Receiver Noise Research Articles

Noise Temperature of Phased Array Radio Telescope: The Murchison Widefield Array and the Engineering Development Array

This article presents a framework to compute the receiver noise temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\mathrm {rcv}}$ </tex-math></inline-formula> ) of two low-frequency radio telescopes, the Murchison Widefield Array (MWA), and the Engineering Development Array (EDA). The MWA was selected because it is the only operational low-frequency square kilometer array (SKA) precursor at the Murchison Radio astronomy Observatory, while the EDA was selected because it mimics the proposed SKA-low station size and configuration. It will be demonstrated that the use of an existing power wave-based framework for noise characterization of multiport amplifiers is sufficiently general to evaluate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\mathrm {rcv}}$ </tex-math></inline-formula> of phased arrays. The calculation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\mathrm {rcv}}$ </tex-math></inline-formula> was done using a combination of measured noise parameters of the low-noise amplifier (LNA) and simulated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters of the arrays. The calculated values were compared to measured results obtained via astronomical observation and both results are found to be in agreement. Such verification is lacking in current literature. It was shown that the receiver noise temperatures of both arrays are lower when compared to a single isolated element. This is caused by the increase in mutual coupling within the array which is discussed in depth in this article.

Short-Baseline High-Precision DGPS for Smart Snow Blower

High-precision positioning is critical for many Internet-of-Things (IoT) applications; however, most existing approaches are too expensive to be used in commercial products. A highly accurate differential global positioning system (DGPS) has not been widely used because of the difficulty in solving integer ambiguities in the single-frequency carrier phase. Multipath interference and receiver noise are the main reasons for limiting the DGPS accuracy and efficiency in solving integer ambiguities. In this article, we propose a combination of anti-multipath antennas and high-performance GPS receivers to effectively mitigate impairments due to multipath propagation and receiver noise. Furthermore, by exploiting more data available from high-performance GPS receivers, we can improve the efficiency of solving carrier-phase integer ambiguities. For applications in a smart snow blower, we installed two GPS receivers with a constant separation between them. The distance between the GPS receivers was used to verify the DGPS results. Furthermore, using the proposed DGPS technology, the smart snow blower can obtain a high-precision orientation estimation, with a standard deviation of 0.299 cm in positioning accuracy and 0.409° in orientation accuracy.

A Modular Design Approach for Ka-Band Front-End Receiver of Synthetic Aperture Interferometric Passive Imager

Electromagnetic Laboratory of Beihang University is engaged in the development of Ka-band synthetic aperture interferometric based passive imager named as BHU-2D-U. The imager is intended for detection of concealed weapons on human body. Noise figure of front-end receiver dictates the dynamic range and consequently the imaging performance of the imager. A modular design approach is presented to obtain improved noise figure as compared to the previous work. Additionally, the modular design gives a flexibility to adopt any desired receiver gain, instantaneous bandwidth, and noise figure and image rejection suppression. The measured gain, noise figure and image rejection is 42 dB, 4.1 dB and 60 dB respectively with 80 dB excellent spurious free spectral response. The reconstructed image performance of the imager is found satisfactory

