RF Channel Research Articles

Localizing Mobile Target using Kalman Filtering and Least Square Boosting Ensemble Learning based Approach

Trilateration-based target localization using received signal strengths (RSS) within wireless sensor networks (WSN) often results in inaccurate location estimates due to the considerable fluctuations in RSS measurements encountered in indoor environments. Enhancing the precision of RSS-based localization systems has been a primary area of interest in extensive research efforts. This study introduces two range-free algorithms, Ensemble Learning (EL) and EL+KF, which leverage RSS measurements for localization. In contrast to trilateration, the EL- based localization approach enables the direct estimation of target locations based on field measurements, eliminating the need for distance calculations. Notably, unlike other cutting-edge localization and tracking (L&T) scheme like the support vector regression (SVR), the LSBoost (Least Squares Boosting) EL based localization architecture can be trained very quickly using RSS measurements to determine the mobile target's position. Furthermore, the proposed EL-based localization scheme incorporates the Kalman filter (KF) to achieve additional refinement in target location estimates. To assess the localization effectiveness of these proposed algorithms in the presence of noisy RF channels and dynamic target motion models, rigorous simulations were conducted. Thanks to the robust generalization capabilities of EL, the simulation results reveal that the presented EL-based localization algorithms exhibit superior performance compared to trilateration and the SVR-based localization scheme, particularly in terms of indoor localization accuracy.

Secrecy outage analysis for RIS-assisted hybrid FSO-RF systems with NOMA

In this paper, we investigate the physical-layer security performance for a reconfigurable intelligent surface (RIS) assisted free-space optical (FSO) communication-radio frequency (RF) system with non-orthogonal multiple access (NOMA). In particular, the source (S) transmits an optical NOMA signal to the relay (R), which forwards the optical-to-electrical converted signal to both users in the presence of an eavesdropper (E). Furthermore, for the far user, the scenario that there is no direct path from R and it can only receive the signal from R via the RIS is considered. While for the near user, three signal transmission scenarios are taken into account: 1) only the direct path from R exists; 2) only the reflected paths from RIS exist; 3) both the direct and the reflected paths exist and superimpose together. In addition, for the first hop of information transmission, E may or may not locate in the region of laser beam divergences of S. Therefore, both scenarios that the first hop may or may not be overheard by E are taken into consideration. Considering the FSO link is with a Gamma-Gamma distribution and the RF channels experience the Nakagami-m fading, the analytic and asymptotic expressions of secrecy outage probability for both users are presented. Monte-Carlo simulations are also conducted to validate the accuracy of the derived expressions.

Influence of the parameters of the aquatic environment on the functioning of wireless channels optical underwater communication in information and measurement systems

The main challenge in creating underwater Internet of Things (UIoT) applications is to select the appropriate type of communication system, which must take into account the unique conditions of the underwater environment and data transmission requirements. Unlike terrestrial systems, where RF channels are widely used, underwater conditions require other solutions, as radio waves are significantly attenuated in the water, severely limiting the transmission range. A specific and little-studied aspect of underwater communications is the use of Underwater Wireless Optical Communications (UWOC). This paper focuses on investigating the effect of the characteristics of the aquatic environment on UWOC performance. The purpose of the study was to identify the relationship between the parameters of the aquatic environment and the UWOC channel in the interest of predicting the effectiveness of its application as part of UIoT networks, to substantiate the feasibility and prospects of using underwater optical wireless communications as part of distributed information and measurement systems. The paper presents the results of research on the relationship between the parameters of the aquatic environment and the underwater optical wireless communication channel. The interrelation of optical characteristics of the aquatic environment with the indicators of efficiency and quality of underwater optical wireless communication: normalised power, communication range, bit error rate, in turn, affecting the accuracy and reliability of the information received by the Consumer at the output of the information-measuring system. The influence of water medium turbulence on the communication indicators is assessed. It is shown that changes in the salinity of the aquatic environment as one of the factors causing turbulence negatively affects the main indicators of underwater optical wireless communication. It is shown that the assessment of the feasibility of underwater optical wireless communication should be made on the basis of a detailed analysis of the parameters of the aquatic environment of the water area in which its implementation is planned. The obtained results confirm the possibility and perspectivity of using underwater optical wireless communication as a part of distributed information-measuring systems on underwater objects located in different types of water areas.

