In this paper, we study and analyze fundamental throughput and delaytradeoffs in cooperative multiple access for cognitive radio systems. We focuson the class of randomized cooperative policies, whereby the secondary user(SU) serves either the queue of its own data or the queue of the primary user(PU) relayed data with certain service probabilities. Moreover, admissioncontrol is introduced at the relay queue, whereby a PU's packet is admitted tothe relay queue with an admission probability. The proposed policy introduces afundamental tradeoff between the delays of the PU and SU. Consequently, itopens room for trading the PU delay for enhanced SU delay and vice versa. Thus,the system could be tuned according to the demands of the intended application.Towards this objective, stability conditions for the queues involved in thesystem are derived. Furthermore, a moment generating function approach isemployed to derive closed-form expressions for the average delay encountered bythe packets of both users. The effect of varying the service and admissionprobabilities on the system's throughput and delay is thoroughly investigated.Results show that cooperation expands the stable throughput region. Moreover,numerical simulation results assert the extreme accuracy of the analyticallyderived delay expressions. In addition, we provide a criterion for the SU basedon which it decides whether cooperation is beneficial to the PU or not.Furthermore, we show the impact of controlling the flow of data at the relayqueue using the admission probability.
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