A robust rate-adaptive hybrid ARQ scheme and frequency hopping for multiple-access communication systems

A frequency-hopped spread-spectrum multiple-access (FH-SSMA) communication system with a rate-adaptive coding scheme is considered. The scheme uses a variable-rate Reed-Solomon code, with a single decoder. Two cases are considered: N-ary frequency-shift keying (FSK) without erasure and N-ary FSK with perfect side information as to whether a channel symbol is hit or not. It is shown that FH-SSMA with this rate-adaptive coding scheme can serve a higher number of users than with fixed-rate coding for the above mentioned cases. This increase in the number of users is due to the higher throughput which results in less interference for the other users. It is shown that perfect side information increases the capacity of the system. The number of users can further increase if more time delay is allowed in the system