Constant envelope phase varying sinusoids of the form\sqrt{2E/T} \cos(\omega_{c}t + \phi(t))are studied, in which the phase function\phi(t)follows some coded pattern in response to data. Power and bandwidth performance are studied for such patterns. The patterns depend on a phase shaping function, a modulation index (h), and a sequence ofM-ary underlying changes in phase which are chosen at random. A cutoff rate-like parameter R0is computed, which guarantees existence of codes at all ratesR < R_{0}bits/T-interval whose error performance varies as exp[-N(R_{0} - R)], whereNis the code word length inT-intervals. Plots of R0are given as a function of interval energyE, the shaping functionhandM. Extensive spectral calculations give the spectra of these phased sinusoids, and their performance is plotted in the power-bandwidth plane. The results give strong evidence that phase codes can approximate any power-bandwidth combination consistent with Shannon's Gaussian channel capacity, and that linear channels are not required for narrow-band transmission.

An analysis of constant envelope digital partial response continuous Phase modulation (CPM) systems is reported. Coherent detection is assumed and the channel is Gaussian. The receiver observes the received signal over more than one symbol interval to make use of the correlative properties of the transmitted signal. The Systems areM-ary, and baseband pulse shaping over several symbol intervals is considered. An optimum receiver based on the Viterbi algorithm is presented. Constant envelope digital modulation schemes with excellent spectral tail properties are given. The spectra have extremely low sidelobes. It is concluded that partial response CPM systems have spectrum compaction properties. Furthermore, at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained. This gain increases withM. Receiver and transmitter configurations are presented.

The aim of this study is to achieve a simple speech codec at low bit rate for mobile radio applications. The vocoder part is obtained by using a low order Discrete Fourier Transform instead of a filter bank. Different baseband waveform coding schemes combined with different baseband bandwidths have been investigated. In particular we have studied a simple scheme for time encoded baseband in which the time intervals between zero crossings are quantized and transmitted. Amplitude information is transmitted with one bit for every zero crossing. The results concerning speech quality and implementation indicate that a simple 4.8 kb/s codec is feasible. It can be implemented with a few low-speed, low-power CMOS LSI circuits since no multiplications are required.

The effect of digital errors in linear pulse code modulation (PCM) systems has been considered by several authors for channels with independent errors. In this paper we present a general approach of analyzing digital errors in linear and nonlinear PCM systems with arbitrary channels. The examples given in this paper cover the different standard nonlinear PCM systems and independent channel errors. The technique used for the analysis leads to the conclusion that there are PCM codes less sensitive to digital errors than the standard binary folded PCM code. An example of such a PCM code is given in this paper.