As the key technology of the international Digital Television Terrestrial Broadcasting (DTTB) standard called Digital Terrestrial Multimedia Broadcast (DTMB), time domain synchronous OFDM (TDS-OFDM) differs from classical cyclic prefix OFDM (CP-OFDM) by replacing CP with known pseudorandom noise (PN) sequence. Channel estimation is an essential component of single-antenna TDS-OFDM systems due to the interference problem over multipath channels, and the timedomain received PN sequence is used to accomplish this task. However, when transmit diversity is applied to TDS-OFDM, PN sequences passing through different channels will mix together at the receiver, so the conventional PN-based channel estimation is invalid any more due to more complex interferences. To realize transmit diversity for TDS-OFDM, the space-time-frequency (STF) orthogonal training sequence design and the corresponding space-frequency and space-time channel estimation methods over time-varying and frequency-selective channels are proposed in this paper. The feasibility of the proposed scheme is validated by the simulation results, which also demonstrate that the bit error rate (BER) performance close to the ideal channel state information case could be achieved as well.
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