Wireless Ad Hoc and Sensor Networks

222 Wireless Ad Hoc and Sensor Networks5.4.2.3 Simulation ExamplesExample 5.4.1: DPC Evaluation in the Presenceof Fading ChannelIn the simulations, all the mobiles in the network have to achieve a desiredtarget SIR value γ i in the presence of channel uncertainties. The SIR valueis a measure of quality of the received signal, and can be used to determinethe control action that needs to be taken. The SIR, can be expressed asγ iγ i= (( E / N )/( W/ R))b0(5.75)where E b is the energy per bit of the received signal in watts, N 0 is theinterference power in watts per Hertz, R is the bit rate in bits per second,and W is the radio channel bandwidth in Hertz.The cellular network is considered to be divided into seven hexagonalcells covering an area of 10 x 10 km (Figure 5.2). Each cell is serviced viaa base station, which is located at the center of the hexagonal cell. Mobileusers in each cell are placed at random. It is assumed that the power offor each mobile user is updated asynchronously. Consequently, the powersof all other mobile users do not change when the power of the ith link isupdated. The receiver noise in the system η i is taken as 10 − 12 . The thresholdSIR, γ , which each cell tries to achieve is 0.04 (13.9794 dB). The ratioEbof energy per bit to interference power per hertz is 5.12 dB. BitN0rate R b , is chosen at 9600 bps. Radio channel bandwidth B cPmaxis consideredto be 1.2288 MHz. The maximum power for each mobile is selectedas 1 mw. Two cases are considered: channel changing sharply at a certaintime instant and channel changing smoothly. The system is simulatedwith different DPC schemes with 100 users. In the first few simulations,the users in each cell are placed at random and are considered stationary.Later, the users are mobile.5.4.2.3.1 Stationary UsersCASE I: CONSTANT BUT ABRUPTLY CHANGING CHANNEL In this scenario,we select the parameters as k v = 001 . and σ = 001 . . Figure 5.27 shows thechange of g ii with time as a result of channel fluctuation, which obeys theRayleigh fading and shadowing. Though channel changes sharply atevery ten time-units only, the channel gain g ii is changed once in everyten time-units, and it is held constant otherwise. Figure 5.28 illustratesthe plot of SIR of a randomly selected mobile user. From this figure, it isclear that the proposed DPC scheme is the only scheme that maintainsthe target SIR in the presence of channel variations. Figure 5.29 presentsthe plot of total power consumed by all the mobiles in the network. Theresult shows that all the schemes consume similar power values (about90 mW) for the entire network. Figure 5.30 shows the plot of outage