High Receiver Sensitivity Research Articles

Enhancing the Performance of Indoor Device-Free Passive Localization

Device-free passive localization (DFPL) has been an emerging application with fast increasing development. Channel State Information- (CSI-) based DFPL is recently paid more attention to for fine-granularity and stability of CSI. However, lots of dead spots exist in the area of interest. And the accuracy of localization is not still completely satisfactory, especially for outside of the first Fresnel zone. In our paper, we put forward a new metric to estimate the sensitivity of a receiver to changes in the detecting area. In our experiment, we observe that the performance of DFPL can be raised when the receiver is placed at the location with high receiver sensitivity. Hence, we develop a new high-performance indoor device-free passive localization (HiDFPL), which employs a Bayesian a posteriori approach and possesses high receiver sensitivity. The experiment results demonstrate the outstanding performance of the proposed scheme.

An inductorless multi-mode RF front end for GNSS receiver in 55 nm CMOS

An inductorless multi-mode RF front end for a global navigation satellite system (GNSS) receiver is presented. Unlike the traditional topology of a low noise amplifier (LNA), the inductorless current-mode noise-canceling LNA is applied in this design. The high-impedance-input radio frequency amplifier (RFA) further amplifies the GNSS signals and changes the single-end signal path into fully differential. The passive mixer down-converts the signals to the intermediate frequency (IF) band and conveys the signals to the analogue blocks. The local oscillator (LO) buffer divides the output frequency of the voltage controlled oscillator (VCO) and generates 25%-duty-cycle quadrature square waves to drive the mixer. Our measurement results display that the implemented RF front end achieves good overall performance while consuming only 6.7 mA from 1.2 V supply. The input return loss is better than −26 dB and the ultra low noise figure of 1.43 dB leads to high sensitivity of the GNSS receiver. The input 1 dB compression point is −43 dBm at the high gain of 48 dB. The designed circuit is fabricated in 55 nm CMOS technology and the die area, which is much smaller than traditional circuit, is around 220 × 280 μm2.

Hyperfine structure of the cyanomethyl radical (CH2CN) in the L1544 prestellar core

The L1544 prestellar core has been observed as part of the ASAI IRAM Large Program at 3 mm. These observations led to the detection of many complex molecules. In this Letter we report the detection of the cyanomethyl radical for the first time in a prototypical prestellar core, which is possible through the high sensitivity of the IRAM EMIR receiver. A complex structure in which we suspect the presence of the hyperfine transitions of the ortho and para forms is observed thanks to the high spectral resolution of ~50 kHz. We computed all transition frequencies and line intensities for all transitions including satellite hyperfine components for the ortho and para forms of CH2 CN at the frequencies observed by ASAI. We report the first detection of the fine and hyperfine structure of the ortho and para forms of the cyanomethyl radical at ~101 GHz, resolved in this cold dense core.

High-Speed Avalanche Photodiode and High-Sensitivity Receiver Optical Subassembly for 100-Gb/s Ethernet

This paper reviews a 25-Gb/s avalanche photodiode (APD) with an inverted p-down structure and its application to a 100-GbE receiver optical subassembly (ROSA). The APD exhibits high responsivity (0.9 A/W), large bandwidth (18 GHz at $M = 10$ ), and a large gain-bandwidth product (235 GHz) by optimum design of the absorption layer (1.0 μm) and InAlAs avalanche layer (0.1 μm). Stable I–V characteristics without edge breakdown were observed owing to a strong confinement of a high electric field in the avalanche layer by two field-control layers and a triple-mesa structure. We also describe a 100-Gb/s (4 × 25-Gb/s) ROSA using a monolithic four-channel APD array and an ultrasmall planar-lightwave-circuit demultiplexer. The performance indicates a record minimum receiver sensitivity of –20 dBm and 50-km error-free transmission without an optical amplifier.

Cost-effective coherent PON using silicon Mach-Zehnder modulator and digital carrier regeneration.

We propose a cost-effective coherent passive optical network (PON) by employing the linear silicon Mach-Zehnder modulator (MZM) with computationally-efficient digital signal processing (DSP). The proposed PON adopts the intensity modulation and coherent detection scheme with discrete multi-tone (DMT) signal to achieve both high spectral efficiency (SE) and receiver sensitivity. Meanwhile, a digital carrier regeneration (DCR) method is proposed to further reduce the optical carrier-to-signal power ratio of intensity modulated DMT signal based on silicon MZM, which will significantly increase the achievable system power budget, especially when a high-order modulation format is adopted. No carrier frequency offset and phase estimations are needed in the receiver, which greatly reduces the complexity for both laser and DSP in coherent detection. Finally, a 10-Gb/s/ch uplink transmission is experimentally demonstrated using the proposed DCR method over 20-km standard single-mode fiber (SSMF), achieving about -44dBm sensitivity under the 7% forward-error-correction (FEC) limit of bit error ratio (BER) = 3.8x10(-3).

