Showing papers on "Quadrature amplitude modulation published in 1979"

Minimum shift keying: A spectrally efficient modulation

Abstract: The ever increasing demand for digital transmission channels, in the radio frequency (RF) band presents a potentially serious problem of spectral congestion and is likely to cause severe adjacent and cochannel interference problems. This has, in recent years, led to the investigation of a wide variety of techniques for solving the problem of spectral congestion. Some solutions to this problem include: 1) new allocations at high frequencies; 2) better management of existing allocations; 3) the use of frequency-reuse techniques such as the use of narrow-beam antennas and dual polarizing systems; 4) the use of efficient source encoding techniques; and 5) the use of spectrally efficient modulation techniques [l]. This article will consider the last approach and analyze, in particular, a modulation scheme known as minimum shift keying (MSK). The MSK signal format will be explained and its relation to other schemes such as quadrature phase shift keying (QPSK), offset QPSK (OQPSK), and frequency shift keying (FSK) pointed out. The main attributes of MSK, such as constant envelope, spectral efficiency, error rate performance of binary PSK, and self-synchronizing capability will all be explained on the basis of the modulation format.

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.

Amplitude and frequency modulators using a switchable component controlled by data signals

Abstract: A modulated signal source derives its modulation information from digital data held in a data store. The digital data is arranged to operate a switch which in the case of amplitude modulation produces pulses of carrier frequency and in the case of frequency modulation introduces phase transitions into a carrier frequency. The use of the digital data and the switch enables the modulation characteristics of the signal source to be exactly predictable and reproducible and it is not degraded by non-linearities of the kind introduced by conventional mixers.

Method and device for training an adaptive equalizer by means of an unknown data signal in a quadrature amplitude modulation transmission system

Abstract: A method and a device for training the equalizer of a receiver used in a QAM transmission system, by means of an unknown data signal, thereby enabling in particular said equalizer to be trained in the cases described above. In accordance with the method of the present invention, in a data receiver wherein, under normal operating conditions, the data is detected with respect to a first constellation, the equalizer is trained by detecting the data with respect to a second constellation which comprises fewer points than said first constellation and by adjusting the coefficients of the equalizer by means of an error signal produced as a result of the detection operation performed with respect to the second constellation. In accordance with a first embodiment of the present invention, the second constellation is comprised of those points of the first constellation that are farthest from its center. In accordance with a second embodiment of the invention, the points of the second constellation are obtained as follows: the first constellation is divided into L sets of points Sl, l=1, 2, . . . , L and a point bl of the second constellation is associated with each set Sl in accordance with the relation ##EQU1## where the ak 's are those points of the first constellation that belong to the set Sl.

System for the quantitative measurement of impairments in the communication channel of a quadrature amplitude modulation data communication system

Abstract: A system is provided for measuring communication channel impairments in a data transmitting system which employs quadrature amplitude modulation. The system rotates each point of sampled eye diagram information by a phase angle determined by the ideal value of the received point information so that the rotated point has its nominally maximum component on the real axis.

Receiving circuit in an interference-suppressing communications system comprising narrow-band conventional message modulation and additional pseudo-noise phase shift keying

Abstract: A receiving circuit for an interference-suppressing communications system having a narrow-band conventional message modulation and additional pseudo-noise phase shift keying (PN-PSK), has a pseudo-random generator whose pseudo-random sequence is identical to the pseudo-random sequence provided by the system transmitter. The pseudo-random generator actuates a phase-shift keying element to cancel the phase shift modulation produced at the transmitter. A matched filter or correlation network for correlation of the pseudo-random sequence at the receiver with the pseudo-random sequence contained in the received signal is provided. The message modulation impairs the function of the matched filter or the correlation network. The degrading influence of message modulation is to be eliminated, at least, reduced. To this end, a demodulation circuit is provided which receives the entire received signal and the signal present after removal of the phase-shift keying to provide an input for the matched filter or correlation network. This signal only exhibits the pseudo-noise phase-shift keying contained in the received signal, but no longer has the message modulation.

Characteristics of a High Capacity 16 QAM Digital Radio System in Multipath Fading

Abstract: Multipath fading effects on a 200 Mbit/s 16 QAM digital radio system have been experimentally investigated. It was found that the outage probability can be accurately estimated using only the in-band frequency response without knowledge of the delay difference between two incident waves. New methods to evaluate the improvement factors for both space diversity reception and dynamic equalizing, which are required to combat multipath fading effects, were also proposed. In particular, the significance of noticing the delay dispersion sign was pointed out when attaining sufficient equalization effect. The validity of these evaluations was confirmed by simulation experiments and a field trial.

Design and Performances of a 200 Mbit/s 16 QAM Digital Radio System

Abstract: A novel long haul 5 GHz 16 QAM digital radio system, which has 200 Mbit/s transmission capacity within the 40 MHz interleaved channel allocation, is proposed and described. It is designed to be overbuilt on existing FDM-FM routes with an approximately 50 km repeater spacing. To achieve the 5 bit/s/Hz RF spectral efficiency, the 16 QAM modulation and Nyquist cosine roll-off spectral shaping techniques ( \alpha = 0.5 ) are investigated. Then a new signal shaping filter, differential encoding and carrier recovery techniques are presented. Finally, the effects of TWT amplifier nonlinearity on a 16 QAM signal are experimentally investigated.

