Wireless Ad Hoc and Sensor Networks

Distributed Power Control and Rate Adaptation 263increase in rate. Hence, the lowest rate should be the most energy-efficient.However, in the proposed protocol, the train of pulses in DPC (Zawodniokand Jagannathan 2004) used to overcome the hidden-terminal problemintroduces an additional energy OH and becomes an important factor tobe considered for rate adaptation. Hence, the lowest rate is not alwaysenergy efficient. Consequently, the most energy-efficient rate is found bycomparing the energy consumed at each rate for a given packet underthe current channel state. The rate with lowest energy consumption thattakes into account the channel state and energy overhead due to thehidden-terminal problem will be selected as the minimum usable rate asdiscussed next.Normally, the energy consumed for transmission is equal toE=D⋅Pt(6.26)where E is the energy consumed, D is the duration of transmission, andPt is the current transmission power. For the case of the DPC algorithmwith the train of pulses illustrated in Figure 6.14, the energy consumedduring transmission is equal toE =E +ETOTAL DPC PULSES(6.27)E TOTALEDPCwhere is the total energy consumed on transmission of the packetwith pulses, represents the energy consumed for the transmission ofthe packet using the power selected by the DPC algorithm, andTx powerP MAXD PULSEpulsedurationD 1pulsesintervalE PULSESP DPCE DPCD PPacket durationTimeFIGURE 6.15Energy consumption during packet transmission.