Wavelength Resource Sharing in Bidirectional Optical Mobile Fronthaul

In this paper, we propose high-capacity spectrally-efficient optical mobile fronthaul (MFH) architectures featuring wavelength resource sharing, where multiple cell sites share one dense wavelength division multiplexing (DWDM) channel instead of occupying a number of separated DWDM channels. In the downlink (DL), subcarrier multiplexing (SCM) is integrated with DWDM passive optical network. The key technical innovation lies in the reception of uplink (UL) signals being optically aggregated with ultrasmall spacing. We introduce two novel schemes for spectrally-efficient and low-complexity upstream transmissions. The first method is based on SCM in remote radio heads (RRHs) and coherent detection in baseband units (BBUs), achieving channel spacing of as small as 100 MHz. For the first time, successful coherent reception of LTE signal, whose symbol rate (15 ksps) is much smaller than the laser linewidth, is achieved by pairing a radio frequency pilot tone from each RRH. Bidirectional transmission of four 20-MHz 16-QAM-OFDM LTE-like signals with 100-MHz spacing aggregated on one wavelength is demonstrated. For the second proposed UL scheme, we report a low-complexity ultradense WDM over DWDM allocation with 1-GHz wavelength spacing and novel phase-noise-insensitive heterodyne detection using MHz-linewidth lasers and an off-the-shelf envelope detector. We experimentally demonstrate the transmission and simple detection of multichannel 100/200 Mb/s OOK or 200 Mb/s 16-QAM-OFDM signals with 1-GHz spacing over 30-km standard single mode fiber using 5-MHz-linewidth lasers. By enabling ultrahigh spectral efficiency, high receiver sensitivity, and low-complexity, the proposed approach achieves a significant breakthrough for future high-capacity mobile fronthaul systems.

Nonlinear phase noise mitigation in phase-sensitive amplified transmission systems.

We investigate the impact of in-line amplifier noise in transmission systems amplified by two-mode phase-sensitive amplifiers (PSAs) and present the first experimental demonstration of nonlinear phase noise (NLPN) mitigation in a modulation format independent PSA-amplified transmission system. The NLPN mitigation capability is attributed to the correlated noise on the signal and idler waves at the input of the transmission span. We study a single-span system with noise loading in the transmitter but the results are expected to be applicable also in multi-span systems. The experimental investigation is supported by numerical simulations showing excellent agreement with the experiments. In addition to demonstrating NLPN mitigation we also present a record high sensitivity receiver, enabled by low-noise PSA-amplification, requiring only 4.1 photons per bit to obtain a bit error ratio (BER) of 1 × 10(-3) with 10 GBd quadrature phase-shift keying (QPSK) data.

Improved Correlator Peak Selection for GNSS Receivers in Urban Canyons

Multipath arises from the reception of reflected or diffracted signals in addition to the Line-Of-Sight (LOS) signal. By using a block processing high sensitivity receiver scheme, this paper aims to obtain better positioning performance in urban canyon areas. Generally, the peak with the most power is utilised in high sensitivity receivers; however, this approach is not always optimal in multipath environments. Noting that signal correlation peaks may be separated in the Doppler domain by a long coherent integration time, a peak identification scheme is proposed in this work, which yields better positioning performance. It is shown that most of the multipath peaks are removed in the receiver after using the proposed algorithm.

Measuring GNSS Multipath Distributions in Urban Canyon Environments

In general, standalone global navigation satellite systems (GNSS) receiver architectures cannot provide a position accuracy suitable for use in vehicular applications in urban canyon scenarios. Specifically, GNSS signals are affected by the surrounding objects, such as high buildings, trees, and so on, which introduces multipath errors. Multipath arises from the reception of reflected or diffracted signals, possibly in addition to the line-of-sight signal, and is one of the most detrimental error sources in GNSS positioning applications. Multipath distributions in the urban canyon area are measured and characterized in this paper. In particular, the Doppler and code phase delay under different conditions are assessed as a function of vehicle speed and signal power, which are different from previous calibration metrics. Specifically, multipath directional-dependence phenomenon (i.e., the variation resulting from the direction of travel of the user) is observed during this process, and the multipath maximum Doppler offset and minimum Doppler offset are derived and verified by the real data. The multipath distribution will eventually affect the search strategy (i.e., search space size, coherent integration time) utilized in the high sensitivity receiver.

