Showing papers on "Signal-to-noise ratio published in 1974"

On estimating signal-to-noise ratio using the sample correlation coefficient (Corresp.)

Abstract: Two versions of a Gaussian signal, corrupted by independent Gaussian noises, are available for estimating the signal-to-noise power ratio. This correspondence demonstrates that the sample correlation coefficient can be used to construct an unbiased estimator that is asymptotically efficient.

Optical Heterodyne Signal Power Obtained from Finite Sized Sources of Radiation

Abstract: A general expression for the optical heterodyne signal power from a finite-sized radiation source is derived that is formally valid for an arbitrary degree of coherence of the source. The signal power is given explicitly in terms of those variables that describe the source of radiation (e.g., total radiated power, brightness distribution, and source size). Finite-sized incoherent and coherent sources are examined in detail, and analytic expressions are derived for various geometries of experimental interest. For a finite-sized incoherent source, we derive a generalization of Siegman’s results for an extended incoherent source, which states that the effective or capture area of the receiver integrated over its field of view is equal to the square of the optical wavelength. In addition, we derive an analytic expression for the heterodyne signal power for a coherent Gaussian laser source and a Gaussian local oscillator. In contrast to the case of an incoherent source, in which the heterodyne signal power increases in proportion to receiver area, the heterodyne signal power from a coherent source tends asymptotically to a constant with increasing receiver area. This implies that, in a shot-noise-limited system, the SNR tends to a constant or decreases inversely as the receiver area for incoherent or coherent sources, respectively.

Maximum-Likelihood Detection of Unresolved Radar Targets and Multipath

Abstract: Interference in the form of multipath or uncooperative targets can seriously degrade the angle-of-arrival estimation accuracy of mutiplebeam processors. In this paper, the generalized likelihood ratio test is used to derive a test to detect the presence of interference for multiple beam processors. The detector performance is then analyzed in detail with respect to its dependence on signal-to-noise ratio (SNR), signal-to-interference ration (SIR), and on the relative phase between the target and interfering signals. It is shown that good detection performance can be obtained unless the phase difference between the target and interference signals is either in or out of phase.

Two Loop Adaptive Delta Modulation Systems

Abstract: Two adaptive delta modulation (ADM) coders, one for A/D conversion of speech and the other for fiat spectrum signals, have been developed by incorporating a second adaptive feedback loop around the basic delta modulation (DM) coder. The dynamic range of the coder for integrated spectrum has been extended to more than 35 dB with a signal-to-noise ratio (SNR) > 28 dB, for a pulse-repetition frequency (PRF) of 32 kbits/s only, by using an adaptive circuit consisting of digital/analog slope detector and an FET expander. For flat spectrum signals, similar results with constant SNR over the band are obtained at a bit rate of 40 kbits/s. Thus the coders have performances equivalent to those of a 7-digit PCM, using only 32 and 40 kbits/s, respectively.

Balance Between Resolution And Signal-To-Noise Ratio In Scanner Design For Earth Resources Systems

Abstract: An outline is presented of a method in which a sensor under design can be evaluated by comparison with an existing sensor of similar spectral response, providing certain performance characteristics are known. An approach for calculating errors in radiance measurements is discussed, giving attention to calibration, error caused by resolution factors, noise effects on accuracy, and combined radiance level accuracies for several scanner designs. The derivation of error caused by the modulation transfer function is also considered.

Random Signal Flaw Detection

Abstract: : This report describes four areas of work In the first area random signal beam forming techniques are developed which make it possible to transmit several independent beams from a phased array using the same number of incoherent noise sources Following this ultrasound beam scanning techniques are demonstrated in which random signal correlation systems and RF correlation systems using quadrature phase techniques are used in methods for scanning the intensity profile of ultrasound transducer beams using respectively broadband signals and narrow band signals In addition two types of deconvolution procedure are described and demonstrated which have been successful in improving the effective resolution of ultrasound correlation systems when viewing surface features Finally the design and construction of a random signal correlation system is described which uses an electronic delay line (Author)

Optimization and Performance of Multilevel Quantization in Automatic Detectors

Abstract: The optimization and performance of the double-threshold or binary method of automatic radar detection has been the subject of numerous studies in the past, and the loss due to this approximation has been shown to be 1 to 2-1/2 dB. By quantization of the input video into more than two levels, this loss can be avoided; however, little information is available on appropriate design procedures and expected performance. In this paper empirical procedures are described to find good settings of the first and second threshold levels, and the corresponding detection performance is determined. These results, which are believed to be close to optimum, show that for the case of quantization into four levels (2 bits), the loss in decibels is reduced to approximately 1/3 of the corresponding value for the binary case. In some cases this is equivalent to a saving of as much as 1-1/2 dB in signal-to-noise ratio.

