Improvement in signal-to-noise ratio of Rayleigh backscatteringmeasurement using optical low coherence reflectometry

I have calculated the signal-to-noise ratio (S/N) of fluctuations remaining in Rayleigh backscattered signal distributions obtained after performing moving and frequency averaging with an optical low coherence reflectometer (OLCR). From the calculation, I obtained the number of measurements needed for each averaging that achieves the required S/N with the minimum sampling data. Specifically, I derived the numbers of measurements numerically for Gaussian and Lorentzian light spectra, respectively. The result was successfully applied to diagnosis on long silica-based waveguides by using an OLCR with a high-power narrow-band light source     

An enhanced first-order sigma-delta modulator with a controllable signal-to-noise ratio

This paper presents an enhanced first-order sigma-delta modulator. The proposed modulator, derived using the Al-Alaoui operator, outperforms the conventional modulator. A comparison is drawn showing that the conventional sigma-delta modulator is a special case of the enhanced sigma-delta modulator. The paper includes an analytical derivation as well as extensive simulations revealing the superiority of the proposed modulator reaching optimal performance.     

Optimization of directivity and signal-to-noise ratio of an arbitrary antenna array

In this paper, a unified formulation is made for the optimization of directivity and signal-to-noise ratio of an arbitrary array, with or without a constraint on the array Q-factor. When there is a constraint, the solution is reduced to that of a polynomial; when there is no constraint, the solution is given in a very simple form. First, it is shown that for a given array geometry there exists a finite permissible range of the Q-factor and this range reduces to zero for large spacings. Second, a detailed comparison between four well-known excitations (uniform, Hansen-Woodyard, optimum cophasal, and optimum) is made and the main results are as follows, 1) The Hansen-Woodyard excitation yields a directivity higher than that of the uniform only when the element spacing is somewhat smaller than a half wavelength (λ/2), but at the price of much higher Q. On the other hand, it is much lower than that of the optimum excitation. 2) For spacing less than λ/2, the optimum excitation is strongly tapered toward the ends of the array and approximately antiphasa (i.e., 0, 180° 0, 180°, ...); whereas for spacing greater than or equal to λ/2, it is nearly uniform and cophasal. 3) For large spacings, the directivity of uniform excitation is nearly optimum. For small spacings, the optimum directivity becomes much higher than all others, but is always associated with an enormously large Q-factor. Therefore in this case a constraint of the Q-factor is important. 4) Hansen-Woodyard and uniform arrays have the interesting property that their sensitivity factors are independent of spacing. The optimization of signal-to-noise ratio is also demonstrated. In particular, the result shows that although an improvement in gain over the uniform excitation is very difficult to realize in practice, a substantial improvement in signal-to-noise ratio is entirely practical. Other numerical results and some extensions of the theory to aperture antennas are also included.     

Architectures with improved signal-to-noise ratio in photonicsystems with fiber-loop delay lines

In a class of photonic systems, the intensity of the noise component caused by crosstalk from internal signals is investigated. The relevant systems are those that use loops of optical fiber as reentrant delay-line memory elements. Three architectural variations are shown to improve the ratio of the intensity of an internal signal to the intensity of this noise component. These variations include providing one extra memory element, minimizing the number of switches in a memory element that a photonic signal must traverse, and designing large systems hierarchically from smaller ones. These architectures, and the detailed formulas used to evaluate them, pertain specifically to a photonic time-slot interchanger, but the concepts are believed to generalize to similar photonic systems with applications in computing and signal processing     

Encoding with frames in MRI and analysis of the signal-to-noise ratio

Recently, many new encoding techniques have been suggested for magnetic resonance imaging and an important image reconstruction problem has been raised in order to fully exploit the advantages promised by these new encoding techniques. In terms of frames in an L2 (R) space, we treat these encoding techniques in a unified perspective and propose a solution for this image reconstruction problem. We first develop a matrix form of frame theory and apply it to numerically construct the duals of the encoding functions, which are the transverse excitation profiles generated by radio-frequency pulses along a linear magnetic field gradient. An analysis of the signal-to-noise ratio (SNR) is also presented. Simulations have been carried out and they show that our image reconstruction algorithm minimizes the mean square error between the original and reconstructed images. The SNRs evaluated from simulations agree with our theoretical predictions.     

An alternative derivation for the signal-to-noise ratio of a SSMAsystem

We present an alternative derivation for the signal-to-noise ratio (SNR) of a phase-coded spread-spectrum multiple access (SSMA) system by use of ensemble-average approach. We show that our formula can be explicitly expressed in terms of system parameters and the expression for the SNR derived by Pursley (1977) is just a special case when the user number is very large     

Enhancing the signal-to-noise ratio of ICA-based extracted ERPs

When decomposing single trial electroencephalography it is a challenge to incorporate prior physiological knowledge. Here, we develop a method that uses prior information about the phase-locking property of event-related potentials in a regularization framework to bias a blind source separation algorithm toward an improved separation of single-trial phase-locked responses in terms of an increased signal-to-noise ratio. In particular, we suggest a transformation of the data, using weighted average of the single trial and trial-averaged response, that redirects the focus of source separation methods onto the subspace of event-related potentials. The practical benefit with respect to an improved separation of such components from ongoing background activity and extraneous noise is first illustrated on artificial data and finally verified in a real-world application of extracting single-trial somatosensory evoked potentials from multichannel EEG-recordings.     

