Showing papers on "Signal-to-noise ratio published in 1970"

Performance limitations and error calculations for parameter estimation

Abstract: Error calculations cannot be carried out precisely when parameters are estimated which affect the observation nonlinearly. This paper summarizes the available approaches to studying performance and compares the resulting answers for a specific case. It is shown that the familiar Cramer-Rao lower bound on rms error yields an accurate answer only for large signal-to-noise ratios (SNR). For low SNR, lower bounds on rms error obtained by Ziv and Zakai give easily calculated and fairly tight answers. Rate distortion theory gives a lower bound on the error achievable with any system. The Barankin lower bound does not appear to give useful information as a computational tool. A technique for approximating the error can be used effectively for a large class of systems. With numerical integration, an upper bound obtained by Seidman gives a fairly tight answer. Recent work by Ziv gives bounds on the bias of estimators but, in general, these appear to be rather weak. Tighter results are obtained for maximum-likelihood estimators with certain symmetry conditions. Applying these techniques makes it possible to locate the threshold level to within a few decibels of channel signal-to-noise ratio. Further, these calculations can be easily carried out for any system.

Noise in amplifiers

Abstract: In practically every type of research program in the physical sciences as well as in sophisticated engineering analyses, very small electrical signals must be measured and, in general, the limit of attainable precision and detectability is set by noise. This is true for the physicist and chemist performing nuclear magnetic resonance or spectroscopy experiments, for medical and biological researchers interested in evoked potentials, for geologists measuring small remanent magnetic fields in rock samples, for the metallurgist making Fermi surface measurements, and for the engineer performing vibration analysis and sensitive bridge measurements. These are only a few examples of applications in which noise plays a critical role in limiting measurement precision and signal detectability. This article discusses some of the inherent problems and describes techniques for improving signal-to-noise ratio.

Apparatus for improving signal-to-noise ratio in logging-while-drilling system

Abstract: The specification discloses a method and apparatus for substantially reducing the uphole noise in a logging-while-drilling system wherein a signal representative of a downhole parameter is generated down a well and is transmitted to the surface in the form of an acoustical wave in the drilling fluid, e.g., mud. Two spaced transducers measure the acoustical pressure at two points in the mudline between the pumps and the well and convert these pressures to corresponding signals. One of these signals is time shifted an amount equal to the travel time of sound in the mud between the two transducers and, after one of these signals has had its polarity reversed, the two signals are added to reduce the uphole noise substantially. By filtering one of the pressure measurement signals with a filter having characteristics related to the distortion of the flow path between the two spaced transducers, noise is further reduced. The combined signals are further filtered with a Wiener type filter which best recovers the signal.

Nonlinear Analysis of an Absolute Value Type of an Early-Late Gate Bit Synchronizer

Abstract: The steady-state phase noise performance of an absolute value type of early-late gate bit synchronizer is developed using the Fokker-Planck method. The results are compared with the performance of two other commonly used bit synchronizer circuit topologies on the basis of either 1) equal equivalent signal to noise in the loop bandwidth in the linear region, or 2) equal loop bandwidth at each input signal-to-noise ratio R s . These comparisons are made as a function of R s . In both cases, the absolute value type of early-late gate yields the best performance (in the sense of minimum phase noise) at every value of R s .

Models for the Brain

Abstract: Willshaw, Buneman and Longuet-Higgins have proposed a nonholographic associative memory model for the brain1. They also criticize the proposal made by myself2 and by Pribram3,4 that the brain would be organized on the holographic principle. They say: “How could the brain Fourier-analyse the incoming signals with sufficient accuracy, and how could it improve on the rather feeble signal to noise ratio of the reconstructed signals ?”.

Optimization of the Performance of a Digital-Data-Transition Tracking Loop

Abstract: The steady-state behavior of a data-transition tracking loop, used as a bit synchronizer in a phase-coherent receiver, is considered. Optimization of mean-square phase noise and mean time to first cycle slip is performed when the average power of the reference cross-correlating signal is constrained. It is shown that by adjusting the quadrature channel gain along with the integration interval, a significant improvement in phase noise and cycle slip performances can be achieved over that system which integrates in the quadrature channel over the full symbol period. All the results are derived for a first-order loop filter merely to indicate the approach to the problem and the relative value of optimizing the system.

