  In this paper, we give a unified performance analysis of interference
alignment (IA) over MIMO interference channels. Rather than the asymptotic
characterization, i.e. degree of freedom (DOF) at high signal-to-noise ratio
(SNR), we focus on the other practical performance metrics, namely outage
probability, ergodic rate and symbol error rate (SER). In particular, we
consider imperfect IA due to the fact that the transmitters usually have only
imperfect channel state information (CSI) in practical scenario. By
characterizing the impact of imperfect CSI, we derive the exact closed-form
expressions of outage probability, ergodic rate and SER in terms of CSI
accuracy, transmit SNR, channel condition, number of antennas, and the number
of data streams of each communication pair. Furthermore, we obtain some
important guidelines for performance optimization of IA under imperfect CSI by
minimizing the performance loss over IA with perfect CSI. Finally, our
theoretical claims are validated by simulation results.
