Date Added: Nov 2012
In the underlay mode of cognitive radio, secondary users can transmit when the primary is transmitting, but under tight interference constraints, which limit the secondary system performance. Antenna Selection (AS)-based multiple antenna techniques, which require less hardware and yet exploit spatial diversity, help improve the secondary system performance. In this paper, the authors develop the optimal transmit AS rule that minimizes the Symbol Error Probability (SEP) of an average interference constrained secondary system that operates in the underlay mode. They show that the optimal rule is a non-linear function of the power gains of the channels from secondary transmit antenna to primary receiver and secondary transmit antenna to secondary receive antenna.