Showing papers on "Demodulation published in 1992"

Fiber Optic Networks

Abstract: Fibre optic networks applications and their requirements fibres, couplers and taps tunable filters laser diodes lightwave amplifiers modulation and remodulation techniques detection and demodulation of optical signals subcarrier (wavelength x frequency) techniques frequency stability and its control organizing the system topologically layered architectures in lightwave networks multiaccess, switching and performance operating third generation links operating third generation multipoints operating third generation networks

Integrated communications terminal

Abstract: An integrated communications terminal including a selectable channel demodulator and decoder, a time-division-multiplexed (TDM) channel demodulator and decoder, a data processor and controller, an audio decompressor, a D/A converter, and a data coder and modulator. The terminal is used with a mobile station having a message display, an input device, RF electronics, and an optional transmitter. The selectable channel demodulator outputs a selectable intermediate-frequency signal as in-phase and quadrature-phase signals for decoding by the selectable channel decoder. The TDM channel demodulator generates a frequency offset signal and outputs in-phase and quadrature-phase TDM signals for decoding by the TDM channel decoder as a TDM-data signal. The data processor and controller time-demultiplexes the TDM-data signal as a control signal, a TDM channel and selectable channel look-up table, and paging and message signals, and generates a transmitter frequency command signal, a selectable data rate and frequency command signal, and a TDM data rate and frequency command signal. The audio decompressor outputs a digital audio data signal. The D/A converter outputs analog audio signals. The carrier signal frequency of the transmitter is set by the transmitter frequency command signal generated by the data processor and controller. The data coder and modulator encodes a data signal and then modulates a carrier signal with the coded data signal to create a data-modulated signal. The transmitter amplifies and transmits the data-modulated signal.

Neural networks for multiuser detection in code-division multiple-access communications

Abstract: Two simple structures employing multilayer perceptrons are proposed for demodulation of spread-spectrum signals in both synchronous and asynchronous Gaussian channels. The optimum receiver is used to benchmark the performance of the proposed receiver; in particular, it is proved to be instrumental in identifying the decision regions for the neural networks. The neutral networks are trained for the demodulation of signals via backpropagation-type algorithms. A modified backpropagation-type algorithm is introduced for single-user and multiuser detection with near-optimum performance that could have applications in other classification and pattern recognition problems. A comparative performance analysis of the three receivers, optimum, conventional, and the one employing neural networks, is carried out via Monte Carlo simulations. An importance sampling technique is employed to reduce the number of simulations necessary to evaluate the performance of these receivers in a multiuser environment. In examples given, the receiver significantly outperforms the conventional receiver. >

Bandlimited quasi-synchronous CDMA: a novel satellite access technique for mobile and personal communication systems

Abstract: Recent trends in digital communications are opening commercial applications to code division multiple access (CDMA). A novel access technique based on bandlimited quasi-synchronous CDMA (BLQS-CDMA) is described, showing all the advantages of synchronizing conventional direct sequence CDMA to drastically reduce the effect of self-noise. Bandlimitation is achieved with no detection loss by means of Nyquist chip shaping, leading to a simple all-digital demodulator structure. Detection losses due to imperfect carrier frequency and chip timing synchronization are analytically derived and numerical results are checked by computer simulations. Impairments due to satellite transponder distortions are evaluated. The full digital modem structure is presented, together with possible applications to mobile and very small aperture terminal (VSAT) satellite communications. >

Theory of polarization shift keying modulation

Abstract: A rigorous analysis of digital coherent optical modulation schemes using the state of polarization as the modulating parameter is presented. The analysis obtains the exact performance of all the polarization-based modulation schemes proposed in the literature so far, including a differential demodulation scheme, named DPOLSK, which does not require either electrooptic or electronic polarization tracking. Preliminary results involving multilevel transmission schemes based on the state of polarization are introduced. A spectral analysis of POLSK signals is also proposed. >

Personal computer with broadcast receiver on expansion board controlled by computer microprocessor

Abstract: A broadcast receiver (22) for receiving television broadcast signals carrying encoded data e.g. teletext information, includes a tuner (30), a demodulator (32) and a data extractor (36) for decoding the data. The receiver is coupled to a computer through a bus (38) and an interface controller (40). The tuner (30), the demodulator (32) and the data extractor (36) are each individually controllable by the interface controller (40) in response to instructions from the computer to vary any of the tuning, the demodulation parameters, or the data extraction parameters. A data processor (54) processes the extracted data, and can also control the tuner (30), the demodulator (32) and the data extractor (36).

