Showing papers on "Demodulation published in 1972"

Coherent Demodulation of Frequency-Shift Keying with Low Deviation Ratio

Abstract: A coherent binary FSK modulation system is discussed, that has the following properties: 1) it is phase coherent; 2) it has a low deviation ratio, h = \frac{1}{2}; 3 ) it occupies a small RF bandwidth, typically only 0.75 times the bit rate, without need for intersymbol interference correction; 4) it uses as receiver a self-synchronizing circuit and a phase detector, which together achieve optimal decisions; and 5) its error performance is about S dB better than that of conventional FSK.

Digital quadrature demodulator

Abstract: A quadrature analog-to-digital sampler, operating at a minimum sampling rate equal to the bandwidth of the input signal provides a pair of quadrature related digital signals which are input to first and second digital computers. The first computer calculates the instantaneous amplitude of the input signal and the second computer computes the instantaneous phase of the input signal. A third digital computer acts on the output of the second computer and differentiates the instantaneous phase of the signal with respect to time to provide frequency modulation output.

First-Order Discrete Phase-Locked Loop with Applications to Demodulation of Angle-Modulated Carrier

Abstract: In this paper, a first-order discrete phase-locked loop that tracks the phase of an incoming analog signal at discrete instants of time occurring once per cycle of the carrier is developed. The functional loop components and the operation of the loop are described in detail. The loop model is developed for both the deterministic and noisy case by a nonlinear coupled difference equation with perturbed (or deviating) arguments. The tracking performance for the inputs of the phase step, the phase ramp, and the sinusoidally modulated carrier is determined and the locking conditions for these input transients are derived. Conceptual designs using this first-order digital loop have been given for the demodulation of phase- and frequency-modulated signals.

Video and audio encoding/decoding system employing suppressed carrier modulation

Abstract: In a television transmission system, particularly a community antenna television system (CATV), although also applicable to broadcast television transmission, a system is disclosed for encoding both the video and audio components of a channel thus rendering the transmitted channel secure against unauthorized viewing and listening, by full or partial suppression of the video carrier such that the video modulation becomes inverted and the minimum 12.5% video carrier level required for intercarrier demodulation of the audio is lost. Sufficient information is transmitted within the encoded channel to permit a decoder at the receiver to produce a signal at the frequency of the suppressed video carrier, and of proper phase and amplitude, to restore the video carrier upon adding it to the suppressed video carrier.

The Digital Phase-Locked Loop as a Near-Optimum FM Demodulator

Abstract: This paper presents an approach to the optimum digital demodulation of a continuous-time FM signal using stochastic estimation theory. The primary result is a digital phase-locked loop realization possessing performance characteristics that approach those of the analog counterpart. Some practical considerations are presented and simulation results for a first-order message model are presented.

Discrete-time demodulation of continuous-time signals

Abstract: Nonlinear stochastic estimation theory is applied to the problem of obtaining discrete-time demodulator structures for the common types of analog communication signals. A stochastic communication model is presented that can be treated with current results in estimation theory. Approximate algorithms are developed for the estimation problem that yield mathematically realizable receiver structures for the cases of AM, PM, and FM. The digital receivers yield performance characteristics that compare favorably with those of their analog counterparts.

Complex demodulation for transient wavelet detection and extraction

Abstract: Research in fields such as communication, speech, oceanography, seismic exploration, economics, and biomedical data processing is often directed toward the analysis of nonstationary or transient data. Complex demodulation is shown to be a valuable method that can be used to decompose a composite signal composed of differing transient wavelets and to estimate spectra. For the latter application it is shown that several other techniques recently advanced in the literature are special cases of complex demodulation. The algorithm discussed can achieve the decomposition of a certain class of noisy composite signals composed of nonidentical unknown multiple wavelets overlapping in time, namely those signals with reasonably well-defined independent resonances in the spectrum. The decomposition estimates the arrival time, peak, envelope, and frequency of the damped oscillatory transient wavelet. The procedure has been tested extensively and several selected experimental results are tendered. It has been found that for wavelets of the type t^{k}e^{-at} \sin (\omegat) , k =0, 1 , that an uncertainty relationship for the product of the 3-dB bandwidth and the time duration of the wavelet must be satisfied. An error analysis has established a relationship between envelope-and phase-estimation errors to wavelet and filter parameters. The results obtained via complex demodulation are discussed relative to those obtained via inverse filtering, the complex cepstrum, and the chirp z transform.

