Impact of antenna selection on cognitive radio system capacity

We examine the effect of transmit antenna selection on the secondary user (SU) and primary user (PU) capacity in a multiple-input single-output cognitive radio system. We consider antenna selection with the aim of improving SU and PU capacity and mitigating the effects of incomplete channel knowledge by the SU. Under a minimum PU signal-to-interference-and-noise ratio constraint, analytical and semi-analytical expressions for the permissible SU transmit power are derived, which are used in obtaining capacity cumulative distribution functions by means of simulations. We show that PU antenna selection is effective at reducing the SU blocking probability, the probability that it cannot transmit, while SU antenna selection leads to significant gains in its capacity. Antenna selection at the SU is also shown to effectively compensate for incomplete channel knowledge and can be used to achieve moderate improvements in PU capacity.