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Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

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218 <strong>Wireless</strong> <strong>Ad</strong> <strong>Hoc</strong> <strong>and</strong> <strong>Sensor</strong> <strong>Networks</strong>where θi() l = [ αi() l ri()]l is a vector of unknown parameters, <strong>and</strong> ψ i () l= ⎡yi() l⎤ ⎣ ⎦ is the regression vector. Now selecting feedback for DPC asωi () lv() l = − 1β ()[ l − ˆ θ () lψ () l + γ + k e ()] li i i i v i(5.62)where θiˆ () l is the estimate of θ i (), l then the SIR error system is expressed ase( l + 1) = k e( l) + θ () lψ () l − ˆ θ () lψ() li v i i T i i T i= k e() l + ̃θ () lψ() lv i i T i(5.63)*TPC: Transmitter power control *DPC: Distributed power controlwhere ̃θi() l θi() l ˆ θi() l is the error in estimation. From Equation 5.63, it isclear that the closed-loop SIR error system is driven by the channel estimationerror. If the channel uncertainties are properly estimated, thenestimation error tends to zero. In this case, Equation 5.63 becomesEquation 5.60. In the presence of error in estimation, only the boundednessof SIR error can be shown. We can show that the actual SIR approaches thetarget provided the channel uncertainties are properly estimated. Figure 5.26illustrates the block diagram representation of the proposed DPC wherechannel estimation <strong>and</strong> power selection are part of the receiver. To proceedfurther, the Assumption 5.4.1 is required <strong>and</strong> therefore stated.= −Interference5.4.2.2 <strong>Ad</strong>aptive Scheme DevelopmentASSUMPTION 5.4.1The channel changes slowly compared to the parameters’ updates.Radio channel with uncertainties (path loss,Rayleigh fading, shadowing)Transmitter∗ TPCTPC comm<strong>and</strong>∗ DPCTarget SIR (dB)Measured SIR (dB)Target SIR(dB)Feedback forpower selectionRadio channelwith uncertaintiesChannel parameterestimationPower selectionReceiverFIGURE 5.26Block diagram representation of distributed power control with channel uncertainties.

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