Research On The Interference Elimination Technology In Multi-user Mimo Relaying Systems

Along with the rapid increase in number of mobile users, the growing demand for high-speed wireless data service as well as the increasing requirements for the quality of service, the future wireless communication systems are in urgent need of solving the problem of high rate transmission in the multi-user system, as well as improving the communication quality of users at. the edge of cell. Multiple Input multiple Output (MIMO) technology can serve multiple users at the same time and provide multiplexing gain by introducing an additional spatial dimension; Relay communication technology can improve the coverage of the base station and provide some cooperative diversity gain through the collaborative transmission with base station. Applying MIMO technology and relay technology to multi-user systems can make use of their advantages, but the resulting interference problem will cause serious effect on system performance. In this dissertation, we mainly focus on the MIMO technology and relay technology applied in multi-user systems. From the perspective of improving the system performance and reducing the system complexity, transmission schemes and interference elimination technology are analyzed according to the characteristics of different communication scenarios. The main work of this dissertation are described as follows:1) Transmission schemes and interference elimination technology in multi-user relay systems are studied and an adaptive relay transmission scheme based on interference cancellation is proposed. Firstly, in order to improve the spectrum efficiency of the system, a scheme to reuse same time-frequency resource during the process of communication are proposed; Secondly, in order to reduce the effect of the co-channel interference during the process of communication, decoding schemes based on interference cancellation are proposed for the Amplify-and-Forward (AF) and Decode-and-Forward (DF) relay, respectively; Thirdly, to obtain both advantages of AF relay and DF relay, an adaptive relay transmission scheme is proposed to further improve the system performance; Finally, the outage probabilities of the above-mentioned schemes are analyzed and the closed form solutions are derived. The simulation results show that, the theoretically derived outage probabilities coincide with the numerical simulation results, which proves their validity; Compared with the traditional relay transmission scheme which needs three time slots, the proposed relay transmission schemes based on the reuse of time-frequency resources and decoding with interference cancellation, can improve the system spectrum efficiency effectively; Compared with the simple AF or DF relay transmission scheme, the proposed adaptive relay transmission scheme can obtain the advantages of both, and further improve the system throughput performance.2) Interference elimination technology in multi-user MIMO broadcasting systems is studied and low-complexity transceiver design as well as the corresponding power allocation algorithm are proposed. Firstly, a traditional block-diagonalization-based precoding scheme to eliminate the multi-user interference is introduced; Secondly, based on the traditional scheme, a low-compelxity transceiver design is proposed, which employs channel inversion and QR decompositions to obtain the precoding matrices at the transmitter, and by utilizing the specific structure of the effective channel matrix after precoding, a simple successive interference cancellation decoding process can be implemented at the receivers to eliminate the interference between antennas; Finally, in order to reduce the effect of error propagation during the decoding process with successive interference cancellation, a power allocation algorithm to minimize the system bit error rate (BER) is proposed. The simulation results show that, compared with the traditional scheme, the proposed transceiver design scheme can provide the same sum-rate performance and better BER performance, while demanding less computation complexity; The proposed power allocation algorithm can further improve the BER performance with slight sum-rate loss at high SNR regime.3) Interference elimination technology in multi-user MIMO relay broadcasting systems is studied and low-complexity pre-processing schemes at relay as well as the corresponding power allocation algorithm are proposed. Firstly, based on the traditional block diagonalization pre-processing scheme at relay, an equivalent low-complexity pre-processing scheme is proposed to eliminate the multi-user interference; Secondly, to maximize the system sum-rate, a corresponding power allocation algorithm is proposed to improve the sum-rate performance; Finally, based on the Minimum Mean Square Error criterion, an enhanced pre-processing scheme is proposed and the corresponding iterative power allocation algorithm is designed to further improve the sum-rate performance. The simulation results show that, the proposed low-complexity pre-processing scheme at relay can eliminate the multi-user interference effectively and demands lower computational complexity compared with the traditional scheme; By make a trade-off between the interference elimination and noise enhancement, the enhanced pre-processing scheme can provide better sum-rate performance; The corresponding power allocation algorithms can further improve the sum-rate performance as well.4) High spectrum efficiency transmission schemes and interference elimination technology in multi-user MIMO relay broadcasting systems are studied and an interference elimination scheme based on the joint relay processing design is proposed. Firstly, to improve the system spectrum efficiency, a transmission scheme based on two path successive relaying (TPSR) is proposed and the interference during the communication process is analyzed; Secondly, a joint relay processing design is proposed to eliminate the inter relay interference; Finally, the residual multi-user interference can be eliminated by the above-mentioned pre-processing scheme in (3). The simulation results show that, after the inter relay interference and the multi-user interference being eliminated by the proposed pre-processing scheme at relays, the TPSR-based multi-user MIMO relay broadcasting systems can reduce the spectrum efficiency loss caused by the half duplex relay effectively and approach the sum-rate performance of ideal full duplex relay sytem.