Preliminary Field Results on a New Transient Induction System Employing Pseudo-Noise Signals

Abstract: An experimental system is described which utilizes pseudo-noise (PN) and cross-correlation techniques to characterize subsurface conducting bodies such as those pertaining to natural resources. The system is essentially an extension of the loop-loop, transient-electromagnetic, induction systems used in ore prospecting. In lieu of a low duty-cycle pulse, this system transmits a wide-bandwidth PN digital waveform. The mapping signature is obtained by cross-correlation of the received signal with a replica of the sounding PN waveform. The receiver also averages several signatures to improve the signal-to-noise ratio. This type of system has the potential advantages over previous transient systems of using smaller antennas and requiring less transmitter power for more portable operation. Preliminary field data is shown and discussed for a high conductivity dike of ilmenite magnetite and for the surrounding low conductivity anorthosite. Frequency response data is obtained digitally via the Discrete Fourier Transform operation on the time domain signatures. Interpretations are given for both time and frequency domain representations.

Vortex swirl flowmeter sensor circuit

Abstract: A vortex swirl flowmeter sensor circuit electrically connected to an electro-thermal sensor generates a voltage signal output from a flowmeter probe with the signal having a large signal to noise ratio. The sensor is electrically connected in a bridge network in the input to an operational amplifier. The output of the amplifier is fed back through a signal enhancement circuit for maintaining the instantaneous temperature of the sensor, and therefore its resistance constant.

Envelope detection of a unit-index amplitude-modulated cartier accompanied by noise

Abstract: The facts concerning the relative merits of linear and square-law envelope detection of a sinusoidally modulated carrier accompanied by Gaussian noise are clarified in this paper. The comparison when the carrier is weakly modulated and has mean power substantially greater than that of the noise in the input circuit has been fully covered in prior technical literature. In this special case the signal-to-noise ratio (SNR) in the detected output is the same for the two methods, and the distortion of the signal is worse with square-law operation because of inherent second-harmonic production. Since noise in the detected output is typically measured in the absence of signal modulation, the fact that the relative performance changes when the index of modulation approaches 100 percent tends to be overlooked. It is shown in the present paper that the noise performance of the square-law detector suffers a penalty approaching 1.8 dB when the carrier is strongly modulated. Also, the distortion in the square-law case is characterized by a second harmonic only 12 dB down from the fundamental, while the second harmonic in the output of the linear detector is practically negligible. These results are important in the evaluation of techniques in diversity reception.

Capabilities of Multiplicative Array Processors as Signal Detector and Bearing Estimator

Abstract: : Investigation is made of a 'multiplicative' receiver array to determine its capability as signal detector and bearing estimator. The same analyses are made of the conventional square-law array for comparison purposes. The probability density functions for the filter outputs of array models are obtained for these arrays for the input signals consisting of monochromatic signals and narrowband additive Gaussian noise. The number of sensor elements, SNR, source bearing, and interelement noise correlation, are treated as parameters of the distribution, and their influences are displayed graphically. Based on these probability density functions for the square-law and multiplicative array processors, the authors then examine their performances as signal detectors and bearing estimators.

Tachistoscopic detectability of dotted lines in dotted visual noise: signal-to-noise ratio.

Abstract: Contrary to earlier findings, the detectability of dotted lines did not level off as the number of dots in those lines ('signal' dots) increased; rather, it appeared to improve continuously. With percent correct as the performance metric, some deceleration was observed, but with d' as the metric, the increase was linear. The regularity of the spacing of the signal dots affected the rate of improved detectability with increasing numbers of signal dots, but not the linear relationship between d' and increasing numbers of signal dots.

Quasi-Optimal Demodulation of Pulse-Frequency Modulation Systems

Abstract: Novel demodulator structures are derived using a theory for the quasi-optimal on-line demodulation of pulse-frequency modulated (PFM) signals in the presence of white Gaussian channel noise. The basic demodulator consists of a phase-locked loop with time-varying gain elements. Furthermore, its integrators are appropriately reset as each new pulse is received. This modulator may be augmented with additional integrators and gain elements to achieve quasi-optimal demodulation with delay. The quasi-optimal demodulation approaches optimal demodulation, in the minimum mean-square-error sense, as the signal-to-noise ratio increases. The various quasi-optimal receivers are derived by application of the extended Kalman filter theory to a state-space signal model.

Operating Characteristics for Maximum Likelihood Detection of Signals in Gaussian Noise of Unknown Level. 1. Coherent Signals of Unknown Level

Abstract: : The detection and false alarm probabilities for maximum likelihood detection of nonfluctuating phase-incoherent signals in stationary Gaussian noise, where the received signal and noise levels are unknown, are derived and evaluated. This procedure is carried through for two cases involving different assumptions about the received signals. In the first case, the signal amplitudes in M potential-signal observations are assumed to be different and unknown values for each sample. In the second case, the signal amplitudes, although unknown, are assumed to be the same for all M observations.

