Spatial–Temporal Queuing Theoretic Modeling of Opportunistic Multihop Wireless Networks With and Without Cooperation

In this paper, we characterize the average end-to-end delay in an opportunistic multihop secondary cognitive radio network overlaid with a primary multihop network. The nodes in both networks use a random medium access control scheme with exponentially distributed backoff. 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 and service times of packets at a secondary node. Then, applying these parameters to an equivalent open single-class 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 to improve their own transmission opportunities. The mathematical results are validated against extensive simulations.