A 0.5–15 GHz reconfigurable IR-UWB receiver in 28 nm CMOS

A 0.5–15 GHz ultra-wideband (UWB) RF reconfigurable receiver in UMC 28 nm CMOS used for IR-UWB (impulse radio UWB) radar system is proposed in this paper. This receiver employs a 0.5–8 GHz path and an 8–15 GHz path to achieve the wide frequency band, and we proposed an RF channel select voltage-to-time converter (VTC) circuit. Two different low noise amplifiers (LNAs) are adopted in the two paths to obtain the high performance of noise figure (NF) and gain. The common drain stage and resistance negative feedback technology as well as the source degeneration inductive technology are introduced to achieve a high flat gain and fine input matching. The R-2R variable load network of a programable gain amplifier (PGA) gives it a nearly 24 dB dynamic range and approximately linear gain control. A 500MS/s time domain analog to digital converter (TD-ADC) with an equivalent sampling rate of 16GS/s is shared for the two paths which can realize the direct RF sampling. The input RF signal path selection is implemented by configuring the Band_sel signal. The receiver has reconfigurability of the RF front end and better power consumption and area. In the frequency of 0.5–8 GHz, the S11 is below −7.9 dB and the NF is smaller than 6 dB. In the frequency of 8–15 GHz, the S11 is below −8dB and the NF is smaller than 11 dB. The receiver dissipates 242.72mW with an area of 1.01 mm2

Energy Efficiency in Open RAN: RF Channel Reconfiguration Use Case

Energy Efficiency in Open RAN: RF Channel Reconfiguration Use Case

Application of IoT network for marine wildlife surveillance

Abstract Every day of the week, wireless communication is almost all around us. The Internet of Things (IoT) is a standard protocol used to describe the rapidly advancing technology in which almost every electronic device is or may be connected to the Internet. These electronic gadgets constantly provide data signals to the gateways, which satellites such as those in Low Earth Orbit may transmit. Because of these networks’ limited resources and the IoT, these transactions must be completed with the least amount of latency and data loss possible. We also analyze the performance implications of implementing RF-based powering for such a network. The techniques presented in this paper may benefit the scientific community and industry in general when it comes to the dynamic distributed parameter allocation methodology for IoT network devices. We will also discuss how research on animals and the natural environment has been impacted by IoT breakthroughs, in particular, animal sensors’ limits and incapacity to broadcast from everywhere. Our analysis illustrates the most effective data transmission technique and establishes the bounds of these restrictions. Furthermore, the physics of the RF channel plays a critical role in the uncertainty of the channel as well as the amount of energy harvested. By employing simulation based on the physics of the RF channel, the article shows the performance of the system considering both the uncertainty of data arrival as well as the variability of the channel. The findings of the simulation show that the devices consume less energy overall as the signal-to-noise ratio rises. Furthermore, a timing factor of 10–15% is shown to be effective in maintaining a constant mean rate and increasing the energy efficiency of the system.

Performance analysis for wireless-powered relaying UWOC-RF systems

In this paper, the system performance for a wireless-powered relaying mixed underwater wireless optical communication-radio frequency (UWOC-RF) network is investigated. In particular, a source sends an optical signal to a power-constrained marine relay, which simultaneously harvests energy from the surrounding environment and processes the received optical signal with an amplify-and-forward protocol and converts it into an electric one before broadcasting it to the destination. Assuming the UWOC and the RF channels undergo a mixture Exponential-Generalized Gamma fading and Nakagami-m fading, the closed-form and asymptotic expressions for outage probability and the diversity order are obtained. Furthermore, the average capacity and average bit error rate are also presented. Monte-Carlo simulations are also used to validate the correctness of those derived results.

Real-Time Machine Learning for Multi-User Massive MIMO: Symbol Detection Using Multi-Mode StructNet

In this paper, we develop a learning-based symbol detection algorithm for massive MIMO-OFDM systems. To exploit the structure information inherited in the received signals from massive antenna array, multi-mode reservoir computing is adopted as the building block to facilitate over-the-air training in time domain. In addition, alternating recursive least square optimization method, and decision feedback mechanism are utilized in our algorithm to achieve the real-time learning capability. That is, the neural network is trained purely online with its weights updated on an OFDM symbol basis to promptly and adaptively track the dynamic environment. Furthermore, an online learning-based module is devised to compensate the nonlinear distortion caused by RF circuit components. On top of that, a learning-efficient classifier named StructNet is introduced in frequency domain to further improve the symbol detection performance by utilizing the QAM constellation structural pattern. Evaluation results demonstrate that our algorithm achieves substantial gain over traditional model-based approach and state-of-the-art learning-based techniques under dynamic channel environment and RF circuit nonlinear distortion. Moreover, empirical result reveals our NN model is robust to training label error, which benefits the decision feedback mechanism.

