High data rate transmission and reception based on mean square error minimization and overhead reduction for the downlink of multiuser MIMO systems

Abstract

Multiple-Input Multiple-Output (MIMO) is a well known technique to increase the capacity of wireless communication links, providing additional degrees of freedom in space domain. However, it has been found that several practical problems impose restrictions on MIMO capacity, such as high correlated antennas and the limited number of antennas at the mobile station. Recently, as a solution to cope with such drawbacks, multiuser MIMO (MU-MIMO) techniques have been intensively studied and implemented in both the academic and industrial field, in which a common base station having multiple antennas communicates with multiple mobile stations, each with multiple antennas. In this thesis, we propose several high data rate algorithms for the downlink of MU-MIMO systems. First, we propose a new random beamforming scheme that exploits multiuser diversity efficiently. Random beamforming is a unitary precoding scheme, which requires only the feedback of downlink channel quality indication. While the conventional random beamforming for MIMO systems assigns the whole spatial layers to the user with maximal MIMO capacity, the proposed scheme assigns the spatial layers to multiple users, each of the spatial layers assigned to the user who benefits the most from the corresponding spatial layer, and thus exploits multiuser diversity efficiently. Simulation results show that the proposed scheme achieves higher capacity than the conventional scheme. Next, we propose a jointly optimized transmit and receive beamforming with reduced overhead. Jointly optimized transmit and receive beamforming, also called coordinated beamforming, is a non-unitary precoding scheme whose transmit beamforming and receive beamforming are optimized jointly based on the channel state information. In the proposed scheme, the orthogonal property among effective channels seen at each user is exploited to reduce the pilot overhead or the control channel overhead, when training users about the receive beamf...