Wideband Radio Channel Research Articles

Time-Varying Channel Estimation Based on Distributed Compressed Sensing for OFDM Systems.

For orthogonal frequency division multiplexing (OFDM) systems in high-mobility scenarios, the estimation of time-varying multipath channels not only has a large error, which affects system performance, but also requires plenty of pilots, resulting in low spectral efficiency. To address these issues, we propose a time-varying multipath channel estimation method based on distributed compressed sensing and a multi-symbol complex exponential basis expansion model (MS-CE-BEM) by exploiting the temporal correlation and the joint delay sparsity of wideband wireless channels within the duration of multiple OFDM symbols. Furthermore, in the proposed method, a sparse pilot pattern with the self-cancellation of pilot intercarrier interference (ICI) is adopted to reduce the input parameter error of the MS-CE-BEM, and a symmetrical extension technique is introduced to reduce the modeling error. Simulation results show that, compared with existing methods, this proposed method has superior performances in channel estimation and spectrum utilization for sparse time-varying channels.

Implementation of the Maximum Bandwidth Ratio of Satellite Radio Communication Systems under the Conditions for Intramodal Dispersion of Transionospheric Radio Channels

The problem of significant extension of the band of the transionospheric radio channel to the maximum possible values is solved to improve the efficiency of satellite communication systems. Hardware and software are created to suppress the group delay dispersion using methods of data mining for experimental diagnostics of a transionospheric communication line. Algorithms and tools for intelligent sensory diagnostics of wideband radio channels with adaptation to dispersion variability are developed. In the absence of adaptation, it is possible to create radio channels of undistorted transmission with a bandwidth ratio of no greater than 4.5%, while adaptation to dispersion variability makes it possible to increase the bandwidth ratio to 11.5%. The greatest bandwidth ratio (20–25%) for dispersion-free transmission can be achieved with the aid of adaptive inverse filtering of the channel frequency response in combination with such intelligent methods as equalization with error, machine learning of channel equalizer, and big data processing.

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.

Joint Modeling of Received Power, Mean Delay, and Delay Spread for Wideband Radio Channels

We propose a multivariate log-normal distribution to jointly model received power, mean delay, and root mean square (rms) delay spread of wideband radio channels, referred to as the standardized temporal moments. The model is validated using experimental data collected from five different measurement campaigns (four indoor scenarios and one outdoor scenario). We observe that the received power, the mean delay, and the rms delay spread are correlated random variables, and therefore, should be simulated jointly. Joint models are able to capture the structure of the underlying process, unlike the independent models considered in the literature. The proposed model of the multivariate log-normal distribution is found to be a good fit for a large number of wideband data sets.

A Comparison of Empirical and Ray-Tracing Models for Indoor Radio-Wave Propagation [Wireless Corner

Both empirical and ray-tracing models are powerful tools for studying propagation in indoor environments. Although the empirical models perform well in many cases, their physical significance is not clearly understood. Ray tracing is based on physics fundamentals, and its application as well as the interpretation of its results is more general. We compare the performance of both models for indoor environments. We found that the path-loss (PL) prediction error of the ray-tracing model is comparable to the error of the linear regression fit of the PL in a site-specific empirical model. Those empirical models provide some advantages when making estimations in the same environment in which they were trained, but their performance degrades in other environments. Ray-tracing models obtain better results when a wider range of application environments is sought. Ray tracing also provides a good insight into the specific propagation phenomena that take place in the wideband radio channel, so the relevant contributions can be identified.

Deterministic Modeling of Indoor Stairwells Propagation Channel

A deterministic approach is presented for modeling a wireless propagation channel in a stairwell environment. The ray-tracing method is used to find the reflected and diffracted rays with the highest contribution to the total received power at a given location. Most significant reflected rays occur at the surfaces of specific steps of the stairwell and the surrounding lateral walls, while most significant diffracted beams emanate from the edges of steps located between transmitter and receiver antennas. The uniform theory of diffraction is used to calculate the diffracted contributions from the edges, whereas the multiple diffractions are calculated using heuristic diffraction coefficients. Unlike the reported models, the proposed model is deterministic and focuses on the radio propagation within stairwells at the X-band frequencies range. Experimental validation is performed using two types of antennas, horns and patches, for an operating frequency of 10 GHz. Simulated results of narrowband and wideband radio channels showed a good agreement with the experimental ones. The correlation coefficient between measured and simulation results is around 80% on average, and the residual errors between measured and simulated total received power results are less than 13%, which means that the proposed model has fair accuracy for such complex environments.

