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Laser diode absorption spectroscopy is used to experimentally measure Ar(1s5) metastable density and translational gas temperature within a 94 GHz microplasma. A square two-dimensional photonic crystal (PhC) at this resonance frequency serves to ignite and sustain the plasma from 20 to 200 Torr (2.7 × 103–2.7 × 104 Pa) by using millimeter wave power from 300 to 1000 mW. Metastable density within the plasma is estimated from the absorption line shape of the laser traversing the PhC. The metastable density reaches an order of 1019 m−3 at lower pressure and decreases as pressure increases. From the Lorentzian line shape of the absorption profile at 811.53 nm, the gas temperature is extracted and found to increase from 500 K at 20 Torr to 1300 K at 200 Torr. These data are analyzed and compared with a zero-dimensional plasma model and with previous experimental plasma results at 43 GHz. [ABSTRACT FROM AUTHOR]

Summary: Millimeter Wave (mmWave) communication has emerged as a transformative technology at the forefront of wireless communication. One of the key challenges in harnessing the potential of mmWave technology is overcoming the increased susceptibility to propagation losses and environmental obstacles. To address these challenges, Three‐Dimensional Massive Multiple‐Input Multiple‐Output (3D Massive MIMO) systems have gained traction. The 3D aspect extends this concept by considering the elevation dimension, allowing for enhanced spatial resolution and coverage. Accurate estimation of the channel in 3D Massive MIMO scenarios is particularly challenging because of the complex propagation characteristics of mmWave signals. This paper introduces an efficient‐Aided Graph Neural Network Combining with Hierarchical Residual Learning (DPrGNN‐HrResNetL), designed specifically for beamspace Channel Estimation (CE)in mmWave‐Massive MIMO environments. The proposed model leverages deep priors and GNN mechanisms to enhance the extraction of spatial features, while hierarchical residual connections facilitate effective information flow through the network. DPrGNN enables the model to capture and understand complex spatial relationships among different antenna elements. The incorporation of deep priors provides a mechanism for leveraging prior knowledge about channel characteristics. This enhances the efficiency of the learning process, allowing the model to learn and adapt more effectively. The integration of hierarchical residual connections facilitates effective information flow through the network. This is particularly important for modeling complex dependencies within the beamspace channel data, enhancing the learning capacity of the network. The performance of the DPrGNN‐HrResNetL model is evaluated across a range of Signal‐to‐Noise Ratios (SNRs), utilizing metrics such as Normalized Mean Squared Error (NMSE) to measure the accuracy of the estimation. The outcomes underscore the resilience and efficacy of the DPrGNN‐HrResNetL approach in achieving precise CE within demanding mmWave scenarios. [ABSTRACT FROM AUTHOR]

Wireless connections in 5G technology are driving the rapid growth of intelligent transport systems and vehicle communications. Wireless channels are impacted by weather, which is most noticeable in millimeter wave bands. This includes rain, fog, snow, sand, and dust. 5G networks now support diverse applications with speed and quality. In an effort to enable the use of millimeter wave frequencies, a recent study examined the impact of dust and sand on 5G channels. This paper examines the impact of heavy and frequent rainfall, along with horizontal polarization, on the propagation of millimeter waves in urban and highway settings. Using theoretical and optimization techniques, the effects of rainfall attenuation, path loss, and connection margin are evaluated at various millimeter wave frequencies. Dependencies on rainfall rate, path variation, and operating frequency are shown by the simulation results. In urban and highway situations, mean path loss and error statistics are examined with and without rainy attenuation. It is observed that the particle swarm optimization approach achieves 94% accuracy in signal propagation, which will enhance the path loss, received power, and overall system performance. [ABSTRACT FROM AUTHOR]

The millimeter wave communication technology used for drones could combine the advantages of drones and millimeter waves, providing high-speed data transmission and wide area network coverage capabilities, and has broad application prospects in military and civilian communication systems. Millimeter wave active antennas have the advantages of miniaturization, high frequency band, and flexible shaping, which is of great significance for ensuring the high-speed dynamic communication ability of drone platforms. In this paper, a millimeter wave active antenna suitable for unmanned aerial vehicles (UAVs) is designed and verified, operating in 24.75-27.5 GHz and adopting Antenna in Package (AiP) design. Frequency band test and communication performance test is conducted. To open and close the RF channels, the antenna's operating frequency range can be shown in the vector network analyzer which meets the design frequency band 24.75-27.5 GHz requirements. By loading 5G millimeter wave standard signals, the antenna can achieve real-time demodulation of 100 MHz, 256QAM signals. The test shows that the system can meet the requirements of beam tracking and real-time information transmission during high-speed dynamic flight of UAVs. It has broad application prospects in UAV communication systems. [ABSTRACT FROM AUTHOR]

Millimeter wave (mmWave) radar technology has potential applications in vital signs detection and medicine. In order to minimize the influence of human micro-movements and respiratory harmonics on heart rate estimation, the vital signs detection method based on mmWave radar is studied in this paper. First, we use median filtering to eliminate baseline drift caused by human micromotion. Next, a differential recursive least squares multiple classification (DR-MUSIC) algorithm is proposed based on the combination of recursive least squares-based adaptive filter (RLS) and multiple signal classification (MUSIC) algorithm. This algorithm effectively suppresses respiratory harmonics and separates respiratory and heartbeat signals. Finally, heart rate value can be precisely estimated using spectral peak search. We invite a number of people to participate in the experiment, which demonstrate that the method successfully suppresse the impact of respiratory harmonics at low SNR. The error rate between the estimated heart rate and the reference heart rate is only 1.69% to 2.61%, which is significantly better than the existing algorithms. [ABSTRACT FROM AUTHOR]

