Receiver Noise Research Articles

Polynomial Fitting-Based Noise Reduction for Correlation Functions in Medium-Frequency Radar

In the theoretical calculation of atmospheric wind fields using the cross-correlation analysis method of Medium-Frequency radar, it is necessary to compute a series of correlation parameters from the received echo signals, such as autocorrelation and cross-correlation functions, within the main lobe range of the antenna array to retrieve atmospheric parameters. However, both theoretical analysis and practical applications have shown that the shape of correlation functions can be affected by atmospheric conditions and receiver noise, leading to significant biases in the estimated correlation parameters within the main lobe range. In this study, we theoretically analyze the influence of noise on the amplitude of autocorrelation and cross-correlation functions. We propose a noise reduction method based on the characteristics of correlation functions at the zero-delay point to calculate the noise factor and process the correlation functions within the main lobe range. Furthermore, we conduct simulation analysis to evaluate the performance of this noise reduction method and summarize the effects of the number of fitting points and fitting methods on the noise reduction performance.

Solid-State NMR 13C sensitivity at high magnetic field

Sensitivity is the foundation of every NMR experiment, and the signal-to-noise ratio (SNR) should increase with static (B0) magnetic field, by a proportionality that primarily depends on the design of the NMR probe and receiver. In the low B0 field limit, where the coil geometry is much smaller than the wavelength of the NMR frequency, SNR can increase in proportion to B0 to the power 7/4. For modern magic-angle spinning (MAS) probes, this approximation holds for rotor sizes up to 3.2 mm at 14.1 Tesla (T), corresponding to 600 MHz 1H and 151 MHz 13C Larmor frequencies. To obtain the anticipated benefit of larger coils and/or higher B0 fields requires a quantitative understanding of the contributions to SNR, utilizing standard samples and protocols that reproduce SNR measurements with high accuracy and precision. Here, we present such a systematic and comprehensive study of 13C SNR under MAS over the range of 14.1 to 21.1 T. We evaluate a range of probe designs utilizing 1.6, 2.5 and 3.2 mm rotors, including 24 different sets of measurements on 17 probe configurations using five spectrometers. We utilize N-acetyl valine as the primary standard and compare and contrast with other commonly used standard samples (adamantane, glycine, hexamethylbenzene, and 3-methylglutaric acid). These robust approaches and standard operating procedures provide an improved understanding of the contributions from probe efficiency, receiver noise figure, and B0 dependence in a range of custom-designed and commercially available probes. We find that the optimal raw SNR is obtained with balanced 3.2 mm design at 17.6 T, that the best mass-limited SNR is achieved with a balanced 1.6 mm design at 21.1 T, and that the raw SNR at 21.1 T reaches diminishing returns with rotors larger than 2.5 mm.

An ultra wide-band, high-sensitivity Q-band receiver for single-dish telescopes, eQ: Rest-frequency determination of CCS (JN = 43–32) and SO (JN = 10–01) and high-redshift CO (J = 1–0) detection

Abstract We report on the development and commissioning of a new Q-band receiver for the Nobeyama 45 m telescope, covering 30–50 GHz with a receiver noise temperature of about 15 K. We name it eQ (extended Q-band) receiver. The system noise temperatures for observations are measured to be ∼30 K at 33 GHz and ∼75 K at 45 GHz. The half-power beam-width (HPBW) is around 38${^{\prime \prime }}$ at 43 GHz. To enhance the observation capability, we tested the smoothed bandpass calibration technique and demonstrated that the observation time can be significantly reduced compared to the standard position switch technique. The wide-bandwidth capability of this receiver provides precise determination of rest frequencies for molecular transitions with an accuracy of a few kHz through simultaneous observations of multiple transitions. Particularly, we determined the rest frequency of SO (JN = 10–01) to be 30.001542 GHz, along with the rest frequency of CCS (JN = 43–32) being 45.379033 GHz, adopting CCS (JN = 32–21) at 33.751370 GHz as a reference line. The SO profile shows a double peak shape at the Cyanopolyyne Peak (CP) position of the Taurus Molecular Cloud-1 (TMC-1). The SO peaks coincide well with the CCS sub-components located near the outer parts of the TMC-1 filament. We interpret that the gravitational infall of TMC-1 generates shocks which enhance the SO abundance. The TMC-1 map shows that carbon-chain molecules are more abundant in the southern part of the filament, whereas SO is more abundant in the northern part. The eQ’s excellent sensitivity allowed us to detect faint CO (J = 1–0) spectra from the high-redshift object at a redshift of 2.442. Our receiver is expected to open new avenues for high-sensitivity molecular line observations in the Q-band.