GPS-based orbital filter to reach the moon

Nowadays, global navigation satellite systems (GNSSs) are used for many new applications that go further than the original goal of providing position, velocity and timing for land, maritime and air applications. In particular, GNSS receivers have been adopted as main navigation system for several low Earth orbits (LEOs) missions, increasing the autonomy of the hosting spacecraft, reducing the networking operation costs. Accordingly, they result in an attractive solution even for higher Earth orbits. However, although many studies have shown that GNSS observations can also be obtained at altitudes above the GNSS constellations by using high sensitivity receivers, the use of these signals is still challenging because of their very weak power and the poor relative geometry between the receiver and the transmitters. In this paper, we describe the implementation of an orbital filter specifically designed for moon missions, which aims to improve the navigation performance achievable when using GNSS observations.

Design and implement of transceiver system for hybrid rocket with coplanar wraparound antenna at 433 MHz

This study aims to implement the telematics between hybrid rockets and the ground receiving station. In order to significantly reduce the rocket weight, fibre-reinforced plastic is used for the hybrid rocket casing, on which coplanar wraparound antennas with an operating frequency of 433 MHz are designed. The antenna structure contains three coplanar printed patches, among which the middle printed patch is the primary radiator and the resonant length appears a wavelength for the metallic surface case. An RF module with high receiver sensitivity and a high-power power amplifier are included to enhance the communication coverage of hybrid rockets and the ground receiving station so that the station can effectively track the hybrid rocket. Finally, the radio wave propagation model is used for calculating the link budget such that the communication coverage between rocket transmitters and the ground receiving station can be estimated, and on-site measurement and verification are preceded.

Indoor doppler error characterization for high sensitivity GNSS receivers

Indoor Doppler measurements in high sensitivity receivers are often biased due to the indoor multipath and user dynamics. The work presented here investigates the relationship between Doppler errors and some key channel parameters. A directional multipath channel model is introduced and some essential channel parameters are defined. In nonsymmetric scattering environments, the Doppler biases are shown to be explicitly related with these parameters. Theoretical simulation and experimental data are analyzed and demonstrated to be consistent.

Angular and polarization response of multimode sensors with resistive-grid absorbers.

High-sensitivity receiver systems with near-ideal polarization sensitivity are highly desirable for development of millimeter and submillimeter radio astronomy. Multimoded bolometers provide a unique solution to achieve such sensitivity, for which hundreds of single-mode sensors would otherwise be required. The primary concern in employing such multimoded sensors for polarimetery is the control of the polarization systematics. In this work, we examine the angular- and polarization-dependent absorption pattern of a thin resistive grid or membrane, which models an absorber used for a multimoded bolometer. The result shows that a freestanding thin resistive absorber with a surface resistivity of η/2, where η is the impedance of free space, attains a beam pattern with equal E- and H-plane responses, leading to zero cross-polarization. For a resistive-grid absorber, the condition is met when a pair of grids is positioned orthogonal to each other and both have a resistivity of η/2. When a reflective backshort termination is employed to improve absorption efficiency, the cross-polar level can be suppressed below -30 dB if acceptance angle of the sensor is limited to ≲60°. The small cross-polar systematics have even-parity patterns and do not contaminate the measurements of odd-parity polarization patterns, for which many of the recent instruments for cosmic microwave background are designed. Underlying symmetry that suppresses these cross-polar systematics is discussed in detail. The estimates and formalism provided in this work offer key tools in the design consideration of the instruments using the multimoded polarimeters.

Focusing on delayed clearance for identifying small-sized metastatic lung tumors using synchrotron radiation angiography with a highly sensitive receiver.

To detect metastatic lung tumors of less than 1 mm in size by focusing on the clearance of contrast material using synchrotron radiation (SR) angiography characterized by high spatial resolution and high-sensitivity receiver. C6 cells, derived from rat glioma cells, were injected to the rat tail vein. Two weeks after injection, the rats underwent SR angiography using a high-gain avalanche rushing amorphous photoconductor (HARP) receiver of extra-high sensitivity with high contrast resolution. The 256-grayscale value was employed in the analysis of images. 19 nodules were identified in images. The tumors were confirmed histopathologically. The average tumor size was 621±193 µm. The clearance curve of the densities was expressed as a logarithm function. Tumors showed delayed clearance of contrast material, taking up to 28 s, compared with arteries, which cleared rapidly at 8 s. In 256 grayscale, the distance was 50. This gap in density clearance made it possible to identify tumors. SR angiography with a HARP receiver provides high sensitivity and spatial resolution and makes it possible to diagnose metastatic lung tumors of less than 1 mm in size by focusing on differences in the clearance times of contrast material.

Spur Mitigation in High-Sensitivity GNSS Receivers

The presence of spurious tones in a Global Navigation Satellite Signal (GNSS) receiver's RF and analog front-end signal spectrum leads it to compute receiver's position erroneously. Addressing spurs is crucial in modern multiconstellation GNSS receivers as their wide bandwidth and coexistence on a shared chip or board with other radios and processors make them highly susceptible to corruption by dynamically varying spurs. Proposed here is a solution to mitigate a large number of spurs in GNSS receivers using a combination of limited number of frequency-tracked digital hardware filters, fast Fourier transform-based spur detectors, and a firmware algorithm predicting and weeding out potentially corrupt satellite measurements. Laboratory validation results from an experimental GNSS receiver in a CMOS system-on-chip are shown to demonstrate its effectiveness.