PERFORMANCE ANALYSIS OF HYBRID FSO / RF COMMUNICATION SYSTEM WITH RECEIVE DIVERSITY IN THE PRESENCE OF CHI-SQUARE/GAMMA TURBULENCE AND RICIAN FADING

Within mobile communication systems, the inherent limitations of mobile devices necessitate a considerable portion of signal processing to occur at the base station. The technique of multiple access at the base station, entailing the amalgamation of diverse received signals, plays a pivotal role in the reconstruction of the original signal. This investigation introduces an innovative hybrid FSO/RF system that operates via a single-hop transfer, adeptly incorporating the concept of receive diversity to effectively counteract the challenges posed by saturated atmospheric turbulence. It is important to note that the FSO channel is observed under the Gamma/Chi-Square turbulence model, while the RF channel adheres to the Rician fading model. Notably, the study also yields a closed-form expression for the outage probability of the system. The results underscore significant enhancements in comparison to conventional FSO and RF systems. Despite the demand for an advanced receiver, the proposed hybrid architecture presents substantial improvements that significantly impact the performance of the communication system. It's noteworthy that at the reception, the Switch and Stay (SSC) combining technique along with Selection Combining diversity (SC) strategies are being observed. This holistic approach not only addresses the challenges posed by atmospheric conditions but also harnesses the benefits of diversity techniques to enhance the overall reliability and performance of the communication system.

Self‐calibrating circuit for phase correction to support phased array antenna systems

AbstractA self‐calibrating circuit system for use within active phased array antennas is presented. The system addresses the issue of unwanted channel phase imbalances and random phase errors which can deteriorate array performance. Basically, unwanted insertion phase offsets that can originate within each RF channel, due to the supporting and active circuit components and possible temperature variations, can be eliminated by our designed, simulated, and experimentally verified self‐calibrating circuit. With existing technologies and calibration approaches, it is practically difficult and time consuming to check the phase feeding accuracy, as typically a large number of data sets are required to achieve similar channel corrections. As an alternative, our proposed circuit system allows for the consecutive phase shift between RF channels to be inspected and self‐corrected within a feedback loop managed by a MATLAB‐Arduino program. The active S‐band feed system can self‐calibrate in about 25 s (or less), using commercially available phase sensors and voltage controlled phase shifters. To the best knowledge of the authors, no similar computer controlled feed‐back circuit to support the self‐correction of active phased arrays has been previously reported.

Research on simulation method for nonlinear effects of airborne SAR electromagnetic interference

In order to simulate the nonlinear interference effect of high-power electromagnetic signals on airborne Synthetic Aperture Radar (SAR) imaging, the walk–stop geometric modeling of airborne SAR was established, and the range time-domain pulse coherence method was used to simulate SAR echo. By establishing a SAR receiver RF channel model, the interference mechanism of high-power electromagnetic signals is combined on RF front-end devices, the nonlinear effects on the echo signal when high-power electromagnetic signals enter the receiver are simulated, and finally the range Doppler algorithm is used to image the echo signal and the interference signal. A method for evaluating the interference effect of high-power electromagnetic signals on airborne SAR imaging using the correlation coefficient of images was proposed. The results showed that the change in the correlation coefficient of images before and after interference relative to the interference signal ratio was consistent with the image interference effect. The correlation coefficient showed a stepped trend with the change in the interference signal ratio, and there was a saturation effect after the interference effect reached a certain level.

