A Cooperative Spectrum Sharing Protocol Using STBC-SM at Secondary User

In this paper, a new cooperative spectrum sharing protocol that employs space-time block coded spatial modulation (STBC-SM) at the secondary user (SU), is proposed for overlay cognitive radio (CR) networks. STBC-SM is applied at the secondary transmitter (ST) which transmits its data by both modulated symbols and antenna combinations while conveying PU's data only by modulated symbols. This protocol avoids interference at both PR and SR. Upper bounds on the bit error probabilities (BEP) of PU and SU are analytically derived for Rayleigh fading channels and supported via computer simulations. Theoretical and simulation results show that the proposed protocol significantly improves SU's BEP performance compared to the reference scheme which causes severe interference at both users by using superposition coding at ST and the noncooperation case.