Global positioning system receiver digital processing technique

Abstract: A Global Positioning System (GPS) commercial receiver is provided with a digital processor that can utilize to advantage P-code modulated L1 and L2 satellite signals which have been modulated with an unknown security code. Integration of the L1 and L2 signals, after demodulation by locally generated carrier and P-code signals, is repetitively accomplished over a duration that is estimated to be the period of the modulation code. The C/A-code L1 signal, which is not modulated with the unknown security code, is also used in locking the locally generated carrier and P-code generators in phase with the received L1 and L2 satellite signals. A interpolative technique is used for adjusting the phase of the locally generated carriers and code in increments much smaller than the period clock sources. Those locked phases can then be utilized to determine position, distance, time, etc., as is done in GPS receivers not utilizing the anti-spoofed signals but with increased accuracy and resolution. A novel structure of the GPS receiver radio frequency and intermediate frequency sections, having a specific combination of demodulating frequencies, is also disclosed.

Discrete multiple tone modulation with coset coding for the spectrally shaped channel

Abstract: A discrete approach to multiple tone modulation is developed for digital communication channels with arbitrary intersymbol interference (ISI) and additive Gaussian noise. Multiple tone modulation is achieved through the concatenation of a finite block length modulator based on discrete Fourier transform (DFT) code vectors, and high gain coset or trellis codes. Symbol blocks from an inverse DFT (IDFT) are cyclically extended to generate ISI-free channel-output symbols that decompose the channel into a group of orthogonal and independent parallel subchannels. Asymptotic performance of this system is derived, and examples of asymptotic and finite block length coding gain performance for several channels are evaluated at different values of bits per sample. This discrete multiple tone technique is linear in both the modulation and the demodulation, and is free from the effects of error propagation that often afflict systems employing bandwidth-optimized decision feedback plus coset codes. >

Dual mode transmitter and receiver

Abstract: A dual-mode transmitter having an antenna (109), a mode controller (103), a source encoder, a tunable-frequency synthesizer (105), a chip-code generator (107), a spread-spectrum modulator (111), a narrowband modulator (113), a power amplifier (115), and an adjustable bandpass filter (117). Also provided is a dual-mode receiver having a mode controller (103), a tunable-frequency synthesizer (105), a chip-code generator (107), an antenna (109), an adjustable bandpass filter (117), a preamplifier (205), a frequency converter (209), an IF amplifier (211), a spread-spectrum despreader (215), a spread-spectrum demodulator (217), a narrowband modulator (213), and a source decoder. For the transmitter and receiver, the mode controller (103) selects receiving a narrowband modulation or a spread-spectrum modulation. The tunable-frequency synthesizer (105) generates a local oscillator signal for the receiver, and a carrier signal for the transmitter. The chip-code generator (107) generates a chip code signal for both the transmitter and the receiver. With a narrowband modulation setting of the mode controller (103), the transmitter and receiver have the adjustable bandpass filters (117) adjusted to a narrowband width for telephone communications. With a spread-spectrum setting of the mode controller, the adjustable bandpass filters (117) and the system are adjusted to transmit and receive a wide bandwidth for passing the spread-spectrum signal.

Error performance of multiple-symbol differential detection of PSK signals transmitted over correlated Rayleigh fading channels

Abstract: The error performance of multiple-symbol differential detection of uncoded QPSK signals transmitted over correlated Rayleigh fading channels is studied. The optimal detector is presented, along with an exact expression for the corresponding pairwise error event probability. It is shown that multiple-symbol differential detection is a very effective strategy for eliminating the irreducible error floor associated with a conventional differential detector. In all of the cases investigated, a detector with an observation interval as small as two symbols is sufficient for this purpose. It is also found that the error performance of a multiple-symbol differential detector is not sensitive to the mismatch between the decoding metric and the channel fading statistics. >

Bit error rate of binary and quaternary DPSK signals with multiple differential feedback detection

Abstract: A differentially coherent detection scheme with improved bit error rate (BER) performance is presented for differentially encoded binary and quaternary phase shift keying (PSK) modulation. The improvement is based on using L symbol detectors with delays of 1, 2, . . ., L symbol periods and on feeding back detected PSK symbols. Exact formulas for the bit error probability are derived for the case that correct symbols are fed back. The effect of symbol errors in the feedback path on the BER is determined by computer simulations. >

