Showing papers on "Demodulation published in 1980"

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.

Receiver performance evaluation of various digital optical modulation-demodulation systems in the 0.5-10 µm wavelength region

Abstract: Error rate characteristics of various digital optical modulation-demodulation schemes are studied. The main concern is whether we can improve receiving power levels to achieve a prescribed error rate by employing a coherent optical transmission system in place of the presently available amplitude-shift-keyed (ASK) baseband direct detection system. The receiving power level reduction in various modulation-demodulation schemes is calculated by taking into account the optical carrier wavelength, data rate, photodetector performance, local oscillator power level, and number of levels in multilevel codes. The phase-shift-keyed (PSK) homodyne detection system requires the least receiving power. The improvement in the receiving power level compared to the conventional ASK baseband direct detection system is expected to be 16-22 dB at the carrier wavelength of \lambda_{c} = 0.5-3 \mu m, 31-36 dB at \lambda_{c} = 3-5 \mu m, and 35-40 dB at \lambda_{c} = 5-10 \mu m.

Remotely triggered portable stereoscopic viewer system

Abstract: A stereoscopic viewer system receives a synchronization signal input from a left-right stereoscopic image pair production system. A viewer system has a transmitter and a modulator associated therewith to transmit into a medium a carrier signal modulated with the synchronization signal. A transmitted signal is received by a receiver which has a demodulator to extract the synchronization signal and to supply it to switching logic. The switching logic supplies switching signals to alternately operate selectively and in accordance with the synchronizing signal each of a pair of electro-optic shutters between the maximum and minimum optical transmission state. Each shutter is positioned in the line of sight of one of the eyes of a user. The system receiving means is powered by a battery power supply.

Amplitude modulator using variable width rectangular pulse generator

Abstract: A method and apparatus for amplitude modulating a carrier signal with an audio or information input signal utilizes an arcsine generator to cause the envelope of the carrier to follow the input signal. The invention stems from the realization that if rectangular pulses of bipolar amplitude are symmetrically centered about 0 and π radians of the carrier signal, the harmonic content can be expressed as a function of the angle of the rectangular pulses. This concept is realized by producing two opposite phase carrier signals which are compared with the modulation input signal to form two opposite phase rectangular pulse signals whose pulse widths are a function of the modulation input signal. Alternate phase pulses are extracted from these two rectangular pulse signals by two NOR gates, and the extracted pulses are combined and filtered to obtain an amplitude modulated output signal.

Optically readable record carrier with track variations which provide clock and tracking signals and apparatus for recording and/or reproducing data from such a record carrier

Abstract: Disclosed is a record carrier for storage of digital data which is provided with a first periodic track variation having a period corresponding to a frequency at which the power spectrum of the digital signals is at a zero level. The first track variation produces a corresponding modulation of the radiation when scanned by a beam so that a clock signal can be derived from the detected radiation for synchronizing readout or recording of the data. The record carrier is further provided with a second periodic track variation in a direction transverse to the track direction having a period of the same order of magnitude, and preferably equal to the period of the first periodic track modulation. The second track variation produces a corresponding modulation of the beam which is detected and is used to generate to a tracking signal, the clock signal being used as phase reference signal for demodulation of the tracking signal. If the periods of the two track variations are equal, low-pass filtering automatically yields the tracking signal.

Frequency shift offset quadrature modulation and demodulation

Abstract: A Frequency Shift Offset Quadrature (FSOQ) signal which is a constant envelope frequency-shift keyed version of an offset quaternary phase shift keyed (O-QPSK) transmission is provided. A technique for generating an FSOQ signal in a manner similar to O-QPSK by modulating offset quadrature channels with selectable pulse shapes which yields the desired 3-tone continuous phase FSK approximation of O-QPSK is disclosed. Receiver synchronization circuits are also provided which enable FSOQ to be detected as a special case of O-QPSK, whereby the detection performance of synchronous coherent QPSK, rather than the relatively inferior performance of FSK detection, is obtained. FSOQ provides a constant envelope and requires less bandwidth than minimum shift keying (MSK).