A complementary filter consisting of a GPS-receiver and an accelerometer

Complementary filters have become widely used to measure the angular position of moving objects in space due to their simplicity and high accuracy. If at first they were used mainly in navigation systems, now they are beginning to be widely used in navigation systems. In such complementary filters, the complementary filter most often includes a GPS receiver and an accelerometer. The problem of reducing the influence of high-frequency interference of the GPS receiver on the accuracy of the system is considered. Direct filtering of the output signal of the GPS receiver has a significant disadvantage, which is the delay of the filter of the measured signal. This is often the main obstacle of using filters. Complementary filters due to the combination of two meters make it possible to filter the signal without affecting the passage of the useful signal. This is the main advantage of complementary filters. It should also be noted that they are very simple to implement, which has led to the widespread use of complementary filters in systems for measuring the motion of objects. The paper proposes a second-order filter structure in which there is no integration of the accelerometer signal that significantly simplifies the implementation of the filter and eliminates the problem of the influence of the non-zero accelerometer signal. The presence of zero offset accelerometer and integration procedures is one of the main problems in solving navigation problems.&#x0D; In the absence of an integrator, the question arises of taking into account the initial value of the output signal of the GPS receiver. This issue in the work is solved by the circuit method. In complementary filters built on the compensation scheme, this problem is solved quite simply. The article considers a simpler complementary filter, built on the filtration scheme. An algorithm for taking into account the initial conditions is proposed for such a filter structure. The influence of the structure of the transfer functions of the filter on the efficiency of its use is analyzed. It is shown that the complementary filter can significantly reduce the influence of high-frequency noise of the GPS receiver. The block diagram of the filter in the Matlab-Simulink environment and the simulation results that show the effectiveness of the proposed complementary filter structure are presented.&#x0D; Such systems can be used in small moving objects like UAVs, in robotics, in the educational process.

Channel Estimation for Intelligent Reflecting Surface Assisted Multiuser Communications: Framework, Algorithms, and Analysis

In intelligent reflecting surface (IRS) assisted communication systems, the acquisition of channel state information is a crucial impediment for achieving the beamforming gain of IRS because of the considerable overhead required for channel estimation. Specifically, under the current beamforming design for IRS-assisted communications, in total KMN+KM channel coefficients should be estimated, where K, N and M denote the numbers of users, IRS reflecting elements, and antennas at the base station (BS), respectively. For the first time in the literature, this paper points out that despite the vast number of channel coefficients that should be estimated, significant redundancy exists in the user-IRS-BS reflected channels of different users arising from the fact that each IRS element reflects the signals from all the users to the BS via the same channel. To utilize this redundancy for reducing the channel estimation time, we propose a novel three-phase pilot-based channel estimation framework for IRS-assisted uplink multiuser communications, in which the userBS direct channels and the user-IRS-BS reflected channels of a typical user are estimated in Phase I and Phase II, respectively, while the user-IRS-BS reflected channels of the other users are estimated with low overhead in Phase III via leveraging their strong correlation with those of the typical user. Under this framework, we analytically prove that a time duration consisting of K + N + max(K - 1, [(K - 1)N/M]) pilot symbols is sufficient for perfectly recovering all the KMN + KM channel coefficients under the case without receiver noise at the BS. Further, under the case with receiver noise, the user pilot sequences, IRS reflecting coefficients, and BS linear minimum mean-squared error channel estimators are characterized in closed-form.

Regular and Irregular-on-Grid Sparse Array Comparison of Connected Aperture Arrays

For square kilometer array (SKA) mid-frequency aperture arrays, dense connected aperture arrays such as Vivaldi antenna arrays are being considered, but to achieve the required system sensitivity for radio astronomical observations, this would mean a large number of antenna elements particularly in the order of millions. Two concepts of regular-on-grid and irregular-on-grid sparse array configuration are introduced for these connected arrays to reduce the number of antenna elements and the sensitivity performance of the two concept arrays is compared. Comparing the effective area of these two configurations, it is shown that a regular-on-grid sparse configuration achieves slightly larger effective area than an equivalent irregular-on-grid sparse configuration. Using the regular-on-grid sparse configuration as a case study, the effect that terminating impedance of the inactive antennas has on the receiver noise temperature of a connected array of Vivaldi antennas is investigated.

System to Control the RF Receiver Noise Parameters of the Radiolocation Pre-Search Station P18 Laura

The article presents a measuring system that allows the noise parameters of the receiver of a radiolocation station to be controlled. The existing solutions of the radiolocation pre-search station P18 Laura control unit have been adapted to the system.

Noise temperature distribution of superconducting hot electron bolometer mixers**Project supported by the Chinese Academy of Sciences (Grant Nos. GJJSTD20180003 and QYZDJ-SSW-SLH043), the National Key Basic Research and Development Program of China (Grant Nos. 2017YFA0304003 and 2018YFA0404701), the National Natural Science Foundation of China (Grant Nos. 11603081, 11673073, U1831202, and 11873099), and PICS projects between the CAS and the CNRS.