HighTcSQUID low frequency receiver and through-wall receving experiments

System and methods for wireless communication that could go through hydrous rocks, seawater, and even soil are investigated. The key components of the system are the high sensitive receivers of commercial HighTcSQUID and high-speed signal acquisition and processing systems. Within the frequency band of 30 Hz to 100 kHZ, the intrinsic noise spectral density of commercial HTcSQUID could be as good as 100 fT/Hz1/2, so that with commercial software, signals could be accurately modulated, collected,demodulated and processed. In the low frequency end, with the features of long penetration depth of electromagnetic wave and high sensitive, small size of HTcSQUID magnetometer, the feasibility of the implementation of portable low-frequency wireless communication system which could be used both under ground and water is discussed preliminarily. Using a 1 m2 square coil as test signal transmitting antenna, with the HTcSQUID magnetometer receiving sensor placed in an electromagnetic shielding cavity which could provide considerable electromagnetic attenuation, the 99 Hz AM signal emitted by the transmitting antenna is successfully collected. The result proves that with the technology of HTcSQUID, practical wireless communications can be realized between the earth's surface and a depth of hundreds of meters underground.

GoGPS: open source software for enhancing the accuracy of low-cost receivers by single-frequency relative kinematic positioning

goGPS is a free and open source satellite positioning software package aiming to provide a collaborative platform for research and teaching purposes. It was first published in 2009 and since then several related projects are on-going. Its objective is the investigation of strategies for enhancing the accuracy of low-cost single-frequency GPS receivers, mainly by relative positioning with respect to a base station and by a tailored extended Kalman filter working directly on code and phase observations. In this paper, the positioning algorithms implemented in goGPS are presented, emphasizing the modularity of the software design; two specific strategies to support the navigation with low-cost receivers are also proposed and discussed, namely an empirical observation weighting function calibrated on the receiver signal-to-noise ratio and the inclusion of height information from a digital terrain model as an additional observation in the Kalman filter. The former is crucial when working with high-sensitivity receivers, while the latter can significantly improve the positioning in the vertical direction. The overall goGPS positioning accuracy is assessed by comparison with a dual-frequency receiver and with the positioning computed by a standard low-cost receiver. The benefits of the calibrated weighting function and the digital terrain model are investigated by an experiment in a dense urban environment. It comes out that the use of goGPS and low-cost receivers leads to results comparable with those obtained by higher level receivers; goGPS has good performances also in a dense urban environment, where its additional features play an important role.

Terahertz FSS for space borne passive remote sensing application

A terahertz frequency selective surface (FSS) which operates inside the spatial filtering front-end of a high sensitivity receiver is proposed and experimentally verified. To achieve this terahertz FSS metamaterial which exhibits extremely low insertion loss and is insensitive to the variations of polarisations and incident angles, the FSS array is constructed by an electrically thick SiO2 layer (quartz wafer) and an ultra-thin high conductivity aluminium layer with periodic aperture unit cells. The micro-machined metallic pattern is shaped by the combination of a sub-wavelength circular ring and a split-ring resonator. Experimental results and predicted spectral responses are shown to be in good agreement over the frequency range of 0.1-0.5 THz.

Software Simulation Method for Digital if GNSS Signal

Data simulation is an important auxiliary method for baseband signal processing algorithm design of digital IF GNSS receiver. Especially when the high sensitivity and high dynamic receivers are developed, or multipath and cross correlation mitigation techniques are considered, exact and complete tests under all kinds of necessary scenes can be carried out with the IF signal data which is generated by software simulation method. With this method, the developing efficiency can be improved and the cost can be cut down. In this paper, precise model of the IF signal is given firstly through analyzing GNSS receivers RF processing flow. Then, considering the discrete characteristic of software processing, the IF signal simulation flow and block of the simulation software are designed. Finally, the specific design process is given through a design example. When the IF signal simulation software is used for testing baseband signal processing algorithms, GNSS receivers IF signal data under every necessary test scene can be generated just by parameter adjustment.

Feasibility study of Multi-Pixel Photon Counter serving as the detector in digital optical communications

The feasibility of Multi-Pixel Photon Counter (MPPC) serving as the detector of the receiver in digital optical communication was discussed in this paper. The theory of the sensitivity of the receiver using MPPC was demonstrated. The analytical solution to the minimum average incident light power required was obtained. The numerical analysis results show that the sensitivity is much better than the existing commercial receivers in the same conditions. It may find applications in fields where high sensitivity of optical receiver is a mandatory requirement.