Propagation Channel Characteristics Research Articles

Millimeter wave channel characteristics of outdoor microcellular based on improved ray tracing method and BP neural network algorithm

The millimeter-wave single-input single-output (SISO) channel and single input multiple output (SIMO) channel are modeled and simulated in the outdoor microcellular scenarios at 28 GHz and 39 GHz based on improved ray tracing method and back propagation (BP) neural network algorithm. Based on the simulation data of wireless channel, the propagation characteristics of millimeter wave channel, such as path loss, root-mean-square (RMS) delay spread and received power, are analyzed and researched. The correctness and effectiveness of the improved ray tracing method are verified by comparing the measured results of the published literature with the simulated results. The results of path loss model parameters fitted by BP neural network algorithm are compared with those of path loss parameters simulated by improved ray tracing method. It is found that the results of path loss parameters fitted by BP neural network algorithm are in good agreement with those obtained by simulation of improved ray tracing method, which verifies that BP neural network algorithm can well predict large-scale parameters of outdoor microcellular millimeter-wave channel. Meanwhile, a universal path loss model for 28 GHz and 39 GHz millimeter-wave channels in outdoor microcellular line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios is presented. The results show that the RMS delay spread and received power in LoS scenario are smaller than those in NLoS scenario. The cumulative distribution function (CDF) of RMS delay spread, horizontal direction angle of arrival and the number of multipath clusters in LoS and NLoS scenarios are found to fit the Gaussian distribution properly. As the frequency increases, the RMS delay spread tends to increase, and the cluster of multipath arriving at receivers shows sparsity in the microcellular scenarios at millimeter-wave band.

Radio Frequency Link and User Selection Algorithm for 5G Mobile Communication System

Based on the millimetre-wave time-domain channel detector, this paper conducts channel measurement and modelling for different scenarios and antenna types in typical frequency bands and thus carries out a study on the propagation characteristics of millimetre-wave channels in typical frequency bands and scenarios for 5G. The time-varying characteristics and modelling methods of millimetre-wave clusters are studied, and the time-varying channel simulation strategy and linear regression fitting method are used to establish the time-varying generation and extinction model of clusters by combining the measured data of 26 GHz large-scale antenna channels. The algorithm is based on the correlation dictionary and achieves the efficient and optimal selection of large-scale antenna arrays in the millimetre-wave band. A low-complexity multiuser hybrid precoding design scheme is proposed based on the wideband millimetre-wave large-scale Multiple-Input Multiple-Output (MIMO) system. The scheme aims to maximize the system spectral efficiency and introduces the net spectral efficiency as a bridge to decouple the analogy precoding design from the digital precoding design, thus significantly reducing the computational complexity. In the analogy precoding stage, a Hungarian algorithm-based beam assignment method is proposed to avoid beam conflicts and maximize the net spectral efficiency of the system; in the digital precoding stage, the equivalent channel matrix of each subcarrier is diagonalized to eliminate multiuser interference. Finally, the effectiveness of the scheme is verified by simulation. In this paper, we focus on the radio frequency (RF) link and user selection algorithm of 5G mobile communication system. Through the study of these two aspects, the RF link of our communication system has high stability and reliability, and through the study of the algorithm used for selection, our results also have a strong practical value.

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.

Modeling and Analysis of Short Distance Sub-Terahertz Communication Channel via Mixture of Gamma Distribution

With the recent developments on opening the terahertz (THz) spectrum for experimental purposes by the Federal Communications Commission, transceivers operating in the range of 0.1THz-10THz, which are known as THz bands, will enable ultra-high throughput wireless communications. However, actual implementation of the high-speed and high reliability THz band communication systems should start with providing extensive knowledge in regards to the propagation channel characteristics. Considering the huge bandwidth and the rapid changes in the characteristics of THz wireless channels, ray tracing and one-shot statistical modeling are not adequate to define an accurate channel model. In this work, we propose Gamma mixture based channel modeling for the THz band via the expectation-maximization (EM) algorithm. First, maximum likelihood estimation (MLE) is applied to characterize the Gamma mixture model parameters, and then EM algorithm is used to compute MLEs of the unknown parameters of the measurement data. The accuracy of the proposed model is investigated by using the Weighted relative mean difference (WMRD) error metrics, Kullback-Leibler (KL)-divergence, and Kolmogorov-Smirnov (KS) test to show the difference between the proposed model and the actual probability density functions (PDFs) that are obtained via the designed test environment. To efficiently evaluate the performance of the proposed method in more realistic scenarios, all the analysis is done by examining measurement data from a measurement campaign in the 240 GHz to 300 GHz frequency range, using a well-isolated anechoic chamber. According to WMRD error metrics, KL-divergence, and KS test results, PDFs generated by the mixture of Gamma distributions fit to the actual histogram of the measurement data. It is shown that instead of taking pseudo-average characteristics of sub-bands in the wide band, using the mixture models allows for determining channel parameters more precisely.

