Two-ray Model Research Articles

Pedestrian-to-Vehicle Communications in an Urban Environment: Channel Measurements and Modeling

As wireless connectivity becomes increasingly ubiquitous, a greater emphasis will be placed upon the seamless integration of dissimilar networking technologies. One such example of this will occur in urban environments, where wearable devices and vehicular networks will operate in close proximity to one another. Clearly, a natural extension to both types of network is their interconnectivity through vehicle-to-pedestrian (V2P) or equivalently pedestrian-to-vehicle (P2V) communications as part of a much greater vehicle-to-X (V2X)-based intelligent transportation system. To this end, we empirically investigate the P2V communications channel at 5.8 GHz for the case of a moving vehicle when a person positioned by the edge of a road was either stationary or walking parallel to the side of the highway. The measurements considered a chest-mounted transmitter and four receiver locations on the vehicle covering the front wing mirrors and two positions on the roof, which simultaneously recorded the received signal power. To characterize the propagation mechanisms which are responsible for shaping the received signal in the P2V channel, we decomposed it into its path loss (PL), large-scale, and small-scale fading components. We first show that although there was evidence of interference caused by multiple rays interacting with one another, the popular two-ray ground-reflection PL model was unable to adequately describe the compounded effects of the vehicle and pedestrian’s body on the signal attenuation in the majority of the considered scenarios. Instead, we found that the overall PL was well characterized using a dual-slope log-distance model, with lognormal large-scale fading. Due to the often severe small-scale fading that was observed in the P2V channel, we have been able to utilize the $\kappa $ - $\mu $ extreme distribution with considerable success to characterize the worse than Rayleigh fading conditions which were encountered.

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

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

Unveiling the Hyper-Rayleigh Regime of the Fluctuating Two-Ray Fading Model

The recently proposed Fluctuating Two-Ray (FTR) model is gaining momentum as a reference fading model in scenarios where two dominant specular waves are present. Despite the numerous research works devoted to the performance analysis under FTR fading, little attention has been paid to effectively understanding the interplay between the fading model parameters and the fading severity. According to a new scale defined in this work, which measures the hyper-Rayleigh character of a fading channel in terms of the Amount of Fading, the outage probability and the average capacity, we see that the FTR fading model exhibits a full hyper-Rayleigh behavior. However, the Two-Wave with Diffuse Power fading model from which the former is derived has only strong hyper-Rayleigh behavior, which constitutes an interesting new insight. We also identify that the random fluctuations in the dominant specular waves are ultimately responsible for the full hyper-Rayleigh behavior of this class of fading channels.

Wireless Channel Propagation Characteristics and Modeling Research in Rice Field Sensor Networks.

Wireless channel propagation characteristics and models are important to ensure the communication quality of wireless sensor networks in agriculture. Wireless channel attenuation experiments were carried out at different node antenna heights (0.8 m, 1.2 m, 1.6 m, and 2.0 m) in the tillering, jointing, and grain filling stages of rice fields. We studied the path loss variation trends at different transmission distances and analyzed the differences between estimated values and measured values of path loss in a free space model and a two-ray model. Regression analysis of measured path loss values was used to establish a one-slope log-distance model and propose a modified two-slope log-distance model. The attenuation speed in wireless channel propagation in rice fields intensified with rice developmental stage and the transmission range had monotone increases with changes in antenna height. The relative error (RE) of estimation in the free space model and the two-ray model under four heights ranged from 6.48–15.49% and 2.09–13.51%, respectively, and these two models were inadequate for estimating wireless channel path loss in rice fields. The ranges of estimated RE for the one-slope and modified two-slope log-distance models during the three rice developmental stages were 2.40–2.25% and 1.89–1.31%, respectively. The one-slope and modified two-slope log-distance model had better applicability for modeling of wireless channels in rice fields. The estimated RE values for the modified two-slope log-distance model were all less than 2%, which improved the performance of the one-slope log-distance model. This validates that the modified two-slope log-distance model had better applicability in a rice field environment than the other models. These data provide a basis for modeling of sensor network channels and construction of wireless sensor networks in rice fields. Our results will aid in the design of effective rice field WSNs and increase the transmission quality in rice field sensor networks.

