Research On Interference Mitigation Schemes Of Multiple Antennas Systems

With the rapid development of the mobile internet and explosive growth of multimedia applications, mobile users put forward a higher demand for system performance. Multiple antennas technology can dramatically improve rate and spectrum efficiency without increasing the power and bandwidth, it’s the key technology for future wireless communication systems. Spectrum resources are still scarce in future systems. In order to maximize the use of scarce spectrum resources, wireless communication system tends to share the same frequency or to use higher spectrum reuse factor. The frequency reuse results serious interference, which makes wireless communication system to be an interference-limited system. Interference has become a key bottleneck to improve the network performance. How to cancel interference and improve the spectrum efficiency has become a challenging and hotspot topic in the academic research. This paper studies interference mitigation of multi-antennas communication system. Many factors cause the interference in the system, which are deeply analyzed and researched. The main contributions and innovative of the dissertation are listed as follows:1. In order to cancel the interference of multiusers MIMO interfering broadcast channels with limited feedback, An iterative optimized precoder design scheme is proposed by minimizing the expected mean square error (MMSE). Using tools from random matrix theory, some statistical characteristics of quantization error for channel state information are obtained. The system performance improvement and interference due to quantization errors are considered. The objective function is minimizing the expected mean square error. The proposed scheme is robust to the channel uncertainties caused by quantization error. Simulation shows the scheme effectively enhanced the system sum-rate and improved the system reliability, compared with coordinated zero forcing scheme.2. Aiming to CSI quantization problem in coordinated Multi-point Transmission (CoMP) system, an adaptive bit allocation algorithm is proposed. We analyze the sum-rate influence due to CSI quantization error for CoMP system. We make full use of the large-scale fading non-uniform characteristics caused by user locations difference. The sum-rate loss minimization is objection function. The analytic solution of bit allocation is derived by arithmetic geometric mean inequality theory. Simulation verifies proposed algorithm is able to achieve better performance comparing to that equal bit allocation, under condition that the sum bit number is limited.3. It’s necessary to share CSI in interference alignment of time-varying MIMO interference channel. It’s unpractical to get perfect CSI in practical communication system due to quantization error and feedback delay. In this paper, quantization error and feedback delay are researched and a channel quantization and feedback mechanism is proposed. Time-varying MIMO channel is modeled by Markov modeling theory. Using tools from random matrix theory, the loss upper bound of system rate and degree of freedom are analyzed due to quantization error and channel time-varying character. This upper bound provides beneficial reference for effective practice of interference alignment in time-varying MIMO interference channel. From the simulation we can see that the rate will increase with reducing the CSI delay or increasing the number of feedback bits within limits, however, when CSI delay is larger, it is little significance to improve the rate performance by increasing the number of feedback bits.4. Aiming to applying interference alignment problem in practical MIMO interference networks, an optimal transmitter deployment scheme is proposed. The transmitter deployment in large dense MIMO interference networks is abstracted particle distribution in Poisson field. The location of transmitter is modeled a spatial homogeneous Poisson point process (PPP). Based on this, some statistical characteristics of CSI quantization are obtained, and the approximate analytical expressions of outage probability and network throughput are derived, which provides a theoretical basis for transmitter deployment in large dense interference networks. Simulation results verify that these analytical results provide effective technical guidance for interference alignment implementation in real MIMO interference networks. These results have important theoretical and practical value.5. In order to mitigate the interference in large cellular and Device-to-Device (D2D) heterogeneous network, an mixed interference management mechanism is proposed. In order to access accurately the performance of interference management, the large heterogeneous network is modeled with stochastic geometry theory. Two strategies including beamforming and interference cancellation are proposed, depending on different transmission mode between cellular and D2D communication. Beamforming strategy can ensure the cellular communication reliability, and interference cancellation strategy can ensure that the cellular has lower interference to D2D. We derive analytical success probability and rate expression in these strategies. Based on this, we analyzes the relaxation effect which cellular base station remaining degrees of freedom make D2D interference constraint. In order to further maximize the total Area Spectral Efficiency (ASE), we propose an optimal allocation scheme by setting the interference cancellation radius. Simulation results show that the mixed interference management mechanism can improve the performance of large cellular and D2D heterogeneous network.