Large SNR Research Articles

RF coil design strategies for improving SNR at the ultrahigh magnetic field of 10.5T.

Toward pushing the boundaries of ultrahigh fields for human brain imaging, we wish to evaluate experimentally achievable SNR relative to ultimate intrinsic SNR (uiSNR) at 10.5T, develop design strategies toward approaching the latter, quantify magnetic field-dependent SNR gains, and demonstrate the feasibility of whole-brain, high-resolution human brain imaging at this uniquely high field strength. A dual row 16-channel self-decoupled transmit (Tx) and receive (Rx) array was developed for 10.5T using custom Tx/Rx switches. A 64-channel receive-only array was built to fit into the 16-channel Tx/Rx array. Electromagnetic modeling and experiments were used to define safe operational power limits. Experimental SNR was evaluated relative to uiSNR at 10.5T and 7T. The 64-channel Rx array alone captured approximately 50% of the central uiSNR at 10.5T, while an identical array developed for 7T captured about 76% of uiSNR at 7T. The 16-channel Tx/80-channel Rx configuration brought the fraction of uiSNR captured at 10.5T to levels comparable to the 64-channel Rx array at 7T. SNR data displayed an approximate dependence over a large central region when evaluated in the context of uiSNR. Whole-brain, high-resolution -weighted and T1-weighted anatomical and gradient-recalled-echo BOLD-EPI functional MRI images were obtained at 10.5T for the first time with such an advanced array. We demonstrated the ability to approach the uiSNR at 10.5T over the human brain, achieving large SNR gains over 7T, currently the most commonly used ultrahigh-field platform. Whole-brain, high-resolution anatomical and EPI-based functional MRI data were obtained at 10.5T, illustrating the promise of greater than 10T fields in studying the human brain.

RF coil design strategies for improving SNR at the ultrahigh magnetic field of 10.5 Tesla.

To develop multichannel transmit and receive arrays towards capturing the ultimate-intrinsic-SNR (uiSNR) at 10.5 Tesla (T) and to demonstrate the feasibility and potential of whole-brain, high-resolution human brain imaging at this high field strength. A dual row 16-channel self-decoupled transmit (Tx) array was converted to a 16Tx/Rx transceiver using custom transmit/receive switches. A 64-channel receive-only (64Rx) array was built to fit into the 16Tx/Rx array. Electromagnetic modeling and experiments were employed to define safe operation limits of the resulting 16Tx/80Rx array and obtain FDA approval for human use. The 64Rx array alone captured approximately 50% of the central uiSNR at 10.5T while the identical 7T 64Rx array captured ∼76% of uiSNR at this lower field strength. The 16Tx/80Rx configuration brought the fraction of uiSNR captured at 10.5T to levels comparable to the performance of the 64Rx array at 7T. SNR data obtained at the two field strengths with these arrays displayed dependent increases over a large central region. Whole-brain high resolution T 2 * and T 1 weighted anatomical and gradient-recalled echo EPI BOLD fMRI images were obtained at 10.5T for the first time with such an advanced array, illustrating the promise of >10T fields in studying the human brain. We demonstrated the ability to approach the uiSNR at 10.5T over the human brain with a novel, high channel count array, achieving large SNR gains over 7T, currently the most commonly employed ultrahigh field platform, and demonstrate high resolution and high contrast anatomical and functional imaging at 10.5T.

Carbon dots for long-term near-infrared afterglow imaging and photodynamic therapy

Imaging-guided photodynamic therapy (PDT) has the features of precise location and non-invasiveness. However, most of the photosensitizers (PSs) for PDT are poor fluorescent emitters, and the inadequate fluorescence is usually interfered by tissue auto-fluorescence. The afterglow phosphorescence could ideally address the issues of fluorescence imaging. Therefore, it is of double benefit to design phosphorescentCDs for enhanced near-infrared (NIR) phototheranostics. Hereon, we synthesized CDs with excellent biosafety, outstanding stability, good water dispersibility and effective photodynamic activity. CDs could emit NIR luminescence with long lifetime over 2 h, which afforded large tissue penetration (10 mm) and high SNR (98.4) for deep-tissue and long-term in vivo persistent luminescent imaging. Moreover, abundant reactive oxygen species generated by CDs enabled NIR afterglow imaging-guided PDT to effectively inhibit tumor growth. This work demonstrates the enormous potential of CDs as multifunctional nanoplatforms for biomedical application.

