TSRA: An Adaptive Mechanism for Switching between Communication Modes in Full-Duplex Opportunistic Spectrum Access Systems

Full-duplex (FD) communications and self-interference suppression (SIS) techniques can be exploited in opportunistic spectrum access (OSA) systems for simultaneous transmission-sensing (TS) or simultaneous transmission-reception (TR). Motivated by the competing goals of primary user (PU) protection (in the TS mode) and secondary user (SU) performance (in the TR mode), we present an optimal adaptive switching strategy and an associated communication protocol for FD OSA systems. Specifically, we optimize the spectrum-awareness/efficiency tradeoff by allowing the SU link to adaptively switch between various modes, depending on the forecasted PU dynamics. The proposed three-stage adaptive mode-selection strategy maximizes an SU utility function subject to a constraint on the PU collision probability. We also propose a protocol that executes the switching mechanism in a distributed fashion. In practice, SIS is imperfect, resulting in residual self-interference that degrades the sensing performance in the TS mode. Accordingly, we study different spectrum sensing techniques in the TS mode, while illustrating their accuracy-complexity tradeoff. We evaluate the performance of the proposed switching scheme against the listen-before-talk (LBT) scheme using numerical results, simulations, and hardware USRP experiments.