Showing papers on "Signal-to-noise ratio published in 1969"

Angle Estimation in Amplitude Comparison Monopulse Systems

Abstract: The problem of estimation of angle of arrival in amplitude comparison monopulse (ACM) radars in the presence of internally generated thermal noise is considered. A pulse-type radar is assumed and angular noise is postulated to be absent. In the treatment of the problem, explicit inclusion of various simple models for the pulse returns is made to draw a relationship between the a priori statistics of the echo signals and the ability to estimate the angle of arrival in ACM radars. A maximum likelihood analysis is made to determine the form of the estimates of angle of arrival for the various cases and the accuracy of these estimates is evaluated as a function of the signal-to-noise ratio per hit and of the number of hits. Although most of the estimates considered have already received attention, many of the results are believed to be new.

M-ary Poisson Detection and Optical Communications

Abstract: This paper presents an investigation of the problem of maximum likelihood detection of one of M Poisson processes in a background of additive Poisson noise. When the observables correspond to counts of emitted photoelectrons, the problem models a discrete version of a coherent M -ary optical communication system using photon counters in the presence of background radiation. Consideration is given to an average distance and a detection probability criterion. The advantages of an M -ary pulsed intensity set (Poisson intensities wholly concentrated in a single counting interval) are demonstrated. The performance of such intensity sets is exhibited in terms of error probabilities, pulse widths, signal-tonoise ratio, and channel capacity. Behavior as a function of number M of intensities is also discussed. By appropriate conversion these results may be used for determining power requirements in an optical pulse position modulation system.

Roundoff noise in floating point fast Fourier transform computation

Abstract: A statistical model for roundoff errors is used to predict output noise-to-signal ratio when a fast Fourier transform is computed using floating point arithmetic. The result, derived for the case of white input signal, is that the ratio of mean-squared output noise to mean-squared output signal varies essentially as u = \log_{2}N where N is the number of points transformed. This predicted result is significantly lower than bounds previously derived on mean-squared output noise-to-signal ratio, which are proportional to ν2. The predictions are verified experimentally, with excellent agreement. The model applies to rounded arithmetic, and it is found experimentally that if one truncates, rather than rounds, the results of floating point additions and multiplications, the output noise increases significantly (for a given ν). Also, for truncation, a greater than linear increase with ν of the output noise-to-signal ratio is observed; the empirical results seem to be proportional to ν2, rather than to ν.

A comparison of roundoff noise in floating point and fixed point digital filter realizations

Abstract: A statistical model for roundoff noise in floating point digital filters, proposed by Kaneko and Liu, is tested experimentally for first- and second-order digital filters. Good agreement between theory and experiment is obtained. The model is used to specify a comparison between floating point and fixed point digital filter realizations on the basis of their output noise-to-signal ratio, and curves representing this comparison are presented. One can find values of the filter parameters at which the fixed and the floating point curves will cross, for equal total register lengths.

Simple Procedures for Radar Detection Calculations

Abstract: The literature of radar contains results of Rice, Marcum, Swerling, and Schwartz in several families of curves, which permit radar engineersto estimate the signal energy ratio required for a given level of detectionperformance. The variety of radar problems, however, makes itimpractical to construct curves for all combinations of radar and targetparameters. The concept of detector loss is used here to evaluate lossesattributable to integration and collapsing, with an accuracy of ±0.3 dBon steady targets. This is added to a separate fluctuation loss, modifiedfor diversity effects, to obtain results on all Swerling target modelsand also on partially correlated targets. The accuracy of the combinedlosses is ±0.5 dB for a wide range of detection and false-alarm probabilities.Starting from the basic single-sample detection curves, onlythree additional graphs are needed to find the energy ratio for givendetection performance in any of these cases. Examples are given whichshow the ease with which different radar options may be compared asto performance on an arbitrary type of target.

Improvement of the Signal-to-Noise Ratio of Photomultipliers for Very Weak Signals

Abstract: For the photoelectric detection of Raman spectra excited with a He–Ne laser, the dark current of an EMI 9558 QA photomultiplier is reduced by magnetic defocusing of the electrons originating from the inefficient part of the photocathode. A lightpipe cone concentrates the light signal to a spot of 2.7 mm diameter and enhances the quantum efficiency of the photocathode by multiple reflection. A pulse counting system with a deadtime of less than 100 nsec is described and compared with dc detection. It is now possible to detect signals with a power of less than 10−17 W or less than 35 photons/sec at 650 nm with a time constant of 1 sec. The improvement in signal‐to‐noise ratio is demonstrated with the Raman spectrum of polycrystalline azobenzene.

