A Hybrid-ARQ Protocol based on a Concatenated Reed-Solomon/Hamming Code

A communications protocol with error correction/detection is described that was designed for the transfer of data files over a half-duplex secure radio link in a channel environment expected to exhibit burst errors and random errors at a bit error rate (BER) as high as 10^-2. This system is being implemented as part of a military tactical communications system. The communications techniques described offer robust performance over poor transmission channels with a practical implementation for tactical applications. Error correction/detection is performed by a concatenated block code featuring an inner binary shortened-extended Hamming(12,7) code and an outer shortened Reed-Solomon(32,28) code over GF(2⁷) with degree-32 character interleaving. The protocol employed is a point-to-point, half-duplex, hybrid-ARQ protocol with selective retransmission. Theoretical performance estimates have been obtained. At a channel BER of 10^-2, the probability that a single transmission of a maximum length packet (containing 198,656 bits) will be decoded correctly is greater than 0.998; the undetected character error probability per 7-bit information character is 6.1 × 10^-7; the decoded BER is 8.7 × 10^-8; and the protocol efficiency (assuming channel idle time due to equipment delays in reversing the direction of transmission of 16,000 bits per packet transmission) is 42%. Performance estimates for channel BERs of interest were verified using a FORTRAN implementation of the concatenated code on a simulated random error channel. The single burst error correction capability is 760 bits per 12,288-bit data block.