Multi-Channel Nonlinearity Mitigation Using Machine Learning Algorithms

This paper investigates multi-channel machine learning (ML) techniques in the presence of receiver nonlinearities and noise, and compares the results with the single-channel receiver architecture. It is known that the multi-channel architecture relaxes the sampling speed requirement of analog to digital conversion and provides significant robustness to clock jitter and front-end noise due to the bandwidth-splitting property inherent in these receivers. However, when a high-voltage swing signal is used in a wireline communication link, the received signal suffers from third-order harmonic distortions and inter-modulation products caused by the nonlinearity profile of the analog front-end (AFE). To this end, this paper proposes the channel decision passing (CDP) algorithm in combination with nonlinear feedback cancellation as a low-complexity candidate for nonlinearity mitigation and compares the performance of this solution with other well-known ML algorithms. Simulation results show significant improvement in a multi-channel receiver architecture equipped with nonlinear feedback cancellation and CDP in comparison with its single-channel counterpart under practical nonlinearity profiles and noise conditions.

Intercomparison of multi-GNSS signals characteristics acquired by a low-cost receiver connected to various low-cost antennas

With the increasing number of low-cost GNSS antennas available on the market, there is a lack of comprehensive analysis and intercomparison of their performance. Moreover, multi-GNSS observation noises are not well recognized for low-cost receivers. This study characterizes the quality of GNSS signals acquired by low-cost GNSS receivers equipped with eight types of antennas in terms of signal acquisition, multipath error and receiver noise. The differences between various types of low-cost antennas are non-negligible, with helical antennas underperforming in every respect. Compared with a geodetic-grade station, GPS and Galileo signals acquired by low-cost receivers are typically weaker by 3–9 dB-Hz. While the L1, E1 and E5b signals are well-tracked, only 72% and 86% of L2 signals are acquired for GPS and GLONASS, respectively. The signal noise for pseudoranges varies from 0.12 m for Galileo E5b to over 0.30 m for GLONASS L1 and L2, whereas for carrier-phase observations it oscillates around 1 mm for both GPS and Galileo frequencies, but exceeds 3 mm for both GLONASS frequencies. Antenna phase center offsets (PCOs) vary significantly between frequencies and constellations, and do not agree between two antennas of the same type by up to 25 mm in the vertical component. After a field calibration a of low-cost antenna and consistent application of PCOs, the horizontal and vertical accuracy is improved to a few millimeter and a few centimeter level for the multi-GNSS processing with double-differenced and undifferenced approach, respectively. Last but not least, we demonstrate that PPP-AR is possible also with low-cost GNSS receivers and antennas, and improves the precision and convergence time. The results prove that selection of low-cost antenna for a low-cost GNSS receiver is of great importance in precise positioning applications.

Influence of different codes on the performance of SAC‐OCDMA over FSO link

SummaryThis paper evaluates the performance of a spectral‐amplitude‐coding optical code division multiple access (SAC‐OCDMA) system over a free space optical (FSO) communication link under various weather conditions such as fog, snow, and rain. The system uses different code families, including modified quadrature congruence (MQC), random diagonal (RD), and diagonal eigenvalue unity (DEU), to address user codes and reduce the effects of multiple access interference (MAI). The system's bit error rate (BER) performance has been analyzed taking into account receiver noises and MAI, and calculates the required optical power for a BER value of 10−9 under different weather conditions. The results show that fog has the most significant impact on the system's performance, while rainy conditions require the lowest optical power. The performance of the system also declines with increasing transmission length and concurrent user count. Finally, the paper compares the performance of different code families under unfavorable weather conditions and concludes that DEU performs better than MQC and RD in bad weather.

