Research On Interference Alignment In Multi-Cell Systems

Due to the lack of frequency spectrum, as well as the need for higher data rate, multi-antenna technology and frequency reuse factor one will be widely used in the next generation cellular systems. In such scenarios, co-channel interference is unavoidable in multi-cell multi-antenna systems, which might impact the high spectrum efficiency derived from multi-antenna technology severely. Consequently, research on interference channels and interference management in multi-cell multi-antenna system has attracted more and more attention.Coordinate multi point (CoMP) transmission could significantly reduce the multi-cell interference, especially for the cell edge users, by coordinated processing at the base stations. Hence, it could improve the system throughput observably. As a realization of CoMP, interference alignment (IA) could achieve the optimal transmission degree of freedom (DOF) in multi-cell multi-antenna systems. In this dissertation, we mainly focus on the IA optimization with perfect channel state information (CSI) and the IA performance with delayed channel state information at the transmitter (CSIT).This paper firstly analyzes the multi-cell multi-antenna interference channels. The classical IA method only considers the interference from the other cells, while ignoring the channel quality of the desired signal, which could result in the desired signal quality reduction at the receiver. Because of the fact described above, we propose an optimized IA precoding method based on eigen-channel for multi-cell multi-antenna systems. As considering the interference from other cells, the proposed scheme pays attention to the channel quality of the desired signal in order to improve the desired signal quality at the receiver. What s more, the insufficiency scatters at the base station or the antenna size restriction at the receiver could lead to the space correlation of the multi-input multi-output (MIMO) wireless channel. The performance of the classical IA method will degrade severely in that environment. However, the proposed method could relieve the impact of the MIMO space correlated channel, and it could provide more obvious improvement comparing to the classical method.In this paper, a further analysis for the IA performance with delayed CSIT is introduced. The signal processing and propagation will bring delay into the system. The delay results in the fact that the signal at the base station could not be aligned perfectly, and then the receiver could not remove the multi-cell interference completely. This article analyzes the impact of delay on interference alignment, and provides the restriction of the delay for achieving the optimal transmission DOF. The analysis results might be useful for the design of the systems to some extent.