Some implications of the cutoff-rate criterion for coded direct-detection optical communication systems

Abstract: The cutoff rate is derived for a digital communication system employing an optical carrier and direct detection. The coordinated design of the encoder, optical modulator, and demodulator is then studied using the cutoff rate as a performance measure rather than the more commonly employed error probability. Modulator design is studied when transmitted optical signals are subject simultaneously to average-energy and peak-value constraints. Pulse-position modulation is shown to maximize the cutoff rate when the average-energy constraint predominates, and the best signals when the peak-value constraint predominates are identified in terms of Hadamard matrices. A time-sharing of these signals maximizes the cutoff rate when neither constraint dominates the other. Problems of efficient energy utilization, choice of input and output alphabet dimension, and the effect of random detector gain are addressed.

Phase-encoded data signal demodulator

Abstract: A demodulator is described for demodulating phase-encoded data signals transmitted on a noisy communication channel, such as, for example, radio communication channels of a radio communication system. The demodulator includes a digital phase-locked loop for phase-locking to the mid-bit transitions of the phase-encoded data signal, which, in the preferred embodiment is encoded according to the well known Manchester coding format, and further includes demodulating circuitry for sampling the phase-encoded data signal a predetermind number of times, weighting the samples according to predetermined weighting factors, totalizing the weighted samples for each bit interval and comparing the totalized samples to a predetermined threshold value for ascertaining the logical state of each bit of the phase-encoded data signal. For example, if the magnitude of the totalized samples is greater than or equal to the threshold value, a logical one state may be provided for the decoded data signal, and, if the magnitude of the totalized samples is less than the threshold value, a logical zero state may be provided for the decoded data signal. In preferred embodiments of the present invention, the weighting factors assigned to each sample may be either binary weighted or sine weighted, although any suitable weighting factors may be utilized depending on the characteristics of the phase-encoded data signal. The phase-encoded data signal demodulator embodying the present invention is particularly well adapted for demodulating high speed, phase-encoded data signals transmitted over radio channels to mobile and portable stations of a radio communication system.

Adaptive phase-jitter tracker

Abstract: An adaptive phase-jitter compensator, which is frequency selective, is disclosed for use in data receivers The filter section (28) of the adaptive compensator receives a derived phase error signal and its own weighted sum output to provide the difference between them as selective noisy estimates of the actual phase via taps of a delay line (52-1 to 52-L) A multiplier (57) accepts each tap signal and the phase error to form a product used to update the coefficients or tap weights used in the filter section An upmodulator (29) impresses the weighted sum output on a carrier signal whose output is used by a lookup table (31) to form components to be compatible with the received data signal A complex multiplier, (23), multiplies the components and the data signal which has been previously split into components and equalized, to provide both demodulation and phase-jitter compensation

Acquisition Behavior of the Cross-Coupled Phase-Locked Loop FM Demodulator

Abstract: In this work, the acquisition behavior of a cross-coupled phase-locked loop (CCPLL) FM demodulator capable of suppressing cochannel and adjacent channel interferers is examined. This novel detector consists of two phase-locked loop (PLL) demodulators interconnected in such a manner as to permit one PLL to lock onto and track the stronger received signal, while the other loop tracks and demodulates the weaker of two received signals. The demodulator has two separate outputs, namely, the outputs of each PLL, and thus possesses the capability of demodulating both the stronger as well as the weaker received signals even though they are cochannel and share the same frequency band. The transient response of the CCPLL system is obtained using computer-aided analysis of the defining coupled nonlinear differential equations. From these results, steady-state "stability regions" are derived which reveal that range of loop parameters where successful separation and demodulation of the received cochannel signals is assured. The CCPLL receiver has numerous technological applications in suppressing unintentional or intentional CW, AM, FM, and AM/FM interferers. Experimental results demonstrating such potential are included.

Wave modulation in a nonlinear dispersive medium

Abstract: A model describing the simultaneous amplitude and phase modulation of a carrier wave propagating in a nonlinear dispersive medium is developed in terms of nonlinear wave‐wave interactions between the sidebands and a low frequency wave. It is also shown that the asymmetric distribution of sidebands is determined by the wavenumber dependence of the coupling coefficient. Digital complex demodulation techniques are used to study modulated waves in a weakly ionized plasma and the experimental results support the analytical model.

