Wireless wave propagation in city street canyons

Abstract

This project aims to determine the characteristics of a wireless communication channel in city-street-canyon scenarios. The channel of a typical city intersection is modeled with a ray tracer and measured with a channel sounder. Then, the results of both tools are compared in terms of the local scattering function.
The channel sounder utilized for the project was initially developed by Rui Wang et al. at the University of Southern California in a software-defined radio (SDR). It has been updated from measuring 15 MHz to 50 MHz, which required the usage of equipment with larger bandwidth and hence, the improvement of the program running on the SDR FPGA. With the updated version of the channel sounder, a measurement campaign was run in an intersection of the city of Vienna.
Correspondingly, the ray tracer was developed by Mingming Gan during her Ph.D. thesis and later updated by Xuhong Li during her master thesis. The same intersection used to take measurements with the channel sounder has been modeled and simulated with the ray tracer. Then, the predictions of the ray tracer have been validated with the channel-sounder results. The comparison between both tools is used to provide a first verdict of whether the ray tracer can be utilized for wireless positioning.

Popular Abstract

At the same time that unmanned aerial vehicles (UAV), e.g. drones, increase in popularity, some concerns about their usage in illegal activities appear in government security agendas. Undesired cases, such as attacks in political gatherings or drug dealing, motivate an increasing interest in determining the position of eventual hostile UAVs. In principle, the location of an UAV can be found based on the signal between the UAV and its remote control. This problem, usually known as wireless positioning, has been already covered by several methods in the literature. The efficiency of the existing solutions could be significantly improved with the usage of geometric-based models, as for example ray tracing. In this project, we study the accuracy of a ray tracer when predicting the characteristics of the wireless communication channel that would exist between an UAV and its remote control. Our studies could be latter used to determine whether finding the position of the UAV can rely on ray tracing predictions.
Ray tracing is a deterministic channel model where the propagation of an electromagnetic wave is represented by multiple rays. Propagation mechanisms such as reflection, diffraction, diffuse scattering, penetration and line of sight are considered in a ray tracer to generate those rays. For this project, we have used the ray tracer developed by Mingming Gan, to simulate a wireless channel in a street intersection of the city of Vienna. In total, three sets of simulations were carried out, each of them representing a possible path that an UAV would take when flying at low altitude.
Simultaneously, we have run a measurement campaign in the same scenario simulated with the ray tracer. As a measurement device, we developed a channel sounder based on the original design of Rui Wang, et al. at the University of Southern California. This channel sounder consists of a transmitter that periodically sends a sounding sequence, and a receiver that collects the corresponding response of the channel. Both devices are synchronized with atomic clocks of rubidium that are disciplined by the GPS satellite system. The sounder is implemented on a software-defined radio that is a flexible device where the radio characteristics of the system can be programmed. We have upgraded the capabilities of the original channel sounder from measuring 15 MHz to 50 MHz, which required the improvement of the original device program.
The measurements taken with the channel sounder are then utilized to validate the predictions of the ray tracer. We have established a comparison between the results of both tools in terms of the local scattering function and some derived expressions. The local scattering function provides the distribution of the channel gain over the signal delay and its Doppler frequency shift. Although some of the details of the local scattering are correctly predicted by the ray tracer, some characteristics are misrepresented, especially in the gain distribution over the Doppler shift. Those inaccuracies suggest that some models of the ray tracer should be revised in order to use it as a wireless positioning tool.

• author: Garcia Albarracin, Andrés Felipe
• supervisor: Fredrik Tufvesson; Zemen Thomas
• organization: Department of Electrical and Information Technology
• course: EITM02 20162
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Channel modeling, Channel sounding, Local scattering function, Ray tracing.
• report number: LU/LTH-EIT 2017-588
• language: English
• id: 8917840
• date added to LUP: 2017-06-26 15:32:30
• date last changed: 2017-06-26 15:32:30