Circuit arrangement for improving the signal-to-noise ratio of a stereo decoder

Abstract: A variable resistor, a photoconductor shone upon by an incandescent lamp the brightness of which is inversely proportional to the carrier strength, or a variable time constant RC-network is connected to the stereo decoder to vary the stereo separation in direct proportion to the carrier strength.

DPSK Versus FSK with Frequency Uncertainty

Abstract: Expressions and curves of error probabilities of differential phase shift keying (DPSK) and noncoherent frequency shift keying (FSK) are obtained as a function of the pulse carrier frequency offset. These indicate that the frequency offset which causes the DPSK error probability to be larger than the FSK error probability is approximately \Delta\omegaT = 0.74. This crossover frequency appears to be a linear function of the signal-to-noise ratio over the range-4 dB to 14 dB. The crossover point is extended by sub-bit processing and the previous curves are modified for this case.

Process and automatic device for signal-to-noise ratio measurement of a television signal

Abstract: Process and device for automatically measuring the signal-to-noise ratio of a television signal wherein the noise is extracted from the transmitted television signal during the blanking interval, i.e., the interval marked by the absence of a video signal. The noise is subjected to amplification and successive attenuation of pre-selected values changed step by step until the noise power is caused to be equal to a pre-selected threshold value. The proper circuitry logic automatically varies the attenuation and computes the signal-to-noise ratio of said television signal from the final attenuation value.

FSK and DPSK Performance in a Mixture of CW Tone and Random Noise Interference

Abstract: The bit error probability performance of both frequency-shift-keyed (FSK) and differential phase-shift-keyed (DPSK) binary systems are described when disturbed by an interference consisting of a mixture continuous wave (CW) tone and narrow-band random noise in addition to the usual broad-band thermal noise background. Performance of the two systems is shown to be identical with the exception that the equivalent DPSK performance occurs at 3 dB less signal-to-thermal-noise ratio. The combination of CW tone and noise interference severely degrades system performance under a broad range of conditions.

Signal-to-Noise ratio and design complexity based on Unified Loss Function - LTB case with Finite Target

Abstract: Taguchi’s quality loss function for larger-the-better performance characteristics uses a reciprocal transformation to compute quality loss. This paper suggests that reciprocal transformation unnecessarily complicates and may distort results. Examples of this distortion include the signal-to-noise ratio based on mean squared deviation and the signal-to-noise ratio based on complexity. The concept of complexity is an important element of axiomatic design and axiomatic quality. This paper shows that a simple linear transformation as used in the unified loss function can give an appropriate and comparable signal-to-noise ratio based on mean squared deviation and signal-to-noise ratio based on complexity for larger-the-better characteristics. Mathematical derivations are given and two examples are discussed to demonstrate the proposed methodology.

Optical receiver having a maximized signal-to-noise ratio

Abstract: A method of maximizing the signal-to-noise (S/N) ratio or a direct-detecting optical pulse receiver for an input pulse having a well-defined duration and receiver apparatus derived therefrom. The S/N ratio is defined as the ratio of the signal output peak instantaneous power to the noise output mean power. The optical receiver comprises an optical detector with fast-response, highsensitivity characteristics followed by a cascade arrangement of amplifiers, two RC dividing networks, one low pass and the other high pass and an amplitude detector. The noise sources comprise the quantum noise generated within the input light-sensitive device and the thermal noise generated within the input load resistor of the device. The dividing networks form a bandpass filter which is designed to maximize the S/N ratio. As a result, the time constants of the filters turn out to be substantially equal and the output load resistance of the detector is set as high as is practical. The method achieves a S/N ratio approaching that obtainable with an ideal matched filter for small values of the input pulse width (to), e.g., of the order of 10 nanoseconds. The S/N ratio improvement over prior art receivers is in the order of 20 db. The receiver is especially effective when to is less than 1 microsecond.

