Channel Sounder Research Articles

Fabrication of Implantable Capsule-Type Channel Sounders for the High-Accuracy Measurement of the Signal Loss of Out-Body to In-Body Channels

This paper proposes a channel sounder to measure the channel properties of an implantable device that transmits data from inside to outside the human body. The proposed channel sounder measures the receiving power of a signal transmitted from outside the human body. The channel sounder is equipped with a Bluetooth module that enables the wireless transmission of the receiving power outside the human body. Wireless transmission enables the channel measurement by isolating the transmitter and receiver inside the channel sounder. Using the proposed channel sounder, the channel properties can be measured without any interference between the transmitter and the receiver.

Millimeter-wave Channel-Sounder Performance Verification using Vector Network Analyzer in a Controlled RF Channel.

A new comparison-to-reference performance verification technique compares an E-band channel-sounder and reference vector network analyzer measurements of the same controlled, static channel. This new technique reduces the number of inaccurate assumptions that exist in other methods providing a stronger verification of the channel-sounder hardware and processing performance. This technique compares the channel-sounder and VNA derived channel metrics from these measurements. Using mechanical switches, we established a controlled, static RF channel. The vector network analyzer has a comprehensive uncertainty analysis that propagates systematic and random uncertainties through to the power delay profiles. The method is suitable for millimeter-wave channel-sounder hardware with removable antennas.

Real-Time mmWave Channel Sounding Through Switched Beamforming With 3-D Dual-Polarized Phased-Array Antennas.

We propose a 28.5-GHz channel sounder that switches through all antennas of multiple dual-polarized 8 × 8 phased arrays at the transmitter and receiver and performs beamforming in postprocessing through digital weights to synthesize a sweepable beam. To our knowledge, we are the first to implement-what we refer to as-switched beamforming with phased arrays for millimeter-wave channel sounding, realized through highly stable Rubidium clocks and local oscillators coupled with precision over-the-air calibration techniques developed in house. By circumventing the time-consuming programming of analog weights that is associated with analog beamforming-what phased arrays are designed for-we can sweep a 3-D double-omnidirectional dual-polarized channel in just 1.3 ms, for real-time sounding. By in turn circumventing the coarse precision of analog weights, we can synthesize ideal beam patterns thanks to the effectively infinite precision of digital weights, enabling fine weight calibration for the nonidealities of the system hardware and fine weight tapering for sidelobe suppression. This translates to average estimation errors of 0.47° in 3-D double-directional angle, 0.48 dB in co-polarized path gain, and 0.18 ns in delay, as substantiated by field measurements.

Design of Sliding Correlator Channel Sounder for Ionospheric Channel Probing Based on Software Define Radio

Observation of wireless channel using channel sounder method is needed in order to obtain the channel characteristics in the form of delay spread (Tm) and doppler spread (fD) parameters for optimizing the design of digital communication systems. This also applies to the ionosphere channels which are known to have dynamic properties in the time and place domains. The Sliding Correlator Channel Sounder technique known as a popular technique due to the advantage in the low level of complexity and relatively low cost. Similar to the advantages of the sliding correlator technique, Software Define Radio (SDR) device is one of the popular inexpensive platforms for implementing the communication system into the real world. The implementation of the sliding correlator channel sounder technique in the SDR platform will increase the advantages of the ionosphere channel measurement system that needed as an effort to obtain the dynamic of ionospheric channel characteristic information. However, the process of implementing a sliding correlator channel sounder system into the SDR device requires precise calculations to guarantee the designed system able to works according to the specifications of the SDR device and also meet the system performance targets. This paper discusses the design of a sliding correlator channel sounder system for observing the characteristics of ionosphere channels using SDR devices. The system design starts with the process of calculating the clock frequency generator bit (fchirp) based on the system performance target which refers to the recommendation of the ionospheric channel characteristics based on ITU-R F.1487 documents. Parallel with the calculation of the fchirp, the calculation of the Pseudo Noise (PN) bit length (L) based on the Dynamic Range (DR) value that meets with the specifications of the SDR hardware also carried out. Based on the obtained fchirp and L values, the calculation of other sliding correlator channel sounder parameters is performed with a limitation of a hardware specification and the target system performance. MATLAB simulation results show that the expected system performance can be met. This systems can also be realized significantly through the results of real signal transmission experiments conducted in a closed room laboratory

A Wideband Sliding Correlation Channel Sounder in 65 nm CMOS: Evaluation Board Performance

