Code combining techniques for FH/SSRA slotted networks

The idea of code combining is applied to slotted frequency-hopping spread-spectrum random-access (FH/SSRA) networks. M-ary symbol modulation schemes with hard-decision decoding are examined. Both cases of decoding, with and without side-information, are considered. In the case of decoding without side-information two decoding methods are examined: in the first (ideal decoding) the decoder uses a large number of decoding trials, while in the second (practical decoding) it uses a smaller number of trials, based on the combining of only the last two available copies of a packet. Asymptotic results are derived as the code-length goes to infinity. It is shown that significant utilization/delay gains are obtained by using code combining techniques. A 20% performance improvement is observed for systems in which side-information is available at the decoder and the number of frequency slots is small. In this case, higher utilization, along with robust system operation is obtained without increased system complexity (only memory size of one codeword is the additional requirement)