Minimum-Noise Filters with Good Low-Frequency Rejection

Abstract: A nuclear pulse spectrometer should have both low noise and minimal sensitivity to slow disturbing signals, e.g. base-line fluctuations due to long CR-couplings. A bipolar filter weight-function (or step response) with area balance is advantageous for the latter, but generally involves increased noise and/or resolving time. This paper derives the optimum area-balanced waveform giving least noise for a defined overall width. Optimum waveforms are illustrated and the noise/signal performance is compared with that of the finite-width unipolar cusp and also with several practical bipolar systems in common use.

The Performance of FSK Permutation Modulations in Fading Channels and Their Comparison Based on a General Method for the Comparison of M-ary Modulations

Abstract: A problem that arises in multipath fading channels is that of finding a modulation which enables one to obtain high data rates and at the same time does not lead to an excessively complicated system implementation or the requirement of excessive transmitter power In many dispersive channels the product of time dispersion and Doppler spread is large, so that coherent modulation systems are not feasible Examples of such overspread or nearly overspread channels are the West Ford channel, the endoionospheric channel when using aurora injection, and, in some instances, the moon relay channel For such channels consideration must be given to the use of incoherent modulation systems Consideration is given to the performance in fading channels of an incoherent modulation system which uses a subclass of permutation modulation called frequency-shift keying (FSK) permutation (PFSK) modulation The channel is assumed to have the following characteristics First, the (Gaussian) noise for each propagation mode is white and independent, with equal noise density spectrums; and second, the fadings for the different propagation modes are Rayleigh distributed and independent with equal variance Extensive curves are given for the performance of various PFSK modulations in terms of the modulation signal-waveform error probabilities (often referred to as the word error probabilities) for the case of frequency-selective fading Bounds on the modulation performance are given for the case of flat fading Consideration is given to the problem of comparing the PFSK modulations with each other and with other available modulations to determine which is best for communicating a given L -ary message sequence, with respect to the transmitter power and bandwidth required Toward this end, a relatively simple method is presented for comparing modulations, which circumvents the problem of requiring detailed knowledge of the mapping from the original information data source (which, for greatest generality, is assumed to consist of s L_{i} -state Markov chains, i = 1,,s, which are to be transmitted simultaneously) to the modulation waveforms The method provides upper and lower bounds for the required receiver signal energy to noise density ratio per L -ary symbol for a specified L -ary error rate (or else, bounds for the L -ary error rates for a specified receiver signal energy to noise density ratio per L -ary symbol) The upper bound is based on the performance of the modulation for the ensemble average of all possible mappings, or, equivalently, for a random mapping (analogous to random coding) The lower bound corresponds to the performance of the modulation for an optimum mapping, which is in effect a generalization of the Gray-code-type mapping used for phaseshift keying (PSK) modulation (To obtain the lower bound on the modulation performance, the details of the optimum mapping need not be known; moreover, it remains to prove the existence of this optimum mapping) The method is general and applicable to a wide class of modulations and channels Applying the technique to FSK, FSK permutation, and amplitude-keyed (AK) carrier modulations yields results which conveniently show, for different L_{i} -ary source sequences, the cost in increased transmitter power required to achieve higher data rates with various modulations The comparison data indicates that, in some instances, relative to the FSK modulation, one can obtain with PFSK modulations increased data rates for a given signal bandwidth without requiring an increased received signal energy to noise density ratio per L -ary source symbolAs a consequence of these results, PFSK modulations should perhaps be of interest to the designer of fading communications channels not having large time-dispersion times Doppler-spread products, as well as to the designer of highly perturbed channels Finally, a means is given for transmitting PFSK modulations in time-dispersive fading channels, which does not require the use of a linear power amplifier

On Optimal Signals for Phase-Locked Loops

Abstract: The performance of phase-locked or delay-locked loops is dependent both upon the signal-to-noise ratio (SNR) of the received signal and the detailed structure of both the received signal and the local-reference signal. Optimum signals for first-order delay-locked loops are determined as functions of the loop SNR using simple optimization criteria.

Apparatus for improving the signal to noise ratio of signals received at two antennas

Abstract: Device for improving the signal/noise ratio S + B1 and S + B2 coming from two aerials, comprising two correlators with polarity coincidence, whose first inputs receive chopped tensions x + y and x - y, x and y being sinusoidal voltages depending respectively on the correlation coefficients of noise B1, B2 and of the said noise put in phase coincidence, and whose second inputs receive chopped tensions S + B1 and S + B2, the required signal being collected at the output of an adder whose inputs are connected to the outputs of the said correlators.

