Research On Precoding Techenologies For MIMO Wireless Communication Systems

As we all know, multiple input multiple output (MIMO) technology as one of the key technologies can improve the spectral efficiency immensely without increasing system bandwith or transmitting power. However, one of the unavoidable problems in these systems is the co-channel interference among different users and different data streams within the same user.Precoding is just the technology taking full advantage of the channel state information at transimitter to cancel or suppress this co-channel interference. Precoding can improve MIMO systems’performance further and decrease the complexity of the receiver.All in all, precoding technology has already focused worldwide.In this paper, the precoding technology for the single user and multi-user MIMO systems is mainly investigated. The main contents of the paper are as follows:Ⅰ. Do deeply into the related knowledge of MIMO systems. Research on the modeling of single user and multi-user MIMO systems.Ⅱ. Three typical precoding techniques for single user MIMO precoding algorithms, including linear zero-forcing percoding, Tomlinson-Harashima precoding (THP) with Orthogonal Triangular Decomposition (QRD) and Geometric Mean Decomposition (GMD), have been sumed up and simulated with the perfect channel state information at the transmitter and receiver. Moreover, the QRD-THP algorithm has been extended to four kinds of block diagram.Ⅲ. Based on the deep analysis and research on the leakage based precoding algorithm and its improved algorithm, a new successive SLNR precoding algorithm named SLNR-GMD-THP is proposed in the multi-user MIMO broadcast channel (BC) systems. In the proposed algorithm, the signal-to-leakage-plus-noise ratio (SLNR) is also selected as the optimization criterion. Different from the previous algorithms, dirty paper coding (DPC) is applied to cancel the known interferences. Therefore, owing to the neglect of part of the leakages in this algorithm, the value of SLNR per user is increased significantly. In addition, this algorithm succeeds in introducing the GMD-THP algorithm for the SU-MIMO system to the MU-MIMO system. Meanwhile, because of the introduction of GMD, the proposed algorithm avoids the apparence of the worst equivalent sub-channels leading to a better performance of the system. This new algorithm can be seen as a combination of the linear precoding and non-linear precoding algorithms.IV. The paper has done the research on precoding techniques for multi-user MIMO precoding algorithms, such as linear block diagonal algorithm. Most importantly, a near-optimal greedy user ordering for the MIMO broadcast channel model based on the BD-GMD-THP algorithm has been proposed. Theoretical analysis and computer simulations have illustrated its low computation complexity relative to the optimal user ordering with little bit error ratio (BER) lose. Moreover, in order to mitigate the impact of users with smaller sub-channel gains to the whole system’s BER performance, a joint pre-processing scheme design of adaptive data streams reduction and greedy user ordering is proposed. By means of choosing different values for the controlling factor, we can obtain different system sum-rate and BER performance to satisfy different quality-of-service (QoS) requirements.