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Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

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186 <strong>Wireless</strong> <strong>Ad</strong> <strong>Hoc</strong> <strong>and</strong> <strong>Sensor</strong> <strong>Networks</strong>where is the unique positive definite solution of the algebraic Ricattiequation (ARE)S iS J S SH H S H T H S J Q( )⎡= − +⎣⎢⎤⎦⎥ +i i T i i i i T i i i i T i i−1(5.15)Then, the resulting time-invariant closed-loop system described byx( l+ 1) = ( J − HK ) x( l)+ Hηi i i i i i i(5.16)is asymptotically stable, if = 0.PROOF Follow the steps as in Lewis (1999).η iREMARK 2The proposed scheme minimizes the performance index∞∑ i=xTx i T i i + vQv i T i i where <strong>and</strong> are weighting matrices.The block diagram in Figure 5.1 explains the process of power controlusing SSCD/optimal schemes. The receiver as shown in the blockdiagram, after receiving the signal from the transmitter, measures theSIR value <strong>and</strong> compares it against the target SIR threshold. The differencebetween the desired SIR to the received signal SIR is sent to thepower update block, which then calculates the optimal power levelwith which the transmitter has to send the next packet to maintain therequired SIR. This power level is sent as feedback to the transmitter,which then uses the power level to transmit the packet in the next timeslot.1 T i Q iInterferenceTransmitter ∗ TPCP iFeedback∗ Transmitter power controlChannel with uncertaintiesTPC comm<strong>and</strong>Radio channelReceiverDPCPower updateIEEE 802.11Target SIR (dB)Measured SIRFIGURE 5.1Block diagram representation of DPC.

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