Receiver Bandwidth Research Articles

Zero-gradient-excitation ramped hybrid encoding (zGRF -RHE) sodium MRI.

Fast bi-exponential transverse signal decay compounds sodium image quality. This work aims at enhancing image characteristics using a special case of ramped hybrid encoding (RHE). Zero-gradient-excitation (zGRF )-RHE provides (1) gradient-free excitation for high flip angle, artifact-free excitation profiles and (2) gradient ramping during dead-time for the optimization of encoding time (tenc ) to reduce T2* signal decay influence during acquisition. Radial zGRF -RHE and standard radial UTE were investigated over a range of receiver bandwidths in simulations, phantom and in vivo brain experiments. Central k-space in zGRF -RHE was acquired through single point measurements at the minimum achievable TE. T2* blurring artifacts and image SNR and CNR were assessed. zGRF -RHE enabled 90° flip angle artifact-free excitation, whereas gradient pre-ramping provided greater tenc efficiency for any readout bandwidths. Experiments confirmed simulation results, revealing sharper edge characteristics particularly at short readout durations (TRO ). Significant SNR improvements of up to 4.8% were observed for longer TRO . zGRF -RHE allows for artifact-free high flip angle excitation with time-efficient encoding improving on image characteristics. This hybrid encoding concept with gradient pre-ramping is trajectory independent and can be introduced in any center-out UTE trajectory design.

On the normalized FRB luminosity function

Thirty-three fast radio bursts (FRBs) had been detected by March 2018. Although the sample size is still limited, meaningful statistical studies can already be carried out. The normalised luminosity function places important constraints on the intrinsic power output, sheds light on the origin(s) of FRBs, and can guide future observations. In this paper, we measure the normalised luminosity function of FRBs. Using Bayesian statistics, we can naturally account for a variety of factors such as receiver noise temperature, bandwidth, and source selection criteria. We can also include astronomical systematics, such as host galaxy dispersion measure, FRB local dispersion measure, galaxy evolution, geometric projection effects, and Galactic halo contribution. Assuming a Schechter luminosity function, we show that the isotropic luminosities of FRBs have a power-law distribution that covers approximately three orders of magnitude, with a power-law index ranging from $-1.8$ to $-1.2$ and a cut off $\sim 2\times 10^{44}\,\rm erg\,s^{-1}$. By using different galaxy models and well-established Bayesian marginalisation techniques, we show that our conclusions are robust against unknowns, such as the electron densities in the Milky Way halo and the FRB environment, host galaxy morphology, and telescope beam response.

An Atomic Receiver for AM and FM Radio Communication

Radio reception relies on antennas for the collection of electromagnetic fields carrying information, and receiver elements for demodulation and retrieval of the transmitted information. Here, we demonstrate an atom-based receiver for AM and FM microwave communication with a 3 dB bandwidth in the baseband of ~100 kHz that provides optical circuit-free field pickup, multiband carrier capability, and inherently high field sensitivity. The atom-based receiver exploits field-sensitive cesium Rydberg vapors in a centimeter-sized glass cell, and electromagnetically induced transparency, a quantum-optical effect, as a readout of baseband signals modulated onto carriers with frequencies ranging over four octaves, from C-band to Q-band. Receiver bandwidth, dynamic range and sideband suppression are characterized, and acquisition of audio waveforms of human vocals demonstrated. The atomic receiver is a valuable receiver technology because it does not require antenna structures and is resilient against electromagnetic interference, while affording multiband operation in a single compact receiving element.

Air bubble artifact reduction in post-mortem whole-brain MRI: the influence of receiver bandwidth.

Air bubble artifacts on SWI post-mortem MRI studies may interfere with the detection of cerebral microbleeds. We investigated whether the utilization of a higher receiver bandwidth of 500Hz/pixel could reduce cortical air bubble artifacts without compromising the detection of cerebral microbleeds in high-field MRI. All microbleeds remained clearly visible whereas a reduction of 17% of the long axis of the "halo" magnitude artifacts was achieved. On corresponding phase images, air bubble artifacts appeared identical.