We report on the investigation of optimal bias region of a wide-band superconducting hot electron bolometer (HEB) mixer in terms of noise temperature performance for multi-pixel heterodyne receiver application in the 5-meter Dome A Terahertz Explorer (DATE5) telescope. By evaluating the double sideband (DSB) receiver noise temperature (Trec) across a wide frequency range from 0.2 THz to 1.34 THz and with a large number of bias points, a broad optimal bias region has been observed, illustrating a good bias applicability for multipixel application since the performance of the HEB mixer is uniquely determined by each bias point. The noise temperature of the HEB mixer has been analyzed by calibrating the noise contribution of all RF components, whose transmissions have been measured by a time-domain spectroscopy. The corrected noise temperature distribution shows a frequency independence relation. The dependence of the optimal bias region on the bath temperature of the HEB mixer has also been investigated, the bath temperature has limited effect on the lowest receiver noise temperature until 7 K, however the optimal bias region deteriorates obviously with increasing bath temperature.

Two-way laser regeneration pseudocode rangefinder of intersatellite optical crosslink

The millimeter-level bidirectional long-distance asynchronous ranging has long been a huge challenge in the field of measurement and instrumentation. Correspondingly, a laser pseudocode ranging algorithm based on regenerative synchronization mechanism is proposed to address the problems obstructing precise distance measurement between asynchronous satellites. First, the synchronization strategy of a double-ended asynchronous terminal based on the regenerative pseudocode is discussed. Subsequently, we look at the algorithm of the generation, transmission, detection, and the code phase tracking loop, which forms the base of obtaining high precision of pseudocode ranging. On this basis, the error of laser pseudocode ranging link is analyzed, which mainly incorporates receiver noise and clock error. In terms of receiver noise, the influence of the photodetector carrier-to-noise ratio on random noise distribution is evaluated, and the design of receiver parameters is guided as such. As for the clock error, we look at the constraint relationship between the range and the precision under the action of the clock error, which provides the basis for the selection of the clock. Finally, the optimized system is tested when a double-ended laser link is set up in the laboratory. As a result, the comprehensive accuracy results of 3.47 mm systematic error and ±1.73 mm random error is obtained, and the long-scale measurement performance has been tested by the temperature-compensated crystal oscillator pulse frequency experiment. In conclusion, the experiment is consistent with the theory proposed in this study, which provides a theoretical and experimental basis for long-distance high-precision intersatellite ranging.

Concerning the Carrier Frequency Selection Method for Continuous Cab Signaling

This paper considers the carrier frequency selection method for continuous cab signaling using a set of criteria for minimum inductive-rail line attenuation and maximum noise immunity. The mathematical expressions used for evaluation of signal attenuation in rail, inductive, and inductive-rail lines are given, and the corresponding conditions and assumptions are indicated. To determine the locomotive receiver noise immunity, the method of simulating its operation was used when receiving an additive mixture of an amplitude-shift keyed signal and impulse noise. It is shown that, under the indicated conditions and criteria, the optimal frequency values are 325 and 375 Hz.

One-Point Microwave Radiometer Calibration

A method for internally calibrating microwave total power radiometers by using only one level of noise injection is presented. It is based on having a previous accurate characterization of the receiver noise temperature, which used de facto as a second calibration standard. The method proves to be at least equivalent to the classical two level, as demonstrated through their intercomparison using the data provided by the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) on board the European Space Agency Soil Moisture and Ocean Salinity (SMOS) Satellite. The long-term stability in terms of retrieved brightness temperature using both methods has similar trends with a small advantage for the one-point approach proposed here.

