Signal-to-noise Ratio Gain Research Articles

Diversity combining via symmetry recovering for asymmetrically clipped optical OFDM

A new diversity combining receiver is proposed for asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM). With the aid of symmetry recovering the odd and even signals of ACO-OFDM are distinguished directly in time domain without complex operation such as inverse fast Fourier transform (IFFT). Simulation results show that the diversity combining receiver we proposed gives a signal-to-noise ratio (SNR) improvement of 2∼3 dB. The receiver proposed also has the same SNR gain as the conventional diversity combining receiver distinguishing the odd and even signals in frequency domain.

Application of adaptive line spectrum enhancer in adaptive matched filter

The most classical detector of active sonar and radar is the matched filter (MF), which is the optimal processor under ideal conditions. Aiming at the problem of active sonar detection, we propose a frequency-domain adaptive matched filter (FDAMF) with the use of a frequency-domain adaptive line enhancer (ALE). The FDAMF is an improved MF. In the simulations in this paper, the signal to noise ratio (SNR) gain of the FDAMF is about 18.6 dB higher than that of the classical MF when the input SNR is -10 dB. In order to improve the performance of the FDAMF with a low input SNR, we propose a pre-processing method, which is called frequency-domain time reversal convolution and interference suppression (TRC-IS). Compared with the classical MF, the FDAMF combined with the TRC-IS method obtains higher SNR gain, a lower detection threshold, and a better receiver operating characteristic (ROC) in the simulations in this paper. The simulation results show that the FDAMF has higher processing gain and better detection performance than the classical MF under ideal conditions. The experimental results indicate that the FDAMF does improve the performance of the MF, and can adapt to actual interference in a way. In addition, the TRC-IS preprocessing method works well in an actual noisy ocean environment.

A Study of TDMR for Magnetic Tape Systems

Multiple-input single-output two-dimensional magnetic recording gain in a magnetic tape system was studied under the condition where the bit aspect ratio is 22%-37% compared to current tape systems. The performance was mainly evaluated in terms of signal-to-noise ratio (SNR) cross-track profile utilizing a 2-D read-back signal synthesized from the waveform acquired with a conventional single-reader tape head. The results show that, depending on the reader pitch selected, either significant gain in tracking margin up to 215% compared to the traditional 1-D signal-processing scheme or an additional SNR gain accompanied with a moderate increase in approximately 30% in tracking margin can be achieved by utilizing the 2-D equalization.

The Effect of Otoacoustic Emission Stimulus Level on the Strength and Detectability of the Medial Olivocochlear Reflex.

Previous work demonstrates the importance of a high signal to noise ratio (SNR) when using transient evoked otoacoustic emissions (TEOAEs) to assay the medial olivocochlear reflex (MOCR). Increasing stimulus level provides one means to increase TEOAE SNR. However, this may come at the expense of a smaller MOCR effect. It is not clear whether the gain in SNR associated with the use of higher stimulus levels outweighs the disadvantage of a potentially smaller MOCR effect. The present study investigated the strength and detectability of the MOCR when assayed using TEOAEs at different stimulus levels. The hypothesis was that although the strength of the MOCR decreases with increasing stimulus level, the occurrence of statistically significant MOCR effects increases due to an increase in TEOAE SNR. Twenty-five young adult females with normal hearing participated in the study. TEOAEs were measured in the right ear with and without broadband noise presented in the left ear. The strength of the MOCR was quantified as the percent difference in the TEOAE between the contralateral noise and quiet conditions. Statistical bootstrapping was used to detect significant MOCR effects in individual subjects across different frequency bands and stimulus levels. The relationship between a detectable MOCR (response variable) and frequency, stimulus level, TEOAE SNR, MOCR strength, and subject (predictor variables) was evaluated using generalized linear mixed-effect models. The number of statistically significant MOCR effects increased with stimulus level at all frequencies. Occurrence was highest for the 2-kHz TEOAE frequency band and lowest for the 4-kHz frequency band. The strength of the MOCR decreased with increasing click level. TEOAE SNR, MOCR strength, and stimulus level were significant predictors of a detectable MOCR: The likelihood of a detectable MOCR increased with TEOAE SNR, MOCR strength, and stimulus level. Despite a reduction in the strength of the MOCR with increasing stimulus level, the detectability of the MOCR increased. This is due, in part, to an increase in TEOAE SNR with stimulus level. For clinical implementation of TEOAE-based MOCR assays, achieving a high SNR is necessary to permit the detection of the MOCR in individual patients.