Asynchronous quadriphase communications system and method

Abstract: A communications system and method for transmitting and receiving two independently timed (asynchronous) binary data signals on a quadriphase carrier. The four phase ambiguity ordinarily resulting from quadriphase transmission and reception is overcome by uniquely identifying each input channel, for example, by scrambling. In reception each channel is demodulated and applied to a corresponding descrambler. The descrambler outputs are sequentially examined to recognize any non-random characteristic of the data signals; recognition indicates connections from the demodulator to the descrambler in the correct sense. If there is no recognition, the connections are reversed and the scrambler outputs are again examined until recognition is achieved thus providing the original binary data signals.

Phase jitter compensator

Abstract: An automated REAL Time Equalized Modem (ARTEM) having a phase jitter compensator. Because a delay is involved in estimating a proper phase for demodulation, the data signals are delayed so that their delay is equal to the carrier phase estimation delay at the point where the final carrier phase correction is applied.

Discrete adaptive delta modulation system

Abstract: In a discrete adaptive delta modulation system, the modulator located at the transmitter converts an analog signal into a digital signal at the rate fs while the demodulator located at the receiver converts the digital signal back into the analog signal. The modulator and demodulator each comprise a programmable pulse generator operating at the rate ft for providing a controlled number of pulses k during each sampling period 1/fs to its associated single stepsize analog integrator. The modulator further comprises a comparator, a quantizer, and a sampling pulse generator operating at the rate fs while the demodulator further comprises a low-pass filter in series with the integrator. The number of pulses k provided by the programmable pulse generator multiplied by the integrator basic stepsize sigma o determines the overall stepsize sigma k in the integrator output signal, where k ft/fs. A feature of this system is that the number n of available stepsizes sigma k, which is a function of the ratio of generator rates ft and fs, can be several hundred without affecting the complexity of the integrating circuitry.

Differential encoded quadriphase demodulator

Abstract: Coherent demodulation of differentially encoded quadriphase modulation is accomplished using initially a non-optimum passive delay line detector to derive a carrier component. The output of the delay line demodulator, comprising I and Q channel data of less than desirable error performance, is differentially encoded for correlation with the original quadriphase modulation resulting in reconstruction of the suppressed carrier frequency. The reconstructed carrier is supplied to a filter bank and frequency synthesizer for generating a synthesized carrier frequency. The synthesized frequency and the reconstructed carrier are supplied to a phase-lock loop which generates phase correction signals. The synthesized frequency is mixed with the original modulation and the resulting signal is supplied to coherent phase detectors, the latter also receiving the phase correction signals from the phase-lock-loop, and serving to optimally demodulate the quadriphase components, yielding I and Q data channels. Efficiency of demodulation is improved further by employing the phase detector acquired I and Q data for reconstruction of the carrier frequency, instead of the initial delay line demodulator source. Matched filter components, comprising bit synchronization and bit regeneration circuitry process the demodulator outputs and contribute accordingly to requirements for minimum error demodulation. Another measure of improved demodulation performance is afforded by weighted comparison of the redundant I and Q channels of data of the delay line demodulator and the coherent phase detectors.

Laser receiver system

Abstract: A multi-tone gas laser emits light to a receiver. The receiver may be on the same vehicle as the light emitting laser, receiving light reflected from a moving vehicle, or the receiver and laser light transmitter may be moving relative to one another. Thus, the light which is received is modulated as a result of the relative vehicle motion. The receiver comprises a coarse 1 to 100 A. interference filter followed by a Fabry-Perot cavity and photo detector. The length of the Fabry-Perot cavity is chosen roughly equal to the cavity length of the transmitter laser, but with provision for fine fractional wave length control of its length. This length is adjusted until the output derived from a photodetector is peaked. A read-out of the vernier length at that time gives a measurement of the velocity. If the transmitter and receiver are relatively non-accelerating and the light transmitted is modulated then the receiver can intelligently demodulate the received signals.

Rate adaptive nonsynchronous demodulator apparatus for biphase binary signals

Abstract: A demodulator apparatus is described for demodulating nonsynchronous binary input signals of the two level biphase type having a nonuniform bit rate The demodulator comprises a reference means including a first digital counter which measures the width of successive input bits and produces time reference signals corresponding thereto so that the magnitude of such reference signal is automatically changed in response to variation in the bit rate A comparator means including a second counter and discriminator is employed for comparing the reference signal of the preceding input bit against the time interval of the biphase information portion of the next succeeding input bit to determine whether it is a binary one or a binary zero By employing this dynamic reference technique to compensate for varying bit rates in the nonsynchronous biphase input signal, one embodiment of the demodulator employing sixteen stage binary counters has been operated over a nonsynchronous bit rate range of 10 to 40,000 bits per second where the change in bit rate between adjacent bits can be between +20 and -35 percent

Extracting circuit for reproducing carrier signals from a multiphase modulated signal

Abstract: A carrier reproducing circuit for demodulating a signal transmitted by a pulse coded modulation-multiphase modulation system in which the output of a carrier extracting circuit is sampled by a clock pulse of a bit repetitive frequency in a sampling circuit and the sampled output is applied to a band-pass filter having a pass band of a carrier frequency to reproduce a carrier of reduced phase jitter.