An Alternative Statistical Characterization of TWDP Fading Model.

Two-wave with diffuse power (TWDP) is one of the most promising models for the description of small-scale fading effects in 5G networks, which employs mmWave band, and in wireless sensor networks deployed in different cavity environments. However, its current statistical characterization has several fundamental issues. Primarily, conventional TWDP parameterization is not in accordance with the model’s underlying physical mechanisms. In addition, available TWDP expressions for PDF, CDF, and MGF are given either in integral or approximate forms, or as mathematically untractable closed-form expressions. Consequently, the existing TWDP statistical characterization does not allow accurate evaluation of system performance in all fading conditions for most modulation and diversity techniques. In this regard, physically justified TWDP parameterization is proposed and used for further calculations. Additionally, exact infinite-series PDF and CDF are introduced. Based on these expressions, the exact MGF of the SNR is derived in a form suitable for mathematical manipulations. The applicability of the proposed MGF for derivation of the exact average symbol error probability (ASEP) is demonstrated with the example of M-ary PSK modulation. The derived M-ary PSK ASEP expression is further simplified for large SNR values in order to obtain a closed-form asymptotic ASEP, which is shown to be applicable for SNR > 20 dB. All proposed expressions are verified by Monte Carlo simulation in a variety of TWDP fading conditions.

SWIPT Enabled Intelligent Transportation Systems With Advanced Sensing Fusion

Internet of Things (IoT) is the connections of embedded sensing technologies that can be integrated with intelligent transportation systems (ITS), which can take advantage of the advanced sensing fusion to implement the intelligent interaction. Moreover, the environmental wireless signals was harvested and utilized to power the charging sensors, which can be used to assist and enhance the ITS and have attracted extensive attentions in industries. The simultaneous wireless information and power transfer (SWIPT) enabled ITS was designed and proposed with the advanced sensing fusion, where the sensor nodes of the source and destination were all equipped with multiple antennas and the maximum ratio transmission (MRT) precoding and maximum ratio combination (MRC) were adopted respectively in the proposed system, where the sensing nodes can be embedded into the data addressing equipment to fusion the sensing information. For the established massive sensing node transmission system, the transmission power, the number of source antennas and destination antennas were considered to fuse and optimize to obtain the maximum energy efficiency (EE) of the ITS. Since the original fusion problem was non-convex and difficult to solve, which can be transformed to convex problem via the large SNR approximation method and thereby the optimal solution of the sensing fusion problem was derived through the Lagrange algorithm and the Lambert function W. The simulation results showed that the proposed fusion algorithm can achieve remarkable EE compared with other algorithms and be utilized to the massive sensors to improve the intelligent predication and transportation for vehicle network.

New high-frequency radio observations of the Cygnus Loop supernova remnant with the Italian radio telescopes

ABSTRACT Supernova remnants (SNRs) represent a powerful laboratory to study the cosmic ray acceleration processes at shocks, and their relation to the properties of the circumstellar medium. With the aim of studying the high-frequency radio emission and investigating the energy distribution of accelerated electrons and the magnetic field conditions, we performed single-dish observations of the large and complex Cygnus Loop SNR from 7.0–24.8 GHz with the Medicina and Sardinia Radio Telescopes, focusing on the northern filament (NGC 6992) and the southern shell. Both regions show a spectrum well fitted by a power-law function (S ∝ ν−α), with spectral index α = 0.45 ± 0.05 for NGC 6992 and α = 0.49 ± 0.01 for the southern shell and without any indication of a spectral break. The spectra are significantly flatter than the whole Cygnus Loop spectrum (α = 0.54 ± 0.01), suggesting a departure from the plain shock acceleration mechanisms, which for NGC 6992 could be related to the ongoing transition towards a radiative shock. We model the integrated spectrum of the whole SNR considering the evolution of the maximum energy and magnetic field amplification. Through the radio spectral parameters, we infer a magnetic field at the shock of 10 μG. This value is compatible with purely adiabatic compression of the interstellar magnetic field, suggesting that the amplification process is currently inefficient.

