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Showing papers on "Quadrature amplitude modulation published in 1974"


Journal ArticleDOI
TL;DR: In this paper an asymptotic (large signal-to-noise ratio) expression is derived for the error rate and it is rigorously proved in the Appendix that the optimum constellations tend toward an equilateral structure, and become uniformly distributed in a circle.
Abstract: A considerable amount of literature exists on the problem of selecting an efficient set of N digital signals with in-phase and quadrature components for use in a suppressed carrier data transmission system. However, the signal constellation which minimizes the probability of error in Gaussian noise, under an average power constraint, has not been determined when the number of signals is greater than two. In this paper an asymptotic (large signal-to-noise ratio) expression, of the minimum distance type, is derived for the error rate. Using this expression, a gradient-search procedure, which is initiated from several randomly chosen N -point arrays, converges in each case to a locally optimum constellation. The algorithm incorporates a radial contraction technique to meet the average signal power constraint. The best solutions are described for several values of N and compared with well-known signal formats. As an example, the best locally optimum 16-point constellation shows an advantage of about 0.5 dB in signal-signal-to-noise ratio over quadrature amplitude modulation. The locally optimum constellations are the vertices of a trellis of (almost) equilateral triangles. As N \rightarrow \infty , it is rigorously proved in the Appendix that the optimum constellations tend toward an equilateral structure, and become uniformly distributed in a circle.

346 citations



Journal ArticleDOI
TL;DR: Three classes of 4-D codes are presented, and an algorithm is given which yields good 4- D codes of any length which exceed that of amplitude- and-phase modulation in two independent two-dimensional channels.
Abstract: This paper examines codes for four-dimensional (4-D) modulation and their performance for digital transmission. The signals are defined by M points inside a sphere in four-dimensional Euclidian space. Three classes of 4-D codes are presented, and an algorithm is given which yields good 4-D codes of any length. Bounds on symbol error probability are plotted versus symbol-energy-to-noise-density ratio. The performance is shown to exceed that of amplitude- and-phase modulation in two independent two-dimensional channels.

73 citations


Journal ArticleDOI
TL;DR: The use of an offset form of QPSK, also known as double-biphase modulation, is shown to yield a probability of bit error in detection that is equal to the average of the detection performances for BPSK and conventional QPSk.
Abstract: Imperfect carrier synchronization causes a performance loss for coherent phase-shift-keyed (PSK) communications. This detection loss is greater for quaternary signaling (QPSK) than for the binary case (BPSK). The use of an offset form of QPSK, also known as double-biphase modulation, is shown to yield a probability of bit error in detection that is equal to the average of the detection performances for BPSK and conventional QPSK. Because of frequency instabilities in communications systems, it is sometimes difficult to obtain carrier synchronization with sufficiently low jitter to preclude significant detection losses. The use of offset QPSK in lieu of conventional QPSK modulation is shown to lower by almost 3 dB the required SNR of the synchronizer phase reference for satisfying a specified value of allowable detection loss.

64 citations


Patent
11 Apr 1974
TL;DR: In this article, the authors proposed a full-duplex communication system with a pair of fullduplex modems, one at each end of a two-wire circuit, each of the modems includes a transmitter for transmitting over the two wire circuit a stream of synchronous data at a first carrier frequency, and a receiver for receiving over two wire circuits, at a second carrier frequency.
Abstract: The disclosed full-duplex communication system includes a pair of full-duplex modems, one at each end of a two wire circuit. Each of the modems includes a transmitter for transmitting over the two wire circuit a stream of synchronous data at a first carrier frequency, and a receiver for receiving over the two wire circuit a stream of synchronous data at a second carrier frequency. The receiver includes means for coherently demodulating the stream of synchronous data. In a preferred embodiment, an asynchronous-to-synchronous converter converts asynchronous input data into a stream of synchronous data for transmission by the transmitter. Also, the preferred embodiment transmits the data and receives the data as double side band suppressed carrier quadrature amplitude modulation. The system includes a remote test capability for automatically looping back test data for comparison with the transmitted test data.