Data demodulator apparatus

Abstract: A MARK/SPACE data demodulator for detecting frequency shift keyed MARK/SPACE incoming signals wherein the reference frequency is obtained at the receiver by detecting the difference in frequency between the MARK and the SPACE frequency signals and utilizing this frequency difference in the data detection process.

Method and apparatus for detecting absolute value amplitude of am suppressed carrier signals

Abstract: Apparatus for detecting the absolute value amplitude of amplitude modulated suppressed carriers includes first and second product detectors which use quadrature phases of a locally generated reference carrier to product detect the modulated carrier producing first and second vector components of the amplitude of the information signal, and an output circuit for obtaining the vector sum of the two components of the information signal amplitude to thereby provide a signal which is proportional to the absolute value amplitude of the information signal. In one embodiment, the vector sum of the two components of the information signal amplitude is obtained by amplitude modulating quadrature phases of a high frequency carrier in separate amplitude modulators, summing the amplitude modulated signals thus produced, and demodulating the resultant signal to translate the high frequency carrier back to the base-band and thereby recover the amplitude information.

Instantaneous adaptative delta modulation system

Abstract: An instantaneous adaptive delta modulation system including a modulator and a demodulator. The modulator comprises a comparator having a first input connected to receive an analog signal, a second input adapted for connection to an integrator located in the conventional feedback loop of the delta modulator, and a shift register connected to the output of the comparator and adapted to store the digits generated at the output of the comparator at sampling time T0 and the digits generated at sampling times T 1 and T 2. A binary up and down counter is connected to the shift register through a control circuit which makes the decision as to whether an up count, a down count, or no count at all is required. The output of the counter is applied to a decoder for converting the binary outputs of the up and down counter into a number of outputs. An amplifier having a corresponding number of values of gain is connected to the outputs of the decoder and is thus responsive to the level of the up and down counter for providing a predetermined gain into the feedback loop of the delta modulator. The integrator is connected to the output of the amplifier and its output is connected to the comparator which compares the output signal of the integrator with the input analog signal and generates a signal depending upon the difference between the two signals. The demodulator is similar to the modulator except that the input signal is fed directly to the shift register and that the output of the integrator is fed to a low-pass filter.

The Performance of a Noncoherent FSK Receiver Preceded by a Bandpass Limiter

Abstract: Many applications of the bandpass limiter involve either coherent or noncoherent demodulation following the limiter. In this paper we study the performance of a noncoherent frequency-shift keying (FSK) receiver when it is preceded by a bandpass limiter. In particular, we obtain expressions for signal suppression- factor, output signal-to-noise ratio (SNR), and error probability from which one can assess the degradation in performance of the receiver due to the presence of the limiter. Both narrow-band and wide-band cases are treated thus covering situations where no frequency uncertainty exists (i.e., known carrier frequency) as well as large-frequency uncertainties. Also discussed is the first-order signal plus noise probability density function (pdf) following noncoherent demodulation.

Digital transmission system

Abstract: In the digital transmission system of the type in which from the transmitter are transmitted VSB- or SSB-modulated pulses of the sampling-point-zero-cross type multi-level pulse signal having the clock or pilot signal for timing and the carrier inserted at the ends of the band of said multi-level pulse signal, and at the receiving end said clock signal and said carrier are recovered to demodulate the modulated multi-level pulse signal, the intersymbol interferences at the sampling points spaced by one and two time slots apart from the center sampling point of the single pulse response in the transmission line are detected and used to automatically control the optimum phases of the recovered clock signal and carrier.

Coherent digital demodulator

Abstract: A digital coherent demodulator for signals pulse-amplitude modulated in the passband of data transmission systems multiplies sampled values of quadrature-related components of received datachannel signals by the respective sampled values of sines and cosines of the demodulating carrier wave and combines these two products to form a sampled baseband signal from which the transmitted data is recoverable. All samples are taken at twice the highest baseband frequency rather than at twice the highest passband frequency. The usual requirement for a low-pass filter to eliminate double-frequency components generated in the conventional demodulation process is also avoided.

An all digital phase locked loop for FM demodulation.

Abstract: A phase-locked loop designed with all-digital circuitry which avoids certain problems, and a digital voltage controlled oscillator algorithm are described. The system operates synchronously and performs all required digital calculations within one sampling period, thereby performing as a real-time special-purpose computer. The SNR ratio is computed for frequency offsets and sinusoidal modulation, and experimental results verify the theoretical calculations.

