Research On Mimo Techniques In Cooperative Communications Systems

In cellular mobile communication systems, the fundamental system design problem is to cope with channel fading and interference which is inherent in wireless propagation channels, and enhance the transmision effectiveness and reliability under time, frequency and power constraints.MIMO (Multiple Input Multiple Output) and cooperative communications techniques have attracted much research interest in the past few years. They serve as the key technologies at physical layer, which can provide resistance to fading and interference and fulfill the rapid increasing demands of the broadband wireless communications. In MIMO system, spatial dimension is introduced by the multiple-antenna configuration at both the transmitter and the receiver, which can increase the system throughput as well as the BER (Bit Error Rate) performance.The fundamental principle of cooperative transmission is that a new signal processing dimension can be introduced via cooperation, which can help to alleviate the impact of fading and inter-cell interference in wireless channels. In cooperative transmission, diversity gain can be obtained via the cooperation between the base stations, the mobile stations or between base stations and low power relay nodes. When multiple antenna techniques are employed in cooperative communications, the signal processing becomes more complicated. This paper focuses on the research on the MIMO techniques in cooperative communications systems, especially in the relay cooperative communications systems and the multi-cell coopeation system.In the first chapter, we introduce the basic technologies of MIMO, review some tradional multi-user MIMO precoding algorithms, and describe the concepet of cooperative communication. They serve as the basis of the research in the remainder of this dissertation.In Chapter2, we devise a robust linear precoding design algorithm at the relay node in two way relay systems with independent source-relay and relay-source channels. Both single strean transmission and multi-stream transmission are considered. Due to delayed and finite-rate feedback, only outdated and quantized channel direction information (CDI) of the downlink channel is available at the transmitter of the relay during the broadcast (BC) phase. To tackle the performance degradation caused by the joint effects of channel quantization error and feedback delay, we propose a robust precoding scheme based on minimizing the expected weighted sum mean squared error (WS-MSE) conditioned on the induced channel uncertainties subject to relay power constraints. Numerical results validate the robustness of the proposed scheme.In this paper, multi-cell cooperation is classified into two categories, namely the "multi-cell joint transmission" related to Chapter3and4, and "multi-cell coordinated transmission" corresponding to Chapter5.To improve the performance of the cell edge users, we propose a transmission solution named "multi-cell collaborative transmission incorporating closed-loop and open-loop techniques" in Chapter3. The proposed transmission structure takes advantage of the cooperation between base stations, and combines both closed-loop and open-loop techniques. With the concept of Closed-loop and Open-loop Effective Channel (COEC), the classic Space Frequency Block Coding (SFBC) decoding scheme can be extended to the multi-cell scenario. Analysis and simulation results show that the proposed scheme can obtain comparable performance with traditional multi-cell joint transmission schemes in terms of sum rates while reducing the feedback overhead remarkably.In the multi-cell joint transmission scenario, we also propose a multi-cell multi-user MIMO precoding algorithm in Chapter4. This method takes into account the characieristics of the multi-cell scenario and takes advantage of effective noise variance based channel extension method and LQ decomposition. It can achieve good balance among pathloss, intra-cell and inter-cell multiuser interference as well as noise, and obtains a good tradeoff between the complexity and sum rates.In Chapter5we study the coordinated signal processing in interfering broadcast channel which is belong to "multi-cell coordinated transmission", and propose a precoding algorithm based on intra-cell and inter-cell signal leakage and Minimum Mean Square Error (MMSE) criterion. The introduced algorithm can obtain the closed-form solution of the precoding matrics, and hence reduces the processing complexity.The researches above are mainly transmitting processing methods. Chapter6introduces the hardware implementation of high-dimension MIMO detection algorithm in the system receivers. Detailed algorithm design, timing design as well as the hardware implementation methods are presented. We also introduce the necessary modifications and improvement for the MIMO detection module when the system spectral efficiency increases from15bps/Hz to30bps/Hz. It is worth noting that the introduced hardware implementation can be applied to both single-cell scenario and the cooperative communications systems.