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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