Determination of cyclic delay for CDD utilizing RMS delay spread in OFDMA multiuser scheduling systems

The multiuser diversity gain increases with the degree and dynamic range of channel fluctuations. For a multi-antenna orthogonal frequency division multiplexing (OFDM) system operating in a channel with limited fluctuations, cyclic delay diversity (CDD) was proposed to increase frequency selectivity. This is achieved by introducing a cyclic delay between the different transmit antennas thereby increasing the effective number of paths in the resulting channel. In this paper, for a multiuser system, we propose a scheme to determine peruser optimal cyclic delay value based on the knowledge of the root-mean-square (RMS) delay spread of the channel. We show that the proposed technique achieves better performance than a conventional fixed cyclic delay scheme and that the throughput is very close to the optimal sum rate possible with CDD.