Nano-Sensor Modelling for Intra-Body Nano-Networks

In this work, the author has evaluated the propagation of electromagnetic waves inside the human tissue such as blood, skin and fat for single-path and multi-path layers according to nano sensor transmit power calculations. In particular, the propagation characteristics of the Intra-Body Nano-Network communication channel are calculated using a theoretical approach. The analysis in this paper provides an evaluation related to the path loss, bit error rate, signal to noise ratio and the channel capacity. The model is evaluated for each single-path effect and multi-path effect. The effects of human tissue for each blood, skin and fat for single-path effect and multi-path are included in the analysis. The model frequency range is chosen from 0.01 to 1.5 THz frequencies, which are ideal for designing nano sensors antennae and using THz range for communication. This paper will also guide other researchers who are working on the electromagnetic radiation performance of Intra-Body Nano-Network and Nano sensors designed at the THz range.

3D Multiple-Antenna Channel Modeling and Propagation Characteristics Analysis for Mobile Internet of Things

The demand for optimization design and performance evaluation of wireless communication links in a mobile Internet of Things (IoT) motivates the exploitation of realistic and tractable channel models. In this paper, we develop a novel three-dimensional (3D) multiple-antenna channel model to adequately characterize the scattering environment for mobile IoT scenarios. Specifically, taking into consideration both accuracy and mathematical tractability, a 3D double-spheres model and ellipsoid model are introduced to describe the distribution region of the local scatterers and remote scatterers, respectively. Based on the explicit geometry relationships between transmitter, receiver, and scatterers, we derive the complex channel gains by adopting the radio-wave propagation model. Subsequently, the correlation-based approach for theoretical analysis is performed, and the detailed impacts with respect to the antenna deployment, scatterer distribution, and scatterer density on the vital statistical properties are investigated. Numerical simulation results have shown that the statistical channel characteristics in the developed simulation model nicely match those of the corresponding theoretical results, which demonstrates the utility of our model.

Spatial characterization of propagation channels for terahertz band

The aim of this work consists in characterizing the Terahertz (THz) propagation channel in an indoor environment, in order to propose a channel model for THz bands. We first described a propagation loss model by taking into account the attenuation of the channel as a function of distance and frequency. The impulse response of the channel is then described by a set of rays, characterized by their amplitude, their delay and their phase. Apart from the frequency selective nature, path loss in THz band is also an others issue associated with THz communication systems. This work based on the conventional Saleh-Valenzuela (SV) model which is intended for indoor scenarios. In this paper, we have introduced random variables as Line of sight (LOS) component, and then merging it with the SV channel model to adopt it to the THz context. From simulation, we noted an important effect when the distance between the transmitter and the receiver change. This effect produces variations in frequency loss. The simulations carried out from this model show that to enhance the performance of THz system it is recommended to transmit information over transmission windows instead over the whole band.

Research on 2.4 GHz Wireless Channel Propagation Characteristics in a Steel Ship Cabin

Wireless sensor network (WSN) has become a popular technology and has a good potential application in naval architecture and marine engineering field. Analysis of transmission ability of wireless signal in steel ship environment is important for network deployment including base station and node installation, which would directly impact network performance and has become a hot research field. This paper investigates 2.4 GHz frequency wireless signal propagation characteristics in the steel ship cabin. A 3D ray-tracing model of 2.4 GHz wave propagation in the ship cabin is established, a multipath propagation prediction is carried on, and receiving power is calculated. Besides, the experimental test is performed in the real ship. The simulated and experimental results are processed and compared; the influence law of large obstacles on the signal is discussed, and the guidance scheme for node and base station deployment of the wireless sensor network is proposed. The results show that this analysis could provide valid interpretation of wireless channel propagation characteristics in steel ships.

