Channel Sounding Measurements Research Articles

A Framework for Developing and Evaluating Algorithms for Estimating Multipath Propagation Parameters From Channel Sounder Measurements

A Framework for Developing and Evaluating Algorithms for Estimating Multipath Propagation Parameters From Channel Sounder Measurements

A Survey on Channel Sounding Technologies and Measurements for UAV-Assisted Communications

A Survey on Channel Sounding Technologies and Measurements for UAV-Assisted Communications

Physical Layer Security: Channel Sounding Results for the Multi-Antenna Wiretap Channel.

Many physical-layer security works in the literature rely on purely theoretical work or simulated results to establish the value of physical-layer security in securing communications. We consider the secrecy capacity of a wireless Gaussian wiretap channel using channel sounding measurements to analyze the potential for secure communication in a real-world scenario. A multi-input, multi-output, multi-eavesdropper (MIMOME) system is deployed using orthogonal frequency division multiplexing (OFDM) over an 802.11n wireless network. Channel state information (CSI) measurements were taken in an indoor environment to analyze time-varying scenarios and spatial variations. It is shown that secrecy capacity is highly affected by environmental changes, such as foot traffic, network congestion, and propagation characteristics of the physical environment. We also present a numerical method for calculating MIMOME secrecy capacity in general and comment on the use of OFDM with regard to calculating secrecy capacity.

THz Band Channel Measurements and Statistical Modeling for Urban D2D Environments

THz band is envisioned to be used in 6G systems to meet the ever-increasing demand for data rate. However, before an eventual system design and deployment can proceed, detailed channel sounding measurements are required to understand key channel characteristics. In this paper, we present a first extensive set of channel measurements for urban outdoor environments that are ultra-wideband, and double-directional where both transmitter and receiver are at the same height. In all, we present measurements at 38 locations, consisting of nearly 50,000 impulse responses, representing both line-of-sight (LoS) and non-line-of-sight (NLoS) cases in the 1-100 m range between 145-146 GHz. We provide modeling for path loss, shadowing, delay spread, angular spread, multipath component (MPC) power distribution and Qtapnumber. We find, among other things, that outdoor communication over tens of meters is feasible in this frequency range even in NLoS scenarios, that omni-directional delay spreads of up to 100 ns, and directional delay spreads of up to 10 ns are observed, while angular spreads are also quite significant, and a surprisingly large number of MPCs are observed for 1 GHz bandwidth and 13° beamwidth. These results constitute an important first step towards better understanding the wireless channel in the THz band.

Scatterer Identification by Atomic Norm Minimization in Vehicular mm-Wave Propagation Channels

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.

Continuous-Wave Propagation Channel-Sounding Measurement System - Testing, Verification, and Measurements

Channel sounders are used to measure channel characteristics for radio systems. There are several types of channel sounders used today: continuous-wave (CW), direct pulse, frequency domain using a vector network analyzer (VNA), correlation-based, and swept-time delay cross-correlator. Each of these has unique advantages and disadvantages. CW systems have a larger dynamic range than other systems with a signal that can propagate further into the environment. As the audio sampling rates allow smaller file sizes than other systems, data collection can be continuous and last for several hours. This article discusses a CW-channel sounder system, which has been used to make numerous propagation loss measurements in various cities in the United States of America. Such propagation measurements should be accurate, reproducible, and free of artifacts or biases. This article shows how to set up the measurement, how to validate and verify that the system is making reliable measurements, and finally, it shows results from some of the measurement campaigns such as repeatability measurements, clutter loss measurements (where clutter loss is defined as the excess loss from free-space transmission loss), and reciprocity measurements.

Continuous-Wave Propagation Channel-Sounding Measurement System - Testing, Verification, and Measurements.

Channel sounders are used to measure channel characteristics for radio systems. There are several types of channel sounders used today: continuous-wave (CW), direct pulse, frequency domain using a vector network analyzer (VNA), correlation-based, and swept-time delay cross-correlator. Each of these has unique advantages and disadvantages. CW systems have a larger dynamic range than other systems with a signal that can propagate further into the environment. As the audio sampling rates allow smaller file sizes than other systems, data collection can be continuous and last for several hours. This article discusses a CW-channel sounder system, which has been used to make numerous propagation loss measurements in various cities in the United States of America. Such propagation measurements should be accurate, reproducible, and free of artifacts or biases. This article shows how to set up the measurement, how to validate and verify that the system is making reliable measurements, and finally, it shows results from some of the measurement campaigns such as repeatability measurements, clutter loss measurements (where clutter loss is defined as the excess loss from free-space transmission loss), and reciprocity measurements.

