Accurate channel models are crucial for designing and evaluating communication systems. As carrier frequencies and array apertures grow, models must account for near-field spherical wavefronts and spatial non-stationarity, departing from the conventional far-field, planar-wave geometry-based stochastic models (GBSMs) used in 3GPP. This work addresses channel characterization and modeling in the near-field via a measurement campaign in the upper mid-band (9.7-10.7 GHz) using a virtual uniform linear array (VULA) with 140 elements having an effective physical aperture of around 2 m. Subsequently, we adopt a recent array-domain framework to characterize near-field spatial non-stationarity by analyzing how channel parameters, such as received power, large-scale fading, and delay spread, evolve across the array aperture. We also evaluate the fidelity of these models by comparing them with our measurements.

Propagation measurements at sub-terahertz (subTHz) radio frequencies are essential for accurate radio channel characterization and for supporting future communication and sensing applications. This paper presents sub-THz dual-band channel characterization results based on double-directional measurement campaigns conducted in a symmetric large hall. The channel frequency responses (CFR) were recorded at multiple transmitter-receiver location combinations. The frequencydependent channel characteristics are analyzed in terms of path loss, delay spread, angular spread, and Rician K-factor. The number of multipath components (MPCs) observed in this environment is very small at both frequencies, with mean values below three. Except for the path loss exponent and Kfactor, the fitting results show that the mean delay spread and angular spread both decrease with increasing frequency, but the reduction is not significant. In addition, we also investigate the impact of symmetrically placed transmitters on sub-THz channel characteristics.

Integrated Sensing and Communication (ISAC) is central to 6G networks, requiring accurate radar cross-section (RCS) modeling for reliable sensing. While monostatic RCS of simple objects is well studied, RCS characterization of autonomous (unmanned) aerial vehicles (AAV or UAV) remains limited due to complexity and cost, especially in bistatic settings. The Monostatic-Bistatic Equivalence Theorem (MBET) and its variants are often used to estimate bistatic RCS, but their validity remains uncertain for complex targets and wide frequency bands. This work investigates the applicability of MBET and its variants for AAVs in ISAC scenarios, assessing their effectiveness in predicting bistatic RCS under non-ideal conditions.

Accurate radar cross-section (RCS) modeling of sensing targets is essential for realistic channel characterization in integrated sensing and communication (ISAC) systems. This letter develops 3GPP-compliant statistical RCS models for autonomous aerial vehicles (AAVs) using monostatic and bistatic measurements acquired across multiple frequency bands (1.8 GHz-27 GHz) and bistatic angles (0(degrees) :15(degrees) :90(degrees) ) in both anechoic far-field and controlled indoor near-field environments. Standard biparametric distributions, including log-normal, Gamma, and Rician, are fitted to the measured RCS. Furthermore, a measurement-validated Gaussian-cluster representation is proposed as a geometry-based stochastic model to reproduce angular AAV RCS fluctuations in ISAC channel simulations. Finally, the fitted RCS models are applied to analyze the impact of target-induced scattering on ISAC path-loss.

To address the stringent requirements of full coverage and ultrahigh data rates in next-generation mobile communications, it is essential to leverage the coexistence of multiple radio frequency (RF) systems operating in well-separated frequency bands within precisely defined scenarios. In this context, an investigation of frequency- and environment-dependent channel characteristics by exploring the spatial and temporal correlations of multipath channels across different frequency bands and different environments is imperative. This article introduces a structural channel similarity index measure (CSIM) that holistically evaluates multiple multipath parameters between two channels, including amplitude, phase, delay, angle of arrival (AoA), and angle of departure (AoD). Based on extensive field measurement campaigns and ray tracing simulations conducted across both centimeter-wave (cmWave) and millimeter-wave (mmWave) bands in typical indoor and outdoor scenarios, the proposed CSIM is proven to effectively measure similarity from specific dimensions as well as the statistical distributions, and the similarities between channels across different frequencies and different environments are presented. Moreover, the feasibility of out-of-band information-assisted beam search, enabled by cross-band channel similarity, is also validated.

