Usman Tahir Virk

Full-wave characterization of indoor office environment for accurate coverage analysis

This paper presents a full-wave characterization of an indoor office environment at wireless local area network (WLAN) and worldwide interoperability for microwave access (WIMAX) frequencies using finite-difference time-domain (FDTD) numerical technique. The aim is to demonstrate the applicability of accurate full wave oriented approach for large scale propagation prediction in contrast to conventional approximate ray models. Numerical simulation were carried out using a 3D full-wave electromagnetic solver SEMCAD-X and simulated results including pathloss and small scale fading characteristics are validated through multiple-input multiple-output (MIMO) channel measurements. The simulated and measured results are found to be in close proximity of each other.

Simulating specular reflections for point cloud geometrical database of the environment

Laser scanning of physical environments allows us to construct their accurate structural database. This database is called a point cloud. Radio channel prediction employing the point cloud is a promising new method for millimeter-wave (mm-wave) frequencies. Reported works that predict the radio channel based on the point cloud utilizes a diffuse scattering model with reasonable accuracy if the environment under consideration is small and diffuse dominant. Specular reflections are also crucial propagation phenomena at mm-wave frequencies. However, a mathematical formulation to predict specular reflections is still lacking. This paper presents the formulation for simulating specular reflections based on a point cloud geometrical description of an environment. It evaluates the total specular reflected field as a coherent sum of the individual field contributions originating from the elementary surfaces over an area approximately equal to the first Fresnel reflection zone. The numerical and experimental results demonstrate the accuracy of the proposed formulation.

A real-time MIMO channel sounder for vehicle-to-vehicle propagation channel at 5.9 GHz

This paper introduces a real-time multiple input and multiple output (MIMO) channel sounder to measure the vehicle-to-vehicle (V2V) propagation channel at 5.9 GHz. Compared to the existing V2V channel sounders, our design emphasizes on improving the stability of the setup and increasing the MIMO snapshot rate. The system stability allows us to develop a high resolution parameter extraction algorithm for the data analysis, which jointly estimates parameters of multipath components such as time-of-arrival, direction of departure, direction of arrival and Doppler shift. The second emphasis increases the maximal absolute Doppler shift to 806 Hz, which the system can estimate without ambiguity. The increased snapshot rate also provides a more fluent representation of the channel dynamics. We verify the design of the channel sounder with actual V2V channel measurements. Results suggest that 80 percent of the sample snapshots have a diffuse power ratio less than 20 percent and the extracted dominant specular paths match well with the environment and dynamics of the measurement.

On-Site Permittivity Estimation at 60 GHz Through Reflecting Surface Identification in the Point Cloud

Accurate site-specific radio propagation simulations provide an important basis for cellular coverage analysis. The quality of these simulations relies on the accuracy of environmental description and electrical properties of constituent materials. This paper presents a novel method of on-site permittivity estimation. The method utilizes an accurate geometrical database of the environment for identifying flat and smooth surfaces producing reflections. The method exploits a limited number of on-site channel sounding to extract reflected multipaths and compare them with ray tracing based on the environmental database. The permittivity of the identified reflecting surfaces is estimated by solving an inverse reflection problem. The method was experimentally tested with limited radio channel measurements at 60 GHz in a large empty office room. The identified reflecting surfaces are classified according to their mean permittivity estimates, showing their consistency with physical material evidence and the permittivity database in the International Telecommunication Union Radiocommunication Recommendation (ITU-R P.2040-1). The estimated permittivity values are visualized as a 3-D map, giving an intuitive understanding of materials constituting the environment. This paper demonstrates on-site permittivity estimation and material classification without the need for isolated measurements of composite materials in an anechoic chamber or in situ measurements of built environments.