Physical Layer Security Over Fluctuating Two-Ray Fading Channels

Ensuring the physical layer security (PHY-security) of millimeter-wave (mmWave) communications is one of the key factors for the success of 5G. Recent field measurements show that conventional fading models cannot accurately model the random fluctuations of mmWave signals. To tackle this challenge, the fluctuating two-ray (FTR) fading model has been proposed. In this correspondence, we comprehensively analyze the PHY-security in mmWave communications over FTR fading channels. More specifically, we derive analytical expressions for significant PHY-security metrics, such as the average secrecy capacity, the secrecy outage probability, and the probability of strictly positive secrecy capacity, with simple functions. The effect of channel parameters on the PHY-security has been validated by numerical results.

Composite <inline-formula> <tex-math notation="LaTeX">$\alpha-\mu$ </tex-math> </inline-formula> Based DSRC Channel Model Using Large Data Set of RSSI Measurements

Channel modeling is essential for design and performance evaluation of numerous protocols in vehicular networks. In this work, we study and provide results for largescale and small-scale modeling of communication channel in dense vehicular networks. We first propose an approach to remove the effect of fading on deterministic part of the large-scale model and verify its accuracy using a single transmitter-receiver scenario. Two-ray model is then utilized for path-loss characterization and its parameters are derived from the empirical data based on a newly proposed method. Afterward, we use {\alpha}-{\mu} distribution to model the fading behavior of vehicular networks for the first time, and validate its precision by Kolmogorov-Smirnov (K-S) goodness-of-fit test. To this end, the significantly better performance of utilizing {\alpha}-{\mu} distribution over the most adopted fading distribution in the vehicular channels literature, i.e. Nakagami-m, in terms of passing K-S test has been investigated and statistically verified in this paper. A large received signal strength indicator (RSSI) dataset from a measurement campaign is used to evaluate our claims. Moreover, the whole model is implemented in a reliable discrete event network simulator which is widely used in the academic and industrial research for network analysis, i.e. network simulator-3 (ns-3), to show the outcome of the proposed model in the presence of upper layer network protocols.

A Performance Evaluation of Location Prediction Position-Based Routing Using Real GPS Traces for VANET

Vehicular ad-hoc network (VANET) is an emerging paradigm for road transportation which minimizes traffic, accidents and improves fuel efficiency. VANET uses the position of the vehicle obtained from satellite system such as global positioning system (GPS), global navigation satellite system, Compass and Galileo as a location id in position-based routing protocol. The position obtained from the satellite system is likely to have an error due to environmental and technical issues which effect the routing performance. Thus, this paper proposes a position-based routing protocol which uses Kalman filter based location prediction technique to improve routing performance by minimizing location error. The routing protocol performance is evaluated on NS-3.23 simulator with real time GPS traces and simulator generated mobility on Two-ray ground and Winner-II propagation model for 500 m transmission range. Further, performance is compared with other prediction-based routing protocol on the metrics of packet delivery ratio, average delay and throughput.

MM-wave wideband propagation model for wireless communications in built-up environments

Millimeter-wave technology is promising for the next generation of wireless communication. An appropriate channel model for typical scenarios in a built-up environment is crucially needed for development of future technologies such as 5G. This paper presents an efficient millimeter wave wideband propagation model that can be used for analysis and design purposes. Unlike the commonly used two-ray and statistical models, the proposed model has higher reliability and accuracy to simulate the considered environment. The uniform theory of diffraction has been used to calculate the total received signal due to multi-reflection–diffraction for both linear and circular polarization. Mathematical formulas have been derived for each considered ray contribution in terms of the building dimensions and the distances between the building, mobile and transmitter. The model has been used to evaluate the performance of the communication system at 28 and 73 GHz based on signal fading characteristics and power delay profile, and the simulation results have been compared with other published works

New Results on the Fluctuating Two-Ray Model With Arbitrary Fading Parameters and Its Applications

The fluctuating two-ray (FTR) fading model provides a much better fit than other fading models for small-scale fading measurements in millimeter wave communications. In this paper, using a mixture of gamma distributions, new exact analytical expressions for the probability density and cumulative distribution functions of the FTR distribution with arbitrary fading parameters are presented. Moreover, the performance of digital communication systems over the FTR fading channel is evaluated in terms of the channel capacity and the bit error rate. The interaction between channel fading parameters and system performance is further investigated. Our newly derived results extend and complement previous knowledge of the FTR fading model.

