Showing papers on "Quadrature amplitude modulation published in 1973"

On the selection of a two-dimensional signal constellation in the presence of phase jitter and Gaussian noise

Abstract: A long-standing communications problem is the efficient coding of a block of binary data into a pair of in-phase and quadrature components. This modulation technique may be regarded as the placing of a discrete number of signal points in two dimensions. Quadrature amplitude modulation (QAM) and combined amplitude and phase modulation (AM-PM) are two familiar examples of this signaling format. Subject to a peak or average power constraint, the selection of the signal coordinates is done so as to minimize the probability of error. In the design of high-speed data communication systems this problem becomes one of great practical significance since the dense packing of signal points reduces the margin against Gaussian noise. Phase jitter, which tends to perturb the angular location of the transmitted signal point, further degrades the error rate. Previous investigations have considered the signal evaluation and design problem in the presence of Gaussian noise alone and within the framework of a particular structure, such as conventional amplitude and phase modulation. We present techniques to evaluate and optimize the choice of a signal constellation in the presence of both Gaussian noise and carrier phase jitter. The performance of a number of currently used or proposed signal constellations are compared. The evaluation and the optimization are based upon a perturbation analysis of the probability density of the received signal given the transmitted signal. Laplace's asymptotic formula is used for the evaluation. Discretizing the signal space reduces the optimal signal design problem under a peak power constraint to a tractable mathematical programming problem. Our results indicate that in Gaussian noise alone an improvement in signal-to-noise ratio of as much as 2 dB may be realized by using quadrature amplitude modulation instead of conventional amplitude and phase modulation. New modulation formats are proposed which perform very well in Gaussian noise and additionally are quite insensitive to moderate amounts of phase jitter.

Decision feedback loop for tracking a polyphase modulated carrier

Abstract: A multiple phase modulated carrier tracking loop for use in a frequency shift keying system is disclosed in which carrier tracking efficiency is improved by making use of the decision signals made on the data phase transmitted in each T-second interval. The decision signal is used to produce a pair of decision-feedback quadrature signals for enhancing the loop's performance in developing a loop phase error signal.

The Properties of Phase Modulated Soliton Trains

Abstract: Using nonlinear LC networks which are equivalent to a one dimensional nonlinear lattice, the solitariness and the recurrence phenomena are experimentally investigated for a pair of soliton trains of which the phases are independently modulated. Using a phase modulation system, up to 30% modulation is obtained. This modulation ratio is about 3 time larger than that for an amplitude modulation system.

A comparison of modulation schemes for binary data transmission

Abstract: The relationships between bit error probability and transmitter power are presented on a common basis for various binary and m-ary modulation schemes operating with the same system data rate. it is assumed that the channel is disturbed by additive white gaussian noise of fixed power spectral density and that optimal matched filter reception is used. the results presented allow a comparison of the efficiencies of the systems in the use of transmitter power to provide a specified bit error probability. the theoretical bandwidth requirements of each system have been considered. sometimes the system designer is constrained to the use of an existing channel of fixed bandwidth and signal/noise ratio. the choice of modulation system under these conditions has also been indicated.

A UHF mobile telephone system using digital modulation: Preliminary study

Abstract: A UHF mobile telephone system using digital modulation is described. The system uses on-off keying of an 836-MHz carrier, the code being supplied by an adaptive delta coder with a clock frequency of 50 kHz. The maximum audio baseband signal-to-noise ratio is approximately 30 dB. The mobile receiver employs space diversity in a maximal-ratio combiner. Due to the use of amplitude modulation of the carrier rather than exponential modulation, the diversity receiver is very simple. The system was tested in the laboratory and in the field. Field tests were made in suburban and urban areas. For the four-branch system, threshold occurred at an average IF signal-to-noise ratio of approximately 12 dB.

A review of multiple amplitude-phase digital signals

Abstract: This paper reviews the data rate, error rate, and signal-to-noise ratio relationship for various uncoded M-ary digital amplitude modulation (AM), phase modulation (PM), and combined AM-PM systems. These signal systems have the common virtue that expanding the number of possible signals to be transmitted increases the data rate but not the bandwidth. A general treatment of the error rate of M-ary digital AM-PM permits development of a simple yet accurate expression which approximates the increase in average signal-to-noise ratio (over that of binary phase shift keying) required for constant error performance. This equation provides insight into why arrays differ in their signal-to-noise ratio requirements.

Holographic visualization of large amplitude vibration using reference beam phase modulation

Abstract: A method of increasing the amplitude range of time averaged holography by a factor of between 5 and 50 is described. This technique uses the principle of reference beam phase modulation to freeze any chosen vibrational amplitude with respect to the hologram, resulting in a bright up effect on this fringe. By multiplexing the hologram at various degrees of phase modulation a series of bright amplitude contours are generated on the holographic image, enabling large vibrational amplitudes to be observed. The integrated exposure time of the multiplex holograms is equal to that of time averaged holography since phase modulation, as opposed to amplitude modulation, permits the full utilization of the available light.

Optimum Deviation Ratio and Observation Interval for Continuous-Phase Binary Frequency-Shift Keying

Abstract: The optimum deviation ratio ( h =1/2 ) and observation interval (2-b periods) for a continuous-phase binary frequency-shift keying (CPBFSK) signal have been determined analytically for particular length sequences based on a squared-distance criterion.

Relative sideband amplitudes versus modulation index for common functions using frequency and phase modulation

Abstract: The equations defining the amplitude of sidebands resulting from either frequency modulation or phase modulation by either square wave, sine wave, sawtooth or triangular modulating functions are presented. Spectral photographs and computer generated tables of modulation index vs. relative sideband amplitudes are also included.