Orthogonal Projection With Optimized Reserved Subcarriers Mapping for Sidelobe Suppression in OFDM Systems

As an efficient sidelobe suppression technique for orthogonal frequency-division multiplexing (OFDM) systems, the orthogonal projection is capable of achieving deep suppression while maintaining low complexity. However, the conventional orthogonal projection for sidelobe suppression (SSOP) with the uniform distribution of reserved subcarriers suffers from noise amplification in data recovery, resulting in a degradation of bit-error-rate (BER) performance. To tackle this problem, an improved SSOP with an optimized mapping of reserved subcarriers (SSOP-OM) is proposed in this paper. Additionally, a fast search algorithm is proposed to obtain this optimized distribution. By maximizing the signal-to-noise ratio (SNR) at the receiver, SSOP-OM can obtain more than 3-dB SNR gain for a 16-QAM-modulated OFDM system with 128 subcarriers and 6 of them reserved over conventional SSOP at the BER of 10−3. In addition, the more reserved subcarriers or the more subcarriers are used in the OFDM, the higher the SNR gain can be achieved. The theoretical analysis and simulations are provided to validate the advantage of the proposed SSOP-OM over the conventional SSOP in terms of BER in both AWGN and multipath channels.

Photonics-based wideband distributed coherent aperture radar system.

A photonics-based wideband distributed coherent aperture radar (DCAR) system is proposed and experimentally demonstrated. In the proposed system, the central controlling system and several spatially dispersed remote transceivers are connected by the optical fiber-based time synchronization network. In the central controlling system, the optical-carried orthogonal/coherent linear frequency modulated waveforms (LFMWs) are generated by a reconfigurable multi-channel optical arbitrary waveform generator (RMOAWG), and the signal processing for the echo waves is also implemented there. While in the remote transceivers, only the optical/RF and RF/optical conversions are carried out. Benefitting from the use of photonics-based methods, bandwidths of the generated radar signals can be large, improving the detection resolution of the system. Due to the centralized signal generation and processing, the remote transceivers can be simplified, reducing the system complexity. Moreover, the fiber-based distribution ensures low loss, good transportability, and great flexibility. Experimentally, a two-unit DCAR system operating in X-band with a bandwidth of 3 GHz is presented. When full coherence is achieved, signal-to-noise ratio (SNR) gains of 8.3 dB and 8.33 dB are obtained over a single radar for radar 1 and radar 2, respectively. Results are in good agreement with theoretical prediction. Theoretically, with such SNR gain, the range detection precision can be improved to about 2.6 times that of a single radar.

246. Analysis of signal-to-noise ratio for a 2-channels coil developed to enable transcranial Magnetic Resonance-guided Focused Ultrasound Surgery (tcMRgFUS) with 1.5 T MRI scanners

PurposeIn recent years trans-cranial Magnetic Resonance-guided Focused Ultrasound Surgery (tcMRgFUS) treatments have aroused large scientific and medical interest [1]. Usually, tcMRgFUS systems are integrated with 3 T systems which allow the use of the body RF coil for both real time imaging and MR-thermometry. At University Hospital of Palermo there is the world-first installation of a tcMRgFUS system integrated with a 1.5 T scanner. Here we present the characterization in terms of signal-to-noise ratio (SNR) of a dedicated RF coils suitably developed (by InSightec) to enable tcMRgFUS treatments with 1.5 T MR units. Methods and materialsThe focused ultrasound equipment (ExAblate 4000, InSightec) integrates with an MRI unit operating at 1.5 T (Signa HDxt, GE) and consists of a hemispheric 1024-element phased-array transducer. T2w-FRFSE images were obtained from a dedicated Dose Quality Assurance phantom using the same MRI protocol used for real treatments. ResultsThe dedicated flexible coil resulted in larger SNR values with respect to that achieved using MRI’s body RF coil. In particular, we obtained for the axial plane a SNR equal to 27.5 using dedicated coil whereas it was equal to 2.5 with RF body coil (SNR gain more than 10 times higher). ConclusionWe can conclude that, even though the SNR linearly increases with magnetic field strength, the use of a dedicated coil on a 1.5 T scanner enabled us to obtain images with a SNR roughly 5 times larger than those acquired on 3T scanners using MRI’s body RF coil. This could facilitate the spread of this cutting-edge technology worldwide [2].

