A simple spectra computing approach for continuous-phase phase modulation (CPPM)

Recently, we have developed a special class of continuous-phase modulation (CPM) scheme, called the continuous-phase phase modulation (CPPM); it transmits the PAM information sequences using time-limited phase shaping pulses. In this paper, the power spectra for this novel CPM are investigated. We employ autocorrelation function approach to modify the CPM spectra computing formula for time-limited phase shaping pulse. Since CPPM is a CPM modulator with time-limited phase shaping function, previous research believed that such modulator will have data-independent spectral lines and suggested to be avoided. However, we show that the spectral lines can be diminished by choosing appropriate modulation index, modulation level and phase shaping pulse. Spectra for two classes of CPPM schemes are given. It is shown that the bandwidth of CPPM scheme can be effectively reduced by using smaller modulation index and/or increasing the correlative length and modulation level. The resultant CPPM schemes have attractive spectral occupancy as compared to conventional CPM.