224-Gb/s Carrier-Recovery-Free Doubly Differential 2ASK-8PSK for Short-Reach Optical Networks

We propose and experimentally demonstrate a carrier-recovery-free 224-Gb/s dual-polarization doubly differential (DD) two-amplitude/eight-phase shift keyed (2ASK-8PSK) signal for 100-km fiber transmission with coherent detection. An 11-tap multi-symbol DD (MSDD) decoding scheme helps to reduce the penalty caused by two differential operations in conventional DD decoding, allowing an optical signal-to-noise-ratio improvement of 3.7 dB for DD quadrature phase shift keying and 4.3 dB for DD 16 quadrature amplitude modulation (QAM). By employing such decoding, a frequency offset (FO) tolerance of 16 GHz has been achieved in a DD 2ASK-8PSK system for a bit-error-rate of $\sim 1\times 10^{-3}$ . Compared with a 224-Gb/s 16QAM system employing conventional carrier recovery algorithms, the proposed system is more robust to FOs, and the FO tolerance range is only limited by the effective receiver bandwidth.

Transmitter skew tolerance and spectral efficiency tradeoff in high baud-rate QAM optical communication systems

Residual IQ skew in a coherent transmitter severely degrades the performance of long-haul coherent optical communication systems. The impairment is particularly detrimental for a high baud-rate system using quadrature amplitude modulation (QAM). Furthermore, Nyquist pulse shaping increases the spectral efficiency for WDM systems. However, sharp roll-off of Nyquist pulse shaping further reduces the tolerance to residual IQ skew. Thus, certain trade-offs between spectral efficiency and roll-off factor should be made to improve the tolerance of residual IQ skew. We experimentally studied this trade-off and determined the optimal roll-off factor, channel spacing, receiver bandwidth, and equalizer length. The results serve as a guideline for high baud-rate coherent WDM systems.

MRI Image Enhancement: Optimized Filtering Mechanism for Achieving High Accuracy in Diagnose Process

Segmentation plays an important role in separating data from medicinal images and also helps in clinical findings. Segmentation is the way toward apportioning the image into different regions. MRI is utilized to extract images of delicate tissues of human body. It is utilized in analyzing the human organs without the requirement of surgery. For the most part MRI images contain a lot of noise caused by operator performance, equipment and the environment, which prompts genuine errors. MRI is a productive way in giving data in regards to the area of tumors and even the volume. The noise present in the MRI image can be evacuated by utilizing different de-noising procedures whichever is most appropriate method depending on the type of image obtained and afterward can be handled by any of the segmentation techniques. The noise in MRI images might be because of field strength, RF pulses, RF coil, voxel volume, or receiver bandwidth. In our proposed paper a review of different noise handling and filtering mechanism is conducted in order to enhance the quality of image. In this paper we modify the adaptive median filter by applying redundancy handling mechanism and enhance the contrast of image by applying histogram equivalence method.

Energy leakage analysis of the radar and communication integrated waveform

When minimum shift keying (MSK)'s carrier is changed as the linear frequency modulation (LFM) signal, it is called as MSK-LFM for short. It is a new type of the radar-communication multifunctional integrated waveform. Under the assumption that the bandwidth of the radar receiver is equal to that of the LFM signal, the energy leakage of MSK-LFM is analysed. The trade-off between the number of modulated bits and the energy leakage is derived analytically. The derived equation demonstrates that the relationship between the radar detection performance and digital communication performance of MSK-LFM, which also gives the principle of designing the integrated waveform. To better ensure the radar detection performance, a method is proposed to reduce the energy leakage at the expense of sacrificing certain communication capacity.

T1 weighted fat/water separated PROPELLER acquired with dual bandwidths.

To describe a fat/water separated dual receiver bandwidth (rBW) spin echo PROPELLER sequence that eliminates the dead time associated with single rBW sequences. A nonuniform noise whitening by regularization of the fat/water inverse problem is proposed, to enable dual rBW reconstructions. Bipolar, flyback, and dual spin echo sequences were developed. All sequences acquire two echoes with different rBW without dead time. Chemical shift displacement was corrected by performing the fat/water separation in k-space, prior to gridding. The proposed sequences were compared to fat saturation, and single rBW sequences, in terms of SNR and CNR efficiency, using clinically relevant acquisition parameters. The impact of motion was investigated. Chemical shift correction greatly improved the image quality, especially at high resolution acquired with low rBW, and also improved motion estimates. SNR efficiency of the dual spin echo sequence was up to 20% higher than the single rBW acquisition, while CNR efficiency was 50% higher for the bipolar acquisition. Noise whitening was deemed necessary for all dual rBW acquisitions, rendering high image quality with strong and homogenous fat suppression. Dual rBW sequences eliminate the dead time present in single rBW sequences, which improves SNR efficiency. In combination with the proposed regularization, this enables highly efficient T1-weighted PROPELLER images without chemical shift displacement.

