Showing papers on "QAM published in 1979"

A Comparison of Modulation Techniques for Digital Radio

Abstract: This paper describes and summarizes the characteristics of the modulation techniques most applicable to digital radio. The modulation techniques discussed are on-off-keying (OOK) with coherent and noncoherent detection, quadrature amplitude modulation (QAM), quadrature partial response (QPR), frequency-shift-keying (FSK) with noncoherent detection, continuous phase FSK (CP-FSK) with coherent and noncoherent detection, minimum-shift-keying (MSK), binary and quaternary phase-shift-keying (BPSK, QPSK) with coherent and differentially coherent detection, offset-keyed QPSK (OK-QPSK), M -ary PSK with coherent detection ( M = 8, 16 ), and 16-ary amplitude and phase-shift-keying (APK). Functional descriptions of these schemes are provided and their performance is compared in a series of tables summarizing the results of the literature of the past 20 years. The modulation schemes are compared with respect to ideal (white Gaussian noise) performance, spectral properties, signaling speed, complexity, and the effects on performance of interference, fading and delay distortion.

Phase-jitter compensation using periodic harmonically related components

Abstract: A quadrature amplitude-modulated (QAM) data signal receiver employs a phase compensation arrangement (16, 31, 33) before the equalizer (17). The arrangement utilizes the assumption that the frequency components typically present in the phase perturbance are power-line related. This enables an effective phase compensator to be of relatively low complexity compared to the equalizer (17). Since the compensator is "pretuned", only the phase and amplitude of the frequency components need be adaptively found. This makes for a relatively stable arrangement with a suitable convergence rate. In an alternative arrangement, a phase compensator (216, 233, 240) is provided for use after the equalizer (217).

The Effect of Selective Fading on Digital Radio

Abstract: In the course of development of the DRS-8 Digital Radio System a series of digital propagation trials were conducted over a 51 km path at 8 GHz to determine the effect of multipath propagation on a 40 MHz bandwidth digital radio system. It was found that the effects of frequency selective fading result in unacceptably high system unavailability unless adaptive equalization and space diversity are employed. Specifically the results are: 1) Multipath induced outage is much higher than would be predicted from the measured flat fade margin of the equipment. For a nondiversity system, the probability of outage for a single hop in the worst fading month is approximately 1 \times 10^{-3} . This is 700 times the objective for a long haul system and corresponds to an effective fade margin of only 27 dB. 2) The primary cause of outage is inband distortion caused by the frequency selectivity of the multipath fading process. 3) Phase adaptive space diversity combining is very effective in reducing the amount of fading. In addition it affords some increase in the effective fade margin of the radio, i.e., it reduces the severity of inband distortion for a given fade depth. Outage for the System with space diversity combining was 2.6 \times 10^{-4} which is about 18 times the long haul objective. 4) A simple adaptive linear amplitude equalizer in conjunction with the phase adaptive space diversity combining provides an additional improvement of approximately a factor of 20, reducing the multipath outage to levels compatible with long haul availability objectives. 5) This same equalizer when applied to a non-diversity channel provides an improvement of about 2. Thus the preconditioning effect of phase adaptive space diversity combining is necessary to reduce distortions sufficiently that they can be dealt with by a relatively simple adaptive equalizer. These results apply to wideband digital radio which operates over long hops using a two dimensional modulation system such as QAM or multiphase PSK.

Method and arrangement for initiating an adaptive equalizer starting from an unknown data signal in a transmission system utilizing quadrature amplitude modulation

Abstract: Dans le recepteur d'un systeme utilisant une modulation d'amplitude en quadrature (QAM) dans lequel en fonctionnement normal les donnees sont detectees par rapport a une premiere constellation A, on initialise l'egaliseur en detectant les donnees par rapport a une seconde constellation B ayant un nombre de point inferieur a celui de la premiere constellation et en ajustant les coefficients de l'egaliseur a partir d'un signal d'erreur obtenu a partir de cette operation de detection. In the receiver of a system using a quadrature amplitude modulation (QAM) wherein in normal operation the data is detected with respect to a first constellation A, initializing the equalizer in detecting the data relative to a second constellation B having a number of lower point than the first constellation and adjusting the coefficients of the equalizer from an error signal obtained from this detecting operation. Application aux systemes de transmission QAM en reseau multipoint. Application to QAM transmission systems multipoint network.

Digital processing type transmitter for quadrature multiple signal

Abstract: PURPOSE:To convert digitally a plural number of complex base-band signals PAM into quadrature multiple QAM signals by generating quadrature multiple signals QAM through a digital processing, by using a Fourier conversion technique which reduces the number of multiplier circuits for an unit time.