Improvement of the Communication between RFID Sensor Network Devices Used to Control and Monitor a Building

In the RFID sensor network (RSN), the devices communicate with each other by RF waves using the antennas through a propagation channel. A poor communication between these devices results in either a significant economic loss or security threats. The communication problems can have several origins depending on the type of antenna used and the nature of the propagation channel. In this work, our objective is to limit the communication problems between the nodes of this network that are linked to the characteristics of an indoor propagation channel. The goal is to predict the channel characteristics using the 3D ray tracing method in order to select the appropriate transmission parameters such as transmission power and duration of a symbol. To achieve this, we have modeled a building that is sectioned as a propagation channel where network devices are deployed for control and monitoring. The communication was made at 915 MHz using the quasi‐isotropic 3D cubic antenna that we designed as well as a conventional dipole antenna in order to compare the results. We have found that the use of the 3D cubic antenna gives several advantages to the RFID sensor network compared to the most commonly used conventional dipole antenna, such as a transmission power of 0 dBm which automatically leads to an increase in the lifetime of the devices, as well as a minimum symbol duration of around 219.78 ns which gives a high bit rate.

Channel Measurement and Modeling Prototype for IEEE 802.22-Based Regional Area Networks

During the design and development of a reliable transceiver, its performance and robustness are evaluated using channel models that simulate the propagation channel characteristics in a real-world environment. In the case of wide-area communication systems in rural areas such as those based on TV white spaces, long delay multipath fading is one of the dominant factors impairing communication quality, and it is important to apply realistic multipath fading channel models in various application scenarios. Therefore, it is necessary to develop channel measurement and modeling systems that adaptively obtain channel factors and reflect multipath propagation characteristics in various wide-area communication environments. In this study, we developed a flexible channel measurement and modeling prototype applicable to mobile IEEE 802.22-based wide-area communication systems, which can be simply implemented by using programmable hardware and software. The prototype includes a new channel modeling framework that applies an improved double exponential slope model to extract the essential factors of multipath propagation characteristics. To validate the developed prototype, a fading emulator is applied to it to measure the raw data used for modeling. As a result, the multipath fading characteristics measured with the prototype were successfully modeled and reproduced by the proposed channel modeling framework with a high fitness of root mean square delay spread distribution. The derived bit error rate characteristics agreed better with the simulation results compared to the conventional channel model.

Spectrum-aware cross-layered routing protocol for cognitive radio ad hoc networks

Cognitive radio network has been proposed as a promising technology to satisfy the manifold requirements of future generation (5G) wireless system by intelligently accessing the underutilized channel of a primary user. However, due to the heterogeneity in channel propagation characteristics, intermittent availability of licensed channel, recurrent hand-offs, and need of a protection to primary users, finding a successful route is more challenging. Also, incorporation of opportunistic spectrum access in cognitive radio network requires a potential spectrum management functions across the network layers. Hence, a cross-layered channel assignment algorithm and routing algorithm is proposed for a cognitive radio ad hoc network which can overcome above-mentioned challenges and provide a stable path for routing of data packets. A novel metric, for the probability of successful transmission of a channel is derived by considering channel statistics, sensing periodicity of the cognitive user, and time-varying channel quality. Also, the number of available channels and their characteristics is considered for the selection of a next-hop node with an aim to avoid the one-hop neighbors located in the PU transmission range. The proposed routing protocol is simulated in ns-2 and compared with the existing similar protocols. The performance shows that the proposed algorithm performs better in terms of throughput, end-to-end delay, number of spectrum hand-offs, and interference to the primary user in a significant manner.

Shock wave propagation in long laboratory sparks under negative switching impulses

A series of 1.27 m air gap discharge tests under negative switching impulses were carried out to characterize shock wave expansion behavior along leader channels. A high-speed Schlieren system was used to identify shock wave propagation characteristics near the high-voltage electrode. According to the Schlieren images, three distinct types of shock waves were recognized during the leader propagation and after the air gap breakdown: (1) spherical shock wave (SSW), (2) cylindrical shock wave (CSW), and (3) bow shock wave (BSW). To the best of our knowledge, it is the first time to recognize SSWs at the point where the space leader meets the main channel and BSWs along the leader branch after the main leader bridges the air gap. According to the proposed velocity calculation method, the propagation velocity of SSW and CSW was calculated as a function of the shock radius, as well as the shock wave head of BSW. Moreover, a transient magnetohydrodynamics model was developed to predict shock wave front propagation characteristics of both straight and bending channels after breakdown. The predicted shock wave propagation velocity and shock radius showed good agreement with Schlieren images.