Radio telephone with position transmission capability

Abstract: A communications link having a position capability responsive to either a manual or remote control actuation. In one embodiment, a remote carrier has a navigation system for outputting signals representative of the carrier location or position. A frequency shift key (FSK) modulator is connected to the navigation system for tone coding the carrier position signals, a transmitter of a transceiver is connected to the modulator for transmitting the carrier position signals, and a position enable switch for controlling selectively the transmittal of the carrier position signals. In another embodiment, a base station is provided with a control station identification signal (ID) generator, an FSK modulator for tone modulating the station identification signal, and a transmitter connected to the FSK modulator for transmitting the tone modulated carrier ID signal, and a remote station is provided with a receiver mounted upon the carrier for receiving the ID signal, said receiver having a demodulator for demodulating the received carrier identification signals, means for recognizing the ID signal, enabling means for enabling a transmitter, a navigation system outputting position information, an FSK modulator connected to the navigation system for tone modulating the carrier position information, a transmitter for transmitting the position information, and in the base carrier a printer having an FSK demodulator connected to the receiver for demodulating and printing the carrier position information.

Costas loop QPSK demodulator

Abstract: A decision-directed Costas loop demodulator, rather than employing decision circuits, i.e. sample and hold circuits, in the path of each of the I and Q channels, contains a single sample and hold circuit at the output of the crosstalk measurement subtraction circuitry that drives the VCO. Functionally, the same decision-directed sampling process that is carried out by dual channel approach is achieved, yet because the decision/sampling circuitry is located downstream of the crosstalk measurement subtraction circuit, it operates on a relatively slowly varying error signal rather than on the rapidly varying I and Q channel signals.

760 Mbit/s Serial MSK Microwave Modem

Abstract: Serial modulation and demodulation provide a significant simplification in the hardware realization of high data rate MSK systems. The serial MSK (SMSK) technique results in theoretical performance charateristics identical to conventional MSK. A 750 kbit/s low data rate system and a 760 Mbit/s high data rate system were constructed to evaluate the feasibility of the design concepts. The low data rate system had an overall BER performance degradation of 1.3 dB at a 10-6BER. The 760 Mbit/s system had a corresponding degradation of 2.0 dB and used direct modulation and demodulation at the 14.7 GHz carrier.

Phase synchronizing circuit

Abstract: A phase synchronizing circuit, wherein two phase detectors are used in quadrature to detect the phase of an input signal and to avoid hang-up when the phase of the input signal changes abruptly by 180° The two detected phase signals are then multiplied by a locally generated reference signal and re-combined, so that a synchronized output signal having reduced phase jitter results This circuit is also incorporated in an N-phase PSK system, where it is used as a synchronizer and not as a demodulator In a receiver for such a PSK system, the frequency of the received signal is multiplied by N, the phase synchronizer circuit of the invention is then used to extract the carrier (at a N times higher frequency), and a divider is then used to convert the synchronized carrier provided by the synchronizer circuit of the invention down to the original frequency

Link performance indicator with alternate data sampling and error indication generation

Abstract: A link performance indicator card analyzes incoming analog data from a demodulator on a bit by bit basis and compares the individual bit amplitudes with a fraction of the average bit signal levels. The data bits that lack sufficient amplitude to be clear-cut "high" or "low" pulses are detected as "pseudo-errors". A bit error rate gate signal controls the detectors in order that circuits operate for only one burst or part of a burst per frame always from the same earth station. A comparator is used for comparing the output of the averaged incoming analog signal with the instantaneous value of the analog signal. Alternate clocking signals are used to perform the averaging function and the comparison function of the average signal with the instantaneous signal. This alternation of the signals frees the comparison operation from the influence of any loading on the circuit. The sample points of the incoming analog signal are adjustable by use of delays on the clock signals fed into the circuits.

Programmable digital detector for the demodulation of angle modulated electrical signals

Abstract: In modem circuitry in which an angle modulated carrier signal is clipped and demodulated, and the demodulated signal is filtered and compared with a threshold value to produce an output signal, the invention features, in one aspect, a delay line whose length and shifting frequency are both programmable and, in another aspect, the combination of a differential detector, having a programmable delay line and a digital filter, having a programmable sampling frequency.

Rapid acquisition shift keyed signal demodulator

Abstract: A shift keyed phase detector having a first input for receiving a signal including data shift keyed modulated on a carrier, such as BPSK, QPSK, MSK, SMSK, etc., and a second input for receiving a reference frequency from a local oscillator, to supply in-phase and quadrature channel data signals at differing phase error angles relative to the local oscillator reference frequency. The in-phase and quadrature channel signals are squared, and the squared signals are summed and filtered to provide a first phase error signal. The in-phase and quadrature channel signals are also multiplied with each other and filtered to provide a second phase error signal. The in-phase and quadrature channel signals are cross-multiplied with each of the phase error signals and then combined to provide a data signal in phase with the original data signal.

