Research On Pre-coding In Massive MIMO System

With the layout and application in LTE system, multiple antenna MIMO as the core technology has been widely used in the current wireless cellular systems scene. In the current field of wireless communications, whether in theory or actual cell scenario, the cell-edge user suffer from adjacent cell’s interference is worsening, and it has become a bottleneck to constrain the development of wireless communication.The interference is seriously affecting the system throughput and channel capacity. In order to reduce inter-cell interference problems, the current academia proposed coordinated multi-point transmission (CoMP) and other related technologies, while these techniques can effectively suppress the inter-cell interference. Nevertheless, these technologies are not fundamentally enhanced the capacity of the system into an order of magnitude to satisfy the needs of users.Massive MIMO technology was proposed in recent year, this technology can not only effectively reduce the inter-cell interference, but also greatly improved the array gain of the system, system capacity and spectral efficiency. In large-scale MIMO system, the base station is equipped with huge number of low-power array antennas, the system serves in a Time-Division Duplexing(TDD) manner. Massive MIMO technology has a huge advantage in wireless communication, attracted widely attention and research. Under the condition of pilot multiplexing or non-orthogonal in multi-cell, the performance of Massive MIMO system is limited by pilot contamination.In the paper, we focus on the pre-coding technology research and analysis, and consider to use pre-coding technology to eliminate or suppress the pilot contamination. Firstly, we have a brief description with the establish of channel model in multi-input multi-output (MIMO) system and its simulation method, while introduce the MIMO pre-coding technology and multi-user MIMO pre-coding algorithm. Then analyze the problem of inter-cell interference, focusing on CoMP technology in heterogeneous network system, comparing with corresponding interference collaborative algorithms.Then we analysis the pilot contamination in Massive MIMO system, including the cause of pilot contamination, uplink channel estimation and pilot contamination optimization strategy. We consider to apply classical interference collaboration algorithm in CoMP technology to Massive MIMO system. In this paper, Max SINR will be investigated and improved for Massive MIMO pre-coding. We optimize the Lagrangian function by KKT conditions and obtain the optimal downlink pre-coding matrix. Numerical results proved that under heavy pilot contamination scenario, the performance of proposed algorithm is better than MF pre-coding. Will effectively mitigate the impact of pilot contamination, and achieve high throughput and effective performance in Massive MIMO system.