Research On Limited Feedback Precoding Techenologies For MIMO Systems

With the significant advantage in improving spectrum efficiency, multiple-input multiple-output (MIMO) technology becomes one of the key technologies of next generation wireless communication system. In multi-user multiple-input multiple-output (MU-MIMO) downlink, a base station communicates with several co-channel users simultaneously in the same frequency and time slots, the spectrum resource utilization is multiplied but co-channel interference (CCI) is also introduced inevitably, including interference between users and sub-streams. Precoding is just the effective measure which can eliminate space signal interference by some pre-processing at the transmitting side. The application of precoding technology greatly reduces the complexity of the receiver on one hand and significantly improves the reliability of the system on the other hand.This paper focuses on the limited feedback precoding schemes in MIMO system. The main contents include following aspects:1. Investigate on the characteristic of radio channel, transmission model of MIMO systems and derivation of system capacity. Research on the existing feedback schemes and precoding techniques. Do in-depth analysis on the basic principles, implementation process, advantages and disadvantages of some typical precoding schemes.2. Aimed at Tomlinson-Harashima Precoding (THP), an optimized scheme which only needs feeding back channel direction information is proposed. Amplitude information is not necessary for the new scheme. It has significantly reduced the feedback bits. Implementation process of the proposed THP scheme based on both vector quantization and scalar quantization is studied. Also system capacity is derived. The effectiveness of the scheme is certified both by theory and simulation.3. Deeply research on THP scheme in time division duplex (TDD) system which obtains channel state information by reciprocity between downlink and uplink. Factors that affect reciprocity, including time-variance of channel, estimation error of channel, asymmetry of RF devices, bandwidth limit of uplink reference signal and etc., are investigated and the corresponding compensation schemes are proposed. The impact of time-variance and RF devices’ asymmetry to channel reciprocity and THP performance is evaluated by simulation.