Joint power and rate control with constrained resources for underwater acoustic channels

Random linear packet coding combined with adaptive power and rate control is being considered as an alternative to traditional ARQ techniques for the underwater acoustic channel. We first analyze a scheme where the number of coded packets to transmit is determined so as to achieve a pre-determined reliability at the receiver, and hence eliminate the need for explicit feedback. We next investigate joint power and rate control with constrained resources. Using the channel gain information which is obtained via feedback from the receiver, the transmitter adjusts its transmit power and the number of coded packets such that the average energy per bit is minimized. We impose two main constraints for the optimization: (a) the transmit power should be within a maximum available power, and (b) the number of coded packets should not exceed a maximum value. Under these constraints, we define adaptation policies to minimize the average energy per bit and show analytical results for average energy savings available from the adaptation policies. We also show experimental results obtained using the measured channel gains from the SPACE-08 experiment, an at-sea experiment conducted off the coast of Martha's Vineyard in Massachusetts.