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The Raindrop size distribution (DSD) is the most effective parameter to calculate rain-induced attenuation, which can be severe at Ka-band and higher frequencies. The authors have investigated the impact of rain rate and DSD on rain-induced specific attenuation over a tropical location Kolkata, India. DSD data from disdrometer has been used to calculate the specific rain attenuation with the help of Mie scattering theorem. Low to medium drop diameters (up to 3 mm) are the largest contributors to the various classes of rain rate and attenuation. Double peaks of drop sizes are significant for medium rain rate. The contribution of smaller drop diameters decrease, whereas the contribution of higher drop diameters increase with increasing rain attenuation. At lower rain attenuation, (up to 1.5 dB), complementary cumulative distribution function (CCDF) shows higher value for stratiform rain, with respect to convective rain. The higher attenuation occurrences are mostly observed during 12–18 Indian standard time (IST), i.e., in the afternoon. The results will be helpful for Ka-band (GSAT-14) and higher frequency satellite communication channel modeling over India. [ABSTRACT FROM AUTHOR]

As one of the channels used by the wireless gigabit (WiGig) protocol, a 58 GHz band has been deployed to realize a data rate of up to 100 gigabits per second (Gbps). Systems at the 58 GHz band point the main beam of the base station toward the mobile stations but suffer from a deep fading due to human body shadowing (HBS). To precisely predict the HBS channel considering the short wavelength at 58 GHz, a simulation method considering the detailed human geometry is needed. This paper proposes screen models and an elliptic cylinder model based on the instantaneous point clouds (PC) of human geometry for the HBS channel simulation using the uniform theory of diffraction (UTD). The proposals enable fair evaluation via a simultaneous measurement of the HBS channel and the PC. The HBS gains at the 58 GHz band in an indoor environment (6.5 m) between the measured and the simulated results based on the proposed models are compared. Compared with the conventional human model, the screen models are suitable for predicting the propagation channel cut-off by tracing the changing posture of the human body, and the elliptic cylinder model is suitable for predicting the shadowing distance by a 75% improvement.

As the millimeter‐wave (mm‐Wave) spectrum is considered to be an essential enabler to the fifth generation (5G) wireless communication systems. Human movements are one of the most significant factors that cause transient blockage in indoor mm‐wave channels. In this letter, human blockage measurements and shadow fading statistics due to human body movements in an indoor office environment are reported for the 28 GHz band. The effect of human bodies on the channel is measured for several scenarios including a variety of population and using diverse antenna heights. The reported shadow fading statistics include both the duration and the depth of the blockage fade, and accordingly, we propose several empirical models that cater for such blockage events. The findings reported in this letter could improve the modeling of indoor radio channels at 28 GHz bands by considering the presence of humans, as well as their movements. [ABSTRACT FROM AUTHOR]

It is crucial to have a dependable and precise channel model in order to study the properties of millimeter wave (mmWave) propagation. The Quasi-deterministic (QD) channel model is employed in this viewpoint, which describes the propagation of mm-Wave as a group of reflected and scattered rays originating from a complex environmental setup. These rays are assumed to travel in clusters, with each cluster consisting of a deterministic ray followed by postcursor rays and preceded by precursor rays. The summation of these rays is the number of multiple path components (MPCs) of each cluster. However, this comes at the cost of higher computational complexity for the channel model, which can hinder the simulation’s scalability. To simplify the QD channel model while maintaining accuracy, one option is to decrease the number of MPCs. In this paper, we present an analysis of path gains (PGs) of specular and diffused rays to reduce the total number of MPCs. Specifically, we propose two different reduction methods namely: i) the reduced post rays (RPR) method ii) the removed surfaces post rays (RSPR) method. The computational performance of the proposed methods is investigated in terms of computational time, and complexity. Additionally, the accuracy validation compared to the original QD model is evaluated in terms of PG cumulative distribution function (CDF), signal-to-noise ratio (SNR), and intra-cluster statistics. The proposed methods’ complexity and accuracy were assessed by examining measured data from indoor and outdoor environments at 60 GHz and 28 GHz, respectively. Both first and second-order reflection orders were tested to illustrate the balance between the two variables. The simplified methods suggested can decrease computational time by approximately 16% and 11% for RSPR and RPR schemes, respectively, when compared to the original QD.

Communications in the mmWave spectrum are gaining relevance in the last years as they are a promising candidate to cope with the increasing demand of throughput and latency in different use cases. Nowadays, several efforts have been carried out to characterize the propagation medium of these signals with the aim of designing their corresponding communication protocols accordingly, and a wide variety of both outdoor/indoor locations have already been studied. However, very few works endorse industrial scenarios, which are particularly demanding due to their stringent requirements in terms of reliability, determinism, and latency. This work aims to provide an insight of the propagation of 60 GHz mmWave signals in a typical industrial workshop in order to explore the particularities of this kind of scenario. In order to achieve this, an extensive measurement campaign has been carried out in this environment and a stochastic channel model has been proposed and validated.

