Wireless Ad Hoc and Sensor Networks

Distributed Fair Scheduling in Wireless Ad Hoc and Sensor Networks 343arrive during listening period – 0 (packet can be sent immediately) –, andaverage delay when packets arrive during sleep period is equal to half ofT sleep = T SMAC /2 (average for [T/2, 0>).In the case of the energy-aware protocol, the average sleep delay for agiven sensor is given byD = T /2sleep newNEW(7.85)where T NEW is the time interval between communications. Packets arrivingat the CH have to wait for the next communication event. Hence, on anaverage it will be equal to the half of the communication interval.The energy consumption can be compared, when other parameters ofthe protocols are held the same in both the cases. Hence, the delay shouldto be equal in both cases. From Equation 7.84 and Equation 7.85 thiscondition implies thatTNEW= T /4SMAC(7.86)Energy expended during communication per sleep cycle for SMACprotocol is equal toESMAC = ELISTEN ∗ TSMAC/2(7.87)where E LISTEN is power consumed by node while listening to radioresources, and T SMAC is the duration of the sleep cycle. For the proposedprotocol, the energy consumption is equal toE = 4∗E ∗TNEW TRANS TRANS(7.88)where E TRANS is the power consumed during communication with a CH,and T TRANS is a duration of this communication. Then, the relative savingof Equation 7.88 when compared to Equation 7.87 is equal to8 ETRANSTSaving = ∗ ∗E ∗TLISTENTRANSSMAC(7.89)Using some typical values: E TRANS = 2 * E LISTEN ; T SMAC = 600 msec; andT TRANS = 1 msec, the energy saving ratio is equal to 0.02666. In other words,the energy-aware protocol consumes 1/0.0266 = 37.5 times less energythan SMAC because of its new sleep-mode option. Similarly, energy savingscan be calculated between the energy-aware and other availableprotocols.