Stable Throughput in a Cognitive Wireless Network

We study, from a network layer perspective, the effect of an Ad-Hoc secondary network with N nodes accessing the spectrum licensed to a primary node. If the sensing is perfect, then the secondary nodes do not interfere with the primary node and thus do not affect its stable throughput. In case of imperfect sensing, it is shown that if the primary node's arrival rate is less than some calculated value, then the secondary transmissions do not affect its queueing stability; otherwise, the secondary nodes should regulate their transmission parameters to reduce their interference on the primary. It is also shown that in contrast with the primary user's maximum stable throughput rate which strictly decreases with increased sensing errors, the throughput of the secondary nodes might increase with sensing errors as more transmission opportunities become available to them. Finally, we explore the use of the secondary nodes as relays of the primary node's traffic to compensate for the interference they might cause. In this case, for appropriate modulation scheme and under perfect sensing, it is shown that the more secondary nodes in the system, the better for the primary user in terms of his stable throughput. Meanwhile, the secondary nodes might benefit from relaying by having access to a larger number of idle slots becoming available to them due to the increase of the service rate of the primary. For the case of a single secondary node, the proposed relaying protocol guarantees that either both the primary and the secondary benefit from relaying or none of them does.