The continuous phase modulation method (CPM) has the property that the phase of the modulated signal changes continuously. This modulation method requires smaller bandwidth and is useful in satellite communication. In the partial response CPM, the signal is modulated by overlapping a number of phase-pulse signals with longer pulse length than the symbol interval. This results in an advantage wherein the phase of the modulated signal changes more smoothly, resulting in a smaller bandwidth than the full-response CPM. On the other hand, the phase of the modulated signal is given as the synthesis of more than one pulse. This makes the signal easily affected by the noise, and a coding is required to improve the error rate. This paper considers a convolutional coded CPM and discusses the effects of the waveform of the phasepulse signal on the error rate and the bandwidth, aiming at the determination of the trellis coded partial response CPM with excellent error rate and bandwidth performances.
First, the effect of the waveform of the phase-pulse signal in the convolutional coded CPM on the minimum Euclid distance and the 99-percent bandwidth are examined. Then the trade-off between the minimum Euclid ^Presently with Tokyo Gas Co. 1 distance and 99-percent bandwidth of the proposed method is compared with other methods, including the traditional methods using L REC and L RC. The waveform of the phase-pulse signal with excellent error rate and the bandwidth performances is indicated. Then the effect of the waveform of the phase-pulse signal on the state trellis of CPM is discussed, in general, and the conditions for the phase-pulse signal to improve the error rate are presented.