| With the rapid development of mobile communication, high-speed multimedia data transmission services have higher requirements. Today’s spectrum scarcity of resources, how to make more effective use of limited spectrum resources is the big problem for the next generation of mobile communication to be solved. As an important member of the fourth generation mobile communication which has the feature of high-speed and low-latency,3GPP LTE/LTE-Advanced use OFDM and MIMO as its core technology to solve the problem. LTE-Advanced system, not just single-user MIMO, also introduces a collaborative user virtual MU-MIMO (Multi-user MIMO) technology. In this paper, MIMO technology of the downlink system in LTE-Advanced was meticulously researched.Single-user MIMO includes three schemes:transmit diversity, spatial multiplexing and beamforming. Transmit diversity by sending several copies of the signals to improve the reliability of system transmission. Spatial multiplexing data multiplex signals on multiple antennas at the same time to improve the system throughput and spectral efficiency. Beamforming transmitted directional signals to improve the performance of cell edge users. Detection algorithms of receiving system of the three techniques were also introduced in this paper.The biggest problem in MU-MIMO is multi-user interference in the collaboration. In this paper, pre-coding algorithms of eliminating multi-user interference and transmitting directional signals to each user, including ZF, MMSE, BD/BD+SVD and MET algorithms are introduced. Because the transmitter should know the channel state information to do the pre-coding, long-term channel correlation matrix and CSI for the TDD and FDD duplex mode are feedback respectively.In order to verify the mentioned MIMO pre-coding algorithm, a MATLAB simulation platform based on the LTE physical layer protocol was built. The simulation results verified the theoretical analysis. Because of the implementation complexity and performance, algorithms mentioned in this paper have a strong engineering feasibility. |
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