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In industrial applications, the large comprehensive wireless channel impulse response (CIR) reference dataset, measured by National Institute of Standards and Technology (NIST), has been a useful tool for understanding propagation within factory environments. The NIST CIR reference dataset is obtained using a precision channel sounder instrument where transmitter and receiver are time-synchronized by two rubidium clocks. While the accuracy of the NIST CIRs is much higher than the CIRs measured by general commercial digital receiver, two types of system errors have been discovered within the dataset from the perspective of signal processing. These errors are significant for wireless localization, physical layer security, and related applications. To calibrate the CIR, two channel sounder error calibration methods (CSEC) is proposed: the CSEC based on phase compensation and carrier frequency offset recovery. Our results reveal that the CSEC method can improve the accuracy of the CIR to the accuracy that precise instruments cannot achieve. To demonstrate the consequence of these systemic errors, a case study involving physical layer authentication is investigated showing a marked improvement in authentication accuracy after the systemic errors in the dataset are removed. Moreover, the CSEC method may be used to correct other CIR datasets with similar systemic errors.

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.

As a vital vertical industry empowered by the sixth-generation mobile communication system (6G), the vision of “smart rail mobility” requires a seamless wireless connectivity with the ultra high-data rate on the order of 100 Gbps or even more. This forms a strong driving force for exploiting the terahertz (THz) band where the available spectrum is massively abundant. In this paper, the smart rail mobility channel is characterized through ultra-wideband (UWB) channel sounding and ray tracing (RT) at 300 GHz band with an 8 GHz bandwidth in the five scenarios – Train-to-infrastructure (T2I), Inside station, Train-to-train (T2T), Infrastructure-to-infrastructure (I2I), and Intra-wagon. Corresponding channel characteristics such as path loss, shadow fading, Rician $K$ -factor, root-mean-square delay spread, azimuth/elevation angular spread of arrival/departure, and cross-polarization ratio are extracted and analyzed. Based on realistic channel information, the performance of THz communication is investigated in terms of channel capacity for all above five scenarios with various antenna patterns and weather conditions (except Intra-wagon) – sunny, rainy, and snowy. The results provide valuable insights into the system design and evaluation for THz communication enabled Smart Rail Mobility.

In order to realize the vision of “smart rail mobility,” a seamless high-data rate wireless connectivity with up to dozens of gigahertz bandwidth will be required. This forms a strong motivation for exploring the underutilized millimeter wave (mmWave) and sub-mmWave bands. In this article, the wireless channel in one “smart rail mobility” scenario—the intrawagon scenario—is characterized through ultrawideband (UWB) channel sounding and ray tracing (RT) at mmWave and sub-mmWave bands. To begin with, a series of horizontal directional scan-sounding measurements are performed inside a real high-speed train wagon at 60 and 300 GHz frequency bands with a bandwidth of 8 GHz. Correspondingly, the channel characteristics such as Rician $K$ -factor, root-mean-square (rms) delay spread (DS), azimuth spread of arrival, and azimuth spread of departure are extracted and analyzed. Based on the measurements, a self-developed RT simulator is validated through the reconstruction of the three-dimensional wagon model and the calibration of the electromagnetic (EM) properties of the main materials. This gives the chance to physically interpret the measurement results and characterize the intrawagon mmWave and sub-mmWave channels more comprehensively through extensive RT simulations.

Wireless networks are the preferred future access networks for both defense and civilian deployments as part of telecommunication networks. The successful implementation of long term evolution (LTE) networks and applications such as the Internet of Things (IoT) in the telecommunication infrastructure has guaranteed rates of up to 100 Mbps while supporting ultra-dense wireless access network. With the incorporation of LTE-Advanced and fifth-generation wireless protocols, the data rates are expected to reach upto 1 Gbps. Hence, there is a pertinent requirement to carry out channel measurements at sub 1 GHz, 2 GHz, and 3 GHz bands to enable the design and implementation of optimum transceivers for pico-cells of LTE and future wireless networks. For the first time measurements and comparison with standard models of channel impulse response models have also been carried out in five different terrains namely Urban, Semi-Urban, Forest, Rural, and Desert terrains in the Indian sub-continent to effectively cover a variety of deployments of future wireless access networks for defense wireless networks

In the future, fifth‐generation communications system (5G) is expected to provide reasonable mobile broadband experience to high‐density users in stadium, gym, shopping mall, etc. As the fundamental limitation is attributed to the propagation environments, it is essential to understand profoundly the high‐density channels, say, the propagation channel in the environments where the user density could be very high. In this article, seven different environments are considered. The targeted environments include stadium (or gymnasium), shopping mall, airport, hall, street canyon, indoor (or indoor office), and crowded area. The propagation investigations in the literature for the seven environments are reviewed in terms of channel sounding, parameter estimation, channel characterization and modeling, etc. The review of the high‐density channel facilitates the “great service in a crowd” defined in 5G. (Less)

While customers rivet their eyes on Wi-Fi 6, in the bowels of the IEEE 802.11 Working Group that creates Wi-Fi standards, the next generation Wi-Fi is being developed. At the very first sight, the new IEEE 802.11be amendment to the Wi-Fi standard is nothing but scaled 11ax with doubled bandwidth and the increased number of spatial streams, which together provide data rates as high as 40 Gbps. A bit deeper dive into the 802.11 activities reveals that 11be will support real-time applications. In reality, 11be introduces many more revolutionary changes to Wi-Fi, which will form a basement for further Wi-Fi evolution. Although by now (May 2020), the development process is at the very early phase without any draft specification, the analysis of the discussion in the 802.11 Working Group gives insights into the main innovations of 11be. In addition to the ones above, they include native multi-link operation, channel sounding optimization that opens the door for massive MIMO, advanced PHY and MAC techniques, the cooperation of various access points. The paper analyzes hundreds of features proposed for the new technology, focusing on the open problems that can be solved by the researchers who want to contribute to the development of 802.11be.

