Cross-Layered Design of Spectrum Sensing and MAC for Opportunistic Spectrum Access

In cognitive radio networks, the secondary users (SUs) are allowed to use the spectrum originally allocated to primary users (PUs) as long as the PUs are not using it temporarily. This operation is called opportunistic spectrum access (OSA), and it is assisted through spectrum sensing. In distributed OSA, the SUs sense the channel independently; once the channel is available, they contend for channel access on a frame-by-frame basis. In this paper, we study the random medium access control (MAC) in conjunction with the sensing protocol design. In particular, we are interested in the design of frame duration, sensing time and MAC random access to maximize the secondary network throughput performance while protecting the PUs from the interference of secondary users´ operations. We formulate the nonlinear constrained optimization problems for the described system model with cross-layered and layered approaches. Simulations show that the cross-layered approach performs much better than layered approach especially when the frame duration is small.