333. A personalized acquisition protocol to optimize 18F-FDG PET/CT whole-body imaging

Purpose PET image quality degradation is encountered in over-weight and obese patients even when administered activity is increased with body weight. For these cases is more appropriate to increase the acquisition time rather than administered activity. Aim of the work is to evaluate a metric related to patient body constitution to optimize 18F-FDG PET/CT Whole-Body (PET-WB) acquisition procedure to guarantee accurate diagnosis with minimal radiation exposure of patients. Methods PET-WB acquisitions were performed with the TruePoint Biograph scanner (Siemens) with 216 mm axial FOV; images were reconstructed with OSEM-3D with 2iterations/8subsets. Initial retrospective analysis was performed on 79 patients studied according to the PET-WB routine protocol: injection of 4.0 ± 0.6 MBq/kg, with a maximum of 500 MBq in obese subjects; acquisition duration of 2 min/bed and 3 min/bed respectively for body weight ⩾ 100 kg. Signal to noise ratio (SNR) measured on liver region was taken as representative parameter of image quality. Diabetic patients and those with hepatic lesions were not included in the analysis. Measured SNR values were normalized to injected activity and acquisition duration (SNRn) and correlated with patient-specific parameters: height to weight ratio (HWR), body mass index (BMI), body surface area (BSA), lean body mass (LBM), fat free mass (FFM). A mathematical model was extrapolated from the parameter most correlated to SNRn values. The developed model was validated prospectively on others 66 patients. Results Retrospective analysis showed a significant SNR decrease with increasing patient size. SNRn values fitted to patient-specific parameters showed the highest R2 (0.86) with HWR. Setting SNR reference value of 9, derived from an image quality deemed acceptable by clinicians for normal-weight patients, the HWR mathematical model allowed to personalize acquisition duration and keep constant image quality for different weight class. By fixing administered maximum activity to 380 MBq for obese subjects an increase of 30% acquisition time corresponded to 30% image SNR gain, with a 30% dose reduction to patient with respect EANM recommendations. Conclusions The application of a model based on specific patient HWR allowed to improve SNR by personalizing acquisition duration without increasing patient dose exposure and to standardize PET-WB procedure.

Wireless performance and mobile fronthaul bandwidth of uplink joint reception with LLR combining in split-PHY processing

In this paper, we evaluate the wireless uplink performance and the mobile fronthaul (MFH) bandwidth of split-physical layer (PHY) processing (SPP), which is a base station (BS) functional split scheme used to link baseband units (BBUs) and remote radio heads (RRHs) in a centralized/cloud — radio access network (C-RAN). SPP enables MFH bandwidth reduction by splitting the BS functions between channel coding/decoding and modulation/demodulation within the PHY layer functions. SPP also enables high coordinated multipoint (CoMP) transmission and reception performance by employing uplink joint reception (JR) with log likelihood ratio (LLR) combining. Link level simulation results show that SPP with LLR combining achieves a block error rate (BLER) performance of 10% with a signal to noise ratio (SNR) penalty of less than 1 dB compared with that of conventional CRAN, which centralizes PHY layer functions in BBU. In addition, SPP has an SNR gain of more than 3 dB over medium access control (MAC)-PHY split, which splits the BS functions between the MAC and PHY layer functions. System level simulation results show that SPP with LLR combining improves the cell-edge user throughput by more than 33% over MAC-PHY split with selection combining and reduces the MFH bandwidth by 91% when compared with conventional C-RAN. Moreover, link and system level simulation results above are also observed when the channel estimation is non-ideal.