Many conventional radio channel models, such as 3GPP TR 38.901, assume far-field conditions and rely on the plane wave approximation. However, as antenna arrays grow in size and link distances decrease, near-field propagation effects become significant, particularly at sub-terahertz (THz) frequencies. This letter proposes an initial extension to the 3GPP channel model to incorporate near-field characteristics at these frequencies. The approach models both line-of-sight and non-line-of-sight paths using exact geometric distances. An image-theory-based method is introduced to model specular reflections. The extended model maintains consistency with the existing 3GPP framework while enhancing modeling accuracy in the near field.

The Industrial Internet of Things (IIoT) enables seamless connectivity between machines, sensors, and control systems, supporting automation, efficiency, and intelligence in modern factories. Terahertz (THz) communications provide ultrahigh bandwidth and fine spatial resolution required to meet these demanding needs. However, THz radio propagation in metal-rich industrial environments remains largely unknown. This paper presents comprehensive bidirectional channel measurements at 318 GHz conducted in representative industrial environments, i.e., a factory hall and a warehouse. The collected data are used for modeling and analysis to extract key channel characteristics, including the number of multipath components (MPCs), path loss, delay spread, and angular spread. The findings offer valuable insights for the practical deployment of THz communications in HoT scenarios.

Differentiable ray tracing-based radio propagation modeling is a powerful tool for learning material properties from channel measurements. Prior approaches rely on idealized, manually crafted triangle mesh models, which often lack smaller geometric details that become important at higher frequencies. In this paper, we perform differentiable ray tracing directly on a noisy point cloud created from RGB-D images, eliminating the need for handcrafted geometry. We optimize channel parameters using THz channel measurements collected at a center frequency of 318 GHz with a 4 GHz bandwidth. Our results demonstrate that the channel characteristics can be extracted well with available measurements and ray tracing. With the optimized parameters, we achieve a mean relative rms delay spread error of less than 5% and a mean absolute error for received power of about 0.36 dB at novel receiver locations.

The ultra-high data rates enabled by terahertz (THz) communications pave the way for the demanding requirements of industrial Internet of Things (IIoT) applications, making the investigation of THz channels in industrial environments a critical research topic. This paper presents a comprehensive statistical analysis of the propagation channel at 318 GHz in an industrial environment. In particular, a new clustering scheme is proposed for the sparsity observed in the multipath components (MPCs) of the measured channel. Furthermore, statistical analyses are conducted separately for the group of strong reflections, defined as primary clusters, and other propagation phenomena, defined as random clusters, in a rich-scattering environment. The results demonstrate that the large-scale parameters are predominantly influenced by these strong reflections. This study provides reliable support and guidance for subsequent THz stochastic channel modeling.

Wireless connectivity is set to be the foundation of industrial automation and next-generation factories. One of the key constraints of the IEEE 802.11 family, which includes Wi-Fi, is its struggle to deliver ultra-reliable and low-latency communications (URLLC) for industrial applications. Wi-Fi 8 ultra-high reliability (UHR) aims to address these challenges. Ensuring adequate coverage and minimizing interference will be essential to delivering UHR in factory settings. Looking beyond Wi-Fi 8, terahertz frequencies offer significant potential for supporting ultra-high data rates. Next-generation industrial environments will require the coordination of multiple frequency bands, ensuring robust, low-latency, and high-speed wireless communication for safe and efficient automation. In this study, directional and omnidirectional antennas are used in ray tracing simulations to evaluate signal coverage in a factory environment at 6.745 GHz, 60.48 GHz and 289.44 GHz.