A cutting-edge antenna system has been developed for new radio (NR) millimeter wave operating from 36.0 to 40.0 GHz frequency range 2 (FR 2) n260 band applications. This innovative system incorporates metasurface-inspired printed dual-port MIMO technology, which includes LP to CP conversion features. The positional orientation of the elements of the MIMO antenna with stacked metasurface provoked the spatial diversity. To convert linearly polarised (LP) waves to circularly polarised (CP) waves, the metasurface layer is suspended above the MIMO antenna. LP to CP polarisation conversion occurs when the conducting strip and rectangular space between strips on the substrate generate π/2 phase-shifted electric field components (Ex and Ey). The proposed stepped impedance-fed antenna elements and metasurface are fabricated on commercially available high-frequency laminates using a double-layer printed circuit board (PCB) fabrication facility. The test findings exhibit a satisfactory level of concurrence with the calculated/measured findings regarding scattering parameters, diversity performance parameters, and realized gain. The result is a highly efficient and versatile antenna system that is ideal for advanced engineering applications. [ABSTRACT FROM AUTHOR]

In recent times, there are considerable research efforts in utilising millimetre wave cellular system for meeting rising mobile traffic volume and escalating data rate demand. In this regard, several analytical models have been developed for obtaining Channel State Information (CSI) for the design of combiner and precoder architectures for millimetre wave communication. One prominent method that has caught the attention of most researchers is the Orthogonal Matching Pursuit (OMP) which performs poorly in noisy condition. As a result, this work introduces Compressed Sampling Matching Pursuit (CoSAMP) as alternative to OMP for obtaining CSI for the design of hybrid combiner. A comparative analysis of all the cases examined reveals that CoSAMP surpasses OMP and Least Square (LS) across SNR range of −30 dB to −10 dB, recording lowest Normalized Mean Square Error (NMSE), highest Spectral Efficiency (SE) and bit rate. For instance at −20 dB, NMSE of CoSAMP exhibits 95% and 86% gain over LS and OMP, respectively while SE and bit rate of CoSAMP are better than OMP and LS by 21% and 91%, respectively. It is therefore seen that CoSAMP is a better technique for estimating CSI and for combiner design in such condition. [ABSTRACT FROM AUTHOR]

This paper presents a 3D-printed fully dielectric bi-material reflectarray with bandgap characteristics for multi-band applications. To achieve bandgap characteristics, a "1D Bragg reflector" unit cell is used. The latter is a layered structure characterized by a spatial distribution of refractive index that varies periodically along one dimension. By appropriately selecting the dimensions, the bandgap can be shifted to cover the desired frequency bands. To validate this bandgap characteristic, a (121.5 mm × 121.5 mm) with an f/D ratio of 0.5 reflectarray was fabricated. The measured gain at 27 GHz is 27.22 dBi, equivalent to an aperture efficiency of 35.05%, demonstrating good agreement between simulated and measured performances within the frequency range of 26–30 GHz. Additionally, the transparency of the reflectarray was verified by measuring the transmission coefficient, which exhibited a high level of transparency of 0.32 dB at 39 GHz. These features make the proposed reflectarray a good candidate for multi-band frequency applications. [ABSTRACT FROM AUTHOR]

Millimeter waves (mmWave) are the only viable solution that is practical to fulfil the enormous bandwidth requirement of the modern era communication systems. Accurate estimation of the wireless channels is necessary for mmWave based multiple input multiple output (MIMO) systems that use directional beamforming. Nevertheless, due to the short wavelengths, mmWave channels exhibit significant variability, which poses a major obstacle to their successful recovery within limited training durations traditionally, there are two conventional channel estimation methods have been used for the operation. One is by using the low rank property of channel matrix and the other is to exploit the sparsity of the channel matrix in angle domain. However, the conventional estimation approaches may have necessitated a high-dimensional channel matrix, so substantially augmenting the intricacy of the traditional channel estimation process. This study addresses the channel estimation problem of wideband mmWave MIMO system by utilizing both low rank and sparsity simultaneously. The fundamental concept of the proposed technique is to frame the channel estimation issue as a combined optimization problem that creates an objective function comprising of l 1 - n o r m and nuclear norm minimization problems. The joint optimization problem is tackled using the expanded version of alternating direction method of multipliers (ADMM) algorithm which takes the advantage of the low rank and sparseness of the channel matrix by using the relaxation technique of the variables. The simulation findings clearly illustrate the superiority of proposed approach in comparison to other benchmarks. [ABSTRACT FROM AUTHOR]

Aiming at the problems of slow speed and poor accuracy of traditional millimeter wave sparse imaging, a sparse imaging algorithm based on graph convolution model is proposed from the perspective of sparse signal recovery. The graph signal model is constructed by combining the low‐rank and piecewise smoothing(LRPS) regular terms, based on which the proximal operator is replaced by the denoising graph convolution network, and the graph convolution sparse reconstruction network LRPS‐GCN is constructed, and the recovered target image is obtained by iterating with the optimal non‐linear sparse variation. For the proposed algorithm, simulation experiments are carried out using synthetic datasets under different target densities, iteration times and noise environments, and compared with the traditional graph signal reconstruction algorithm and the deep compressed sensing reconstruction algorithm, and then use the measured data with varying degrees of sparsity to validate. The experimental results show that the reconstructed images by this algorithm have better performance in terms of normalised mean square error, target to background ratio, reconstruction time and memory usage. [ABSTRACT FROM AUTHOR]

This research article presents wideband multiport (two, four, and six) high isolation multiple-input multiple-output (MIMO) antennas for 5G millimeter wave communication systems. The MIMO single unit uses a partially grounded slotted patch structure to achieve wideband response in a minimal footprint. The MIMO structure attains high port isolation through spatial and polarization diversity schemes. In addition, coupling the four-port MIMO antenna to an artificial magnetic conductor (AMC) plane results in a large (threefold) improvement in gain. The proposed antenna prototypes are fabricated and tested. The prototype results are also compared with the reported state-of-the-art results. The AMC-coupled MIMO antenna offers large bandwidth (43%), high gain (8.54 dBi), high isolation (> 25 dB), and excellent diversity metrics (envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), and channel capacity loss (CCL)). The listed credentials are ideal for 5G communication networks and devices. [ABSTRACT FROM AUTHOR]