DEVELOPMENT OF OPTICAL WIRELESS RECEIVER AMPLIFIER USING HYBRID ENHANCEMENT

In the new communication era, signal will be transmit to the receiver via wireless. However, the signal might be loss during the transmission. Therefore, the signal received at the receiver is totally not originally from the transmitter. In some cases the signal must be amplified. This project will focuses on the concept of wireless optical in receiver communication system. The objectives of this project is to design a receiver amplifier using hybrid bandwidth enhancement in the approximately of Giga hertz range. The receiver amplifier is designed using Micro-Cap. The configuration of this design receiver is by using combination of bootstrapping and cascade technique. Bootstrapping technique offers the reduction on the photo detector capacitances which is the main limiting factor for the bandwidth of optical wireless front-end receiver. While, the cascade technique is used to arrange the electrical components such as transistor. Using the designed receiver Bootstrap Amplifier with Double Peaking Coil has been designed and fabricated. The cut-off frequency for this circuit is 400MHz.

0.36 V PGA combining single‐stage OTA and input negative transconductor for low energy RF receivers

An ultra-low voltage and ultra-low power programmable gain amplifier (PGA) using a closed-loop single-stage operational transconductance amplifier (OTA) and an input negative transconductor is proposed. The circuits are implemented in a 180 nm CMOS process using two stacked transistors and PMOS bulk forward bias to operate well down to 0.36 V, to be robust to PVT variations and to reach the bandwidth of low energy RF receivers. The PGA measured results at 0.36 V show a programmable voltage gain from 0.2 to 18.4 dB, 15.4 μW power dissipation, 0.98 MHz bandwidth and 0.0243 mm 2 area.

102-nm, 44.5-MHz inertial-free swept source by mode-locked fiber laser and time stretch technique for optical coherence tomography.

A swept source with both high repetition-rate and broad bandwidth is indispensable to enable optical coherence tomography (OCT) with high imaging rate and high axial resolution. However, available swept sources are commonly either limited in speed (sub-MHz) by inertial or kinetic component, or limited in bandwidth (<100 nm) by the gain medium. Here we report an ultrafast broadband (over 100 nm centered at 1.55-µm) all-fiber inertial-free swept source built upon a high-power dispersion-managed fiber laser in conjunction with an optical time-stretch module which bypasses complex optical amplification scheme, which result in a portable and compact implementation of time-stretch OCT (TS-OCT) at A-scan rate of 44.5-MHz, axial resolution of 14 µm in air (or 10 µm in tissue), and flat sensitivity roll-off within 4.3 mm imaging range. Together with the demonstration of two- and three-dimensional OCT imaging of a mud-fish eye anterior segment, we also perform comprehensive studies on the imaging depth, receiver bandwidth, and group velocity dispersion condition. This all-fiber inertia-free swept source could provide a promising source solution for SS-OCT system to realize high-performance volumetric OCT imaging in real time.

Kramers–Kronig Receivers for 100-km Datacenter Interconnects

In this paper, we review in detail experimental demonstrations of Kramers–Kronig (KK) based direct detection systems with high per-carrier interface rates, high spectral efficiencies, and ∼100-km reach. Two realizations of KK-based receivers are summarized, including single-polarization and dual-polarization versions. Critical aspects of the KK receiver such as the carrier-to-signal power ratio and receiver bandwidth limitations are discussed. We show 220-Gb/s single-diode detection and 4 × 240-Gb/s dual polarization (dual-diode) detection in a WDM system at 5.3 bits/s/Hz spectral efficiency.