An indoor path loss model for wireless sensor networks

In this paper, path loss measurements were conducted and a path loss model was proposed for wireless sensor networks (WSNs) operating in indoor environment. This is done with a view to study transmit power requirements in indoor application of WSNs. The proposed model is a hybrid of the two-ray ground reflection model and the log-normal model and considers frequency and three-dimensional link trajectory as key parameters in evaluating path loss. The study highlights the effect of height on path loss exponent by means of various measurements taken in indoor environment. Comparison with the empirical data and other models in the literature was conducted and had very favourable results for the proposed model.

Power Optimization Assisted Interference Management for D2D Communications in mmWave Networks

Aiming at the problem of aggravated interference caused by the increasing number of devices, a transmitting power optimization algorithm is proposed, which combines the device association and beamwidth selection. In the premise of guaranteeing, the authenticity of millimeter wave (mmWave) application scenario, an mmWave device-to-device (D2D) network model is introduced, which integrates the roll off feature of Gaussian directional antenna model and the reflectivity of two-ray channel model. Specifically, the device association performed through distributed framework, and the beamwidth scheme optimized by the particle swarm optimization (PSO) algorithm, solve the non-convexity problem of transmitting power optimization in mmWave D2D networks. Simulation results indicate that, compared with the existing interference management algorithms which ignore the transmitting power of devices, the proposed algorithm can effectively reduce the transmitting power and interference, and the superior performance can be achieved.

Empirical Study of Near Ground Propagation in Forest Terrain for Internet-of-Things Type Device-to-Device Communication

This paper presents continuous-wave power measurements conducted in forest terrain with a focus on path-loss in a device-to-device (D2D) communication scenario. The measurements are performed at 917.5 MHz with measurement ranges extending to more than 2.5 km, using a purpose-developed measurement system with a dynamic range of 180 dB. The impact of different antenna heights has been investigated by placing antennas at 1.5-, 2.5-, and 3.5-m elevation over the terrain. The measurements show that the antenna elevation in the given scenario has no significant impact on the received power. The measurements also show that the dominant path of propagation is through the foliage for the first approximately 1000 m, resulting in foliage excess loss being the dominant loss mechanism in this region. After approximately 1000 m, the measured received power tends to follow the fourth-power law, indicating that the dominant loss mechanism in this region is the distance-dependent path-loss. The measurement results have been compared to models proposed in the literature based on empirical data, as well as models proposed by ITU and COST. The comparison shows that only two models predicted the limit in the foliage excess loss in the measurement data. By applying these excess loss models in combination with path-loss models, it is possible to model the measured total path-loss with a root-mean-square error of less than 10 dB. This is achieved by either applying a model proposed by Tewari or a combination between the two-ray path-loss model and the ITU-R P.2108 clutter loss model.

Multipath Robust Azimuthal Direction of Arrival Estimation in Dual-Band 2.45–5.2 GHz Networks

This paper presents a technique capable to ameliorating the impairment caused by radio channel multipath, in the estimation of the wireless communications direction of arrival (DoA). This feature is enabled by a space division multiple access approach supported by a DoA technique based on the combination of the estimates achieved at both 2.45 and 5.2 GHz. The DoA estimation relies on a comparison between the real-time received signal strength indicator and the predicted signal level distribution, which can be estimated and stored without the need of lengthy offline measurement. The experimental setup adopted for the technique validation involves an active interferer, by which arbitrary multipath levels can be implemented. An equivalent reflection coefficient signal-to-interference ratio is defined as the ratio of the unperturbed signal and the induced coherent isofrequency interferer signal, compatible with the two-ray model of the multipath impairment. The proposed technique exploits a dual-band frequency planning, and because of the combined use of the data at the two frequencies, a mean error of 2.6° is observed within a domain ranging from 0.5 to 4 m, for the entire 360° angle in the reference anechoic scenario. The 90th percentile of the cumulative error distribution is 5.4°. In the presence of a strong coherent interferer, compatible with a total reflection from the walls, the mean error is 4.9°, while the 90th percentile of the cumulative error distribution is 10.5°. In the presence of the strongest coherent interferer signal available, which is more severe than the worst case of total reflection, the mean error is 7.1°, while the 90th percentile of the cumulative error distribution is 15.1°.

