Performance Investigation on High Resolution CSI Enhancement for 5G Massive MIMO Systems

In the 5th generation (5G) mobile networks, an important enhancement aspect for massive MIMO is Channel State Information (CSI) feedback. For massive MIMO, quantities of antennas are utilized to provide better coverage, which brings challenge for implementation as well as opportunity for improving multi-user (MU)-MIMO performance. To provide better performance for MU-MIMO, high resolution CSI feedback was introduced in Rel.14. Base stations can acquire more accurate channel information from high resolution CSI to facilitate scheduling for multiple users with reduced inter-user interference. However, high resolution CSI feedback specified in current 3GPP still has large room to be improved due to big gap between current CSI feedback and ideal CSI feedback. In this paper, we investigate possible enhancement directions towards high resolution CSI, e.g., to improve the quantization resolution by combining more beams, to increase the supported rank, etc. High resolution codebook construction and higher rank multi-user scheduling schemes are provided. System evaluation is performed to verify the effectiveness of those schemes. Simulation results show that improving quantization resolution can bring decent performance gain, and supporting higher ranks can bring larger performance gain. Both schemes will introduce large overhead. To balance performance and overhead, supporting higher rank high resolution is preferred. The challenges to specify these schemes are also analyzed.