Transmit Antenna Selection for Interference-Outage Constrained Underlay CR

Transmit antenna selection (TAS) is a technique that achieves better performance than a single antenna system while using the same number of radio frequency chains. We propose a novel TAS rule called the lambda-weighted interference indicator rule (LWIIR). We prove that for the general class of fading models with continuous cumulative distribution functions, LWIIR achieves the lowest average symbol error probability (SEP) among all TAS rules for an underlay cognitive radio system that employs binary power control and is subject to the interference-outage constraint. This constraint imposes a limit on the probability that the interference power at the primary exceeds a threshold. It is a generalization of the widely studied peak interference constraint. We then derive the average SEP of LWIIR. The insightful performance analysis applies to any number of transmit and receive antennas and to many constellations. We also analyze the practical scenario in which the secondary transmitter has imperfect information of the channel gains from itself to the secondary and primary receivers. We show that the imperfections in these two sets of channel gains have different impacts on the system. Our benchmarking shows that LWIIR outperforms many selection rules considered in the literature.