A parametric study of long-range atmospheric sound propagation using Bellhop Ray-tracing Model

In the context of research on the measurement of long-range attenuation of noise from terrestrial sound sources, a parametric study of atmospheric sound propagation channel characteristics as a function of source height, ground characteristics and meteorological conditions is presented. The study relies on ray tracing. The Bellhop ray-tracing model which is well known in underwater acoustics has been used here. In this paper, the accuracy of Bellhop's predictions in the atmosphere is first addressed by comparison with published benchmarks cases by Attenborough et al and results from Salomon's ray model. No significant discrepancy was noticed with respect to these references. The second part of the paper presents a parametric study for source heights ranging from 0.05 m to 200 m, a grid of receivers at ranges between 200m and 2 km from the source and between 2 and 50 m height. A homogeneous flat absorbing ground described by a complex reflection factor is assumed. For the atmospheric conditions, a subset of the WiSi classification was considered. The results are analyzed from the point of view of the receiver and discussed in terms of attenuation, number of arrivals and number of reflections from the ground.

Channel Characterization and Realization of Mobile Optical Wireless Communications

Link instability induced by users’ mobility is one of the challenges of optical wireless communications (OWC) inherited from the propagation nature of light. Hence, good understanding of the optical channel characteristics in dynamic environments plays a vital role in developing robust resource management strategies in OWC networks. Unfortunately, it is quite difficult to collect accurate indoor optical channel data in dynamic environments. In addition, indoor trajectory dataset is not publicly available. To overcome such limitations, this paper proposes a mobile terminal-centric analytical framework that captures the propagation channel characteristics in a mobile OWC network whose downlink is based on visible light and uplink is based on infrared light. We abstract the nature of human behavior by integrating both macro and micro mobility patterns. These patterns are then used to realize the spatio-temporal characteristics of optical wireless channels under long-term environment-confined mobility. The statistics derived from the developed framework indicate that the mobile line-of-sight (LOS) channel gain follows space-time-dependent multiple-peak Nakagami distributions, whereas the non-line-of-sight (NLOS) channel gain adheres to various space-time-dependent single peak distributions under different indoor layouts. The overall distribution of NLOS bandwidth follows space-time-dependent multiple-peak log-logistic distributions in downlinks and space-time-dependent generalized log-logistic distributions in uplinks. Our investigation demonstrates that the indoor layout and the user’s environment-confined mobility pattern significantly impact the LOS dynamics but present limited impact on NLOS components. Motivated by the need for better channel models for mobile OWC, the proposed framework fills up an important gap in literature and help the research community to understand better the indoor optical wireless channel characteristics.

Antenna-Independent Frequency- and Time-Domain Representation of Wireless Channel

Propagation channel characterization and modeling is an important aspect in the wireless communication domain prior to the design and implementation of any RF system, especially in the millimeter-wave band for the 5G ecosystem. Several methods have been proposed in the literature for different environments where the antenna effects present inherently in the measured results caused by ambiguous channel characterization and model. The results are antenna specific and unreliable for other antennas. In this letter, the standalone channel response (frequency and time domain) excluding the antenna effects has been derived using a two-port network approach. Identical horn antennas operating in the C -band have been used to measure the channel transfer function and impulse response. A comparative investigation of the measured results with and without the antenna effects is presented. It is observed that measuring the channel characteristics without excluding the transmitting and receiving antenna effects adds additional time delays and reduced coherence bandwidth of the channel.

Ultra-Wideband Air-to-Ground Propagation Channel Characterization in an Open Area.

This paper studies the air-to-ground ultra-wideband channel through propagation measurements between 3.1 GHz to 4.8 GHz using unmanned-aerial-vehicles (UAVs). Different line-of-sight (LOS) and obstructed-LOS scenarios and two antenna orientations were used in the experiments. Multipath channel statistics for different propagation scenarios were obtained, and the Saleh-Valenzuela model was found to provide a good fit for the statistical channel model. An analytical path loss model based on antenna gains in the elevation plane is provided for unobstructed UAV hovering and moving (in a circular path) propagation scenarios.

