Interpolation- Based Multi-Mode Precoding for MIMO-OFDM Systems with Limited Feedback


N. Khaled, B. Mondal, Robert W. Heath Jr, G. Leus and F. Petre.


IEEE Trans. Wireless, vol. 6., no. 3, pp. 1003-1013, March 2007.


Spatial multiplexing with multi-mode precoding provides a means to achieve both high capacity and high reliability in multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. Multi-mode precoding uses linear transmit precoding that adapts the number of spatialmultiplexing data streams ormodes, according to the transmit channel state information (CSI). As such, it typically requires complete knowledge of the multi-mode precoding matrices for each subcarrier at the transmitter. In the considered limited-feedback scenario, the entailed feedback overhead may become prohibitive. In this paper, we propose to reduce the feedback requirement by combining codebook-based precoder quantization, to efficiently quantize and represent the optimal precoder on each subcarrier, and multi-mode precoder frequency down-sampling and interpolation, to efficiently reconstruct the precodingmatrices on all subcarriers based on the feedback of the indexes of the quantized precoders only on a fraction on the subcarriers. To enable this efficient interpolation-based quantized multi-mode precoding solution, we introduce (1) a novel precoder codebook design that lends itself to precoder interpolation, across subcarriers, followed by mode selection, (2) two precoder interpolators and, finally, (3) a clustered mode selection approach that significantly reduces the feedback overhead related to the mode information on each subcarrier. Monte-Carlo bit-error rate (BER) performance simulations demonstrate the effectiveness of the proposed quantized multi-mode precoding solution, at reasonable feedback overhead.

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