This paper analyzes THz communications, by comparing 300 GHz channel measurements from a conference room with corresponding raytracing simulations. The room geometry, as well as the material parameters are carefully measured, to ensure accurate simulation results. Additionally, all relevant interaction mechanisms, i.e. reflections, diffractions and scattering, are used during the raytracing simulations. Afterwards, simulated annealing is used, to improve the accuracy of the previously measured material parameters, to obtain better results for the raytracing simulations. It is shown, that the match between the channel measurements and raytracing simulations significantly improve through the usage of the proposed simulated annealing algorithm.

This paper quantifies the weight of the different physical mechanisms (reflection, diffraction, and scattering) in a typical indoor THz wireless communication environment and provides an intercomparison of raytracing tools. Two state-of-the-art raytracing tools - Wireless InSite and Sionna - are utilized to analyze the capabilities of currently available opensource and commercial raytracing engines for THz simulations. A channel sounder measurement campaign at 300 GHz was conducted in a conference room at Fraunhofer HHI, which is used to validate the raytracing simulations. Additionally, the measurements are compared to a proprietary raytracer, optimized for THz simulations. This paper presents a guideline to increase the capabilities of state-of-the-art raytracing tools, to obtain good results for high frequency simulations. The comparisons show, that currently used raytracing tools are not sufficiently accurate for THz simulations. However, these inaccuracies can be mitigated by the implementation of new features, such as the inclusion of different scattering mechanisms and the incorporation of atmospheric attenuation, while utilizing precise geometry and accurate material parameter models. Index Terms-THz communications, propagation channels, raytracing, interaction mechanisms.

This paper investigates the antenna capabilities of a near-field measurement probe, such as the return loss (S11), radiation pattern and peak gain. For this purpose, a rectangular open ended waveguide (OEWG) is used, while minimizing its scattering cross section (SCS), to increase the accuracy of near-field measurements. In this context, the relation between tapering and dielectric loading of the measurement probe is analyzed, since the taper is simultaneously utilized as an air to dielectric transition for the antenna. Furthermore, absorbers are used around the opening of the OEWG, to reduce the SCS even further. It is shown, that the tapering and dielectric loading of the measurement probe are highly correlated and significantly influence the antenna capabilities. Finally, the best constellations to reduce the SCS and increase the antenna capabilities of a rectangular OEWG are shown with improvements up to 15 dBsm.

Among the several features and capabilities introduced by every new 3GPP release on 5G cellular systems, the latest Release 17 will be remembered as the first that specifies a set of enhancements and adaptations to support mobile broadband services via satellite direct access. Specifically focused on the necessary physical layer mechanism and procedure modifications, this paper will present in detail the 3GPP work about the inclusion of satellite systems in 5G networks.

Fifth Generation (5G) communications are envisioned to be an important part of future vehicle to vehicle (V2V) communications. Therefore, the characterization of V2V channels is a growing research area. Several different methods, such as ray tracing are used for the channel modeling. In this context, the geometries for the ray tracing simulations are key to obtain correct channel models. This paper focuses on the car geometries for urban scenarios, since they are one of the most important objects in urban environments. Car models with different accuracies are used, to perform ray tracing simulations, in order to assess the effect of the car accuracies on the simulations. It can be observed, that low poly car models provide the best trade-off between computational complexity and simulation accuracy for ray tracing simulations. So the computational complexity is significantly reduced, while the simulation results are changing between 5% to 15%, depending on the scenario.

The frequency bands for communication standards are continuously increasing, as it can be seen from fifth generation (5G) and beyond 5G communications. This is done, to increase the capabilities of communication systems and enable new technologies, e.g. autonomous driving and wireless sensor networks. Therefore, reliable channel characterization methods, such as ray tracing, are needed to implement and guarantee the functionality of these new technologies. The effects of vegetation on ray tracing simulations are often times dismissed, due to their modeling challenges and high resulting computational overhead for simulations, as well as their generally small influence on the communication channel. However, with increasing frequencies for 5G, these effects cannot be dismissed anymore. So despite the modeling challenges, vegetation effects have to be included in ray tracing simulations for an accurate channel characterization. This paper aims to create a vegetation model with low computational complexity for ray tracing simulations, while depicting the effects of real vegetation as close as possible. It is shown, that even simple approaches to model vegetation with low computational overhead are often times sufficient to capture significant effects on the communication channel.

