Full length articleInvestigation of corner diffraction for different materials in vehicular channels at urban street intersection
Introduction
Intelligent transportation systems are envisioned to increase road traffic safety using vehicular communications in sub-6 GHz band. The non-line-of-sight (NLOS) inter-vehicle communications at urban street intersection is a critical case for safety and has been widely researched in recent years [1], [2], [3]. Multiple reflections from building walls along street canyons are the most important propagation mechanism in such scenarios. Corner diffraction has significant influence on total received power when separation between the vehicles is less than m [4]. Therefore contribution from corner diffraction must also be included into propagation models for accurate channel predictions [5]. Reflection from building walls and diffraction around building corners to model radio propagation in micro-cellular environments with quasi-static mobile receivers has been largely addressed in the literature [6], [7], [8], [9], [10]. However, to the author’s best knowledge, diffraction around building corners for different types of materials in context of vehicle-to-vehicle (V2V) communications has not been much explored.
There are several studies [11], [12], [13], [14], [15] that look into Diffraction coefficient to model diffracted field from corners. Umul in [11] used modified theory of physical optics to derive diffracted field expression for a wedge with different face impedances. Deng et al. in [12] performed measurements and analysis of diffraction around corners, pillars and irregular objects at , and GHz. It was found that knife edge diffraction model fits well with measured data for indoor environments whereas an empirical linear model was developed to fit well with measurements for outdoor environments. Wang et al. in [13] used polynomial curve fitting to obtain simplified expressions for characterization factors of the Diffraction coefficient. The formulation proposed in the study was found to be more accurate in radio channel prediction than well-known heuristic models. El-Sallabi et al. in [14] investigated the influence of corner shapes on accuracy of received power prediction. It was found that representing the corners having flat surfaces with simple sharp corners results in lower predicted value than measured as contribution of reflection from flat surfaces is not included. Rizk et al. in [15] compared the performance of Diffraction coefficient for perfectly conducting wedges using the uniform theory of diffraction (UTD), perfectly absorbing wedges and wedges with impedance faces against measured data. The comparison was performed for diffraction from single-corner, two-corner intersection and four-corner intersection in an urban environment. It was found that all the three models show a good agreement with measurements.
A number of analytical and empirical models [16], [17], [18], [19], [20], [21] to predict pathloss at urban street intersection under NLOS conditions have been proposed in the literature. Le et al. in [16] used a simple formula to compute diffraction loss using UTD. The model replaced Diffraction coefficient with a scattering parameter and included free space pathloss from ITU-R model [17] to propose simple pathloss models for 1-turn NLOS and 2-turn NLOS scenarios in urban street-grid environments. The model was validated against measured data for a device-to-device (D2D) link at 3.7 GHz for both line-of-sight (LOS) and NLOS conditions. Lu et al. in [18] proposed a similar approach with two-ray model to account for contribution from a direct ray and a ground reflected ray as well. Both the models in [16] and [18] proposed an adjustable scattering parameter to account for reflection from building walls, diffraction from street corner and scattering from traffic and random objects in the environment. Sun et al. in [19] proposed simple analytical models to compute pathloss contribution from significant rays including reflections, reflection followed by diffraction, diffraction followed by reflection and double diffractions. The pathloss formulae are derived using geometrical optics and UTD for ideal urban street-grid environments. Schack et al. in [20] and Mangel et al. in [21] proposed empirical models for pathloss prediction in V2V channels at urban street intersection under NLOS conditions. These models however provide total pathloss that accounts for all the propagation mechanisms including reflection, diffraction and scattering from surrounding objects in the environment. The models discussed above do not explicitly account for surface roughness and constitutive parameters of the materials. The pathloss is given in terms of simple expressions with certain adjustable variables and the geometrical parameters of the environment. This paper investigates diffraction from building corners at urban street intersection under NLOS conditions for different materials in sub-6 GHz vehicular channels. The effect of material constitutive parameters, surface roughness and orientation of corners with respect to mobile radios is investigated. In particular, the behaviour of Diffraction coefficient as given by UTD is investigated for different corners and materials. This paper thus aims to give some new insights into radio propagation in inter-vehicle communications at an urban street intersection for future intelligent transportation systems. This paper makes use of the UTD model as it is the de facto model for computation of diffraction from corners and wedges. The model has been widely used in the literature to compute diffraction from over-rooftops and vertical edges of the buildings [6], [7], [8], [9], [10]. To the best of author knowledge, the propagation analysis of Diffraction from four-corner intersection in vehicular channels is not previously reported in the literature. The propagation analysis presented in this work thus cannot be compared with a previous model. However in order to make sure that the UTD model is accurately applied in this study, a comparison against the ITU-R model [17] is also presented. The waveguide effect due to significant contributions from multiple reflections along street canyons is not considered in the analysis as it is beyond the scope of this work.