A physical layer secret key consistency enhancement scheme using constellation decision information

Secret key generation based on a wireless channel (WC-SKG) is a promising solution to address the security issues in wireless communication. However, the consistency of channel estimation between two legal communication nodes in WC-SKG is often poor due to the receiver noise, signal power, etc., leading to a low secret key generation rate (SKGR). Although there are several denoising algorithms such as orthogonal transformation to address this issue, existing schemes overlook the fact that data symbols are also affected by the channel. This results in existing schemes only using the pilot symbols for channel estimation and not fully utilizing the received signal power of the WC-SKG. To address this issue, we propose a consistency enhancement algorithm based on constellation decision information (CEA-CDI), which utilizes both pilot symbols and soft decision information of data symbols to improve SKGR. Monte Carlo simulation and numerical results demonstrate that our proposed scheme can improve performance by approximately 16 dB compared to initial channel estimation.

Dual-tuned high-swing variable-gain amplifier with enhanced dB-linear control

In this work, an analog-controlled variable gain amplifier (VGA) is proposed that demonstrates high linearity across a wide range of control voltages and low noise for analog front-end receivers. This work presents a dual-tuning technique utilizing diode-connected P-MOS load and pseudo-exponential approximation based source degeneration (DCPL-PESD), which enables simultaneous tuning of different control voltages to achieve the required dB-linear characteristic. The gain is increased by cross-coupling the input transistors of the differential pair. To extend the gain range, three single-stage VGAs are cascaded. The design and implementation of this VGA were carried out using the Cadence Virtuoso tool in 180 nm CMOS technology. Post-layout results indicate that the 3-stage cascaded VGA offers a gain range of 67.5 dB, of which 55 dB is dB-linear. By tuning the control voltage VC, it provides a continuous 18 dB dB-linear gain. The overall VGA consumes 0.232 mA from a 1.8 V power supply, with a power consumption of 417 μW. The bandwidth of 3-stage VGAs is measured as 46 MHz. The minimum input-referred noise (IRN) of this VGA is 4.158 nVHz. The total area, including the bias circuit and buffer, is 0.0054 mm2, and the output 1 dB compression point is −2.83 dBm at the gain of −1 dB.

The Effects of the Local Environment on a Compact Radio Interferometer I: Cross-Coupling in the Tianlai Dish Pathfinder Array

The visibilities measured by radio astronomical interferometers include non-astronomical correlated signals that arise from the local environment of the array. These correlated signals are especially important in compact arrays such as those under development for 21[Formula: see text]cm intensity mapping. The amplitudes of the contaminated visibilities can exceed the expected 21[Formula: see text]cm signal and represent a significant systematic effect. We study the receiver noise radiated by antennas in compact arrays and develop a model for how it couples to other antennas. We apply the model to the Tianlai Dish Pathfinder Array (TDPA), a compact array of 16, 6-m dish antennas. The coupling model includes electromagnetic simulations, measurements with a network analyzer, and measurements of the noise of the receivers. We compare the model to drift-scan observations with the array and set requirements on the level of antenna cross-coupling for 21[Formula: see text]cm intensity mapping instruments. We find that for the TDPA, cross-coupling would have to be reduced by three orders of magnitude in order to contribute negligibly to the visibilities.

Self-Interference Cancellation Techniques for In-Band Full-Duplex Wireless Communication Systems: A Review

In-Band Full-Duplex (IBFD) systems have the capability of simultaneously transmitting and receiving signals through the channel and require the same resources as half-duplex systems. Unfortunately, IBFD systems have self-interference (SI) issues that prevent the system from gaining double throughput with respect to half-duplex systems. Therefore, the IBFD system will be more reliable if SI is mitigated more. This contribution will look at SI cancellation in wireless radio and underwater acoustic systems. The reviewed documents cover all types of SI cancellations, including passive, analog, and digital cancellations. In a practical full-duplex system, the SI cancellation for all domains must cancel the SI below the receiver noise floor.