We present a technique to jointly estimate the channel taps and the frequency offset due to the Doppler effect of a special class of doubly dispersive aeronautical channels. The algorithm includes the use of pulse repetition techniques at the transmitter and the “power method” subspace iteration at the receiver. We show that transmitting constant-amplitude zero-autocorrelation sequences for channel sounding yields estimators with low computational complexity. Numerical simulations indicate performance comparable to the estimation-theoretic lower bound.

While millimeter-wave (mmWave) wireless has recently gained tremendous attention with the transition to 5G, developing a broadly accessible experimental infrastructure will allow the research community to make significant progress in this area. Hence, in this paper, we present the design and implementation of various programmable and open-access 28/60 GHz software-defined radios (SDRs), deployed in the PAWR COSMOS advanced wireless testbed. These programmable mmWave radios are based on the IBM 28 GHz 64-element dual-polarized phased array antenna module (PAAM) subsystem board and the Sivers IMA 60 GHz WiGig transceiver. These front ends are integrated with USRP SDRs or Xilinx RF-SoC boards, which provide baseband signal processing capabilities. Moreover, we present measurements of the TX/RX beamforming performance and example experiments (e.g., real-time channel sounding and RFNoC-based 802.11ad preamble detection), using the mmWave radios. Finally, we discuss ongoing enhancement and development efforts focusing on these radios.

Tremendous research funding and efforts have been invested in millimeter-wave (mmWave) communication systems for fifth-generation (5G) and beyond wireless communications. Understanding the influence of the surrounding environment on the propagation channel is vital to mmWave system design and deployment. In this paper, principal multipath components (MPCs) are studied in in an outdoor microcell scenario at 39 GHz. The direction-scan channel sounding measurement is conducted in a typical urban living district. By adapting the 3D environment model and material parameters, the ray-tracing simulator is tuned to match the simulated MPCs with the measurement. Based on this, the main propagation mechanisms and influential objects are identified. The method, observations, and analysis in this work are useful for understanding mmWave channel and developing communication systems.

This paper reports the development of a compact and highly programmable 28-GHz phased array subsystem that is currently being integrated in a city-scale testbed for advanced wireless research and experimentation. The subsystem hardware consists of a 28-GHz 64-element state-of-the-art dual-polarized phased array antenna module (PAAM), low-noise DC-DC power regulators with a single 12-V input, current sensors and an ADC for real-time supply monitoring, a PLL for LO (5 GHz) generation, IF (3 GHz)/LO splitters, IF/LO baluns, and programmable switches. All of these components are integrated in a compact (10” x5.75”) PCB which also supports the direct plug-in of a commercial-off-the-shelf FPGA system-on-module (SoM). The IF switches and splitters couple the PAAM to 20 IF ports that enable a rich set of MIMO configurations, including up to 8 simultaneous 16-element independent beams in each TX/RX mode. The FPGA and associated software enable the configuration of all subsystem features from a high-level application program interface (API), facilitating MIMO millimeter-wave wireless experiments. 28-GHz channel sounding measurements using the phased array subsystem coupled with software-defined radios is presented as a testbed-level experiment example.

This article presents the design of a complete radio system receiver to detect, in real time, the direction of arrival (DOA) of an incoming industrial, scientific, and medical (ISM)-band signal at 5.8 GHz. When a transmitter continuously sends a binary phase-shift keying (BPSK), modulated pseudo-noise (PN) code, the receiver estimates the DOA based on the received signal strength (RSS) and performs the channel sounding. The device that we describe includes a pattern-reconfigurable monopole antenna array, a front end, and a systemon-module (SOM). The SOM controls the antenna's main lobe direction by positive-intrinsic-negative (p-i-n) diode switching, configures the front-end modules, completes the data acquisition, and performs the digital signal processing (DSP) for the DOA estimation. The system has an average DOA resolution of 90d in the horizontal plane, with a success rate higher than 90%. It is presented as an educational platform for electrical engineering undergraduate and M.S. degree students.

Wireless radio transmission from a satellite-based emitter to a receiver located on an aircraft is of interest for many applications such as internet access for passengers, air traffic management or positioning by global navigation satellite systems especially when a worldwide service shall be granted. In particular, the last two mentioned applications are related to the safety of life requiring realistic and accurate channel models for software-based system testing. State-of-the-art channel models for the satellite-to-aircraft case lack of accuracy in terms of modelling all propagation impairments. In this contribution, the authors describe airborne propagation experiments using Global Positioning System signals for channel sounding, the data evaluation and the derived channel model.

