Showing papers on "Continuous phase modulation published in 1976"

An MSK Approach to Offset QASK

Abstract: This paper demonstrates that an offset quadrature amplitude-shift-keyed (OQASK) signal can be represented as an ncomponent version of a minimum-shift-keyed (MSK) signal. For example, the signal set obtained by summing two MSK signals which are 6 dB different in power and are formed by continuous phase, frequency modulating the same oscillator with two independent binary antipodal data streams, is spectrally equivalent to an OQASK signal set composed of 16 signals in which the symbol pulse is a half-cycle sinusoid rather, than the conventional rectangular form. Such generalizations as the above allow for potentially simpler implementation of spectrally shaped OQASK.

A generalization of MSK-type signaling based upon input data symbol pulse shaping

Abstract: Minimum-shift-keying (MSK), which is a special case of continuous phase frequency-shift-keying (CPFSK) with frequency deviation ratio equal to 0.5, is known to be spectrally equivalent to a form of offset quadrature phase-shift-keying (OQPSK) in which the symbol pulse shape is a half-cycle sinusoid rather than the usual rectangular form. Appropriate shaping of the input data symbols allows one to generate an entire class of constant envelope, MSK-type signals, whose spectral properties are in some applications more desirable than those of MSK or OQPSK. The present study derives and presents a set of conditions on the input pulse shaping which in turn describes the class of envelope shapes allowable. The autocorrelation function and power spectral density of this class of signals are then derived, and specific examples are given to illustrate the desirable spectral properties. Such properties are important considerations in system design where interchannel and intersymbol interference degradations must be kept to a minimum.

Multiple carrier modulation synthesis

Abstract: Two carriers are gated on and off in an alternating sequence. The same group of different digital sample point values signifying various modulation levels required for each carrier at successive points in time are read out in timed sequence and applied to modify each of the carrier waves by one sample point value during each period when a carrier wave is gated on to thus modify the carriers in a manner recognized by a receiver as modulation.

Circuit arrangement for the demodulation of a phase-modulated signal

Abstract: Apparatus for demodulating phase modulated signals is described. The latter signals are produced by modulation of a carrier or harmonically related carriers. The modulated signal, constituted by consecutive modulation sections, is coupled to an analogue multiplier, the output of which is connected to an integrator. The integrator produces the demodulated signal. A pulse generator produces a sequence of pulses, each of which occurs within a given modulation section. The duration of each pulse equals the reciprocal of the fundamental frequency. A carrier corresponding in frequency and synchronized with the transmitted carrier is produced in the receiver. The transmitted carrier and receiver-produced carrier are coupled to the multiplier. The latter carrier is switched prior to its application to the multiplier using the output of the pulse generator.

A bandwidth-compressive modulation system

Abstract: The phrase 'bandwidth-compressive modulation' means that the compression is achieved not by removing redundancy from the data (data compression), but rather by modulating the carrier phase and amplitude with blocks of data bits. The modulation described here is quadrature amplitude shift keying (QASK), a logical extension of quadrature phase shift keying, (QPSK, or quadriphase). QASK is a cost-effective form of combined phase-and-amplitude modulation. That is, n-bit QASK, like most phase-amplitude forms of modulation, requires considerably less transmitter power than comparably performing n-PSK, while among the class of all n-bit phase-modulation types, n-bit QASK performs nearly optimally but requires the least circuit complexity. A simple, unique microwave transmitter is described which provides high-rate QASK modulation with 4:1 bandwidth compression. A suppressed carrier multiple-loop QASK receiver provides the necessary phase tracking, automatic gain control (AGC), and symbol timing.

Phase Effects in Cross-Modulation

Abstract: CATV amplifiers can convert amplitude cross-modulation into phase cross-modulation. It has been generally assumed that this is desirable. A theory is developed and checked experimentally that shows that the fm deviations caused by the phase shifts are visible in television receivers. If the phase shift exhibits a rise time of about 100 ns or less, phase cross-modulation and amplitude cross-modulation are equally visible if the sidebands of the two modulation processes are equal for a 15 kHz squarewave. The visibility of the phase cross-modulation is rise-time dependent, showing a 12 dB decrease in visibility as the rise time is lengthened to about 300 ns.