Measuring the radiation pattern of on-board antennas at sea

Measuring the radiation pattern from antennas operating on ships is costly in terms of time and money. Due to the reflections on the sea surface, multipath influences measurement results. The standard procedures recommend repeating the measurement process several times and then applying a statistical analysis to suppress the multipath effect and obtain the correct antenna radiation pattern. However, a close analysis of the multipath problem using a two-ray model may help to find a measurement setup that minimizes the multipath effect and reduces the need for measurement repetitions. This would dramatically reduce the time and cost of measurements and improve the efficiency of the process.

Special features of radio control link for energy efficient LED light sources

The aim of the study is to reveal the special features of radio control link model in LR-WPAN under operating conditions of interference of the reflected and the line-of-sight component and to evaluate the radio link's range of positive light source control. The results of development and practical implementation of controlled spectrally tunable light emitting diode (LED) light sources with ISM- and ZigBee (IEEE 802.15.04)-based radio frequency transceivers are presented. A software application developed in LabVIEW simulation of a radio control link for light sources and used for evaluating the radio control link's range of various combinations of polarization of transmitting and receiving antennas has been discussed. It was established and experimentally verified that the received energy was able to be computed using the two-ray model: a line-of-sight ray and the reflected one. This approach is simpler as compared to cellular networks in which multiple reflections from various objects result in multi-path propagation without line-of-sight component.

Measurement and Analysis on Land-to-Ship Offshore Wireless Channel in 2.4 GHz

In this letter, measurement results of land-to-ship offshore wireless channels are presented. Large-scale and small-scale fading characteristics of 2.4 GHz frequency band are investigated by implementing narrowband channel measurement system between quay and a sailing coast patrol boat. For large-scale fading, free space path loss model, ITU-R P.1546 model, and two-ray model are compared with the empirical PL data. The results of an extensive measurement were used to determine that the existing ITU-R P.1546 model is inconsistent with the empirical PL data for offshore environment, whereas the two-ray model considering sea wave height agrees well with overall empirical data. Destructive and constructive interferences around distances of 200–500 m are observed from the empirical PL data, which ensures the validity of the two-ray model for offshore environment. For small-scale fading, the Kolmogorov–Smirnov test is utilized to verify goodness of fit, and it is shown that the result agrees best with the Rician distribution, compared with Nakagami-m or Rayleigh distributions.

Air–Ground Channel Characterization for Unmanned Aircraft Systems—Part III: The Suburban and Near-Urban Environments

Applications for unmanned aircraft systems (UAS), or “drones,” are increasing rapidly. In order to provide safe and reliable links to integrate UAS into the National Airspace System (NAS), control and nonpayload communication (CNPC) system requirements are being specified. A comprehensive knowledge of the air-to-ground (AG) channels in the bands of interest (C-band and L-band) plays an essential role. The NASA Glenn Research Center has sponsored an AG channel measurement campaign for most of the typical ground site (GS) local environments, including over water [8] , hilly/mountainous [9] , suburban, and near-urban. As a continuation of our prior study, this paper addresses the suburban and near-urban scenarios. Our developed AG channel models include path loss, small-scale fading Ricean K factors, spatial and interfrequency correlations for multiple aircraft antennas, root-mean-square (RMS) delay spread, and wideband tapped delay line (TDL) models. The path loss is described by either log-distance or two-ray models, with small corrections for flight direction. The K factors were 12 (14) dB in L-band and 27.4 (28.5) dB in C-band in near-urban (suburban) environments. The interband signals were uncorrelated, but the intra-band signals were highly correlated, with the median correlation coefficient greater than 0.85. The C-band RMS delay spread was on average 10 to 60 ns, with maximum of approximately 4 μs. The TDL models are composed of the line-of-sight (LOS) component, a ground reflection, and up to seven intermittent multipath components (MPCs). Relative power, phase, occurrence probability, duration, and excess delays for these intermittent MPCs are quantified. An algorithm to simulate the AG channel impulse response (CIR) via the TDL models is provided.