To provide substantially high capacity, future 6G networks will be able to operate in higher frequency bands than current 5G networks. However, owing to the significant differences in channel characteristics between lower bands (<100 GHz) and subterahertz (sub-THz) band (i.e., 100-300 GHz), novel waveform and air interface design for sub-THz systems need to account for the radio channels observed by practical beam patterns. In this article, we investigate the beamforming impact on the characterization of angular and time dispersion based on extensive measured channel data at 142 GHz across multiple scenarios. A postprocessing method for analysis of beamforming impact on channel dispersion is proposed using measured propagation channel data. Since sub-THz radio links necessitate high antenna gains, we first find the potential beam directions from beamformed channels and then form single-beam and multibeam patterns toward desired directions under practical constraints. The angular spread of the beamformed channels observed by steered beams will be widened especially in line-of-sight scenarios. The beam-weighted radio channel is considered the basis of calculating time dispersion parameters, i.e., beam gains are multiplied by the measured propagation path gains before the analysis. Preliminary results show that the reduction of delay spread and maximum excess delay depends mainly on scenario, link distance, and used beamwidth, and partly on sidelobe level.

Sub-Terahertz (sub-THz), which encompasses a frequency range between 100-300 GHz, is anticipated to be an important element in the development of future sixth-generation (6G) communication systems due to its vast untapped bandwidth resource. Developing the realistic sub-THz channel model is essential for designing and deploying future 6G communication systems. We presented the channel measurements and characterization of a recent sub-THz channel measurement campaign conducted in an indoor hall scenario at sub-THz bands in this work. The channel measurement campaign was conducted with 55 transmitter (Tx)-receiver (Rx) deployment locations (including two pre-defined ‘L’-shape routes) covering the Tx-Rx distance range of [3, 58]m at 99-101 GHz using a phase-compensated long-range channel sounder. A channel parameter estimation algorithm is exploited to extract the multipath component (MPC) parameters. The composite channel parameters, i.e., path loss, delay spread, angular spread, and K -factor, are calculated and analyzed using the extracted MPC parameters. It is seen that the spreads of delay and angular and the K -factor statistically obey log-normal distributions and the normal distribution, respectively, and the fitting parameters are concluded for statistical modeling. An MPC trajectory tracking algorithm was also utilized to trace the MPC trajectories in the two routes. The MPC-level channel parameters were then investigated based on the trajectory results. The proposed 100 GHz channel model for the indoor scenario was also compared with the existing channel models. This work provides an accurate and comprehensive indoor channel characterization, filling the gap in statistical channel models for this frequency band.

The sixth generation (6G) wireless communication nowadays is seeking a new spectrum to inherit the pros and discard the cons of sub-6 GHz, millimeter-wave (mmWave), and sub-terahertz (THz) bands. To this end, an upper mid-band with a Frequency Range (FR) spanning from 7 GHz to 24 GHz, also known as FR3, has emerged as a focal point in 6G communications. Thus, as an inevitable prerequisite, a comprehensive investigation encompassing spectrum utilization and channel characteristics is the first step to exploiting potential applications and prospects of using FR3 in the 6G ecosystem. In this article, we provide FR3 synergies with emerging technologies including non-terrestrial network (NTN), massive multi-input multi-output (mMIMO), reconfigurable intelligent surface (RIS), and integrated sensing and communications (ISAC). Furthermore, leveraging ray-tracing simulations, our investigation unveils the similarity of channel characteristics in FR3 with other FRs. The analysis of RIS-aided communication shows the insight of higher spectral efficiency achieved in FR3 compared to other FRs when using the same RIS size. Finally, challenges and promising directions are discussed for wireless systems in FR3.

Wireless connectivity in the subterahertz (sub-THz) band, spanning from 100 GHz to 300 GHz, is envisioned as an enhanced feature of 6G and beyond. Due to significant propagation losses at these frequencies, the transmission of sub-THz signals relies heavily on high antenna directivity, realized by beamforming. In this article, we present a newly developed sub-THz stored channel model, and perform a realistic evaluation of the impact of beamforming on sub-THz link establishment and data transmission. Unlike the propagation channel between the transmitting and receiving antennas, the radio channel is observed by a pair of beams. Incorporating the impact of beamforming into measured sub-THz propagation channel data enables to gain insights into the key factors that determine, among others, sub-THz beam alignment strategy and waveform design, ultimately enhancing spectral efficiency.

