Enhanced access schemes based on channel statistics for cognitive wireless networks

We study from a network-layer perspective a simple cognitive network consisting of one primary user (PU) and one secondary user (SU) sharing the spectrum with the primary. We propose and analyze two different access schemes at the SU aiming at maximizing its stable throughput while guaranteeing the stability of the PU´s queue. These schemes exploit the SU´s knowledge of the statistics of the channels as well as the average arrival rate to the PU. The first scheme is where the SU does not perform any sensing but accesses the channel at all slots with fixed probability p*. The second scheme is where the SU senses the channel at all slots and accesses the channel with probabilities p₁* and p₂* when the PU is sensed to be idle and busy respectively. We also compare these schemes to the traditional opportunistic spectrum access (OSA) where the SU accesses the channel with probability one only if the channel is sensed to be idle. The analysis shows that if the PU and/or SU receivers can decode simultaneous transmissions with high success probability, then schemes with no sensing are preferred as they provide to the SU more duration for data transmission and they outperform schemes with sensing. In this case, the OSA scheme is over- protective. Otherwise, schemes with sensing are preferred since sensing is crucial for PU protection. Therefore, using complex receivers that can handle simultaneous transmissions successfully alleviates the need of complex SU transmitters with strong sensing capability which might be preferred in some circumstances.