The Power Spectrum of PCM/FSK-AM/PM

Abstract: This paper derives the power spectrum of a modulating scheme under consideration by NASA for commanding scientific satellites. In this scheme the commands are frequency-shift keyed onto a subcarrier, then the clock is amplitude modulated onto the resultant. This PCM/FSK-AM waveform is then phase modulated onto a prime carrier. The method used in the paper can be easily extended to derive the spectrums of alternate command waveforms, such as PCM/FSK-AM/ FM, PCM/PSK-AM/PM, etc.

Analysis of radio paging errors in multitransmitter mobile systems

Abstract: Many mobile telephone and personal paging systems require signaling simultaneously from multiple transmitters. This paper analyzes the factors that cause paging errors due to interference when the signaling format consists of audio tones sent simultaneously from two FM transmitters. The factors considered are: drift in carrier and modulation frequencies, and misequalization of land-line amplitude and audio delay. The following results are shown: 1) the interference errors are eliminated if the land lines are amplitude and phase equalized, 2)if the lines are not equalized but the modulation frequencies are equal, then the interference errors can be decreased by an order of magnitude if the transmitters are mistuned such that their difference carrier frequency is just greater than the modulation tone filter bandwidth in the receiver, and 3) if the modulation frequencies are slightly different, then the interference errors can be decreased somewhat by misequalizing the modulation indicies. It is then concluded that if the land lines are not equalized and the signaling tones are not exactly equal, the interference errors cannot be eliminated, but can be decreased by properly aligning the system.

Modulation Waveform Study.

Abstract: : TRANSMISSION SYSTEMS, MODULATION), (*RADIO RELAY SYSTEMS, *MODULATION), ELECTRONIC COUNTER COUNTERMEASURES, DIGITAL SYSTEMS, MULTIPLE OPERATION, DETECTORS, MULTIPLEXING, FREQUENCY MODULATIONTIME DIVISION MULTIPLEXINGThe Modulation Waveform Study is addressed to the determination of the optimum spread-spectrum modulation technique for use in a ground sensor-to-airborne relay communications link. The study is conducted under a set of guidelines concerning digital message error rates, message structure, communication link distance, frequency, multiple access capability (i.e., self-interference) and processing gain against intentional jamming. Pseudonoise, time hop, frequency hop, and hybrid modulation techniques are examined and only two are found to be suitable for satisfying the study guideline: frequency hop and time hop/pseudonoise. (Author)

The choice of data transmission system for efficient use of transmitter power

Abstract: The relationship between system error probability and transmitter power is investigated for block and convolutional codes operating in conjunction with binary phase-reversal keying. The following assumptions are made: (i) all systems accept the same data rate, (ii) a very large bandwidth expansion is not acceptable, (iii) the channel is disturbed by white Gaussian noise, (iv) a matched filter receiver is used.The performances of these coded systems are compared with those of optimal binary and M-ary modulation schemes to give an indication of the systems to be considered in order to achieve efficient use of transmitter power for given system bit error probabilities.

An operator treatment of modulated carriers

Abstract: An operator treatment of modulated carriers in linear, time-invariant, nongenerative networks is given. The modulation is split up into an in-phase and a quadrature component. An operator (jω 0 + λ) is introduced, ω 0 /2π being the carrier frequency and λ the operator d/dt acting on the modulation only.

FSK Bit Synchronization by Combined AM

Abstract: A bit-synchronization method in a frequency-shift-keying (FSK) data channel has been investigated experimentally and results are presented. The bit-timing information is conveyed by a square wave, with a frequency of half the data bit rate, modulated onto the signal amplitude. It has been shown that for a system using a peak-peak-to-peak frequency deviation of 0.7 times the bit rate and a receiver bandwidth restricted to 1 times the bit rate, the minimum error rates are obtained for an amplitude modulation index of 0.1. Further, in order for the system to have a performance comparable with an ordinary FSK system with the same values of frequency deviation and receiver predetection bandwidth and with perfect timing available at the receiver, an additional signal power of 0.9 dB is needed.

An Evaluation of Modulation Systems

Abstract: : The report summarizes the results of a theoretical and experimental study of the relative strengths and weaknesses of amplitude shift keying, phase shift keying and quadriphase shift keying systems. The report is a combination review report and research monograph. Ideal theoretical results are discussed, and methods of practical realization are described. New research results include the determination of the standard deviation of the arrival time as a function of modulation, simple formulas for the degradation in both digital and analog systems due to adjacent-channel interference, and simple upper bounds for intersymbol interferences. The use of the formulas are all examined experimentally.

A mobile-radio space-diversity receiving system using delta modulation with a "STAR" type cophasing scheme

Abstract: A multiple branch predetection combining diversity receiver technique using pulse-envelope modulation of the transmitted signal is described The receiver branches use the "STAR" scheme of multiple heterodyning of the received signal with itself to eliminate all exponential modulation components imparted by the transmission medium Each branch can be shown to be mathematically equivalent to a simple square-law detector A modulation scheme using low-bit-rate (50 kHz) companded delta modulation is proposed which provides a reasonable output signal-to-noise ratio (30-40 dB) The convenience of received signal gain control before pulse regeneration and the possible application of conjugate phase retransmission could make this technique useful

Effect of Quadrature and Demodulation Phase Errors in a Quadrature PSK System

Abstract: Quadrature and demodulation phase errors in a quadrature PSK system cause crosstalk between channels. It is shown that the tracking loop signal-to-noise ratio must be at least 5 dB greater than for PSK to give the same performance.