Wireless Ad Hoc and Sensor Networks

Distributed Power Control and Rate Adaptation 293In blue, the output power at the transmitter is plotted. It shows that thechange in transmitter power follows the power pattern of the interferer.6.11.5 Abruptly Changing Channel with Slow UpdateThe setup here is the same as the previous experiment, except that theinterferer varies the transmission power randomly. The rate for the powerupdate is three times faster than the rate of the interferer. This is consideredas a very brutal interferer. The interference level is shown here in Figure 6.35.In Figure 6.36, we can observe that the SNR at the receiver is not very wellleveled compared to a slowly varying channel because of the vast brutalinterferer. However it is still kept at an acceptable margin around 45 dB.6.11.6 Abruptly Changing Channel with Fast UpdateIn this setup, the same interferer is used as the previous experiment. Howeverthe rate for the power update is now 10 times faster than the interferer.With the desired SNR equal to 45 dB, we can observe from Figure 6.37 thatthe SNR at the receiver performs very well with a faster update rate.Example 6.11.2: DAPC for Four NodesNext the DAPC is implemented on four nodes. One can treat this as anRFID system (see Chapter 10) where passive tags harvest energy from the7060SNR (dB)Power (dBm)50Power (dB)/SNR (dBm)403020100−10−200 200 400 600 800 1000 1200 1400 1600 1800 2000PacketsFIGURE 6.35Power variation of an interferer with random output power.