The mutual benefits of primary-secondary user cooperation in wireless cognitive networks

In cognitive radio networks, secondary users (SUs) may cooperate with the primary user (PU) in order to obtain more transmission opportunities and thus maximize their throughput. The synergy consists in the following: the SU opts to cooperate by using its own transmit power to improve the probability of successful transmission of the PU. By increasing the probability of successful packet transmission for the PU, the SU essentially increases the service rate of the PU queue and thus, for given packet arrival rate, it increases the chances that it will be empty, and the channel will be free to use. Due to power limitations however, SUs have to take intelligent decisions on whether to cooperate or not and at which power level. Cooperation policies in this framework require the solution of a constrained Markov decision problem with infinite state space. In our work, we restrict attention to the class of stationary policies that take randomized decisions of an SU activation and its transmit power in every time slot based only on spectrum sensing. The proposed class of policies is shown to achieve the same set of SU rates as the more general policies, while significantly enlarging the stability region of the PU queue. Finally, a lightweight distributed protocol based on the proposed class of policies is presented, which is amenable to implementation in realistic scenarios.