16 QAM Modulation for High Capacity Digital Radio System

Abstract: A computational method allowing the calculation of bit error rate in the presence of filtering and some other impairments is described for 16 QAM modulation; a breadboard working at a bit rate of 140 Mbits/s has been implemented and experimental results are compared with calculated values. The possible use of this modulation type for a high capacity digital radio-relay system is considered. Some parameters are introduced for this purpose, especially the net fade margin parameter. In the case of the 140 Mbit/s system in the 10.7-11.7 GHz frequency band, 4 PSK and 8 PSK modulation types are compared with 16 QAM. System gain, frequency arrangement, nodal capacity and outage performances are evaluated.

Method and apparatus for quadriphase-shift-key and linear phase modulation

Abstract: A submultiple (30Fl) of an S-band transmitter output frequency (240Fl) is divided equally between a linear phase modulation branch and a QPSK modulation branch. The linear modulation branch includes a multiplier (X7) to increase the carrier frequency to a level (210Fl) which, when combined with the carrier in the QPSK branch in an up-converter (utilizing a mixer at the input thereof followed by a bandpass filter), produces the transmitter output frequency. This allows the QPSK modulator to operate at one-eighth of the output frequency where repeatable and precisely controlled modulation can be easily achieved. This also allows linear phase modulation at one-eighth the output frequency where low modulator deviation and good linearity can be easily maintained.

A Class of MSK Baseband Pulse Formats with Sharp Spectral Roll-Off

Abstract: Minimum frequency-shift-keying (MSK) is a very attractive modulation technique because of its spectral properties and the constant envelope property of the signal, but out-of-band energy spillover must sometimes be minimized to control co-channel interference. This problem has recently received attention in published articles and, since the pulse shape is the main parameter, many different MSK pulse formats have been described. In this note, a general shaping function, which allows various asymptotic spectral fall-off characteristics, is presented; then DSFSK (Double Sine Frequency Shift Keying) is derived from it, and its spectrum is computed, analyzed and compared with Rabzel's results.

Modulation strategies of three phase PWM inverters: Analysis and comparative study

Abstract: Presents a systematic study and analysis of the various modulation strategies for three phase pulse width modulated (PWM) inverters. Analytical expressions are derived to obtain harmonic components of output voltages for duty ratio, sine, triangular and step modulation. A comparative study of the merits and demerits of the various modulation technique is presented. The effects of ratios of carrier and reference frequencies, and the instant of synchronisation are investigated. Use of a particular modulation strategy for a particular application is discussed.

Digital Radio Receiver Responses for Combating Frequency-Selective Fading

Abstract: Frequency-selective fading in a radio channel, caused by multipath propagation or any other phenomenon, can seriously degrade the effectiveness of digital transmission. Receiver processing that adapts in an appropriate way to the prevailing channel response can strongly reduce the harmful effects of such fading. We examine here the theoretical possibilities of adaptive processing by deriving and analyzing receiver responses for three different criteria. The criteria used permit an analytical approach that is simple and exact. The performance characteristics derived for the three receivers bracket the "best" performance that is possible in practice and reveal possible tradeoffs between performance and practicality. The analysis applies generally to the broad class of quadrature amplitude modulation (QAM) signals, which are assumed to be filtered in the transmitter to enforce spectral emission requirements. For each receiver response we derive a formula for the "power penalty", defined as the increase in transmitter power (over some theoretical minimum) needed to compensate for transmit filtering and channel fading. The power penalty formulas are evaluated for a two-ray multipath fading channel and for each of two common forms of modulation/transmit filtering. Graphical results are given for numerous combinations of the multipath parameters and the transmitter bandwidth-to-symbol rate ratio. The results of this study can be used to predict the probability (time fraction) of multipath outage, provided that the statistics of the channel parameters are known. Some cursory comparisons are made between the new results and those of a previous analysis for fixed receivers. The outage reductions made possible by using appropriate receiver responses are found to be quite large, possibly two or more orders of magnitude.

Modulation distortion reducer

Abstract: A double-sideband amplitude modulated (DSBAM) carrier passed through band-pass circuits wich are too narrow for the modulated carrier or are misaligned, may have one or both side-bands altered in relative amplitude, or in phase relative to the carrier. These effects result in amplitude modulation distortion and produce angle modulation of the carrier, with the same waveform as the amplitude distortion. In this invention the angle modulation is detected and applied to an amplitude modulator in the required phase and amplitude to substantially eliminate the distortion of the modulated carrier.

Compatible AM stereo system employing a modified quadrature modulation scheme

Abstract: A compatible AM stereo system including a modified quadrature modulation scheme. Two stereo modulators are described which each generate composite modulated signals including a carrier component and two phase-shifted components. The two phase-shifted components, corresponding to the left (L) and right (R) source signals, are phase shifted by equal phase angles θ on either side of the carrier, where θ is between 10° and 20°. A limiter is included which operates to limit the magnitude of the source signals supplied by the stereo modulator. The limiter allows each source signal to contribute up to 80% of the total modulation, as long as total modulation constraints are not exceeded due to the combined amplitudes of the two source signals. A receiver is described for demodulating the composite modulated signal.