LoS 및 NLoS 환경에서의 경로 손실을 고려한 LoRa의 모의실험 및 실측 결과 분석

최근 사물인터넷 (IoT; Internet-of-things)의 필요성이 급격하게 대두됨에 따라 Low Power Wide Area (LPWA) 표준에 대한 관심이 커지고 있다. 이 논문에서는 LPWA의 표준 중의 하나인 LoRa 기술에 대한 성능을 실측 데이터에 기반하여 분석한다. 특히, Line-of-sight (LoS) 및 Non-line-of-Sight (NLoS) 환경에서 수신 신호의 Received Signal Strength Indication (RSSI) 값을 측정하여 이론적인 경로손실 모형을 적용한 RSSI 값과 비교한다. 이를 위해 다양한 경로손실 모형 중에서 Log-distance 및 Two-ray 모형 그리고 실측 데이터에 기반한 통계적 모형인 Okumura-Hata 모형을 적용한다. 그 결과, LoS 및 NLoS 환경 모두에서 Okumura-Hata 모형이 RSSI 실측 데이터와 가장 근접한 것으로 분석되었다. 이러한 결과는 LoRa를 이용하여 네트워크를 구성할 때 최적의 노드 배치를 위한 기준을 제공하는데 활용될 수 있을 것이다. Recently, a demand of Internet-of-things (IoT) rises dramatically and an interest in Low Power Wide Area (LPWA) grows larger accordingly. In this paper, performance in LoRa which is included in LPWA standard is analyzed. Particularly, after measuring Received Signal Strength Indication (RSSI) of received signal on Line-of-sight (LoS) and Non-line-of-sight (NLoS) environment and it is compared with RSSI which theoretical path loss model is applied to. Among many path loss models, the simulation for theoretical RSSI use Log-distance, Two-ray model and Okumura-Hata model that is based on the test database. Consequently, the result of Okumura-Hata model is the most similar with the measured RSSI. When a network based on LoRa is built, this result can used to decide optimal node arrangement.

A Deterministic VOR Error Modeling Method—Application to Wind Turbines

VOR devices are sensitive to multipath. These perturbations yield an error on the azimuth information received by the aircraft. This article presents a simulation method to estimate the impact of the environment on the received VOR signal. This method uses a two-ray model and a hybridization between parabolic equation (PE) and physical optics (PO). The direct field between the VOR station and the aircraft is given by a two-ray model, PE is used to compute the propagation between the VOR station and the obstacles, and PO is used to compute the scattered field. Finally, the VOR error is deduced from the direct and the scattered fields. The hybridisation between PE and PO is performed as follows: the obstacles are meshed and the PE incident field is cast as a plane wave on each facet to efficiently compute the scattered field. The simulation method is confronted to in-flight measurements in the presence of a wind farm around a VOR station in Boulogne-sur-Mer, France. The maximum VOR error along the trajectories is retrieved within 1.1 $^\circ$ and the statistical behavior is reproduced. The standard deviation is within 0.3 $^\circ$ , and the skewness and Kurtosis differ of less than 2 between simulations and measurements. Finally, parametric studies performed with this method show that the rotor blades can be neglected in this scenario. It is also shown that the knowledge of the aircraft trajectory is of major importance to predict or reproduce VOR error measurements.

Simulation of X-Band Signals in a Sand and Dust Storm With Parabolic Wave Equation Method and Two-Ray Model

In this letter, a parabolic wave equation (PWE) method is modified to include the effects of Rayleigh scattering and absorption by dust particles to study microwave signals propagating in a sand and dust storm (SDS). A three-dimensional (3-D) SDS model is proposed, in which the total number density is height-dependent and is circularly symmetric in the horizontal plane. The effects of Earth curvature and ground reflection on microwave wave traversing an SDS are studied by using the PWE method and a two-ray model. A time record of microwave attenuation is also simulated and compared to the measurement data to verify the efficacy of the proposed method.