Novel Downlink Beamforming Method Using Selective STBC with Common Eigenvectors for MIMO-OFDM Systems

Riichi KUDO

IEICE TRANSACTIONS on Communications   Vol.E89-B    No.8    pp.2170-2179
Publication Date: 2006/08/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.8.2170
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
MIMO,  eigenvector,  OFDM,  achievable spectrum efficiency,  STBC,  beamforming,  maximum Doppler frequency,  feedback overhead,  

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To achieve a very high data rate within a limited frequency band in orthogonal frequency division multiplexing (OFDM) systems, multi-input multi-output (MIMO) techniques are very promising. Moreover, if a transmitter has the channel state information (CSI), the achievable spectrum efficiency can be maximized using the eigenbeam-space division multiplexing (E-SDM). However, this scheme demands accurate channel estimation. Therefore, in a closed-loop transmission scheme, an increase in the amount of feedback is absolutely necessary for the E-SDM. This paper describes a downlink beamforming method that significantly reduces the amount of feedback needed by using the common transmission weight vectors in all sub-carriers, compared to the amount required for E-SDM. The proposed method also applies transmission diversity to compensate for the quality. The effectiveness of the proposed method was confirmed using computer simulations in both Ricean and Rayleigh fading environments.