Transmit beamforming for multiuser mimo systems
Abstract
The uplink of multiuser multiple-input multiple-output (MIMO) systems is considered. We conduct research on a variety of designs for transmit beamforming vectors (beamformers) of multiple users. The collection of the channel state information between each user and the base station is referred to as the full multiuser channel state information (FMCSI). We first design multiuser transmit beamformers under the assumption that the FMCSI is perfectly known not only to the receiver at the base station, but also to all the mobile users. Such an assumption can be realized through cooperation among the users, and thus transmit beamforming for multiple MIMO users under such an assumption is termed cooperative beamforming (CBF). Three designs are investigated for CBF: orthogonal cooperative beamforming (OCBF) schemes which lead to the simplest multiuser detector structure; SINR-Max CBF algorithm to maximize the signal to interference-plus-noise ratio (SINR); jointly optimized transmit-receive beamforming under individual power constraints and target SINR values. The assumption that FMCSI is ideally known to the multiple users indicates that the capacity of feedback links from the base station to the multiple users is infinite. We further consider a more realistic situation where only a limited number of bits are allowed on feedback links. In this situation, codebooks for transmit beamformers are designed and the best beamformer in the codebook is designated by the fed-back bits. We adopt the Lloyd vector quantization methods and genetic algorithms to design codebooks for SINR-Max CBF and jointly optimized transceive beamforming.
Degree
Ph.D.
Advisors
Zoltowski, Purdue University.
Subject Area
Electrical engineering
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