Dual PN padding TDS-OFDM for underwater acoustic communication

A time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) scheme with dual Pseudonoise (PN) sequence is proposed for underwater acoustic (UWA) communication. Instead of using cyclic prefix (CP) or zero padding (ZP) as the guard interval, the proposed TDS-OFDM scheme uses two identical PN sequences as guard interval, and utilizes them for frame synchronization and channel estimation. The proposed TDS-OFDM increases the spectrum efficiency over the conventional CP or ZP OFDM systems where additional pilots have to be inserted for channel estimation. With the dual PN at each frame header, compressed sensing channel estimation is adopted and a rather simple equalization design reduces the receiver complexity. With a low-density parity-check (LDPC) code, the proposed system is simulated in doubly selective underwater acoustic channels with long multipath delay spread and severe Doppler spread. The results show that the TDS-OFDM achieves slightly better BER performance and higher spectrum efficiency than the conventional ZP-OFDM.