Showing papers on "Noise (signal processing) published in 1973"

Some Optimum and Suboptimum Frame Synchronizers for Binary Data in Gaussian Noise

Abstract: In this correspondence we investigate the performance of several optimum and suboptimum devices for locating a sync word in data corrupted by Gaussian noise. One suboptimum synchronizer, which is extremely simple to instrument, is shown to perform virtually optimally over the entire range of interesting signal-to-noise ratios.

Noise reduction systems

Abstract: A noise reduction system comprising a compressor feeding an information channel and a complementary expander treating the output of the channel. The system is applicable to audio and visual signals using compressors and expanders with appropriately scaled frequency selective circuits which narrow the band in which compression and expansion take place as the signal level rises. Distortion and tracking accuracy problems are reduced by the use of compressor and expander configurations embodying a main signal circuit and a further signal circuit, the main circuit providing a first signal which has dynamic range linearity with respect to the input signal and the further circuit providing a second signal which is restricted to a small part of the dynamic range of the signal in the main circuit. The restriction may be effected by one or more variable filter means having a pass band which narrows to exclude large signal components from the compression or expansion action. The second signal is combined additively with the first signal for compressor operation and subtractively for expander operation. True complementarity is attainable by the use of a compressor and expander together to provide an overall noise reduction action without introducing defects into the signal being processed.

Optimal test signal design for linear S.I.S.O. system identification

Abstract: A sufficient condition for consistent estimates of parametera in linear S.I.S.O. system identification is that the input signal should be ‘ persistently exciting ’, However,. in practice the exact nature of the test signal has a direct bearing upon the identification accuracy. This paper shows how a-priori knowledge of the approximate system and noise model parameters may be used to design a test signal which will minimize the variance of the parameter estimates. The design procedure is computationally efficient as full advantage is taken of the special structure of linear S.I.S.O. systems. The optimal test signals are shown to result in a significant reduction in the parameter variances. This is of considerable practical importance as either the experiment time may be reduced for the same model accuracy or for fixed experiment time a model of much higher accuracy may be obtained.

Practical application of fractional Brownian Motion and noise to synthetic hydrology

Abstract: A synopsis of self-similar stochastic processes is presented with special emphasis on fractional Brownian motion and noises. Detailed analysis and discussion are on the approach of ‘fast fractional Gaussian noises’ by Mandelbrot and his collaborators. Modifications are incorporated and parameter selection criteria suggested so that the method becomes simpler, more flexible to use, and easier to follow. A step-by-step procedure is included for convenience of application.

Signal amplification circuit with phase detecting means and variable signal level recognition means

Abstract: A circuit is described for generating an output signal pulse of substantial uniform magnitude in response to an input signal which may be variable over a range of signal magnitude such that large signal noise may exceed the magnitude of the small signals The circuit provides automatic threshold adjustment in response to the magnitude of the immediately preceding input signal to discriminate against noise signals on the input lead The circuit also provides for automatically switching out of the threshold controlling means when the input signal threshold value has been exceeded so that the turning off of the output signal may be accomplished substantially in response to the ''''zero voltage crossing'''' of the input signal to provide an electrical event which may have a predetermined time relationship to a sensed mechanical event for subsequent utilization purposes

Enhancing resolution in analog-to-digital conversion by adding statistically controlled noise to the analog input signal

Abstract: The resolution of analog-to-digital conversion is enhanced by combining the analog input signal, prior to sampling, with a statistically controlled noise signal. The noise signal has a defined probability density function, and its power density spectrum is outside the spectra of the analog input signal and the sampling signal so that none of the noise energy is in the frequency interval of the data of interest following sampling.

Noise spectrum equalizer

Abstract: Apparatus for noise spectrum equalization of applied spectrum samples to enhance detection of periodic signals embedded in noise. Equalization is achieved with apparatus which repetitively searches for and detects strong periodic signals within the total signal spectrum and subsequently disregards the detected signals in computing an equalizing signal representative of background noise. The applied power spectrum is divided by the equalizing signal to obtain an equalized, flat, spectrum of zero mean, yet of unchanged signal levels relative to noise variance. The use of iterative detection of strong periodic signals in computing the equalizing signal results in noise spectrum equalization apparatus that is insensitive to the unwanted effects of strong periodic signals.

