In this paper, we propose a novel protocol for cognitive radio networks, termed spectrum co-access protocol (SCAP), for secondary users to transparently and simultaneously access spectrum with primary users. The motivation is to eliminate the disruption to secondary user communications by the resurgence of primary user transmission. This protocol enables mutually beneficial coexistence between the primary user network and the secondary user network. Through spectrum co-access, SCAP creates a virtual secondary user control channel in licensed spectrum that is invisible to the primary user. As a result, SCAP is a medium access control protocol that allows for simultaneous spectrum access between the secondary user and the primary user networks. The performance evaluation indicates that SCAP provides significant performance improvement for the secondary user network over the existing opportunistic spectrum access scheme.
Backens, J., Xin, C., & Song, M. (2015). A novel protocol for transparent and simultaneous spectrum access between the secondary user and the primary user in cognitive radio networks. Computer Communications, 69, 98–106. https://doi.org/10.1016/j.comcom.2015.07.004