Sparse scatterer identification with atomic norm minimization (ANM) techniques in the delay-Doppler domain is investigated for a vehicle-to-infrastructure millimeter wave propagation channel. First, a two-dimensional ANM is formulated for jointly estimating the time-delays and Doppler frequencies associated with individual multipath components (MPCs) from short-time Fourier transformed measurements. The two-dimensional ANM is formulated as a semi-definite program and promotes sparsity in the delay-Doppler domain. The numerical complexity of the two-dimensional ANM limits the problem size which results in processing limitations on the time-frequency sample matrix size. Subsequently, a decoupled form of ANM is used together with a matrix pencil, allowing a larger sample matrix size. Simulations show that spatial clusters of a point-scatterers with small cluster spread are suitable to model specular reflection which result in significant MPCs and the successful extraction of their delay-Doppler parameters. The decoupled ANM is applied to vehicle-to-infrastructure channel sounder measurements in a sub-urban street in Vienna at 62 GHz. The obtained results show that the decoupled ANM successfully extracts the delay-Doppler parameters in high resolution for the channel’s significant MPCs.

An interferometric phase transmitarray is proposed for spatial power combining to enhance the equivalent isotropically radiated power (EIRP) of the millimeter-wave (mmW) transmitters. The study shows that the multiple beams emitting from the ideal point sources located at different positions are combined into one beam to radiate in the boresight direction of the transmitarray, namely, achieving spatial power combining. As an example, the prototyped transmitarray fed by two patch antennas operating over the bandwidth of 23–27 GHz shows that with the spatial power combining, the proposed antenna achieves the combined gain realized by two feeds of 19.6 dBi at boresight 2.5 dB higher than the realized gain of the single feed, so that the EIRP of the two-feed transmitarray is enhanced by 5.5 dB because of 2.5 dB from the gain enhancement of two-feed transmitarray and 3 dB by the two-way power combining. [ABSTRACT FROM AUTHOR]

Millimeter-wave rotary-wing (RW) unmanned aerial vehicle (UAV) air-to-ground (A2G) links face unpredictable Doppler effect arising from the inevitable wobbling of RW UAV. Moreover, the time-varying channel characteristics during transmission lead to inaccurate channel estimation, which in turn results in the deteriorated bit error probability performance of the UAV A2G link. This paper studies the impact of mechanical wobbling on the Doppler effect of the millimeter-wave wireless channel between a hovering RW UAV and a ground node. Our contributions of this paper lie in: i) modeling the wobbling process of a hovering RW UAV; ii) developing an analytical model to derive the temporal autocorrelation function (ACF) for the millimeter-wave RW UAV A2G link in a closed-form expression; and iii) investigating how RW UAV wobbling impacts the Doppler effect on the millimeter-wave RW UAV A2G link. Numerical results show that different RW UAV wobbling patterns impact the amplitude and the frequency of ACF oscillation in the millimeter-wave RW UAV A2G link. For UAV wobbling, the temporal ACF decreases quickly and the impact of the Doppler effect is significant on the millimeter-wave A2G link. [ABSTRACT FROM AUTHOR]

In this letter, rain rate measurements performed in Ecuador are used to evaluate the performance of prediction models for estimating complementary cumulative distributions (CCDs) of rainfall rate at 1-minute integration time, which are required, for example, for rain attenuation estimation in wireless communication systems operating at frequencies above 10 GHz. Additionally, the aforementioned measurements are utilized in order to analyze the interannual variability of the rain rate, useful for the assessment of the reliability of the CCDs in terms of communication system availability. It was observed that overall the Recommendation ITU-R P.837-7 Annex 1 exhibited the best performance in estimating equivalent 1-minute integration time rain rate statistics. Furthermore, it was found that the lowest level of inter-annual variability of the rainfall rate was observed in the western zone adjacent to the Andes Cordillera of Ecuador. [ABSTRACT FROM AUTHOR]

As the throughput requirements for wireless communication links keep rising, characterization of sub-THz radio channels is necessary. This paper presents the results of a radio channel measurement campaign in which we characterize the full D-band, ranging from 110 to 170 GHz, for distances up to 5 m. We measured penetration and reflection loss for a broad set of materials that are commonly used in indoor environments, including wood, glass, acrylic, and concrete, and measured corner diffraction losses. Measurements over the full 60 GHz bandwidth reveal frequency selectivity as well as a periodic variation of both penetration and reflection loss, which is attributed to the thin film effect. Based on measurements in a conference room and outdoors, we create a spatio-temporal channel model for the conference room and an outdoor path loss model. The channel models show that the radio channel is extremely sparse to multipath components, containing only a Line-of-Sight path with signal attenuation close to path loss in free space, and first-order reflections with a measured attenuation that corresponds to the sum of the path and reflection loss.

Recent research has indicated considerable potential for millimeter-waves in copper access, with data-rate estimations up to 1 Terabit per second for a reach of 100 m. This line of research exploits millimeter-waves and their corresponding higher-order propagation modes inside the twisted pair cable binder. Unlike the conventionally used transmission-line mode (currents through copper wires), the approach relies on the copper and plastics present in these cables to form a low-loss waveguide. Here, we take a closer look at the potential of millimeter-wave propagation in twisted pair cables by refining the idealized assumptions, used by Cioffi et al., and identifying the limiting factors. To this end, we introduce the concept of transformation optics as an efficient method of calculating the propagating modes on a twisted pair. Leveraging this technique allows us to calculate modal propagation using realistic material parameters, exposing an important trade-off between loss and confinement. Our modeling results yield achievable data rates that are orders of magnitude lower than those achieved under idealized assumptions. According to our results, 1 Terabit per second can be achieved up to a distance of about 10 m over a twisted-pair with a plastic sheath.

