Enhanced Cognitive Relaying for Providing Continuous Connections in Wireless Networks

Typically, when a target user moves from its own network, which is denoted Net1, into another one, which is denoted Net2, its services would be interrupted. In this case, the target user can be viewed as a secondary user (SU), whereas the user of Net2 is a primary user (PU). By taking the advantage of cognitive radios, we propose a two-phase cognitive relaying (TCR) protocol to provide continuous connections for Net1 while guaranteeing the quality-of-service (QoS) of Net2 in wireless networks. The interference cancelation and time optimization techniques are also employed in TCR to further improve the transmission performance of Net1. Under TCR, both the downlink and uplink transmissions of the target user are investigated. We derive the closed-form expressions of outage probabilities for traditional and proposed transmission protocols over Rayleigh fading channels, respectively. Simulation results demonstrate that, with a guaranteed QoS of Net2, TCR transmissions can not only ensure continuous connections for the target user but achieve lower outage probabilities than traditional cases as well. In addition, it is shown that the outage probabilities of TCR transmissions can be minimized by optimizing the transmission time allocation.