Imperfect CSI impact on sum-rate performance of IA: A comprehensive analysis

Imperfect channel state information (CSI) always hinders the practical implementation of interference alignment (IA) in current mobile communication systems, where channel estimation error, delay and frequency offset are major factors that cause the unmatched CSI with unignorable error. In this paper, we quantitatively analyze the imperfect CSI impact on the sum-rate performance of IA system, in multiple-input multiple-output (MIMO) cellular networks. Based on the 3GPP spatial channel model (SCM), we obtain the relationships between the sum-rate loss and all factors that cause the imperfect CSI, and show which one incurs the more serious sum-rate loss. Furthermore, applying Cochran's theorem, the accurate closed-form expression of ergodic sum-rate under imperfect CSI is first derived. Our results will shed some significant lights on the IA design under practical scenarios.