connection between a transmitter and areceiver is set up. At the same time, a constant interfering source is introducedto alter the channel with small variations per step. The time-varyingtransmission power for the interfering source is displayed in Figure 6.33.The transmission power for the interferer varies from 16dBm to 13 dB ata slow rate. Note that the rate for power update at the receiver is threetimes faster then rate of change of output power on the interferer.At the desired SNR value equal to 45 dB from Figure 6.34, we can observethat the SNR seen at the receiver is obtained very close to the desired value.