Emerging applications such as wireless sensing, position location, robotics, and many more are driven by the ultra-wide bandwidths available at millimeter-wave (mmWave) and Terahertz (THz) frequencies. The characterization and efficient utilization of wireless channels at these extremely high frequencies require detailed knowledge of the radio propagation characteristics of the channels. Such knowledge is developed through empirical observations of operating conditions using wireless transceivers that measure the impulse response through channel sounding. Today, cutting-edge channel sounders rely on several bulky RF hardware components with complicated interconnections, large parasitics, and sub-GHz RF bandwidth. This paper presents a compact sliding correlation-based channel sounder baseband built on a monolithic integrated circuit (IC) using 65 nm CMOS, implemented as an evaluation board achieving a 2 GHz RF bandwidth. The IC is the worlds first gigabit-per-second channel sounder baseband implemented in low-cost CMOS. The presented single-board system can be employed at both the transmit and receive baseband to study multipath characteristics and path loss. Thus, the singleboard implementation provides an inexpensive and compact solution for sliding correlation-based channel sounding with 1 ns multipath delay resolution.

Comparison of GNSS and INSAT-3D sounder retrieved precipitable water vapour and validation with the GPS Sonde data over Indian Subcontinent

Precipitable water vapour (PWV) plays a key role in the atmospheric processes from climate change to micrometeorology. Its distribution and quantity are critical for the description of state and evaluation of the atmosphere in NWP model. Lack of precise and continuous water vapour data is one of the major error sources in short term forecast of precipitation. The task of accurately measuring atmospheric water vapour is challenging. Conventional in situ measurements of atmospheric water vapour is provided by GPS Sonde humidity sensors profile twice a day at 0000 and 1200 UTC mainly from limited land regions. In recent years India Meteorological Department (IMD) is computing PWV from 19 channel sounder of INSAT-3D in three layers 1000-900 hPa, 900-700 hPa and 700-300 hPa and total PWV in the vertical column of atmosphere stretching from surface to about 100 hPa under cloud free condition. These data most commonly were validated using spatially and temporally collocated GPS Sonde measurements. In this paper, INSAT-3D satellite retrieved PWV data are validated with column integrated PWV estimates from a network of ground based Global Navigation Satellite System (GNSS) over Indian subcontinent. The PWV retrieved by INSAT-3D sounder platform is very promising, being in a good agreement with the GNSS data recorded over India for the period June, 2017 to May, 2018. The root-mean-square (rms) differences of 5.4 to 7.1 mm, bias of -4.7 to +2.1 mm and correlations coefficient of 0.79 to 0.92 was observed between INSAT-3D and GNSS PWV. The correlations coefficient between GPS Sonde and GNSS derived PWV ranges from 0.85 to 0.98.

DeepMux: Deep-Learning-Based Channel Sounding and Resource Allocation for IEEE 802.11ax

MU-MIMO and OFDMA are two key techniques in IEEE 802.11ax standard. Although these two techniques have been intensively studied in cellular networks, their joint optimization in Wi-Fi networks has been rarely explored as OFDMA was introduced to Wi-Fi networks for the first time in 802.11ax. The marriage of these two techniques in Wi-Fi networks creates both opportunities and challenges in the practical design of MAC-layer protocols and algorithms to optimize airtime overhead, spectral efficiency, and computational complexity. In this paper, we present DeepMux, a deep-learning-based MU-MIMO-OFDMA transmission scheme for 802.11ax networks. DeepMux mainly comprises two components: deep-learning-based channel sounding (DLCS) and deep-learning-based resource allocation (DLRA), both of which reside in access points (APs) and impose no computational/communication burden on Wi-Fi clients. DLCS reduces the airtime overhead of 802.11 protocols by leveraging the deep neural networks (DNNs). It uses uplink channels to train the DNNs for downlink channels, making the training process easy to implement. DLRA employs a DNN to solve the mixed-integer resource allocation problem, enabling an AP to obtain a near-optimal solution in polynomial time. We have built a wireless testbed to examine the performance of DeepMux in real-world environments. Our experimental results show that DeepMux reduces the sounding overhead by 62.0% ~ 90.5% and increases the network throughput by 26.3% ~ 43.6%.

