Combined Signal-to-noise Ratio Research Articles

Multi-channel magnetic resonance spectroscopy graphical user interface (McMRSGUI).

This work introduces an open-sourced graphical user interface (GUI) software enabling the combination of multi-channel magnetic resonance spectroscopy data with different literature-based methods for the improvement of the quality and reliability of combined spectra. The multi-channel magnetic resonance spectroscopy graphical user interface (McMRSGUI) is a MATLAB-based spectroscopy processing GUI equipped to load multi-channel MRS data, pre-process, combine, and export combined data for evaluation with open-source quantification software (jMRUI). A literature-based, decision-tree process was incorporated into the combination type selection to serve as a guide to minimize spectral distortion in selecting between weighting methods. Multi-channel, simulated spectra were combined with the different combination techniques and evaluated for spectral distortion to validate the code. The incorporation of the combination methods into a single processing software enables multi-channel magnetic resonance spectroscopy (MRS) data to be combined and compared for improved spectral quality with little user knowledge of combination techniques. Through the spectral peak distortion simulation of the combination methods, combined signal-to-noise ratio (SNR) values from the literature were verified. The spectral peak distortion simulation provides a secondary tool for researchers to estimate the spectral SNR levels when spectral distortion could occur and use this knowledge to further guide the selection of their combination technique. The McMRSGUI provides a software toolkit for evaluating multi-channel MRS data and their combination. Simulations evaluating spectral distortion at different noise levels were performed for each combination method to validate the GUI and demonstrate a method for researchers to assess the combined SNR levels at which they could be introducing spectral distortion.

Closed-Form Analysis of Various Diversity Techniques for Multiband OFDM UWB System Over Log-Normal Fading Channels

In this paper, we investigate the effect of multipath fading on the combined signal-to-noise ratio (SNR) in conjunction with multiband orthogonal frequency division multiplexing ultra-wideband system with different diversity schemes such as maximal ratio combining, equal gain combining and selection combining. In particular, we derived the probability density function of the combiner output SNR followed by performance measures, average combined SNR, outage probability and average bit error rate, in the case of L-fold log-normal fading channels. The derived mathematical expressions are illustrated by applying the method to some selected numerical examples of interest showing the impact of fading variance as-well-as a number of diversity paths, which is combined, on the performance metrics of combiner output for above diversity techniques. The results show that the number of diversity paths significantly improve the effect of multipath fading on derived performance measures.

Reducing signal‐to‐noise ratio degradation due to coil coupling in a receiver array for 35Cl MRI at 9.4 T: A comparison of matching and decoupling strategies

AbstractNext to conventional magnetic resonance imaging (MRI), which utilizes hydrogen nuclei, other nuclei, so‐called X‐nuclei, are of increasing interest since they can provide additional diagnostic information. However, X‐nuclei MRI is challenging due to the lower Signal‐to‐Noise Ratio (SNR) compared to 1H (35Cl provides approximately 200 000 times lower SNR than 1H). In order to compete with this challenge, the use of high‐field strengths and optimized hardware is crucial. In this work, a transmit‐only receive‐only (TORO) system for 35Cl MRI at a preclinical 9.4 T scanner is presented, composed of a volumetric birdcage coil and a 3 channel Rx array. SNR degradation despite preamplifier decoupling can no longer be neglected since the resonance frequency of 35Cl is low. This paper will prove the SNR degradation due to the coil coupling of the receiver coils for this setup and evaluate three different approaches to mitigate the SNR degradation. The performance of the different approaches is evaluated via single channel and combined SNR maps using phantom measurements. Finally, the SNR maps acquired with the Rx array are compared to the SNR map acquired using the Birdcage coil as a reference.

Fuzzy weighting approach for single point positioning with single-frequency pseudo-range observations

The Single-frequency receiver based on pseudo-range single point positioning (SPP) technology is widely used due to its advantage of low cost. As the weighted least squares (WLS) estimation in SPP is used to calculate the user’s position, optimizing weight estimation may be a strategy to improve the positioning accuracy. So far, lots of effective weighting approaches have been developed, such as satellites elevation angle, signal-to-noise ratio (SNR), measurement residual and priori-variances weighting approach. Most of these weighting approaches use one factor or more factors without considering the correlation between them to estimate the weight matrix, possibly leading to imprecise weight estimation. However, the situation in building weighting model with multiple factors and their correlation are complicated and difficult. In this study, we try to develop a new weighting approach called fuzzy weighting approach to improve the positioning accuracy. This approach adopts the fuzzy control theory to estimate the weights of the observations. It does not limit numbers of factors involving into the weight estimation and require the precise mathematic model describing the relation between factors and weight. This study presents the results of the static and kinematic experiments of pseudo-range SPP with WLS using four weighting approaches: SNR-based, elevation-dependent, combined SNR and elevation and fuzzy weighting approaches. The results show fuzzy weighting approach more effectively improves the positioning accuracy.