Adaptive differential PSK demodulator

Abstract: An adaptive differential phase shift keyed (PSK) signal demodulator which optimally tracks changes in the symbol rate of the signal. An input signal is delayed by one symbol period by passing the signal through a charge coupled device (CCD) clocked by pulses phase locked to the symbol rate (Fbr) by a phase locked loop, the phase locked loop also outputting clock pulses at the symbol rate to strobe a symbol decision circuit. The CCD has L stages and is clocked at a rate L·Fbr. As the phase locked loop tracks changes in the symbol rate, the clock pulses are varied in rate so that the CCD delay is adaptively optimized for a given symbol rate. Digital tuning is provided by an adjustable divider circuit coupling the voltage controlled oscillator of the phase locked loop to the CCD, so that by digitally selecting the division ratio the demodulator is tuned to a different symbol rate.

A generalized formulation of minimum shift keying modulation

Abstract: The modulator structure consisting of a single-input two-output sequential transducer whose output sequences control the modulated signal in the manner s(t) = x(i)p(t) + y(i)q(t) is considered. Here, iT is less than or equal to t, which is less than iT + T, where T is the modulation bit duration and where x(i) and y(i) take values in /+1, -1, 0/. The behavior of a sequential transducer is characterized by means of a 'trellis'. It is shown that, provided only that the 'carriers' p(t) and q(t) have the same energy in every bit interval, the optimum demodulator for the additive white Gaussian noise channel need process the received signal over only two bit intervals in making each data bit decision. It is demonstrated that particular choices of the sequential transducer yield differential minimum shift keying and differential staggered quadriphase shift keying. Possible generalizations of this approach are discussed.

Method and apparatus for multiplying an electrical signal

Abstract: A multiplier circuitry which multiplies an electrical signal by a multiplier signal comprises an oscillator which oscillates at a frequency having a predetermined relationship with respect to the multiplier signal, a first signal generator for producing an asymmetrical square wave signal in response to the output signal of the oscillator, a frequency divider for dividing the frequency of the asymmetrical square wave signal from the first signal generator by two to produce at least one asymmetrical square wave signal, and a second signal generator for multiplying an input electrical signal by the asymmetrical square wave signal and subsequently by a symmetrical square wave which is obtained from the asymmetrical square wave signal. The methods and apparatus for multiplying an electrical signal according to the present invention may be adapted to a phase comparator, modulator, demodulator and the like.

Multiple terminal passive multiplexing apparatus

Abstract: An apparatus for multiplexing a plurality of sensor signals onto a common transmission line without employing electrically active devices at each sensor. A modulated carrier signal is coupled to propagate along the common transmission line to a plurality of sensor terminals wherefrom portions of the carrier signal energy are coupled to the sensors for the inclusion of data signals and returned therefrom to propagate through a common transmission line to a common demodulator. Modulated carrier signals from each sensor are distinguished by providing a different round trip path length for each sensor, thus establishing unique round trip time delays. These time delays may be utilized with pulse amplitude modulation applied to the carrier signals and concomitant pulse amplitude modulated carrier signal returns that may be resolved by determining the time of arrival or with linear fm cw amplitude modulation applied to the carrier signal and concomitant delayed linear fm cw returns which may be resolved by determining a constant frequency difference between the linear fm cw signal applied to the carrier signal coupled to the transmission line and the linear fm cw signals returned from each sensor.

Two-transducer Doppler flowmeter with swept oscillator

Abstract: A flowmeter clamped onto the outside of a conduit uses doppler techniques for measuring the flow velocity of a fluid within the conduit. Separated transmitter and receiver transducers are connected to different locations on the conduit. An oscillator connected to the transmit crystal causes the crystal to produce a continuous high frequency output wave which is injected through the pipe wall and into the fluid. The frequency of the transmit oscillator is cyclically swept through a given frequency range. The receiver transducer receives reflected sonic signals from particles moving with the fluid whose velocity is to be measured. The receiver crystal also receives, through the pipe wall, the transmitted wave form. The transmitted signal and received signal are added together to produce an amplitude-modulated envelope having a beat frequency related to the flow velocity of particles producing the reflected signal received by the receiving crystal. By using frequency sweep or dither, the effect of standing waves at the receiving crystal is eliminated since, during the sweep cycle, at least one transmitter signal amplitude will be present to produce an optimum beat frequency output when added to the reflected signal. The measured amplitude-modulated wave is applied to an amplitude demodulator which, in turn, is connected to a flow indicator. Means are provided to control the amplitude of the transmit signal which is added to the receive signal to prevent the receive signal from overwhelming the pipe conducted transmit signal in the summation process producing the beat frequency.

