Showing papers on "Continuous phase modulation published in 1972"

Coherent Demodulation of Frequency-Shift Keying with Low Deviation Ratio

Abstract: A coherent binary FSK modulation system is discussed, that has the following properties: 1) it is phase coherent; 2) it has a low deviation ratio, h = \frac{1}{2}; 3 ) it occupies a small RF bandwidth, typically only 0.75 times the bit rate, without need for intersymbol interference correction; 4) it uses as receiver a self-synchronizing circuit and a phase detector, which together achieve optimal decisions; and 5) its error performance is about S dB better than that of conventional FSK.

Spectral Density Bounds on an FM Wave

Abstract: Upper and lower bounds on the spectral density of a sinusoidal carrier frequency modulated by a band-limited Gaussian noise signal are derived and we show that these bounds are very close to each other if the ratio of the rms frequency deviation to the maximum modulating frequency is even moderately high. We then show that the results obtained from the quasi-static approximation, often used in such cases, are too small for large f and that this low-frequency approximation cannot be used in cases where the behavior on the tails is of importance.

Complex Detection: A Waveform Preserving Technique for Single-Sideband Demodulation

Abstract: The full-carrier single-sideband signal is of the minimal phase type with limited phase excursion and contains sufficient information to recover completely the message waveform. A receiving system is described that makes use of both the envelope and the phase information in the signal. Operation is independent of input signal level and requires no wide-band quadrature network.

Method and apparatus for synchronizing a receiver for phase-difference modulated data signals

Abstract: A method and apparatus for synchronizing a receiver for phase difference modulated data signals are described. The system under consideration herein transmits binary coded data by means of predetermined phase shifts at intervals corresponding to a modulation period and assigned to the various data step combinations. Correction signals for the clock rate and the reference carrier derived from the received carrier are supplied. In the receiver the clock rate for a scanning signal and the reference carrier are derived from a constant frequency generator. Phases of the received carrier wave modulated with phase shifts and phases of the reference carrier formed in the receiver are compared at time intervals corresponding to a carrier wave period. A correcting signal occurs only when the difference in the phase changes of the two signals being compared exceeds a given value. The correcting signal is compared with the receiver clock rate, and upon occurrence of the correcting signal, the clock interval before the timing pulse is shortened. Upon appearance of the correcting signal, after the timing pulse, the clock interval is lengthened. The clock initiates the comparison between the received carrier frequency pulse and the received carrier signal. When there is a difference between the phase of the carrier wave and the reference carrier wave, a phase correction is initiated in the reference carrier wave.

Spectrum of a Carrier Frequency Modulated by Poisson Pulse Train With Applications to Feedback Diversity

Abstract: Modeling the occurrence times as a Poisson process, the spectrum of a carrier frequency modulated by a random pulse train is studied. In general, the corresponding phase modulation is nonstationary, but the modulated carrier is shown to be wide-sense stationary, so that its RF spectrum can be obtained as the Fourier transform of its correlation function. Closed-form asymptotic results show that RF spectrum is proportional to ω-4if the frequency modulation is discontinuous, and as ω-6if it is continuous, where ω is the radian frequency measured from the carrier frequency. Numerically evaluated spectra are obtained for the particular case of a stationary tone-burst modulation, a form used in a proposed mobile-radio feedback diversity system. These results show that even for modulation indices as small as 0.5, the spectrum of the tone bursts themselves is not a good approximation to the RF spectrum. Finally, the spectral broadening caused by adding tone-burst modulation to a carrier already modulated by a flat-band Gaussian process is evaluated numerically. These results show that the modulation index of the bursts should be kept to unity or less in order to restrict the spectral broadening to 10 percent or less if the rms phase deviation of the Gaussian modulation is less than three radians.

FSK Spectra Generation

Abstract: : The results of a study of a phase locked modulation technique applicable to phase coherent FSK are presented. This technique employs a continuous phase, frequency shifted, phase locked loop to produce controlled, non-instantaneous, frequency transitions between the mark and space frequencies. Operational and spectral analyses have been conducted, and spectral data have been calculated for the modulated carrier signal and its corresponding effective modulating signal. It is shown that effective modulation wave-shaping can be achieved and that the corresponding signal bandwidths can be controlled within certain limits by variation of the loop parameters, undamped natural frequency and open loop gain. Representative data are presented, corresponding to a selected class of loop parameters, as a function of modulation index and the ratio of frequency transition time to bit length.