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Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

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264 <strong>Wireless</strong> <strong>Ad</strong> <strong>Hoc</strong> <strong>and</strong> <strong>Sensor</strong> <strong>Networks</strong>E PULSES denotes the additional energy consumed for the generation ofpulses. Therefore, E DPC <strong>and</strong> E PULSES can be expressed using Equation 6.26 asE DPC =PtDPC ∗ Pktsize/R(6.28)<strong>and</strong>E = ( Pkt / R) ∗( D / D ) ∗(Pt −PtC)PULSES size PULSE I MAX DP(6.29)After substituting Equation 6.28 <strong>and</strong> Equation 6.29 into Equation 6.27we get,E TOTAL = ( Pktsize/ R) ∗Pt DPC + ( Pktsize/R) ∗(DPULSE/ DI) ∗( PtMAX −PtDPC)(6.30)It is important to note that for the given packet size <strong>and</strong> rate, the totalenergy consumed varies linearly with transmission power. Also, the DPCscheme increases the transmission power for a given rate proportional tothe target SNR as per Equation 6.23. Thus for a rate k, Equation 6.30 isexpressed asE = ( Pkt / R )[( D / D ) ∗Pt + ( Pkt / R )TOTAL,k size k PULSE I MAXsize× ( SNR / SNR ) ∗( 1 −( D / D )) Pt ( t)]k 0 PULSE I 0k(6.31)The upper <strong>and</strong> lower thresholds of the DPC power (calculated forthe lowest supported rate) need to be found so that the most energyefficientrate can be selected. By equating Equation 6.31 for the twosuccessive rates, the threshold values for the rate adaptation aredetermined asE =ETOTAL,kTOTAL,k+1( Pkt / R )[( D / D )∗Pt + ( SNR / SNR ) ∗( 1 −( D / D )) Pt ( t)]size k PULSE IMAX k 0 PULSE I 0= ( Pkt / R )[( D / D ) ∗ Pt + ( SNR / Ssize k+ 1 PULSE I MAX k+1 NR0∗( 1 −( D / D )) Pt ( t)]PULSE I 0(6.32)Using Equation 6.31, the rate’s upper threshold using power as a constraintis given by)ϕ 1 αkPt O,k = Pt1 − ϕ∗ −∗γ −α ∗γk k k+ 1MAX(6.33)where α k =R k / R k+ 1, γ k =SNR k / SNR 0 <strong>and</strong> ϕ =DPULSES/DI.

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