BER minimization for cognitive radio systems with difference antenna selection

In this paper, we analyze the bit-error rate (BER) of the secondary transmission in a wireless cognitive radio (CR) system with difference antenna selection, whereby a single transmit antenna is selected at the secondary transmitter out of M possible antennas such that the weighted difference between the channel gains of the data link and the interference link is maximized. We propose a method of minimizing the BER of the secondary data link subject to constraints on the average secondary transmit power and the average interference power as seen by the primary receiver. Minimization is performed over two parameters: the average secondary transmit power and the difference selection weight δ ∊ [0,1]. Furthermore, we show that, interestingly, the diversity gain of the secondary link is an impulsive function of δ, in that full diversity is achieved when δ = 1 and no diversity is achieved otherwise. We discuss the implications of this finding on practical system design, and address the effects that the constraints have on the BER.