Probability of error in digital communication systems with intersymbol interference and dependent symbols (Corresp.)

Abstract: An upper and lower bound to the probability of error is presented for a digital communication system with dependent symbols affected by additive noise and intersymbol interference. Explicitly considered are two systems in which independent binary symbols are encoded into ternary dependent symbols, i.e., a bipolar code and a dicode. The bounds practically coincide under a proper choice of certain integers; hence the true value of probability of error can be computed as a function of signal to noise ratio.

Optimizing the window of an Anger camera

Abstract: Quality of scintiscans taken with an Anger camera is dependent on the window settings. The authors derive an analytic expression to find the optimum window based on maximizing the signal to noise ratio. The signal is defined as the unscattered radiation both totally and partially absorbed in the NaI crystal, the noise is defined as scattered and background radiation. Signal and noise are characterized by an energy spectrum which are approximated by two Gaussians to simplify calculations. The effect of window settings on the line spread function obtained by an Anger camera with a 99Tcm line source in a water phantom were determined experimentally. The results suggest that the optimum window setting can be calculated using measured energy spectra of signal and noise.

Reliability of Human Visual Signal Detection in the Presence of Noise

Abstract: This report is concerned with the reliability of human detection of certain classes of signals of simple shape embedded in low-pass filtered white gaussian noise recorded on paper. Results are compared with performance of an optimum matched filter detector which operated on the same set of data. The signal-to-noise ratio obtained at the output of such a filter can be used to predict the reliability of detection and the false alarm rate in subjects' performance. For signal-to-noise ratio greater than one, subjects make fewer errors (i.e., misses plus false alarms) than the optimum filter, and the difference is a monotonically decreasing function of the signal-to-noise ratio. Factors concerned with these two observations are discussed.

Exact Angular Accuracy of an Amplitude Comparison Sequential-Lobing Processor

Abstract: Assume E1 and E2 are the squares of two sequential envelopes from the sequential lobing of an antenna in a given plane. Independent thermal noise is generally present in the envelopes. The statistic e = (E2 ? E1)/(E2 + E1) has been used as an estimate of the angle to a target for the significant region of small angles compared to a beamwidth. For a nonfading target, the probability density and characteristic function of e are obtained in closed form. Thence, the exact bias, standard deviation, and rms error in estimating the noise-free value e of e are obtained for all e and signal-to-noise ratios. The same type of statistic as e can be used to estimate time delay in a split range gate tracker.

ERGs and Noise: Detection Probability, Time and Amplitude Errors

Abstract: The effect of background noise on a waveform is to change it in a manner which to some extent depends upon statistical parameters of the signal and the noise When the signal-to-noise ratio is low the signal may be masked by the noise so that it is not detected most of the time, that is the probability of detection is close to zero As the signal-to-noise ratio increases, the probability of detecting the signal increases This process can be described by a curve of probability of detection as a function of signal-to-noise ratio Measurements of the amplitude and implicit time of the signal have ranges of errors associated with them which also depend upon the signal-to-noise ratio, tending to be large when the signal-to-noise ratio is low, and decreasing as the signal-to-noise ratio improves These general concepts can be readily applied to electroretinography measurements, and some model ERG and noise waveforms are described and compared with live recordings The model system is used to obtain measurements of the probability of detection and of the time and amplitude errors which occur at different signal-to-noise ratios Some techniques are discussed for estimating these effects in practical cases

Factors Limiting the Signal-to-Noise Ratio of Negative-Conductance Amplifiers and Oscillators in FM/FDM Communications Systems (Short Papers)

Abstract: A derivation is presented for the signal-to-noise ratio of negative-conductance amplifiers and oscillators in FM/frequency division multiplexing (FDM) communications applications. Results indicate the limiting value of signal-to-noise ratio depends on the semiconductor properties and channel loading only. This means circuit adjustments, such as Q, cannot increase the signal-to-noise ratio without bounds. Typical specifications are given. Limiting values of signal-to-noise ratio for Gunn and Si IMPATT devices are given in typical applications. Results indicate that Gunn devices have a clear advantage over Si IMPATT'S in a signal-to-noise sense.

Estimating a seismic station's detection capability from noise. Application to VLPE stations

Abstract: : Since the detection of a seismic event depends on the signal-to-noise ratio at a receiving site or station one may derive detection threshold magnitudes from the ambient noise levels. The statistical distribution of either peak noise amplitudes or RMS noise levels then determine the probability of detecting an event of a given magnitude. The conditions for the validity of this method of estimating detection capabilities, and the parameters involved, are specified. The analysis shows that results obtained from this method should differ little from maximum likelihood direct method estimates. Application of this method to stations of the Very Long Period Experiment (VLPE) confirms the analytical results. As few as 30 reliable daily noise samples yield good 50% detection threshold estimates.