A dual-polarized endfire array is presented in this article for millimeter application. The substrate integrated mode-composite transmission line is introduced to exciting the dual-polarized radiation. Specially, the horizontal polarization is excited by the transverse electromagnetic (TEM) mode, whereas the vertical polarization is based on the TE10 mode. Two metal blocks sandwich the substrates to form a sandwich structure, and an open-ended slot is designed on the block edge to construed complementary sources radiation. Benefiting from the wideband feature of complementary sources, the proposed dual-polarized endfire array achieved a considerable bandwidth performance of 26.9% (24.8–32.5 GHz) based on the standard that both the voltage standing wave ratios of the two ports are less than 2. In terms of the key factor of dual-polarized antenna and isolation, measured results show a high port isolation of over 36 dB and a cross-polarization discrimination rate of over 30 dB. The excellent dual-polarized performance gives the proposed endfire array the potential of application in millimeter-wave mobile communications. [ABSTRACT FROM AUTHOR]

For outdoor millimeter-wave mobile radio systems, the main service area is expected to be in line-of-sight (LOS) and semi-line-of-sight (SLOS) environments. The modeling of propagation in a mixed LOS/SLOS environment is thus important in system design. For modeling propagation in an SLOS environment, the application of the Loo model developed for land mobile satellite service with roadside shadowing is promising because this model reflects the physical mechanism of radio propagation. However, the model is inconvenient in practice because its calculation involves numerical integration over an infinite range. In this article, we approximate the Loo distribution using three basic distributions, namely the Nakagami-Rice distribution (or Rician distribution), Nakagami-m distribution, and lognormal distribution. Based on the evaluation results, we propose the use of the Nakagami-m distribution in place of the Loo distribution. We demonstrate the conversion of Loo distribution parameters to Nakagami-m distribution parameters. Finally, we examine a multistate model that expresses environments composed of LOS, SLOS, and non-LOS conditions. [ABSTRACT FROM AUTHOR]

A compact photonically-driven wireless emitter based on a Uni-Traveling-Carrier photodiode (UTC-PD) which directly connects to a short asymmetrical inductive dipole (SAID) antenna is presented. The design exploits the dependence of the UTC-PD output impedance with the reverse bias voltage to provide maximum power transfer via conjugate impedance matching at different operative frequencies within the Ka band (26.5–40 GHz) with 6 dB antenna directivity and 1 GHz 10 dB return loss channel width. Electro-optical transmission measurements confirm that the photodiode responsivity is maintained throughout the whole voltage swing used for reconfigurability. • A wireless emitter with UTC photodiode directly connected to a planar SAID antenna. • Ka-band simulations and measurements show 6 dB directivity and 1 GHz bandwidth. • Antenna geometry with independent adjustment of real and imaginary impedance parts. • Conjugate-impedance matching through optimization of antenna geometry. • Frequency reconfigurability with voltage control of the photodiode bias. • Optimum photodiode responsivity within the whole bias voltage swing. [ABSTRACT FROM AUTHOR]

Satisfying the exponential data growth is one of the main challenges for the design of future wireless networks. Given the abundant spectrum availability at millimeter-wave bands, exploiting these frequencies is a natural choice. WiGig (also known as 60 GHz WiFi) allows multi-gigabit transmissions in short range wireless links. The maximum data transfer rates occur in line of sight (LOS) connections. Given the small operating wavelength, obstructing the LOS causes significant power losses, severely impacting the attainable throughput of each user. This article presents empirical results to parameterize typical small-scale fades caused by pedestrians when blocking the LOS, in areas where a WiGig access point serves indoor users. Our results show that fades can be as large as 21 dB, in average. Furthermore, burst of fades are common, lasting up to 5200 ms in 90% of the observed cases.

The miniaturization of transceivers and antennas is enabling the development of Wireless Networks-on-Chip (WNoC), in which chip-scale communication is utilized to increase the computing performance of multi-core/multi-chip architectures. Although the potential benefits of the WNoC paradigm have been studied in depth, its practicality remains unclear due to the lack of a proper characterization of the wireless channel at the chip scale and across the spectrum, among others. In this paper, the state of the art in wave propagation and channel modeling for chip-scale communication is surveyed. First, the peculiarities of WNoC, including the design drivers, architecture, environment, and on-chip electromagnetics are reviewed. After a brief description of the different methods to characterize wave propagation at chip-scales, a comprehensive discussion covering the different works at millimeter-wave (mmWave), Terahertz (THz) and optical frequencies is provided. Finally, the major challenges in the characterization of the WNoC channel and potential solutions to address them are discussed, providing a roadmap for the foundations of practical WNoCs.

