Showing papers on "Quadrature amplitude modulation published in 1980"

Frequency domain data transmission using reduced computational complexity algorithms

Abstract: In this paper we describe a frequency domain data transmission method to be used for digital data transmission over analog telephone lines which exploits recently derived reduced computational complexity algorithms, such as the Winograd Fourier Transform, to achieve a significantly lower computational rate than comparable time domain QAM modems implemented digitally using signal processing techniques. In addition to the lower computational rate, the proposed method also allows for better channel bandwidth utilization by allowing optimal signal power allocation based on the channel's signal to noise versus frequency characteristics. Experimental results on this method are presented, indicating that it may be possible to send over 10,000 BPS over an unconditioned telephone line while maintaining a 10-5BER.

Carrier and Bit Synchronization in Data Communication--A Tutorial Review

Abstract: This paper examines the problems of carrier phase estimation and symbol timing estimation for carrier-type synchronous digital data signals, with tutorial objectives foremost. Carrier phase recovery for suppressed-carrier versions of double sideband (DSB), vestigial sideband (VSB), and quadrature amplitude modulation (QAM) signal formats is considered first. Then the problem of symbol timing recovery for a baseband pulse-amplitude modulation (PAM) signal is examined. Timing recovery circuits based on elementary statistical properties are discussed as well as timing recovery based on maximum-likelihood estimation theory. A relatively simple approach to evaluation of timing recovery circuit performance in terms of rms jitter of the timing parameters is presented.

Optimal phases of maximal length sequences for asynchronous spread-spectrum multiplexing

Abstract: Optimal phases are given for maximal length linear feedback shift-register sequences (m-sequences) of periods 31 and 63 which are to be employed as signature sequences in an asynchronous direct sequence spread-spectrum multiple access communications system. The performance measure considered is the average signal/noise ratio at the output of the correlation receiver. The data presented is applicable to various forms of direct sequence spread-spectrum modulation including binary phase-shift keying, offset quadriphase-shift keying, and minimum shift keying modulation.

Digital multi-level multi-phase modulation communication system

Abstract: A 16 QAM communication system is provided wherein the proper arrangement and polarity of the four pulse trains on the receive side is determined by adding frame sync bits of a specific modulating character on the send side and reordering the receive side pulse trains in dependence upon the bits appearing in selected receive side pulse trains during the frame sync slots. The relation between the receive pulse trains and the transmit pulse trains is determined by the phase ambiguity between the transmit and receive carriers. By modulating the transmit carrier to have a specific amplitude during the frame sync slot, detecting this time at the receiver, and determining the bit values in certain of the pulse trains at the same time, the phase ambiguity can be determined and the pulse trains corrected.

Matched swept-frequency digital modulation for binary signaling in inhomogeneous dispersive media

Abstract: A digital modulation technique which is most suitable for binary signaling through inhomogeneous dispersive media is introduced. Space-time rays are used to synthesize frequency-modulated input pulses that are either compressed in the medium with enhanced output or dispersed in the medium with widely spread output. The synthesized binary signals are shown to be in the form of swept-frequency signals which are matched to the dispersive properties of the medium. For media with quadratic phase functions, or under narrow-band conditions, the matched binary signals are linearly frequency modulated (chirp) with sweep rates that are related to the medium dispersion. The medium response to the matched chirp-modulated signals is investigated in detail. Conditions for the enhancement of the performance of the proposed modulation technique due to the available bandwidth are also discussed.

Method and device for training an adaptive equalizer by means of an unknown data signal in a transmission system using double sideband-quadrature carrier modulation

Abstract: This invention relates to automatic adaptive equalizers used in those data transmission systems which rely upon a double sideband-quadrature carrier (DSB-QC) modulation technique. The term DSB-QC modulation is used here in a broad sense and includes all systems wherein the transmitted signal can be represented by superimposing two amplitude modulated quadrature carriers. Thus, the term DSB-QC includes, in particular, phase-shift keying, amplitude phase-shift keying and quadrature amplitude modulation. More particularly, this invention relates to a method and a device for training an adaptive equalizer by means of an unknown data signal sent to the receiver, and is especially useful in a data transmission system configured as a multipoint network.

Method for generating modem transmission signals with quadrature amplitude modulation

Abstract: A method for generating modem transmission signals with quadrature amplitude modulation (QAM) wherein scanned values of elementary bandpass signals are stored in digitally coded form, the elementary bandpass signals are weighted with coefficients depending on the information to be transmitted and the modem transmission signals are formed by superposition of the thus weighted elementary bandpass signals; and wherein in the case of n-PSK modulation, where n=4, 8, 12, 16 . . . , the phase positions of all elementary bandpass signals are selected such that the phase diagram is symmetrical to the axis φ=0, and no elementary bandpass signal coincides with the axis φ=0; 1/4n elementary bandpass signals, which cannot be derived from any other bandpass signal of phase diagram neither due to symmetry with the axis φ=0 or the axis φ=90°, respectively, nor by symmetry to the origin of the diagram, are stored in a digital memory; and the remaining, e.g. 3/4n, elementary bandpass signals are obtained by weighting the stored elementary bandpass signals with +1 or -1, respectively, and/or reading out the memory in a forward or a backward direction, respectively.