Ray tracing is a simulation tool to determine propagation paths and create channels for communication applications. Mobile links or environments with moving objects, require several ray tracing simulations to create representative communication channels. This paper proposes a dynamic ray tracing approach, by utilizing a frame based technique, depicting scenarios with moving objects as sequential snapshots. However, the computational complexity and calculation times are very high without further optimization and complexity reduction. This paper analyzes and evaluates two different techniques, to accelerate the calculation time of the simulations, in order to enable a feasible framework for dynamic ray tracing. A match of 1% to 15% is observed, between the original and optimized dynamic ray tracing results, depending on the utilized technique.

This paper studies the relation between the mono-static scattering cross section (SCS) of a near-field measurement probe and its antenna capabilities, e.g. the return loss (S11), radiation pattern and peak gain. For this purpose, a highly parameterized model is created and several simulations are conducted with a rectangular open ended waveguide (OEWG), to assess the effects of polarization and geometry. Different techniques are used to reduce the SCS, while maintaining a high antenna performance. The first one is to reduce the aperture of the antenna, by reducing the taper opening of the OEWG. Furthermore, the effects of dielectric loading and adding absorber material around the OEWG are analyzed. The employed techniques are assessed based on their capability to reduce the SCS of the measurement probe, while maintaining the antenna performance. It is shown, that the polarization is significantly more important than geometrical variations with differences between 3 to 15 dBsm for co-polar and cross-polar cases. An SCS reduction of around 10 dBsm can be achieved, by combining the different techniques, employed in this paper. The advantages and disadvantages of these techniques are described and a guideline to reduce the SCS of OEWGs is presented.

This paper investigates the required amount of orders of interaction to obtain accurate ray tracing (RT) simulations for line-of-sight (LOS) and non-line-of-sight (NLOS) mmwave indoor scenarios. For this purpose, RT simulations with varying orders of interaction, from one to six, are analyzed and compared with previously conducted channel measurements of a kitchen scenario at 28 GHz. Most importantly, all relevant interaction mechanisms, i.e. reflections, diffractions and scattering, are utilized and varied for the comparison and analysis. It is shown, that three to five orders of interaction, for LOS and NLOS scenarios respectively, are needed for the best possible agreement between measurements and RT simulations. Any further increase of the orders of interaction only increases the computational complexity of the simulations without providing any relevant improvements for the respective scenarios.

Low Earth orbit (LEO) satellite networks will become an integral part of the global telecommunication infrastructure. Modeling the radio-links of these networks and their interaction with terrestrial systems is crucial for the design, planning and scaling of these networks. The 3rd generation partnership project (3GPP) addressed this by providing guidelines for such a radio-channel model. However, the proposed model lacks a satellite orbit model and has some inconsistencies in the provided parameters. This is addressed in this paper. We provide a general satellite motion model that can be integrated into geometry-based stochastic channel models (GSCMs) such as the quasi deterministic radio channel generator (QuaDRiGa). We then use this model to obtain the GSCM parameters from a simplified environment model and compare the results to the 3GPP parameter set. This solves the inconsistencies, but our simplified approach does not consider many propagation effects. Future work must therefore rely on measurements or accurate ray-tracing models to obtain the parameters.

In this work, we demonstrate how a channel sounding campaign is recreated using a proprietary ray-tracing (RT) based radio propagation simulator and evaluate the simulation in terms of the achieved accuracy. In the 3.7 GHz campaign, we used a uniform cylindrical array (UCA) in an urban macro campus scenario in downtown Berlin to determine single directional channel impulse responses. Initial results for the path loss were determined from the processed simulation and measurement data. Although a similar trend can be observed, there is still room for improvement. Impacts from the RT configuration with respect to the chosen 3D geometry data, the considered material properties as well as physical effects are discussed.