Distributed ISAR Imaging of Rotating Target Based on Homotopy L1L0 Method

The distributed ISAR technique can form multiple virtual equivalent sensors to observe the target from multiple observation angles, and can obtain more spatial sampling data at the same time than monostatic ISAR, so it has the potential to increase the cross-range resolution. In this paper, sparse signal recovery algorithms are proposed to obtain the cross-range image of the distributed ISAR when the conventional Fourier transform imaging method is not applicable due to (1) nonuniform rotation of the target (2) large echo gap and (3) low echo SNR. After obtaining the distributed ISAR echoes, the range migration of the scatterer in each equivalent sensor is analyzed, and a cross-range phase that causes a positioning error is compensated. Then, the sparse representation of the echo in each range bin is given and the homotopy L1L0 (HL1L0) method is introduced. Singular value decomposition (SVD) is used to improve the robustness of the algorithm. Simulation results show that the sparse recovery algorithms can achieve high cross-range resolution, and HL1L0 method is better than orthogonal matching pursuit (OMP) and smoothed L0 (SL0) under different echo gaps and SNRs according to the four proposed evaluation criteria. Real data experiment verifies the advantage of the distributed ISAR and the effectiveness of the proposed method.

Low overhead NOMA receiver with automatic modulation classification techniques

Recently non-orthogonal multiple access (NOMA) technique has been proposed for boosting spectral efficiencies in 5G cellular networks. In NOMA the transmitter maps a predefined number of user symbols on to the same resources. The conventional receiver for NOMA is the well-known serial interference cancellation. To overcome the problem of high overhead signalling, a receiver with an automatic modulation classification (AMC) algorithm for a K-user NOMA which identifies the modulation scheme of users before symbol detection is proposed. First, a two-user NOMA (TU-NOMA) scheme is treated and the receiver is extended to more general cases. For evaluating the performance of the proposed receiver its bit error rate (BER) for TU-NOMA case has been driven and shown that this can be approximated as the sum of the demodulator BER and the AMC algorithm error probability. The simulation results show the BER degradation can be neglected if an enough number of symbols with sufficiently large SNR values are available.

Antithetic Dithered 1-Bit Massive MIMO Architecture: Efficient Channel Estimation via Parameter Expansion and PML

Drawing from a recent work on negative noise correlation in quantization and statistics, we propose a novel antithetic dithered 1-bit massive MIMO receiver architecture and develop efficient channel estimation algorithms that exploit the natural and induced negative correlated noise in the system. We illustrate that both linear and nonlinear estimators can benefit from negative correlation. We provide a rigorous analysis of a low-complexity nonlinear estimator for channel estimation. In the process, we developed a generalized statistical framework to analyze correlated quantized output arising from this generalized linear model. We formalized the approximation technique used in this work as a special case of the more general pseudo maximum likelihood method. A parameter expanded expectation maximization (PX-EM) algorithm applied to such a system is shown to exhibit fast convergence, possessing an upper bounded convergence guarantee and a graceful monotonic estimation performance over a large SNR range. Stochastic Gibbs sampling algorithms are constructed to evaluate truncated multivariate normal distributions and to implement an asymptotically exact data augmentation algorithm for comparison.

Disentangling the effects of high permittivity materials on signal optimization and sample noise reduction via ideal current patterns.

To investigate how high-permittivity materials (HPMs) can improve SNR when placed between MR detectors and the imaged body. We used a simulation framework based on dyadic Green's functions to calculate the electromagnetic field inside a uniform dielectric sphere at 7 Tesla, with and without a surrounding layer of HPM. SNR-optimizing (ideal) current patterns were expressed as the sum of signal-optimizing (signal-only) current patterns and dark mode current patterns that minimize sample noise while contributing nothing to signal. We investigated how HPM affects the shape and amplitude of these current patterns, sample noise, and array SNR. Ideal and signal-only current patterns were identical for a central voxel. HPMs introduced a phase shift into these patterns, compensating for signal propagation delay in the HPMs. For an intermediate location within the sphere, dark mode current patterns were present and illustrated the mechanisms by which HPMs can reduce sample noise. High-amplitude signal-only current patterns were observed for HPM configurations that shield the electromagnetic field from the sample. For coil arrays, these configurations corresponded to poor SNR in deep regions but resulted in large SNR gains near the surface due to enhanced fields in the vicinity of the HPM. For very high relative permittivity values, HPM thicknesses corresponding to even multiples of λ/4 resulted in coil SNR gains throughout the sample. HPMs affect both signal sensitivity and sample noise. Lower amplitude signal-only optimal currents corresponded to higher array SNR performance and could guide the design of coils integrated with HPM.

