Research Of LTE Downlink Closed-loop MIMO Precoding Technology

ABSTRACT:LTE (Long Term Evolution) is Long Term Evolution project of3GPP, it is compatible with3G communication system and evolution of3G. It has a high transmission quality, high data transfer rate100Mbps and be able to adapt to high speed scenario. Long Term Evolution-Advanced is the next generation of4G communication systems in the real sense. As the smooth evolution of LTE, it adds some new features. For downlink closed-loop transmission, MIMO and precoding technology have been an important part in LTE/LTE-A system. Precoding technology is the key to help MIMO technology improve the throughput and reliability. For better performance, we do some research on precoding compared with3GPP specification and contribution.First, based on the the closed-loop transmission over LTE downlink, we propose a proposal that by shifting the respective phases of different antenna port to improve the accuracy of beamforming and demodulation signal to noise ratio got by terminal. For reducing the system overhead, we put forward a quantitative strategy, which to average the minimum shifting phase in specifications to some equal segmentations makes quantitative values can be mapping to the index value. So when the feedback can be an index value instead of the whole matrix. Link level simulation results show that compared with the scenario defined in3GPP specifications and contributions, when the feedback delay is4ms the throughput can be increased by7%and improvement is associated with the feedback delay.Secondly, in order to take full advantage of the demodulated signal to noise ratio among different layer, this paper presents a precoding matrix with rotation matrix way to average the demodulated signal to noise ratio.The rotation matrix is constructed from the U matrix of TM3, because the U matrix is used to mixed different layers.This paper proves the SNR average of different layers caused by rotation matrix by the demodulation SNR curve of different layers. The link level simulation results show that, the precoding with rotation matrix will have an improvement on throughput when the antenna configuration is4Tx and2Rx, and the gain arrives1-3dB. But with the improvement of antenna, the antenna gain will improve, and the gain caused by rotation may be ignored.Finally, based on the link level simulation platform, we got the simulation result and analyze the different scenario to prove the gain.