Channel Sensing-Order Setting in Cognitive Radio Networks: A Two-User Case

This paper investigates the sensing-order problem in two-user multichannel cognitive medium access control. When adaptive modulation is not adopted, although brute-force search can be used to find the optimal sensing-order setting of the two users, it has huge computational complexity. Accordingly, we propose two suboptimal algorithms, namely, the greedy search algorithm and the incremental algorithm, which have comparable performance with that of brute-force search and have much less computational complexity. It is shown that, with a high probability, either suboptimal algorithm can reach an optimal point if a backoff mechanism is used for contention resolution. When adaptive modulation is adopted, it is observed that the traditional stopping rule does not lead to an optimal point in the two-user case. Furthermore, we demonstrate that the adoption of adaptive modulation affects the optimal sensing-order setting of the two users, compared with the case without adaptive modulation. These findings imply that the stopping rule and the sensing-order setting should be jointly designed from a systematic point of view.