Interference alignment in multi-user MIMO systems

As a promising technique to obtain optimal degree of freedom (DoF) on multi-user wireless communication systems, interference alignment (IA) has been studied extensively in recent years. The most effective approach of IA is to deploy optima linear transceiver by exploiting spatial characteristics of wireless channels, and it is evaluated in measured multi-input multi-output (MIMO) interference channels. The number of alignment constraints and channel diversity are two main issues faced by IA. Moreover, imperfect, noisy, localized and possibly delayed nature of channel knowledge feedback to the transmitters remains also as the urgent problem to be solved. These challenges have excited ingenious solutions in the implementation of IA schemes. In this work, we present a review of existing techniques for IA in typical multi-user MIMO systems, and on this basis, consider some future research issues related to implement. The study covers IA´s feasibility conditions, solution algorithms in MIMO interference channel and MIMO multi-cell networks, with an emphasize on the CSI feedback technology which remains as the major challenge of IA.