Fluorine-19 MRI at 21.1\xa0T: enhanced spin\u2013lattice relaxation of perfluoro-15-crown-5-ether and sensitivity as demonstrated in ex vivo murine neuroinflammation

ObjectiveFluorine MR would benefit greatly from enhancements in signal-to-noise ratio (SNR). This study examines the sensitivity gain of 19F MR that can be practically achieved when moving from 9.4 to 21.1 T.Materials and methodsWe studied perfluoro-15-crown-5-ether (PFCE) at both field strengths (B0), as a pure compound, in the form of nanoparticles (NP) as employed to study inflammation in vivo, as well as in inflamed tissue. Brains, lymph nodes (LNs) and spleens were obtained from mice with experimental autoimmune encephalomyelitis (EAE) that had been administered PFCE NPs. All samples were measured at both B0 with 2D-RARE and 2D-FLASH using 19F volume radiofrequency resonators together. T1 and T2 of PFCE were measured at both B0 strengths.ResultsCompared to 9.4 T, an SNR gain of > 3 was observed for pure PFCE and > 2 for PFCE NPs at 21.1 T using 2D-FLASH. A dependency of 19F T1 and T2 relaxation on B0 was demonstrated. High spatially resolved 19F MRI of EAE brains and LNs at 21.1 T revealed signals not seen at 9.4 T.DiscussionEnhanced SNR and T1 shortening indicate the potential benefit of in vivo 19F MR at higher B0 to study inflammatory processes with greater detail.

Optimal tone detection for optical fibre vector hydrophone

An optimal tone detector based on the Neyman-Pearson criterion is proposed for the optical fibre vector hydrophone (OFVH). The detector takes account of the difference between noise levels on the acoustic pressure channel and the three particle acceleration channels of an OFVH. Explicit expressions for the impulse responses of pre-filters that are central to the proposed detector are given. Analyses show that the proposed detector is equivalent to the minimum variance distortionless response beamformer for the OFVH. In the case of identical noise on all particle acceleration channels, the signal-to-noise ratio (SNR) gain of the detector is 101g(1 + μ) dB (μ is the noise power ratio of OFVH channels at the tone frequency), whereas the SNR gain also depends on target direction and is bounded by 101g(1 + μ min ) and 101g(1 + μ max ) dB when noise on all particle acceleration channels are different. Results from both simulations and lake experiment data show that the proposed detector outperforms tone detectors that use (i) the acoustic pressure signal, (ii) the particle acceleration signals and (iii) equally the combination of acoustic pressure signal and particle acceleration signals.

How Reliable and Capable is Multi-Connectivity?

Multi-connectivity (MCo) is considered to be a key strategy for enabling reliable transmissions and enhanced data rates in fifth-generation mobile networks, as it provides multiple links from source to destination. In this work, we quantify the communication performance of MCo in terms of outage probability and throughput. For doing so, we establish a simple, yet accurate analytical framework at high signal-to-noise ratio (SNR), in which the number of links, the spectral efficiency, the path loss, and the SNR are incorporated, giving new insights into the potentials of MCo as compared with single-connectivity (SCo). These are our main contributions: (1) finding the exact coding gain of the outage probability for parallel block-fading channels; (2) quantifying the performance improvement of MCo over SCo in terms of SNR gain; and (3) comparing optimal and suboptimal combining algorithms for MCo at the receiver side, namely joint decoding, selection combining, and maximal-ratio combining, also in terms of SNR gain. Additionally, we apply our analytical framework to real field channel measurements and thereby illustrate the potential of MCo to achieve high reliability and high data rates in real cellular networks.

Improvement of signal-to-noise ratio in parallel neuron arrays with spatially nearest neighbor correlated noise.