Coherent optical QPSK intradyne system: concept and digital receiver realization

Abstract: A receiver concept based on optical quadrature phase-shift keying (QPSK) and a digital realization of synchronous demodulation including phase synchronization is presented. To keep the signal processing bandwidth low a phase diversity receiver, called an intradyne receiver, with an orthogonal electrical demodulation is proposed. Basic principles of the synchronous orthogonal and digital demodulation are described. After the evaluation of the shot noise limit some aspects of the digital phase-locked loop (PLL) are presented. In a 100-Mb/s transmission system a receiver sensitivity of -51.6 dBm has been measured. The loss in relation to the shot noise limit of -66.3 dBm (18 photons/b) is mostly due to the low local laser power and the influence of the receiver input noise. >

Device for the coherent demodulation of time-frequency interlaced digital data, with estimation of the frequency response of the transmission channel and threshold, and corresponding transmitter

Abstract: A coherent demodulation device, for the demodulation of a digital signal of the type constituted by digital elements distributed in the time-frequency space and transmitted in the form of symbols constituted by a multiplex of N orthogonal carrier frequencies modulated by a set of the digital elements and broadcast simultaneously, the digital signal comprising reference elements, having a value and a position, in the time-frequency space, that are known to the demodulation device, comprising means for the estimation, by Fourier transform, of the frequency response of the transmission channel at any instant, carrying out the transformation of the received samples, corresponding to reference elements, from the frequency domain to the temporal domain, the multiplication in the temporal domain of the transformed samples by a rectangular temporal window (f n) and the reverse transformation, after the multiplication, of the obtained samples from the temporal domain into the frequency domain, the estimation means comprising means for the thresholding of the samples in the temporal domain, providing for the systematic elimination of the samples below a certain threshold.

A double Nyquist digital product detector for quadrature sampling

Abstract: A technique for digitally obtaining the in-phase (I) and quadrature (Q) components of an IF signal is presented. Initially, the input bandpass signal is mixed to a carrier frequency that is one-fourth of the sampling rate of a single A/D converter. The digitized bandpass signal is converted into its I and Q components at one-half the A/D sample rate by a digital product detector (DPD) composed of a commutator, two sign alternators, and two FIR fractional-phase interpolator filters. This simple structure can yield image performance that is limited by A/D quantization using relatively low interpolator filter orders and IF bandwidths as large as one-half the sampling rate of the A/D converter. The DPD performs Nyquist limit demodulation of the sampled bandpass signal and, therefore, requires a minimal sampling rate. The theory of operation, an analytic proof, design methodology, and simulated performance results are presented. Simulated results show that -86 dB images can be obtained with 8-tap FIR interpolators and a 12 bit A/D converter. A VLSI implementation is also presented. >

Process for digital transmission and direct conversion receiver

Abstract: The transmitter uses a synthesized oscillator (1A) whose reference (24) is provided by the clock (H) of the data (P, Q). The demodulation oscillator (13A) of the receiver is a synthesizer which is functionally identical to that (1A) of the transmitter, and its reference (23) is provided by the clock (H, 36) recovered from the received data.

Multi-frequency communication system with an improved diversity scheme

Abstract: In a transmitting section, a modulator modulates a first carrier with datao be transmitted, thereby producing a modulated output fm, a local oscillator generates a local oscillating signal to be used as a second carrier fLO, a mixer mixes the modulated output and the local oscillating signal, thereby generating waves of different frequencies These waves include an upper side band wave fLO +fm and a lower side band wave fLO -fm A transmitting antenna radiates electromagnetic waves into the air, which includes the waves of different frequencies generated by the mixer In a receiving section, a receiving antenna receives the electromagnetic waves, a diversity section extracts at least one of the upper side band and lower side band waves fLO +fm, fLO -fm from the waves of different frequencies received by the receiving antenna, a local oscillator generates a local oscillating signal corresponding to the second carrier, a mixer mixes the one wave extracted by the diversity section and the local oscillating signal generated by the local oscillator, thereby generating an output, and a demodulator extracts a signal corresponding to the first carrier, from the output of the mixer, and demodulates the signal thus extracted, thereby outputting data corresponding to the data transmitted from the transmitting section

Carrier synchronization for homodyne and heterodyne detection of optical quadriphase-shift keying

Abstract: Through analysis and simulation, the authors investigated the performance of four carrier-synchronization techniques suitable for both homodyne and heterodyne detection of optical quadriphase-shift keying: the discrete-time decision-directed loop, the analog decision-directed loop, the Costas quadriphase loop, and the fourth-power phase-locked loop. Accounting for shot noise, laser phase noise, and feedback delay, they optimize the loop natural frequency and specify laser-linewidth requirements. The performance discrepancy between the best and worst of these loops is found to be small; accounting for inherent loop delays only, the linewidth requirements range from Delta vT >

Data communication system with automatic power control

Abstract: A communication system comprised of a transceiver (101) for transmitting and receiving data signals and a modulation/demodulation apparatus (102) to modulate the data signals from an accessory (109) for transmission and demodulate data signals after reception by the transceiver (101). A processing device (103) controls power to the various components of the communication system.

