Limited Feedback MU-MIMO in LTE-A System: Concepts, Performance, and Future Works

In wireless communications, interference is known as a major restricting factor in achieving system capacity. Therefore, in the Long-Term evolution (LTE) system, a transmitter and a receiver collaborate together to tackle the interference. To do so, in the frequency division duplex system, information of downlink channel must be shared among the transceivers via a limited feedback technique. In this regard, this paper discusses the downlink transmission of multi-user multiple-input multiple-output with limited feedback in the LTE-Advanced system. Extensive studies are conducted on all steps of downlink transmissions and receptions which include techniques such as receive antenna combining, channel state information (CSI) acquisition, CSI quantization, precoding, and user scheduling. By utilizing a LTE-A standard compliant simulator, the link-level performance of the system is evaluated under different receive antenna combiners and quantization codebooks. Moreover, the main system constraints such as channel delay and imperfect CSI are applied to the system which results show that the system performance severely degrades under imperfections, especially when the number of transmit antennas increases. The results mainly reveal that to achieve the capacity of LTE-A, with the presence of interference, delay, and limited feedback, more sophisticated methods are required. Hence, this study precisely addresses the future works on CSI quantization, precoding, and user scheduling.