Showing papers on "Quadrature amplitude modulation published in 1982"

Circuit for amplitude and phase modulation of carrier signal by two respective input signals

Abstract: An electronic arrangement for generating an amplitude and phase-modulated carrier signal having a phase modulation stage with two inputs for receiving two modulation signals, which modulation stage generates two different phase-modulated signals having the same carrier frequency and substantially the same amplitude, and an output stage to which the phase-modulated signals are applied for assembling by means of summation of the phase-modulated signals to produce the amplitude and phase-modulated carrier, the amplitude of which is modulated in dependence on the phase difference of the phase-modulated signals and the phase of which is modulated in dependence on the sum of the phases of the phase-modulated signals.

Partially Coherent Detection of Digital Full Response Continuous Phase Modulated Signals

Abstract: Recently bandwidth efficient constant envelope digital modulation schemes have been shown also to he power efficient, if detected coherently. In this paper the performance of such systems is analyzed for an optimum noncoherent or partially coherent detector, at large signal-to-noise ratios. The considered schemes are M -ary with arbitrary pulse shaping over one symbol interval (full response). The performance is analyzed by means of a parameter called equivalent minimum Euclidean distance, mathematically playing the same role as the minimum Euclidean distance used for coherent detectors. It is shown that noncoherent detectors perform as well as coherent, although the observation interval must be increased.

High-speed digital transmission experiments in 920 MHz urban and suburban mobile radio channels

Abstract: Field experiments have been conducted to clarify the feasibility of introducing a newly developed Gaussian filtered minimum shift keying (GMSK) modulation method into 920 MHz mobile radio systems, and have been performed in the Tokyo urban, and the Yokosuka suburban areas.

Minimum Euclidean Distance and Power Spectrum for a Class of Smoothed Phase Modulation Codes with Constant Envelope

Abstract: A class of smoothed phase modulation codes is analyzed in terms of power spectral density and error probability for large signal-to-noise ratios. The signals have constant envelope and the information-carrying phase function is of multi- h partial response continuous phase type. A cyclic variation of modulation index from symbol time interval to symbol time interval is introduced. Coherent transmission and an additive white Gaussian channel are assumed. Both power- and bandwidth-efficient signals are to be found in the above class. Comparisons are made between fixed- h and multi- h systems both for the binary and multilevel cases. Tradeoff is performed between bandwidth and error probability performance for large signal-to-noise ratios. It is concluded that quaternary and octal systems always seem preferable. Increasing the number of modulation indexes from one in the fixed- h case to two in the simplest multi- h case gives performance advantages at the expense of increased system complexity.

Comparison of Performance of Digital Modulation Techniques in the Presence of Adjacent Channel Interference

Abstract: The performance of four digital modulation techniques are compared to one another when each is received in the presence of adjacent channel interference. The interfering waveforms that each modulation format sees are identical to the modulation format under consideration. The four types of modulation are QPSK, 8-PSK, 16QASK, and QPR. Upper bounds to the probability of error are derived and used to evaluate the relative merits of the different schemes.

Switched-capacitor modulator

Abstract: The modulator (12) provides a means for simultaneous modulation of two carrier signals (CXR1, CXR2) in quadrature by two input signals (22, 24) in such a way that the gains of the two modulations are exactly the same. A switched-capacitor modulator (12) is provided having a plurality of input signal sources for quadrature amplitude modulation. The modulator (12) includes a single common switched-capacitor network (14) with multiple switches or multiple switched-capacitor networks for each incoming modulating signal. A switched-capacitor network utilized to form and modulate a carrier signal for shaping the carrier to reduce sidebands of the third and fifth harmonics in the modulated signal is also disclosed.

