Title:  High performance receivers for next generation wireless communication systems

Committee: 

Dr. Ma, Advisor   

Dr. Chang, Chair

Dr. Barry

Abstract:

The objective of the proposed research is to explore the relation between channel quality and detection performance in multi-input multi-output (MIMO) systems and develop high-performance receivers by improving the channel quality within reasonable complexity. Wireless communications have become a crucial part of our daily life. MIMO technology greatly improves the spectral efficiency and reliability of wireless communication systems. As the demand on spectral efficiency keeps increasing, large MIMO has been proposed for next generation wireless systems, where tens or hundreds of antennas are equipped at either or both ends of the communication link. In such cases, it is critical to design high-performance detectors with affordable complexity. In this proposal, we first show with a fixed number of transmit antennas (Nt) that if the number of receive antennas (Nr) exceeds a bound, the channel is of "good" quality for linear detectors to collect the same diversity as that of the maximum likelihood detector in practice. When Nr is close to Nt, such as in highly loaded multiuser (MU) MIMO systems, lattice reduction (LR) algorithms can be used to enhance channel quality and system performance. For MU MIMO uplinks where users employ Alamouti code, we develop LR-aided detectors that utilize the symmetric structure of the equivalent channel. For MU MIMO downlinks, we design LR-aided transceivers to minimize the sum of the mean-squared errors. To extend the preliminary research, we propose a channel-assisted automatic retransmission request (ARQ) strategy, where an ARQ of a data frame is sent as soon as the receiver decides the channel is "bad". To improve the adaptivity of LR algorithms, we propose LR agents that learn to improve the channel quality through trial-and-error. The effectiveness of our proposed receivers is verified by extensive simulations.