A performance comparison between DSSS, M-FSK, and frequency-division multiplexing in underwater acoustic channels

Three modulation schemes are compared for underwater acoustic communications: M-ary frequency-shift keying (MFSK), direct-sequence spread spectrum (DSSS, single carrier), and frequency-repetition spread spectrum (FRSS, multi-carrier), which is a special case of frequency-division multiplexing. The MFSK receiver is based on energy detection, whereas DSSS and FRSS are coherent schemes equipped with an adaptive equalizer. A validated acoustic channel simulator is applied to distort the signals, driven by an archive of in situ measurements of the time-varying impulse response in the 4-8 kHz band. It is shown that the geographical area (channel conditions) may have a large influence on the relative performances. When the error statistics are averaged over all available channels, MFSK offers the best overall performance at high SNR, and FRSS at low SNR.