Outage probability based comparison of underlay and overlay spectrum sharing techniques

Three spectrum sharing schemes-spreading-based underlay, interference avoidance (IA) based overlay and spreading-based underlay that implements IA, are compared in this paper. The comparison is based on the influence of these techniques on the performance of an existing legacy static radio system with which the spectrum-sharing radios coexist. Outage probability is used to evaluate the performance of the static radio system. It is shown in the paper that IA techniques dramatically reduce the interference at the static receiver. Hence the performance of an IA-based overlay scheme is much better than a spreading-based underlay scheme. However, a spreading-based underlay scheme that incorporates IA provides benefits over the IA-based overlay scheme. The advantage obtained is more pronounced when the bandwidth available to the agile radio system is increased. It is also shown that the degradation in performance in the absence of perfect information about the static radio system is lesser for the IA-based spectrum underlay scheme than the IA-based spectrum overlay scheme