Research Of MIMO Algorithm Based On LTE Communication System

In order to ensure the competitiveness in the next decade or even longer,3 GPP organization launched an evolutional UTRA/UTRAN project, namely LTE (Long time evolution). The main target of LTE project is to develop communication system which has better performance, for example, higher user rate and longer coverage and shorter time delay and less operating expense. At the same time, whereas MIMO technology can break through the capacity "bottleneck" and improve the reliability of wireless communication system, MIMO has been regarded as a key technology of LTE project. In this paper, based on the understanding of the MIMO communication theory and the needs and protocol of LTE project, we have deeply researched the MIMO algorithm and realization of LTE downlink MIMO scheme, including spatial multiplexing, spatial diversity, etc. At last, Link and System simulation platform has been built to conduct an evolution and analysis of the designed MIMO algorithm.The following work will be completed:(1)Research the basic principles of spatial diversity and spatial multiplexing in LTE system. Combined with the advantages of OFDM technology, a MIMO-OFDM link model of physical layer, which provides a theoretical basis for later study of MIMO, has been established.(2) Based on many MIMO solutions for LTE physical layer, this paper will conduct theory analysis and simulation verification to get the best spatial diversity and spatial multiplexing applied for LTE system. At the same time, the best schemes will be evaluated to determine whether they meet the defined demands of LTE.(3) In view of the fast-moving scenes which have serious Doppler Effect, rapid change of channel state information and other characteristics, this paper presents an open-loop adaptive MIMO scheme based on the "maximum capacity" criteria. In this scheme, we use "minimum error probability" as the criteria to predict the feedback channel information.(4) Based upon the configured downlink LTE parameters, such as frame structures, modulation mode and OFDM parameters, we have built link-simulation and system-simulation platform to verify the performance of the designed MIMO scheme such as bit error rate, throughput and coverage.Simulation results show that:(1) the best spatial diversity which applies to LTE system are SFBC (2Tx) and SFBC+FSTD (4Tx) schemes. Under the aimed BLER, those schemes need lower SNR which can enhance the anti-interference ability and coverage; (2) The best spatial multiplexing which applies to LTE system are channel-dependent precoding scheme and large delay CDD combined with channel-dependent precoding scheme which satisfy the LTE predefined target such as average cell spectral efficiency, average user spectrum efficiency and cell edge user spectral efficiency. (3) The proposed open-loop adaptive MIMO scheme applied to the middle and high mobile scenario whose speed is higher than 30km/h can achieve performance compromise between cell throughput and coverage. What's more, this scheme can be implemented based on the closed-loop MIMO structure to avoid excess complexity overhead.