This paper presents an ultra-wideband polarization converting metasurface (PCM) for millimeter wave which can manipulate the linear polarized (LP) incident wave to its orthogonal counterpart in the frequency range of 49.7 to 142.2 GHz with an ultra-wide bandwidth of 92.5 GHz and a fractional bandwidth (FBW) of 96%. The proposed PCM shows outstanding results in achieving higher fractional bandwidth with overall polarization conversion ratio (PCR) > 90% in the desired band. The proposed PCM has low profile dimensions with thickness and periodicity of 0.5 mm (0.083 λo) and 1.43 mm (0.24 λo), where λo is the maximum wavelength at the lower operating frequency. Surface current distribution is studied to show the physics of polarization conversion. The design is versatile and adoptable in low-profile applications where minimum thickness is required and can be utilized in remote sensing, microwave relays, and astronomy. [ABSTRACT FROM AUTHOR]

Cell-free millimeter wave (mmWave) multiple-input multiple-output (MIMO) can effectively overcome the shadow fading effect and provide macro gain to boost the throughput of communication networks. Nevertheless, the majority of the existing studies have overlooked the user-centric characteristics and practical fronthaul capacity limitations. To solve these practical problems, we introduce a resource allocation scheme using statistical channel state information (CSI) for uplink user-centric cell-free mmWave MIMO system. The hybrid beamforming (HBF) architecture is deployed at each access point (AP), while the central processing unit (CPU) only combines the received signals by the large-scale fading decoding (LSFD) method. We further frame the issue of maximizing sum-rate subject to the fronthaul capacity constraint and minimum rate constraint. Based on the alternating optimization (AO) and fractional programming method, we present an algorithm aimed at optimizing the users' transmit power for the power allocation (PA) subproblem. Then, an algorithm relying on the majorization–minimization (MM) method is given for the HBF subproblem, which jointly optimizes the HBF and the LSFD coefficients. [ABSTRACT FROM AUTHOR]

The capability to identify the frequency of unknown microwave signals with an ultra‐wide measurement bandwidth is highly desirable in radar astronomy, satellite communication, and 6G networks. Compared to electronic solutions, the integrated photonic technology‐enabled dynamic instantaneous frequency measurement (DIFM) approach is attractive as it offers unique advantages, such as ultra‐wide frequency measurement bandwidth, high flexibility, and immunity to electromagnetic interference. However, so far the bandwidth of the reported DIFM systems based on integrated photonic technology is limited to below 30 GHz due to the finite bandwidth of electro‐optical modulators (EOMs), limiting their applications, particularly in the field of millimeter wave technology (30–300 GHz). Here, the first integrated dynamic microwave instantaneous frequency measurement system with a record‐breaking operation bandwidth (ranging from 5 to 65 GHz) and low root‐mean‐square (RMS) error (≈300 MHz) is presented on the lithium niobate on insulator (LNOI) integrated photonic platform. This demonstration paves the way for high‐performance millimeter wave photonic integrated devices using the LNOI platform. [ABSTRACT FROM AUTHOR]

It is demonstrated that single‐crystalline and highly doped GaAs membranes are excellent candidates for realizing infrared‐transparent shields of electromagnetic interference at millimeter frequencies. Measured optical transmittance spectra for the semiconductor membranes show resonant features between 750 and 2500 nm, with a 100% maximum transmittance. The shielding effectiveness of the membranes is extracted from measured scattering parameters between 65 and 85 GHz. Selected GaAs membranes and membranes/polyamide films exhibit shielding effectiveness ranging from 22 to 40 dB, which are suitable values to ensure the safe operation of infrared devices for commercial applications. Theoretical calculations based on a plane wave model show that the interplay of primary reflection and multiple internal reflections of the radio‐frequency waves results in broadband shielding capabilities of the membrane between 10 and 300 GHz. [ABSTRACT FROM AUTHOR]

A millimeter wave interferometer based on a Ka-band CW signal generator and a high-speed oscilloscope has been implemented, which makes it possible to carry out measurements without frequency conversion. The experimental measurements of the amplitude of transverse deformations of a metal rod caused by impact loading have been carried out. A good agreement between the calculated and measured data was revealed, demonstrating the possibility to measure microsecond-duration surface deviations with an accuracy of about 1 μm and a relative error of about 8%. [ABSTRACT FROM AUTHOR]

This study proposes the integration of a beamforming neural network (BFNN) and multiple-input single-output based non-orthogonal multiple access (MISO-NOMA) with hybrid beamforming (HBF) for cell edge users (CEU) in a millimeter wave (mmWave)-based beyond 5G cellular communication system. This system is referred to as MISO-NOMA-HBFBFNN. The proposed scheme has been implemented to support multiple users simultaneously and also to considerably enhance and significantly improve the overall the sum channel capacity (SC) and user channel capacities. Additionally, the simulation results demonstrate the superiority of the proposed MISO-NOMA-HBF-BFNN scheme over the existing MISONOMA with HBF and MISO-OMA with HBFBFNN based schemes in terms of user capacities and SC. [ABSTRACT FROM AUTHOR]

Copyright of Automotive Engineer (1674-6546) is the property of Auto Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to serve the explosive demands of triple play services or multimedia services with high quality of data transmission in Fifth Generation (5G) communication systems which has availability of large spectrum unlike Fourth Generation (4G), low latency, improved transmission, and increased reliability, an access networks with optical fiber distribution network and wireless enabled technology is urgently needed and therefore, a prominent technology known as Radio over Fiber (RoF) is suggested by researcher/Scientists due to a perfect blend of flexible fiber technology and wireless mobility. RoF technology is helping the data transmission systems from last thirty years with great success and has numerous advantages such as scalability, transparency, antenna site complexity reduction, low installation cost, accessibility of radio carrier by diverse antenna sites dynamically. Millimeter waves (Mm waves) integration in 5G wireless RoF systems comes out to be an encouraging candidate to cater the bandwidth hungry current as well as future generation internet application such as high definition TV (HDTV), online games, video conferencing, and voice over IP (VoIP) etc. For the prolonged reach, economical installations, and improved performance, optimal Mm wave generation methods should be incorporated in 5G such as employing multi carrier generation technique (MCG). Deployment of single mode fiber (SMF) in 5G offers high speed, large capacity, improved security, etc., but also has a prominent limitation of nonlinear effects and it is unwanted phenomenon which degrade the system performance by introducing intermodulation distortion, distortion of signal phase, harmonic distortion, and interference in the neighbouring channels. Minimum modifications of architecture and minimum cost should be spent on the compensation of nonlinear effects or Kerr's effects in RoF systems and recently mode division multiplexing has emerged as an ultimate solution. In this review article, detailed discussion of an evolutionary technology, i.e., RoF is presented with a literature review, present evaluations, and future challenges. Our utmost goal is to enrich the young researchers with precious aspects for RoF technology on single platform and also encourage them to conduct the technology advancement research works in various fields such as nonlinear compensation, Mm wave generation, dispersion compensation, cost reduction, complexity reduction, and security enhancements for 5G RoF systems. [ABSTRACT FROM AUTHOR]

