ANALYSIS AND OPTIMIZATION OF ADAPTIVE MULTICOPY TRANSMISSION ARQ PROTOCOLS FOR TIME-VARYING CHANNELS

This paper outlines an efficient method to concurrently optimize a mul tiplicity of design variables for continuous Selective-Repeat (SR) and Go-Back-N (GBN) automatic repeat request (ARQ) strategies, both in no iseless and noisy feedback channels. For these ARQ protocols, me adapt either the number of identical message blocks sent in each transmissi on (in case of GBN scheme) or the number of copies of a block retransm itted to handle a NACKed codeword (for the SR protocol) dynamically to the estimated channel condition. The channel state information is obt ained by counting the contiguous acknowledgment (ACK or NACK) messages . Exploiting the asymptotic properties of the steady-state probability expressions, we show analytically that the optimum solution indeed li es in the infinite space. Subsequently, a simple expression to estimat e the suboptimal design parameters is suggested. Our approach of minim izing the mean-square error function yields to a quantitative study of the appropriateness of the selected parameters. Exact analytical expr essions that allows us to compute the throughput crossover probability between any two arbitrary multicopy transmission modes are derived. T he results provide fundamental insights into how these keg parameters interact and determine the system performance.