A Study on Link Adaptation Scheme with Multiple Code Words for Spectral Efficiency Improvement on OFDM-MIMO Systems

Abstract

In this paper, we propose the stream multiplexing scheme to achieve the high spectral efficiency on OFDM-MIMO system considering (a) the effects of the inter-stream interference suppression techniques, (b) the influence of the quality measurement in the receiver to select the modulation and coding scheme (MCS) and (c) the influence of the signaling overheads to the spectral efficiency. Two kinds of schemes for stream multiplexing, namely Multiple CodeWord (MCW) and Single CodeWord (SCW) are investigated and compared. In the simulations, we assume real channel estimation for SINR measurement for MCS selection and we compare the schemes with the spectral efficiency taking into account overheads. In consequence, it is presented that MCW can achieve the higher efficiency than SCW in the middle to high SINR region. Moreover, in 4 × 4 antenna configuration, a 2CW-MCW scheme where 2 codewords mapped onto 4 streams according to SINR of each streams is proposed. The scheme gives higher throughput by improving the MCS selection in the low SINR region due to increase of data length per a codeword and by reducing the signaling overhead due to the decrease of the number of codewords. As a result, the proposed scheme achieves spectral efficiency improvement in whole SINR region.