We demonstrate experimentally a bandwidth-reconfigurable mmWave Fiber Wireless (FiWi) fronthaul bus topology for spectrally efficient and flexibly reconfigurable 5G Centralized-Radio Access Networks (C-RAN). The proposed fronthaul architecture includes four 1 Gb/s Intermediate Frequency over Fiber (IFoF) channels that can be flexibly allocated among two in-series Reconfigurable Optical Add/Drop Multiplexer (ROADM) integrated nodes, supporting in total 8 V-band 32-element Phased Array Antenna (PAA) terminals. The ROADM was fabricated as an integrated photonic device exploiting the ultra-low loss Si3N4 TriPleX waveguide integration platform and an architectural layout based on cascaded MZI interleavers. The device has flat top response of 32.5 GHz with a Free Spectral Range (FSR) of 100 GHz and fiber-to-fiber losses of 5 dB, while the V-band PAA supports analog RF beamsteering capabilities within a 90°-sector and 1m wireless distance. Each of the FiWi links carries a 250 MBd QAM16 waveform enabling a total of 1 Gb/s rate per end user beam, complying with the 5G Key Performance Indicator (KPI) user-rate requirement. Bandwidth-reconfigurability is experimentally demonstrated by selectively dropping channels either at the first or at the second ROADM node, allowing in this way the bandwidth allocation to be flexibly defined between two different network segments. Both uplink and downlink performance are experimentally validated for different ratios of bandwidth allocation among the two nodes, revealing Error Vector Magnitude (EVM) values that meet the respective 3GPP signal quality specifications. The two-stage FiWi IFoF/mmWave fronthaul bus topology, based on a miniaturized, integrated, low loss Si3N4 ROADM and supporting high-capacity wireless beamsteering capability can form a promising roadmap towards flexible and reconfigurable 5G C-RAN architectures. [ABSTRACT FROM AUTHOR]

Holographic communication is intended as a holistic way to manipulate, with unprecedented flexibility, the electromagnetic field generated or sensed by an antenna. This is of particular interest when using large antennas at high frequency (e.g., at millimeter-wave or terahertz), whose operating condition may easily fall in the Fresnel region (radiating near-field), where the classical plane wave propagation assumption is no longer valid. This article analyzes the optimal communication involving large intelligent surfaces realized, for example, with metamaterials as possible enabling technology for holographic communication. It is shown that traditional propagation models must be revised and that, when exploiting spherical wave propagation in the near-field region, new opportunities are opened, for example, in terms of feasible orthogonal communication channels. [ABSTRACT FROM AUTHOR]

The super-high-frequency band is used in the fifth-generation (5G) mobile communication system, and the introduction of massive multiple-input–multiple-output (MIMO) to 5G is being considered. In an environment with substantial propagation loss, such as that in the case of millimeter waves, massive MIMO can realize beamforming according to the position of terminal stations. Therefore, it is important to understand the direction of arrival of millimeter waves. In this letter, we clarify the relationship between power, delay time, and direction of arrival while focusing on the horizontal direction, using a 48-element massive array in the 20 GHz band in urban Japan. In addition, we obtain direction-of-arrival (DoA) estimation results using an iterative reduction threshold algorithm (ISTA), which is based on compressed sensing. It is shown that the dominant path can be estimated by using the ISTA even with approximately five elements. [ABSTRACT FROM AUTHOR]

Most outdoor-to-indoor (O2I) propagation studies in millimeter-wave (mmWave) frequency bands have been focused on power loss characteristics such as building penetration and building entry losses. To provide robust traffic services, knowledge of the multipath propagation characteristics is required in the design and evaluation of mmWave 5G systems. In this paper, we investigate the multipath dispersion characteristics of O2I propagation in the angular and delay domains. This study is based on field measurement data conducted at 32 GHz in two different office building sites: traditional building and thermally-efficient building. To derive reliable statistics, we collected measurement data at as many points as possible throughout the building areas (including various environments such as open-space offices, conference rooms, classical closed-room offices, computer labs, halls, corridors, etc). By analyzing power angular and power delay profiles, we found that there were two dominant signal directions and we considered how this property can be utilized in mmWave beamforming. By comparing the angular and delay spreads, we found that the angular and delay statistics do not show any significant differences between the two building measurements. We believe that the property of dominant beam directions, as well as the dispersion statistics (angular and delay spreads), will be useful in the 5G system design.

The time-variant vehicle-to-vehicle radio propagation channel in the frequency band from 59.75 to 60.25 GHz has been measured in an urban street in the city center of Vienna, Austria. We have measured a set of 30 vehicle-to-vehicle channel realizations to capture the effect of an overtaking vehicle. Our experiment was designed for characterizing the large-scale fading and the small-scale fading depending on the overtaking vehicle's position. We demonstrate that large overtaking vehicles boost the mean receive power by up to 10 dB. The analysis of the small-scale fading reveals that the two-wave with diffuse power (TWDP) fading model is adequate. By means of the model selection, we demonstrate the regions where the TWDP model is more favorable than the customarily used the Rician fading model. Furthermore, we analyze the time selectivity of our vehicular channel. To precisely define the Doppler and delay resolutions, a multitaper spectral estimator with discrete prolate spheroidal windows is used. The delay and Doppler profiles are inferred from the estimated local scattering function. Spatial filtering by the transmitting horn antenna decreases the delay and Doppler spread values. We observe that the RMS Doppler spread is below one-tenth of the maximum Doppler shift 2f v/c. For example, at 60 GHz, a relative speed of 30 km/h yields a maximum Doppler shift of approximately 3300 Hz. The maximum RMS Doppler spread of all observed vehicles is 450 Hz; the largest observed RMS delay spread is 4 ns.

