Efficient Faster-Than-Nyquist Transceiver Design for Underwater Acoustic Communications

Abstract

Faster-than-Nyquist (FTN) signaling is an attractive technology to improve the spectral efficiency. In this paper, an efficient FTN transceiver is proposed for underwater acoustic (UWA) communications. At the transmitter, the FTN signaling is implemented via the serial concatenation of a sample-rate-convertor (SRC) based on the well-known Farrow filter and the Nyquist pulse shaping. Compare with the conventional FTN signaling, it facilitates the convolution operation and thus achieves the efficient FTN signaling. On the receiver side, the direct-adaptive turbo equalization is employed to combat the hybrid inter-symbol interference (ISI) of the artificial ISI introduced by FTN signaling and the UWA channel-ISI. Wherein the improved proportionate normalized least mean squares (IPNLMS)-based direct-adaptive equalizer (DAE) with the data reuse (DR) aid is adopted as the soft equalizer. As for the channel coding, an irregular convolutional code (IrCC) is designed by matching the extrinsic information transfer (EXIT) curve of the DR-IPNLMS-DAE, leading to a low signal-to-noise ratio (SNR) threshold of the turbo iteration. Underwater experimental results verify the advantage of the FTN transmission over the higherorder modulation in terms of improving the spectral efficiency, and they show the proposed FTN transceiver scheme has the better detection performance than the traditional turbo equalization.