Energy-efficient cooperative relaying protocol for full-duplex cognitive radio users and delay-aware primary users This paper considers a network in which a primary user (PU) may cooperate with a cognitive radio (CR) user for transmission of its data packets. The PU is assumed to be a buffered terminal operating in a time-slotted fashion. We develop an energy-efficient protocol that involves cooperation and coordination between primary and secondary users. To satisfy certain quality-of-service requirements, users share time slot duration and frequency bandwidth. Moreover, the secondary user (SU) may leverage the primary feedback channel. The proposed protocol is designed such that the secondary rate is maximized and the primary queueing delay is maintained less than the queueing delay in case of non-cooperative PU. In addition, the proposed protocol guarantees the stability of the primary queue and maintains the average energy emitted by the CR user below a certain predefined value that depends on the application. The proposed protocol provides more robust and potentially continuous service for SUs compared to the conventional practice in cognitive networks where SUs transmit in the spectrum holes and silence sessions of the PUs. We include primary source burstiness and sensing errors to the analysis of the proposed cooperative cognitive protocol. Numerical results show the beneficial gains of the cooperative protocol in terms of SU rate and PU throughput, PU queueing delay, and PU average energy savings.