In this paper, a novel form of the folded normal (FN) distribution has been proposed to model the small-scale fading in wireless communications. From a multiple-input multiple-output (MIMO) measurement campaign conducted in a lab environment with the line-of-sight (LOS) conditions at both the 60 and the 94 GHz bands, the authors obtain the parameters of the Rician, FN, and k-μ distributions. These parameters have been calculated by using the least square (LS) approximation and with techniques of statistical inference. The FN distribution provides the best fitting to the experimental results using the Kolmogorov-Smirnov (K-S) test for the inferred estimators with values of the fulfillment of 100% and 69.82% at the 60 and 94 GHz bands, respectively, for a significance level of 1%.

Extending the frequency range of the Walfisch‐Bertoni (W‐B) model, which is a representative theory‐based model, was investigated. To extend the W‐B model, three changes to the original W‐B model were made: (i) remodeling over rooftop path, (ii) introducing a slant path, and (iii) modeling of multiple reflections between buildings. To validate the proposed model, propagation loss predicted by the model was compared with measurement results. Comparison with the measurement results shows that root mean square errors of propagation loss predicted by the proposed model are 5.8 dB for radiowave frequency of 2.2 GHz, 6.6 dB for 5.2 GHz, and 3.3 dB for 26.4 GHz. It is therefore concluded that the proposed model has can achieve high estimation accuracy for all measured frequency bands. Key Points: Extending the frequency range of the Walfisch‐Bertoni (W‐B) model, which is a representative theoretical model, was investigatedTo extend the W‐B model, three changes to the original W‐B model were madeTo validate the proposed model, propagation loss predicted by the model was compared with measurement data [ABSTRACT FROM AUTHOR]

In modern day communication systems, the massive MIMO architecture plays a pivotal role in enhancing the spatial multiplexing gain, but vice versa the system energy efficiency is compromised. Consequently, resource allocation in-terms of antenna selection becomes inevitable to increase energy efficiency without having any obvious effect or compromising the system spectral efficiency. Optimal antenna selection can be performed using exhaustive search. However, for a massive MIMO architecture, exhaustive search is not a feasible option due to the exponential growth in computational complexity with an increase in the number of antennas. We have proposed a computationally efficient and optimum algorithm based on the probability distribution learning for transmit antenna selection. An estimation of the distribution algorithm is a learning algorithm which learns from the probability distribution of best possible solutions. The proposed solution is computationally efficient and can obtain an optimum solution for the real time antenna selection problem. Since precoding and beamforming are also considered essential techniques to combat path loss incurred due to high frequency communications, so after antenna selection, successive interference cancellation algorithm is adopted for precoding with selected antennas. Simulation results verify that the proposed joint antenna selection and precoding solution is computationally efficient and near optimal in terms of spectral efficiency with respect to exhaustive search scheme. Furthermore, the energy efficiency of the system is also optimized by the proposed algorithm, resulting in performance enhancement of massive MIMO systems. [ABSTRACT FROM AUTHOR]

Ubiquitous multicore processors nowadays rely on an integrated packet-switched network for cores to exchange and share data. The performance of these intra-chip networks is a key determinant of the processor speed and, at high core counts, becomes an important bottleneck due to scalability issues. To address this, several works propose the use of mm-wave wireless interconnects for intra-chip communication and demonstrate that, thanks to their low-latency broadcast and system-level flexibility, this new paradigm could break the scalability barriers of current multicore architectures. However, these same works assume 10+ Gb/s speeds and efficiencies close to 1 pJ/bit without a proper understanding of the wireless intra-chip channel. This paper first demonstrates that such assumptions do not hold in the context of commercial chips by evaluating losses and dispersion in them. Then, we leverage the system’s monolithic nature to engineer the channel, this is, to optimize its frequency response by carefully choosing the chip package dimensions. Finally, we exploit the static nature of the channel to adapt to it, pushing efficiency-speed limits with simple tweaks at the physical layer. Our methods reduce the path loss and delay spread of a simulated commercial chip by 47 dB and $7.3\times $ , respectively, enabling intra-chip wireless communications over 10 Gb/s and only 3.1 dB away from the dispersion-free case. [ABSTRACT FROM AUTHOR]

Composite materials have become indispensable in a wide variety of technical fields, where they are viewed as the key technological component. Due to their structural complexity, these materials are prone to errors while in the manufacturing process, thus non-destructive inspecting becomes a crucial step in the processing chain and further maintenance of said material. However, a tomographic characterization of these components is often only possible to a limited extent—a capability which is essential to exploit the full potential of this technology. Measurement systems based on millimeter waves (mmWs) have the potential to achieve exactly that, by providing valuable information on the internal structure of such components. Yet, these non-destructive and non-contact methods have not found wide usage in practical applications. One reason for this is that the effects composite materials have on the propagation behavior of mmW signals have not been a major subject of study in the past. Therefore, a model for predicting the propagation properties of mmW signals in composite materials is presented here. Based on coupled wave analysis, the propagation of arbitrary electromagnetic signals in composite materials can be simulated. These results can be directly incorporated into the design of respective measurement systems. The introduced model is verified through a comparison of simulation and measurement results, obtained via a focused frequency modulated continuous wave (FMCW) radar, operating in the $H$ -band (220–325 GHz), directed at glass fiber reinforced plastic samples. [ABSTRACT FROM AUTHOR]

