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Cooperative MAC for Cognitive Radio Network with Energy Harvesting and Randomized Service Policy

This paper studies the queues stability and delay in cooperative multiple access for cognitive radio systems in which the secondary user (SU) has finite energy sources. The SU has two queues with a battery for energy storage. One of the SU's queues is used to store the relayed packets from the primary user (PU) queue. While the other one is used to store its own packets. Each transmission consumes a fixed amount of energy, and the battery is replenished through energy harvesting. A PU's packet is admitted to the relay queue with an admission probability. Moreover, the SU serves either the queue of its own data or the queue of the PU relayed data with certain service probabilities. The finiteness of energy has an effect on the system throughput and how it is affected by varying the service and admission probabilities. The analysis of this system is non- trivial due to the interdependence between the battery and SU's packet queues. This results in an interacting system of queues. To decouple this interaction, and characterize the stability region, we resort to a dominant system approach for the analysis. The obtained stability region is compared with the stability region of the system without energy constraints, and the losses due to finite energy are identified. Furthermore, the average delay encountered by the packets of both PU and SU is shown not to be affected by the finiteness of the energy within the stability region.