ANALISIS UKURAN PORI BIOKOMPOSIT [SERICIN-BIOPLASTIK] PADA BERBAGAI PEMBEKUAN DENGAN METODE TAGUCHI

Increased demand for medical materials, triggering research into alternativemedical materials. Alternative materials should have the same characteristics for the patient's body. Sericin is a protein that has biocompatible, biodegradable and other important properties. Sericin is widely used in biomedical applications, it is thought that sericin is a promising natural resource as an alternative medical material. This study analyzed pore diameter in sericin-bioplastic biocomposites by Taguchi method. Bioplastics of 3 variations of tapioca starch were 16 g, 14 g, and 10 g, mixed 80 ml of aquades and 6 ml of glycerin. Sericin was determined 0.03%, 0.1%, and 0.3% by weight of tapioca starch. The biocomposite undergoes freeze drying process and is frozen at -25oC, -45oC, and -80oC for one day. SEM test to see pore diameter and biocomposite structure. Optimal analysis was performed for optimal combinations of sericin-bioplastic biocomposites. The SEM results showed pore diameters qualified for regeneration of skin tissue on freezers C -C, F, and I -25oC biocomposites of 41.94 μm, 33.416 μm and 32.743 μm respectively. Calculation of average response and maximum SNR at 16 g tapioca starch, 0.03% sericin and -25oC temperature. The predicted and confidence interval values for averages are large from 11,656 μm and small from 54,602 μm, SNR is large from 31,940 μm and small from 33,642 μm. The optimal experimental conditions for confirmation of large pore diameter for averages were large from 32.342 μm and small from 34.206 μm, large SNR of 32.342 μm and small from 34.206 μm.Keywords: Composition optimization, alternative medical materials, sericin- bioplastic biocomposites, Taguchi Methods, SEM

Enhancement of the Performance and Data Processing Rate of an Optical Frequency Domain Reflectometer Distributed Sensing System Using A Limited Swept Wavelength Range.

A novel optical frequency domain reflectometer (OFDR) processing algorithm is proposed to enhance the measurable range and data processing rate using a narrow swept spectrum range and reducing the time consuming of the process distributed sensing results. To reduce the swept wavelength range and simultaneously enhance strain measurable range, the local similarity characteristics of Rayleigh scattering fingerprint spectrum is discovered and a new similarity evaluation function based on least-square method is built to improve the data processing rate and sensing performance. By this method, the strain measurable range is raised to 3000 µε under a highest spatial resolution of 3 mm when the swept spectrum range is only 10 nm and the data processing rate is improved by at least 10 times. Experimental results indicate that a nonlinearity of less than 0.5%, a strain resolution of better than 10 µε, a repeatability at zero strain of below ±0.4 GHz and a full-scale accuracy is lower than 0.85 GHz under a highest spatial resolution of 3 mm can be achieved. Advantages of this method are fast processing rate, large strain measurable range, high SNR, and applicability with current OFDR systems.

Channel Capacity Calculation at Large SNR and Small Dispersion within Path-Integral Approach

We consider the optical fiber channel modelled by the nonlinear Shrödinger equation with additive white Gaussian noise. Using Feynman path-integral approach for the model with small dispersion we find the first nonzero corrections to the conditional probability density function and the channel capacity estimations at large signal-to-noise ratio. We demonstrate that the correction to the channel capacity in small dimensionless dispersion parameter is quadratic and positive therefore increasing the earlier calculated capacity for a nondispersive nonlinear optical fiber channel in the intermediate power region. Also for small dispersion case we find the analytical expressions for simple correlators of the output signals in our noisy channel.

