Random linear packet coding for fading channels

Random linear packet coding is considered for use over underwater acoustic channels where long delays challenge the efficiency of standard ARQ. Adaptive power control and rate control are explored to overcome the effect of fading, while minimizing the average energy per successfully transmitted bit of information. Two extreme scenarios are considered: independent fading where the channel varies independently from one data packet to the next, and block fading where the channel stays fixed over a block of packets. For the case of block fading, we design a power (rate) adaptation strategy under an outage criterion. We show that there exists an optimal transmission power (number of coded packets) for which the average energy per bit is minimized. Finally, we quantify the benefits of adaptive power (rate) control using real channel data recorded over a mobile link in the 10kHz acoustic band. These results show that energy savings are available from adaptive power (rate) control strategies.