46 citations


Patent
Thomas Mann Dennis1
12 Aug 1974
TL;DR: In this article, a high-speed digital data transmission system combines quadrature amplitude modulation with scrambling-descrambling, differential amplitude coding-decoding, and Gray-to-rotational codingdecoding of multilevel data symbols channeled at baseband, including frequencies extending down to zero, onto parallel bit streams with a minimization of error multiplication.
Abstract: A high-speed digital data transmission system combines quadrature amplitude modulation with scrambling-descrambling, differential amplitude coding-decoding, and Gray-to-rotational coding-decoding of multilevel data symbols channeled at baseband, i.e., including frequencies extending down to zero, onto parallel bit streams with a minimization of error multiplication. Scrambling and descrambling facilitate timing recovery and equalizer adjustment. Differential and rotational encoding and decoding compensate for phase ambiguities in the signal constellation, i.e., points on a space diagram representative of the tips of multilevel symbol vectors.

30 citations


Patent
Harold Seidel1
03 Sep 1974
TL;DR: In this paper, the phase modulation distortion due to phase modulation error in an interferometer type modulator is minimized by extracting a portion of the phase modulated carrier frequency signals in the two branches of the interferometers and sensing the resulting amplitude modulation in an auxiliary Interferometer circuit.
Abstract: Modulation distortion due to phase modulation error in an interferometer type modulator is minimized by extracting a portion of the phase modulated carrier frequency signals in the two branches of the interferometer and sensing the resulting amplitude modulation in an auxiliary interferometer circuit. The modulation signal is compared with the input modulation signal and a weighted error signal is formed. The latter is then used to impress an error correcting phase modulation on the carrier frequency signals.

27 citations


Journal ArticleDOI
R. de Buda1
TL;DR: The optimum observation interval for phase-continuous frequency-shift keying (FSK) is longer than 2T .
Abstract: The optimum observation interval for phase-continuous frequency-shift keying (FSK) is longer than 2T .

16 citations


Journal ArticleDOI
TL;DR: In this article, the constructive design of finite order equalizer filters for data transmission systems employing decision feedback equalization is presented, both transmitter design with power constraints and receiver design with ambient noise considerations are treated.
Abstract: We present the constructive design of finite order equalizer filters for data transmission systems employing decision feedback equalization. Both transmitter design with power constraints and receiver design with ambient noise considerations are treated. Expressions for the filter tap settings which maximize a signal-to-noise ratio are found for both baseband pulse amplitude modulation and quadrature amplitude modulation (QAM) systems. Design examples are given in a passband equivalent (of QAM) formulation for an average toll telephone connection. Neglecting the possibility of error propagation, these examples demonstrate that decision feedback equalization requires fewer taps for acceptable system performance as compared to linear equalization. The problem of postcursor size in a decision feedback equalized response is treated and shown to diminish in importance when a hybrid equalization procedure is imposed on the linear tap adjustment. The price one pays for allowing the linear filter taps to reduce the postcursor sizes in this hybrid equalizer is a lower signal-to-noise ratio.

15 citations


Patent
21 May 1974
TL;DR: In this article, a system for conducting amplitude modulation of a carrier wave of sine or quasi-sine waveform in the manner in which the carrier wave is defined into a plurality of blocks and all the cycles but one at least within each block are subjected to amplitude modulation by a digital data signal.
Abstract: The system of the present invention comprises means for conducting amplitude modulation of a carrier wave of sine or quasi-sine waveform in the manner in which the carrier wave is defined into a plurality of blocks and all the cycles but one at least within each block are subjected to amplitude modulation by a digital data signal; and demodulating means for reproducing the digital data signal from the modulated carrier wave by the output of a comparator for comparing the amplitude of the amplitudemodulated cycle within each block with a reference level in the same block, that is, the amplitude of the amplitude-in-modulated cycle.

