On Low Crosstalk Data Communication and its Realization by Continuous-Frequency Modulation Schemes

Modulation waveforms with continuous derivatives in conjunction with a receiver whose impulse response has continuous derivatives is shown to generate crosstalk interference in a correlation demodulator that decreases at least as the cube of the carrier spacing between waveforms. Constant envelope, continuous-frequency modulations called Continuous (Frequency) Shift Keying (CSK) are proposed which not only achieve this asymptotic crosstalk behavior but are better then Phase Shift Keying (PSK) and Minimum Shift Keying (MSK) for carrier spacings of at least 1.1 times and 2.0 times the data rate, respectively. CSK can be demodulated in Gaussian noise with no loss with respect to optimum hard-decision receivers of antipodal signals, i.e., with the same performance as PSK and MSK.