Researches On Pilot Contamination Reduction In Massive MIMO Systems

With the steady development of wireless network system and popularity of intelligent terminals, higher transmission rate and reliability are required in modern communication system. On the other hand, with the rapid growth of mobile communication services, the wireless spectrum resources are increasingly strained. Therefore, the technician tried to discover the potential of the multiple-input multiple-output(MIMO) antenna technology in fourth generation mobile communication system. MIMO technology can not only provide a significant improvement in spectral efficiency, but also make the wireless link more reliable.On the basis of existing MIMO technology, Massive MIMO achieves a better system performance and effectiveness against the explosion demand of wireless data. Compared with the traditional MIMO technology, Massive MIMO can be implemented simply via adding huge number of antennas(tens or hundreds of antennas) in the base station. By means of increasing the degree of freedom, this technique can improve system capacity without additional bandwidth. However, in the cellular network system, it is difficult to obtain a sufficient number of orthogonal pilot sequences, and this will lead to reuse pilot sequence between inter-cells. This problem called pilot contamination, and as a result, it will severely limits the system performance because of the inaccurate channel state information.Therefore, the main research contents of this article are to solve the problem of pilot contamination in massive MIMO system. The major research work are as follows:Firstly, we focus on the technical advantage and hot research areas of massive MIMO system, then analyzes the performance characteristics of this technology, including system models, spatial fading channel models in detail. And on this basis, we analysis and compare several solving schemes for pilot contamination. After that, we analysis the channel estimation and precoding scheme about massive MIMO system in detail.Secondly, After analyzes and research the synchronized pilot transmission scheme in massive MIMO system, we explored the reason of pilot contamination. After that, we analyze the time-shifted pilot transmission scheme, this scheme let different users in different cells transmit pilot at non-overlapping times. Then verified the validity of the its effectiveness by mathematical deduction and simulation.Finally, combined with the analysis of channel estimation mean square error performance of synchronized pilot transmission scheme in massive MIMO system, wepropose time-interleaved pilot transmission scheme. This scheme is based on partitioning cells into groups of cells, cells belong to different groups use different pilot frame structure.At last, we verify its superiority by simulation compare with synchronized pilot transmission scheme.