Efficient Selective Repeat ARQ Strategies for Very Noisy and Fluctuating Channels

This paper investigates memory and selective repeat ARQ techniques when channels in both directions are very noisy. It demonstrates that a difficulty arises when memory ARQ is used in these situations, and proposes a remedy-the similarity test. The paper considers 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. The following items are featured. 1) Discussion and analysis of the similarity test. 2) A memory ARQ technique which employs double null zone reception and 3 bits of past information storage per binary digit. 3) For modified memory ARQ procedures, a discussion of how to resolve problems of confusing the identity of the two halves of the rate 1/2 code used.