The Effect of a Bandpass Nonlinearity on Signal Detectability

Abstract: When an angle-modulated signal plus noise constitute the input to a bandpass device exhibiting a nonlinear input-output power characteristic and AM to PM conversion, the noise component of the output has altered first- and second-order statistics. A method of evaluating the two-dimensional first-order statistics of this noise is presented. The effect on signal detectability of a nonlinearity inserted between two channel noise sources is studied; expressions for the mean square received phase error and probability of error (for coherent digital phase modulation) are derived. The hard limiting satellite channel, with Gaussian noise on the up and down links, is examined in detail, and it is demonstrated that the limiter can significantly affect signal detectability.

Pseudo-noise test set for communication system evaluation

Abstract: A test set for communications systems includes a pseudo-noise sequence generator providing a test signal which is fed to a pair of signal channels The first channel includes a spectrum shaping filter and a conditioning amplifier The second channel includes a variable delay circuit, a spectrum shaping filter matched to the first filter, and an amplifier The output of the first channel is applied to the system under test The output of the system and the output of the second channel are compared to determine the degree of distortion suffered by the test signal due to the communications system

Heuristic solution of a signal design optimization problem

Abstract: This paper discusses a heuristic solution procedure for a combinatorial optimization problem that originates in designing signal constellations for modems. The design problem is to place m signals in a two-dimensional space to minimize the average error rate under specified noise conditions, using a maximum-likelihood decoding scheme. Intuitively, it amounts (roughly) to spreading the signal points as far apart as possible, according to the distance measurement implied by the noise function. We show how this problem can be reduced to a discrete one: Given an l by n matrix P, and m 1 , …, i m } of the rows of P that maximizes and then describe an efficient procedure for finding this maximizing set. Experiments indicate that the procedure is a useful tool, both for analysis of existing and proposed signal constellations and for finding new, near-optimum ones.

Apparatus for detecting and elminating a transfer of noise records to a data processing apparatus

Abstract: Noise detection apparatus included in a peripheral controller operates to detect automatically when a noise record has been stored in the controller buffer storage unit. The detection apparatus includes control apparatus associated with the buffer storage unit which keeps track of the number of storage locations into which data characters have been stored during a transfer operation. Also included are means for selectively establishing one or more counts corresponding to a minimum number of data characters which must be stored in the buffer storage unit before the controller starts to transfer any data characters to a data processing unit. Each time a minimum number of characters has not been previously stored in the buffer unit when the controller receives a signal indicating the completion of the transfer, the controller clears the buffer storage unit of data characters and continues the transfer.

Automatic gain control circuit

Abstract: An automatic gain control circuit particularly desirable for use in a magnetic recording and/or reproducing apparatus includes a variable impedance element interposed in a signal shunt path to control the gain in accordance with the impedance of such element which is varied by a control signal from a plurality of capacitor charging circuits having different time constants and being supplied with the output of a rectifier for the received signal. The arrangement is such that the automatic gain control function is made dependent on the time duration of the received signal level, that is a short recovery time is provided for restoration of the original gain when an impulse or noise of short duration and high level is received, and a relatively long recovery time is otherwise provided for increasing the dynamic range of the output signal.

The structure of least-mean-square linear estimators for synchronous M -ary signals (Corresp.)

Abstract: Several authors have shown that the structure of the least-mean-square linear estimator of the sequence of random amplitudes in a synchronous pulse-amplitude-modulated signal that suffers intersymbol interference and additive noise is a matched filter whose output is periodically sampled and passed through a transversal filter (tapped delay line). It is our purpose in this paper to generalize this result to synchronous m -ary signals (e.g., FSK, PSK, PPM signals). We prove that the structure of the least-mean-square linear estimator of the sequence of random parameters in a synchronous m -ary signal, which suffers intersymbol interference and additive noise, is a parallel connection of m matched filters followed by tapped delay lines. A similar structure is derived for the continuous waveform estimator of a synchronous m -ary signal. Finally, we present a structure for estimation-decision detection of synchronous m -ary signals, which is based on least-mean-suare linear estimates of a posteriori probabilities.

Zero sense after peak detection circuit

Abstract: A zero sense after peak detection circuit for rejecting noise signals includes a peak detect and hold circuit which resets a latch only if the input signal has exceeded a predetermined negative threshold voltage which is a fixed percentage of a valid signal. After the input signal exceeds the predetermined negative threshold voltage and the latch is reset, the latch is then set when a zero sense circuit senses the input signal crossing zero.