14 citations


Patent
Pietro Porzio Giusto1
10 Jul 1974
TL;DR: In this article, a binary data stream of cadence f to be transmitted by PSK (phase-shift keying) modulation is split into two pulse sequences, composed of alternate bits of that data stream, which are translated into 180* phase shifts of respective sinusoidal carrier waves in quadrature with each other.
Abstract: A binary data stream of cadence f to be transmitted by PSK (phase-shift keying) modulation is split into two pulse sequences, composed of alternate bits of that data stream, which are translated into 180* phase shifts of respective sinusoidal carrier waves in quadrature with each other, the frequency f of the two carrier waves being the reciprocal of the pulse width 2/f of the two pulse sequences in a specific instance. A pair of interleaved trains of trigger pulses, each coinciding with the zero crossings of a respective carrier wave, enable the operation of associated phase shifters - in response to amplitude changes of the respective pulse sequences - only at a peak of a carrier wave in trailing position or at a zero crossing of a carrier wave in leading position, thereby minimizing the amplitude excursions occurring upon a subsequent passage of the combined carrier waves through a band-pass filter or other network of limited bandwidth.

Journal ArticleDOI
01 Sep 1974
TL;DR: Preliminary investigations into a method of differential phase modulation applied to chirp data signals is described, which improves the chirP-system performance in white noise and single carrier interference, and essentially retains the inherent protection that chir p signals have in multipath conditions.
Abstract: Chirp communication systems have been constructed that use signals having ascending and descending linear frequency sweeps to define mark and space data states, respectively. Such signal states are approximately orthogonal, and are generally detected noncoherently. The paper describes preliminary investigations into a method of differential phase modulation applied to chirp data signals. This improves the chirp-system performance in white noise and single carrier interference, and essentially retains the inherent protection that chirp signals have in multipath conditions. Also, improved bandwidth utilisation may be achieved with multiphase operation.

Journal ArticleDOI
TL;DR: The performance of multilevel DPSK is compared with the performance of Type I amplitude-phase modulation on a frequency dispersive channel with additive noise to determine the appropriate amount of amplitude modulation to be employed in a high rate Type I system.
Abstract: Differentially coherent phase shift keying (DPSK) is commonly used to provide data communication on frequency dispersive channels. To obtain higher data rates one can increase the number of phases or employ combined amplitude-phase modulation. In this paper we compare the performance of multilevel DPSK with the performance of Type I amplitude-phase modulation on a frequency dispersive channel with additive noise. For the Type I system differential modulation is used to amplitude encode a single bit, and ordinary DPSK is used to encode up to four phase bits. Curves of bit error probability versus the effective signal-signal-to-noise ratio of the channel are presented for both the amplitude and phase encoded bits. From these curves the appropriate amount of amplitude modulation to be employed in a high rate Type I system can be obtained. Performance comparisons between multilevel DPSK and Type I modulation are then presented under conditions of both equal average and peak transmitter power.

Patent
29 Mar 1974
TL;DR: In this paper, the authors measure the conversion of amplitude modulation to phase modulation and use it to test devices used in frequency modulated multichannel communication systems having amplitude modulation-to-phase modulation conversion.
Abstract: This method and apparatus measures conversion of amplitude modulation to phase modulation and is useful for any application wherein resultant unwanted phase modulation is to be measured, but is mainly intended for testing devices used in frequency modulated multichannel communication systems having amplitude modulation to phase modulation conversion which causes distortion of a desired frequency modulated signal.

01 Jan 1974
TL;DR: An automatic gain control loop is presented for use with M -ary amplitude- and phase-shift keying (MAPSK) systems and is shown to have a negligible degradation on the symbol probability of error for most practical cases.

Journal ArticleDOI
TL;DR: The Volterra series approach was used to derive a simplified expression relating the single channel and multichannel cross modulation in a CATV amplifier as discussed by the authors, where the cross modulation from n unwanted carriers synchronously modulated is seen to be dependent upon the phase versus frequency variation of the third-order VOLTERRA transfer function of an amplifier only when the phase is constant for any frequency of interest is the increase in the magnitude of the cross-modulation vector given by 20 log n, n being the number of synchronous modulated carriers.
Abstract: The Volterra series approach is used to derive a simplified expression relating the single channel and multichannel cross modulation in a CATV amplifier The cross modulation from n unwanted carriers synchronously modulated is seen to be dependent upon the phase versus frequency variation of the third-order Volterra transfer function of an amplifier Only when the phase is constant for any frequency of interest is the increase in the magnitude of the cross-modulation vector given by 20 log n, n being the number of synchronously modulated carriers