WBAN Channel Characteristics Between Capsule Endoscope and Receiving Directive UWB On-Body Antennas

This paper presents a study on the ultra wideband (UWB) radio channel characteristics between a capsule endoscope and a directive on-body antenna in different parts of the small intestine. The study is conducted using a finite integration technique (FIT) based electromagnetic simulation software CST Studio Suite and four of its anatomical voxel models. The capsule endoscope model is set inside different areas of the small intestine of the voxel models. A recently published directive on-body antenna designed for in-body communications is used in the evaluations. The obtained frequency and time domain channel characteristics are compared with previously published results with another directive on-body antenna designed for capsule endoscopy communications. Power flow presentations are used to understand differences obtained with two on-body antennas. Different rotation angles of the capsule are also considered in this study. It is found that channel characteristics vary remarkably depending on the antenna location in the small intestine and location of the on-body antenna. Thus, the on-body antennas should be located carefully to ensure coverage over the whole intestine area. Path loss does not only depend on the distance between a capsule and the on-body antenna but also on the tissues between the capsule and on-body antennas. Obviously, the antenna patterns have clear impact on the received signal’s strength. Furthermore, orientation of the capsule affects also strongly impact when linearly polarized antennas are used.

Measurement of Wideband Indoor Radio Propagation Channel Using USRP

This paper describes the measurement of wideband radio channel sounding techniques for indoor radio propagation. The system consists of multiple frequency band- switching scheme, which is able to extend the overall sounding bandwidth without changing operation bandwidth of the hardware. It is used for low mobility and high data rate communications. The system of the channel sounding is developed on a universal software radio peripheral (USRP) that employs an orthogonal frequency division multiplexing signal at 2.1902.290 GHz. In each sounding cycling, ten sub band frequency (10 MHz bandwidth) are used to reach an equivalent measurement over a 100-MHz bandwidth, corresponding to 10 ns time delay resolution. The validation test was perform using Vector Network Analyser (VNA). It will be showed variation result of channel impulse response consist of radio channel accuration and resolution between VNA and USRP. At the end of the chapter the proposed system will be used for measuring indoor channel propagation using five scenarios line of sight (LOS) and non-line of sight (NLOS).

A line-of-sight propagation performance study for underground mining in an arched-shaped tunnel environment

ABSTRACTThis article investigates the effect of antenna polarization, directivity and placement on the line-of-sight wideband radio channel characteristics of an arch-shaped underground mine tunnel over the 2.4 GHz frequency band. Access point-to-access point and access point-to-mobile wireless communication configurations were examined for linearly and circularly polarized antennas mounted in the center, on the wall and ceiling. The circularly polarized directional antennas offer higher coherent bandwidth, whereas the linearly polarized omni-directional antennas offer lower attenuation rate. A higher directive antenna enhances coverage area, coverage reliability and channel coherent bandwidth. For access point-to-mobile communication, a circularly polarized directional antenna with a horizontally polarized omni-directional antenna gives the best performance in terms of attenuation rate and coherent bandwidth.

Wideband MIMO Channel Estimation for Hybrid Beamforming Millimeter Wave Systems via Random Spatial Sampling

Millimeter Wave (mmWave) massive Multiple Input Multiple Output (MIMO) systems realizing directive communication over large bandwidths via Hybrid analog and digital BeamForming (HBF) require reliable estimation of the wideband wireless channel. However, the hardware limitations with HBF architectures in conjunction with the short coherence time inherit in mmWave communication render this estimation a challenging task. In this paper, we develop a novel wideband channel estimation framework for mmWave massive MIMO systems with HBF reception. The proposed framework jointly exploits the low rank property and the available angular information to provide more accurate channel recovery, especially for short beam training intervals. We introduce a novel analog combining architecture that includes a random spatial sampling structure placed before the input of the analog received signals to the digital component of the HBF receiver. This architecture supports the proposed matrix-completion-based estimation approach in providing the sampling set of measurements for recovering the unknown channel matrix. The performance improvement of the proposed approach over representative state-of-the-art techniques is demonstrated through numerous computer simulation results.

Comprehensive Study on the Impact of Sternotomy Wires on UWB WBAN Channel Characteristics on the Human Chest Area

This paper presents a comprehensive study on the impact of the sternotomy wires on the characteristics of ultra wideband (UWB) radio propagation channel in the human chest area. The study is conducted using two simulation models: a planar layer model and a three-dimensional elliptical layer model. The study includes antennas designed for on-body and in-body communications. Furthermore, the measured data and propagation path calculations are presented to verify the simulation results. The main purpose is to show how the steel wires affect the on-body channel characteristics and in-body propagation within the tissues when the monitoring antennas are located in close vicinity of the human body. The study is conducted by evaluating: 1) channel characteristics in both frequency and time domains; 2) 2D power flow figures; and 3) Poynting vector values. Furthermore, the impact of the fat layer thickness on the visibility of sternotomy wires is studied. Moreover, the impact of sternotomy wires is studied for the case of the recently operated patient, for which the sternotomy wires are on the sternum bone surface, as well as for the case where the sternotomy wires are embedded into the sternum bone. It is found that sternotomy wires have a clear impact on the channel. The strength of the impact depends on the antenna types used by the monitoring devices, the thickness of the fat layer in the sternum area, and whether the sternotomy wires are on the sternum surface or whether they have already been embedded on the sternum as it happens with time.

