Research On Interference Mitigation Schemes Of MIMO Systems

With the rapid development of multimedia service and broadband internet, more and more wireless users require high quality mobile data services.1Due to the limitation of spectrum resources, the interference becomes an important problem in wireless communication system. In order to improve the effectiveness and reliability of wireless communication system, the research on the cellular/multiuser MIMO system is a recent research hotspot in wireless communication.The dissertation does research on interference cancellations for several scenarios in wireless communication Multiple Input Multiple Output (MIMO) systems, and proposes interference cancellation schemes, which improve the capacity and Bit Error Rate (BER) performances. The main contributions and innovative research finds are listed as follows:(1) In order to improve the effectiveness and reliability of wireless communication in cellular MIMO systems and multiuser MIMO interference systems, the space time diversity technoglogy for interference alignment are investigated, and the space-time diversity schemes for interference alignment in uplink cellular systems and multiuser MIMO interference channels are proposed. Based on corresponding scenarios, the proposed schemes adopt different interference alignment methods in each time slot, thus the channel for each user is transformed to a time-varying equivalent channel and the space diversity is transformed to time diversity. The time diversity gains in time-varying equivalent channels are achieved by special space-time processing technology. Theoretical analysis and simulation results show that, compared with existing scheme, the proposed scheme can significantly improve BER performance without reducing degrees of freedom (DOF).(2) In order to improve the capacity of hierarchical interference alignment scheme for MIMO heterogeneous networks in low Signal Noise Ratio (SNR) region, a regularized interference alignment scheme using weighed minimum mean square error (W-MMSE) is proposed in this dissertation. In the proposed scheme, the equivalent channel matrices in hierarchical interference alignment scheme are used as weighed matrices, precoding and post-processing matrices are iteratively optimized, hence the interferences are eliminated and power allocation is optimized. Theoretical analysis and simulation results show that, the proposed scheme has fast convergence, and improves the capacity in whole SNR region.(3) In order to further improve the effectiveness and reliability of multi-cell MIMO downlink system, the nonlinear interference alignment is investigated in this dissertation, and an interference alignment scheme for multi-cell multiuser system through Tomlinson-Harashima precoding (THP) is proposed in this dissertation. The design criterion of the proposed scheme is derived, the appropriate feedback triangular matrices, feedforward matrices and receiving matrices are designed to align the interferences, hence each cell’s capacity and BER performance are effectively improved. Theoretical analysis and simulations demonstrate that the proposed scheme can obtain more capacity and lower BER compared with existing scheme.(4) Interference alignment can effectively enhance the DOF of MIMO X relay, however, complete interference alignment requires each user to be equipped with many antennas. In this dissertation, a partial interference alignment transmission scheme is proposed to improve the capacity of MIMO X relay for the case with fewer user antennas. The feasibility condition of partial interference alignment in MIMO X relay is induced, and an iterative algorithm is given to realize partial interference alignment. The proposed scheme can be fit for various antenna configurations of users and relay, and enhance DOF. Simulation results prove the effectiveness of the proposed scheme. (5) In order to improve the capacity of MIMO multi-way relaying system, this dissertation studies the parallel transmission in multi-way relaying, and proposes a parallel asymmetric transmission scheme for multi-way relaying. The proposed scheme develops a new multi-way relaying transmission model, transmits and receives multiple data streams in parallel and asymmetrically by using multiple antennas, designs corresponding precoding matrix and zero forcing matrices to eliminate interference, hence realizes asymmetric transmission in two time slots on condition that no increase in the number of relay antennas. The system capacity expression is derived in this dissertation. Theoretical analysis and simulation results show that the proposed scheme reduces the energy consumption, effectively improves the capacity of multi-way relaying system, and further reduces the requirement for relay antennas if multi-group users are served.