Interference Alignment Algorithm For MIMO Uplink Multi-cell Networks

In the field of wireless communications, multiple input multiple output(MIMO) can greatly improve the capacity of system without increasing bandwidth. But the intra-user interference(IUI) and inter-cell interference(ICI) degrade the performance of the system significantly. Therefore, interference management has become an urgent problem to be solved.Firstly, the basic principle and core idea of interference alignment(IA) are studied, and the degree of freedom is used to measure the capacity of system. According to analyze three kinds of interference alignment algorithms in the uplink networks, the advantages and disadvantages of each scheme are pointed out.Secondly, a scheme of interference alignment and interference cancellation that can be applied to Gauss interference multiple access channel is analyzed in details, and the feasibility of this scheme is verified by theoretical deduction. In this algorithm, interference alignment is achieved by the method of graph theory, interference cancellation is achieved by using the backhaul link between base stations(BS). This algorithm can only be applied to the scenario which the association between base stations and users are fixed, and the optimal degree of freedom is not obtained.In view of the shortcomings of the existing schemes, a new algorithm that joint base station association and interference alignment and cancellation is proposed in this paper. This algorithm can be suitable for the scenario which the association between base stations and users are unfixed for multi-cell MIMO uplink networks. In this algorithm, the mathematical model of the association between the base stations and the users is carried out, and the mathematical model is transformed into sub-problems which solved by mixed integer linear programming. Three theorems are presented in the process of discussing the feasibility of the sub-problems, with the optimal association between base stations and users,we obtain the maximized degree of freedom. In this scenario, two methods were used to eliminate the inter-cell interference: the first one is to use the backhaul link in the system model and implement the interference cancellation through base stations cooperation, the second is to design the precoding and decoding matrixs to implement interference alignment.Finally, in different system configurations, the proposed algorithm in this paper is simulated and analyzed. The performance of the proposed algorithm is verified by the simulation results, it can obtain a greater degree of freedom.