A Sparsity-Aware Cooperative Protocol for Cognitive Radio Networks With Energy-Harvesting Primary User

We consider a cognitive setting composed of multiple primary frequency bands each of which consists of a limited-battery energy-harvesting primary user and a secondary user. The primary user is equipped with a limited-capacity energy queue to maintain the energy harvested from the environment. We propose a novel cooperative protocol for the secondary users. The secondary user assigned to one of the primary frequency bands is aided by a set of nearby secondary users, which we refer to as secondary relays. We assume that each secondary relay participates in relaying the secondary packets with a certain probability. The proposed protocol exploits the sparsity of the participating-relays set and is efficient as it allows dynamic relay assignment. When the secondary user's direct link is in outage, the received secondary packets at the relays are stored in a relaying queue for future retransmissions. The relays perform cooperative beamforming to achieve a cooperative diversity gain for the secondary source. We study two types of quality-of-service requirements for the primary user. We analyze the impact of the primary user energy queue arrival rate and capacity on the secondary user throughput. In addition, we investigate the impact of the relaying queue capacity and the number of relays participating in spectrum sensing on the secondary user throughput.