EFFICIENT SELECTIVE REPEAT ARQ STRATEGIES FOR VERY NOISY AND FLUCTUATING CHANNELS

An investigation is made of the memory and selective repeat ARQ techniques when channels in both directions are very noisy. The authors demonstrate that a difficulty arises when memory ARQ is used in these situations, and propose a remedy--the similarity test. They consider a combination of both memory ARQ techniques, where an unacknowledged block is retransmitted exactly as before, and modified memory ARQ, where alternate transmissions together form a rate 1/2 code. After describing the similarity test, the authors outline a memory ARQ technique which employs double null zone reception and 3 bits of past information storage per binary digit. For modified memory ARQ procedures, a discussion of how to resolve problems regarding the identity of the two halves of the rate 1/2 code used is presented.