Channel Training and Estimation in Distributed Space-Time Coded Relay Networks with Multiple Transmit/Receive Antennas

This paper investigates the channel training and estimation problems for distributed space-time coding (DSTC). To use DSTC in multi-antenna relay networks, the receiver needs to know the channels between the relays and the receiver (Relay-R channels) and also the equivalent channels between the transmitter and the receiver (Equ-T-R channels). By sending pilot signals from the relays, the training of the Relay-R channels is equivalent to that of a multi-input-multi-output (MIMO) system. The training of the Equ-T-R channels can be conducted directly using DSTC; but it requires a long training period. Thus, a separate-training method is proposed, in which an estimation on the Equ-T-R channels is obtained from estimations on the channels from the transmitter to the relays (T-Relay channels) and the Relay-R channels. The pilot code designs that minimize the trace of the error covariance matrix are investigated. The requirements on the training period are also derived, from which an adaptive training-period design is proposed. Simulation shows that in some networks, even with shorter training period, the separate-training scheme can achieve better performance than the direct-training scheme.