Uplink communications with AWGGN over non-homogeneous fading channels

In this paper, the performance of single-input-multiple-output (SIMO) networks which represented an uplink communication with additive generalized Gaussian noise (AWGGN) over non-homogeneous fading conditions such as η–μ, λ–μ, and κ–μ are analyzed. First, approximate error probability (Pe) expressions are presented for SIMO operating in η–μ, λ–μ, and κ–μ fading channels by using the probability density functions (PDF) of the instantaneous signal-to-noise ratio at the receiver side. Then, the asymptotic Pe expressions based on these PDF expressions are also derived. To these end, we show the Pe performances for different configurations of fading parameters, the number of receiver antennas, modulation schemes, and noise types. Finally, the exact simulations are provided to evaluate the accuracy of the proposed analytical frameworks for the considered system models.

Quantum Theory of Noise in Stokes Vector Receivers and Application to Bit Error Rate Analysis

Polarization-modulated optical signals can be demodulated via direct detection of Stokes vectors. In this article, we develop a quantum theory of noise in the Stokes vector receiver. Examining the conditions that enable simultaneous measurement of three elements of the Stokes vector, we demonstrate that an optical pre-amplifier in front of the Stokes vector receiver can reduce the power penalty associated with simultaneous measurements, down to the quantum limit of 3 dB. Then, the 3-D Gaussian noise model for the shot noise and optical pre-amplifier noise is discussed. Subsequently, based on the noise analyses, we derive bit error rate formulae for the cubic-lattice polarization modulation format and evaluate the sensitivity of the Stokes vector receiver.

Design and Performance of Relay-Assisted Satellite Free-Space Optical Quantum Key Distribution Systems

This paper studies the design and performance analysis of relay-assisted satellite free-space optics (FSO) quantum key distribution (QKD) systems for secure vehicular networks. High-altitude platforms (HAPs) equipped with optical amplify-and-forward nodes are used as relay stations. Secrecy performances in terms of quantum bit error rate and ergodic secret-key rate are analytically investigated under the effects of transceiver misalignment, receiver's velocity variation, receiver noises, and atmospheric turbulence conditions. Based on the analyzed results, the design criteria for the legitimate user are determined so that the security of the considered system could be guaranteed.

Погрешности измерения угловой координаты протяженных целей моноимпульсным методом в зоне Френеля линейной антенной решетки

Introduction. The basic theoretical information on measuring systems in radar is presented, an analysis is performed to determine the errors of direction finders, and calculation expressions are found to determine the magnitude of the direction-finding errors by a single-pulse method in the Fresnel zone of a linear receiver antenna array caused by the combined action of the internal noise of the radio direction finder receiver and the angular noise of extended reflective interference. Purpose of the study. To consider the influence on the magnitude of the errors of direction finding together of the levels of the side lobes of both the differential and total directivity characteristics of the receiving antenna of the radio direction finder in the Fresnel zone. Materials and methods. Approaches for determining the magnitude of direction-finding errors are a generalization to the Fresnel zone of the known result of calculating the error during operation of a monopulse direction finder in the far zone of the receiving antenna. Results. The influence of the angular size and the distance size of a multi-point reflector on the magnitude of direction-finding errors by a single-pulse method in the Fresnel zone of a receiving linear antenna array of a radio angular system is investigated. Conclusion. Theoretical methods of measurement in radar are considered and it is shown that expanding the functionality to ensure high accuracy of measuring an information parameter will improve the accuracy of determining errors in direction finding systems.

A Method for the Routine Testing of Digital X-Ray Units

A method for the routine monitoring of digital X-ray diagnostic systems is presented, with assessment of the performance of the X-ray unit and the digital detector by medical staff before the patient arrives. The operability (inoperability) of one part or another is determined from results obtained by indirect assessment of anode voltage, the quantity of electricity, and the gain and the level of internal noise in the X-ray receiver. The time required for testing is generally no more than 5 min.

