Open-Loop Correlation Reduction Precoding in Overloaded MIMO-OFDM Systems

Abstract

This paper proposes an open-loop correlation reduction precoding scheme for overloaded multiple-input multipleoutput (MIMO) orthogonal frequency division multiplexing (OFDM) systems. In overloaded MIMO-OFDM systems, frequency diversity through joint maximum likelihood (ML) decoding suppresses performance degradation owing to spatial signal multiplexing. However, on a line-of-sight (LOS) channel, a channel matrix may have a large correlation between coded symbols transmitted on separate subcarriers. The correlation reduces the frequency diversity gain and deteriorates the signal separation capability. Thus, in the proposed scheme, open-loop precoding in order to reduce the correlation between codewords transmitted on different signal streams is employed at the transmitter of an overloaded MIMO system. The proposed precoding scheme changes the amplitude as well as the phase of the coded symbols transmitted on different subcarriers. Numerical results obtained through computer simulation show that the proposed scheme improves the bit error rate performance on Rician channels.

Performance Optimization for Overloaded MIMO Systems with Virtual Channel Approach

“…In an overloaded MIMO system, the channel correlation practically exists, which may lead to a serious system performance degradation, especially in the massive MIMO systems. In [13], an open-loop and nonadaptive precoding scheme with predetermined coefficients is proposed for the overloaded MIMO-OFDM systems to reduce the correlation effect. A WL-MMSE precoder employing real-valued transmit symbols for the downlink large-scale MIMO systems presented in [14] has shown that it achieves a substantially higher sum rate than the systems employing the conventional MMSE precoding.…”