This paper discusses recent studies on Chirp Slope Keying (CSK) as a scheme suitable for underwater communications and presents a new study on the performance of a time-frequency receiver in a Rayleigh fading environment. As expected, CSK proves to be a digital modulation scheme inferior in the AWGN channel as compared to traditional schemes but very promising in more detrimental channels present in underwater communications. In effect, while most schemes’ performances decay abruptly with the addition of new disturbances, a time-frequency CSK receiver’s performance deteriorates slowly with increasing Rayleigh fading. Intuition dictates that CSK will overpower other schemes as channel conditions continue to worsen. The receiver first uses the Wigner distribution to transform the incoming signal to the joint time-frequency domain and then computes the Radon transform to determine the binary digit received.
Incer, Inigo X. and Edit J. Kaminsky, "Performance of Chirp-Slope Keying with Joint Time-Frequency Detectors," Proceedings of the SPIE, Vol. 1677, Wireless Sensing and Processing II, 65770H, (2007). doi: 10.1117/12.717771