A new modulation scheme for multitransmitter simulcast digital mobile radio communication

Abstract: Many mobile radio communication systems require digital signaling simultaneously from multiple transmitters from the viewpoints of efficient frequency utilization and simplified receiver construction. A new modulation scheme intended to realize simulcast digital transmission is described. In this method, a modulation signal is made by superimposing a specific wave on an ordinary rectangular digital wave. The two conditions necessary for obtaining a diversity effect equivalent to the maximal-ratio combining are mathematically derived. The specific waves for the various transmitters may be sinusoidal waves having a frequency equal to the original bit rate, and phases which differ from one transmitter to another. In order to clarify the feasibility of this technique, experimental simulation tests have been performed in the 900-MHz band in a two-transmitter configuration. It is proved that this modulation scheme, in comparison with the carrier-frequency offset strategy, not only gives the same amount of improvement in digital signaling in an overlapped area, but also makes the allowable carrier frequency drift more than ten times larger.

16‐qam carrier recovery with selective gated phase‐locked loop

Abstract: It is important for the 16QAM carrier recovery circuit to have low phase jitter as well as only four stable phase points. In this paper, a novel carrier recovery with selective gated phase-locked loop (PLL) is proposed which uses only the error information of the 4PSK signal and an identical phase signal; its construction and noise characteristics are also described. First, a concrete construction based on a working priciple and digitalized circuitry is given. Next, the phase jitter due to additive white Gaussian noise in a carrier tracking loop with binary phase comparator (PC) characteristic is analyzed using an equivalent linearization technique; also, it is shown that the carrier recovery loop can be described in a linear model of the past by introducing equivalent linear gain, equivalent input noise and the degradation factor caused by the symbol error. From this study, we conclude that with the selective gated PLL, the phase jitter performance of the carrier recovery can be improved by about 6 dB over that of the carrier recovery without the selective gated PLL. This has enabled us to improve the phase noise, power density, locking characteristic, tracking characteristic, etc., by about 100%. The noise characteristics are almost the same as that of 4PSK carrier recovery. The numerical calculations have been done for the equivalent PC. This recovery system does not have false lock points.

Threshold Effect on Error Probability in QAM Systems

Abstract: This paper considers the effect of the carrier phase error on the probability of error in a binary quadrature amplitude modulation (QAM) data transmission system in the presence of intersymbol interference and additive Gaussian noise. The analysis shows that there exists a threshold value of the carrier phase error such that the error probability remains almost unchanged as long as the carrier phase error is less than that threshold value, but increases rapidly once the threshold is exceeded. Good agreement between theory and computer simulations is obtained. Some practical implications of this threshold effect are discussed.

On efficient spectrum utilization from the standpoint of communication theory

Abstract: This paper reviews the concepts of spectrum efficiency, the parameters for assessing system performance, and the techniques for improving spectrum utilization. The rationale of possible bandwidth reduction and power savings by combined modulation techniques is discussed and special attention is given to combined amplitude and phase modulation (APSK) systems. It is believed, based on the available results of several analyses over additive Gaussian noise channels, that certain combined modulation systems can have significant power savings over single-parameter modulation systems when the number of bits per symbol of the signal is large and can achieve more efficient use of the spectrum for signal-to-noise ratios greater than certain levels.

Generalized minimum shift keying (Corresp.)

Abstract: A generalized minimum shift keying (GMSK) signal is defined, and its equivalence to a modified offset quadrature shift keying signal is shown. A simple formula for the spectrum of a GMSK signal is presented and the spectrum and out-of-band power are computed for two examples.

Clock controlled monolithically integrable scanning circuit.

Abstract: A receiving circuit, provided in a noise-suppressing communication system with narrow-band conventional information modulation and additional pseudo-random phase shift keying modulation (PN-PSK), comprising a pseudo-random number generator the pseudo-random sequence of which is identical with the received pseudo-random sequence and which operates a phase shift keying circuit (PU), which cancels the phase shift keying modulation applied at the transmitting end, and comprising a matching filter or correlation network for correlating the pseudo-random sequence generated at the receiver end with the pseudo-random sequence contained in the received signal. The information modulation impairs the operation of the matching filter or of the correlation network. The interfering influence of the information modulation is to be eliminated but, at least, reduced. For this purpose, the invention provides a demodulation circuit (EM) which, on the one hand, is supplied with the entire received signal and, on the other hand, the signal present after the phase shift keying and from which a signal is taken which now only exhibits the pseudo-random phase shift keying modulation contained in the received signal but no longer the information modulation, for input into the matching filter or into the correlation network. A receiving circuit according to the invention is suitable for use in a noise-suppressing spread-spectrum communication system.

