Retransmission error control options for dedicated access and packet switched random access satellite channels

Two forms of Automatic Repeat-Request (ARC) system of error control involving retransmissions are examined for two modes of data transfer, (1) the conventional dedicated access as in FDMA or TDMA, and (2) the new packet switched random access, known as 'Aloha schemes'. The forms, the Go-Back-N and the Selective Repeat, are feasible for implementation on operating satellite data circuits at voice band speeds. Hybrid error control using ARQ and some limited degree of Forward Error Correction (FEC) yields high throughput while maintaining good reliability, and is expected to perform better than ARQ or FEC alone. The average bit error rate is a guideline in choosing an error control technique, so that for error rates less than 0.0001, Go-Back-N is better or comparable to SRQ on end-to-end circuits involving burst error producing terrestrial segments. For higher error rates, though SRQ (Selective-Repeat ARQ) is relatively superior to Go-Back-N, its throughput efficiency becomes quite low with increasing error rate. In random access systems, ARQ is much similar to SRQ in continuous data transmission when error rates are low.