We theoretically investigate the signal-to-noise ratio (SNR) of a parallel array of leaky integrate-and-fire (LIF) neurons that receives a weak periodic signal and uses spatially nearest neighbor correlated noise. By using linear response theory, we derive the analytic expression of the SNR. The results show that the amplitude of internal noise can be increased up to an optimal value, which corresponds to a maximum SNR. Given the existence of spatially nearest neighbor correlated noise in the neural ensemble, the SNR gain of the collective ensemble response can exceed unity, especially for a negative correlation. This nonlinear collective phenomenon of SNR gain amplification may be related to the array stochastic resonance. In addition, we show that the SNR can be improved by varying the number of neurons, frequency, and amplitude of the weak periodic signal. We expect that this investigation will be useful for both controlling the collective response of neurons and enhancing weak signal transmission.

Parallel Counters for Low-Pass Phase Modulation–Demodulation ADCs

The signal-to-noise ratio (SNR) of a low-pass phase modulation-demodulation analog-to-digital converter (LP PMD ADC) depends on the number of channels in its demodulator (synchronizer or race arbiter). For 3, 7, and 15 channels, this gives 9.5, 16.9, and 23.5 dB theoretical SNR gain in comparison to a single channel. We have designed a family of parallel counters that sums the unweighted outputs of each synchronizer channel to produce a binary code. A 7-to-3 counter that can be truncated into 3-to-2 and extended into 15-to-4 adders was fabricated using 10 and 20 kA/cm 2 MIT-LL processes and successfully tested. The completed designs of 1-, 3-, and 7-channel LP PMD ADC are also briefly discussed.

Combining techniques of weak signals in the bistable parallel array system

Bistable parallel array system can efficiently improve the signal-to-noise ratio (SNR) gain and further significantly lower bit-error-rate (BER) when the SNR is low. The bistable parallel array system is widely studied due to its outstanding advantages. This study presents a new method that applies combining techniques including maximum ratio combining (MRC), equal gain combining (EGC), and selection combining (SC) to the bistable parallel array system, and derives the formulas of the SNR gain, energy efficiency, and numerically calculates the BER. Through comparative analysis of these three combining techniques, it demonstrates the BER performance of the EGC technique in bistable parallel array system slightly inferiors to MRC, and the worst is SC. While the performance of all these three kinds of combining techniques is better than that of the single branch case. Importantly, higher SNR gain, higher EE and lower BER can be obtained in non-Gaussian noise cases than that in Gaussian noise cases.

Trellis code‐aided high‐rate M‐QAM space‐time labeling diversity using a unitary expansion

SummaryIn this paper, we present a high‐rate M‐ary quadrature amplitude modulation (M‐QAM) space‐time labeling diversity (STLD) system that retains the robust error performance of the conventional STLD system. The high‐rate STLD is realised by expanding the conventional STLD via a unitary matrix transformation. Robust error performance of the high‐rate STLD is achieved by incorporating trellis coding into the mapping of additional bits to high‐rate codes. The comparison of spectral efficiency between the proposed trellis code‐aided high‐rate STLD (TC‐STLD) and the conventional STLD shows that TC‐STLD with 16‐QAM and 64‐QAM respectively achieves a 12.5% and 8.3% increase in spectral efficiency for each additional bit sent with the transmitted high‐rate codeword. Moreover, we derive an analytical bound to predict the average bit error probability performance of TC‐STLD over Rayleigh frequency‐flat fading channels. The analytical results are verified by Monte Carlo simulation results, which show that the derived analytical bounds closely predict the average bit error probability performance at high signal‐to‐noise ratios (SNR). Simulation results also show that TC‐STLD with 1 additional bit achieves an insignificant SNR gain of approximately 0.05 dB over the conventional STLD, while TC‐STLD with 2 additional bits achieves an SNR gain of approximately 0.12 dB.

Outage behaviour and SCK‐based power allocation for analogue network coding protocol in cooperative networks

In this study, the authors consider the communication scenario where two sources communicate with the help of a single relay, modelled as a half-duplex butterfly network. Closed-form expressions of the outage probabilities are derived in the high signal-to-noise ratio (SNR) regime for the orthogonal amplify-and-forward and non-orthogonal amplify-and-forward protocols. Then the expressions are approximated to enable power allocation. Closed-form power allocation schemes are proposed for each protocol, where only statistical channel knowledge is required. It is shown that the authors analyses match well with simulation results and the approximated versions are very close to the simulation results. The proposed power allocation schemes achieve a large SNR gain over the equal-power strategies and approach the optimal power allocation schemes.