High-Speed Digital and Analog Parallel Transmission Technique Over Single Telephone Channel

Abstract: A new technique for parallel transmission of digital and analog signals over a single telephone channel is presented. The modulation scheme treated in this paper is quadrature amplitude modulation, wherein the digital and analog information are mapped separately as in phase and quadrature components. In the realization of the high-speed parallel transmission, adaptive equalization and carrier phase control are significant problems. In the hybrid QAM modem a two-dimensional error signal cannot be measured accurately at the demodulator output. This causes difficulty in implementing the conventional decision directed circuitry, which is usually employed in the adaptive equalizer and the carrier phase control circuit. The new decision directed schemes which are applicable to parallel transmission are derived by using an error signal measurement defined independent of the analog part. Computer simulation for the parallel transmission scheme of 4.8 kbit/s digital and 2.4 kHz sampled analog sequences is carried out for a typical dispersive telephone channel. Simulation results show that this scheme is useful for high fidelity analog signal transmission.

Power Spectrum of Angle Modulated Correlated Digital Signals

Abstract: The paper deals with the spectral analysis of both phase and frequency modulated digital signals with correlated messages, where correlation is obtained by encoding. Also, a possible general filtering of the baseband digital signal is taken into account. The method of computation is fast, since the computational complexity increases linearly with the baseband pulse duration. The main result is concerned with frequency modulation. It is shown that for some well-known baseband encoding schemes, such as bipolar, pair selected ternary, high density bipolar, and bipolar with n zeros substitution, the spectrum exhibits lines no matter what the value of the modulation index.

Design of quadrature modulator for digital FM signaling with digital signal processing

Abstract: To introduce digital transmission into mobile communications, various digital FM methods with a modulation index of 0.5, such as TFM and GMSK, have been studied. Stable operation of these transmission systems requires high accuracy in setting the modulation index and carrier frequency in the modulator. This paper describes a quadrature modulator that provides accurate phase control using digital signal processing (DSP). GMSK is used as a modulation scheme, and its characteristics are discussed in detail. In general, the output of a modulator adapting DSP contains deviations from the ideal analog waveforms attributable to sampling, quantization and truncation errors. These errors are superposed as noise on the modulating waves and cause degradation in signal transmission. The relation between the noise spectra and the circuit parameters is first analyzed and the design procedure is then made clear in a form of a flowchart. An example of circuit parameters yielding a ratio of the signal-to-noise spectra of 60 dB is given. We fabricated a DPS orthogonal modulator using these parameters and confirmed that the desired modulation characteristics could be obtained.

Carrier recovery arrangement for sixteen-state amplitude and phase modulation and receiving system for digital data, comprising such an arrangement

Abstract: Carrier recovery arrangement in a receiving system for digital data which are transmitted by sixteen-state amplitude and phase modulation (16 QAM), the arrangement having, successively six parallel paths (V 1 -V 6 ) each including the series arrangement of a multiplying circuit (M i ) and a low-pass filter (F i ); a selection circuit for selecting one of the three pairs of filter output signals thus obtained; a phase control circuit having a Costas signal processing circuit receiving the selected pair of signals and producing a signal representative of the phase error of the received signal, a filter and a voltage-controlled oscillator; and a phase-shifting circuit receiving the output signal of the oscillator in order to couple this output signal to respective second inputs of the multiplying circuits (M 1 )-(M 6 ), this signal coupling being effected with a phase shift zero for (M 1 ), θ for (M 3 ), 2θ for (M 5 ), and with a phase shift π/2 for (M 2 ), θ+π/2 for (M 4 ), and 2θ+π/2 for (M 6 ), where θ is equal to tan -1 (1/2).

Intermediate frequency slope compensation control arrangements

Abstract: In a microwave digital radio transmission system receiver in which a modulated carrier wave is converted to an I.F. signal (1) which is demodulated (11-17) to produce phase quadrature signals (I, Q), an apparent frequency error of the carrier wave is detected from the phase quadrature signals (I, Q) and used to control an I.F. amplitude equalizer (2), for compensating for amplitude slope of the I.F. signal. A control signal is produced by low pass filtering (25) a product (22 or 23) of one phase quadrature signal (I or Q) with the time differential (20 or 21) of the other, or the difference (24) between the products of each phase quadrature signal with the time differential of the respective other phase quadrature signal.

