Throughput of a FHMA system for variable rate coding and interference estimates

Frequency hopped multiple access (FHMA) systems are sed to provide a secure link in military communication systems. The author considers a decentralized FHMA packet communication system in which a collection transmitter-receiver pairs share a common channel. One criterion to measure the performance of a FHMA system effectively is the average normalized throughput. The optimum average normalized throughput of the system is a function of both the number of users simultaneously supported and the information rate of each user. This information rate is determined by the error correction code employed in the system. Intuitively, as the number of users increases the throughput will increase; however, the multi-user interference will require additional error protection, thereby lowering the information rate. For a given number of simultaneous users, there is an optimum code rate which maximizes throughput. The authors investigate the average normalized throughput performance of a FHMA system for several cases. There are two extreme cases: The case in which number of users in the system is unknown, but the probability is modeled as a random distribution, and the case in which the number of users is exactly known. The more interesting and practical case is the situation in which imperfect estimates of the number of active users are available. These estimates could be generated by monitoring a few frequency slots at any given time. The authors investigate the performance of the FHMA and the choice of optimal code rate for a variety this case. Reed-Solomon codes are considered