Adaptive Dynamic Filter using MOSFET Receiver

In Optical wireless communication systems a reliable link is required for user mobility under different channel conditions. In this paper, concept of adaptive receiver for bandwidth system using MOSFET is discussed that will maintain and enhance the reliability of the optical link for different channel conditions. The proposed system is found to be more sensitive to any variations in signal-to-noise ratio (SNR) at higher noise magnitudes. The circuit design consists of four circuits which are rectifier, low pass filter, dynamic filter, and output amplifier. The circuit was simulated for 43.775 kHz (0.01μf) to 0.2 MHz (44pF). The designed adaptive system can be used in existing optical system to vary the bandwidth of receiver for different applications.

A Pseudorange Measurement Scheme Based on Snapshot for Base Station Positioning Receivers.

Digital multimedia broadcasting signal is promised to be a wireless positioning signal. This paper mainly studies a multimedia broadcasting technology, named China mobile multimedia broadcasting (CMMB), in the context of positioning. Theoretical and practical analysis on the CMMB signal suggests that the existing CMMB signal does not have the meter positioning capability. So, the CMMB system has been modified to achieve meter positioning capability by multiplexing the CMMB signal and pseudo codes in the same frequency band. The time difference of arrival (TDOA) estimation method is used in base station positioning receivers. Due to the influence of a complex fading channel and the limited bandwidth of receivers, the regular tracking method based on pseudo code ranging is difficult to provide continuous and accurate TDOA estimations. A pseudorange measurement scheme based on snapshot is proposed to solve the problem. This algorithm extracts the TDOA estimation from the stored signal fragments, and utilizes the Taylor expansion of the autocorrelation function to improve the TDOA estimation accuracy. Monte Carlo simulations and real data tests show that the proposed algorithm can significantly reduce the TDOA estimation error for base station positioning receivers, and then the modified CMMB system achieves meter positioning accuracy.

Comparison of the leading-edge timing walk in pulsed TOF laser range finding with avalanche bipolar junction transistor (BJT) and metal-oxide-semiconductor (MOS) switch based laser diode drivers.

Timing walk error in pulsed time-of-flight based laser range finding was studied using two different types of laser diode drivers. The study compares avalanche bipolar junction transistor (BJT) and metal-oxide-semiconductor field-effect transistor switch based laser pulse drivers, both producing 1.35 ns current pulse length (full width at half maximum), and investigates how the slowly rising part of the current pulse of the avalanche BJT based driver affects the leading edge timing walk. The walk error was measured to be very similar with both drivers within an input signal dynamic range of 1:10 000 (receiver bandwidth of 700 MHz) but increased rapidly with the avalanche BJT based driver at higher values of dynamic range. The slowly rising part does not exist in the current pulse produced by the metal-oxide-semiconductor (MOS) based laser driver, and thus the MOS based driver can be utilized in a wider dynamic range.

Performance Improvement of Brillouin Ring Laser Based BOTDR System Employing a Wavelength Diversity Technique

In this paper technique is employed in a Brillouin optical time domain reflectometry (BOTDR) using a Brillouin ring laser (BRL) as a local oscillator. In the wavelength diversity technique, multiple wavelengths are injected into the sensing fiber, while the peak power of each wavelength is set below the nonlinear threshold level. This technique significantly maximizes the overall launch pump power, without activating the nonnegligible nonlinear effects, which overcomes the limitation of the conventional BOTDR system. The BRL, which is simple and cost-effective, that can be used to reduce the receiver bandwidth in the order of few MHz. In addition, a passive depolarizer is used to reduce the polarization noise. The proposed system is validated experimentally over a 50 km sensing fiber with a 5 m spatial resolution. The experimental results demonstrate a signal-to-noise ratio improvement of 5.1 dB, which corresponds to 180% improvement compared to a conventional BOTDR system.

Tissue oxygenation mapping by combined chemical shift and T1 magnetic resonance imaging.