A Wideband Radio Channel Sounder for Non-Stationary Channels: Design, Implementation and Testing

The increasing bandwidths and frequencies proposed for new mobile communications give rise to new challenges for system designers. Channel sounding and channel characterization are important tasks to provide useful information for the design of systems, protocols, and techniques to fight the propagation impairments. In this paper, we present a novel radio channel sounder capable of dealing with non-stationary channels. It can be operated in real-time and has a compact size to ease transport. For versatility and cost purposes, the core of the system is implemented in Field Programmable Gate Arrays (FPGAs). Three measurement campaigns have been conducted to illustrate the performance of the sounder in both static and non-static channels. In its current configuration, the sounder reaches an RF null-to-null bandwidth of 1 GHz, providing a delay resolution of 2 ns, a maximum measurable Doppler shift of 7.63 kHz, and 4.29 s of continuous acquisition time. A comparison with other channel sounders in the literature reveals that our proposal achieves a good combination of performance, cost, and size.

Directive mmWave radio channel modeling in a ship hull

AbstractWireless connectivity has been realized for multiple environments and different frequency bands. However, little research exists about mmWave communication in industrial environments. This paper presents the 60 GHz double-directional radio channel for mmWave communication in a ship hull for Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) conditions. We performed channel measurements using the Terragraph channel sounder at different locations in the ship hull and fitted LOS path loss to a one-slope path loss model. Path loss and root-mean-square delay spread of the LOS path is compared to the reflected path with lowest path loss. NLOS communication via this first-order reflected path is modeled by calculating the path distance and determining the reflection loss. The reflection losses have a considerable contribution to the signal attenuation of the reflected path. The channel models are implemented in an indoor coverage prediction tool, which was extended with a ray launching algorithm and validated by comparison with an analytical electromagnetic solver. The results show that the mmWave radio channel allows high-throughput communication within a ship hull compartment, even when no LOS path between the transmitter and receiver is present.

Stochastic cluster models of wideband high-speed-train channel based on passive measurement in in-service 5G-NR networks

In this paper, a passive channel sounding system specifically designed for the 5G is used to conduct channel measurements on sub-6 GHz frequency bands in time-variant cases on high-speed-train with 250 km/h, and a based-cluster channel model based on measurement data is established. This passive channel sounder, built with dual-channel software-defined radio (SDR) peripherals, high-performance mobile workstation and other ancillaries, can be applied to collection of exact 5G downlink signals with center-frequencies of 2−4 GHz, bandwidth of 100 MHz in in-service 5G new radio (NR) networks. Based on post-processing of downlink signals of different types, multi-dimensional channel power spectra in delay, Doppler frequency and direction of arrival, as well as the estimates of parameters of multipath component (MPC) are obtained. A discussion of the difference between this new 5G-NR model and existing WINNER II model is provided and comments on the model applicability for system performance evaluation.

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.

A Non-Time-Limited Channel Sounding Protocol for Key Generation

The traditional channel sounding protocol requires that the whole sounding process must be completed within a coherent time. When the communication delay is close to or greater than the coherent time, the protocol will not work properly. In order to solve this problem, a novel Non-Time-Limited channel sounding protocol is proposed. The proposed channel sounding protocol does not need to guarantee the channel reciprocity, has no limit on the communication delay and has strong multi-relay scalability. At the same time, a relay-assisted security extension mechanism is proposed to prevent the collaborative eavesdropping of the neighboring attackers. Simulation experiments show that the Non-Time-Limited channel sounding protocol can get rid of the influence of channel change speed on key generation, effectively improve key consistency in high-speed mobile scenarios, and still maintain good key agreement rate performance in underwater acoustic communication.

A UAV-aided channel sounder for air-to-ground channel measurements

Unmanned aerial vehicle (UAV) is a promising platform for future communication systems due to its high mobility, maneuverability, and low cost. The unique features that distinguish UAV communications from conventional land communications include the high altitude, mobility, and three dimensional (3D) trajectories. Thus, it is urgent to measure and analyze the characteristics of air-to-ground (A2G) channels. In this paper, a UAV-aided channel sounder for characterizing A2G channels is developed, which includes two components, i.e., the air transmitter and ground receiver. For measuring the channels, the raw channel impulse response (CIR) is extracted from the measured channel data firstly. According to the parametric channel model, the simplified and more practical CIR is then reconstructed by the clustering and parameter estimation algorithms. In order to verify the effectiveness and accuracy of proposed channel sounder, a commercial channel emulator is used to reproduce realistic channels in the lab and calibrate the measured results by the proposed channel sounder. Finally, the channel sounder is applied to measure the air-to-ground channels under campus scenarios, which shows that the measured channel parameters such as path loss and path delay are consistent with the theoretical ones.

