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In this paper, we characterize the average end-toend delay in an opportunistic multi-hop secondary cognitive radio network overlaid with a primary multi-hop network. Nodes in both networks use random medium access control (MAC) scheme with exponentially distributed back-off. We first model the network as a two-class priority queuing network and use queuing-theoretic approximation techniques to obtain a set of relations involving the mean and second moments of the interarrival time and service time of packets at a secondary node. Then, applying these parameters to an equivalent open singleclass G/G/1-queuing network, we obtain expressions for the average end-to-end delay of a packet in the secondary network using a diffusion approximation. Next we extend the analysis to a case where secondary nodes cooperatively relay primary packets so as to improve their own transmission opportunities. The mathematical results are validated against extensive simulations.

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This paper considers cooperation between primary and secondary users in shared spectrum radio networks via caching. A network consisting of a single macro (primary) base-station and multiple small (secondary) base-stations is considered. Secondary basestations can cache some primary files and thereby satisfy content requests generated from nearby primary users. For this cooperative scenario, we develop two caching and scheduling policies under which the set of primary and secondary user request generation rates that can be supported increases from the case without cooperation. The first of these algorithms provides maximum gain in the set of supportable primary and secondary request generation rates. However under this algorithm primary packet transmissions from secondary base-stations do not have higher priority than that of secondary packets. As a result, we propose another sub-optimal (with respect to set of supportable request generation rate vectors) algorithm wherein primary packet transmissions from secondary base-stations have higher priority than that of secondary packets. Extensive simulations are conducted to compare the performance of both algorithms with that of a noncooperative algorithm that is optimal, with respect to set of supportable request generation rates, among all noncooperative policies.

In this paper, we characterize the average end-toend delay and maximum achievable per-node throughput in an opportunistic secondary cognitive radio network co-existing with a primary network where both networks consist of static nodes that use random medium access schemes. Assuming an ideal sensing mechanism, we first model the secondary network as a two-class priority queuing network and use queuing approximation techniques to obtain a set of relations involving the mean and second moments of the inter-arrival time and service-time of packets at a secondary node. Then, utilizing these parameters in an equivalent open G/G/1 queuing network, we obtain closed form expressions for average end-to-end delay of a packet in the secondary network and the maximum achievable throughput of a secondary node. The results are validated against extensive simulations.