ARQ Protocols and Unidirectional Codes

Forward error control (FEC) and automatic-repeat request (ARQ) are two main techniques used for reliable data transmission in computer and communication systems. In this paper, some simple, low cost error control techniques for ARQ protocols used with binary unidirectional channels, are described. The proposed schemes can correct up to [t/2] unidirectional errors using t-unidirectional error detecting codes and code combining with much less number of retransmissions. First we show how to do code combining for unidirectional errors. To use code combining with unidirectional codes, we need to identify the type of error (0 rarr 1 or 1 rarr 0) from the received word. We show how this can be done for various unidirectional codes