To propose a method for determining tissue oxygenation via the measurement of fat T1 . The method is based on a 2D fat/water chemical shift-encoded and T1 -weighted acquisition. A 2D data set was acquired with a fast spin echo sequence with several echo asymmetries and repetition times, wherein one dimension is related to the fat/water phase modulation and the other to the T1 saturation recovery. A joint magnitude-based process of phase modulation and T1 evolution allowed for the collection of the fat fraction and T1 maps with resolved fat or water dominance ambiguity while avoiding the phased error problem. In vitro imaging allowed for the attribution of fat content for different water/oil emulsions that demonstrated longitudinal relaxation rate (R1 ) sensitivity to the oxygenated emulsion environment. The fat R1 values were subsequently compared to reference values, which were measured using low receiver bandwidth acquisition to enhance water and fat signal separations. In vivo feasibility of tissue oxygenation assessment was demonstrated by investigating interscapular brown adipose tissue modifications during an air/carbogen challenge in rats. The proposed method offers a precise and robust estimate of tissue oxygenation illustrated by the method's ability to detect-brown adipose tissue oxygenation modifications. Magn Reson Med 79:1981-1991, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

A 10-Gbps receiver bridge chip with deserializer for FPGA-based frame grabber supporting MIPI CSI-2

A 2.5-Gbps/lane receiver bridge chip, which fully supports the protocol of the D-PHY version 1.2 for the mobile industry processor interface (MIPI) camera serial interface (CSI)-2, is proposed for a field-programmable gate array (FPGA)-based frame grabber. The proposed receiver bridge chip converts four-lane high-speed data of scalable low-voltage signaling (SLVS) of the MIPI CSI-2 into 32 low-speed data of low-voltage CMOS (LVCMOS) signaling for a parallel interface with a FPGA chip. In order to achieve this, each data lane of the proposed receiver bridge chip has a 1-to-8 deserializer including a byte synchronizer. Furthermore, an asynchronous delay line per lane compensates the time skew among the five lanes, including a clock lane. A common-gate level shifter (CGLS) with a continuous-time linear equalizer (CTLE) is proposed to improve the voltage fain and bandwidth of the high-speed receiver. The proposed receiver bridge chip is implemented using a 0.11 μm CMOS process with a 1.2 V supply. The area and power consumption of the proposed receiver bridge chip are 5.29 mm2 and 7.2 me/Gbps/lane, respectively. The proposed CTLE of the high-speed receiver achieves the improved peak-to-peak time jitter of 0.3UI at a data rate of 3.0 Gbps/lane. The FPGA-based frame grabber processes the image or video data supplied by a camera sensor with the MIPI CSI-2 by using the proposed receiver bridge chip.

Metal Artifact Reduction Magnetic Resonance Imaging Around Arthroplasty Implants: The Negative Effect of Long Echo Trains on the Implant-Related Artifact.

Long echo train length (ETL) is an often recommended but unproven technique to decrease metal artifacts on magnetic resonance imaging (MRI) scans. Therefore, we quantitatively and qualitatively assessed the effects of ETL on metal artifact on MRI scans using a cobalt-chromium-containing arthroplasty implant system. Using a total ankle arthroplasty system implanted into a human cadaver ankle and a clinical 1.5 T MRI system, turbo spin echo (TSE) pulse sequences were acquired with ETL ranging from 3 to 23 and receiver bandwidth (BW) from 100 to 750 Hz/pixel, whereas effective echo time and spatial resolution were controlled. A compressed sensing slice encoding for metal artifact correction TSE prototype pulse sequence was used as reference standard. End points included the total implant-related artifact area and implant-related signal void areas. Two raters evaluated the overall image quality and preference across varying BW and ETL. Two-factor analysis of variance, Friedman test, Kruskal-Wallis test, and Pearson correlation were used. P values of less than 0.05 were considered statistically significant. The total implant-related artifact area ranged from 0.119 for compressed sensing slice encoding for metal artifact correction (BW, 600 Hz/pixel; ETL, 3) to 0.265 for TSE (BW, 100 Hz/pixel; ETL, 23). Longer ETL significantly increases the total implant-related artifact area (P = 0.0004), whereas it decreased with increasing BW (P < 0.0001). Implant-related signal void areas were not significantly affected by larger echo train length, but reduced with higher BW (P < 0.0001). Readers had a significant preference for images with high BW and short ETL (P < 0.0001). High receiver BW is the most effective parameter for reduction of arthroplasty implant-induced metal artifact on MRI scans, whereas in contradiction to prevalent notions, long echo trains fail to reduce implant-related metal artifacts, but in fact cause degradation of image quality around the implant with resultant larger appearing total metal artifacts.