It is essential to capture joint channel characteristics in cooperative multi-link systems in order to make realistic performance assessments and channel modeling. This paper investigates the joint statistical properties of large-scale parameters (LSPs) in high-speed railway (HSR) multi-link propagation scenarios. A dedicated long-term evolution (LTE) network-based multi-link channel sounding system is established, which breaks the constraints in HSR measurements and supports simultaneous time–frequency–space measurements for multiple links. To guarantee the effectiveness of multi-link measurements, a time-delay-window-based partition method is used to identify channel impulse responses from different links. Based on the processed multi-link data, the statistics of LSPs, involving shadow fading, K-factor, delay spread, and azimuth spread, is estimated and compared for the two links in a plain viaduct scenario on HSR. Then, auto-correlations and two kinds of cross correlations, such as intra-link correlation and inter-link correlation in the measured scenario, are calculated and analyzed. In addition, a simulation model of joint statistical characteristics for LSPs is proposed and validated according to the obtained measurement results. These results can be used to assess the actual performance of cooperative multi-link systems on HSR, and the proposed model can provide realistic inputs for channel models in HSR multi-link propagation scenarios.

Channel effects can severely degrade performance and reliability of a wireless communication system if they are not taken into account. An accurate characterization is indispensable for the proper design and parametrization of such data links. In this paper, the focus is on aircraft to ground station channel sounding and characterization to lay the foundation for unmanned aerial vehicle (UAV) control and non-payload communication (CNPC) link designs. After a comprehensive review of related work, an introduction into the implemented channel sounding principle with the aid of a custom-made sounder is given, followed by a detailed description of the two measurement campaigns at Ingolstadt/Manching airport, Germany. The obtained large-scale fading results are presented, including shadowing and antenna misalignment effects. Then, small-scale fading is discussed by means of K-factors, delay, and Doppler spread statistics. For all evaluations, the recorded data set has been classified to work out and compare the characteristics of typical phases of UAV operation. Implications of the presented analyses on the parametrization of CNPC links are mentioned as well.

This article presents a novel, low-cost, beam-switchable $2 \times 10$2x10 antenna array system operating at 60 GHz. This antenna system is constructed of two rows of Chebyshev-tapered microstrip antenna arrays. Each row is a 10 element series-fed array which are fed by a $90 \circ $90 circle coupler. The designed antenna array has only two input ports, but it is capable of generating three switchable beams. This antenna system can spatially scan $90 \circ $90 circle with at least -5 dB normalised gain using only one SPDT switch and a single transceiver. The maximum gain realised by the system was measured as 16.4 dBi and the bandwidth (BW) was >1 GHz. The features of the proposed antenna system make it applicable to do mmWave research such as beamforming algorithms and channel sounding, and to use in handsets for 5G communication.

Outdoor to indoor penetration loss is one of the crucial challenges faced at millimeter-wave frequencies. This paper presents the results from 28-GHz channel sounding campaigns performed to investigate the impact of this phenomenon on the wireless propagation channel characteristics in small cell and fixed wireless access scenarios. The measurements are performed with a real-time channel sounder equipped with phased array antennas that allow beam-forming and electronic beam steering for directionally resolved measurements. Thanks to the short measurement time and the excellent phase stability of the system, we obtain both directional and omnidirectional channel power delay profiles without any delay uncertainty. We compare the measured path loss, delay spread, and angular spread for indoor and outdoor receiver locations for two different types of buildings. We find that the penetration loss strongly depends on the angle of incidence, and the scatterers on the outside of the building strongly impact how much power is coupled into the building. Based on the results, we provide statistical models for path loss, delay spread, and angular spread.

Channel state information (CSI) has been proposed to enhance physical layer security by functioning as a shared secret between a transmitter and a receiver, because it decorrelates over half wavelength distances and cannot be predicted based on locations of the transmitter and receiver in rich scattering environments. Consequently, CSI was employed to generate passwords, to authenticate the source of packets, and to inject artificial noise to thwart eavesdroppers. However, in this paper, we present CSIsnoop , and show that an attacker can infer CSI in a multi-user MIMO WLAN, even when both channel sounding sequences from the access point and CSI measurement feedback from the clients are encrypted during downlink (explicit) channel sounding, or when uplink (implicit) channel sounding is employed. The insights of CSIsnoop are that the CSI of clients can be computed based on transmit beamforming weights at the access point, and that the transmit beamforming weights can be estimated from downlink beamforming transmission. In other words, we reveal the fundamental conflict between using CSI to optimize PHY design by beamforming and ensuring the confidentiality of CSI. We implement CSIsnoop on a software defined radio and conduct experiments in various indoor environments. Our results show that on average CSIsnoop can infer CSI of the target client with an absolute normalized correlation of over 0.99, thereby urging reconsideration of the use of CSI as a tool to enhance physical layer security in multi-user MIMO WLANs.

Fixed performing antennas are ineffective in providing optimum performance in a changing multipath environment, such as underground mines where channel conditions quickly change as the antenna is moved. Hence, we investigated the performance of a pattern reconfigurable antenna (RA) in improving the wireless communications link in a hard rock underground mine. An RA and a dipole were characterized and compared in line-of-sight (LOS) and nonline-of-sight (NLOS) propagation scenarios. As a proof of concept, experiments were performed at the University of Queensland Experimental Mine using a 1 GHz frequency band centered at 2.45 GHz. Analysis of complex channel impulses captured through the frequency-domain channel sounding is presented. Also, the results show that reconfigurability in the rich multipath environment achieves a 20% and 34% improvement in path loss and delay spread, respectively, compared to a fixed-beam antenna in NLOS propagation. Furthermore, more than 34% improvement in coherence bandwidth is observed in LOS and NLOS. Therefore, reliable high-data-rate communication is achievable in underground mines by the effective management of multipath effects using the RA.