In the fifth generation (5G) new radio (NR) wireless communication system, using a multiple-input multiple-output (MIMO) system for signal transmission and reception of the millimeter wave frequency band can effectively improve data rate performance and received signal quality. Besides, precoding is an important method of beamforming in MIMO transmission. With the properly selected precoding matrices, the transmitter and receiver can adjust the transmitting and receiving behaviors in accordance with the changes of the current channel state to reduce the interferences between users and increase the received signal strength. In this paper, a low complexity precoding selection method is proposed based on the steering angle characteristics of the precoding matrices of 5G NR. In addition, for this paper, we used the software defined radio to implement the precoding selection following the requirement of the specifications of 5G. With this implementation, both the transmitter and receiver can determine the suitable precoding matrices according to different precoding selection methods. Results showed that with a little error vector magnitude performance degradation, the proposed precoding selection method can reduce at least 50% of the required computational complexity of the full search method. [ABSTRACT FROM AUTHOR]

We consider a millimeter wave (mmWave) multiple input multiple output (MIMO) multiple-relay aided system in beyond 5G (B5G) and 6G with a multiple antennas source, multiple amplify-and-forward (AF) X-duplex (XD) relays with single transmit and single receive antenna, and one multiple antennas destination. XD relays can switch adaptively between half-duplex (HD) relaying and full-duplex (FD) relaying modes to improve the system performance. We derive an expression for the outage probability of the system by assuming a relay selection scheme based on the maximum end-to-end (E2E) signal to interference plus noise ratio (SINR). Moreover, both Rician small scale fading and large scale fading includes blockage effect and path-loss are considered in source to relay and relay to destination mmWave channels, in addition, a realistic model for residual self-interference is studied. Simulation results present the accuracy of the theoretical expression of the outage probability of XD relaying in the mmWave MIMO system and show that it has superior outage performance compared with both HD and FD relaying. [ABSTRACT FROM AUTHOR]

Gestures are one of the most natural and intuitive approach for human-computer interaction. Compared with traditional camera-based or wearable sensors-based solutions, gesture recognition using the millimeter wave radar has attracted growing attention for its characteristics of contact-free, privacy-preserving and less environment-dependence. Although there have been many recent studies on hand gesture recognition, the existing hand gesture recognition methods still have recognition accuracy and generalization ability shortcomings in shortrange applications. In this paper, we present a hand gesture recognition method named multiscale feature fusion (MSFF) to accurately identify micro hand gestures. In MSFF, not only the overall action recognition of the palm but also the subtle movements of the fingers are taken into account. Specifically, we adopt hand gesture multiangle Doppler-time and gesture trajectory range-angle map multi-feature fusion to comprehensively extract hand gesture features and fuse high-level deep neural networks to make it pay more attention to subtle finger movements. We evaluate the proposed method using data collected from 10 users and our proposed solution achieves an average recognition accuracy of 99.7%. Extensive experiments on a public mmWave gesture dataset demonstrate the superior effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The AlInGaN/GaN heterojunction epitaxy material with high cutoff frequency and saturated power density has become a very popular candidate for millimeter wave applications in next-generation mobile communication. In this study, an advanced voltage-controllable capacitor based on the AlInGaN/GaN-Si (111) epitaxy was proposed by employing a bi-directional series MIS capacitor structure. The capacitor was fabricated by using a pad area of 40 μm × 40 μm, with a 1 μm distance between the positive and negative electrodes. The test results show that the capacitance is turned on with a saturation capacitance density and a maximum leakage current density of 0.30 fF/μm2 of 0.37 pA/μm2, respectively, for the control voltage from −6.5 V to 6 V. In particular, in the proposed design method, the saturation capacitance required for the practical application can be obtained by simply adjusting the capacitance area. The capacitor showcases characteristics of rapid turn-on and turn-off responses coupled with low loss, underscoring its promising prospects for deployment in RF switching applications. [ABSTRACT FROM AUTHOR]

Recognizing sleep posture is crucial for the monitoring of people with sleeping disorders. Existing contact-based systems might interfere with sleeping, while camera-based systems may raise privacy concerns. In contrast, radar-based sensors offer a promising solution with high penetration ability and the capability to detect vital bio-signals. This study propose a deep learning method for human sleep pose recognition from signals acquired from single-antenna Frequency-Modulated Continuous Wave (FMCW) radar device. To capture both frequency features and sequential features, we introduce ResTCN, an effective architecture combining Residual blocks and Temporal Convolution Network (TCN) to recognize different sleeping postures, from augmented statistical motion features of the radar time series. We rigorously evaluated our method with an experimentally acquired data set which contains sleeping radar sequences from 16 volunteers. We report a classification accuracy of 82.74% on average, which outperforms the state-of-the-art methods. [ABSTRACT FROM AUTHOR]

This work presents an on-chip 60 GHz lumped element transmission line (TL) using cascaded T-networks with a high Quality factor. Each T-network consists of a series inductance with a shunt capacitance at its center. We have derived the design equations for this TL configuration and proved that a TL whose electrical length ≥ 60° achieves additional miniaturization when implemented with three or more cascaded T-networks. The inductance is implemented using a straight wire model with no ground below it, while the capacitance is implemented using a parallel plate model with a grounding pedestal. Both configurations guarantee maximum inductance per unit length and capacitance per unit area to further improve the miniaturization level. A quarter wavelength TL with three cascaded T-networks is fabricated as proof of concept. The measured and simulated results of the fabricated TL have good agreement, and the measured quality factor is 17 at 60 GHz. [ABSTRACT FROM AUTHOR]