This paper presents a summary of the results of the 5G-ALLSTAR project. It describes the enablers that have been developed and validated and will help make 5G and beyond satellite-terrestrial multi-connectivity (MC) a reality in the near future. We proposed and evaluated solutions for critical aspects of the integration of non-terrestrial networks into a 5G and beyond terrestrial network. The OpenAirInterface implementation of the 5G physical layer (PHY) has been upgraded to meet the satellite radio channel constraints. We addressed the issue of co-tier interference between satellite and terrestrial systems. We designed and implemented customized 5G Physical layer, specifically adapted for terrestrial-satellite spectrum sharing. On top of the dedicated beam-forming and hardware design, we validated the full potential of MC by conceiving and testing our proposed resource allocation algorithms based on a custom multipath TCP protocol. The contribution of MC in vehicular use cases has been demonstrated onsite by implementing a terrestrial 5G PHY in conjunction with a satellite/terrestrial traffic controller. Finally, radio resource management solutions were examined. Thanks to these tools, the presence of industry partners in the consortium and to an active participation in standardization, the 5G-ALLSTAR project is an accelerator for the integration of non-terrestrial networks in 5G and beyond.

In recent years, a high connectivity demand started being experienced in wireless communication. Practically, everyone and everything needs to be connected because of the huge variety of applications existing today. This is a challenging situation for terrestrial telecommunications infrastructure that they cannot address on their own. Therefore, the 3rd Generation Partnership Project (3GPP) started in 2017 to study the integration of satellites as a part of the 5G ecosystem involving both cellular and satellite stakeholders. The substantial value added by satellites as part of the access technology mix for 5G is now becoming clear, especially for mission critical and other applications where ubiquitous coverage is crucial. For example, NTN can broaden service delivery to unserved or underserved areas, by complementing and extending terrestrial networks (Liolis, K., Geurtz, A., Sperber, R. et al. (2018). Use cases and scenarios of 5G integrated satellite-terrestrial networks for enhanced mobile broadband: the SaT5G approach. International Journal of Satellite Communications and Networking 37: 91–112; Hofmann, M. (2020). Satellite communication in the age of 5G. Journal of ICT Standardization 8(3). https://journals.riverpublishers.com/index.php/JICTS/article/view/4327/3093 ). In this chapter, we will elaborate on the current standardization of NTN in 5G and further detail the architecture and research challenges toward 6G-NTN.

In this article, a review of the achieved accuracy in the literature for ray tracing (RT) based channel modeling is presented with a focus on outdoor propagation scenarios in the sub-6 GHz frequency range. The achieved accuracy is analyzed from three perspectives: 1) The input parameters which include the environmental description in the form of digital maps and the corresponding constitutive material parameters; 2) from the interaction mechanisms perspective and 3) from the output perspective where the achieved accuracy of predicted path loss is reviewed. Uniform assignment of materials to the entire propagation scenario is observed in most of the works in the literature which is attributed to the composite nature of common building materials and the difficulty of characterizing all material properties especially for outdoor scenarios. The digital maps are shown to introduce a certain degree of uncertainty in the RT predictions as most common sources of the maps hardly publish the accuracy. Notwithstanding, the prediction of path loss in most RT tools is observed to be rather robust against the inaccuracies in the input parameters with most RT tools achieving a prediction accuracy with a mean error below 4 dB and a standard deviation (STD) below 8 dB.

Industrial Internet of Things (IIoT) is an emerging area that fifth-generation (5G) mobile communication system penetrates industrial manufacturing applications. The indoor factory has larger space and there are a lot of metal machine tools distributed in it, which makes its radio propagation characteristics and corresponding channel models significantly different from those of the indoor office and indoor hotspot. To support the design and the evaluation of the IIoT techniques, the 3rd Generation Partnership Project (3GPP) released the first 5G IIoT standard model in October 2019. In this article, we give a detailed explanation of this IIoT model and compare it with other indoor models. First, we introduce the standardization of 3GPP IIoT channel model and its motivation. Second, four IIoT subscenarios, which are classified according to the clutter density and antenna height, are described. Third, the potential frequency bands of 5G IIoT are summarized. Fourth, the models of channel parameters, including the path loss and the line-of-sight (LOS) probability, the root mean-square (RMS) delay spread, and the angular spread, are given. Among them, the models of path loss and LOS probability take the antenna height and clutter density into consideration. The model of RMS delay spread changes from frequency-dependent to volume-dependent in order to catch the size variation of factories. Finally, two newly added key channel characteristics, dual mobility and absolute time of arrival, which help to describe the robot movement and positioning, are also presented.