High throughput wireless communication between vehicles and infrastructure will rely on millimeter-wave carriers and technology, which provide access to large bandwidths whilst still being able to establish stable links over distances of hundreds of meters. The work presented here, evaluates the quality of such signals in a mini-urban campus environment, by comparing detailed channel sounding results with signal quality parameters such as the error vector magnitude and the established data throughput. This provides insights into the relationships between fundamental parameters used to establish channel models and the quality of service parameters used in applications and standards. For the environment investigated, a strong threshold dependence of the signal quality on the received power is observed and explained in detail.

Millimeter wave, especially the high frequency millimeter wave near 100 GHz, is one of the key spectrum resources for the sixth generation (6G) mobile communication, which can be used for precise positioning, imaging and large capacity data transmission. Therefore, high frequency millimeter wave channel sounding is the first step to better understand 6G signal propagation. Because indoor wireless deployment is critical to 6G and different scenes classification can make future radio network optimization easy, we built a 6G indoor millimeter wave channel sounding system using just commercial instruments based on time-domain correlation method. Taking transmission and reception of a typical 93 GHz millimeter wave signal in the W-band as an example, four indoor millimeter wave communication scenes were modeled. Furthermore, we proposed a data-driven supervised machine learning method to extract fingerprint features from different scenes. Then we trained the scene classification model based on these features. Baseband data from receiver was transformed to channel Power Delay Profile (PDP), and then six fingerprint features were extracted for each scene. The decision tree, Support Vector Machine (SVM) and the optimal bagging channel scene classification algorithms were used to train machine learning model, with test accuracies of 94.3%, 86.4% and 96.5% respectively. The results show that the channel fingerprint classification model trained by machine learning method is effective. This method can be used in 6G channel sounding and scene classification to THz in the future.

Millimeter wave wireless spectrum deployments will allow vehicular communications to share high data rate vehicular sensor data in real-time. The highly directional nature of wireless links in millimeter spectral bands will require continuous channel measurements to ensure the transmitter (TX) and receiver (RX) beams are aligned to provide the best channel. Using real-world vehicular mmWave measurement data at 28 GHz, we determine the optimal beam sweeping period, i.e. the frequency of the channel measurements, to align the RX beams to the best channel directions for maximizing the vehicle-to-infrastructure (V2I) throughput. We show that in a realistic vehicular traffic environment in Austin, TX, for a vehicle traveling at an average speed of 10.5 mph, a beam sweeping period of 300 ms in future V2I communication standards would maximize the V2I throughput, using a system of four RX phased arrays that scanned the channel 360 degrees in the azimuth and 30 degrees above and below the boresight. We also investigate the impact of the number of active RX chains controlling the steerable phased arrays on V2I throughput. Reducing the number of RX chains controlling the phased arrays helps reduce the cost of the vehicular mmWave hardware while multiple RX chains, although more expensive, provide more robustness to beam direction changes at the vehicle, allowing near maximum throughput over a wide range of beam sweep periods. We show that the overhead of utilizing one RX chain instead of four leads to a 10% drop in mean V2I throughput over six non-line-of-sight runs in real traffic conditions, with each run being 10 to 20 seconds long over a distance of 40 to 90 meters., Comment: IEEE 93rd Vehicular Technology Conference (VTC-Spring)

ORAL; International audience; This paper presents the first V2I channel sounding campaign with the real-time massive MIMO radio channel sounder named MaMIMOSA. This equipment has been jointly developed by ULille (FR) and UGhent (BE) for 5G V2X applications. The system is equipped with a massive 64-antenna array for Tx whereas up to 16 individual antennas can be deployed for Rx. The MaMIMOSA hardware and software capabilities allow to freely adapting the sounding parameters to the investigated scenario demonstrating its versatility and flexibility. Radio channels were measured at 5.89 GHz with 80 MHz bandwidth at the ULille campus using with mean vehicle speed of 30 km/h. In addition to this suburban mobility scenario, Obstructed Line-Of-Sight static radio channels were collected for a roadside to parking setup to study the influence of vegetation. Very preliminary Doppler characteristics are reported from the measured radio channels.

This paper studies a WiFi indoor localisation technique based on using a deep learning model and its transfer strategies. We take CSI packets collected via the WiFi standard channel sounding as the training dataset and verify the CNN model on the subsets collected in three experimental environments. We achieve a localisation accuracy of 46.55 cm in an ideal $(6.5m \times 2.5m)$ office with no obstacles, 58.30 cm in an office with obstacles, and 102.8 cm in a sports hall $(40 \times 35m)$. Then, we evaluate the transfer ability of the proposed model to different environments. The experimental results show that, for a trained localisation model, feature extraction layers can be directly transferred to other models and only the fully connected layers need to be retrained to achieve the same baseline accuracy with non-transferred base models. This can save 60% of the training parameters and reduce the training time by more than half. Finally, an ablation study of the training dataset shows that, in both office and sport hall scenarios, after reusing the feature extraction layers of the base model, only 55% of the training data is required to obtain the models' accuracy similar to the base models., 5 pages, 5 figures, has been accepted for lecture presentation at the 2021 IEEE Radar Conference (IEEE RadarConf 2021)

To date various wireless systems using millimeter-wave bands have already been developed. However, the demand for more accurate channel models is still increasing. In this study, a millimeter-wave double-directional channel sounding system using commercial off-the-shelf RF transceivers is presented where an analog beamformer based electrical beam-steering offers a fast double-directional channel acquisition. In addition, this paper developed a high-resolution multi-path parameter estimation algorithm from the multi-dimensional power spectrum. Finally, as validation, the scattering processes were identified by comparing the path parameters extracted from the power spectrum obtained from measurements with the interacting objects in the real environment.

