Opportunistic cognitive relay with 1-bit feedback

In this paper, we propose a limited feedback based underlay spectrum sharing scheme where a secondary decode-and-forward opportunistic relay network shares the spectrum with a pair of primary users. The primary destination and each of the N secondary relays send 1-bit feedback of channel quality information to their corresponding transmitters. By overhearing the primary feedback and receiving the secondary feedback, one of the secondary relays is scheduled at the secondary transmitter in each fading block. By maximizing the average secondary rate under the average primary rate loss constraint and average secondary power constraint, the asymptotically optimal solutions of secondary thresholds and power allocation are derived analytically for large N. With the increase of the number of secondary relays, the average achievable rate of secondary user grows as 1/2 log log N.