Phase estimation and synchronization using a PSK demodulator

Abstract: A digital demodulator and method for demodulating digital data representing a phase shift keyed (PSK) signal are provided. The demodulator comprises a phase detector, automatic frequency controller, automatic timing recovery controller, data decoder, and unique word detector. According to the method of the present invention, a PSK signal is received and digitized to substantially remove the signal's amplitude characteristics. The phase detector receives an input of the digital data and based upon transitions in the data from a high state to low state and from a low state to a high state, provides phase estimates. The phase estimates are converted by the data decoder into binary data representing the symbols transmitted to form the PSK signal. A number of overlapping windows of digital data are used to determine phase estimates. The unique word detector receives an input of binary data from the data decoder and using a correlation technique identifies one set of windows which substantially maximizes synchronization of the demodulator with the received PSK signal. After the synchronizing window has been identified the automatic frequency controller monitors any frequency drift of the PSK signal and corrects the phase estimates based on the frequency error. The automatic timing recovery controller uses the corrected phase errors from early and late windows with respect to the synchronizing window to adjust the timing of the synchronizing window by advancing or delaying the demodulator's symbol timing signal to further maximize synchronization with the received PSK signal.

Stepped frequency ground penetrating radar

Abstract: A stepped frequency ground penetrating radar system is described comprising an RF signal generating section capable of producing stepped frequency signals in spaced and equal increments of time and frequency over a preselected bandwidth which serves as a common RF signal source for both a transmit portion and a receive portion of the system. In the transmit portion of the system the signal is processed into in-phase and quadrature signals which are then amplified and then transmitted toward a target. The reflected signals from the target are then received by a receive antenna and mixed with a reference signal from the common RF signal source in a mixer whose output is then fed through a low pass filter. The DC output, after amplification and demodulation, is digitized and converted into a frequency domain signal by a Fast Fourier Transform. A plot of the frequency domain signals from all of the stepped frequencies broadcast toward and received from the target yields information concerning the range (distance) and cross section (size) of the target.

Digitally implemented fast frequency estimator/demodulator for low bit rate maritime and mobile data communications without the use of an acquisition preamble

Abstract: A low-bit-rate, low-cost, all-digital preambleless demodulator for maritime and mobile data communications operates under severe high noise conditions, fast Doppler frequency shifts, large frequency offsets, and multipath fading. Sophisticated algorithms, including an FFT-based burst acquisition system, a cycle-slip resistant carrier phase tracker, an innovative Doppler tracker, and a fast acquisition symbol synchronizer, provide reliable burst reception. The compact DSP-based demodulator includes an input buffer receiving a complex sampled baseband input signal and providing a baseband output to a coarse frequency estimator fast Fourier transform (FFT) or discrete Fourier transform (DFT) module which produces a first estimation of the carrier frequency. A fine frequency estimator FFT or DFT module receives the first estimation and provides a second estimation of the carrier frequency. An extra coarse frequency estimator FFT or DFT module may be provided between the buffer and the coarse frequency estimator.

Communications using synchronized chaotic systems

Abstract: A chaotic transmitter (100) operates according to preselected chaotic protocols, such as a set of Lorenz equations. Modulation is accomplished by modifying a predetermined parameter of the set of chaotic Lorenz equations with a message signal, thereby producing a spread spectrum chaotic transmitted signal. A corresponding receiver (200) reconstructs a synchronizing drive signal, which is used by a demodulator (412) of the receiver (200) to detect the message signal.

Apparatus for improved underwater acoustic telemetry utilizing phase coherent communications

Abstract: An underwater acoustic communications system utilizes phase coherent modulation and demodulation in which high data rates are achieved through the use of rapid Doppler removal, a specialized sample timing control technique and decision feedback equalization including feedforward and feedback equalizers. The combined use of these techniques drammatically increases data rates by one and sometimes two orders of magnitude over traditional FSK systems by sucessfully combating fading and multipath problems associated with a rapidly changing underwater acoustic channel that produce intersymbol interference and make timing optimization for the sampling of incomming data impossible.