Bar geometry verification system for bar-coded characters

Abstract: Logic circuitry for generating a signal when bar-coded information includes noise signals. The logic circuitry detects instances in which the width of a bar is too narrow, or too wide, or the height of a bar too small, and generates an error signal when any such condition occurs. An error signal is also generated if the width of a bar is incorrect and not determinable.

Recognition and identification system with noise rejection capabilities

Abstract: An improved electronic recognition and identification system for recognizing and identifying the resonant frequency of a coded external passive network. The system comprises an active network including a sweep oscillator driving a sensing coil to generate an external electromagnetic field for inductive coupling to the passive resonant network when said passive network is brought within the proximity of the sensing coil, detector means for detecting variations in the signal across the sensing coil due to said passive network and for generating time base signals representative of the resonant frequency of the passive network, an internal reference signal generator network for generating reference signals representative of the reference identification frequency, a comparator network responsive to said detector and said reference signals for generating control signals indicative of coincidence or noncoincidence of the detector and reference signals, and noise rejection network responsive to noise signals generated from external or internal noise sources and adapted to inhibit operation of the system in the event noise signals are sensed.

Self-scanning photo diode array

Abstract: An improved self-scanning photo-diode array is disclosed which utilizes a shift counter as a scan generator. The high level clocking signals and start signal used by the scan generator are generated on the same chip which includes the diode array from an externally provided low level timing signal. The symmetry of the array eliminates much of the noise associated with switching transients present in prior art devices.

Signal discriminating device

Abstract: A signal discriminating device comprising a band-pass filter for selectively passing a signal-frequency component at a predetermined frequency and another band-pass filter for selectively passing a noise-frequency component at a frequency other than but close to the signal frequency, wherein the discrimination of signal from noise is effected on the basis of existance or non-existance of the signal-frequency component and the noise-frequency component in such a manner that when only the signal-frequency component is detected the reception of signal is determined and when both the signal-frequency component and the noise-frequency component are simultaneously detected the reception of noise is determined.

Communication receiving apparatus employing several samples of baseboard noise to detect an incoming signal and turn on the apparatus

Abstract: Communication receiver employing squelch circuitry to turn on the receiver during receipt of an incoming signal. The RF and IF sections of the receiver are turned on periodically and the baseband noise originating in the IF limiter is sampled. The baseband noise pulses during the sample period are counted. If the number of pulses is less than a certain number, this information is stored as an indication that an incoming signal is present. If the certain number of pulses are counted during a period, an indication that an incoming signal is not present is stored. Based on several stored indications decision circuitry determines whether or not an incoming signal is present and causes operating power to be supplied to all sections of the receiver only if the determination is made that an incoming signal is present.

Adaptive control system using command tailoring

Abstract: An adaptive control system for the tailoring of outer loop error command signals so that established performance capabilities of inner loop elements are not exceeded. Self-adaptive optimal response control is accomplished by monitoring instrumented signal levels and derivatives, comparing these to component limitations and adjusting all outer error signal gains proportionally to allowable signal level. This technique can be used on either proportional or bang/bang control. The sequential incorporation of error command signal tailoring, moving out from inner elements to inner loops to succeeding outer control loops in high gain multiple feedback control systems provides a very practical means of implementing a self-adaptive control system which optimizes performance within physical hardware constraints and under conditions involving extreme variations in intrinsic gains command activity or signal levels, and noise influences.

Constant-Factor Delta Modulator

Abstract: A companded delta modulator, employing an adaptation principle that produces voltages fed back to the error point in the coder which are discrete and multivalued, is achieved with just a 1 bit memory and simple signal processing, and is a significant invention. The constant-factor-delta-modulator system described here is an extension of this principle, which gives an improved signal/noise ratio at the output of the decoder and remove an objectionable hunting characteristic. These improvements are acquired due to a slight increase in the complexity of the coder.