Effects of sweepout on HgCdTe detectors under high bias conditions

Abstract: A model is developed for the sweepout of minority carriers under high bias conditions in a HgCdTe semiconductor. The equations for the signal and generation-recombination (g-r) noise are presented under high bias conditions. Results show that, during sweepout, g-r noise is affected differently than is signal. A peak in the signal to noise ratio (SNR) is obtained for an optimum bias across the detector. Solution of the ambipolar transport equation shows that the sweepout of excess carriers causes the peak in SNR. The signal is shown to have the usual 6 db/octave rolloff in the high bias case as it does in the low bias case. The g-r noise at high bias is shown to have a sinc (fT a ) rolloff where Ta is twice the effective sweep-out lifetime, as predicted previously(1). The results, modified for a long diffusion length (i.e., L D ≈ 13 µm) alters the equations and thereby eliminates the higher frequency nulls in the sinc (fT a ) rolloff for large geometry detectors, whereas the nulls are evident in small geometry detectors. Experimental data on 12-µm HgCdTe detectors is presented and correlated with the theory. Frequency spectra of the g-r noise and signal response from a modulated CO 2 laser, a PbSe laser, and a GaAs diode are presented.

Evaluation of Walsh Power Spectrum of Nearly White Signals

Abstract: An expression for evaluating the Walsh power spectra of random signals with very short time correlations is given.

Output Signal-to-Noise Ratio for Amplitude and Intensity Modulated Laser

Abstract: General expressions are obtained for output SNR for both amplitude- and intensity-modulated lasers, where bandlimited Gaussian noise has been chosen as a modulating signal, and in the presence of background light. Two types of modulating signals are considered: the baseband and bandpass modulating signals. Detailed calculations are made for output SNR when an ideal narrowband optical filter is used. The dependence of output SNR on several parameters, such as the center frequency of the modulating signal, the effective average quantum rate, and input SNR, are discussed. In addition, the difference in performance between amplitude and intensity modulation is discussed. The detection characteristics of the homodyne system are also considered.

Horizontal Directionality of Ocean Ambient Noise.

Abstract: : This report presents recommendations for future measurements and techniques for estimating the horizontal directionality of ocean ambient noise The recommendations are based upon (a) evaluations of present measurement data and techniques, (b) assessments of possible measurement-array configurations and techniques, and (c) the sensitivities of horizontal directionality measurements to vertical arrival structures

An evaluation of adaptive-beamforming techniques applied to recorded seismic data

Abstract: : This report presents time-domain maximum likelihood adaptive beamforming results for data from the Alaska Long-Period Array and the Korean Short-Period Array. Adaptive-beamforming detection gain relative to beamsteering is investigated for unmixed long-period seismic events in the presence of background noise and for simulated mixed events where two data samples, each containing a signal, are summed to create a composite sample containing an interfering event. In the adaptive beamforming studies for background noise, the performance of two different adaptive algorithms, the effect of using closely-spaced partial arrays instead of the full ALPA array, and the effect of different frequency filters applied to the input channels before array beamforming are examined. In the interfering-event analysis, the relative on-azimuth to off-azimuth event strength at which an on-azimuth event detection is possible determines the detection gain of adaptive multichannel filtering over time-shift-and-sum beamforming.

Microchannel electron multiplier - uses varying wall resistivity for low signal to noise ratio or low emission dispersion

Abstract: This electron multiplier uses either a single microchannel or a multiple assembly. The internal walls of the channel have the property of secondary emission and their resistivity varies by a factor of 1.5 to 10 relative to the average linear resistivity along the channel. When the value is low at the input (e) then the input field will be weaker and the parasitic electron emission will also be low giving a low signal to noise ratio. When this condition is reversed at the output (s) then a low electron dispersion is obtained.

Output Signal-to-Noise Ratios for Amplitude-Modulated Noise-Like Lasers

Abstract: A general expression of the output SNR of a photodetector is derived for a noise-like laser amplitude-modulated by a stationary Gaussian random modulating signal in the presence of a background light. The electric field Vx(t) of the noise-like laser is assumed to be a stationary narrowband Gaussian random process with zero mean. Two types of modulating signal are considered, the baseband and bandpass modulating signals. More specifically, the effects of the center frequency of the modulating signal, the modulating degree, the bandwidth ration of the noise-like laser to the modulating signal, the effective average quantum rate, and input CNR on output SNR are studied. The detection characteristics of the noise-like laser are also made clear by comparison with the case of a coherent laser.