This paper studies the indoor localisation of WiFi devices based on a commodity chipset and standard channel sounding. First, we present a novel shallow neural network (SNN) in which features are extracted from the channel state information (CSI) corresponding to WiFi subcarriers received on different antennas and used to train the model. The single-layer architecture of this localisation neural network makes it lightweight and easy-to-deploy on devices with stringent constraints on computational resources. We further investigate for localisation the use of deep learning models and design novel architectures for convolutional neural network (CNN) and long-short term memory (LSTM). We extensively evaluate these localisation algorithms for continuous tracking in indoor environments. Experimental results prove that even an SNN model, after a careful handcrafted feature extraction, can achieve accurate localisation. Meanwhile, using a well-organised architecture, the neural network models can be trained directly with raw data from the CSI and localisation features can be automatically extracted to achieve accurate position estimates. We also found that the performance of neural network-based methods are directly affected by the number of anchor access points (APs) regardless of their structure. With three APs, all neural network models proposed in this paper can obtain localisation accuracy of around 0.5 metres. In addition the proposed deep NN architecture reduces the data pre-processing time by 6.5 hours compared with a shallow NN using the data collected in our testbed. In the deployment phase, the inference time is also significantly reduced to 0.1 ms per sample. We also demonstrate the generalisation capability of the proposed method by evaluating models using different target movement characteristics to the ones in which they were trained., Comment: Accepted for presentation at the 25th International Conference on Pattern Recognition (ICPR), IEEE, 2020

Understanding multi-node vehicular wireless communication channels is crucial for future time-sensitive safety applications for human-piloted as well as partly autonomous vehicles on roads, railways and in the air. These highly dynamic wireless communication channels are characterized by rapidly changing channel statistics. In this paper we present the first fully mobile multi-node vehicular wireless channel sounding system, which is capable of simultaneously capturing multiple channel frequency responses, ensuring that measurement conditions are identical for all observed links. We use it to analyze road scenarios with multiple vehicles and a large obstructing double-decker bus. The empirical measurement data is used to parametrize a model for the large obstructing vehicle within a geometry-based stochastic channel model. We compare the time-variant channel statistics obtained from our channel model with the ones from the measurement campaign. By means of a channel emulator we obtain the packet error rates of commercial modems for the measured and the simulated wireless communication channels and compare them, in order to validate the model at the link level. We find that the path loss, the root mean square (RMS) delay spread, and the RMS Doppler spread deviate by less than $3.6\,\mathrm{dB}$, $78\,\mathrm{ns}$, and $52\,\mathrm{Hz}$, respectively, for $80\%$ of the total simulation duration. The PER obtained from measured data is within the maximum and minimum bounds of our model for $86\%$ of the simulation duration.

The future of railway operation will rely on train-to-train (T2T) communications. Hence, we investigate the propagation mechanisms based on channel sounding measurements and derive channel models for T2T communications. For every wireless communication, the environment significantly influences the wireless propagation. For railway environments, especially regular installed objects along track like overhead line masts cause pronounced multipath components (MPCs).In this paper, we analyze the MPCs from a T2T propagation measurement with two high speed trains. In detail, we extract the MPCs, identify the ones caused by overhead line masts and derive a distance-variant fading statistic for this kind of objects. Furthermore, we provide an outline on a T2T geometry-based stochastic channel model (GSCM) and how we incorporate the statistics of overhead line masts in the GSCM.

This letter presents the analysis of a channel sounding campaign in the hull of a bulk carrier vessel at sub-6 GHz frequencies 868 MHz and 2.4 and 5.25 GHz as well as millimeter-wave (mmWave) frequency 60.48 GHz. For the sub-6 GHz frequencies, path loss (PL) is measured using omnidirectional antennas. The measured PL is fitted to a one-slope PL model that takes into account attenuation due to engine room floor crossings, obstructions, and walls. The fitted model has a reference PL lower than free space and a PL exponent around 1.2. For mmWave wireless communication, high gain directive antennas are typically used. Therefore, the directive radio channel for line-of-sight (LOS) communication is measured using the Terragraph channel sounder and an antenna beamwidth dependent PL model is created. At mmWave frequencies, LOS PL in the vessel is close to PL in a free-space environment, but angular spread values are lower compared to other indoor scenarios.

This paper reports the far-distance achievable reflected paths of indoor material groups such as glass, wood, paper , and plastic at frequencies ranging from 270 GHz to 330 GHz. A VNA equipped with ~ 25.45 dBi horn antenna as transceiver is employed to retrieve and evaluate these reflections. The beam spot size illuminated by the horn antenna from a distance of interest to the material under test (MUT) is aforethought and considered during the channel sounding. Thus, approximately 14.4 m long reflections are detected. The knowledge of the reflective properties of indoor building materials is virtuous in terms of facilitating propagation modeling and design of efficient future indoor wireless systems at terahertz (THz) frequencies. The results obtained taking into account the beam spot size are the first ever published.