Millimeter-wave channel modeling is the basis of fifth-generation (5G) communication network design and applications. In urban microcellular environments, the roughness of wall surfaces can be comparable to the wavelengths of millimeter waves, resulting in walls that cannot be considered as smooth surfaces. Therefore, channel modeling methods based on only traditional three-dimensional ray tracing (RT) or the three-dimensional parabolic equation (PE) result in the limited computational accuracy of millimeter-wave channel models for urban environments. Based on the scattering theory of a rough surface and the typical scattering characteristics of a millimeter wave, the end field of the three-dimensional vector PE is regarded as the initial field of three-dimensional RT. Moreover, the number of scattered rays and scattering angles are introduced. Finally, a three-dimensional fully polarized millimeter-wave hybrid propagation channel model (3DFPHPCM) is proposed. The proposed model improves the computational accuracy of a single deterministic model. Millimeter-wave channel measurements in non-line-of-sight (NLOS) environments were carried out to verify and optimize the proposed 3DFPHPCM. The results show that the root mean square error (RMSE) and mean absolute error (MAE) of the proposed 3DFPHPCM are both minimized when compared to three-dimensional RT or the three-dimensional PE, which indicates that the proposed 3DFPHPCM has higher computational accuracy. Moreover, its runtime is the shortest among the methods. The results presented herein provide technical support for the layout of base stations. [ABSTRACT FROM AUTHOR]

Network densification is a key technology to meet the rapid growth of 5G traffic. Millimeter wave has rich spectrum resource, short propagation distance and obvious directivity. Therefore, the dense millimeter wave network can reduce co-frequency interference and improve network capacity. To make full use of spectrum resource, this paper proposes a user association algorithm in multi-band millimeter wave network, which maximizes the weighted total rate of network while meeting the requirement of users and backhaul bandwidth constraint of base stations (BS). To enrich resource management method of network, the resource proportion of BS allocated to each user is also jointly optimized. For the mixed integer optimization problem which is difficult to solve after modeling, we adopt penalty function and Marks–Wright algorithm to obtain solution. Simulation results show that compared with three similar algorithms, the proposed scheme can rationally utilize network resource, avoid load imbalance, and has the highest total rate of network. [ABSTRACT FROM AUTHOR]

In this paper, a filterless 32-tupling millimeter wave generation scheme based on eight MZMs is proposed. The system has an upper and lower parallel two-branch structure. The upper branch consists of two subsystems Sub-A and Sub-B in cascade, each subsystem contains four MZMs, and the MZMs are all operating at maximum transfer point (MATP). Sub-A mainly generates ±8th order optical sideband signal as the incident light signal of Sub-B. After modulation of Sub−B, the output signal is mainly ±16th order optical sideband signal containing the central optical carrier component. The optical attenuator (OATT) and optical phase shifter (OPS) of the lower branch are used to regulate the phase and amplitude of the optical carrier. The upper and lower branches are coupled, and the central optical carrier component is superimposed and cancelled so only the ±16th order optical sideband signal is retained. Finally, the 32-tupling frequency millimeter is generated by the photodiode (PD) receiver after photoelectric detection which receives and generates a 32-tupling frequency millimeter wave signal. The simulation results show that the 160 GHz millimeter wave signal can be obtained by driving the MZM with a 5 GHz RF signal, and the optical sideband suppression ratio (OSSR) and the RF sideband suppression ratio (RFSSR) are 52.6 dB and 44.75 dB, respectively. Theoretical analysis and simulation experiments are carried out for the proposed scheme which proves the feasibility of the scheme. [ABSTRACT FROM AUTHOR]

Respiration is an invaluable signal that facilitates the real‐time observation of physiological dynamics. In recent years, the advancement of noncontact measurement technology has gained momentum in capturing physiological activities in natural settings. This technology is anticipated to be found not only in humans but also in nonhuman primates. Currently, the predominant noncontact approach for nonhuman animals involves measuring vital signs through subtle variations in skin color. However, this approach is limited when addressing areas of the body covered with hair or when working in outdoor settings under fluctuating sunlight. To overcome this issue, we focused on noncontact respiratory measurements using millimeter‐wave radar. Millimeter‐wave radar systems, which employ millimeter waves that can penetrate animal fur and estimate respiration‐derived periodic body motion, exhibit minimal susceptibility to sunlight interference. Thus, this method shows potential for conducting noncontact vital measurements in natural and outdoor settings. In this study, we validated a millimeter‐wave radar methodology for capturing respiration in outdoor‐housed rhesus macaques (Macaca mulatta). The radar was positioned beyond the captive enclosure and maintained at a distance >5 m from the target. Millimeter waves were transmitted to the target, and the reflected waves were used to estimate skin surface displacement associated with respiration. The results revealed periodic skin surface displacement, and the estimated respiratory rates weres within the reported range of respiratory rates for rhesus macaques. These results suggest the potential applicability of millimeter‐wave radar for noncontact respiration monitoring in outdoor‐living macaques without anesthesia or immobilization. The continued advancement of noncontact vital measurement technology will contribute to understanding primate mental and physical dynamics during their daily life. Research Highlights: Millimeter‐wave radar systems succeeded in the outdoor noncontact measurement of respiration in unrestricted rhesus macaques from >5 m. Our results demonstrate the feasibility of radar‐based remote monitoring to better understand primate ecology. [ABSTRACT FROM AUTHOR]

As global internet traffic continues to increase, technologies for generating high-frequency signals, such as sub-terahertz (sub-THz) bands, through photonics are gaining attention. In this study, we demonstrate the generation of millimeter waves at approximately 17 GHz and sub-THz waves at approximately 300 GHz by converting the frequency difference of a two-wavelength tunable laser, fabricated using silicon photonics, into an optical–electrical signal. This device is expected to be used as a compact and low power consumption, two-wavelength tunable light source for THz wave transceivers. [ABSTRACT FROM AUTHOR]