Efficient Pulse Shaping Using MSK or PSK Modulation

Abstract: The increasing requirement for high data rate, bandwidth efficient digital radio systems has led to the development of MSK-type modulation methods designed to achieve a compact signal spectrum. These modulation methods include sinusoidal frequency shift keying (SFSK), special MSK-type pulse shapes, and multiamplitude minimum shift keying (MAMSK). When more compact signal spectra are required, bandlimited filtering must be introduced. This note considers the use of conventional MSK or PSK modulators followed by newly developed bandlimited pulse shaping filters. With this approach, it is shown that MSK and offset QPSK modulators yield identical signals on the channel when filtered by properly designed bandlimited pulse shaping networks.

A new modulation scheme for multitransmitter simulcast digital mobile radio communication

Abstract: Many mobile radio communication systems require digital siganling simultaneously from multiple transmitters from the viewpoints of efficient frequency utilization and simplified receiver construction. This paper describes a new modulation scheme in order to realize a simulcast digital transmission. In this method modulation signal is made by superimposing a sinusoidal wave on an ordinary rectangular digital wave. When Manchester-coded type signal is used, the frequency of the sinusoidal wave is twice as much as that of the original bit-rate and the relative phase difference between the two waves is different at each base station. In order to clarify the feasibility of this technique, experimental simulation tests are performed on 900-MHz band in two transmitter construction. It is proved that this modulation scheme does not only give the same amount of the improvement effect on the digital signaling on an overlapped area, but also makes the allowable carrier frequency drift several times lager than that of the carrier frequency offset strategy.

The Effect of Bandlimiting Filters on Probability of Error of MSK

Abstract: Minimum Shift Keying (MSK) is a method of modulation which can be viewed as a special case of Frequency Shift Keying or a special form of Offset Quadrature Phase Shift Keying; therefore, it can be detected either by a discriminator or with a pair of matched filters. In the latter case, the system is optimal, provided there are no bandlimiting filters in the transmitter and receiver. These filters introduce intersymbol interference and hence degrade the performance of the system. In this paper we investigate analytically the effect of a bandlimiting filter in the receiver on the error probability of the system, presenting numerical results when that filter is of the Butterworth type. It is shown that a very simple suboptimal detector outperforms the matched filter detector so long as 2W/R_{b} , where R b is the bit rate and W is the single sided 3 dB bandwidth of the bandlimiting filter.

Interface circuitry for acoustic coupler compensation

Abstract: For the type of modem that transmits information by way of quadrature amplitude modulation (QAM) over a telephone line, an electronic circuit for compensating for amplitude distortion created by use of an acoustic coupler with an ordinary telephone handset. The circuit is positioned in the acoustic coupler between the modem and the coupler's microphone and receiver. This circuit compensates for amplitude distortion introduced by the acoustic coupling within the data transmission frequency bands of the modem.

The RF Reference Line for PEP

Abstract: A RF phase reference line in 6 segments around the 2200 meter circumference PEP storage ring is described. Each segment of the reference line is phase stabilized by its own independent feedback system, which uses an amplitude modulated reflection from the end of each line. The modulation is kept small and decoupled from the next segment to avoid crosstalk and significant modulation of the RF drive signal. An error evaluation of the system is made. The technical implementation and prototype performance are described. Prototype tests indicate that the phase error around the ring can be held below 1 degree with this relatively simple system.

Wide-band spectrum analysis with area modulation.

Abstract: Nonlinearity of the film characteristics is a major problem in optical spectrum analysis with density modulation. The problem of nonlinearity can be avoided by using area modulation due to its binary recording format. The feasibility of using area modulation for wide-band signal analysis [ ThomasC. E., Appl. Opt.5, 1782 ( 1966)] is demonstrated. The results obtained with area modulation is shown to be similar to that of density modulation. However, area modulation requires a larger system space. Therefore, the available space–bandwidth product for a given system size is smaller with area modulation than with density modulation.

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.

The Application of Spectrum Conserving Modulation Methods to High-Capacity Digital Microwave Radio Relay Systems

Abstract: The planned introduction of digital switching by the British Post Office has motivated the development of high capacity digital transmission systems. It is intended that the radio relay bands currently carrying FDM-FM analogue transmissions will be re-used for digital systems. The application of spectrum conserving techniques has been found necessary for the realisation of digital radio-relay systems to make efficient use of the spectrum. Various modulation methods have been investigated and this paper illustrates how the application of spectrum conserving modulation methods influences the complexity and required technical standard of the equipment.

Gigabit 4-Phase Modulation-Demodulation Circuits for Microwave Digital Systems

Abstract: An extremely high speed modulation-demodulation performance is discussed when data-rate becomes close to carrier frequency. A 4-phase PSK modulation-demodulation circuit with a newly designed transformer is described. The error-rate performance on 1.6 Gb/s data-rate was successfully undertaken at a 1.7 GHz carrier frequency.