Application of digital filtering in improving the resolution and the signal-to-noise ratio of nuclear and magnetic resonance spectra

Abstract: The digital filtering was proven to be useful in processing convolved signals. In this paper an application of this method in order to improve the resolution of nuclear and magnetic resonance spectra is presented, An emphasis is laid on the possibility of diminishing the noisy secondary effects. The processing was achieved using the FFT algorithm. Some practical results obtained are delivered.

Room-temperature close-confinement GaAs laser with overall external quantum efficiency of 40 percent

Abstract: The most efficient room-temperature GaAs injection lasers have been made by use of the close-confinement (heterostructure) technique. Differential external quantum efficiency in excess of 50 percent was observed on lasers having threshold current densities as low as 8500 A/cm2.

Adaptive Radar Beacon Forming

Abstract: Propagation errors along paths between an array radar and a distribution of targets cause degradations in angle measurements and detection range. The overall objective of the research described in this paper was to analyze and demonstrate the use of conjugate reflections for compensating adverse effects of path errors. The effect of reflecting the conjugate of an incident wave is described mathematically and is demonstrated by computer simulation. Repeated conjugate reflections are shown to result in the formation of a single beam usually focussed on a target highlight. Echoes from this spatial reference, or "beacon" are shown to provide the means by which aperture phase errors may be effectively compensated. Results of radar simulations include two-way patterns computed for an example involving a distribution of three-point targets and half-wave-length Gaussian aperture errors. Without compensation a gain loss of 12 dB is computed; with error correction, based on echoes from an adaptively focussed beam, the two-way pattern is within a small fraction of a dB of the ideal pattern. The effect of noise on adaptive beacon forming was considered for a case involving one target. Repeated conjugate reflections improve signal-to-noise ratio as long as the effect of noise is less than the effect of aperture dephasing on the power reflected back to the target. An example is presented in which signal-to-noise ratio at the output of the receiver combining network is increased from 4 to 11.8 dB.

On Optimizing Array Reception of Multipath

Abstract: This paper reviews system configuration requirements and analyzes detectability performance characteristics for maximum likelihood array reception of multipath. Performance is analyzed to determine the effects of channel multipath structure (multipath delay and signal power division among the paths), space-time correlation properties of the incident processes, and the array spacing. It is shown by a series of case studies, that for single element coupling, as well as array coupling, an increased multipath delay factor results in decreased system detectability for fixed signal and noise intensity levels. The performance capacity is degraded as the available signal power tends to distribute more uniformly between the paths. These effects are attributed to the loss of effective signal energy concentration, resulting in a lower effective pre-detection signal-to-noise ratio. An investigation of the effects upon system performance, due to array element spacing, shows that performance is enhanced by increasing the spacing relative to the multipath delay factor and the reciprocal signal bandwidth. The former is the result of a more directive detectability (beam) pattern arising from the increased spacing. In effect, with increased spacing, the main lobe of the pattern is narrowed, while the side lobes are optimally suppressed by the required noise related array element link, frequency filters (weights).

Improved signal-to-noise ratio in the laser velocimeter

Abstract: Light emitted from a laser contains modulation due to power supply, intermode modulation, plasma noise, etc. A method for noise cancellation and therefore an improvement of signal-to-noise ratio in heterodyning signal is described.

Tracking Performance of a Monopulse Radar in the Presence of Multiple Targets

Abstract: The equations derived by A. J. Rainal for the probability density function of the angle error output of a monopulse radar excited by a Gaussian signal and Gaussian thermal noise are generalized to include the presence of multiple targets. The examples given demonstrate the radar's behavior for various combinations of target and noise parameters.