Detection of multi-frequency weak signals with adaptive stochastic resonance system

Aiming at the poor detection rate of multi-frequency weak signals under a strong background of noise, a novel method based on adaptive stochastic resonance (SR) theory is proposed in this paper. The optimal parameters can be obtained automatically via measurement by establishing an adaptive SR system model and using the reverse location method. After passing through the adaptive SR system, the spectrum values of all eight signals greatly improve, the largest spectrum value gain increases from 12.41 to 2033 when the frequency is 0.01 Hz, which is an improvement of a factor of 162.8, and the signal-to-noise ratio (SNR) gain of the whole system is 10.3134 dB. Under the condition of different input noise intensities and signal amplitudes, the mean SNR of the system increases from –13.1136 to –2.7614 dB, which is a 78.9% increase, and the largest SNR gain is 13.4702 dB when the noise intensity D = 1.2 and signal amplitude A = 0.11. Compared to the single optimal spectrum value, when defining multiple optimum spectrum values as the SNR criterion, the detection sensitivity is less than 0.35 when the input noise intensity is between 0.5 and 2.5, and the sensitivity value is 6.29 times higher when D = 2.5. The system successfully realizes the adaptive detection of twelve weak signals, and the SNR gain is 7.9743 dB, which improves the channel capacity of signal detection. The experimental results demonstrate the high efficiency and strong applicability of the system, improving the signal processing efficiency and speed of signal transmission.

Super-sensitive two-wavelength fringe projection profilometry with 2-sensitivities temporal unwrapping

Since the early 1970s, optical two-wavelength phase-metrology (TWPM) has been used in a wide variety of experimental set ups. In TWPM one may compute the phase-sum and the phase-difference of two close phase measurements. Early TWPM optically computed the phase difference and phase sum by double exposure holography. However soon after, TWPM became almost synonymous to calculating the phase-difference only. The more sensitive phase-sum was largely forgotten. The standard application for phase-difference TWPM is to extend the phase measurement depth without phase-unwrapping for discontinuous phase-objects. This phase-difference, while non-wrapped, decreases however the signal-to-noise ratio (SNR) of the estimated phase. On the other hand, the phase-sum increases the phase sensitivity, and the SNR of the estimated phase. In spite of these two great advantages, the use of the phase-sum in TWPM has been almost ignored. In this paper we review and set the stage for digital TWPM for super-sensitive phase-sum estimation. This is coupled with two-sensitivity phase-unwrapping to obtain extended-range super-sensitive fringe-projection profilometry estimations. Here we mathematically prove, and experimentally show that using the phase-sum one obtains a huge increase in SNR with respect to using the phase-difference alone. The pioneer works on double exposure TWPM holography that uses the phase-difference and phase-sum are also properly acknowledged. Finally, two experimental results from fringe-projection profilometry that clearly show the huge SNR gain of the phase-sum, with respect to the phase-difference is now mathematically well established.

RETRACTED: Local Correlated Noise Improvement of Signal-to-Noise Ratio Gain in an Ensemble of Noisy Neuron

We theoretically investigate the collective response of an ensemble of leaky integrate-and-fire neuron units to a noisy periodic signal by including local spatially correlated noise. By using the linear response theory, we obtained the analytic expression of signal-to-noise ratio (SNR). Numerical simulation results show that the rms amplitude of internal noise can be increased up to an optimal value where the output SNR reaches a maximum value. Due to the existence of the local spatially correlated noise in the units of the ensemble, the SNR gain of the collective ensemble response can exceed unity and can be optimized when the nearest-neighborhood correlation is negative. This nonlinear collective phenomenon of SNR gain amplification in an ensemble of leaky integrate-and-fire neuron units can be related to the array stochastic resonance (SR) phenomenon. Furthermore, we also show that the SNR gain can also be optimized by tuning the number of neuron units, frequency and amplitude of the weak periodic signal. The present study illustrates the potential to utilize the local spatially correlation noise and the number of ensemble units for optimizing the collective response of the neuron to inputs, as well as a guidance in the design of information processing devices to weak signal detection.