In this letter, we present the design, fabrication, and characterization of a 3-D photonic crystal (PhC) waveguide based on an optimized woodpile structure operating in the millimeter-wave band. By carefully adjusting the size and shape of the air defect, a silicon electromagnetic bandgap (EBG) woodpile waveguide can be created: this dielectric waveguide supports a well-confined TE10-like mode. Numerical results for this structure have been obtained using the finite element method (FEM) simulation software Ansys HFSS and present very good agreement with the measured ones. [ABSTRACT FROM AUTHOR]

Wireless electromagnetic detection of non-visible processes is a vital challenge when visual signals are difficult to decipher or blocked, such is the case in pipelines, chemical reactions, or the human body. To guide the design of future microwave resonator sensors, investigative experiments into resonator sensitivity, sensing distance, and RFID array alignment were performed. A horn antenna reader was coupled to a singular flexible ring resonator as well as a flexible ring resonator array with a measured $S_{11}$ notch frequency of 2.6 – 2.9 GHz. The experimental results closely compared to simulation and the computer model illustrated the detection of an introduced material around the high E-field regions of the coupled ring tag. In the fabricated circuit, liquids in a microfluidic channel are detected by a notch frequency and amplitude variation of 300 MHz and −30 dB, respectively, which can be matched with simulations to determine the materials’ permittivity. Other application-based requirements are also investigated such as the sensing range of the antenna-tag structure (measured up to 20 cm), the small size of the sensing tag (9 square cm) and the ability to detect through material barriers. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) and millimeter wave communications are key technologies for the fifth-generation of cellular networks and beyond, and the coexistence of these two techniques is critical. This paper characterizes the system performance through the outage probability and achievable downlink rate for large-scale millimeter wave NOMA networks by using stochastic geometry. In order to reflect spatial randomness, we consider homogeneous Poisson point processes to model the base stations and user equipments. Moreover, blockages which affect the channel characteristics, power allocation based on the combined channel gain, and imperfections in the successive interference cancellation are considered. The aggregate co-channel interference at a user is characterized based on the moment generating function. Finally, the outage probability and downlink rate are derived for a two-user NOMA scenario under two user-base station association schemes: 1) closest base station association and 2) closest line-of-sight base station association. It is seen that using NOMA under millimeter wave channels increases the achievable downlink rate while keeping the performance impact on individual users low, and that the closest line-of-sight base station association scheme is comparatively advantageous. Moreover, a dense base station deployment generally improves the performance further. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel real-time multiple-input multiple-output (MIMO) channel sounder for the 28 GHz band. Until now, most investigations of the directional characteristics of millimeter-wave channels have used mechanically rotating horn antennas. In contrast, the sounder presented here is based on a phased array structure that performs fast electronic steering of the beams in the horizontal and vertical domains. This approach drastically shortens the measurement times for measurements that are directionally resolved both at the transmitter (TX) and the receiver (RX), and the measurement time per location is reduced from minutes or hours to milliseconds. This not only enables measurement of more TX–RX locations for a better statistical validity but also allows to perform directional analysis in dynamic environments. The sounder also has high phase stability, which, in conjunction with the short measurement time, leads to a low phase drift between TX and RX. This in turn enables phase-coherent sounding of all beam pairs even when TX and RX have no cabled connection for synchronization, and thus avoids any delay ambiguity. Furthermore, the phase stability over time enables complex RX waveform averaging to improve the signal-to-noise ratio during high path loss measurements. The paper discusses the system design as well as the measurements performed for verification of the sounder performance. Furthermore, we present sample results from double directional measurements in dynamic environments. [ABSTRACT FROM AUTHOR]

In this paper, we propose a model for the effect of misalignment of antennas due to mechanical vibrations and experimentally validate its accuracy in a Ka-band (26-40 GHz) transmission link. Our approach provides a valuable tool that is analytically tractable and physically simple to implement. To highlight the applicability of the model, a setup based on a centralized radio access network (C-RAN) transmitting and receiving wireless signals in the Ka-band is implemented. With this tool, the robustness of 5G networks to antenna misalignments can be evaluated in terms of bit-error rate. We show how the presence of misalignment in this type of systems induces an error floor observable in the bit-error-rate performance. A simple static decision threshold is implemented taking into account the amount of displacement and, directly related to that factor, on the expected number of fades per unit time. The closed-form expressions derived through this paper are in perfect agreement with the experimental measurements taken from the implemented system. [ABSTRACT FROM AUTHOR]

In this paper, the impact of considering diffuse multipath components at mm-wave frequencies as well as the significance of selecting appropriate diffuse scattering model parameters is shown. Two different diffuse models, namely, the Lambertian model and the directive model, have been parameterized for several materials typically present in indoor environments. These models are formulated to embed the diffuse scattering phenomenon easily into ray tracing tools. The estimation of the parameters has been performed by comparing measurements and simulations using the models. Once the best fitting parameters have been estimated, they are included in the diffuse components simulation section of a general ray tracing tool. This tool has been used to simulate the power delay profile at 60 GHz in an indoor scenario, including single and double bounce diffuse components. Thanks to the estimated model parameters, the wireless channel at the 60-GHz band can be analyzed, including the diffuse scattering phenomenon, without the need for any previous measurement or simulation. Thus, the channel analysis with ray tracing tools, including dense components, becomes easier, faster, and more reliable.

