Spatial transmit diversity techniques for broadband OFDM systems

In this paper, we investigate different spatial transmit diversity concepts for orthogonal frequency division multiplexing (OFDM) systems. The idea is to artificially increase the frequency and time selectivity of the resulting channel transfer function at the receiver antenna by specific time-variant phase rotations of the signal at the transmit antennas. The achievable performance gains with the proposed transmit diversity concepts are presented for convolutionally coded OFDM systems in typical indoor and outdoor environments. The new concepts can be implemented in already standardized and existing OFDM systems like DAB and DVB-T or HIPERLAN/2, IEEE 802.11 and MMAC, without changing the standards and the receivers. Moreover, we show further performance improvements by combining the spatial transmit diversity concepts for OFDM with code division multiplexing (CDM).