On the periodicity of superimposed training sequence for OFDM systems

It is conventionally supposed that the periodicity of superimposed training (ST) sequence designed for channel estimation has no impact on the ST system's performance, as long as the channel identification condition is satisfied. Accordingly the shortest sequence period equal to channel length is always preferred in ST-OFDM systems for its computational tractability. However, with additional consideration on extraction of the transmitted information, not only focusing on the accuracy of channel estimation, analysis and simulation indicate that the period length of ST sequence may have an unignorable influence on BER performance of ST-OFDM systems. As a special case, we show that ST with training sequence period equal to channel length can bring OFDM no benefit but BER performance degradation compared with its frequency-divided pilot counterpart.