A hybrid ARQ scheme with parity retransmission for error control of satellite channels

A novel type of hybrid automatic-repeat-request (ARQ) scheme for error control in data communication systems is described which is based on the sending of parity check digits for error correction to the receiver only when they are needed. When a data block D is detected to be in error, the retransmissions are alternate repetitions of a parity block P(D) and D. When a parity block is received, it is used to recover the originally transmitted data block either by inversion or by decoding operation. The repetitions of P(D) and D are alternately stored in the receiver buffer for error correction until D is recovered. It is shown that the hybrid ARQ scheme proposed offers both high throughput and high system reliability, being especially useful in high speed data communication systems with significant roundtrip delays, such as those encountered in satellite channels.