Differential pulse code modulation transmission system

Abstract: Two embodiments of a transmission system capable of the direct encoding of frequency multiplexed color television signals into differential pulse code modulation signals are disclosed. In the first embodiment, the transmitter includes a pre-emphasis filter whose transfer function assumes a minimum value in the vicinity of the frequency of the color subcarrier signal. The output of the pre-emphasis filter is connected to a noise feedback pulse code modulation coder which delivers quantized signals as its output. A code converter converts the quantized signals to a differential pulse code modulated signal for transmission. The receiver includes a de-emphasis filter having the inverse transfer function of said pre-emphasis filter. The second embodiment is equivalent to the first but instead of a pre-emphasis filter employs a predictive filter connected in a feedback path around the quantizer. The transfer function P of the predictive filter is such that the value (1-P) assumes a minimum value in the vicinity of the frequency of the subcarrier signal.

Fault-detecting system for a multi-channel relay system

Abstract: In a digital transmission system for transmitting in parallel a plurality of information channels, and including a plurality of relay stations, a technique for detecting faults and particularly for distinguishing between faults in individual channels and a fault common to all channels which may arise due to rainfall attenuation. The method involves determining a first fault threshold level which is proportional to the level of interfering signals on a channel caused by the signals on neighboring channels and a second fault threshold level proportional to the level of noise signals on a channel resulting from channel components. At at least one relay station, a monitoring signal is developed for each channel which is representative of the level of the incoming signal to the relay station for the corresponding channel and the level of the monitoring signal is compared to the first and second threshold levels. If the monitoring signal level falls below the first threshold level, it is an indication of a single channel fault. If it is determined that the levels of the monitoring signals on all the channels fall below the first threshold level, it is an indication of a common fault to all of the channels. If only a single channel fault is determined, the incoming channel signal is switched to a standby channel. If, on the other hand, a common fault to all of the channels is determined, a switch-over to an alternate route is effected when the monitoring signal level falls below the second threshold signal level. Apparatus for developing the monitoring signals, for comparing the monitoring signals with the threshold levels and for effecting the appropriate switch-overs are described.

Apparatus and method for measuring the signal to noise ratio for a periodic signal

Abstract: Apparatus for measuring the signal-to-noise ratio of a television signal wherein the noise and signal level of the signal are derived from the on-the-air television signal horizontal sync pulses. The noise is derived by sampling the sync pulses and bandpass filtering the samples, while the signal level is derived by D.C. filtering the sync pulse samples. The signal-to-noise ratio is the ratio between the derived signals which ratio is provided by a suitably calibrated meter.

Signal processing circuit

Abstract: In sound target detection equipment, at least three microphones are used in a broadside array manner to ascertain the presence of a selected sound source. The outputs of the three microphones all include the sought signal S and respectively contain noise components X, U and Y. These outputs are combined to provide X-U and X-Y. These two signals are then applied as separate inputs to a discriminator which applies the rules: (a) when the input signals are both of the same polarity, the discriminator selects the input closer to zero and presents it as the output; (b) when the input signals are of opposite polarity, the device presents zero as the output. The output from the discriminator is then subtracted from one of the original microphone outputs in a manner tending to cancel out the noise contents, and the resulting signal examined for the presence of the sought signal S. The invention is applicable also to non-aural signal detection equipment.

Statistical noise processor

Abstract: A statistical processing device for improving the signal to noise ratio of signals and transients within a noise environment Samples of electrical signals indicative of ocean noise are applied to a calculator that obtains the mean, variance and third moment of the electrical signal A delay circuit delays the calculator output signal for comparison with later produced electrical signal samples A second calculator receives the outputs from the delay circuit and manipulates the difference between a first higher order moment signal to obtain an output signal having an amplitude indicative of a transient or target The output signal is displayed on a lofargram which provides an enhanced visual indication of the sampled electrical signal contents

Noise reduction system and apparatus using a compression and expansion system

Abstract: A noise reduction system employs a compression and expansion system using a compressor and an expandor to reduce noise in a signal transmitted through a transmission system. The compressor side of the system comprises a compression circuit means provided in an open loop, through which the signal passes. A control circuit means generates a control voltage in accordance with the level of the output signal from the compression circuit means. This control voltage is applied to the compression circuit means, thereby to control compression ratio. The expandor side comprises an expansion circuit means which is provided in a negative feedback loop of a negative feedback amplifier. A control circuit means generates a control voltage in accordance with the level of the input signal to the negative feedback amplifier. This control voltage is applied to the expansion circuit means, thereby to control expansion ratio. The compressor and the expandor are so constructed that a coefficient k of amplitude control characteristic of the compressor, and a feedback ratio β of the expandor become equal to each other. The expansion apparatus can be constructed independently and used in the aforementioned system.