Statistical characterization of coprime sensor arrays: Array gain vs. spatially correlated noise

Sensor arrays suppress spatially-uncorrelated noise through conventional beamforming (CBF). Array Gain (AG) quantifies the SNR improvement at the CBF output compared to the sensor-level SNR. The AG for a CBF Uniform Line Array (ULA) in uncorrelated noise is the number of sensors. A Coprime Sensor Array (CSA) is a sparse array geometry interleaving two undersampled ULAs, multiplying the subarray CBF outputs to achieve the same resolution as a fully populated ULA of the same aperture using fewer sensors [Vaidyanathan & Pal, 2010]. The CSA product process AG in uncorrelated noise is asymptotically equal to the number of sensors for large input SNR [Adhikari & Buck, 2015]. This research derives the AGs for CSAs and ULAs using the traditional SNR definition and deflection statistics [Cox, 1973] for a spatial first-order autoregressive process. This process introduces spatial correlation and is a simple model for turbulent flow noise over a towed array. Although the CSA AG is lower than the ULA for uncorrelated noise, the CSA's AG degrades more slowly than the ULA's AG with increasing noise correlation, due to larger spacing in the CSA subarrays. The CSA is more robust to correlated noise than the ULA AG. [Funded by NUWC & ONR.]

Ptychographic reconstruction algorithm for frequency-resolved optical gating: super-resolution and supreme robustness

Frequency-resolved optical gating (FROG) is probably the most popular technique for complete characterization of ultrashort laser pulses. In FROG, a reconstruction algorithm retrieves the pulse from a measured spectrogram, yet current FROG reconstruction algorithms require and exhibit several restricting features that weaken FROG performances. For example, the delay step must correspond to the spectral bandwidth measured with large enough SNR a condition that limits the temporal resolution of the reconstructed pulse, obscures measurements of weak broadband pulses, and makes measurement of broadband mid-IR pulses hard and slow because the spectrograms become huge. We develop a new approach for FROG reconstruction, based on ptychography (a scanning coherent diffraction imaging technique), that removes many of the algorithmic restrictions. The ptychographic reconstruction algorithm is significantly faster and more robust to noise than current FROG algorithms, which are based on generalized projections (GP). We demonstrate, numerically and experimentally, that ptychographic reconstruction works well with very partial spectrograms, e. g. spectrograms with reduced number of measured delays and spectrograms that have been substantially spectrally filtered. In addition, we implement the ptychogrpahic approach to blind second harmonic generation (SHG) FROG and demonstrate robust and complete characterization of two unknown pulses from a single measured spectrogram and power spectrum of only one of the pulses. We believe that the ptychograpy-based approach will become the standard reconstruction procedure in FROG and related diagnostics methods, allowing successful reconstructions from so far unreconstructable spectrograms.

Joint Relay and Antenna Selection in MIMO PLNC Inter-vehicular Communication Systems over Cascaded Fading Channels

We investigate the joint relay and antenna selection performance in a multiple input multiple output (MIMO) Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme at the relay antenna. Analytic results are derived under the cascaded Nakagami-m fading channel model assumption, which covers cascaded Rayleigh and conventional cellular channel models as well. We evaluate the performance of the system in terms of joint outage probability of sources and derive closed-form expressions for lower and upper bounds while an exact expression is found as a single integral form. Besides, the asymptotic diversity order is analyzed and quantified as a function of number of relays and antennas installed on the source and relay vehicles, and channel parameters. Finally, we verify the analytic derivations by computer simulations. Our results show that the outage probability performance decreases with the increasing cascading degrees of the channels but joint relay and antenna selection enhances the performance of the system superbly with the increasing number of relays and antennas. Also it is shown throughout all the simulation results, the lower bound for the joint outage probability seems to consistently be well tight for large SNR. Therefore it can be used for practical design of inter-vehicular communication systems which contain multiple relays and antennas.

