Abstract: Since long delay multipath channels and impulsive noise cause decoding errors, this paper proposes an M-ary noncoherent communication system to address these impairments. At the transmitter side of the system, the data symbols in the time-frequency domain of the multicarrier system are modulated into a cross-zero subcarriers form to avoid the effects of multipath transmission expanding the spacing of neighboring data symbols. At the receiver side of the proposed system, a weighted square law combining algorithm is introduced. The channel and noise power parameters required in the weight calculation derive from joint maximum likelihood estimation. Simulations demonstrate that the system proposed in this paper achieves error-free transmission with a signal-to-noise ratio greater than 4 dB in a shallow time-varying underwater acoustic channel containing impulse noise. Experiment uses shallow sea channel data from the hard substrate burial trial with impulsive noise. Operating in 7.5−12.5 kHz. There are 12 channels in this experiment, the system exhibits multipath delays of 7−35 ms, received SNRs of 2−28 dB, and communication distances of 1−8.1 km. The proposed system achieves error-free transmission at both 293 bit/s and 195 bit/s.