Wireless Ad Hoc and Sensor Networks

Distributed Power Control and Rate Adaptation 289Time...…….GetRSSI_BufferRSSI_bufferFinish receiving packetWriteRSSI_bufferStore noisestrengthReceiveIdleStore signalstrengthPreamble detectionFinish transmittingpacketOutgoing packetreadyTransmitFIGURE 6.30Baseband flowchart.at the reception of every byte. When the radio is in the idle mode, anyincoming data is discarded; however, the RSSI value is still recorded every8 bits. To separate preamble from noise, a small “RSSI_buffer” stores thepast N values of RSSI, where N equals to the length of preamble bytes.Any reading beyond N is averaged as the “noise_power.” After the radioenters the receive mode, RSSI is recorded and averaged along with thevalues in the RSSI_buffer to provide “signal_power.” A flowchart diagramof the mode switching and RSSI reading is shown in Figure 6.30.6.11.2.5 DAPC MAC controllerFigure 6.31 illustrates the block diagram representation of the proposedDAPC control loop inside a transmitter and receiver.At the receiver side, signal strength P i , noise level I i and, therefore, theSNR R i are measured at the reception. Ouput power at the transmitter P tis known from the previous calculation. Given P t and P i , the channelattenuation g ii for the previous transmission can be calculated. Now,update θ i and P t using Table 5.3. P t is then embedded into the MAC headerof the next outgoing packet to the corresponding transmitter. At the receptionof the next packet, the cycle begins again.