Quantum scaling atomic superheterodyne receiver

Measurement sensitivity is one of the critical indicators for Rydberg atomic radio receivers. This work quantitatively studies the relationship between the atomic superheterodyne receiver’s sensitivity and the number of atoms involved in the measurement. The atom number is changed by adjusting the length of the interaction area. The results show that for the ideal case where only interaction noise is present and the RF waves are uniformly distributed, the sensitivity of the atomic superheterodyne receiver exhibits a quantum scaling: the amplitude of its output signal is proportional to the atom number, and the amplitude of its read-out noise is proportional to the square root of the atom number. Hence, its sensitivity is inversely proportional to the square root of the atom number. This work also gives a detailed discussion of the properties of transit noise in atomic receivers and the influence of some non-ideal factors on sensitivity scaling. This work is significant in the field of atom-based quantum precision measurements.

On measurements of spurious components of heterodyne signal in radiometric receivers

With a heterodyne frequency conversion, a significant contribution to the intrinsic noise of the radiometric receiver is made by a heterodyne. The spectral components generated by the heterodyne will be present in the processed signal at the output of the radiometric receiver and may manifest themselves when analyzing the received signal in spectral lines when high frequency resolution is required for processing. The purpose of the work is to analyze various types of modulation of the heterodyne signal, including modulation with an arbitrary phase shift between the components in the lower and upper side bands of the heterodyne signal. In this article, the methods of frequency transfer used in determining the spectral composition of the signal received by a radiometric receiver are considered. For heterodyne frequency conversion, in addition to the classical types of parasitic modulation of the heterodyne signal described in the literature – amplitude, phase (frequency) and single-band modulation, modulation with an arbitrary phase shift between the components in the lower and upper side bands of the heterodyne signal is considered. It is shown that with a small deviation of the frequencies of the modulating signal, ambiguity is possible in determining the level of components when using signal analyzers to measure the characteristics of heterodynes of radiometric receivers. The results of the analysis performed in the article can be used in the design of heterodynes with multiple output frequencies, taking into account the spectral comtent of the synthesized signal. The study was carried out at the expense of the grant of the Russian Science Foundation No. 22-19-00063 dated 13.05.2022. https://rscf.ru/project/22-19-00063.

Reconfigurable Adaptive Channel Sensing

This paper proposes an energy-efficient detection scheme, referred to as AdaSense, that is particularly suitable in the sparse regime when events to be detected happen rarely. To minimize energy consumption, AdaSense exploits the dependency between the receiver noise figure (i.e., the receiver added noise) and the receiver power consumption; less noisy channel observations typically imply higher power consumption. AdaSense is duty-cycled and begins each cycle with a few channel observations in a low-power-low-reliability mode. Based on these observations, it makes a first tentative decision on whether or not a message is present. If no message is declared, AdaSense waits till the beginning of the next cycle and starts afresh. If a message is tentatively declared, AdaSense enters a confirmation second phase, takes more samples, but now in a high-power-high-reliability mode. If these observations confirm the tentative decision, AdaSense stops, else AdaSense waits till the beginning of the next cycle and starts afresh in the low-power-low-reliability mode. Compared to prominent detection schemes such as the clear channel assessment algorithm of the Berkeley Media Access Control (BMAC) protocol, AdaSense provides relative energy gains that grow unbounded in the small probability of false-alarm regime, as communication gets sparser. In the non-asymptotic regime, energy gains are 30% to 75% for communication scenarios typically found in the context of wake-up receivers.

Adaptation of an IRAM W-Band SIS Receiver to the INAF Sardinia Radio Telescope: A Feasibility Study and Preliminary Tests.

Radio telescopes are used by astronomers to observe the naturally occurring radio waves generated by planets, interstellar molecular clouds, galaxies, and other cosmic objects. These telescopes are equipped with radio receivers that cover a portion of the radio frequency (RF) and millimetre-wave spectra. The Sardinia Radio Telescope (SRT) is an Italian instrument designed to operate between 300 MHz and 116 GHz. Currently, the SRT maximum observational frequency is 26.5 GHz. A feasibility study and preliminary tests were performed with the goal of equipping the SRT with a W-band (84-116 GHz) mono-feed radio receiver, whose results are presented in this paper. In particular, we describe the adaptation to the SRT of an 84-116 GHz cryogenic receiver developed by the Institute de Radio Astronomie Millimétrique (IRAM) for the Plateau de Bure Interferometer (PdBI) antennas. The receiver was upgraded by INAF with a new electronic control system for the remote control from the SRT control room, with a new local oscillator (LO), and with a new refrigeration system. Our feasibility study includes the design of new receiver optics. The single side band (SSB) receiver noise temperature measured in the laboratory, Trec ≈ 66 K at 86 GHz, is considered sufficiently low to carry out the characterisation of the SRT active surface and metrology system in the 3 mm band.