Massive multiple-input multiple-output (MIMO) systems operating in the centimeter-wave (cmWave) and millimeter-wave (mmWave) region offer huge spectral efficiencies, which enable to satisfy the urgent need for higher data rates in mobile communication networks. However, the proper design of those massive MIMO systems first requires a deep understanding of the underlying wireless propagation channel. Therefore, we present a fully-digital MIMO measurement system operating around 28 GHz. The system enables to take fast subsequent snapshots of the complex MIMO channel matrix. Based on this method we statistically analyze the time-dependent channel behavior, the achievable signal quality and spectral efficiency, as well as the channel eigenvalue profile. Furthermore, the presented calibration approach for the receiver enables an estimation of the dominant absolute angle of arrival (AoA) and allows us to draw conclusions about the line-of-sight (LOS) dominance of the scenario. In total, 159 uplink communication measurements over 20 seconds are conducted in three different small cell site scenarios to investigate the wireless propagation behavior. The measurements reveal the existence of several spatial propagation paths between the mobile transmitter and the base station. Furthermore, an insight into their likelihood in different propagation scenarios is also given.

In this paper, sub-THz channel sounding is discussed for indoor scenarios. A directional D-band channel sounder, operational in the full band ranging from 110 to 170 GHz, is presented. We examine the influence of the antenna characteristics on the channel sounder. The channel sounder is used for Line-of-Sight path loss (PL) modelling at sub-THz frequencies for distances up to 4 m. Validation measurements confirm the small beamwidth of the antenna, ranging from 12 degrees for 110 GHz to 11 degrees for 170 GHz. An antenna de-embedding methodology is presented. Fitting Line-of-Sight PL at center frequency 140 GHz to a one-slope model gives a reference PL of 76.0 dB at 1 m and a PL exponent of 1.9. The reference PL is slightly higher than free space PL, whereas the PL exponent is slightly lower.

Large bandwidths are needed to meet the high-throughput requirements of future wireless communication systems. These larger bandwidths are available at mmWave and sub-THz frequencies, such as the V-band ranging from 50 to 75 GHz and the D-band ranging from 110 to 170 GHz. In this paper, we present channel measurements in an office environment, covering the full D-band. Line-of-Sight (LOS) path loss (PL) is modeled as a function of frequency and distance. Both a single-frequency floating-intercept and multi-frequency alpha-beta-gamma model provide a good fit to the measured LOS PL data. Attenuation due to blockage of the LOS path by various desk objects, such as computer peripherals and cables, is determined, as well as attenuation due to plant obstructions. Attenuation due to an obstructed LOS path ranges from 3 dB for a single universal serial bus (USB) cable, and up to 25 dB for a laptop power supply, computer mouse, computer monitor, or plant. Because of a higher diffraction angle, the measured attenuation is higher when the distance between the antennas decreases. We measure diffraction around a computer monitor for dual polarization and verify whether communication via the reflected non Line-of-Sight path makes high-throughput wireless communication possible when the LOS path is blocked.

In this paper we investigate the codebook design for a time division duplex (TDD) non-antenna switching system, where the user device is equipped with two receive radio frequency (RF) chains but only one transmit RF chain. To acquire the channel state information at transmitter (CSIT), we resort to a mixture of channel sounding and limited feedback, where the former is employed to obtain the CSIT of the antenna connected to the transmit RF chain and the latter is employed for the other antenna. We propose a deep learning method to design the codebook for limited feedback. The learned codebook is distinguished from the traditional ones in two ways. First, the learned codebook is so-called personalized, which is not fixed but adapt to the partially known CSIT. Second, the codebook exhibits different beam patterns from the traditional codebook that is designed for quantization error minimization. Simulation results demonstrate that the learned codebook can achieve higher data rate with lower complexity than traditional codebook.

Characterization of the millimeter wave wireless channel is needed to facilitate fully connected vehicular communication in the future. To study the multipath-rich, rapidly varying nature of the vehicular propagation environment, fast millimeter wave channel sounders are required. We present a channel sounder design capable of covering 360 degrees in azimuth and 60 degrees in elevation with 200 individual beam directions in 6.25 ms by using four phased arrays simultaneously. The channel measurements are accompanied by high resolution positioning and video data, allowing channel sounding to be conducted while either the transmitter, or the receiver, or both are moving. Channel sounding campaigns were conducted at multiple urban locations with light traffic conditions in Austin, Texas. Preliminary results show that beam selection at the receiver can lower the effective pathloss exponent to 1.6 for line-of-sight and 2.25 for non line-of-sight., Comment: GLOBECOM 2020 - 2020 IEEE Global Communications Conference, Taipei, Taiwan, Dec. 2020