Power Adaptation Based on Truncated Channel Inversion for Hybrid FSO/RF Transmission With Adaptive Combining

Hybrid free-space optical (FSO)/radio-frequency (RF) systems have emerged as a promising solution for high-data-rate wireless communications. In this paper, we consider power adaptation strategies based on truncated channel inversion for the hybrid FSO/RF system employing adaptive combining. Specifically, we adaptively set the RF link transmission power when FSO link quality is unacceptable to ensure constant combined signal-to-noise ratio (SNR) at the receiver. Two adaptation strategies are proposed. One strategy depends on the received RF SNR, whereas the other one depends on the combined SNR of both links. Analytical expressions for the outage probability of the hybrid system with and without power adaptation are obtained. Numerical examples show that the hybrid FSO/RF system with power adaptation achieves a considerable outage performance improvement over the conventional system.

Average Error Rate Expressions for DF relay Networks with CE Error for PSA-CE schemes Over Rayleigh Fading Channels

This paper provides a framework for evaluating the error rate performance of decode and forward (DF) relay cooperative transmission in the presence of channel estimation (CE) error caused by pilot symbol assisted-channel estimation (PSA-CE) schemes over Rayleigh fading channels. Average bit error rate (BER) and average symbol error rate (SER) are expressed as the well-known closed-forms by using error-events at relay nodes and moment generating function (MGF) of the received signal-to-noise ratio (SNR), which quantifies the SNR penalty arising from CE errors. Moreover, the effects of erroneous detection and transmission at relay nodes are verified in terms of both the combined SNR and the average error rate, and cooperative diversity is observed from closed-form error rate expressions. Simulation results are finally presented to validate derived analytical performance ma-trices.

On the Performance of Arbitrary Transmit Selection for Threshold-Based Receive MRC with and without Co-Channel Interference

The performance of multiple-antenna diversity systems in which the receiver combines signal replicas per threshold-based maximal ratio combining (MRC) and transmitter uses only a single antenna according to receive combined signal strength is studied. The impact of imperfect channel estimation and the effect of phase and time misalignments between desired and undesired signals are implicitly investigated. It is assumed that the desired signal replicas and interfering signals undergo statistically independent flat Rayleigh fading. The analysis is applicable for arbitrary transmit antenna selection, based either on receive combined signal-to-noise ratio (SNR) or receive combined signal-to-interference-plus-noise ratio (SINR). For the scenario of identical multiple-antenna channels, closed-form analytical results for the combined SNR statistics and some performance measures are first presented. The SNR-based and SINR-based selection algorithms are then employed to obtain expressions for the distribution of combined SINR and outage probability performance, which are applicable for different statistical models of interfering signals. The adopted system models herein as well as the analytical development add enhancements on many existing results, and can be used to study the performance of different architectures under various channel conditions when the implementation complexity is of interest.

Analysis of SNR for acoustic vector sensor linear array in volume and surface-generated noise fields

Acoustic vector sensor consists of pressure and particle velocity sensors, which measure the three-dimensional acoustic particle velocity, as well as the pressure at one location at the same time. By preserving the amplitude and phase information of the pressure and particle velocity, they possess a number of advantages over traditional scalar sensors. Signal-to-noise ratio (SNR) gain (which is often called array gain) is one of such advantages and is always interested by all of us. But it is not unchangeable if the spatial correlation of the noise field varies. Much more important, it is difficult to be given if the noise becomes complex. In this paper, spatial correlation of the vector field of isotropic volume-noise and surface-generated noise has been introduced briefly. Based on the results, the combined SNR output of a vector linear array is investigated and the maximum gain is given in the specified noise. Computer simulation shows that the output of one array in the same noise is not the same in different gestures. And then we find the best gesture through SNR calculation and obtain the biggest gain, which has important meaning to guide how to deploy an array in practice. We also should use the array with respect to the characteristics of the real ambient noise, especially in anisotropic noise field.

