Interference Suppression Techniques In MIMO Cellular Systems

Multiple input multiple output (MIMO) systems using multiple transmit and receive antennas are widely recognized as one of the key technologies for the future wireless communications. However, The cellular MIMO systems become interference-limited because of the existence of co-channel interference (CCI) in cellular environments. This thesis focuses on the research of the interference suppression methods in the cellular MIMO systems. Following issues were discussed:This thesis investigates cellular MIMO systems in-depth, extends the technologies of point-to-point and multiuser MIMO systems into cellular MIMO environment. Some suggestions of system design are also presented for interference suppression. Besides, we also compare and evaluate these methods under the consideration of imperfect conditions in reality systems, and gotten some valuable conclusions for system design.In this paper, a proactive processing algorithm is proposed for interference suppression. The interfering signals caused by a base station (BS) and imposed on neighbor cells are suppressed at this interfering BS through precoding independently. This method will not change the topology of current wireless systems with a lower complexity.Based on the idea of proactive processing, two algorithms are proposed for interference suppression in cellular MIMO systems: One is named proactive zero-forcing, in which the subspaces spanned by interference channels are zero-forced; another algorithm mitigate the CCI based on the cancelation of the Maximum eigenmode of interfering channels, and this method would increase the degrees of freedom for transmission in local cells compared with the previous one.To reduce the link load used for feedback in uplink, we also proposed a limited feedback algorithm for interference suppression in cellular MIMO systems. Codebooks are used at receivers to quantize subspaces spanned by interfering channels, and the quantization information is sent back to interfering base stations, where a proactive precoding is carried out for interference mitigation. Theory analysis and simulation results quantified the effectiveness of this method.