Improved spectrum access control of cognitive radios based on primary ARQ signals

Cognitive radio systems capable of opportunistic spectrum access represent a new paradigm for improving the efficiency of current spectrum utilisation. In this work, the authors present a novel cognitive channel access method based on learning from both primary channel transmissions and the receiver ARQ feedback signals. This new sensing-plus-confirmation scheme constitutes a non-trivial generalisation of the more traditional `Listen-Before-Talk` (LBT) strategy that merely listens to and yields to primary transmissions regardless of primary receiver (PRx) responses. Our new method exploits the bi-directional and interactive nature of most wireless communication links to facilitate better opportunistic secondary access while achieving PRx protection. By allowing the secondary users to learn from both primary transmissions and the corresponding receiver confirmations, our approach allows secondary cognitive users to exploit critical information that PRxs regularly send to their transmitters. The authors show that, by monitoring both primary transmissions and receiver feedback signals, secondary radio access can improve throughput over the traditional LBT while limiting the probability of collision with primary user signals.