Towards 6G: Paradigm of realistic terahertz channel modeling

Terahertz (THz) communications are envisioned as a key technology for the sixth-generation wireless communication system (6G). However, it is not practical to perform large-scale channel measurements with high degrees of freedom at THz frequency band. This makes empirical or stochastic modeling approaches relying on measurements no longer stand. In order to break through the bottleneck of scarce full-dimensional channel sounding measurements, this paper presents a novel paradigm for THz channel modeling towards 6G. With the core of high-performance ray tracing (RT), the presented paradigm requires merely quite limited channel sounding to calibrate the geometry and material electromagnetic (EM) properties of the three-dimensional (3D) environment model in the target scenarios. Then, through extensive RT simulations, the parameters extracted from RT simulations can be fed into either ray-based novel stochastic channel models or cluster-based standard channel model families. Verified by RT simulations, these models can generate realistic channels that are valuable for the design and evaluation of THz systems. Representing two ends of 6G THz use cases from microscopy to macroscopy, case studies are made for close-proximity communications, wireless connections on a desktop, and smart rail mobility, respectively. Last but not least, new concerns on channel modeling resulting from distinguishing features of THz wave are discussed regarding propagation, antenna array, and device aspects, respectively.

Measurement‐based determination of parameters for non‐stationary TDL models with reduced number of taps

This study proposes a new strategy of extracting parameters for tapped delay line (TDL) channel models from vehicle to infrastructure channel measurements. The proposed approach is based on an already existing method to derive parameters for a non-stationary model using first-order Markov chains. It will be shown that with the proposed method, the number of taps necessary to regenerate the delay spread of a channel can be significantly reduced. An approach will be discussed to evaluate the performance of the model. The feasibility of the method will be confirmed using channel sounding measurements.

Channel modelling of a cooker hob environment for smart kitchens

This study presents a study on the radio channel modelling for realising reliable wireless communication in kitchen environments. The study allows optimising the wireless communication between a cooking pot and the kitchen hood in a smart home's kitchen. The delay, angular and path loss characteristics of the wireless channel are obtained from channel sounding measurements. The authors compared path loss at frequencies 868 MHz, 2.4 and 5.25 GHz. The influence of the metallic pot on the antenna characteristics is assessed by measuring the radiation pattern of the antenna. The antenna gain increases when the antenna is placed next to the metallic pot. Based on the channel sounding measurements and antenna model, a two-ray channel model is proposed consisting of one line-of-sight component and a component caused by reflections on the hood and hob. For the validation of the proposed model, a narrowband patch antenna is designed and used for measurements in a real kitchen. The validation confirms the general applicability of the proposed method. The results of the joint channel and antenna model are used in link budget calculations. Via the link budget, the minimum required TX power to allow reliable wireless communication is calculated.

Industrial wireless channel measurements in a 2.4 GHz ISM radio band using a low-cost SDR-based channel sounder

Industrial wireless channel is a challenge for the design of communication systems, due to non-Line-of-Sight transmission, caused by the presence of many highly reflective obstacles, and machines in operation, which are a source of the increased noise level. The main effect, which must be analyzed, is multipath propagation. In this article, a low-cost sounding system is proposed, based on Software Defined Radio (SDR) equipment, with the intention of making sounding devices more accessible to a larger group of researchers. Likewise, the mathematical foundations and the software/hardware implementation of the wireless channel sounding system are presented, and the solutions to mitigate the synchronization issues and SDR limitations are also introduced. The performance of the proposed sounder is validated through a measurement campaign in an industrial workshop, considering the 2.4 GHz Industrial, Scientific, Medical (ISM) band. Channel sounding measurements corroborate the accuracy of the results, which converge with the channel mathematical models proposed for several industrial environments and reported in the state-of-the-art literature. In this sense, the proposed channel sounder can be used to investigate the wireless propagation environments.

