Effect of secondary nodes on the primary´s stable throughput in a cognitive wireless network

We consider a cognitive network consisting of one primary source-destination pair and N secondary cognitive source-destination pairs that randomly access the channel during the primary user´s idle slots. We first study the effect of the secondary nodes´ transmission parameters such as power and channel access probabilities on the stable throughput of the 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. Finally, we propose a multinode relaying protocol based on distributed space-time orthogonal block codes, that uses 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.