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Showing papers on "Quadrature amplitude modulation published in 1971"


Journal ArticleDOI
TL;DR: The constraints of digital satellite communications systems have led to the derivation of a method for resolving the problem of recovered-carrier phase ambiguity in a coherent fourphase phase-shift-keying communications system while simultaneously providing synchronization information.
Abstract: The constraints of digital satellite communications systems have led to the derivation of a method for resolving the problem of recovered-carrier phase ambiguity in a coherent fourphase phase-shift-keying (PSK) communications system while simultaneously providing synchronization information. This method is described for the general case and a general implementation is given. In addition, implementations are given for two particularly simple special cases.

26 citations


Patent
08 Nov 1971
TL;DR: In this article, digital sample point values signifying various modulation levels required at successive points in time are stored in a digital memory and read out in timed sequence and applied to modify a carrier wave in a manner such as to be recognized as modulation by a receiver.
Abstract: Digital sample point values signifying various modulation levels required at successive points in time are stored in a digital memory and read out in timed sequence and applied to modify a carrier wave in a manner such as to be recognized as modulation by a receiver.

11 citations


Journal ArticleDOI
TL;DR: In the presence of impulsive noise, DPSK systems have, for the same SNR, an error rate which is nearly twice the error rate obtained for PSK, so that a considerable improvement in SNR is required to improve performance.
Abstract: A method previously presented by the authors for the evaluation of error probabilities in digital systems when impulsive noise is the main cause of incorrect decisions is here applied to differential phase-shift keying (DPSK) modems. Specifically, the receiver impulsive characteristic, which is proportional to the error rate, is evaluated for binary DPSK systems both in the linear and hard-limited modes of operation. Two encoding systems are considered, in-phase encoding and quadrature encoding, and it is shown that they yield essentially the same performance, at least when the binary symbols are equally likely. The results are compared with the performance of phase-shift keying (PSK) and it is found that, in the presence of impulsive noise, DPSK systems have, for the same SNR, an error rate which is nearly twice the error rate obtained for PSK. However, the dependence of error rate on SNR is generally a slowly decreasing function so that a considerable improvement in SNR is required to improve performance.

10 citations


Patent
D Toman1
15 Nov 1971
TL;DR: In this paper, digital sample point values signifying various modulation levels required at successive points in time are stored in a digital memory and read out in timed sequence and applied to modify a carrier wave in a manner such as to be recognized as modulation by a receiver.
Abstract: Digital sample point values signifying various modulation levels required at successive points in time are stored in a digital memory and read out in timed sequence and applied to modify a carrier wave in a manner such as to be recognized as modulation by a receiver.

7 citations


Journal ArticleDOI
W. Hubbard1
TL;DR: The derivation of a rigorous (and tight) upper bound on the probability of error in a binary pulse-code modulation (PCM) twin channel optical receiver in the absence of thermal noise is sketches.
Abstract: In this concise paper we sketch the derivation of a rigorous (and tight) upper bound on the probability of error in a binary pulse-code modulation (PCM) twin channel optical receiver in the absence of thermal noise. This result is valid for any binary system, described by Poisson statistics in each of its states, in which the binary decision is based on which state has the larger count. Examples of such systems include polarization modulation, binary pulse position modulation, frequency-shift keying with separate detectors, and differentially-coherent phase-shift keying.

6 citations


01 Dec 1971
TL;DR: In this article, the use of linear-maximal shift register sequences either to amplitude modulate (AM) or to angle modulate a sinusoidal carrier was described, and it was shown that the ratio of the average power to the peak power for AM is only one-half as large as for either BM or CM.
Abstract: : The report describes the use of linear-maximal shift-register sequences either to amplitude modulate (AM) or to angle modulate a sinusoidal carrier. Two cases of angle modulation are considered: biphase modulation (BM) and complement-phase modulation (CM). In biphase modulation the carrier angle switches between (+ pi/2) and (- pi/2), whereas in complement-phase modulation the carrier angle switches between (+ pi/4) and (- pi/4). It is shown that the ratio of the average power to the peak power for AM is only one-half as large as for either BM or CM. On the other hand, the ratio of the carrier power to the average power for either AM or CM is one-half, but for BM this ratio is approximately zero. Finally, a replica-correlation technique for use with any of the three modulations is described.

6 citations


Patent
19 Feb 1971
TL;DR: In this article, the interference caused by amplitude modulation of the input signal is compensated by using a circuit which converts amplitude modulation into phase modulation corresponding to the interfering phase modulation, and then the circuit is used to convert the amplitude modulation to phase modulation.
Abstract: Interfering phase modulation of the current passage through an FM- quadrature demodulator as a result of amplitude modulation of the input signal is compensated by using a circuit which converts amplitude modulation of the input signal into phase modulation corresponding to the interfering phase modulation.

4 citations


Patent
03 Sep 1971
TL;DR: In this article, a 30 Hz variable phase test signal and a 9960 Hz subcarrier reference phase signal are applied to an amplitude modulation means with the modulation means acting on the frequency modulated subcarriers alone and selectively introducing controlled amplitude modulation levels of predetermined amplitude modulation components as exist in VOR transmission.
Abstract: Amplitude modulation techniques are applied to a 9960 Hz subcarrier signal of the type defined by VOR navigation systems by means separately applying a 30 Hz variable phase test signal and a 9960 Hz subcarrier reference phase signal to an amplitude modulation means with the modulation means acting on the 9960 Hz frequency modulated subcarrier alone and selectively introducing controlled amplitude modulation levels of predetermined amplitude modulation components as exist in VOR transmission, with subsequent recombination with the 30 Hz variable phase signal to provide a selectively controlled composite modulation signal comprising a 30 Hz variable phase signal and a 9960 Hz frequency modulated reference subcarrier, the latter signal being amplitude modulated at selected modulation levels with predetermined amplitude modulation frequency components.

2 citations


Patent
07 Dec 1971

1 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that when comparing the two systems on the basis of equal relative sideband power, the bandwidth of SSB angle modulation is always less than conventional angle modulation.
Abstract: It is noted that the essential results published by Mazo and Salz were previously disclosed and obtained using simple and direct Fourier transform computer techniques. When comparing the rms bandwidth of this system with the analogous double-sideband spectrum on the basis of equal modulating signal strength in the two systems, the bandwidth crossover point is actually lower than the value stated by Mazo and Salz. However, when comparing the two systems on the basis of equal relative sideband power, the bandwidth of SSB angle modulation is always less than conventional angle modulation.

Journal ArticleDOI
TL;DR: In this article, the problem of crosstalk transferred to the PM carrier from a single subcarrier which is biphase modulated with pulse-code modulation (PCM) data is studied.
Abstract: Under the unified carrier concept several anglemodulated subcarriers are combined and PM on an RF carrier. As a practical matter in a hardware system the angle-modulated subcarriers will contain a certain amount of amplitude ripple. Conceptually, a subcarrier with AM ripple can be viewed as a constant envelope subcarrier with a continuously varying modulation index. It follows that a continuous transfer of AM between the components in the unified carrier spectrum will occur due to the varying envelope (modulation index) of any data subcarrier. This paper discusses in some detail the problem of crosstalk transferred to the PM carrier from a single subcarrier which is biphase modulated with pulse-code modulation (PCM) data. The implications to carrier false lock and tracking are studied. Analytic and experimental results are presented.