Showing papers on "Continuous phase modulation published in 1977"

Differential encoding and decoding scheme for digital transmission systems

Abstract: Digital transmission systems operating over microwave radio generally employ phase modulation rather than amplitude modulation because phase modulation is less sensitive to non-linearities in the transmitter. Coherent demodulation is typically employed in the receiver to ensure maximum immunity to the thermal noise of the radio receiver. This, in turn, requires that the receiver include circuitry to recover an unmodulated carrier from the incoming digital signal for use as a phase reference in the demodulation process. Unfortunately, the phase of the recovered carrier is subject to ambiguities which may result in the demodulated digital signal being transposed and/or inverted, resulting in gross transmission errors. Differential encoding of the digital signal, prior to modulation, overcomes this problem but may create additional problems, such as the inability of the receiver to monitor transmission errors by means of the parity bits which are included in the digital signal to be transmitted. The instant invention comprises an encoding algorithm which encodes the digital signal prior to modulation so that phase ambiguities in the recovered carrier signal become unimportant, yet at the same time preserves the ability of the receiver to check for transmission errors. The algorithm comprises two separate but complementary encoding rules, one of which is employed if the last three outputs of the encoder are logical equivalents and the other if they are not. A similar decoding algorithm is employed at the receiver.

Phase lock loop carrier generator for receiver of phase modulated carrier pulse signals

Abstract: Demodulator for phase modulated carrier pulse signals or phase codes in which the pulses are coded according to a plurality of N phases of the carrier. It comprises a digital phase lock loop system for locking to a frequency equal to N times the carrier frequency which includes at least a two input phase detector, a loop integrator and a voltage controlled oscillator having an output connected to the first input of the phase detector, means for dividing by N the frequency of this oscillator and for generating a reference carrier signal. The phase codes are decoded by comparing the phases of the carrier of the phase codes to the phase of the reference signal. In order to derive from all the phase codes a train of synchronous pulses a multiphase shifter receives the carrier of the phase codes and locally generates a plurality of carriers having phase shifts equal to 0, 2π/N, 2×2π/N, . . . ([N/2]- 1) ×2π/N with respect to the carrier of the received phase code and means are provided for generating passing through zero pulses coinciding with the passage through zero of said received and locally generated carriers. Those of said passing through zero pulses which occur during the central part of each phase modulated carrier pulse are gated through gating means. These gated passing through zero pulses are applied to the second input of the phase detector.

Frequency-agile fire control radar system

Abstract: A signal processing system for simultaneously transmitting a plurality of rrier frequencies and receiving certain of said frequencies to the exclusion of others. In a radar system employing the disclosed technique, a CW carrier and pulsed modulated carrier are transmitted simultaneously from a single antenna. The CW carrier and the echo frequency from the modulated carrier are received by a receiver protector circuit which passes the low power echo of the pulse modulated carrier to receiver processing circuitry while suppressing the CW carrier having a power level above a predetermined threshold. The receiver protector enables the use of plural carrier frequencies in a frequency agile system with decreased frequency separation.

Frequency-and Amplitude-Dependent Phase Effects In Television Broadcast Systems

Abstract: The television broadcast system in this paper is defined as those elements between and including the modulation process at the transmitter and the demodulation process at the receiver. The effects to be considered include: 1. Time-domain distortion due to departure from linear phase vs frequency (and from flat amplitude response vs frequency). 2. Non-linear distortion (with envelope demodulation) due to the quadrature-phase signal component resulting from vestigial sideband asymmetry. 3. Differential phase and other distortions due to incidental phase modulation of the visual carrier. 4. Intercarrier noise due to visual carrier incidental phase or frequency modulation.

Carrier control system for suppressed carrier modulators

Abstract: A suppressed carrier radio signaling system is described in which there is a servo loop utilizing balanced circuit techniques and using the carrier as the reference, in which a phase detector (or coherent demodulator) constantly senses the phase difference between the carrier source and the carrier component in the output signal to derive an error signal which is used to vary the amount of the carrier component toward zero.

Effect of emphasis on threshold in angle modulation systems

Abstract: Emphasis can be used in angle modulation systems (frequency and phase modulation) to improve receiver output signal-to-noise ratio (SNR). It is shown that the threshold input SNR increases when emphasis is used. The increase may be well over one decibel, depending on system parameters, when the message is Gaussian and random.