A choke ring horn antenna has been designed for use as an RF applicator in a compact range in vitro 28 GHz bioelectromagnetic exposure system. The 30 mm × 50 mm horn antenna was fabricated and measured to operate from 27.75 GHz to 34.5 GHz with a −20 dB measured S11 and a measured antenna gain of more than 10 dBi. A wide sectoral (flat top) and symmetric E- and H-plane pattern with a half-power beamwidth of more than 60 degrees was achieved with a cross-polarization discrimination of better than 28 dB. Electromagnetic slots were introduced in the antenna to suppress excess cavity mode radiation which inherently impacts the cross-polarization levels of choke ring antennas. The proposed antenna was successfully integrated into the compact measurement chamber in partnership with the Korea Telecommunication Research Institute (ETRI) and is currently in use for real-time 5G millimeter-wave dosimetry studies. [ABSTRACT FROM AUTHOR]

Presented in this paper is an evaluation of human tissue penetration by millimeter wave (mmW) energy, particularly at 30, 35, 40 and 45 GHz. Numerical simulations show that the penetration depths in the tissue are (0.1000, 0.0937, 0.08869 and 0.08882) mm at the aforementioned frequency, respectively. It is also demonstrated that all mmW at those frequencies attenuate to zero at the epidermis which is the layer adjacent to the skin surface, without getting into the dermis which is the next layer. Crucially, these discoveries present fresh, previously unmentioned data within the current research literature. Furthermore, at the lower frequency of 24 GHz, computer simulations presented show that the propagating wave penetrates deeper (depth of 0.12 mm) and attenuates to zero at the dermis. This shows that the depth of penetration increases further at lower frequencies which strongly conforms to the principles of physical reasoning, thereby bolstering the reliability of the findings presented in this paper. The results collectively indicate that the absorption of mmW into the human tissue have limited significance when assessing compliance with electromagnetic field standards at mmW frequencies. It is reinforced in this paper why the human skin reduces the harmful effects of ultra-violet radiation. To lend credence to our formulation, certain aspects of the results obtained in this investigation when compared with similar results in the literature, show good agreements. [ABSTRACT FROM AUTHOR]

Due to cost and energy concerns with digital beamformers, much of the beamforming is done by hybrid beamformers in mm-wave (mm) massive multiple input multiple output (MIMO). Various works in hybrid beamforming structures considered either phase shifters, switches, or radio frequency lenses individually as switching mechanisms between antennas and precoding systems. Works that consider the hybrid use of phase shifters, switches, and radio frequency lenses need further investigation since there is a tradeoff between cost and system performance in each switching mechanism. The main aim of this research is to analyze the performance of a hybrid switch, a 1-bit phase shifter, and radio frequency (RF)-Lens in a hybrid beamforming network as a switching network. Simulation results showed that the hybrid of three has a spectral efficiency (SE) performance of 59.04 bps/Hz, which increases by 6.9 bps/Hz from that of the switch and lens antenna array network. The energy efficiency (EE) of the switch, phase shifter, and lens showed a performance of 46.41 bps/Hz/W, while the switch and lens antenna array, phase shifter, and lens antenna array showed a performance of 48.52 bps/Hz/W. The result also shows that the hybrid network achieves optimum performance at the expense of higher computational complexity. [ABSTRACT FROM AUTHOR]

The combination of non-orthogonal multiple access (NOMA) and intelligent reflective surface (IRS) is an efficient solution to significantly increase the energy efficiency of the wireless communication system. This paper considers a downlink IRS-based Millimeter wave (mmWave) massive Multiple-Input Multiple-Output (MIMO)-NOMA system. In this work, a two-layer hierarchical AGglomerative NESting- DIvisie ANAlysis Clustering Algorithm (AGNES-DIANA) user grouping (2L-HAD-UG) is proposed to group users. In the proposed 2L-HAD-UG, the first layer will use the AGNES algorithm to efficiently group the users into different clusters. After the first level of clustering, some user groups are larger than others, and perhaps some users with weakly correlated channels are assigned to the same groups. To address these concerns, the large user groups are divided into several smaller groups, and each user whose channels are weakly correlated is isolated as a separate group. In the second layer, the DIANA Hierarchical Clustering is used to divide the larger clusters based on the channel correlation value. After user grouping, a new joint active and passive beam-forming design problem is formulated to maximize the achievable rate of each user in each cluster under the Quality of Service (QoS) requirements of other users, the conditions of Successive Interference Cancellation (SIC) decoding rate, the constraints of IRS reflection components and the transmission power restrictions. The formulated optimization problem is solved by proposing a new Successive Chaotic Group Search Approximation (SCGSA) algorithm. With the proposed massive mmWave MIMO-NOMA system, the spectral efficiency, energy efficiency, and sum rate are achieved to 18.56 bits per second (bps)/Hertz (Hz), 57.56 bps/Hz/Watt (W) and 21.58 bps/Hz, respectively. [ABSTRACT FROM AUTHOR]

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This paper investigates a new vortex wave imaging approach to improve the imaging quality of small metal targets of size less than 1.5 mm. Antennas with different spiral phase plates are designed to efficiently transmit vortex beams with orbital angular momentums (OAMs). By analyzing the OAM spectrum of the target, it was discovered that the predominant reflection contains a particular OAM mode that carries abundant azimuthal information. This can be explained by the OAM selectivity of the target and the guidance of the vortex transmitting beam. A simple reflection vortex imaging system was designed to capture the phase information. Measurement results show that the high image contrast reaches 14.9%, which is twice as high as that of the imaging without OAM. Both of simulations and experiments demonstrate that the vortex phase imaging approach proposed in this paper can effectively improve the imaging quality at 80 GHz. This approach is suitable for other millimeter wave imaging systems and is helpful to improve the resolution in anti-terrorism security checks. [ABSTRACT FROM AUTHOR]