Large-Scale Fading Characteristics and Models for Vehicle-to-Pedestrian Channel at 5-GHz

Vehicle-to-Pedestrian (V2P) communication is essential to enable a reliable collision avoidance system for vehicles and vulnerable road users (VRUs). In order to develop a reliable communication system accurate channel models are required. However, no dedicated channel model for V2P communication in critical scenarios has been proposed so far. To develop a channel model, we conducted wideband channel sounding measurements considering a typical collision scenario between a vehicle and a pedestrian in line-of-sight (LoS) and non-LoS (NLoS) situations. The wideband measurement data is used to study the characteristics of large-scale or shadow fading, pathloss and diffraction loss. The spatial correlation of shadow fading is examined and different models are proposed. For NLoS scenario, a 3D scenario model is designed to simulate the diffraction at a row of parked vehicles. The diffraction loss due to parked vehicles is analyzed and modeled based on multiple knife-edge diffraction model combined with a two-ray pathloss model. The results show that the proposed diffraction model provides a good match to the measured pathloss.

High Resolution Estimation of AoA, AoD and TdoA from MIMO Channel Sounding Measurements with Virtual Antenna Arrays: Maximum-Likelihood vs. Unitary Tensor-ESPRIT

Estimating the parameters of a geometric propagation model from MIMO channel sounding measurements will be considered, which requires the solution of an inverse problem. Thus, a model of the measured data is derived, which incorporates a model of the measurement system as well as the parameters of interest. Based on the data model a maximum-likelihood estimator will be derived to infer the model parameters. Because virtual antenna arrays are considerer, formed by step-wise rotating directive antennas at transmitter and receiver side, the MIMO measurements are conducted in the beam-space. Hence, the data model can be described by a multidimensional convolution of the measurement system and the propagation channel. Based on the convolutional modelling, the parameter estimation problem is transformed into a harmonic retrieval problem, which can be solved by an Unitary Tensor-ESPRIT algorithm. The maximum-likelihood and ESPRIT estimator are compared by Monte-Carlo simulations according to their root-mean-square estimation error.

Analysis of Multipath Component Parameter Estimation Accuracy in Directional Scanning Measurement

To resolve the crowded radio spectrum problem observed in conventional microwave bands (below 6 GHz), new frequency bands higher than 6 GHz are being considered to facilitate the use of a much wider bandwidth for next-generation wireless systems. Various channel sounding measurements have been conducted to elucidate the radio propagation properties at such new frequency bands. For a high-frequency channel sounding measurement, directional scanning with high-gain antennas is a popular method adopted to save the development cost of a full antenna array. This letter presents the analysis of the maximum likelihood multipath component parameter estimation accuracy where a Gaussian beam antenna pattern obtained by the scaled von Mises distribution function is used for the ease of analysis. The numerical analysis shows that the angle estimation error is approximately proportional to the square of the antenna half-power beamwidth (HPBW) and the square root of the angular sampling interval (ASI), respectively, and the amplitude and phase estimation error is approximately proportional to the HPBW and the square root of the ASI, respectively. The intrinsic performance of the used antenna is also discussed.

Millimeter Wave Channel Measurements and Implications for PHY Layer Design

There has been an increasing interest in the millimeter wave (mmW) frequency regime in the design of next-generation wireless systems. The focus of this work is on understanding mmW channel properties that have an important bearing on the feasibility of mmW systems in practice and have a significant impact on physical (PHY) layer design. In this direction, simultaneous channel sounding measurements at 2.9, 29 and 61 GHz are performed at a number of transmit-receive location pairs in indoor office, shopping mall and outdoor environments. Based on these measurements, this paper first studies large-scale properties such as path loss and delay spread across different carrier frequencies in these scenarios. Towards the goal of understanding the feasibility of outdoor-to-indoor coverage, material measurements corresponding to mmW reflection and penetration are studied and significant notches in signal reception spread over a few GHz are reported. Finally, implications of these measurements on system design are discussed and multiple solutions are proposed to overcome these impairments.

Capacity analysis of an IEEE 802.11n system in a residential house based on estimated specular and dense multipath components

This study analyses the multiple-input multiple-output (MIMO) capacity in a residential house. The capacity calculation is based on physical radio channels estimated from channel sounding measurements. Both specular and dense multipath components are estimated from the channel sounding data with the RiMAX maximum-likelihood algorithm. In particular, the capacity analysis is made for a 2x2 IEEE 802.11n MIMO system that conforms to the legacy mode of the standard and operates in the 2.4GHz ISM band. The contribution of dense multipath to the channel capacity is quantified by calculating the capacity of radio channels for which the dense multipath is ignored and only the specular multipath is retained. It is found that ignoring dense multipath underestimates the capacity on average by 1.1, 9.1, and 37.8% for line-of-sight, obstructed line-of-sight, and non-line-of-sight situations, respectively.

