Spectrum and Energy Efficient OFDM Multicarrier Modulation for an Underwater Acoustic Channel

Time domain synchronization orthogonal frequency division multiplexing technique (TDS-OFDM) can offer better efficiency in spectrum and energy use than standard cyclic prefix and zero padding schemes by replacing the guard interval with a pseudorandom noise sequence. In this paper, a type of frequency domain pseudorandom noise training sequence is proposed for underwater acoustic channel as a TDS-OFDM training sequence and used to update the Doppler scaling factor estimation obtained by using a preamble signal after the initial system is synchronized. A significant improvement can also be achieved in bit error rate performance by the use of the compressed sensing theory to estimate underwater acoustic channel impulse response based on the proposed TDS-OFDM training sequence. Furthermore, the guard interval amplitude in TDS-OFDM can be reduced to improve the resultant energy efficiency and signal-to-interfered-signal ratio. The proposed techniques are carefully developed based on intuitive analysis and combined in a receiver design. Such receiver is evaluated in a measured underwater acoustic channel and a simulated channel. Both technical analysis and experiment results show significant and consistent performance improvements in spectral and energy use.