Wireless Ad Hoc and Sensor Networks

478 Wireless Ad Hoc and Sensor Networks1000Output powermW50000 5 10 15 20 25 30 35 40Interfernce−30dBm−40−500 5 10 15 20 25 30 35 40Detection range4Meters200 5 10 15 20 25 30 35 40TimeFIGURE 10.6Output power, interferences, and detection range as a function of time in seconds.power; however, the interference level is too high and, therefore, the readerreaches maximum power and enters the selective backoff scheme. It is alsoobserved that as the reader backs off to low power value, the interferencelevel increases, meaning that other readers are taking the advantage andaccessing the channel. This plot also demonstrates the changes in backofftime corresponding to the desired range achievement; for example, timeinterval 12 to 24 sec and 28 to 37 sec.The performance in sparse networks is discussed first. With the minimumdistance of 9 m between any two readers, the average percentageof time r that the desired range is attained across all readers is presentedin Figure 10.7. Note that each reader has a maximum detection range of3 m without interference, and the desired range is set to 2 m in the presenceof multiple readers. The DAPC is observed to have superior performanceover the two PPC algorithms for this sparse network. The DAPC convergesto 100% desired range achievement with the appropriate parameterestimation and closed-loop feedback control described in Section 10.3. Theresults justify the theoretical conclusions. It is also shown that Beta(2, 2)performs better than Beta(0.1, 0.1) in terms of r. With a Beta(2, 2) distribution,every reader will be on and transmitting at medium power most of thetime. With sparse networks and small interferences, the medium power