Differential Faraday rotation of the linear polarization of millimeter-wave (mmW) Gaussian beams has been observed from a magnetoelastic material system consisting of a silicone membrane that was infused with aligned nickel microparticles, mounted to a piezoelectric annulus, and immersed in a static magnetic field. The piezoelectric crystal was driven near its radial mode of resonance by an ac voltage signal so as to periodically stretch the membrane about the axis of mmW propagation. The stretching modulated the distribution of nickel microparticles and resulted in a change in magnetic properties of the material, specifically the effective Verdet constant. A customized, quasi-optical apparatus was phase locked with the ac driving signal to determine the difference in Faraday rotation due to the stretched and un-stretched states of the membrane. [ABSTRACT FROM AUTHOR]

Satellite communications require more bandwidth due to the necessity of increasing the capacity of communication channels and bandwidth to end-users. As a result, looking for new bands is required in the electromagnetic spectrum including millimeter and sub-millimeter wavelengths. Recent technological developments made the extremely high frequencies (EHF) above 30 GHz as a candidate for wireless applications such as the fifth generation (5G) of mobile communications, high resolution radars, and remote sensing. The EHF communication systems are becoming more and more commercial, cheap, and compact. However, the fact that the atmospheric medium is not completely transparent to millimeter waves requires considerations of the frequency selective absorption and dispersion effects emerging in this band. These phenomena affect also remote sensing in the millimeter and sub-millimeter waves (the terahertz frequencies). The atmospheric effects on the propagation of millimeter and sub-millimeter wave transmission from land to satellite are discussed. It is shown that not only atmospheric absorption plays a significant role on the received signal strength but also the refraction index of the atmospheric medium. The inhomogeneous refractivity causes the beam to "bend" along the propagation path, and it may even "miss" its destination. This phenomenon should be considered in the design of a link operating in extremely high frequencies involving highly directive antennas. [ABSTRACT FROM AUTHOR]

Highlights • Wideband measurements are conducted at 28 and 38 GHz using a 1 GHz RF bandwidth. • Path loss models have been investigated in indoor environment. • At 28 GHz reflections reduce the path loss till 12 dB/decade compared to FSPL model. • At 38 GHz reflections increase the path loss till 8 dB/decade compared to FSPL model. • CH3 has high RMS delay spread of 120 ns and 250 ns for 28 GHz and 38 GHz, respectively. Abstract To meet 5G requirements, industries are looking forward to a new set of frequency allocation in the millimeter spectrum space, where there is huge amount of bandwidth for wireless gigabit communications. In this paper, the statistics of large-scale path loss and time dispersion parameters are investigated based on ultra-wideband measurements using a steerable directional horn antenna at transmitter (Tx) and omni-directional antenna at the receiver (Rx). The measurement was conducted in a dining room line-of-sight (LOS) scenario, which represents a typical closed-plan for in-building communication. The single-frequency, multi-frequency directional and omni-directional large-scale path loss models are evaluated at 28 GHz and 38 GHz bands based on data acquired from unique Tx and Rx antennas with combination pointing angles. The results show that the large-scale path loss models for indoor propagation developed in this paper is less complex, and yet more physically-based than those used in the third-generation partnership project (3GPP) systems, which involve additional model parameters but yield less accurate results. The time dispersion statistics for mmWave systems using directional antennas and omni-omni antennas configuration at both Tx and Rx are presented for co-polarization scenarios. We show that the multipath root mean square delay spread can be reduced when Tx and Rx antenna are pointed to each other, which results in the strongest received power. [ABSTRACT FROM AUTHOR]

We have designed and built an optically isolated millimeter-wave detection system to prevent interference from a nearby, powerful, 2.45 GHz microwave source in millimeter-wave propagation experiments in the TORoroidal Plasma EXperiment (TORPEX). A series of tests demonstrates excellent system noise immunity and the ability to observe effects that cannot be resolved in a setup using a bare Schottky diode detector. [ABSTRACT FROM AUTHOR]

The exponential increase in wireless data transmission from smartphones has led to the saturation of the sub-6-GHz bands where cellular networks have operated to date forcing providers to migrate to the millimeter-wave (mmWave) regime for 5G. Although available channel bandwidths will grow from tens of megahertz to several gigahertz, propagation loss will be substantially higher. To compensate the link budget, phased array antennas with 20 dBi40-dBi gain will be employed at the base and mobile stations. Since beamwidth is inversely proportional to gain, the resultant pencilbeams will be only 315 wide and thus must be electronically steered to ensure that they are aligned between the stations. The high directionality of 5G systems will fundamentally change channel propagation models and channel sounding systems and techniques used to measure the model properties. The National Institute of Standards and Technology is on the forefront of defining that change. In this article, we provide an overview of mmWave channel sounding through three types of systems: switched array, virtual array, and phased array, at 28 GHz, 60 GHz, and 83 GHz. In addition, we describe how mmWave channel models, for path loss, dispersion, multipath tracking, Doppler spread, and blockage, differ from sub-6-GHz models, substantiated by some of our most recent results. [ABSTRACT FROM AUTHOR]