Single-chip CMOS MSK coherent demodulator

Abstract: We have fabricated a single-chip coherent demodulator for MSK (minimum shift keying), i.e. FFSK (fast frequency shift keying), which is one of the most effective modulation schemes for nonlinear digital radio communication systems. Carrier and clock recovery circuits are also integrated into the same chip. The demodulator operates at a bit rate of 32 kbit/s and a carrier frequency of 455 kHz at 5 V.

Error Rate Bounds for Differential PSK

Abstract: Differential phase-shift keying (DPSK) and coherent phase-shift keying (CPSK) are two of the techniques widely used in digital communications over channels such as satellite, terrestrial radio, and voiceband telephone. Because of the linear nature of the demodulation process in CPSK, the error performance of CPSK with various sources of impairments has been exhaustively treated, but even with additive Gaussian noise, only asymptotic approximations are available to determine the detection performance of M -ary DPSK, M > 2. In this note, the error performance of nonbinary DPSK in additive Gaussian noise channels has been bounded in terms of tabulated functions and various approximations are then derived.

Multiple amplitude and phase shift keyed signal modulation method

Abstract: In a multi-phase modulation method in which digital words each having a word length of at least 3 bits control the generation of a modulated carrier in a manner such that each digital word value is associated with a particular amplitude and phase of the modulated carrier, and in which the modulated carrier is formed of a combination of three oscillating signals having identical frequencies, shifted in phase by 120° relative to one another, and each having a selected amplitude, the digital words are associated with the oscillating signals in such a manner that a first group of digital words is represented only by modulated carrier phases which possess equal angular spacings in the 360° phase plane and a plurality of further digital words is represented by a zero amplitude carrier formed by combining all three oscillating signals each having the identical selected amplitude or by suppressing all three oscillating signals

Vector summation power amplifier

Abstract: A time sequence of square waves is summed to provide minimum distortion h power voltage sinusoids. The phase difference of two identical sinusoids is varied to control the resultant summed amplitude. Amplitude modulation of the sum sinusoid is achieved through varying the phase relationship between the two identical sinusoids. Frequency and phase modulation is achieved through digital control of the individual square waves.

16 QAM Carrier Recovery PLL for Service-Channel Transmission Using FSK Additional Modulation

Abstract: This paper describes the design and performance of the 16 QAM carrier recovery PLL for service-channel transmission using FSK additional modulation. When FSK additional modulation is applied, tracking phase error occurs and corrupts the 16 QAM signal. To reduce the phase error without widening the loop noise bandwidth is an important issue in the 16 QAM-FSK double modulation scheme. An analytical expression to estimate the peak phase error due to class 4 partial response FSK is established, By using the approximation formula, an optimization of the carrier recovery PLL is presented. Moreover, experiments and computer simulations are carried out for the 200 Mbit/s 16 QAM and 64 kbit/s SC double modulation system. As a result, it is demonstrated that a 0.1 dB 16 QAM equivalent power loss and an 8 dB frequency deviation margin of SC transmission performance can be obtained.

Phase shift keying/amplitude shift keying (PSK/ASK) system with any number of stages

