A hybrid approach to spatial multiplexing in multiuser MIMO downlinks
EURASIP Journal on Wireless Communications and Networking - Special issue on multiuser MIMO networks
Design of FIR precoders and equalizers for broadband MIMO wireless channels with power constraints
EURASIP Journal on Wireless Communications and Networking - Special issue on multiuser MIMO networks
SPPRA'06 Proceedings of the 24th IASTED international conference on Signal processing, pattern recognition, and applications
MIMO transceiver design via majorization theory
Foundations and Trends in Communications and Information Theory
IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences
Utility of beamforming strategies for secrecy in multiuser MIMO wiretap channels
Allerton'09 Proceedings of the 47th annual Allerton conference on Communication, control, and computing
Symbol-wise beamforming for co-channel interference reduction in MIMO-OFDM systems
GLOBECOM'09 Proceedings of the 28th IEEE conference on Global telecommunications
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Multi-input multi-output (MIMO) channels have been shown in the literature to present a significant capacity increase over single-input single-output ones in some situations. To achieve this theoretical capacity, the constituent parallel subchannels arising from the MIMO channel have to be properly used. Many practical schemes are being currently developed to achieve this goal. We first show that, from an information-theoretic point of view, beamforming becomes asymptotically optimal as the spatial correlation of the channel fading increases. In light of this result, wideband beamvectors are jointly derived for both transmission and reception. We allow a controlled partial response and design zero-forcing and minimum mean-squared error transmit-receive filters. Conceptually, the beamforming scheme is shown to decompose into two stages: the first one corresponds to a spatial flattening of the MIMO channel, i.e., choosing the subchannel with the highest gain at each frequency; the second stage depends on the particular design criterion and performs a power distribution at the transmitter and defines the equalizer at the receiver. These methods are further extended to the general case of multiple beamforming, i.e., when more than one subchannel are used. An exact and practical implementation of a modified "waterfilling" solution required for the filter design is proposed. All derived methods are assessed and compared in terms of capacity and bit-error rate.