Broadband Extended Array Response-Based Subspace Multiparameter Estimation Method for Multipolarized Wireless Channel Measurements

The clustered delay line channel model, in which each cluster consists of many rays, is widely used for link-level evaluations in mobile communications. Multiple parameters of each ray, including the delay, amplitude, cross-polarization ratio (XPR), initial phases of four polarization combinations, and the azimuth and elevation angles of arrival and departure, must be known and are measured using a channel sounder. The number of rays in every cluster is usually greater than the number of elements in the antenna array of the channel sounder, which represents a challenging issue in multipolarized channel measurements. Based on the broadband extended array response of an electromagnetic vector antenna array, a new subspace estimation method is proposed to resolve a large number of rays. The inter-element spacing of the array can be greater than half the carrier wavelength, which reduces inter-element coupling and simplifies the array design, especially for millimeter-wave bands. The delay of each cluster is first estimated using the reference antenna element. Next, two-dimensional angles of every ray are estimated using the classic rank-deficient multiple signal classification algorithm. Finally, the initial phases, XPR, and amplitude of every ray are estimated. Simulation results validate the proposed method.

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.

Human Sensing in Reverberant Environments: RF-Based Occupancy and Fall Detection in Ships

In this paper, we explore the possibility of estimating the number of people inside a below-deck ship compartment using the theory of room electromagnetics. Most RF-based occupancy detection solutions focus on residential environments. Confined metallic spaces such in industrial environments are more hostile and exhibit features of a reverberant cavity. The theory of room electromagnetics provides a simple characterization of microwave propagation in such environments. By considering the indoor environment as a lossy cavity, the exponential decay rate of the power-delay profile (PDP), also known as reverberation time (RT), is related to the total absorption inside the room. First, we verify the reverberating nature of the room by measuring the RT at different locations inside the room. The PDPs are calculated from the channel impulse response (CIR) measured using the MIMOSA radio channel sounder. Then, the relation between RT and the number of people inside the room is investigated. We show that it is possible to estimate the number of stationary people with a good accuracy, depending on the number of antennas used. With a success rate of 88%, the estimation error is only one person when 16 spatially averaged PDPs are used. Higher success rates are achievable with more spatial averaging. Moreover, off-the-shelf (OTS) ultra wide band (UWB) devices are used to estimate the number of people inside the same room. Results show that temporal averaging of PDPs can further improve the success rate to 95% when people inside the room are moving. In addition, the detection of a lone person falling to the ground is investigated based on the Doppler analysis of the measured CIRs. It is shown that the Doppler spread in case of a fall has higher peak values compared to normal activities, such as walking and sitting. With the use of a simple Bayes classifier, a fall is detected with 98% accuracy and 100% sensitivity.

Device-Free Indoor Location Estimation System Using Commodity Wireless LANs

In recent years, propagation channel characteristics have been effectively used in several applications such as motion sensing and position detection. Considerable attention has been paid to channel-sounding methods that are easy to utilize using low-cost devices. This paper presents a device-free indoor location estimation method using the spatio-temporal features of radio propagation channels using a 2.4 GHz-band three-by-three multiple-input-multiple-output (MIMO) channel sounder developed using commodity wireless local area network (WLAN). The measurement results demonstrated a reasonable performance of the proposed method with a small number of antennas.

Quasi-Deterministic Channel Propagation Model for an Urban Environment at 28 GHz.

We reduced the parameters of the Quasi-Deterministic channel propagation model, recently adopted by the IEEE 802.11ay task group for next-generation Wi-Fi at millimeter-wave (mmWave), from measurements collected in an urban environment with our 28 GHz switched-array channel sounder. In the process-as a novel contribution-we extended the clustering of channel rays from the conventional delay and angle domains to the location domain of the receiver, over which the measurements were collected. By comparing channel realizations from the model to realizations from a leading commercial ray-tracer, we demonstrated that the model effects no detriment to accuracy while maintaining the benefit of significantly reduced complexity.

Distributed MIMO for Li-Fi: Channel Measurements, Ray Tracing and Throughput Analysis

LiFi has been considered as a promising candidate for future wireless indoor networks. The IEEE P802.15.13 and P802.11bb standardization groups agreed upon channel models generated using the non-sequential ray tracing approach of OpticStudio. In this paper, in order to validate the channel modelling approach, at first 2×2 multiple-input multiple-output (MIMO) channel measurements are carried out over 200 MHz bandwidth using a channel sounder. The experimental scenario is also modeled in 3D by applying ray tracing. The obtained results indicate good agreement between simulations and measured channel impulse responses, from which parameters such as path loss and delay spread are derived. After validating the channel modeling approach, we investigate the singular values and the effect of user mobility onto the performance in a 4×4 distributed multi-user MIMO scenario.