Bandwidth efficient frequency-shift keyed communication systems

The performance of Pulse Code Modulation with Frequency Modulation (PCM/FM) is evaluated. A numerical algorithm is developed to compute the power spectral density function of PCM/FM. By choosing proper baseband signaling pulse and modulation index (h), the waveform of PCM/FR can be made identical to that of MSK, SFSK, and CPFSK. Thus, the spectral property of these modulation schemes can be obtained directly from that of PCM/FM. The spectral efficiency of PCM/fm is evaluated based on the criteria of out-of-band power bandwidth and channel crosstalk bandwidth. Both spectral measures are functions of the modulation index, the baseband signaling pulse, and the shape parameter thereof. For a given bandwidth or channel separation, these two spectral measures might result in different choices of optimum baseband signaling pulses. In general, through, the rectangular pulse results in better spectral performance for very narrow bandwidths, the trapezoidal pulse outperforms for medium bandwidths, and the raised cosine pulse prevails for wider bandwidths.