Joint Channel-Estimation and Equalization of Single-Carrier Systems via Bilinear AMP

We propose a novel soft-input soft-output equalizer for single-carrier transmissions over unknown frequency-selective block-fading channels. Our equalizer leverages the recently proposed parametric bilinear generalized approximate message passing algorithm for joint channel-estimation and symbol-detection, and exploits fast Fourier transform (FFT)-processing to achieve a per-symbol complexity that grows only logarithmically in the channel delay-spread. Furthermore, it supports the use of Gaussian mixture models to support the approximately sparse nature of wideband wireless channel responses. Numerical experiments, conducted using physically motivated Saleh–Valenzuela channel models, show that the proposed approach achieves channel normalized mean square error and bit error rate that are significant improved over existing turbo frequency-domain equalization approaches for unknown channels. Additional experiments show that the proposed scheme facilitates much higher spectral efficiencies than sparse deconvolution methods based on convex relaxation.

Performance Analysis of Different Indoor Ultra Wide Band Channel Indicators


 
 
 In this paper, performance of different indicators for the profiling of Ultra Wide Band (UWB) wireless propagation channel are analyzed. In particular, the γ-indicator and the kurtosis index k are compared in terms of the standard error. In order to improve the accuracy in the kurtosis case, results of the bootstrap error procedure are also accomplished. Further, an evaluation on the computational time needed for error estimation, is also provided. The comparison is made according to a real set of data derived from UWB measurement campaign accomplished within a modern laboratory/office building in which the two above mentioned indicators have been evaluated.
 
 

Indoor Corridor Wideband Radio Propagation Measurements and Channel Models for 5G Millimeter Wave Wireless Communications at 19 GHz, 28 GHz, and 38 GHz Bands

This paper presents millimeter wave (mmWave) measurements in an indoor environment. The high demands for the future applications in the 5G system require more capacity. In the microwave band below 6 GHz, most of the available bands are occupied; hence, the microwave band above 6 GHz and mmWave band can be used for the 5G system to cover the bandwidth required for all 5G applications. In this paper, the propagation characteristics at three different bands above 6 GHz (19, 28, and 38 GHz) are investigated in an indoor corridor environment for line of sight (LOS) and non‐LOS (NLOS) scenarios. Five different path loss models are studied for this environment, namely, close‐in (CI) free space path loss, floating‐intercept (FI), frequency attenuation (FA) path loss, alpha‐beta‐gamma (ABG), and close‐in free space reference distance with frequency weighting (CIF) models. Important statistical properties, such as power delay profile (PDP), root mean square (RMS) delay spread, and azimuth angle spread, are obtained and compared for different bands. The results for the path loss model found that the path loss exponent (PLE) and line slope values for all models are less than the free space path loss exponent of 2. The RMS delay spread for all bands is low for the LOS scenario, and only the directed path is contributed in some spatial locations. For the NLOS scenario, the angle of arrival (AOA) is extensively investigated, and the results indicated that the channel propagation for 5G using high directional antenna should be used in the beamforming technique to receive the signal and collect all multipath components from different angles in a particular mobile location.

Multipath Multiplexing for Capacity Enhancement in SIMO Wireless Systems

This paper proposes a novel and simple orthogonal faster than Nyquist (OFTN) data transmission and detection approach for a single input multiple output system. It is assumed that the signal having a bandwidth $B$ is transmitted through a wireless channel with $L$ multipath components. Under this assumption, this paper provides a novel and simple OFTN transmission and symbol-by-symbol detection approach that exploits the multiplexing gain obtained by the multipath characteristic of wideband wireless channels. It is shown that the proposed design can achieve a higher transmission rate than the existing one [i.e., orthogonal frequency division multiplexing (OFDM)]. Furthermore, the achievable rate gap between the proposed approach and that of the OFDM increases as the number of receiver antennas increases for a fixed value of $L$ . This implies that the performance gain of the proposed approach can be very significant for a large-scale multi-antenna wireless system. The superiority of the proposed approach is shown theoretically and confirmed via numerical simulations. Specifically, we have found upper-bound average rates of 15 and 28 bps/Hz with the OFDM and proposed approaches, respectively, in a Rayleigh fading channel with 32 receive antennas and signal-to-noise ratio of 15.3 dB. The extension of the proposed approach for different system setups and associated research problems is also discussed.

