Limited Feedback Precoding for Distributed Space-Time Coding in Wireless Relay Networks

Distributed orthogonal space-time block code (DOSTBC) designs have the potential to achieve significant diversity gain in relay networks but such designs do not use any channel information at the transmitter to optimize the system performance. When channel information is available fully or partially at the relays, transmit beamforming can be employed to enhance the performance of the wireless relay network. In this paper, we combine transmit beamforming and distributed space-time coding through a linear precoding to transmit information from multiple relay network. This paper investigates a limited feedback approach that uses a codebook of precoding matrices known a priori to both relay terminals and the receiver. The receiver chooses a matrix from the codebook based on the current channel and conveys the optimal precoder matrix to the relays through an error-free finite rate feedback channel. The SNR analysis shows that the proposed scheme achieves the optimal diversity order. Moreover, the symbol error rate (SER) performance with finite feedback bits is shown to offer performance improvements by a SNR margin of 4 - 6 dB.