ВЛИЯНИЕ ВЗАИМОДЕЙСТВИЯ ЭЛЕМЕНТОВ АНТЕННО–ФИДЕРНОГО ТРАКТА РАДИОЛОКАТОРА НА ШУМОВЫЕ ХАРАКТЕРИСТИКИ КАНАЛА ПРИЕМА

The influence of the interaction effects of the transmitting and receiving antennas of a mil-limeter-range radar, as well as the direct transmission of the transmitter signal to the receiver input via the internal circuits of the microwave chip on the level of the decorrelated phase noise is under consideration. It is shown that for a certain amount of interaction between the anten-nas, the delay time of signal propagation along the paths of additional reception, the receiver noise factor and the level of phase noise of the carrier frequency of the transmitter at the detun-ing frequency equal to the frequency of the useful signal, the output noise power of the receiver converter by the additional receiving channel and the receiver’s own noise become comparable. Due to the additional noise reception channel, the signal-to-noise ratio decreases and the range of the radar action decreases as well. The calculation uses data for the noise factor of the re-ceiver and the spectral density of the phase noise of the synthesizer of the AWR1243 millimeter–wave transceiver chip from Texas Instruments in the frequency range from 77 till 81 GHz. The effect of a dielectric antenna shelter on the coupling between the transmitting and receiving antennas, and on the spectral noise power density at the receiver input, is considered. The de-pendences of the spectral density of the decorrelated phase noise due to additional communi-cation channels in comparison with the receiver’s own noise are show

Millimeter Wave Radar for Intelligent Transportation Systems: a Case Study of Multi-Target Problem Solution

The influence of millimeter-wave radar receiver noise on the probability of unambiguous determination of unmanned vehicles speed and range in the intelligent transportation system of the «smart city» is investigated. For the proposed new multi-target detection method for FMCW radar, the effect of the technical parameters of the vehicle radars on the required signal-to-noise ratio (SNR) of the receiver is estimated to ensure the probability of true determination of target parameters at 98%.

Deep Learning-Based Wireless Channel Estimation for MIMO Uncoded Space-Time Labeling Diversity

Uncoded space-time labeling diversity (USTLD) is a space-time block coded (STBC) system with labeling diversity applied to it to increase wireless link reliability without compromising the spectral efficiency. USTLD achieves higher link reliability relative to the traditional Alamouti STBC system. This work aims to design a bandwidth-efficient and blind wireless channel estimator for the USTLD system. Traditional channel estimation techniques like the least-squares (LS) and the minimum mean squared error (MMSE) methods are generally inefficient in using the channel bandwidth. The LS and MMSE channel estimation schemes require the prior knowledge of transmitted pilot symbols and/or channel statistics, together with the receiver noise variance, for channel estimation. A neural network machine learning (NN-ML) channel estimator with transmit power-sharing is proposed to facilitate blind channel estimation for the USTLD system and to minimize the required channel estimation bandwidth utilization. We mathematically model the equivalent noise power and derive the optimal transmit power fraction that minimizes the channel estimation bandwidth utilization. The blind NN-ML channel estimator with transmit power-sharing is shown to utilize 20% of the LS and MMSE wireless channel estimators’ bandwidth to achieve the same bit error rate (BER) performance for the USTLD system in the case of 16-QAM and 16-PSK modulation.

Detection of Information Hiding at Physical Layer in Wireless Communications

This paper concerns the problem of detecting the use of information hiding at the physical layer in wireless communications. Prior schemes for detecting physical layer based information hiding are either heuristic based or machine learning based. Our insight is that embedding information on wireless signals at the physical layer will inevitably have negative impact on the decodability of the cover signals, such as the increase of the error probability at the receiver (as well as the monitor). In our approach, after the monitor demodulates and decodes the cover signals, it will re-encode and re-modulate the cover signals, and then compare the resulting recovered signals with the raw signals that it received from the sender. We further propose a new estimation scheme for calculating receiver noise variance and conducted theoretical analysis. Specifically, we propose two hidden information detection schemes, a noise grouping based detection scheme and a constellation distance based detection scheme, both taking estimation errors into consideration. Our experimental results show that when the received SNR is more than 20 dB, our approach with the new estimation scheme has the probability of detection more than 0.95, and our constellation distance based detection scheme can correctly pinpoint all embedded locations.