Tracking of Wideband Multipath Components in a Vehicular Communication Scenario

A detailed understanding of the dynamic processes of vehicular radio channels is crucial for its realistic modeling. In this paper, we present multipath components (MPCs) tracking results from a channel sounder measurement with 1 GHz bandwidth at a carrier frequency of 5.7 GHz. We describe in detail the applied algorithms and perform a tracking performance evaluation based on artificial channels and on measurement data from a tunnel scenario. The tracking performance of the proposed algorithm is comparable to the tracking performance of the state-of-the-art Gaussian mixture probability hypothesis density filter, yet with a significantly lower complexity. The fluctuation of the measured channel gain is followed very well by the proposed tracking algorithm, with a power loss of only 2.5 dB. We present statistical distributions for the number of MPCs and the birth/death rate. The applied algorithms and tracking results can be used to enhance the development of geometry-based channel models.

Measurement-Based Wideband Analysis of Dynamic Multipath Propagation in Vehicular Communication Scenarios

Realistic propagation modeling requires a detailed understanding and characterization of the radio channel properties. This paper is based on channel sounder measurements with 1 GHz bandwidth at a carrier frequency of 5.7 GHz and particular tracking methods. We present statistical models for the number of, birth rate, lifetime, excess delay and relative Doppler frequency of individual multipath components (MPCs). Our findings are concluded from 72 measurement runs in eight relevant vehicular communication scenarios and reveal wide insights into the dynamic propagation process in vehicular communication scenarios.

A Semiblind Tracking Algorithm for Joint Communication and Ranging With OFDM Signals

Range-based positioning by estimating the time of arrival (ToA) of the line-of-sight (LoS) path using orthogonal frequency-division multiplexing (OFDM) signals has gained remarkable attention. Multipath propagation significantly influences the ToA estimate, resulting in position errors. To mitigate these errors, the multipath channel needs to be accurately estimated, usually with a large number of known pilot symbols. A tradeoff between the data rate and the multipath channel estimation performance must be made for joint communication and positioning applications. This paper proposes a semiblind range tracking algorithm, which allows the reduction of the required number of pilot symbols significantly. For moving receivers, the algorithm needs, only in the beginning, an OFDM symbol with known pilot symbols, which increases the data rate dramatically. Instead of tracking the complex amplitude of individual subcarriers, the proposed algorithm directly tracks the multipath channel parameters, including the complex amplitude, delay, and angle of arrival (AoA) of individual multipath components. The estimated delay of the first arrived path, i.e., its ToA, is used to calculate the range between the transmitter and receiver antennas. Evaluations of the algorithm are provided by simulations in an artificial scenario and using channel sounder measurement data. The results show that the proposed tracking algorithm can effectively track the range between transmitter and receiver and detect the data.

Capacity of Broadband Body-to-Body Channels Between Firefighters Wearing Textile SIW Antennas

Reliable, high-data rate indoor communication is essential to transfer crucial information between firefighters for improving their safety and decreasing the number of casualties caused by indoor fires. Since electronic monitoring systems, including antennas implemented inside the firefighter jacket, should provide high data rates, communication over a wideband channel is required. We study an 80-MHz-wide body-to-body channel at 3.6 GHz between two firefighters of a Rapid Intervention Team (RIT) performing the primary search for victims, by static and dynamic channel sounder measurements. Two ultra-wideband (UWB) substrate integrated waveguide (SIW) cavity-backed slot textile antennas were unobtrusively deployed in the front and the back sections of the firefighters’ jackets, providing up to $2\times 2$ MIMO communication. We calculate the achievable single-input single-output (SISO)-, single-input multiple-output (SIMO)-, multiple-input single-output (MISO)-, and multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) capacities for realistic indoor broadband body-to-body communication channels between two firefighters. Furthermore, we analyze implementations of one-dimensional (1-D) spatial waterfilling and two-dimensional (2-D) space-frequency waterfilling, studying their ability to further enhance transmission of live sensor data, pictures or videos between mobile firefighters.