Optimization of capacity in non-Gaussian noise models with and without fading channels for sustainable communication systems

The highest rate at which information may be reliably sent via a communication link is known as its capacity. In the case of non-Gaussian noise, the capacity of the channel depends on the specific characteristics of the noise, which can cause severe errors and reduce the reliability of communication systems over a fading channel. The Gaussian mixture impulsive noise model (GMINM), which is a more general and flexible non-Gaussian model for impulsive noise, has been compared in this paper with the Middleton Class-A impulsive noise model (MCAINM) in terms of derived channel capacity normalized by channel bandwidth (C/BW) with and without Rayleigh fading (Rf) channels. It also investigated the trade-off between complexity and accuracy in modeling the impulsive noise using two simplified Middleton Class-A impulsive noise models based on derived C/BW. The derived C/BW of these models under various conditions, such as different signal-to-noise ratios and impulsive noise parameters and models, have been performed and evaluated using two different scenarios: the exact method and the semi-analytical method. When the impulsive noise parameters and A are both near 0 in GMINM and MCAINM, respectively, the capacity of the impulsive noise channel is found to be equivalent to that of the Gaussian channel sustainable, as shown by the findings based on Monte-Carlo simulations. We have shown that when the impulsive noise decreases, the capacity increases in all models; however, the capacity of Gaussian noise is higher than the capacity of non-Gaussian noise, which in turn is higher than the capacity of non-Gaussian noise over the Rf channel overall values of SNR in dB. Moreover, multi-channel configuration introduces spatial diversity and multiplexing gains that have been proposed to sustainably optimize the ergodic capacity for the challenge case when the channel state information (CSI) is unknown at the transmitter in non-Gaussian noise over Rf channel. In today's rapidly evolving world, sustainable communication systems play a crucial role in ensuring efficient and responsible utilization of resources. As the demand for wireless communication continues to rise, it becomes imperative to optimize the capacity of communication channels, especially in scenarios involving non-Gaussian noise models and fading channels.

Performance Analysis for Dual-Hop UWOC-RF Systems With NOMA

In this study, we investigate a non-orthogonal multiple access (NOMA)-assisted dual-hop underwater wireless optical communication-radio frequency (UWOC-RF) network. Specifically, an optical source forwards a NOMA signal to a marine relay, which first deploys either the heterodyne detection or intensity modulation direct detection to process the received signal, and then encodes and re-transmits a superimposed signal to two terrestrial destinations. Assuming the UWOC channel is subject to a unified mixture Exponential-Generalized Gamma distribution and the RF channels experience Nakagami-m fading, the analytical as well as asymptotic expression for outage probability is obtained in the form of the Meijer’s G-function. Moreover, the average achievable rate is also investigated by utilizing the bivariate Fox’s H-function. In addition, the accuracy of those expressions is verified with Monte-Carlo simulations.

On the Study of Multiuser Mixed Dual-Hop RF/THz Systems

A multiuser mixed radio frequency/terahertz (MRFTHz) system is studied, where the multiple RF channels experience <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\eta$</tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> fading and the THz channel obeys <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu _{1}$</tex-math></inline-formula> fading with pointing errors (PEs). Both fixed-gain (FG) amplify-and-forward (AF) and decode-and-forward (DF) protocols are considered in the relay. Firstly, the exact expressions of the cumulative distribution functions of the overall signal-to-noise ratio under AF and DF schemes are derived. On this basis, the Fox's H-function (FHF) and bivariate FHF are used to obtain exact analytical expressions of the outage probability (OP), average bit error rate, and average channel capacity. Additionally, the asymptotic results at high signal-to-noise ratios (SNRs) are provided to gain the system's diversity order (DO). Results show that the DOs of the AF and DF relaying systems are decided by the PEs and channel fading parameters (FPs). In addition, considering the FG AF relaying and multi-antenna scenarios, the asymptotic OP at high SNRs is derived, which obtaining the DO is determined by the numbers of the antenna, PEs, and FPs. Finally, we apply the Monte Carlo simulations to verify numerical results. Results show that the path loss, PEs, FPs, and the number of users can significantly affect the proposed multiuser MRFTHz system.

Combination of FSO and RF channels by using Ethernet link aggregation

AbstractHybrid free‐space optical and radio frequency (FSO/RF) systems have attracted much attention for more than a decade because of their enhanced reliability and capacity as comparison to single FSO or RF systems. Existing schemes to construct such a hybrid system are usually to use either switching or encoding/decoding strategies for combination of channels. The proposed scheme, based on packet sharing strategy of Ethernet link aggregation, provides a different way to combine FSO and RF channels. Theoretical analysis and Experimental results show that the proposed scheme does enhance the reliability and utilize both channel capacities for a multi‐channel system. Moreover, this scheme is simple and scalable because more channels can be combined based on such a packet sharing strategy without modifying the physical channel structures, therefore, this scheme may provide a good solution for constructing an efficient and cost‐effective hybrid FSO/RF system.