Massive MIMO is considered as a promising technology to meet the explosive growth of data demand in fifth generation systems. To develop massive MIMO systems and industry standards, it is important to conduct thorough investigation of the underlying channel characteristics. This article provides an overview of the concept and ongoing research in the field of massive MIMO propagation channels, including the key differences from conventional MIMO, recent advances in channel measurement campaigns, and the channel modeling approaches. Furthermore, we also point out several key challenges and open issues for future research. [ABSTRACT FROM AUTHOR]

Fifth generation cellular systems will be deployed in the microwave and millimeterwave (mmWave) frequency bands (i.e., between 0.5100 GHz). Propagation characteristics at these bands have a fundamental impact on each aspect of the cellular architecture, ranging from equipment design to real-time performance in the field. While we have a reasonable understanding of the propagation characteristics at microwave (< 6 GHz) frequencies, the same cannot be said for mmWave. This article explains key differences in the propagation characteristics between the microwave and mmWave bands, and further gives examples of how these differences impact 5G system design. [ABSTRACT FROM AUTHOR]

Utilization of drones as aerial access points (AAPs) is a promising concept to enhance network coverage and area capacity promptly and on demand. The emerging millimeter-wave (mmWave) communication technology may in principle deliver higher data rates, thus, making the use of AAPs more effective. By extending the conventional (planar) stochastic geometry considerations, we construct a novel three-dimensional model for drone-based mmWave communication that captures the high directionality of transmissions as well as the random heights of the communicating entities. Choosing signal-to-interference ratio as our primary parameter of interest, we assess system performance with an emphasis on the impact of the “vertical” dimension in aerial mmWave connectivity. We also demonstrate that accurate performance assessment is only possible with simplified models for certain ranges of input parameters. [ABSTRACT FROM AUTHOR]

Mm-wave offers a sensible solution to the capacity crunch faced by 5G wireless communications. This paper comprehensively studies physical layer security in a multi-input single-output mm-wave system, where multiple single-antenna eavesdroppers are randomly located. Concerning the specific propagation characteristics of mm-wave, we investigate two secure transmission schemes, namely maximum ratio transmitting beamforming and artificial noise (AN) beamforming. Specifically, we first derive closed-form expressions of the connection probability for both schemes. We then analyze the secrecy outage probability in both non-colluding eavesdroppers and colluding eavesdroppers scenarios. Also, we maximize the secrecy throughput under a secrecy outage probability constraint, and obtain optimal transmission parameters, especially the power allocation between AN and the information signal for AN beamforming. Numerical results are provided to verify our theoretical analysis. We observe that the density of eavesdroppers, the spatially resolvable paths of the destination and eavesdroppers all contribute to the secrecy performance and the parameter design of mm-wave systems. [ABSTRACT FROM PUBLISHER]

In this paper, a channel measurement campaign is introduced, which utilizes direction-scan-sounding to capture the spatial characteristics of 28-GHz wave propagation channels with 500-MHz sounding bandwidth in office environments. Both line-of-sight and non-line-of-sight scenarios were considered. Measurements were performed by fixing a transmit pyramidal horn antenna, and rotating another one in the receiver site at 10° steps in azimuth. The antenna outputs are viewed as array signals, and a space-alternating generalized expectation-maximization (SAGE) algorithm is applied to estimate delay and angular parameters of multipath components. Benefiting from high resolution achieved by using the SAGE and deembedding of antenna radiation pattern and system responses, more multipath clusters with less spreads in delay and azimuth are found per channel compared with existing works on 28-GHz propagation. The statistics of channel parameters extracted here constitute a preliminary stochastic multipath-cluster spatial channel model.

The coexistence of microwave and millimeter-wave technologies becomes the inexorable trend of future wireless communication systems. The corresponding components of the system are required to cover these two frequency bands simultaneously. However, it is difficult for the existing dual-band antenna configurations to achieve a frequency ratio larger than 3. In this paper, a novel topology is proposed to solve this problem. For the desired dual-band operation, a signal routing approach is proposed to guide the microwave/millimeter signals to the specific elements, respectively. The classical aperture coupling mechanism is deliberately utilized to block the millimeter-wave signal from feeding to the microwave antenna element and route the millimeter-wave signal into the millimeter-wave antenna element. Meanwhile, the substrate- integrated waveguide (SIW)-based millimeter-wave antenna element has the high-pass nature to reject the microwave signal. Therefore, the antenna elements for microwave and millimeter-wave bands can be designed separately with a high flexibility. First, a dual-band antenna was implemented to support 5.8 and 30 GHz simultaneously by integrating an annular-ring antenna element and an SIW slot antenna element. Furthermore, different radiation properties at the two bands can be easily realized owing to the high flexibility of the proposed approach. For validation, these two antennas were fabricated and measured. [ABSTRACT FROM PUBLISHER]