Phase Noise Effects on Wideband Mobile Radio Channel Sounding

In this work three wideband mobile radio channel sounding methods are simulated and compared using computational tools. The considered sounders include the traditional STDCC and two other proposed sounding methods that are based on OFDM digital transmission and detection procedures and on matched filtering. The impact of the phase noise introduced by the receiver local oscillator in the precision of the examined sounders is analyzed by comparing the estimated channel results with the simulated reference channel. Other impairments factors like thermal noise or nonlinear distortion affecting the system are not considered.

Inter-Floor Wide Band Radio Channel Measurements and Simulation Applying Saleh-Valenzuela Model

This paper explores the accuracy of Saleh-Valenzuela (SV) statistical simulation model in time of arrival domain (ToA) applied on inter-floor wide band indoor radio channels. In order to extract the model parameters, an extensive measurement campaign was performed inside a modern building by applying vector network analyzer method at frequency of 1.8 GHz. The measurement results are presented in form of path loss exponent and delay spread statistics for each number-of-floors (NOF) distance between the antennas (up to 4). Path loss exponent was found to be around 3 for antennas on a same floor and around 5.5 for any other case when antennas were on separated floors. CDFs of rms delay spread may be divided into two groups: the first group is made of single-floor (SF) case and distanced-floors (DF) cases (three or more floors separated antennas) which showed similarities performing median value at 20 ns. For neighboring-floors (NF) cases (one and two floors separation) this value was increased to 35 ns. SV simulation, run with the extracted parameters, assessed delay spread statistics sufficiently good for the first group of CDFs. In order to assess the second group results, it was necessary to introduce simple corrections in SV model application.

Dynamic denoising studies in wideband radio channel measurement and modeling

The fixed level and dynamic denoising method was studied based on indoor-to-outdoor measured channel impulse responses (IRs) at 5.25 GHz with radio frequency (RF) 100 MHz bandwidth. It is found that the dynamic ranges, peak powers and noise floors of the IRs are with close correlations. The comparisons with different denoising methods are given by deriving the power delay profiles (PDPs), root mean square (RMS) delay spread (RMS DS), number of paths (NOPs) and Ricean K-factors. It is concluded that the traditional fixed level noise cut is under estimate of DS and NOPs. The Ricean K-factors are of little sensitive to noise cut irrespective of what kind of methods applied. The PDPs are not very sensitive to the fixed level noise cut, however, obvious changes can be found by dynamic noise cut. The dynamic noise cut is preferred when clear noise floors is observed and decided from the measured IRs, it's of importance in data post processing for wideband radio channel measurements as well as the relevant modeling work.

Measurement, Characterization, and Modeling of the Helicopter Satellite Communication Radio Channel

The satellite-to-helicopter radio channel is measured, characterized, analyzed, and modelled. We used a sweep time delay cross correlation sounder operating at 14.25 GHz and actual helicopters for the experiment. From the measurements, signal fading, delay and Doppler spread are estimated. Wideband radio channel results show that the signal delay spread is small enough, so 32 MHz satellite transponders could be used with no need of equalization. We also observed two important propagation impairments on the received signal envelope, both of them caused by the main rotor blades. The first one is the power attenuation produced when the LoS is obstructed by the blades. We demonstrate that this effect could be mitigated by using spatial or polarization diversity technique in the receiver end. The second one is the presence of multipath propagation leading to a power level oscillation dependent on the amplitude of the received multipath components. An UTD-based 3-D ray tracing model was used to conclude that the main multipath components are generated by diffraction on the rotor blade edges.

Joint Approximately Sparse Channel Estimation and Data Detection in OFDM Systems Using Sparse Bayesian Learning

It is well known that the impulse response of a wideband wireless channel is approximately sparse, in the sense that it has a small number of significant components relative to the channel delay spread. In this paper, we consider the estimation of the unknown channel coefficients and its support in OFDM systems using a sparse Bayesian learning (SBL) framework for exact inference. In a quasi-static, block-fading scenario, we employ the SBL algorithm for channel estimation and propose a joint SBL (J-SBL) and a low-complexity recursive J-SBL algorithm for joint channel estimation and data detection. In a time-varying scenario, we use a first-order autoregressive model for the wireless channel and propose a novel, recursive, low-complexity Kalman filtering-based SBL (KSBL) algorithm for channel estimation. We generalize the KSBL algorithm to obtain the recursive joint KSBL algorithm that performs joint channel estimation and data detection. Our algorithms can efficiently recover a group of approximately sparse vectors even when the measurement matrix is partially unknown due to the presence of unknown data symbols. Moreover, the algorithms can fully exploit the correlation structure in the multiple measurements. Monte Carlo simulations illustrate the efficacy of the proposed techniques in terms of the mean-square error and bit error rate performance.