Joint resource allocation and power allocation scheme forMIMOassistedNOMAsystem

AbstractMultiple input multiple output (MIMO) plays an integral role in improving energy efficiency for enhancing all users' quality of service (QoS). For 5G wireless communication (WC), the NOMA strategy is used with the MIMO system to improve the system's sum rate and computational complexity. In this, terahertz (THz) band communication is introduced for future demand to carry more users and obtains high multiplexing gain. Multiple antenna arrays are used in the MIMO‐NOMA system to achieve high signal transmission. However, the use of antenna arrays increases as the number of users increases. A beam‐forming‐based signal transmission is introduced in this work to overcome this issue. For performing digital and Analog beam‐forming, a hybrid minimum mean square error (MMSE) with zero‐forcing (ZF) pre‐coder is proposed to eliminate the inter‐cluster interference. Initially, user clustering is undertaken using a fuzzy k‐means clustering (FKM) algorithm, and beam‐forming is performed among the user clustering. The joint power allocation (PA) and resource allocation (RA) is done using a hybrid artificial gorilla troop with leader optimization (HGTLO) technique to achieve a maximum sum rate of the RF channel. The performance of a proposed method is analyzed using the MATLAB tool. In the experimental scenario, the performance of energy efficiency (EE), spectral efficiency (SE), achievable sum rate, throughput, bit error rate (BER), and mean square error (MSE) attains the value of 35.82 bits/Hz/Joules, 198.11 bps/Hz, 116.78 Mbps, 93.06%, .003 and .011 respectively. The performance measures prove the efficacy of a proposed method.

Windowed cross polarization at 55 kHz magic-angle spinning

Cross polarization (CP) transfers via Hartmann-Hahn matching conditions are one of the cornerstones of solid-state magic-angle spinning NMR experiments. Here we investigate a windowed sequence for cross polarization (wCP) at 55 kHz magic-angle spinning, placing one window (and one pulse) per rotor period on one or both rf channels. The wCP sequence is known to have additional matching conditions. We observe a striking similarity between wCP and CP transfer conditions when considering the flip angle of the pulse rather than the rf-field strength applied during the pulse. Using fictitious spin-1/2 formalism and average Hamiltonian theory, we derive an analytical approximation that matches these observed transfer conditions. We recorded data at spectrometers with different external magnetic fields up to 1200 MHz, for strong and weak heteronuclear dipolar couplings. These transfers, and even the selectivity of CP were again found to relate to flip angle (average nutation).

Focus on test, measurement, quantum metrology, and analytical equipment

Focus on test, measurement, quantum metrology, and analytical equipment

Design and performance analysis of a dual channel RF MEMS switch with separate bias voltage and signal paths for aerospace applications

Design and performance analysis of a dual channel RF MEMS switch with separate bias voltage and signal paths for aerospace applications

A Portable 28-GHz Channel Sounder Platform and Measurement Results From Close-to-Ground Field Tests

This article describes a novel, bespoke, and low-cost 28 GHz RF TX and RX front end design that has been combined with a commercial Software Defined Radio and Raspberry Pi controller to realize a portable propagation measurement system for the 28 GHz band. The complete sounder system can resolve an impulse from RX powers down to -107 dBm (3 dB impulse SNR) and the sounder TX can generate a signal of -8 dBm. Therefore, using 20 dBi antennas supports path loss measurements of 139 dB. The sounder can resolve time domain reflections to 33 ns in a channel measurement bandwidth of 60 MHz, producing both time domain and frequency domain results. The complete sounding system has been used to perform close-to-ground RF channel measurements, with propagation loss models and time domain impulses extracted. Close-to-ground measurement is an underreported area of propagation research that is relevant for novel use-cases, such as in military applications or for mobile device-to-device communications. A key initial finding from the trials is that the path losses for 28 GHz indoor and outdoor links at circa 70 cm above ground seem close to that of free space, with very few strong reflections with delays exceeding 33 ns.