Degradation of signal-to-noise ratio due to amplitude distortion

The effect of filtering on the signal-to-noise ratio (SNR) of a coherently demodulated band-limited signal is determined in the presence of worst-case amplitude ripple. The problem is formulated as an optimization in the Hilbert space L₂. The form of the worst-case amplitude ripple is specified, and the degradation in the SNR is derived in closed form. It is shown that, when the maximum passband amplitude ripple is 2δ (peak-to-peak), the SNR is degraded by at most (1-δ²), even when the ripple is unknown or uncompensated. For example, an SNR loss of less than 0.01 dB due to amplitude ripple can be assured by keeping the amplitude ripple under 0.42 dB     

Multiple integration method for a high signal-to-noise ratio readout integrated circuit

A multiple integration method is reported that greatly improves the signal-to-noise ratio (SNR) for applications with a high-resolution infrared (IR) focal plane array. The signal from each pixel is repeatedly sampled into an integration capacitor and then output and summed into an outside memory that continues for n read cycles during each period of a frame. This method increases the effective capacity of the charge integration and improves sensitivity. Because a low-noise function block and high-speed operation of the readout circuit is required, a new concept is proposed that enables the readout circuit to perform digitization by a voltage skimming method. The readout circuit was fabricated using a 0.6-/spl mu/m CMOS process for a 64/spl times/64 midwavelength IR HgCdTe detector array. The readout circuit effectively increases the charge storage capacity to 2.4/spl times/10/sup 8/ electrons and then provides a greatly improved SNR by a factor of approximately 3.     

Prediction of the standard deviation of the signal-to-noise ratio in a data-transmission system with orthogonal subcarrier frequencies

Expressions for prediction of the standard deviation of the signal-to-noise ratio (SNR) in a wireless data-transmission network in which orthogonal frequency division multiple access (OFDMA) technology of data transmission is used are obtained. It is shown that the proposed prediction is more accurate than the predictions based on the mean value.     

Evaluation of signal-to-noise and distortion ratio degradation in nonlinear systems

This paper presents a new figure-of-merit to evaluate signal-to-noise and distortion (SINAD) ratio degradation in nonlinear systems, herein referred to as the noise and distortion figure (NDF). In order to obtain a mathematical formula for this NDF, the best linear approximation calculation is presented for memoryless and dynamic nonlinear systems, which can be modeled by a finite Volterra series. To the best of the authors' knowledge, this is the first time such an attempt of calculating the NDF for a nonlinear and dynamic system is made. NDF results are discussed in both types of systems by means of numerical simulations of systems up to the third order.     

Computation of the signal-to-noise ratio of high-frequency magnetic resonance imagers

A method of computing the signal-to-noise ratio (SNR) in high-frequency magnetic resonance (MR) imaging systems is presented. The method uses a numerical solution to Maxwell's equations which can capture all relevant electrodynamic effects at high B0-field strengths. Using this method, the intrinsic SNR of both volume and surface coils loaded with the human head is calculated as a function of frequency. It is shown that although the available SNR from any point scales favorably with frequency, phase inhomogeneity over the volume of the head may pose a challenge to achieving improved SNR with traditional imaging techniques at high B0-field strengths.     

Detection of nerve action potentials under low signal-to-noise ratio condition

We propose a method for detection of action poten. tials (APs) under low signal-to-noise ratio condition. It is based on multiresolution analysis. Three parameters are used for detection. Two of them are for determining if there is an AP or not, and the other is for the estimation of waveforms. Our method provides better estimated waveforms than the conventional de-noising approach.     

An adaptive digital filter for improving the signal-to-noise ratio of a signal with additive noise (Corresp.)

An adaptive digital filtering scheme is developed to deal with the problem of improving the signal-to-noise ratio of a signal corrupted by noise when only general {em a priori} assumptions regarding the signal and the noise are possible. Specifically, the noise is assumed to be white zero-mean and uncorrelated; while the signal is considered to be band-limited, possibly with slowly varying spectrum. The proposed adaptive digital filtering scheme is based upon a class of variable wave digital filters. Adaptation of the digital filter multipliers is accomplished through the use of an identification procedure based on an adaptive spectral estimation method.     

An alternate derivation of the distribution of the conditioned signal-to-noise ratio

A result in multiple regression analysis is used to derive the probability distribution of the conditioned signal-to-noise ratio.     

Relation of radar range resolution and signal-to-noise ratio to phased-array bandwidth

Phased-array radar systems using wide-band linear-FM pulses suffer from array dispersion. This causes a loss in signal-to-noise (S/N) ratio and in radar range resolution (a broadening of the compressed-pulse width). Depending on the choice of the receiver matched filter (MF) and weighting filter (WF) one or the other of these effects may be minimized. The effects of dispersion in a square planar array with either a parallel feed or a center-fed series feed are studied. Loss in S/N ratio and in range resolution are determined for typical cases, and general curves are given for arrays with arbitrary size, scan range, and signal bandwidth. It is shown that there is an optimum or maximum-useful signal bandwidth for each array, for which the minimum S/N-loss MF-WF design is the same as the ideal-compressed-pulse-shape MF-WF design. For pulses having greater signal bandwidths, time delay steering should be used in the array.