Wide swaths of bandwidth at millimeter-wave (mmWave) and Terahertz (THz) frequencies stimulate diverse applications in wireless sensing, imaging, position location, cloud computing, and much more. These emerging applications motivate wireless communications hardware to operate with multi Gigahertz (GHz) bandwidth, at nominal costs, minimal size, and power consumption. Channel sounding system implementations currently used to study and measure wireless channels utilize numerous commercially available components from multiple manufacturers that result in a complex and large assembly with many costly and fragile cable interconnections between the constituents and commonly achieve a system bandwidth under one GHz. This paper presents an evaluation board (EVB) design that features a sliding correlator-based channel sounder with 2 GHz null-to-null RF bandwidth in a single monolithic integrated circuit (IC) fabricated in 65 nm CMOS technology. The EVB landscape provides necessary peripherals for signal interfacing, amplification, buffering, and enables integration into both the transmitter and receiver of a channel sounding system, thereby reducing complexity, size, and cost through integrated design. The channel sounder IC on the EVB is the worlds first to report gigabit-per-second baseband operation using low-cost CMOS technology, allowing the global research community to now have an inexpensive and compact channel sounder system with nanosecond time resolution capability for the detection of multipath signals in a wireless channel., 6 pages, 8 figures, Globecom 2020

Due to the known issue that the ranging in the 802.15.4™-2015 standard is prone to external attacks, the enhanced impulse radio (EiR), a new amendment still under development, advances the secure ranging protocol by encryption of physical layer (PHY) timestamp sequence using the AES-128 encryption algorithm. This new amendment brings many changes and enhancements which affect the impulse-radio ultra-wideband (IR-UWB) ranging procedures. The timestamp detection is the base factor in the accuracy of range estimation and inherently in the localization precision. This paper analyses the key parts of PHY which have a great contribution in timestamp estimation precision, particularly: UWB pulse, channel sounding and timestamp estimation using ciphered sequence and frequency selective fading. Unlike EiR, where the UWB pulse is defined in the time domain, in this article, the UWB pulse is synthesized from the power spectral density mask, and it is shown that the use of the entire allocated spectrum results in a decrease in risetime, an increase in pulse amplitude, and an attenuation of lateral lobes. The paper proposes a random spreading of the scrambled timestamp sequence (STS), resulting in an improvement in timestamp estimation by the attenuation lateral lobes of the correlation. The timestamp estimation in the noisy channels with non-line-of-sight and multipath propagation is achieved by cross-correlation of the received STS with the locally generated replica of STS. The propagation in the UWB channel with frequency selective fading results in small errors in the timestamp detection.

Directional communication systems based on millimeter-wave phased arrays have reached a significant level of maturity and have entered the commercial space for 5G networks. In order to realize their full potential, Si -based phased arrays must be integrated efficiently at the system level with digital control electronics, firmware, and software. This paper describes key architecture approaches for such vertical integration from digital-RF co-integration in the IC to API definition in software. The important benefits of low-latency and versatile control of beam forming and radio functions from high-level APIs is illustrated with application examples at 28 GHz including directional channel sounding, spatio-temporal beamforming, and 3D imaging.

Indeed, self-interference cancellation has been proven to be the key-enabling technique for realizing a full-duplex duplexing scheme. However, a self-interference canceller must possess an up-to-date knowledge about its sensed self-interference wireless channel. In wireless communication systems, these channels usually possess multi-path and time-invariant properties. Moreover, they are very environment dependant. Therefore, in this paper we chose to investigate outdoors experienced channels, more specifically, ones are encountered in a street-level deployment scenario. Furthermore, we narrowed down the focus to concentrate on cross-polar self-interference channels. These channels are observed in dually polarized antenna's configurations among transmitter and receiver ones. In nutshell, we have dedicated this paper to study the multi-path propagation characteristics of outdoor cross-polar self-interference radio channels. By means of an empirical method, time dispersion behavior of our measured self-interference channel was analzyed. To measure a cross-polar self-interference channel, a channel sounding experiment equipped with a dually-polarized ridged horn antenna was performed. For that purpose, we assembled a channel sounding setup, which is composed of a vector network analyzer connected to the dually polarized antenna. The measurement antenna was placed at 3.5 m height, where measurement data were captured at 26 different locations - on a route parallel to the street. Additionally, for the sake of investigating the frequency dependancy on a cross-polar self-interference channel, two broad frequency bands were measured: A band between 2.9 GHz and 4.1 GHz, and a band between 5.9 GHz and 7.1 GHz. Finally, we derive - from measurement data - empirical probability distributions of channels' time dispersion parameters, such as the maximum peak of the self-interference backscatter (SIBS) channel gain, channel delay spread, and maximum excess delay. These statistical analysis results are presented for both measured frequency bands.

Channel modeling often provides a basis for the design and deployment of wireless technology. Engineers design systems to operate under certain expected channel conditions. Channel models are typically based on the statistics of a collection of many measurements performed by channel sounders in nominally similar radio-propagation environments. In 2016, researchers at the US Department of Commerce National Institute of Standards and Technology (NIST) and the National Telecommunications and Information Administration Institute for Telecommunication Sciences (ITS) began a collaboration to conduct a series of channel sounder verifications to identify sources of uncertainty due to systematic and random effects in a channel sounder hardware. This report describes conducted-channel measurements designed to focus on errors within the channel sounding hardware as a base-line test of the channel sounder’s performance. Repeat measurements and an analysis of the random components of uncertainty were performed. Sample results are reported and analyzed. The work concludes with guidance and best-practice procedures with the intent of allowing users to perform similar verifications of their channel sounders.

The paper addresses the problem of mitigation of dispersion distortions in transionospheric satellite communication channels with the use of the data on the propagation medium obtained from global navigation systems. Distortions mitigation is performed by a correction device that operates in the following modes: compensation for dispersion, channel sounding, equalizer training. In addition to this, the influence of stochastic errors that corrupts the total electron content (TEC) measurements on the dispersion correction was considered. The full-scale experiments carried out in Yoshkar-Ola allowed to produce daily variations in the total electron content, frequency dispersion parameters and channel lifetime with the use of data from the GLONASS / GPS satellite systems.