Signal-To-Noise Ratio Out of an Ideal FM Detector for SSB FM Plus Gaussian Noise at the Input

Abstract: The signal-to-noise ratio (SNR) at the output of an ideal FM detector is determined as a function of the modulation index for the case of an SSB-FM signal plus narrow-band Gaussian noise at the input, where the input SNR is large. The modulation is assumed to be sinusoidal, and the noise is taken to be flat over the intermediate frequency band.

Apparatus for increasing signal to noise ratio in television low light level scenes

Abstract: A circuit arrangement for increasing the signal-to-noise ratio of the picture output signal of a television camera tube by alternately blanking the scanning of the image applied to the tube during at least one line scanning period and scanning, during a following line scanning period, a band which covers an adjacent image portion associated with the at least one blanked scanning line.

Maximization of Signal-to-Noise Ratio in an Optical Filter

Abstract: where xeE , S = {xeE :0 0, (ii) B is symmetric and positive definite, (iii) # > 0. This problem arises in the maximization of the signal-to-noise ratio in a spectral filter for infrared detectors (see [7]). The term 2 represents the incoming signal and + ,B is the variance of the background signal. The constraint S reflects the fact that the filter can transmit no more than 100 % and not less than 0 % of the total energy. A paper detailing the physics of the problem is in preparation. Although various general-purpose algorithms have been developed which may be applied to obtain solutions to this problem, the special nature of the objective function and the constraints can be exploited to obtain more efficient solution techniques. Two related algorithms are presented here and are both based on a parametric analysis of the problem. The second method is based on the first and offers some computational advantages that the first does not possess. The derivation of the second method involves the notion of the "conjugate function" [6] in a unique manner and should be of interest in itself since the practical applications of this notion have heretofore been extremely limited.

Methods for Improving the Signal‐to‐Noise Ratio of Photon‐ and Electron‐Beam‐Accessed Magnetic‐Film Memory Systems

Abstract: Methods are described for reducing shot‐noise in magnetic‐film memories which are to be read magneto‐optically with the auxiliary aid of an electron beam. In such memories the principal source of shot noise is from the light which is used to illuminate the memory array. The following methods of reducing array shot noise are considered: (1) selective background, (2) magneto‐optical balance, (3) temperature control of magneto‐optical spectra in rare‐earth iron garnets (REIG). It is concluded that the use of REIG spectra appears to offer not only the best, but also a satisfactory solution to the array shot‐noise problem.

System for plural channel signal reception and readout and method of operation

Abstract: The invention pertains to a radio receiver system, and to a method of operation thereof, in which two channels having the same message thereon are received. The noise levels in the respective channels are measured and the two channels are continuously sampled proportionately on the basis of sampling the quieter channel for a greater length of time than the noisier channel. The samples are combined and the resulting composite signal has a better signal to noise ratio than either channel before sampling. A proportionately combined binary representing signal with its improved signal to noise ratio is further enhanced by bit decoding using integration over a full bit period.

Remarks on the signal to noise ratio in the vibroseis system

Abstract: The paper presents a discussion of some of the noise features of the VIBROSEIS SYSTEM*** and their bearing on the determination of the optimally weighted stack.

Beam-steering of large randomly-spaced long-period arrays

Abstract: Beam-steering of a U.S.-wide randomly-spaced array of long-period LRSM instruments is shown to yield a √ n gain in signal to noise ratio for P signals and somewhat less for S signals. Bandpass filtering of these records yields an additional factor of 2 gain in signal to noise ratio.

Effect of Duration on Amplitude Discrimination in Noise

Abstract: Amplitude‐discrimination performance is found to be independent of the duration of the signals to be discriminated for durations ranging from 20 to 200 msec provided that the ratio of signal energy to noise‐power density is kept constant. If the ratio of signal energy to noise‐power density is manipulated by altering either the noise‐power density or the signal duration, then discrimination performance is also independent of that ratio once it exceeds 20 dB. The implication of these findings is discussed.

Practical Factors Influencing the Signal-to-Noise Ratio of Photographic Images

Abstract: When the photographic process is used at the limits of detection, as in many scientific applications, it is important to optimize the signal-to-noise ratio of the photographic image. This may involve using exposing and processing techniques other than those which are customary for more general conditions of use.The results presented here are concerned with the influence of development on equivalent quantum efficiency. It is concluded that in general detection can be improved by using slightly shorter development times than are customary for more conventional purposes.