Design of a phase-sensitive detector to maximize signal-to-noise ratio in the presence of Gaussian wideband noise

Abstract: A design is presented for a phase-sensitive detector (PSD) based on matched filter theory, which is implemented using digital signal processing (DSP). The signal-to-noise ratio (SNR) improvement given by the new design is equal to that of the matched filter for the signal under consideration, and hence is maximal when the noise is Gaussian and additive. The theory of operation of analogue phase-sensitive detectors is discussed, and the SNR improvement obtained by using an ideal PSD is derived, along with the specific conditions under which this SNR can be expected. The limitations of real PSDs are then discussed. The new design is then presented in detail and its performance is compared to the analogue PSD. Experimental results are given which support the theoretical model of the demodulator, and an example of the use of the demodulator in a real application is given.

Demodulator for digitally modulated wave

Abstract: A QPSK modulated wave is inputted to an in-phase detector and an orthogonal detector. The detected components are converted to substantially a base band, and each component is digital-converted by A/D converters. Each digital component is spectrum-shaped by digital LPFs. The outputs of digital LPFs are inputted to a complex multiplier and calculated by use of first and second reproduction carriers and expressed as first and second calculation outputs, and inputted to a phase detector. The phase detector obtains phase difference data between the phase expressed by the first and second calculation outputs and a predetermined phase and quadrant data of the phase. The phase difference data is used for a PLL. The phase difference data is is inputted to a frequency error detection circuit detecting a frequency error. The frequency error output is smoothed by a filter of an AFC loop, and used as a control signal controlling the oscillation frequency of the local oscillation unit. If the frequency error is large, the frequency error detection circuit controls the AFC loop to be in an operation state and the PLL loop and the PLL loop to be in a fixed state. If the frequency error is small, the frequency error detection circuit contains the control state of the AFC loop and switches the PLL loop to be the operation state.

Transmission of multiple carrier signals in a nonlinear system

Abstract: A narrow band complex input signal, typically having multiple independently modulated carriers, is processed to produce an output signal. The process separates the multiple input signals (10) into an amplitude-limited angle-modulated carrier component (14) and an envelope component (18), and then combines these components by a form of pulse-duty-factor modulation such as pulse-duration modulation (16), at a sufficiently high sampling rate. The combined signal is input to a nonlinear power amplifier (22). Unwanted sidebands are rejected by bandpass filtering (24) at the amplifier output so as to pass only the carrier and its signal bandwidth.

Microphone and microphone system

Abstract: An infrared-ray cordless microphone including a modulator for modulating an acoustic-to-electric converted sound signal through a predetermined process; and an infrared-ray transmitter for transmitting an output infrared signal obtained by converting the modulated sound signal from the modulator; wherein the infrared-ray transmitter is disposed at a lower end of the microphone body. There is also provided an infrared-ray cordless microphone system comprising such a microphone and a sound output means which includes an infrared-ray receiver for receiving the infrared signal from the microphone, a demodulator for demodulating the received infrared signal, and an electric-to-acoustic converter for converting the demodulated signal into a sound signal.

Pseudo-noise modem and related digital correlation method

Abstract: A pseudo-noise (PN) correlation and demodulation method and apparatus, in which received signals are correlated with locally generated PN codes and correlation measurements are maintained for multiple time bins corresponding to signals received over possible multiple paths. Instead of selecting one or a small number of significant correlation measurements to control data demodulation, the method of the invention performs data demodulation over the multiple time bins, and then selects data values corresponding to significant correlation measurements and combines the selected data values, weighting them in accordance with their relative strengths a determined during correlation. Use of the invention provides improved performance in terms of signal quality and continuity in the presence of multipath conditions. Careful selection of design parameters allows the improved performance to be obtained in a compact and easily portable implementation including transmitter and receiver modules.

Fourier transform evaluation of interference patterns: demodulation and sign ambiguity

Abstract: The Fourier-transform method determines the interference phase distribution from an interference pattern. If evaluating only a single pattern, the sign remains unknown. Methods for interactive sign correction and for determination of the sign by two phase shifted interferograms are presented. For demodulation of the wrapped phase, a path independent algorithm is described.

Detecting false-locking and coherent digital demodulation using the same

Abstract: In a method of detecting false-locking the trains of clock signals corresponding to the two phase offset initially modulated trains of signals, the phase offset between said trains of clock signals is monitored, and false-locking is detected when the phase offset changes signal. Also, a method of demodulation implements this method of detecting false-locking. Also, a device for implementing the method of detecting false-locking contains a flip-flop in series with a monostable.