The 802.15.4z standard, still under development, advances the secure ranging protocol by encryption of PHY timestamp sequence using AES-128 encryption algorithm. The paper analyses the key parts of PHY which have a great contribution in range estimation precision, particularly: UWB pulse, channel sounding and timestamp estimation using ciphered sequence. The propagation analysis in UWB channel shows that the frequency selective fading gives worse effects than multipath propagation in the timestamp estimation.

A comprehensive treatment of wireless underground channel modeling is presented in this chapter. The impacts of the soil on bandwidth and path loss are analyzed. A mechanism for the UG channel sounding and multipath characteristics analysis is discussed. Moreover, novel time-domain impulse response model for WUC is reviewed with the explanation of model parameters and statistics. Furthermore, different types of the through-the-soil wireless communications are surveyed. Finally, the chapter concludes with discussion of the UG wireless statistical model and path loss model for through-the-soil wireless communications in decision agriculture. The model presented in this chapter is also validated with empirical data.

Large scale multiple-input multiple-output (MIMO) or Massive MIMO is one of the pivotal technologies for future wireless networks. However, the performance of massive MIMO systems heavily relies on accurate channel estimation. While the acquisition of channel state information (CSI) in such systems requires an increasingly large amount of training overhead as the number of users grows. To tackle this issue, in this paper, we propose a deep learning assisted blind channel estimation technique for orthogonal frequency division multiplexing (OFDM) based massive MIMO systems. We prove that by exploiting the asymptotic orthogonality of the massive MIMO channels, the channel distortion can be averaged out without the prior knowledge of channel impulse responses, and after some mathematical manipulation, different users transmitted data symbols can be extracted. Thus, by deploying a denoising convolutional neural network algorithm (DnCNN), we mitigate a remaining channel and noise effect to accurately detect the transmitted data symbols at the channel sounding stage. Using the detected data symbols as virtual pilots, we estimate the CSI of all the users at each BS antennas. Our simulation results testify the efficacy of our proposed technique and demonstrate that it can provide a mean square error (MSE) performance which coincides with that of the data-aided channel estimation technique., Comment: 6 pages and 4 figures

We report an ultra-wideband channel sounding enabled by an optical dual-comb and photonic asynchronous sampling. A 2-18 GHz rich-multipath wireless channel is measured by a 1 kHz highest refresh rate.

In this work we present low cost time-domain wireless channel sounding using software defined radio (SDR). We performed SDR based time-domain wireless indoor channel sounding using random sequences. We used three random sequences for channel measurements because of their excellent auto-correlation and cross-correlation properties. More specifically PN code sequence, Gold code sequence, and Zadoff-Chu sequences are used. The channel measurements are performed in indoor laboratory environment at two locations at RF frequency of 5.2 GHz and 5.8 GHz respectively. Channel measurements are performed by transmitting sequences with software defined radio in indoor laboratory environment.

Wireless body area networks (BANs) have many important applications such as wearable communication devices and Internet of Things. Wireless propagation in on-body channels has been measured and modeled in the past. However, a crucial element that is usually ignored is the impact of the body size of the user—a 50-kg person obviously creates a different on-body channel than a 150-kg person. The status-quo “one-size-fits-all” approach to channel characterization in BAN is thus incomplete. In this paper, we provide a detailed description of a propagation measurement campaign that employs a self-developed $4 \times 4$ ultrawideband multiple-input-multiple-output array channel sounding system to perform BAN channel sounding both in an anechoic chamber and indoor laboratory environments. A total of 60 human subjects were investigated in our work. These human subjects had widely varying body mass index (BMI) values, which were grouped into three different categories, i.e., 20 per BMI category. Various propagation properties such as path gain, frequency-decay factor, shadowing gain, rms delay spread, amplitude fading, and spatial correlation are extracted for each on-body channel under consideration. A comparison of statistics among the BMI categories reveals considerable differences, emphasizing the fact that the aforementioned propagation properties are BMI dependent. Parameters such as path gain showed a monotonic decrease across the BMI categories with values ranging from 1–2 to almost 13 dB in some channels. This paper proposes a propagation channel model for the BMI-dependent parameters and validates that it can reproduce the measured channel capacities.

Estimating the entire channel state information (CSI) is essential for building and keeping a robust RF link between a master device and the mobile-station and base-station in a wireless transmission system. The channel sounding system can be used to evaluate the radio environment for wireless communication to take account the effect of terrain and obstacles, wireless signals propagate in multiple paths (the multipath effect). In a multipath system, the wireless channel is frequency dependent, time dependent, and position dependent. The parameters describe the channel in a multipath system [1], including direction of departure (DOD), direction of arrival (DOA), time delay, Doppler shift, and complex polarimetry path weight matrix. Generally Space-Alternating Generalized Expectation Maximization (SAGE) algorithm [2] or the Multiple Signal Classification (MUSIC) estimation algorithm [3] can be used to estimate the angle information but those methods demand a MCPU with highly computing power. To reduce the computing load, this study proposes the use of monopulse [4] tracking algorithm for angle estimation. Numerical simulation results validate the proposed method.