This paper is organized as follows. Section 2 describes the system model and simulations setup. Section 3 performs the propagation analysis of diffracted fields from building corners for different materials. Finally, Section 4 lists the results of this theoretical study.
Section snippets
The system model
The model presented in this paper investigates diffraction from corners of buildings at an urban street intersection for inter-vehicle communications under NLOS conditions. The environment considered in this work is taken from Munich city and is shown in Fig. 1. The average height of buildings in the environment is m. Transmitter and receiver antennas are placed on top of two vehicles that are moving towards a street intersection at the speed of km/hr. The vehicles are moving in the
Propagation analysis
The total instantaneous power (20) at the receiver as the vehicles move towards the street intersection has been computed for different materials and is shown in Fig. 2. The received power has also been computed using the ITU-R recommendations P.1411-10 [17]. The horizontal axis shows the distance of transmitter from the centre of street intersection where the transmitter and receiver lines (hypothetically) intersect each other. It can be seen that the power received from PEC is highest
Results
Before we discuss the results of the analysis presented above, a comparison between the UTD model and ITU-R recommendations P.1411-10 is presented. The ITU-R recommendations P.1411-10 provide an empirical model for diffraction loss () from a corner as following [17]. and, where,
: distance between transmitter and centre of street intersection
: distance between receiver and centre of street intersection
: street
Conclusion
Diffraction from building corners at a typical street intersection under NLOS has been investigated for different materials in vehicular channels. The effect of material constitutive parameters, surface roughness, corners geometry and orientation with respect to mobile radios is investigated using the well-known uniform theory of diffraction. Diffraction coefficient depends on incidence diffraction component , reflection diffraction component and Fresnel Reflection coefficient . The
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Sajjad Hussain received the B.Sc. degree in electrical engineering from the University of Engineering and Technology at Taxila, Taxila, Pakistan, in 2006, the M.Sc. degree in telecommunications engineering from the University of Liverpool, Liverpool, U.K., in 2008, and the Ph.D. degree in electronic engineering from Dublin City University, Dublin, Ireland, in 2017. From 2009 to 2013, he was a Technical and Test Engineer with Vodafone Automotive Ltd., Manchester, U.K. He is currently an
References (28)
- et al.
Observations of 5.9 GHz radio propagation and 802.11p network performance at road junctions
Radio Sci.
(2019) - B.E.Y. Belmekki, A. Hamza, B. Escrig, Outage performance of NOMA at road intersections using stochastic geometry, in:...
- M. Abdulla, E. Steinmetz, H. Wymeersch, Vehicle-to-Vehicle communications with urban intersection path loss models, in:...
- et al.
Geometry based vehicle-to-vehicle channel modeling for large scale simulation
IEEE Trans. Veh. Technol.
(2014) - et al.
Simulation and measurement based vehicle-to-vehicle channel characterization : accuracy and constraint analysis
IEEE Trans. Antennas and Propagation
(2015) - et al.
The relative importance of different propagation mechanisms for radio coverage and interference prediction in urban scenarios at 2.4, 5.8, and 28 GHz
IEEE Trans. Antennas and Propagation
(2006) Fast two-dimensional diffraction modeling for site-specific propagation prediction in urban microcellular environments
IEEE Trans. Veh. Technol.
(2000)- et al.
A UTD propagation model in urban microcellular environments
IEEE Trans. Veh. Technol.
(1997) - et al.
A comparison of theoretical and empirical reflection coefficients for typical exterior wall surfaces in a mobile radio environment
IEEE Trans. Antennas and Propagation
(1996) - et al.
Diffraction around corners and its effects on the microcell coverage area in urban and suburban environments at 900 MHz, 2 GHz, and 6 GHz
IEEE Trans. Veh. Technol.
(1994)
Physical optics-based diffraction coefficient for a wedge with different face impedances
Appl. Opt.
A parametric formulation of the UTD diffraction coefficient for real-time propagation prediction modeling
IEEE Antennas Wirel. Propag. Lett.
Influence of diffraction coefficient and corner shape on ray prediction of power and delay spread in urban microcells
IEEE Trans. Antennas and Propagation
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Sajjad Hussain received the B.Sc. degree in electrical engineering from the University of Engineering and Technology at Taxila, Taxila, Pakistan, in 2006, the M.Sc. degree in telecommunications engineering from the University of Liverpool, Liverpool, U.K., in 2008, and the Ph.D. degree in electronic engineering from Dublin City University, Dublin, Ireland, in 2017. From 2009 to 2013, he was a Technical and Test Engineer with Vodafone Automotive Ltd., Manchester, U.K. He is currently an Assistant Professor with the School of Electrical Engineering and Computer Science, National University of Sciences and Technology, Islamabad, Pakistan. His research interests include channel modelling for future radio networks.