MGF-based performance analysis of selection diversity with switching constraints in nakagami fading

This paper focuses on the performance evaluation of selection combining (SC) diversity with switching constraints over independent non-identically distributed (i.n.i.d.) Nakagami-m fading channels. New closed-form expressions for the moment generating function (MGF) of the SC output signal-to-noise ratio (SNR) in Nakagami-m fading channels, as a function of channel decorrelation, have been obtained. These expressions have been the starting point to derive performance measures like average combined SNR, outage probability, and average bit error probability of various modulation schemes

Effect of noise imbalance on dual-MRC over Rayleigh fading channels

The performance analysis of dual (two-branch) maximal ratio combining (MRC) under imperfect weight, named imperfect MRC, due to the noise imbalance is derived over independent but non-identical Rayleigh fading channels. Considering the system (or channel) conditions that the noise level of each branch is different, we present the accurate performance analysis of imperfect dual MRC in terms of average combined signal-to-noise ratio (SNR), outage probability and average symbol error rate for a large class of modulations in closed-form and compare them with the performance of the perfect MRC and the perfect selection combining (SC) over non-identical but independent Rayleigh fading channels based on the interesting statistical results on the combined SNR. From the performance results we provide the criterion in choosing the imperfect MRC, perfect MRC, or SC depending on the degree of the difference of the noise level between branches.

Performance evaluation of generalized selection diversity systems over Nakagami‐m fading channels

AbstractThe generalized selection combining (GSC) scheme that adaptively combines a subset of M strongest paths out of L available diversity paths finds applications in several wideband receivers and broadband wireless communications. In this paper, exact closed‐form expressions for the moment generating function (MGF), the probability density function (PDF) and the cumulative density function (CDF) of the GSC(M, L) output signal‐to‐noise ratio (SNR) in independent and identically distributed (i.i.d) Nakagami‐m fading channels are derived while the fading index is a positive integer. These expressions hold for any M and L and provide a comprehensive framework for performance analysis including the derivation of closed‐form formulas for the average symbol error probability (ASEP) of a broad class of binary and M‐ary modulations, mean combined SNR and the outage probability of GSC(M, L) receiver structures. When the Nakagami‐m fading index is not an integer, the MGF of GSC(M, L) output SNR is derived as an (M − 1)‐fold infinite series. With this MGF, analytical expressions for both the outage probability and error rates can be readily obtained. An easily programmable recursive solution of the MGF of GSC(M, L) output SNR is also outlined for both the positive integer and noninteger fading severity index cases. Copyright © 2002 John Wiley & Sons, Ltd.

Analysis of hybrid selection/maximal-ratio diversity combiners with Gaussian errors

The paper examines the impact of Gaussian distributed weighting errors (in the channel gain estimates used for coherent combination) on both the output statistics of a hybrid selection/maximal-ratio (SC/MRC) receiver and the degradation of the average symbol-error rate (ASER) performance as compared with the ideal case. New expressions are derived for the probability density function, cumulative distribution function and moment generating function (MGF) of the coherent hybrid SC/MRC combiner output signal-to-noise ratio (SNR). The MGF is then used to derive exact, closed-form, ASER expressions for binary and M-ary modulations in conjunction a nonideal hybrid SC/MRC receiver in a Rayleigh fading environment. Results for both selection combining (SC) and maximal-ratio combining (MRC) are obtained as limiting cases. Additionally, the effect of the weighting errors on both the outage rate of error probability and the average combined SNR is investigated. These analytical results provide insights into the tradeoff between diversity gain and combination losses, in concert with increasing orders of diversity branches in an energy-sharing communication system.

An algorithm for the optimum combination of data from arbitrary magnetic resonance phased array probes

When summing the spectra acquired with phased array coils, signals with low signal-to-noise ratio or wrongly corrected phase may degrade the overall signal-to-noise ratio (SNR). Here we present a mathematical expression predicting the dependence of combined SNR on the signal-to-noise ratios and errors in phase correction of composite signals. Based on this equation, signals that do not lead to an overall increase in signal-to-noise ratio can be identified and excluded from the weighted sum of signals. This tool is particularly useful for the combination of large numbers of signals. Additionally, a simple and robust algorithm for calculating the complex weighting factors necessary for the signal-to-noise weighted combination of spectroscopic data is presented. Errors in the calculation and correction of relative phase differences between composite spectra are analysed. The errors have a negligible effect on the overall spectral SNR for typical clinical magnetic resonance spectroscopy (MRS). The signal combination routine developed here has been applied to the first in vivo MRS study of human rectal adenocarcinomas at 1.5 T (Dzik-Jurasz A S K, Murphy P S, George M, Prock T, Collins D J, Swift I and Leach M O 2001 Magn. Reson. Med. at press), showing improvements of combined spectral SNR of up to 34% over the maximum SNR from a single element.

