Power Spreading in Distributed Transmit Antennas

In distributed antenna system (DAS), delay spreads between the receiver and each transmit antenna are different due to the unequal propagation delays from distributed transmit antennas to mobile receivers. To exploit the merit of DAS, power spreading in distributed transmit antennas is proposed for OFDM-based MIMO systems over frequency-selective fading channel. In this scheme, partial power of the same symbol can be transmitted simultaneously in the distributed antennas after spatial power spreading. Then the multipath-faded symbol information from different transmitter can be resolved at the receiver. It can be considered that M_TL duplicates of original symbol are obtained where L is the number of channel taps and M_T is the number of transmit antennas, and hence higher multipath diversity could be achieved. Combined with frequency power spreading and ML detection, this scheme can achieve better performance than that without spatial power spreading. Simulation results are provided with 2 transmit and 2 receive antennas, demonstrating about 1.5 dB signal to noise ratio (SNR) gain is obtained at bit error rate (BER) of 1e-3.