Journal ArticleDOI
M. Massaro1
TL;DR: The distribution function of the probability of error in the presence of Rayleigh fading and Gaussian noise is determined for the basic binary modulation schemes of coherent frequencyshift keying, noncoherent frequency-shift keying (NCFSK), differential phase-shiftkeying (DPSK), and coherent phase- shifts (CPSK).
Abstract: The distribution function of the probability of error in the presence of Rayleigh fading and Gaussian noise is determined for the basic binary modulation schemes of coherent frequencyshift keying (CFSK), noncoherent frequency-shift keying (NCFSK), differential phase-shift keying (DPSK), and coherent phase-shift keying (CPSK). General expressions for the distribution function of error probability are also derived when linear maximal-ratio diversity combining is employed. Results are given for various values of average error probability and various orders of diversity.

Journal ArticleDOI
TL;DR: Comparisons with binary frequency modulation of the same data rate show that biternary frequency modulation can offer lower error rates only for receiver bandwidths less than 0.63 times the bit rate.
Abstract: The performance of a biternary f.m. system is investigated in the presence of additive Gaussian noise and receiver band limitation. The receiver bandpass-filter bandwidth is varied and, for each bandwidth, the frequency-deviation index that minimises the error probability is found. Comparisons with binary frequency modulation of the same data rate show that biternary frequency modulation can offer lower error rates only for receiver bandwidths less than 0.63 times the bit rate.


Patent
Coackley Robert1
22 Jan 1974
TL;DR: In this article, the amplitude modulation to phase modulation conversion of limiters and other devices caused distortion of the desired frequency modulated signal, and the resultant unwanted phase modulation is measured.
Abstract: This apparatus measures conversion of amplitude modulation to phase modulation and is useful where resultant unwanted phase modulation is to be measured, but is mainly intended for testing devices used in 70 MHz frequency modulated communications systems where, for example, the amplitude modulation to phase modulation conversion of limiters and other devices cause distortion of the desired frequency modulated signal.

Journal ArticleDOI
TL;DR: An analysis of the spectra of digital signals is presented that includes Lundquist's and Glance's results for PSK signals as special cases while at the same time being much simpler than previous analyses.
Abstract: An analysis of the spectra of digital signals is presented that includes Lundquist's and Glance's results for PSK signals as special cases while at the same time being much simpler than previous analyses. The signal is assumed to be modulated in phase and/or amplitude by a sequence of pulses that may have different shapes for different symbols. In addition, the pulse representing a given symbol may be affected by neighboring symbols, so that intersymbol interference in the modulating process is permitted. The results, nevertheless, take a simple form, and they are applied to two binary cases.

Journal ArticleDOI
TL;DR: It is shown that amplitude modulation (AM, OM, SSB, VSB) can be produced by nonrecursive, semirecursive or recursive twodimensional digital filters (also phase modulation for digital modulating signals).
Abstract: Modulation can be mathematically interpreted as a special case of two-dimensional convolution. Hence, it is possible to use two-dimensional sampled-data filter techniques for the realization of modulators in modern communication systems. The modulator structures consist of active elements and resistors only, and for that reason they are well adapted to large-scale integration (LSI) circuit design. It is shown that amplitude modulation (AM, OM, SSB, VSB) can be produced by nonrecursive, semirecursive or recursive twodimensional digital filters (also phase modulation for digital modulating signals). From the viewpoint of realization, the semirecursive modulator structures are of predominant interest. Some details are given of a simulated single-sideband data transmitter equipped with such a modulator structure.

Journal ArticleDOI
TL;DR: In this paper, a discussion and analysis of a synchronous operating point modulation in a non-linear oscillator with automatic voltage control (AVC) is given, where the effect of the modulation depends upon the phase angle between the modulation and the generated wave.
Abstract: A discussion and analysis of a synchronous operating point modulation in a. non-linear oscillator with automatic voltage control (AVC) is given. The results are obtained by an extension of the quasi-linearization method to practical cases where a small synchronous operating point modulation appears in addition to the proper oscillation amplitude. Such a procedure is found to be justified if the synchronous modulation amplitude changes during one cycle can be ignored, identical to the condition that must fulfil the envelope of the generated oscillation. The effect of the modulation depends upon the phase angle between the modulation and the generated wave.