Throughput performance of frequency comb multiple access (FCMA)

In satellite multiple access communications a variety of measures exist with which to compare the performance of the various competing schemes. However, the results of these comparisons can be misleading. In particular, when comparing VSAT schemes which typically have a very large potential user population and a relatively small number of simultaneously active users, then traffic statistics must be included if the comparison is to have any relevance. A performance measure is introduced that takes into account the arrival statistics of the active users. This measure, termed the normalised throughput is then used to compare the performance of two schemes. The first scheme, FCMA, is a multiple access scheme proposed by the authors for application in VSAT networks. This new scheme uses signatures composed of discrete frequency elements, with well defined mathematical properties to M-ary modulate the data and simultaneously permit access to the channel resource. FCMA is suited to VSAT applications in which a small number of active users are randomly selected from a much larger potential user population. The second scheme, VFHMA, is a frequency hop satellite multiple access scheme, proposed by Viterbi (1978) and generally regarded as a benchmark against which the performance of competing schemes is measured. The comparison demonstrates that FCMA gives superior performance to VFHMA, for the range of parameters given and that both schemes outperform the traditional Aloha and Slotted Aloha channel access techniques