Digital Phase Sampling for Microcomputer Implementation of Carrier Acquisition and Coherent Tracking

Abstract: By sampling zero crossings at the Nyquist rate (i.e., the predetection bandwidth) the phase of a narrow-band signal may be extracted directly with respect to an arbitrary, stable reference. Analysis, simulation, and experimental results are presented validating this all-digital technique for acquisition and coherent tracking of a Doppler-shifted carrier at a low carrier/noise ratio and a large percentage bandwidth. The key advantage of this scheme for microcomputer-based implementation is that phase comparison is accomplished by arithmetic subtraction, without the coordinaterotation transformation which is necessary for conventional I , Q sampling. Also, the phase-sampling process is independent of the phase error, which exists only as a numerical representation in the digital tracking algorithm. The technique is applicable to Costas suppressed-carrier tracking and to BPSK bit synchronization and demodulation, by programming the appropriate digital algorithms.

Method of testing transceiver and transceiver including testing apparatus

Abstract: An ultra high frequency transceiver which transmits a modulated carrier wave and mixes a received signal with a locally generated signal to produce an intermediate frequency signal is tested by using the same transmitter as used during normal transceiver operation and by modulating the carrier with a wave having sudden transitions. A portion of the transmitted wave is reflected back to a receiver segment of the transmitter to produce an i.f. signal that is detected by a demodulator. Each transition causes the demodulator to detect a pulse signal. In response to the pulse signal being detected and not being detected during a testing interval, indications are derived to signal that the transceiver is and is not operating properly, respectively.

Constant Envelope Bandlimited BPSK Signal

Abstract: A modified BPSK modulation technique using premodulation filtering is presented. The modified BPSK modulator achieves a smooth phase transition from 0 to π rad by going through an intermediate value of \pi/2 rad. The resultant PSK signal has a very low AM component, particularly suitable for data transmission through nonlinear channels. Experimental tests performed in a channel having a high degree of AM nonlinearity (AM-to-AM conversion), have shown that the modified BPSK signal, when passed through a hard-limiter, has a spectrum with greatly reduced spectral sidelobes compared to the conventional BPSK signal. The modified BPSK signal has spectral lines at the carrier frequency plus multiples of the signaling frequency, which in some cases might be useful for timing recovery in the demodulation process.

MSK Demodulator frequency acquistion apparatus and method

Abstract: A phase shift keyed (PSK) demodulator includes a closed loop wherein a phase error signal is generated to control a voltage controlled oscillator (VCO) to track the carrier frequency of an input signal for demodulation A frequency discriminator is incorporated with the PSK demodulator to provide a frequency error voltage which is also applied to the VCO to improve the tracking of the carrier frequency by substantially eliminating false locks and removing the dependence of the apparatus on the modulation of the received signal

Surface acoustic wave unique word detector and coherent demodulator.

Abstract: A surface acoustic wave device is used as a unique word detector and coherent demodulator for a digital code differential phase-shift signal. The device improves code word detection by providing a coherent reference with a correlation gain of 10 log M dB. M is the additional number of fingers introduced into the surface acoustic wave device, which determine the phase of the unique word. To achieve this result with higher reliability and higher correlation coefficient, use is made also of a few bits of the clock recovery which precede the unique word in a preamble as used in Time Division Multiple Access (TDMA) systems. The device requires two interdigital output transducers, one (23) of which provides maximum output in response to surface acoustic waves corresponding to a preassigned pattern of the unique word, such as a sequence of all zeros combined with a partial sequence of the clock recovery bits. The outputs of the two interdigital output transducers are maximized at the same instant to detect the auto-correlation peak of the unique word with performance equivalent to coherent demodulation. Also, clock and data are recovered in the second set of interdigital transducers.