A Subspace-Based Optimization Strategy for Downlink Systems with Ill-Conditioned MIMO Channels

Yung-Yi WANG  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E94-A   No.8   pp.1706-1714
Publication Date: 2011/08/01
Online ISSN: 1745-1337
DOI: 10.1587/transfun.E94.A.1706
Print ISSN: 0916-8508
Type of Manuscript: PAPER
Category: Communication Theory and Signals
MIMO,  MMSE,  spatial multiplexing gain,  

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We propose an innovative and practically attainable downlink multi-cell MIMO system with distributed transmit beamforming design. The proposed system is referred to as the MIMO-MAP system which is aimed to mitigate the rank deficiency problem of those MIMO wireless channels that can not support high-order multiplexing gains. In the MIMO-MAP system, each mobile station is allowed to receive several independent data streams from multiple access points at the same time and the same frequency. To do this, a set of noise-subspace-based receive beamformers are employed to suppress the interference among the data streams from different access points. On the other hand, if we consider each receive beamformer as part of its associated wireless channel, we virtually reduce the antenna array at each receive mobile station to a single antenna. With this arrangement, we may have the transmit signal dimension high enough to pre-cancel the inter-stream-interferences at each transmit access point. As a result, the MIMO-MAP channel can be decomposed into a large number of independent subchannels which significantly increase the channel capacity.