ABSTRACT
This chapter presents a general methodology for optimal selection of automatic repeat request (ARQ) parameters. It discusses the distinction between the line ARQ gain and the net ARQ gain, the first related to the total increase in data transmission and used in the bit loading, the second discounted for forward error correction (FEC) redundancy and retransmissions. The line ARQ gain maximizing the channel throughput is shown to be a sum of the channel signal-to-noise ratio and some function of the bit load and FEC parameters. The chapter describes a fast method of determining the optimum ARQ parameters at the actual channel conditions, based on their values at some reference conditions, the latter being either stored in the modem memory or calculated prior to channel initialization.