Precise Absolute Velocity Estimation of Human Space Flight In Leo Using Navic Doppler Shift Measurements

The Low Earth Orbit (LEO) is the most significant for diverse applications like imaging, human space flight and scientific observations; the number of satellites in LEO is ever increasing. To estimate the Position and Velocity (PV) conventionally multiple ranging sessions are conducted. It increases burden on the ground support staff and computation delays are introduced. These delays will lead to inaccurate estimation errors. Additionally, propagation errors are introduced into the PV estimation. Also, for human space flight applications, safety is of utmost importance, and hence precise and instantaneous determination of orbital parameters is crucial. This makes autonomous determination of the position and velocity of the satellite a necessity on board. In this study, it is proposed to use indigenously developed NavIC (Navigation by Indian Constellation) by Indian Space Research Organization Doppler shift measurements, for precise kinematic estimation of absolute velocity and receiver’s clock bias rate of the human space flight. The novelty of this research work is the usage of the NavIC Doppler shift measurements, for precise kinematic absolute velocity and receiver clock bias rate estimation, for the orbit of the human space flight in LEO, for the first time. This will extend the footprints of indigenously developed navigation technology to space applications. Extensive simulation and analysis is performed to study the Doppler collision at LEO. Thus establishing the suitability of the method, as the LEO will not exhibit Doppler collision unlike on ground. The mean value and Standard Deviation (SD) values of the velocity estimation error are [-0.0027 -0.0001 -0.0045] m/s and [0.1191 0.3550 0.1319] m/s respectively for the best case. The mean and 3-σ standard deviation of clock bias rate estimation error are 0.00075 m/s and 0.6 m/s respectively when the number of visible satellites is six. Additionally, simulations are carried out for a highly inclined sun synchronous orbit; with nominal and 50% higher standard deviation receiver noise, in Doppler measurements. The performance of velocity and clock bias rate estimation error is consistent for different orbits. However, the performance degrades with higher receiver noise.

Multiple Cooperative Attackers for Tag-Based Physical Layer Authentication

This article concerns the problem of ensuring the security of the tag-based Physical-Layer Authentication (PLA) schemes under multiple cooperative attackers. This problem is important and challenging because of the following reasons. First, if more attackers launch a cooperative attack, the success probability of launching an eavesdropping attack will be improved. Second, based on a cooperative communication system, cooperative attackers can launch more advanced attacks, e.g., a cooperative attack that traps the legitimate user to re-transmit the same tag again. Thus, it is challenging and desirable to construct a secure tag-based PLA scheme under multiple cooperative attackers. For effectively defending against a cooperative attack under multiple cooperative attackers, we propose a new tag-based PLA scheme, referred to as the PLA with the Detection of a Cooperative Attack (PLA-DCA) scheme. The basic idea of the PLA-DCA scheme is to utilize the extra noise in a replayed signal, since a replayed signal inevitably changes the distribution property of receiver noise, e.g., increment of the noise variance. Then, we implemented the proposed scheme and conducted extensive performance comparisons to demonstrate the superiority of the proposed scheme. We evaluate the security of various schemes through equivocation, which represents the uncertainty of estimating a tag. From the simulation results, we verify that the proposed scheme provides higher security than the prior tag-based PLA schemes.

