Research On Lattice Reduction Based Low-complexity Precoding Technique For Multi-user MIMO Systems

Multiple-Input Multiple-Output(MIMO) technology relies on multiple antennas to simultaneously transmit multiple streams of data in wireless communication system. It can greatly improve the spectrum efficiency of the system without additional bandwidth and power. As an extension of the traditional single-user MIMO technology, multi-user MIMO technology can serve multiple users at the same time-frequency resource, which not only improves the spectrum efficiency of the system, but also greatly increases the capacity of the system. Thus, multi-user MIMO technology has received widespread attention. However, due to the reason that the users can’t cooperate mutually, the traditional detection algorithm can’t eliminate the Multi-User Interference(MUI). In this case, the precoding techniques are used at the transmiter to eliminate the interferences. With the number of antennas equipped at the transmitter and the receiver increasing in the wireless communication system, the computational complexity of precoding algorithm has become the focus of current researches, and designing efficient and low-complexity multi-user MIMO precoding algorithm is the development direction of future precoding technology.In recent years, the Lattice Reduction(LR) technology has been widely applied in the field of wireless communication, especially in the MIMO system. The Lattice Reduction based precoding algorithm is highly concerned by many researches. In the SU-MIMO system, the Lattice Reduction based linear precoding algorithms can significantly enhance the performance of traditional linear precoding algorithms. In the multi-user MIMO system, the low-complexity precoding algorithm combined with Lattice Reduction technology has become the focus of current researches.At first, this paper makes a deep study on the Lattice Reduction technology. The Lattice Reduction based detection algorithm and precoding algorithm are researched in the single-user MIMO system. Then the traditional multi-user MIMO precoding algorithms are briefly analyzed. At last, the deep research is made around the Lattice Reduction based precoding algorithm in the multi-user MIMO system. The main research contents and creative achievements in this paper are summarized as follows:(1) In the study of Lattice Reduction technology, the LLL Lattice Reduction algorithm and the CLLL Lattice Reduction algorithm in complex domain are analyzed deeply. Then, this paper proposes a modified CLLL Lattice Reduction algorithm on the basis of CLLL Lattice Reduction algorithm, the proposed modified CLLL Lattice Reduction algorithm can generate not only the reduced basis matrix and unimodular matrix, but also the inverse matrix of the unimodular matrix at the same time, which can reduce the computational complexity of matrix inversion.(2) This paper focuses on the research of Lattice Reduction based low-complexity precoding algorithm in the multi-user MIMO system. A simplified QR decomposition and Lattice Reduction based low-complexity BD precoding algorithm is proposed, not only reducing the complexity of traditional BD precoding algorithm, but also improving the performance of the system significantly.