Space–Time Trellis-Coded OFDM Systems in Frequency-Selective Mobile Fading Channels

Space-time trellis code (STTC) techniques provide both coding gain and diversity gain to orthogonal frequency-division multiplexing (OFDM) systems without reducing bandwidth efficiency. However, factors such as residual carrier frequency offset due to Doppler shift destroy the orthogonality among subcarriers, which results in intercarrier interference (ICI) in mobile fading channels and bit error rate (BER) degradation. This brief presents three STTC-based OFDM systems to improve BER in frequency-selective mobile fading channels. First, a new STTC-ST method is developed with OFDM to form a new STTC-ST-OFDM system. Second, a Walsh-Hadamard (WH) transform is employed as a precoder to form a new STTC-WH-ST-OFDM system with limited growing computation. Third, the STTC-WH-ST-OFDM system is integrated with an ST conjugate cancelation (CC) scheme to form an STTC-WH-STCC-OFDM transceiver with expanding bandwidth in order to combat ICI. Simulations indicate that the STTC-WH-STCC-OFDM system outperforms both STTC-WH-ST-OFDM and STTC-ST-OFDM systems, whereas the STTC-WH-ST-OFDM system outperforms the STTC-ST-OFDM system. All three schemes are simple and are backward compatible with existing OFDM systems. They can serve as baseband building blocks for multiuser OFDM systems, specifically in downlink networks.