Research On The Coordinated Multiple Point Transmission Technology In The Downlink MU-MIMO System

The downlink co-channel interference is an important factor in the mobile communication system to improve system throughput, especially for the LTE system with the frequency reuse factor set as1. Co-channel Interference that users suffer from in the LTE system mainly comes from three aspects, namely intra-cell interference between users, the interference between different data streams in the same user, as well as inter-cell interference. For intra-cell interference, some scholars have proposed a variety of pre-coding schemes. For example, BD (Block Diagonalization) linear precoding solution completely eliminates the intra-cell interference between users and the interference between different data streams in the same user. But in the multi-cell system, the BD precoding scheme can’t suppress the inter-cell interference. The cell-edge users suffer from the dramatically decrease of spectrum efficiency because of co-channel interference. In order to solve the problem,3GPP standards organization launched the LTE-Advanced project in March2008. CoMP (Coordinated Multiple Point transmission and reception) is one of the key technologies of LTE-A, which can effectively improve the spectral efficiency performance of system, especially for the spectrum efficiency performance of cell-edge users. This paper pays more attention to CS/CB in urban environment with dense tall buildings and the research work is based on BD-MIL (BD based on Minimum Interference Leakage), which was put forward by the previous scholars. The main research work of this paper is as follows:1, the simulation assessment scheme based on3D-MIM0equivalent system is proposed to deal with the problem that the simulation results are inaccurate in the complex propagation environment if transmission of electromagnetic waves is only assumed in the horizontal plane. Firstly, the paper analyzes the application scenarios of BD-MIL algorithm and other classic precoding algorithms. The assumption that electromagnetic wave propagation is only in the horizontal plane does not apply to urban environment with dense tall buildings. Because the dense urban area propagation environment is complex, and the electromagnetic wave comes from the three-dimensional space. Subsequently, the paper presents a simulation and evaluation scheme based on WINNER II, which applies to dense urban areas with tall buildings. The proposed scheme takes the three-dimensional electromagnetic space features into consideration, such as three-dimensional geometrical parameters of the antenna array,3D patterns and other characteristics. So the proposed simulation assessment scheme is more suitable for dense urban areas and other complex electromagnetic wave propagation scenarios.2, the BD-SML (BD based on Sub-Minimum Interference Leakage) precoding scheme is proposed. Firstly, this paper draws lessons from the BD method to eliminate the interference between the users and the interference between different data streams within the same user, while at the same time, it draws on the idea that the interference leaking to the users in the neighboring cells is minimized. Then, this proposed scheme based on the idea of MMSE (Minimum Mean Squared Error) instead of water filling algorithm takes the spectral efficiency of the system performance and system BER performance into account. Simulation results show the proposed scheme can effectively improve the error rate performance with slight loss of system spectrum efficiency.