Carrier Phase Residual Modeling and Fault Monitoring Using Short-Baseline Double Difference and Machine Learning

Global Navigation Satellite Systems (GNSS) are used to provide accurate position, navigation, and time (PNT) information to users in various sectors of our society including transportation. Augmentation systems such as differential GNSS (DGNSS), real-time kinematics (RTK), and Precise Point Positioning (PPP) improve the GNSS performance, and providing reliable measurements from its reference station is very crucial. To ensure safe and accurate PNT solutions, code and carrier measurements must be monitored for potential faults or a performance degrade. Although there exist numerous methods to model and monitor the measurements, research on the carrier phase measurements is not as extensive as the code measurements. This paper introduces a split of residuals into receiver noise and multipath components to customize their estimation according to their respective statistical properties. This study also proposes a method to use machine learning-based non-linear regression to effectively model and monitor potential faults in the GNSS measurements including the carrier phase. A training dataset is used to model the nominal quantities of GNSS measurement residuals, and inflation factors are applied to over-bound the fault-free residuals. These inflated residuals are coupled with uncertainty factors to compute thresholds for monitoring carrier phase residuals, and the effectiveness of the thresholds is validated with a test dataset by achieving the false alarm rate of 6.61×10−6, slightly lower than the desired level of 10−5.

An X-Band Multifrequency Difference Frequency-Shift Keying CMOS Radar for Range Tracking and AI-Based Human Gesture Recognition

This article presents an X-band single-chip fully integrated multi-frequency difference frequency-shift keying (FSK) I/Q direct-conversion radar transceiver implemented in a 130-nm CMOS process. Combined with the artificial intelligence (AI)-based algorithm, accurate gesture recognition are realized. The PLL-based dual-frequency difference FSK waveform and ranging algorithm are proposed to solve the trade-off between the maximum unambiguous range and the ranging accuracy. The loop bandwidth optimized integer-N phase-locked loop (PLL) is integrated to generate standard-compliant FSK signals with predictable frequency difference. The relationship between instantaneous ranging bias and PLL loop parameters is analyzed in detail. The proposed bias noise filter fully suppresses the flicker noise and improves the receiver noise figure (NF). The quadrature signal generator (QSG) adopts a fully differential amplifier buffered resistance compensation quadrature all-pass filter (QAF) to improve the I/Q balance and insertion loss. The chip consumes a current of 56-mA, and provides a conversion gain (CG) of 22-102 dB. The single-ended transmit power is 1.5-dBm. To the best of our knowledge, the implemented transceiver is the first recorded X-band FSK radar transceiver and provide a low-cost solution for indoor human detection.

Experimental Measurement of Noise Figure and Radiation Efficiency With the Antenna Y-Factor Method at X-Band

To optimize the design of a high-sensitivity receiver, it is valuable to be able to assign noise budget contributions to various parts of the system. The system noise and aperture efficiency can be characterized using the antenna Y factor method, which has been added recently to the IEEE Recommended Practice for Antenna Measurements, Std 149-2021. We extend the antenna Y factor method by showing that it can be used to measure the noise figure of an active antenna and receiver system.With an additional measurement of the receiver noise, the antenna radiation efficiency can be determined. We demonstrate the extended antenna Y factor method experimentally at X band for antennas under test including a horn with near 100% efficiency, microstrip patch antenna with efficiency near 80%, and a patch antenna array with 40% nominal efficiency.

Detection and localization of F-layer ionospheric irregularities with the back-propagation method along the radio occultation ray path

Abstract. The back-propagation (BP) method consists of diffractive integrals computed over a trajectory path, projecting a signal to different planes. It unwinds the diffraction and multipath, resulting in minimum disturbance to the BP amplitude when the auxiliary plane coincides with the region causing the diffraction. The method has been previously applied in global navigation satellite system (GNSS) radio occultation (RO) measurements to estimate the location of ionospheric irregularities but without complementary data to validate the estimation. In this study, the BP method is applied to a Communications/Navigation Outage Forecasting System (C/NOFS) occultation event containing scintillation signatures caused by an equatorial plasma bubble (EPB), which was parameterized with the aid of collocated data and reproduced in a wave optics propagator (WOP) simulation. In addition, a few more test cases were designed to assess the BP method with regard to the size, intensity, and placement of single- and multiple-irregularity regions. The results show a location estimate accuracy following the resolution at which the method is implemented (single bubble, reference case), whereas a bias is observed in multiple-bubble scenarios. The minimum detectable disturbance level and the estimation accuracy depend on the receiver noise level and, in the case of several bubbles, on the distance between them. These remarks provide insight into the BP results for two Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) occultation events.