Abstract: The invention provides a general-purpose phase shift keying/amplitude shift keying (PSK/ASK) system with any number of stages, selectable both inside (m = 2 ) and outside (I = 2 -k) a geometric progression (n = number of bits/transmission stage, k = integer). For this purpose, n parallel binary baseband signals with n sine-wave carriers gn(t), in each case phase-shifted by the angle @1...@n of the carrier frequency fc representing an integral multiple of the bit clock (fbit) or the line clock (fs), are amplitude-modulated in n ring modulators at the transmitting end and combined with one another in a hybrid coupler with n inputs to form an m = 2 -stage PSK/ASK transmission signal or, in the case of transmission-end coding and receiving-end decoding of the k non-unique signal states, to form an I = (2 -k)-stage PSK/ASK transmission signal. The carrier frequency fc for the sine-wave carriers gn(t) and the bit clock fbit or line clock fs are coupled in phase-locked fashion by means of a phase-locked loop. At the receiving end, the carrier frequency fc is recovered from the spectral line of the bit or line clock derived from the envelope of the received signal with the aid of a simple phase-locked loop. The mean effective carrier power and the maximum carrier power are particularly low in the I-PSK/ASK systems (e.g. 7 PSK/ASK). In a practically implemented n = 8-PSK/ASK system, compared with the ideal values ... Original abstract incomplete.

Error Probability Bounds for Unbalanced QAM Over the Gaussian Phase-Jittered, Dispersive Channel

Abstract: The purpose of this paper is to present an analysis concerned with a hybrid QAM system capable of simultaneously handling digital as well as analog data. Upper bounds are computed for the error probability in two- and four-level digital data streams as a function of the noise power, linear distortion, and phase jitter of the channel and of the relative power of the analog and digital signals.We show that the digital error probability is less than 10-5if the noise and intersymbol interference in the digital channel are more than 24 dB below the signal level, the power of the analog signal appearing in the quadrature channel differs by no more than 3 dB from that of the in-phase digital signal, the crosstalk from the analog into the digital channel is more than 40 dB down, and rms phase jitter is at most 1 degree for the four-level and 2 degrees for the two-level digital signal.

VHF radio link for ground-air-ground communications using an integrated voice-data modulation

Abstract: A possible realisation of a data channel between aircraft and ground station is presented, which utilises a combined amplitude-phase modulation. Amplitude modulation is used to transmit a voice signal, while phase modulation is used for data transmission. Performance of this system is evaluated through a computer simulation.

Combined phase and amplitude demodulation

Abstract: For a combined phase and amplitude demodulation process, with an integrated Brownian phase and a log normal amplitude, the error performance of the optimal demodulator is studied by Monte Carlo methods. We found that in certain cases more amplitude variance can produce better phase tracking. Further, in these cases, the observations contain more information about the phase.

Automatic gain controlling circuit

Abstract: PURPOSE:To realize automatic gain control by simple constitution, by executing a logical operation between A/D converting outputs of 2 phase detector outputs for detecting an orthogonal amplitude modulating signal, and obtaining a control signal of an amplitude controlling circuit. CONSTITUTION:An input signal (16QAM signal) IN is inputted to an amplitude controlling circuit 1, in which it is controlled to a prescribed level by a control signal of an output of an LPF6, and is inputted to a 16QAM demodulator 2. The 16QAM demodulator 2 detects orthogonally phase of the input signal, and outputs demodulating signals S1, S2. The demodulating signals S1, S2 are converted to signals (X1, X2, X3), (Y1, Y2, Y3) by A/D converters 3, 4. In this case, the signal X1 shows a quadrant of a receiving signal and the signal X3 shows a shift of amplitude of the receiving signal, therefore, the amplitude controlling circuit 1 is controlled by operating these signals by an EX-OR circuit 5 and obtaining an amplitude control signal without using the quadrant.

Relation between power spectrum and phase spectrum of oscillators

Abstract: The single-sideband to carrier power ratio L(f) and the phase fluctuations spectral density Sδϕ(f) are two convenient means of characterising the spectral purity of oscillators, and, for low-modulation indices, numerically Sδϕ = 2L, the letter briefly reviews the fundamental concepts and extends the above relationship to any modulation depth. Theoretical results for frequency modulation by bandlimited white Gaussian noise are presented. Computations are discussed and dimensional aspects have been checked experimentally.