Comparisons of the Sentence Recognition Scores andSound Qualities as a Function of Compression Ratios

Abstract: The purpose of the present study was to investigate how the sentence recognition scores (SRSs) in noise are changed as a function of the compression ratios (CRs) and what CR is preferred by the individual listeners in terms of sound quality when speech is presented in quiet. Participants consisted of 31 individuals with sensorineural hearing loss ranging in age from 65 to 85 years (mean = 77.0 years) and divided by two groups according to their hearing aids; hearing aid used or non-used. Korean Standard Sentences mixed with white noise of +6 and 0 dB signal-to-noise ratios (SNR) and varied 1:1, 2:1, and 3:1 CR with attack time of 2 msec and release time of 5 msec were presented in most comfortable level. Results showed that SRSs were significant for the SNRs, but the other variables did not differ significantly on the SRS and sound quality including CR. However, analysis of individual participant data, highest SRS and most preferred sound quality was observed in 2:1 CR. Conclusively, this results may help to determine of compression ratio of non-linear hearing aid for Korean hearing impaired.

The Response of Hard-Limiting Bandpass Limiters to PM Signals

Abstract: The signal-to-noise ratio of the output of a hard-limiting bandpass limiter to a PM signal is calculated by using the probability density function of the random phase variable. The signal-to-noise ratio transfer characteristics are plotted for comparison.

Processing partially coherent large seismic array for discrimination

Abstract: Seismic signals in a band of frequencies near 1.0 Hz. can be detected from underground explosions and earthquakes at distances of several thousand kilometers. A stochastic model has been proposed to characterize observed signal variations within a Large Aperture Seismic Array (LASA). The model assumes that the observed signal spectrum at a seismometer is some average spectrum multiplied by a random gain and phase. Within a subarray (7 km. aperture) the mean value of the modulus squared of the random term is approximated by 1.0 +0.18 f2 where f is frequency in Hz. For sensors drawn from the full LASA (200 km. aperture) the value is 1.0 +2.0 f2. Two alternative methods for extracting spectral information above 1.0 Hz for discrimination between event types are compared. Beamforming spectra are obtained from the Fourier transform of the average received signal. An alternative incoherent processing method, spectraforming, is to calculate the average spectrum from individual seismometers. Both can be corrected for bias. It is demonstrated that although beamforming will give more noise rejection than spectraforming, that the latter can be superior in terms of output signal to noise ratio when input signal variations between sensors are large. Spectraforming may be of significant value for obtaining spectral information in the 1.0 - 3.0 Hz band for events with Richter magnitudes in the range 4.0 - 4.5. This magnitude range is of considerable current interest for the purpose of nuclear test detection and discrimination.

Estimation of Signals in Multiple Noise: A Unified Approach

Abstract: : A unified approach for the estimation of signals in multiple noise is given. In the general form of the method the authors allow for several signals to be estimated simultaneously. It is possible to use prior knowledge of the signal. Existing methods fall out as special cases as the authors simplify their model. The large sample statistical properties are studied and it is proved that use of prior knowledge is essential for consistent estimates.

Adaptive optimization of signal to noise ratio in receiving arrays

Abstract: Receiving dipole antenna array signal to noise ratio optimization based on steepest descent method

Transmission of MFSK Signals in Several Frequency Uncertain Channels

Abstract: The performance metric (symbol error rate) of the optimum in-the-limit receivers for the detection of a frequency uncertain M -ary frequency shift-keyed (MFSK) transmission in additive Gaussian noise is derived By in-the-limit, we mean the limiting cases of high and low signal-to-noise ratio (SNR) The performance of the two receivers are compared for some special cases The MFSK wide-band receiving (optimum low SNR receiver for the channel Just described) symbol error rate in a three component-two-path channel is derived when the delay between the direct path and reflected path compared with the data rate is very small

Application Filtering in of Digital Improving the Resolution and the Signal-to-Noise Ratio of Nuclear and Magnetic

Abstract: The digital filtering was proven to be useful in processing convolved signals In this paper an application of this method in order to improve the resolution of nuclear and magnetic resonance spectra is presented An emphasis is laid on the possibility of diminishing the noisy secondary effects The processing was achieved using the FFT algorithm Some practical results obtained are delivered