The effect of Gaussian error in selection diversity combiners

AbstractSelection diversity combining (SDC) is one of the simplest and most commonly implemented diversity mechanism for mitigating the detrimental effects of deep fades experienced on wireless channels. While SDC improves the mean combined signal‐to‐noise ratio (SNR) over that of a single branch with increasing diversity order, its main advantage is the reduction of the probability of deep fades. The effect of Gaussian errors in the branch gain estimates on the SDC receiver performance is investigated by deriving new closed‐form expressions for the probability density function, cumulative distribution function and the moment generating function of the combiner output SNR statistic. Mathematical expressions for quantifying the degradation in the mean combined SNR, outage probability and the average symbol error rate of a broad class of binary and multilevel modulation schemes owing to imperfect branch SNR estimates in Rayleigh fading are also derived. It is shown that combiner errors affect the mean combined SNR negligibly in comparison to their effect on the deep fades. Copyright © 2001 John Wiley & Sons, Ltd.

Optimum spreading bandwidth for selective RAKE reception over Rayleigh fading channels

Building on the developments in the performance analysis of generalized selection combining (GSC), this paper examines the optimum spreading bandwidth for a fixed-complexity GSC diversity receiver operating over independent identically distributed Rayleigh paths. For this purpose, the study considers three performance criteria: (1) average combined signal-to-noise ratio (SNR) at the GSC output; (2) average bit error probability (BEP); and (3) outage probability of the instantaneous combined SNR at the GSC output. For the average BEP criterion, results are presented for both coherent and noncoherent combining. For the average combined SNR and some instances of the average BEP optimization problem, an accurate approximate estimate of this optimum bandwidth in the form of a solution of a transcendental equation is provided. In other cases, where the optimization is not easily tractable in an analytic fashion, a numeric-search procedure is used to find this optimum bandwidth for different performance criteria and system parameters of interest. Finally, simplified rule-of-thumb-type formulas are also presented as a good reference for picking the optimum spreading bandwidth given a set of system parameters and a particular performance criterion of interest.

An MGF-based performance analysis of generalized selection combining over Rayleigh fading channels

Using the notion of the spacing between ordered exponential random variables, a performance analysis of the generalized selection combining (GSC) diversity scheme over Rayleigh fading channels is presented and compared with that of the conventional maximal-ratio combining and selection combining schemes. Starting with the moment generating function (MGF) of the GSC output signal-to-noise ratio (SNR), we derive closed-form expressions for the average combined SNR, outage probability, and average error probability of a wide variety of modulation schemes operating over independently, identically distributed (i.i.d.) diversity paths. Because of their simple form, these expressions readily allow numerical evaluation for cases of practical interest. The results are also extended to the case of non-i.i.d. diversity paths.

SNR of generalized diversity selection combining with nonidentical Rayleigh fading statistics

A closed-form expression for the average signal-to-noise-ratio (SNR) of generalized diversity selection combining, using the m largest (in instantaneous SNR) diversity signals, for arbitrary m, assuming that the Rayleigh fading statistics on each diversity branch are identically, independently distributed (i.i.d.), already exists in the literature. In this paper, a similar closed-form expression, but for nonidentically distributed statistics, is derived, This expression specializes to known results, such as the average SNRs of maximal-ratio combining with either i.i.d. or non-i.i.d. diversity statistics and that of conventional selection combining (CSC) with i.i.d. diversity statistics. In addition, it provides, for the first time, a simple closed-form solution to the combined SNR of CSC with non-i.i.d. diversity statistics. Further, the closed-form solution for the SNR of selecting the m, largest diversity signals has negligible computational complexity.

Channel assignments for improved gain in baseband array feed compensation systems

The performance of a real-time digital combining system for use with array feeds has been considered in previous articles. The purpose of the combining operation is to recover signal-to-noise ratio (SNR) losses due to antenna deformations and atmospheric effects. Previously, arbitrary signal powers and noise variances were assumed, but no attempt was made to match the receiver channels to the available signal powers. Here it is shown that for any signal power and noise variance distribution, a "best" channel assignment exists that maximizes the combined SNR in the limit of vanishingly small combining losses. This limit can be approached in practice by observing sufficiently many samples. Specific signal power and noise variance distributions are considered, and it is shown that even relatively "noisy" channels can be used effectively to recover SNR losses resulting from signals diverted out of a "high-quality" channel by antenna deformations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>