A sampling FM wide-band demodulator useful for laser Doppler velocimeters

Abstract: A sampling FM demodulator of large bandwidth, consisting of a swept filter and an oscilloscope, is described. The sampled FM function is reconstructed and displayed on an oscilloscope. For a detection bandwidth of 100 MHz and a spectral resolution of 3 MHz (3 percent) the temporal resolution is as high as dv/dt = 1014s-2= 100 MHz/µs in the case of a periodic modulation signal (e.g., flow oscillations). Measurements at an SNR as low as -40 dB, referred to the detection bandwidth, are still possible. Transient FM's can be investigated at a reduced temporal resolution of dv/dt = 3 MHz/µs. The system transfer characteristic is linear to better than 0.5 percent over the whole range and is not affected by the random AM of the Doppler signal. A theoretical analysis and experimental investigations of the system and its application are given.

Signal processing system for television receiver having acoustic surface wave devices for improved tuning and video demodulation

Abstract: This disclosure depicts a number of signal processing circuits for a television receiver which include acoustic surface wave devices for improved tuning and video demodulation. In each embodiment an IF stage has an acoustic surface wave bandpass filter. In one embodiment a reference oscillator forming part of a synchronous video detector and also part of an APC loop has a frequency-selective surface wave filter for establishing its frequency of oscillation. Another embodiment has an AFC circuit including a surface wave discriminator. In all embodiments the acoustic surface wave devices have similar thermal characteristics and thermal exposure so as to cause temperature tracking of the frequency characteristics thereof and thereby to temperature stabilize the receiver. The surface wave filter devices which are associated in the disclosed systems may utilize thermally homogeneous piezoelectric substrate means.

Multiplex color television demodulator

Abstract: A color television demodulator is disclosed for processing the NTSC color signal. The video signal is converted to base band and two color difference components are derived in two four-quadrant multipliers during video. During burst, which precedes each line of video information, two control signals are derived in a time multiplexed fashion from the same pair of four-quadrant multipliers. The demodulated color difference components are re-combined with the luminance to provide the R, G, B signals for display. The demodulated burst is used to derive a phase control voltage for synchronizing the local oscillator used in the demodulation process. The demodulated burst is also used for deriving a color amplitude control voltage for stabilizing the color intensity. The demodulator circuitry is designed for integrated circuit fabrication with a minimum "pin" count and a minimum of outboarded components.

Theory of Operation and Design of an All-Digital FM Discriminator

Abstract: The theory of operation and the design of an all-digital FM discriminator is presented in this paper. It is shown that the digital discriminator is equivalent to the Foster-Seely demodulator, i.e., a discriminator that converts the FM signal into an AM signal and then recovers the AM by using envelope detection. The output signal-to-noise ratio is found analytically above and below threshold and the results are verified experimentally. The theoretical analysis includes the effect of quantization noise, frequency jitter in the internal oscillator, and thermal noise. The system can be integrated and with the use of readily available emitter-coupled logic (ECL) can operate at intermediate frequencies suitable for many space, industrial, and commercial applications.

Transmission system for stereophonic signals

Abstract: The invention relates to a transmission system for the transmission of two coherent stereophonic signals by means of single sideband modulation in which one of the signals is transmitted as an upper sideband signal and the other signal is transmitted as a lower sideband signal and in which the required single sideband modulators are controlled by carrier signals of unequal frequency. These carrier signals are derived in both the transmitter and the receiver through selection circuits from a carrier circuit controlled by a generator, which circuit is incorporated in an automatic phase correction loop (AFC-loop) provided with a phase detector and a modulator to which the output signals from the selection circuits are applied as modulating signals and to which a modulation signal derived from the carrier circuit is applied for generating an output signal having a frequency which is equal to that of the generator, which output signal is applied together with a control signal to the phase detector for generating a control signal controlling a frequency-determining member of the generator.

Synchronizing system for phase-modulation telecommunication system

Abstract: The burst acquisition time in a phase-modulated TDMA satellite communication system is reduced by means of a novel demodulator at a receiving station. The received carrier frequency is filtered out of the two-phase phase-modulated preamble word portion of the received signal and a reference carrier signal is extracted therefrom. The N-phase phase modulated information word portion is reverse phase-modulated and phase-shifted so that its carrier frequency has the same relative phase as that of the preamble word portion, and a reference carrier signal is extracted therefrom. Consequently, the reference carrier is continuously recovered across the boundary of the preamble and information word portions and is available to demodulate the burst signal.

Self-monitoring of radio receivers

Abstract: Continuous monitoring of a radio receiver without impairing normal receiver operation is provided by an internally generated carrier signal combined at low level with the received signal. The test carrier is so modulated as to not affect normal receiver detection process, and the test modulation signal component, as present in the output of the receiver detector, is synchronously demodulated and monitored to provide indication of faulty receiver threshold level and signal distortion.