This paper investigates the diffraction mechanism at D-band and its polarization dependency in a concise way. The results are compared with the conventional knife edge diffraction (KED) model. A thin metal, laminated board, and a slab of absorber are used as blockage for characterization. Logarithmic fit functions are provided to demonstrate the impact of material properties in diffraction. In most of the cases, KED model provided a good agreement with measurements. The findings also suggest that the XPR is preserved in diffraction for both co-polarized and cross-polarized scenarios.

The prospect of offering huge amounts of available bandwidth to achieve extremely high data rates makes sub-terahertz (sub-THz) communication seen as a key enabler for 6G use cases requiring extreme throughputs on the order of 10s or 100s of Gbps. The design and planning of wireless communication systems are affected by the radio channels in which they will operate. Physical modeling of sub-THz channels requires sufficient channel-sounding data collected across multiple frequency bands and environments for statistical analysis. In this paper, we present a modular correlation-based sub-THz channel sounder using commercial off-the-shelf (COTS) instruments. It can be easily scaled for multi-band channel measurements by using different frequency extenders while sharing the same baseband units. The validation measurements at 150 GHz are conducted in an indoor corridor using the proposed sounder, together with the ray-tracing simulation results for performance validations in identical settings.

To enable a wide range of joint communications and sensing applications, future channel models must support dynamic variations of the propagation environment. Moreover, when discovering sensing applications, it is essential to connect physical objects and actions to the radio channel characteristics. In this paper, we perform computer vision (CV) aided automatic mapping and showcase that channel measurements can be linked to the dynamic actions and objects in the environment, thus supporting sensing applications. The proposed method employs a vector network analyzer-based channel measurement system operating at 300 GHz and a camera to enable CV for tracking the object in the radio link. Using human hand as the blockage object, the CV-extracted coordinates and the measured channel responses are combined to generate radio channel footprints for different hand movements.

The transition to higher frequency bands, such as millimeter-wave (mmWave) and terahertz (THz), will be capitalized in the long term for future wireless communications. One of the challenges relates to rapid establishment of mmWave/THz links with low beam training overhead due to highly directional transmission. A promising solution is to take advantage of the coexistence of sub-6 GHz, mmWave, and THz wireless networks and to use out-of-band spatial information for enabling fast beam search. Success depends on the spatial similarity of radio channels across different frequency bands. In this article, we promote a feasibility study of low-frequency spatial channel information assisted high-frequency beam search from a radio channel point of view. We develop a multi-band channel similarity measure of desired beam directions extracted from radio channels, which is obtained via filtering propagation paths by different beam patterns at different frequencies. Measurement-and ray-tracing-based evaluations across multiple frequencies and environments are performed, which prove the usability of out-of-band information aided beam search strategy in a line-of-sight (LoS)-dominated scenario and even in a non-LoS scenario. Finally, we discuss the challenges associated with exploiting spatial channel similarity.

A novel millimeter-wave massive MIMO system using asymmetric transceiver, i.e., unequal number of transmitting (Tx) and receiving (Rx) radio frequency chains, is expected to maintain the advantages of conventional fully digital beamforming architectures, but partly reduce the implementation cost and power consumption. However, uplink and downlink radio channels may become non-reciprocal due to the different dimensions of Tx-Rx antenna arrays. In this paper, we analyze the reciprocity of radio channels observed by practical antenna patterns with different beamwidths. Two metrics are leveraged to measure spatial channel reciprocity based on 142 GHz outdoor channel measurement data and 28 GHz indoor ray-tracing simulation data. The power angular spectrum reciprocity of uplink and downlink radio channels does not hold when the beam pattern of base station Tx array becomes much narrower than that of Rx array. Meanwhile, it becomes increasingly likely that in the extreme case (e.g., significant beamwidth difference between Tx and Rx beam patterns), pronounced angle reciprocity can still be observed in the sparse channels with less multipath components.