Performance analysis of multiple-input multiple-output interference alignment with user selection

The performance analysis of the multiple-input multiple-output interference alignment (IA) with user selection in small-cell interference channels is investigated. In this system, the authors consider the user selection using spatially independent scheduling in which a transmitter sends the data stream of the selected user providing the maximum effective signal-to-noise ratio (SNR). As the first step, this study derives exact and approximate probability density functions of the effective SNR of the proposed IA with user selection. Next, exact closed-form expressions of the bit-error rate (BER) for the M-ary quadrature amplitude modulation, M-ary phase shift keying modulation and outage probability are presented. Using asymptotic analysis, the BER and outage probability of the proposed IA system with user selection are approximated, and the diversity order and SNR gain are quantified, respectively. Also, the authors derive tight closed-form expression of the proposed system for ergodic capacity using the Taylor series expansion of logarithm function. The analytical results show that diversity order of the IA system with user selection is superior to that of the conventional iterative algorithms. Also, the ergodic capacity of the proposed system is superior to that of the conventional iterative algorithms at high SNR. This performance gain comes from multi-user diversity. The analytical results are verified through simulation results.