Fifth generation new radio (5G NR) is bringing revolutions in almost every field such as healthcare, industrial automation, smart farming, and defense. These fields utilize three major use case scenarios of 5G NR viz. eMBB, URLLC, and mMTC. 5G NR deployment relies on two major frequency bands such as sub-6 GHz and high-frequency bands (millimeter waves). Among all sub-6 GHz bands, the n78 band (3300–3800 MHz) is gaining popularity due to its unique characteristics viz. higher capacity and coverage, wide bandwidth, and higher data rate. Despite these unique characteristics, in the 5G standalone architecture, users expect high-speed video/voice transmission without delay and good quality of services (QoS) requirements. QoS is one of the important paradigms that indicates the quality of services experienced by end users instead of services claimed by service providers. In this work, we have designed a QoS scenario that utilizes the n78 band with an "urban macro mixed office scenario with low loss" path loss model. As per types of services are concerned, the scenario utilizes six different traffic templates (i.e., FTP, Voice, Video, COAP, CBR, and Email). The path loss model operates on non-line-of-sight scenarios with Rayleigh fading and eigen beamforming using 64 × 32 antenna elements. The performance of the proposed scenario is examined through different metrics i.e., throughput, packet drop ratio, and delay. Here, priorities to different traffic templates are assigned based on GBR and non-GBR resource types. In addition, the proportional fair scheduling algorithm is employed to schedule the resources. It was observed that video services achieved a higher throughput of 25.93 Mbps due to their prioritization in the QoS model. Conversely, FTP services experienced higher delay, measured at 64 ms, and a packet delivery ratio of 5.94%. [ABSTRACT FROM AUTHOR]

Subject and Purpose. The improvement of the atmosphere brightness temperature measuring method at frequencies of about 100 GHz is considered. The possibilities of the atmospheric carbon monoxide (CO) remote sensing instrument, developed at Institute of Radio Astronomy of the National Academy of Sciences of Ukraine were analyzed. They show that the functional of this instrument can be significantly expanded. It can provide more operational information about the troposphere, useful for aeronomy and radio astronomy. The purpose of this work is to improve the atmosphere brightness temperature measuring method in relation to the existing instrument. We determine the possibility of the spectroradiometer broadband channel to measure the sky brightness temperature. Methods and Methodology. A detailed analysis of the existing installation for monitoring atmospheric CO was carried out and the measurement method was improved. It is shown that the broadband channel of this instrument, created as a service, can be used to measure atmosphere brightness temperature. Such measurement will allow creating a database of the zenith brightness temperature of the sky at frequencies of about 100 GHz. Results. It is possible to create the base data of the brightness temperature of the sky at frequencies about 100 GHz. In order to do this, it is necessary to make only some modifications of the instrument. The main thing is to make changes to the data capture file of the broadband channel and create a program to convert the data obtained from the instrument into brightness temperature values according to the specified formulas. All necessary formulas for presenting observational results in the form of brightness temperatures are given. Conclusions. It has been proven that there is a possibility to create the base date of the troposphere brightness temperature over Kharkiv (Ukraine) at the frequencies of the short-wave part of the mm range. The high stability of the radiometric part of the installation allows determining the brightness temperature of the sky with an accuracy that is sufficient for aeronomical, radioastronomical and radiophysical studies. On the basis of analytical calculations and experimental data, the necessary modifications for creating such a base data are defined.

Hybrid analog and digital beamforming is gaining attention for its practical application in large-scale antenna systems. It offers significant cost savings, reduced complexity, and lower power consumption compared to entirely digital beamforming, all while maintaining comparable performance. This article proposes a hybrid beamforming architecture aimed at addressing these challenges by using a reduced number of radio frequency (RF) chains while achieving performance comparable to entirely digital schemes. The study demonstrates that matching the number of RF chains to the total number of data streams enables hybrid beamforming to compete effectively with entirely digital beamformers. The adopted approach focuses on computing analog and digital precoders and combiners using the metaheuristic method of genetic algorithms, in a point-to-point multiple input multiple output (MIMO) system scenario. The objective is to simplify the system and reduce costs by optimizing the number of antennas, RF chains, and data streams, all while maintaining comparable performance to entirely digital beamforming. The study's results show that increasing the number of antennas significantly impacts the quality and capacity of the hybrid massive MIMO beamforming system. Conversely, reducing the number of RF chains has a negligible effect on quality and capacity, but simplifies the design and minimizes costs. [ABSTRACT FROM AUTHOR]

In-cabin occupancy detection has become increasingly important due to incidents involving children left in vehicles under extreme temperature conditions. Frequency modulated continuous wave (FMCW) radars are widely used for non-contact monitoring and sensing applications, particularly for occupancy detection. However, the confined and metallic environment inside vehicle cabins presents significant challenges due to multipath reflections. This paper introduces a novel approach that detects the occupied space in each seat to determine occupancy, using the variance of detected points as an indicator of volume occupancy. In an experimental study involving 70 different scenarios with single and multiple subjects, we classify occupants in each seat into one of three categories: adult, baby, or empty. The proposed method achieves an overall accuracy of 96.7% using an Adaboost classifier and a miss-detection rate of 1.8% for detecting babies. This approach demonstrates superior robustness to multipath interference compared to traditional energy-based methods, offering a significant advancement in in-cabin occupancy detection technology. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to designing beam codebooks for downlink multiuser hybrid multiple-input–multiple-output (MIMO) wireless communication systems, leveraging multi-agent reinforcement learning (MARL). The primary objective is to develop an environment-specific beam codebook composed of non-interfering beams, learned by cooperative agents within the MARL framework. Machine learning (ML)-based beam codebook design for downlink communications have been based on channel state information (CSI) feedback or only reference signal received power (RSRP), consisting of an offline training and user clustering phase. In massive MIMO, the full CSI feedback data is of large size and is resource-intensive to process, making it challenging to implement efficiently. RSRP alone for a stand-alone base station is not a good marker of the position of a receiver. Hence, in this work, uplink CSI estimated at the base station along with feedback of RSRP and binary acknowledgment of the accuracy of received data is utilized to design the beamforming codebook at the base station. Simulations using sub-array antenna and ray-tracing channel demonstrate the proposed system's ability to learn topography-aware beam codebook for arbitrary beams serving multiple user groups simultaneously. The proposed method extends beyond mono-lobe and fixed beam architectures by dynamically adapting arbitrary shaped beams to avoid inter-beam interference, enhancing the overall system performance. This work leverages MARL's potential in creating efficient beam codebooks for hybrid MIMO systems, paving the way for enhanced multiuser communication in future wireless networks. [ABSTRACT FROM AUTHOR]