Modulation and demodulation system of digital multii value and multiiphase

Abstract: PURPOSE:To reduce the code error rate by differential logic conversion, by performing four-notation differential logic conversion to a pair of digital signals and avoiding the necessity for another pair of digital signals, when this system is applied to 16 QAM communication system. CONSTITUTION:At the transmission side, a pair of base band digital signals S1, S2 are in four-notation differential logic conversion at the sum logical circuit 7, and another pair of base band digital signals S3, S4 are inputted to the D/A converters 9, 10. Further, the 16QAM signal is obtained at the synthesizer 6 by driving the amplitude modulators 4, 5 with tetral signals P and Q. At the reception side, P, Q signal demodulated at the QAM demodulator 11 is in A/D conversion, four- natation differential logic conversion is made at the differential logic circuit 14, and the signal in agreement with the signals S1, S2 is reproduced. Further, the signal S1, S2 are fed to the discrimination circuit 16 via the sum logical circuit 18, the drawing in phase state of the reference carrier is discriminated at the circuit 16, to obtain the signals G1-G4. The signals G1-G4 are fed to the gate 17 to reproduce the signals S3, S4.

Method for initializing an adaptive equalizer starting from an unknown data signal in a transmission system using a double side band modulation with quadrature carriers

Abstract: In a receiver of a system using a modulated double sideband carrier-band quadrature (DSB-QC), it initialize the equalizer adjusts its coefficients so as to minimize the dispersion of order p, E indicates the expectation, zn is the equalized signal and R is a positive real constant To minimize dispersion D

Spectral shaping by simultaneous amplitude and frequency modulation

Abstract: In an attempt to simplify the design of separation filters in frequency-division multiplexed digital data transmission by FSK, it was found that the energy on one side of the FSK carrier can be reduced by suitably modulating the amplitude of the FSK signal. We present a simple technique for controlling the energy on one side of the carrier of an FSK signal. The method entails modulating the amplitude of the FM wave in unison with the frequency. In other words, if the energy in the region above the carrier must be reduced, the envelope is somewhat suppressed while the higher frequency is transmitted. The proposed hybrid modulation technique is applicable in frequency-division multiplexed digital data transmission by FSK and can often ease the design of separation filters. Here we investigate this modulation technique theoretically as well as experimentally. Our theoretical results include closed-form formulas for the various power spectra of interest. We also determine the optimum amount of amplitude modulation to achieve the greatest amount of sidelobe energy suppression for a fixed amount of total average power. The experimental investigations substantiate the analysis, and we make comparisons of the technique with alternative approaches.

Performance Analysis of Mixed-Base Modulation System

Abstract: In this paper the performance of the mixed-base modulation (MBM) system is analyzed for the case where the input signal is a sample function of a Gaussian random process and an optimum stretching is employed. The comparison of theoretical performance of the MBM system with that of other common modulation schemes such as FM and PCM/PSK shows that it provides performance much better than that of those schemes where the same bandspread factor is employed.

A digital processing for modulation with a sampling rate conversion

Abstract: This paper describes a digital processing method for modulation which consists of sampling rate matching and digital filtering. Processing in a digital modulation system consists of spectrum shifting, filtering and orthogonalization of signals, etc. Because of several sampling rates existing within a modulation system, matching of these sampling rates is vital. Depending on the variation of the sampling rate, the amplitude and higher harmonic distribution of the spectrum of the time-sequence signal obtained by sampling vary. By utilizing higher harmonics produced by conversion for sampling rate matching, and filtering these harmonics by means of a digital filter, it is possible to shift the spectrum to any arbitrary frequency and orthogonalize the signals. It is shown that a modulation system can be constructed without carrier multiplications. Further, modulation systems that can be processed by this method and processing methods for practical realization are illustrated.

6 GHz 16 QAM MIC Modulator with Phase Linearity Improved

Abstract: A 6GHz 16 QAM linear MIC ring modulator with improved linearity has been developed. The BER measurements show S/N degradation by the MIC modulator to be 0.3 dB greater than that of an IF modulator at an error rate of 10/sup -6/.

Amplitude Modulation with Sign Tracking

Abstract: A new technique is proposed for carrying out amplitude modulation/demodulation. The scheme is power efficient in that it does not require the transmission of a separate carrier. Receiver complexity is limited in that phase locking circuitry is not employed. Performance is evaluated and shown to be better than that of Double Side-Band (envelope detection) for the broadcast transmission of speech.