Frequency hopping, multiple frequency-shift keying, coding, and optimal partial-band jamming

Abstract: : The performance of frequency-hopping systems with multiple frequency-shift keying is determined for operation against optimal partial-band jamming. The effects of Reed-Solomon, binary block, convolutional, and concatenated codes are analyzed. Continuous-phase frequency-shift keying with limiter-discriminato demodulation is shown to offer potentially improved performance in frequency-hopping systems. (Author)

A Simplified Approach to Direct Sequence Carrier Modulation and its Selection

Abstract: Direct sequence modulated spread spectrum systems are quite similar in many ways to more conventional digital communications systems They employ some form of phase shift amplitude shift frequency shift keying to modulate their carriers and provide the desired spread bandwidth A key consideration, however, is the choice of carrier modulation to provide maximum antijamming margin while operating in nonlinear processing, plus minimizing impact on synchronization and cost/complexity of the modulators, demodulators, and synchronizers required This paper examines the relationships that exist between the various candidate waveforms and shows their common roots Also defined are the criteria that affect the choice of a waveforms, where various implementations are possible

An All Digital Maximum a Posteriori based Synchronizer for MSK

Abstract: A digital joint maximum a posteriori (MAP) symbol synchronizer and phase estimator is realized for minimum shift keying (MSK) modulation. This development permits direct digital implementation of closed loop synchronization and coherent demodulation. Advantages derived from this approach are parameter stability and accuracy with system flexibility and reliability.

A control method of variable resonance type adaptive equalizer for a digital radio system

Abstract: In a microwave-band highly efficient digital radio system, transmission characteristics deteriorate remarkably due to multipath fading generated on propagation paths. This paper describes a control method of adaptive equalizer using a variable resonance-type equalizer circuit which has been developed for the correction of multipath fading. Since a received power spectrum is used for the detection of fading characteristics, the bandwidth and response speed of the detector are optimized first and, then, its control algorithm is investigated. A microcomputer is introduced for the first time in the control circuit, enabling advanced control. As a result, a well-convergent algorithm, taking advantage of equalizing circuit characteristics, is developed. Laboratory experiments, in a 200 Mbit/s 16 QAM (transmission speed, 50 Mband) digital radio system, using a two-ray fading simulator confirmed that the control method has good convergency and the adaptive equalizer has sufficient equalization effects.

Digital pulse frequency demodulation using state-space filtering

Abstract: Independently of the method of demodulation, the time quantisation of a pulse frequency modulated signal causes an error proportional to the demodulator bandwidth, to the time quantisation interval, and to the ratio of the modulation frequency to the modulation frequency range. The necessity of having a very short quantisation interval leads to a very high effective input sampling rate to a digital demodulator. This high effective sampling rate, together with large time constants needed to demodulate the signal, precludes the use of a conventional digital filter. It is possible, however, to take advantage of the special form of the demodulator input signal to design a computationally efficient state-space filter.

Addressing and Modulation for Frequency-Hopping Multiple Access

Abstract: This paper describes the common structure of a large class of frequency-hopping multiple-access address sequences of the so-called "one-coincidence" type. We show methods for expanding the address sets to great size without compromising performance, and compare frequency and phase modulation methods. We also describe methods for dealing with unsynchronizable signalling alphabets, which arise as a result of expanding the MFSK sets.

The design and implementation of Biphase Costas Loop

Abstract: At present, transmitting data or digital message in carrier band via digital modulation such as digital radio has become more and more popular, and the various digital modulation techniques most oftenly employed almost invariably involve changing the carrier phase in some particular way according to the baseband message entering the modulator. These can be grossly termed “phase shift keying” (PSK). Phase shifted keyed carrier band signal must be detected “coherently”, i. e. at the receiver a locally generated carrier whose phase closely tracks the phase of the carrier signal at the transmitter is required. The process of generating such a local, phase coherent carrier is usually called “carrier recovery”. Since it has been well known that the quality of recovered carrier has a profound effect on the whole PSK receiver system performance (e. g. the bit error rate, etc.), carrier recovery circuit must be analyzed and designed carefully. In this paper, the “Costas loop”—one of the most efficient and...