In a recent paper entitled "Generation of constant envelope signals," Dickerson and Warren introduced a technique for the generation of a constant envelope signal which does not require hard limiting. The nonlinear distortion of the resultant phase modulator is, however, quite high. In this correspondence, we suggest two simple but effective modifications to improve the phase linearity of the modulator.

We present in this correspondence a numerical approach to the problem of minimizing the fractional out-of-band power for a class of digital constant envelope modulated signals known as MSKtype signals. The present optimization procedure is much more manageable than a recently suggested analytical one while achieving the same results.

A collection of easily generated signaling waveforms for a binary baseband data system is presented along with the required transmit filter functions. Filtering is based on the criterion of zero intersymbol interference and optimum Peversus receiver input signal-to-noise ratio. The channel considered is a linear one of bandwidth equal to[(1 + \alpha)/2]Hz/baud; α being allowed to vary between zero and one. The results apply, as well, to multilevel data and to bandpass systems, such as digital radio.

For all MSK-type signals proposed until now, the main lobes of their power spectral densities were observed to be always wider than those for conventional PSK. Although it is intuitively believed that this observation can be extended to cover all other MSK-type signals not yet found, no formal proof has been reported yet. The present paper attempts to give such a proof.

It is shown that it is possible to generate a band-limited PSK signal using a ROM and a four-quadrant multiplying D/A Converter.