Wireless Ad Hoc and Sensor Networks

234 Wireless Ad Hoc and Sensor Networksused to compare the proposed scheme with that of 802.11. The proposedMAC protocol renders significant increase in throughput in the presenceof channel variations compared with 802.11 although consuming lowenergy per bit.6.1 Introduction to DPCThe objectives of transmitter power control include minimizing powerconsumption while increasing the network capacity and prolonging thebattery life of mobile units by managing mutual interference so that eachmobile unit can meet its SIR and other quality of service (QoS) requirements.Rigorous work on DPC was performed for cellular networks (Bambos1998, Dontula and Jagannathan 2004, Jagannathan et al. 2002,Jagannathan et al. 2004, Hashem and Sousa 1998). A few DPC schemes(Park and Sivakumar 2002, Jung and Vaidya 2002, Gomez et al. 2001, Karn1990, Pursley et al. 2000) were developed for wireless ad hoc networkswhere the topology constantly changes because of node mobility andcommunication link failures. Similarly, see Maniezzo et al. (2002), Wooand Culler (2001), Ye et al. (2002), Singh and Raghavendra (1998).Unlike wired networks, radio channel uncertainties in a wireless network,for instance path loss, shadowing, and Rayleigh fading, can attenuatethe power of the transmitted signal causing variations in the receivedSIR and thus degrading the performance of any DPC. Low SIR meanshigh bit error rate (BER), which is unsatisfactory. Reported DPC schemes(Park and Sivakumar 2002, Jung and Vaidya 2002, Gomez et al. 2001, Karn1990, Pursley et al. 2000) for ad hoc networks assume that: (1) only pathloss is present, (2) no other channel uncertainty exists, and (3) the mutualinterference among the users is held constant during power update ofeach user. Moreover, improvement of spatial reuse factor is not adequatelyaddressed. Our previous effort (Jagannathan et al. 2004) was to developnew protocols to accommodate channel uncertainties for cellular networks.No work is currently reported for ad hoc wireless networks thataccommodate channel uncertainties.Furthermore, in an ad hoc network as mentioned in Chapter 1, requestto send (RTS) and clear to send (CTS) messages are used to establish aconnection for data transmission between a transmitter and a receiver.In (Jung and Vaidya 2002, Gomez et al. 2001), authors propose usingmaximum transmitter power only for RTS-CTS, whereas DATA andACK transmission is accomplished at a much lower power. This lowerpower is calculated according to RTS and CTS reception conditions.However, the channel state can change between the RTS and the DATAtransmissions resulting in an inaccurate power selection. On the other hand,