A rapid magnetic resonance acoustic radiation force imaging sequence for ultrasonic refocusing

Magnetic resonance guided acoustic radiation force imaging (MR-ARFI) is being used to correct for aberrations induced by tissue heterogeneities when using high intensity focusing ultrasound (HIFU). A compromise between published MR-ARFI adaptive solutions is proposed to achieve efficient refocusing of the ultrasound beam in under 10 min. In addition, an ARFI sequence based on an EPI gradient echo sequence was used to simultaneously monitor displacement and temperature with a large SNR and low distortion.This study was conducted inside an Achieva 3T clinical MRI using a Philips Sonalleve MR-HIFU system to emit a 1 ms pulsed sonication with duty cycle of 2.3% at 300 Wac inside a polymer phantom. Virtual elements defined by a Hadamard array with sonication patterns composed of 6 phase steps were used to characterize 64 groups of 4 elements to find the optimal phase of the 256 elements of the transducer. The 384 sonication patterns were acquired in 580 s to identify the set of phases that maximize the displacement at the focal point. Three aberrators (neonatal skull, 8 year old skull and a checkered pattern) were added to each sonication pattern to evaluate the performance of this refocusing algorithm (n = 4).These aberrators reduced the relative intensities to 95.3%, 69.6% and 25.5% for the neonatal skull, 8 year old skull, and checkered pattern virtual aberrators respectively. Using a 10 min refocusing algorithm, relative intensities of 101.6%, 91.3% and 93.3% were obtained. Better relative intensities of 103.9%, 94.3% and 101% were achieved using a 25 min refocusing algorithm. An average temperature increase of 4.2 °C per refocusing test was induced for the 10 min refocusing algorithm, resulting in a negligible thermal dose of 2 EM.A rapid refocusing of the beam can be achieved while keeping thermal effects to a minimum.

Hitchhike: A Preamble-Based Control Plane for SNR-Sensitive Wireless Networks

Recently, carrying control signals on passing data packets has emerged as a promising direction for efficient control information transmission. With control messages carried on data payload, the extra air time needed for control packets like RTS/CTS is eliminated and thus channel utilization is improved. However, carrying control signals on the data payload of a packet requires the data packet to have a sufficiently large SNR, otherwise both the data packet and the control messages are lost. In this paper, we propose Hitchhike , a technique that utilizes the preamble field to carry control messages. Hitchhike completely decouples the control messages from the payload and therefore the superposition of (multiple) control messages has little adverse effect on the operation of the payload decoding. We implement and evaluate Hitchhike in the USRP2 platform with five nodes. Evaluation results demonstrate the feasibility and effectiveness of Hitchhike. Compared with the state-of-the-art, e.g., side-channel in 802.15.4, Hitchhike improves the detection accuracy of control messages by 40% and reduces the data loss caused by control messages by 15%.

Diversity Combining Using Maxima Ratio Combining for All Modulation Mode

The destruction caused by channel can be seen by the existence of Amplitude and Phase Shift. By using the 6 Ways Diversity Combining method (6 Antennas/Receivers), it is expected that the disruption caused by Amplitude and Phase Shift can be suppressed as small as possible. In addition, by using diversity combining module, we will get a large SNR output which has a value sum of SNR of each diversity path. The design of Diversity combining module begins with MATLAB functional design as a big picture of the whole system. Subsequently, it will be made the hardware based on the MATLAB functional. This architectural design that will be the cornerstone in the MATLAB bit precision manufacturing. Then MATLAB bit precision will be designed as the foundation of the VHDL design. Diversity combining the output module meets the standards specified by the DVB consortium. In the hardware (FPGA) test results of diversity combining, the maximum working frequency is 44.56 MHz which has shown that is qualified with the standard sampling clock (9.142 MHz). This design also needs 4% of total FPGA Cyclone II 484I8 combinational units which is 2499 units and it needs also 3% of total register of FPGA Cyclone II 484I8 which is 1720 register units.

Beamforming with Kerdock Codes in LTE System for High-Speed Railway

Beamforming technique based the reciprocity of LTE communication system for high-speed railway is a practical way to improve the system performance in this paper. Kerdock codes, which facilitate efficient codebook and codeword search, are implemented in the LTE system for high-speed railway as the beamforming precoding codebook. The analysis of complexity and simulation results about the communication system of the beamforming with Kerdock codes (KBF) show that the proposed KBF can eliminate complex multiplications and improve the Bit Error Rate (BER) performance at large SNR compared with the existing beamfoming communication system for high-speed railway.