Experimental Field Trials on MU-MIMO Transmissions for High SHF Wide-Band Massive MIMO in 5G

The field trial results for massive multi-user multiple-input multiple-output (MU-MIMO) transmission at 28 GHz with 500 MHz bandwidth are reported in this paper. In this experiment, hybrid beamforming with block diagonal precoding is employed, in which channel state information is acquired by uplink sounding assuming channel reciprocity in a time division duplex system. 8-user MU-MIMO scenarios with various user distributions are considered, and the downlink transmission performance and propagation channel characteristics are evaluated. The trial results show that digital precoding improves the system performance and that over 20 Gbps total throughput can be achieved for a variety of user distributions. The performance of the precoding is evaluated in terms of eliminating inter-user interference.

Measurement and Modeling of LTE‐Railway Channels in High‐Speed Railway Environment

AbstractHigh‐speed railway (HSR) is becoming one of the most effective and important transportation modes. To ensure the safety of HSR, a stable communication system is necessary. The understanding of propagation characteristics of radio channel is important for HSR communication system design. In this paper, a wideband measurement in suburban HSR scenarios at 460 MHz is presented. Some typical channel parameters such as the large‐scale fading, Ricean factor, power‐delay profile, and root‐mean‐square delay spread are extracted from the measurement data. The different distributions of small‐scale fading are also compared. The relationships between the channel parameters and the distance of transmitter (base station) and receiver are also explored. The results could provide a reference for the design and evaluation of HSR communication network, especially for the Long‐Term‐Evolution (LTE)‐railway system.

Novel Unmanned Aerial Vehicle-Based Line-of-Sight MIMO Configuration Independent of Transmitted Distance Using Millimeter Wave

Recently, the millimeter-wave band has been used in outdoor wireless communications to improve the frequency utilization efficiency. In this study, we propose a method to realize line-of-sight multiple-input multiple-output (LOS-MIMO) transmission independent of the transmitted distance using a two-dimensional (2-D) fixed antenna element arrangement, assuming millimeter-wave-band communication by small autonomous unmanned aerial vehicles. In conventional LOS-MIMO transmission with uniformly spaced antenna elements, the theoretical upper bound of the channel capacity is obtained, which decreases at a certain transmitted distance. Therefore, we focus on the fact that the propagation channel characteristics in pure LOS are geometrically determined by the transmitted distance, and consider the optimization of the arrangement of antenna elements. The element arrangement is fixed without using antenna selection from the viewpoint of system simplification. In addition, from the viewpoint of array size, we study the optimization corresponding to a 2-D element arrangement. The proposed method approximates the optimal arrangement from a vast number of 2-D element arrangements using a genetic algorithm. We evaluate the channel capacity characteristics of the proposed method by computer simulation and show that the characteristic degradation due to change in the transmitted distance in conventional LOS-MIMO transmission is improved. In addition, we evaluate a $4\times4$ MIMO transmission in an outdoor environment. The $4\times4$ MIMO propagation channel is also measured by an actual measurement equipment in the 66-GHz band and it is shown that the measured and calculated results agree with each other.

Unsupervised Specific Emitter Identification Method Using Radio-Frequency Fingerprint Embedded InfoGAN

Machine learning approaches are becoming increasingly popular to improve the efficiency of specific emitter identification (SEI). However, in most non-cooperative SEI scenarios, supervised and semi-supervised learning approaches are often incompatible due to the lack of labeled datasets. To solve this challenge, an unsupervised SEI framework is proposed based on information maximized generative adversarial networks (InfoGANs) and radio frequency fingerprint embedding (RFFE). To enhance individual discriminability, a gray histogram is first constructed according to the bispectrum extracted from the received signal before being embedded into the proposed framework. In addition to the latent class input and the RFFE, the proposed InfoGAN incorporates a priori statistical characteristics of the wireless propagation channels in the form of a structured multimodal latent vector to further improve the GAN quality. The probabilistic distribution of the bispectrum is derived in closed-form and the convergence of the InfoGAN is analyzed to demonstrate the influence of the RFFE. Numerical results indicate that the proposed framework consistently outperforms state-of-the-art algorithms for unsupervised SEI applications, both in terms of evaluation score and classification accuracy.