To meet the requirement of autonomous driving development, high-quality point cloud generation of the environment has become the focus of 4D mmWave radar development. On the basis of mass producibility and physical verifiability, a design method for improving the quality and density of point cloud imagery is proposed in this paper, including antenna design, array design, and the dynamic detection method. The utilization of apertures is promoted through antenna design and sparse MIMO array optimization using the genetic algorithm (GA). The hybrid strategy for complex point clouds is adopted using the proposed dynamic CFAR algorithm, which enables dynamic adjustment of the threshold by discriminating and calculating different scanning regions. The effectiveness of the proposed method is verified by simulations and practical experiments. Aiming at system manufacture, analysis methods for the ambiguity function (AF) and shooting and bouncing rays (SBR) tracing are introduced, and an mmWave radar system is realized based on the proposed method, with its performance proven by practical experiments. [ABSTRACT FROM AUTHOR]

Nonlinear mechanism of photodetector in the communication band of 1550 nm was researched in this article. Then nonlinear frequency doubling mechanism was used to generate millimeter wave signals that can be used in millimeter wave communication systems. In the article, the layer structure of the photodetector was optimized to further improve the power of millimeter wave signals. Different from the fundamental frequency output power, the frequency doubling output signal exhibits completely different characteristics at low input optical power and high input optical power. Therefore, the structure design of the photodetector was optimized for different input optical power application scenarios. Finally, the influence of the incident optical field distribution on the nonlinear output of the photodetector was studied. The results showed that when the photodetector did not reach saturation, the Gaussian distribution situation could produce a larger nonlinear signal power than uniform distributed optical field. [ABSTRACT FROM AUTHOR]

In recent years, the significance of millimeter wave sensors has achieved a paramount role, especially in the non-invasive and ubiquitous analysis of various materials and objects. This paper introduces a novel IoT-based fake currency detection using millimeter wave (mmWave) that leverages machine and deep learning algorithms for the detection of fake and genuine currency based on their distinct sensor reflections. To gather these reflections or signatures from different currency notes, we utilize multiple receiving (RX) antennae of the radar sensor module. Our proposed framework encompasses three different approaches for genuine and fake currency detection, Convolutional Neural Network (CNN), k-nearest Neighbor (k-NN), and Transfer Learning Technique (TLT). After extensive experiments, the proposed framework exhibits impressive accuracy and obtained classification accuracy of 96%, 94%, and 98% for CNN, k-NN, and TLT in distinguishing 10 different currency notes using radar signals. [ABSTRACT FROM AUTHOR]

A novel chamfered V-shaped microstrip meander line (MML) slow-wave structure (SWS) based on the V-shaped MML SWS for W-band traveling-wave tube (TWT) is proposed to decrease the transmission loss and thus to improve the output power and beam-wave interaction efficiency. The high-frequency characteristics, transmission characteristics, and the beam-wave interaction processes of the novel structure are investigated by simulations. The simulation results show that the S21 parameters of the chamfered V-shaped MML SWS are improved by 4.3 dB for 100 periods compared with that of the traditional V-shaped MML SWS at 95 GHz. Besides, the particle-in-cell simulations indicate that the output power of the TWT with the novel structure is 30% higher than the V-shaped MML SWS in W-band. Finally, two types of SWSs with 100 periods are fabricated, assembled, and experimentally tested. According to the experimental test results, while the S11 parameters are below − 20 dB, the "cold" S21 parameters are − 17.04 dB vs − 20.74 dB at 95 GHz, which shows potential advantages of the proposed novel SWS in millimeter wave and even terahertz spectrum. [ABSTRACT FROM AUTHOR]

The rollout of the fifth-generation (5G) mobile network was completed in 2020. Now, the focus shifts towards exploring the new perspectives of Beyond 5G (B5G) and 6G. Despite being a key enabler of 5G, millimeter wave technology has not yet been fully implemented due to various deployment challenges. Over the past decade, numerous efforts have been dedicated to modeling the propagation channel across the spectrum from 0.5 to 100 GHz. Propagation models such as Close-In (CI), Floating Intercept (FI), and single frequency Alpha-Beta-Gamma (ABG) have been extensively utilized. However, a significant deviation between co- and cross-polarization models has been observed in many estimated models in the literature. In this paper, we propose an optimization of the classic CI model by considering both TX and RX antenna heights, along with a correction coefficient. Initially, we estimate the propagation channel using the classic CI model in indoor environments, revealing a notable deviation between co- and cross-polarization models. Subsequently, we introduce a new model aimed at reducing this deviation and optimizing the Path Loss Exponent (PLE). With our proposed model, the estimated channel depolarization in Line-of-Sight (LOS) conditions stands at 2.8 dB, 5.6 dB, and 2.9 dB for room, corridor, and stairwell environments, respectively. In contrast, utilizing the conventional model yields channel depolarization figures of 4.8 dB, 8.2 dB, and 7 dB for the same environments. This disparity in channel depolarization can have significant implications for millimeter wave propagation, particularly during meteorological events such as rainfall. [ABSTRACT FROM AUTHOR]

This paper presents method for integrating two dual port multiple input multiple output (MIMO) antennas on a common substrate based on substrate integrated waveguide (SIW) technology. One of the dual port MIMO antennas (MIMO_1) resonates at 31.2 GHz with an impedance bandwidth of 1 GHz while the other dual port MIMO antenna (MIMO_2) exhibits an impedance bandwidth of 925 MHz and resonates at 36 GHz. The radiators etched on the SIW cavities are complementary slotted annular rings (CSAR). Isolation between the ports is more than 20 dB which is inherently achieved by SIW cavity backed structures. The MIMO antenna realized at 31.2 GHz exhibit a peak realized gain of 8.5 dBi while the MIMO antenna realized at 36 GHz displays a peak gain of 9.8 dBi. The diversity gain of both the MIMO antennas is around 9.9 dB and the envelope correlation coefficient (ECC) of the MIMO antenna realized at 31 GHz is below 0.004 while the ECC of MIMO antenna at 36 GHz is below 0.006. It is also confirmed that simulated results closely correlate with the measurement results. [ABSTRACT FROM AUTHOR]