A Cascaded LMMSE Channel Estimator with High Spectral Efficiency for Distributed STBC-OFDM

A cascaded linear minimum mean square error (LMMSE) channel estimator is proposed to increase the spectral efficiency in distributed space-time block coded orthogonal frequency division multiplexing (DSTBC-OFDM) systems. In our cooperation scenario, assuming the channel state between relay and destination nodes is not less than that between source and destination nodes, the relay is allowed to reduce the number of pilot symbols from the source, where extra-data symbols are transmitted to increase spectral efficiency. For the relay-to-destination channel, coarse and fine LMMSE channel estimators are cascaded to maintain the bit error rate (BER) performance in the destination. The coarse estimator only exploits the reduced pilot symbols to obtain maximum ratio combined (MRC) data symbols, whereas the fine estimator does both of them: reduced pilot and MRC data symbols.