Jonathan S. Lu

Site-Specific Models of the Received Power for Radio Communication in Urban Street Canyons

This paper presents site-specific models for the real-time prediction of the received power from waves propagating through urban street canyons (i.e., in the horizontal plane containing the transmitter and receiver) for radio communication in urban environments. The line-of-sight (LOS) and non-line-of-sight (NLOS) models presented here are based on the two-ray model and are used to predict the small-area average received power (i.e., long-term/shadow fading and distance-dependence). These models have two adjustable parameters that account for clutter such as road traffic and pedestrians, and for scattering from objects and buildings at street intersections, respectively. Validation of these models is performed with mobile-to-mobile measurements recorded in the high-rise sections of Denver and New York City for frequencies ranging from 430 MHz to 4.86 GHz.

Measurement and Characterization of Various Outdoor 60 GHz Diffracted and Scattered Paths

This paper investigates diffracted and scattered waves in unlicensed millimeter wave mobile-to-mobile, access and backhaul radio links. Narrowband 60 GHz measurements of diffraction at building corners, and scattering by a car, lamppost and building, as well as blocking by humans are presented. Semi-analytical corner diffraction and human blocking models are proposed and verified based on the measurements. Analysis of the diffraction and scattering shows that the contributions from vehicular and lamppost scattered paths can be dominant compared to corner diffracted paths. Measurements also show that the majority of power from building scattering arrives in and near the horizontal plane containing the transmit and receive antennas.

The Influence of Terrain Scattering on Radio Links in Hilly/Mountainous Regions

Current rural propagation models only consider paths (direct, ground reflected, terrain diffracted, troposphere scattered) that lie in the vertical plane containing the transmitter and receiver. This paper shows that nonspecular scattering from terrain can give significant additional contributions to the received signal in hilly/mountainous environments. To show this, we have carried out Monte Carlo simulations of scattering in many different types of rural regions. These simulations model scattering using the bi-static radar equation with a Lamberts law coefficient. In order to permit simulations for many radio links and many terrain databases, we have developed a novel algorithm to rapidly search for terrain scattering elements that are visible to both the transmit and receive antennas. Results show that in sufficiently rugged terrain, the scattered paths can give a greater contribution to received power than vertical plane paths in more than 80% of links. Conclusions are drawn for radio channel characteristics, such as angle spread and short-term spatial fading. Statistical models dependent on terrain variation for path loss, and temporal response are also developed.

Simplified path gain model for mobile-to-mobile communications in an urban high-rise environment

The goal of this work is to create a short-range urban propagation model to predict small area average path gain for mobile to mobile communications with computer running time on the order of 10 ms per link. To achieve such short computation time for a high-rise urban environment, only significant ray paths which travel in the horizontal plane (HP) are considered. The path gain for line of sight (LOS) receiving and transmitting antenna orientation is modeled with the 2-Ray model. For Non-Line of Sight (NLOS) orientations, the dominant ray paths are ray paths that diffract at building corners in the horizontal plane. To compute the contribution to path gain from these diffracted ray paths, approximations on the 2-Ray model and the Geometric Theory of Diffraction (GTD) are utilized. This urban propagation model was validated against empirical models and measurements taken in San Francisco, Boston, Philadelphia, and Manhattan.

Ray Tracing RF Field Prediction: An Unforgiving Validation

The prediction of RF coverage in urban environments is now commonly considered a solved problem with tens of models proposed in the literature showing good performance against measurements. Among these, ray tracing is regarded as one of the most accurate ones available. In the present work, however, we show that a great deal of work is still needed to make ray tracing really unleash its potential in practical use. A very extensive validation of a state-of-the-art 3D ray tracing model is carried out through comparison with measurements in one of the most challenging environments: the city of San Francisco. Although the comparison is based on RF cellular coverage at 850 and 1900 MHz, a widely studied territory, very relevant sources of error and inaccuracy are identified in several cases along with possible solutions.

Scale Model Investigation of Mechanisms for Scattering From Office Buildings at 2 GHz

In this work, a 60 GHz empirical investigation on a scale model is performed to give insight into building scattering at 2 GHz. From the presented building scattering measurements, the relative effects of the furniture and building surface on the building scattered signal are determined. The fading statistics of the scattered signal are also determined and are found to be Rayleigh distributed. Lastly, a simple method to compute the scattered power from a building using the effective roughness approach is presented and validated using the measurements.

60 GHz investigation of building scattering at 2 GHz using a scale model

In this work, we investigate building scattering at 2 GHz by performing 60 GHz scattering measurements on a 1/30 scale building model. The materials used to build this model were chosen to have similar reflected and transmitted power characteristics at 60 GHz to common building materials at 2 GHz. Co-polarized and cross-polarized scattering measurements of the model were performed with and without furniture and the front building surface. Near the specular direction, results show that the contribution from waves that enter a building, internally scatter and/or reflect, and then exit the building are not significant compared to those that only interact with the features on the front building surface. However, away from the specular direction, this contribution can be observed.

Extension of the ITU-R P.1411-8 urban path loss models to high antennas

This paper presents an extension of the ITU-R P.1411-8 urban low antenna path loss models to higher antennas. The Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) urban canyon models presented in the paper are typically used for street level peer-to peer or cellular communications, but can be more generally used to account for radio waves propagating through urban street canyons. It is shown through comparisons with measurements of varying transmit antenna height and large variations of height difference between transmit and receive antennas, that the presented urban street canyon models are applicable to taller microcellular antennas. The measurements that are used in the comparisons and analysis were obtained in an urban high-rise environment in San Francisco at 850 and 1920 MHz frequencies.

Semi-deterministic urban canyon models of received power for microcells

In this paper, line-of-sight (LOS) and non-line-of-sight (NLOS) models of the small-area average received power are presented for microcellular radio links. These computationally efficient models consider the propagation loss incurred by path loss and shadow fading through urban street canyons. The models are validated with microcellular measurements recorded at 850 and 1900 MHz in San Francisco. Comparisons are also performed with the Cost-231-Walfisch-Ikegami model and show the importance of including urban canyon contributions in microcellular propagation prediction.

Dependence of radio channel characteristics on terrain variability in hilly/mountainous regions

This paper investigates how the temporal response and spatial fading statistics for mobile-to-mobile links in hilly and mountainous terrain depend on terrain variations. Fading statistics are generated from Monte Carlo simulations using several terrain databases. These simulations employ a computer code that accounts for diffraction over terrain obstacles and for non-specular scattering from terrain elements. Based on the simulations, we have developed path loss, slow fading, and tapped delay line models for use in the evaluation of communication systems.