This paper provides an overview of recent research activities of the 5G AgiLe and fLexible integration of SaTellite And cellulaR (5G-ALLSTAR) project which aims to develop Multi-Connectivity technology that integrates the cellular and satellite networks to provide seamless, reliable and ubiquitous broadband services. 5G-ALLSTAR also entails developing millimeter-wave (mmWave) 5G New Radio (NR)-based cellular access system and investigating the feasibility of NR-based satellite access for providing broadband and reliable 5G services. In addition, spectrum sharing between cellular and satellite networks is studied. With all the technologies developed, 5G-ALLSTAR will showcase the first fully integrated satellite and cellular prototype system for 5G and beyond 5G (B5G) services at a big event (e.g., sporting event like Roland-Garros) in 2021. This paper also provides a preliminary techno-economic analysis on potential use cases targeting vertical markets, and introduces recent standardization activities of relevance.

This paper reports the first results of the 5G- ALLSTAR project [1] aiming at providing solutions and enablers for spectrum sharing in a 5G cellular and satellite multi-connectivity context. First, we present an exhaustive study of the frequency bands eligible for these systems in the short and medium term. A ray-tracing based and a geometry-based stochastic channel models developed in the project are then described. These models can be used to simulate systems involving terrestrial and non- terrestrial networks. We then describe three different ways investigated in the project for managing interference: signal processing (hardware implementation of a 5G New Radio compatible physical layer), beamforming (steering and switching beams in order to avoid the interference while preserving the spectral efficiency) and radio resource management (tool designed for joint optimization of satellite and terrestrial resource sharing).

The 3rd generation partnership project (3GPP) new radio (NR) channel model introduced spatial consistency and a correlation model for multiple frequencies. Future extensions of this model will incorporate mobility at both ends of the link. These features are essential for many emerging wireless technologies in the 5G era. However, the existing small-scale-fading (SSF) model does not integrate these features coherently. To solve this problem, we propose a new SSF model that seamlessly integrates with the remaining NR model and allows the simultaneous simulation of all three features. We demonstrate this integration by showing that the output of the new SSF model agrees well with large-scale fading (LSF) parameter distributions provided by 3GPP. This enables the simulation of new wireless technology proposals that were difficult to realize with existing geometry-based stochastic channel models (GSCMs).

In this work we evaluate urban macro single input multiple output (SIMO) channel measurement performed at 3:7GHz in Berlin city. In the evaluation we focus on spatial correlation of multi-user channels for varying user densities and distributions in line of sight (LOS) and non line of sight (NLOS) scenarios Therefore, we calculate the correlation matrices, i.e. the covariance matrix of the macro-BS antenna across subsequent channel samples in time. In addition, we estimate the Shannon sum-rate and user data rate distributions for different antenna configurations to clarify fifth generation (5G) performance gains due to spatial multiplexing in a realistic environment.

Providing reliable low latency wireless links for advanced manufacturing and processing systems is a vision of Industry 4.0. Developing, testing and rating requires accurate models of the radio propagation channel. The current 3rd generation partnership project (3GPP) new radio (NR) model as well as the quasi deterministic radio channel generator (QuaDRiGa) lack the propagation parameters for the industrial indoor scenario. To close this gap, measurements were conducted at 2.37 GHz and 5.4 GHz at operational Siemens premises in Nuremberg, Germany. Furthermore, the campaign was planned to allow the test and parameterization of new features of the QuaDRiGa channel model such as support for device-to-device (D2D) radio links and spatial consistency. A total of 5.9 km measurement track was used to extract the statistical model parameters for line of sight (LOS) and Non-LOS propagation conditions. It was found that the metallic walls and objects in the halls create a rich scattering environment, where a large number of multipath components arrive at the receiver from all directions. This leads to a robust communication link, provided that the transceivers can handle the interference. The extracted parameters can be used in geometric-stochastic channel models such as QuaDRiGa to support simulation studies, both on link and system level.