Recovery of System Transfer Functions from Noisy Photographic Records

Abstract: The recovery of photographic system transfer functions from film records is invariably complicated by the presence of grain noise, which often causes these experimentally determined functions to oscillate wildly, and introduces into the calculated data a positive bias with respect to the correct transfer functions. However, by utilizing the contrast between the random behavior of grain noise and the more well behaved photographic system transfer function, we may remove a substantial amount of noise-caused error through the use of suitable smoothing techniques. To demonstrate the merit of a particular smoothing technique, which improves the signal to noise ratio in the frequency domain by convolving the raw transfer function with a variable bandwidth smoothing function, noisy photographic edge image traces were synthesized using a CDC-3300 computer, the Fourier analysis program, FRAF, and microdensitometer traces of an evenly exposed film sample. The application of the smoothing technique to the raw transfer functions produced from this edge data and the utilization of the smoothed transfer functions in the calculation of line and three-bar image cross sections serve to illustrate the effectiveness of the method.© (1969) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Orbit allocation of domestic communications satellites

Abstract: An efficient method of packing domestic communications satellites is described. In this method, inclined elliptical synchronous orbits are used instead of inclined circular synchronous orbits. The total number of communications satellites is, for example, 8.4 times larger than that for the equatorial system only.

Improvement of Signal-to-Noise Ratio of Image Converters with S-1 Photocathodes

Abstract: Publisher Summary This chapter discusses the improvement of signal-to-noise ratio of image converters with S-1 photocathodes Image converters with the cathodes give a distinct output from the fluorescent screen, even when no light is falling on the cathode An image resulting from a faint illumination of the cathode would, therefore, disappear in the background or would have so little contrast that the information content of the picture would be seriously diminished It is shown that in the case of the eye, the difference in the numbers of visual events caused by the emitted electrons must be about five times higher than the average fluctuation The upper limit of resolution is given either by the maximum resolution of the eye itself at the luminance of the output screen, or by the fluctuations in the number of electrons leaving the photocathode of the first stage of the tube The limits of resolution as well as the resolving power of the eye in conjunction with an image converter are presented It is found that the resolution of the eye was increased both by reducing the thermal emission, and by increasing the picture brightness

Correction to "A comparison of roundoff noise in floating point and fixed point digital filter realizations"

Abstract: Equation (17) is an explicit formula for the elements of the function matrix P = g (A). It does not (directly) require the knowledge of the similarity transformation matrices T and T-' in (3). Thus, the elements of P can be computed directly from the knowledge of the companion matrix A, its eigenvalues, and the function g. Now, it will be shown that (17) has also a remarkable recursive property (24), which allows one to compute the function matrix P using somewhat less than 6n2 multiplications and n2 divisions. The preceding statement assumes, of course, that all eigenvalues of A are known, and all g(Ai) (i= 1, n) are also known. It is also interesting to note that the evaluation of P using the similarity transformation (3) would require about n3 multiplications and n3 additions more than is required using (24), which is derived below. From (8) and (14) it is easy to see that qi,j-1 = qi.j& + am-,+ 1 (18) These values are now used to obtain the remaining two elements of the matrix P, using the recursive formula (24). Note that the subscript i in (24) must vary faster than the subscript j. Also note that j = n-l n-2. .. Upon completion of these simple computations, the matrix P has the following form, And, of course, it can be easily checked that P 2 = A. The evaluation of g = exp (A) can be performed in a similar manner. ACKNOWLEDGMENT and The thor wishes to thank Dr.

The effect of bandpass limiting on noise with a Gaussian spectrum

Abstract: The effect of limiting on the spectrum of Gaussian noise is computed where the noise has a Gaussian spectrum before limiting, and the output spectral density is plotted for various noise-to-limit level ratios. A decibel scale displays the spectral spreading due to limiting with an accuracy not available in previously published data. The results have application to radar and sonar signal processors which attempt to detect targets in clutter.

Noise, Radar Moving-Window Detectors, and False Returns

Abstract: Moving-window false report probability is shown to overestimate effects of noise. "False-report-start" probability is calculated and compared to the usual false report probability. The ratio of the two exceeds a simple function of window length, threshold, and noise probability, which is tabulated for some representative values.

Instrumentation for Analog Differentiator at Low Frequencies

Abstract: Sources of errors and noise in analog differentiators are reviewed, together with techniques for minimizing signal distortion. A modified basic operational differentiator is augmented with a linear phase filter. Accurate derivatives are obtained over the range spanning dc to 1 Hz. An inexpensive instrument is presented which reduces noise to a low level while minimizing delay distortion of the signal.

Error Rates in Diversity FDM-FM Digital Troposcatter Transmission

Abstract: This paper evaluates the error probabilities due to both additive noise and frequency selective fading for predetection diversity combining FDM-FM systems using the troposcatter channel. Graphical results are presented for channel and modulation parameters of typical links.