Combining Spatial Multiplexing and Transmit Diversity in SCFDE Systems in High-Mobility Environment

This paper addresses the combination of spatial multiplexing (SM) with space-frequency block coding (SFBC) for SCFDE systems, in high mobility environment. Coding across different antennas and different subcarriers, such as SFBC, is more suitable than space-time block coding (STBC) in high-mobility environments of interest for future wireless systems. However, the application of SFBC schemes to SCFDE is not straightforward as in OFDM systems, since it requires the access to the subcarriers at the transmitter, which is not directly available in SCFDE. This paper firstly presents a low complexity implementation of SFBC in SCFDE. This processing is then used in a 4 times 2 scheme which combines SM with SFBC. The comparison in terms of spectral efficiency with a 4 times 2 quasi-orthogonal transmit diversity scheme, where the 4 transmit antennas are used only to get diversity gain and the higher spectral efficiency is achieved by higher order constellations, shows that the hybrid SM-SFBC combination is much more robust to the frequency selectivity of the channel and to the spatial correlation. The same is not observed when the presented hybrid scheme is applied to OFDM systems.