Soo Yong Lim

Synthetic Aperture Radar (SAR) Signal Generation

This paper outlines the trend of signal generation in synthetic aperture radar particularly chirp (linear FM signal) generation using digital approach. A study in fundamental of FM signal and typical analog FM signal generation is highlighted. Various signal generation in SAR using digital techniques is discussed and finally the some of the digital chirp generators are presented.

Propagation Modeling and Measurement for a Multifloor Stairwell

Reliable wireless communications in stairwells are crucial to law enforcement and firefighting safety. Understanding the radio propagation in stairwells is necessary to successfully design such communications systems. In this letter, we study the radio propagation in a multifloor stairwell using measurements and simulations. Fundamental propagation mechanisms such as reflection from stairwell walls and transmission through the stair steps are investigated. It is found that the stairwell walls in this studied case do not reflect much of the incoming energy and that the transmitted energy through the stairs has significant contributions to the total received power. An image-based ray tracing scheme is used to identify the various propagation mechanisms. The ray-tracing simulation results match the measurements very well. Furthermore, physics-based explanations were provided for the trends and characteristics in the obtained results.

Use of Geospatial Resources for Radio Propagation Prediction in Urban Areas

A method for extracting the three-dimensional (3D) building structures using their single-view images available on the Internet/cyberspace is described. Height measurement technique is combined with two-dimensional (2D) projective transformation to obtain the 3D building information. It is shown that the reconstruction method is accurate for path-loss calculations using ray-tracing algorithms. Simulated path losses/gains are compared to results in literature, and good agreement is observed. The effect of building footprint and height inaccuracies on path-loss calculations is also examined and is found to result in errors within the common error range between experimental measurements and ray-tracing predictions.

Radio Wave Propagation Prediction Based on 3-D Building Structures Extracted From 2-D Images

A new method is proposed for the extraction of three-dimensional (3-D) building structures for simulating radio waves propagation in urban environments. The procedure is based on obtaining readily available high-resolution 2-D images (satellite and/or aerial photos) and images on the Internet (e.g., the google earth); and building accurate 3-D models of structures through a process of coordinates and dimensions matching. The new method provides an efficient and economic way for 3-D structure extraction. Combined with the computationally efficient ray-tracing algorithms recently developed by our group and reported in the literature, it is now possible to carry out radio wave propagation predictions for many outdoor urban areas efficiently and accurately.

Propagation Measurement and Modeling for Indoor Stairwells at 2.4 and 5.8 GHz

The propagation characteristics of indoor multi-floor environments have been studied extensively and empirical models for many scenarios are available. These studies usually do not concern about stair structures. In this paper we study radio propagation in four typical stairwells through measurement at two frequencies (2.4 GHz and 5.8 GHz). Values of path loss exponent n have been derived for vertical and horizontal polarizations. These n-values for stairwells are found to be higher than the n-values for multi-floor environments. We also propose a new path loss model based on the so-called “accumulative distance” the receiver has traveled, in addition to the conventional separation distance between transmitting and receiving antennas. The new path loss model has lower n values and, most importantly, smaller standard deviation and can thus be considered a better model fitting the measurement data. The results in this study can be useful for designers of small cell wireless communications system such as pico- and femto-cells.

Measurement of a Tunnel-Like Structure for Wireless Communications [Measurements Corner]

This paper attempts to analyze the behavior of a radio signal inside a partially open drain environment using the empirical approach. The proposed research topic concerns a unique situation in several Asian countries, because the drainage systems in these countries differ notably from those in the US and Europe, in that the former are partially open on the top while the latter are primarily below ground and covered. A series of measurements at 900 MHz, 2.4 GHz, and 5.8 GHz have been conducted inside one drain, as well as on the ground next to the drain, located on the Sunway University campus. The differences between the measurement results at the three frequencies are discussed, along with the measurement results collected from the ground next to the drain. Understanding the complicated wave-propagation behavior inside the partially open drain and the ground nearby serves as a useful indicator in designing reliable wireless communication systems, especially in environments where such drains are present. Additionally, knowledge gained from the measurement results will aid in improving the accuracy of radio-propagation prediction, which, in turn, can help in establishing dependable wireless communication networks in urban and other complex propagation environments.

Radio propagation modeling in indoor stairwell: A K-means clustering approach

The propagation characteristics in indoor stairwell differ from those of the conventional indoor signal propagation across different floors and hence, deserve independent scrutiny. In this work, the propagation characteristics in four indoor stairwells have been examined by means of extensive field measurements at two frequency bands - 2.4 and 5.8 GHz respectively. It has been found the values of the path loss exponent n for stairwell are higher than those for other indoor environments. More importantly, the standard deviation of the n-values are high, leading to less accurate propagation models. This paper proposes the use of K-means clustering for the path loss data and values of path loss exponent n of stairwells are subsequently computed. The newly-computed path loss exponents n are lowered and their standard deviation values are significantly reduced. The path loss characteristics are useful for understanding radio propagation in pico- or femto-cells that have great potential in increasing the capacity and reducing the operational cost for wireless communications systems.

Radio propagation in stairwell: Measurement and simulation results

Propagation characteristics in a stairwell are investigated through simulation and experimental measurements. Field measurement has been carried out at 2.4 GHz on every step of the stairwell up to second and half of the 3rd floor. In our measurements, the transmitter was placed outside the building. These results are then used for comparison with simulation results that take into consideration four different types of rays, namely the direct rays, reflected rays, transmitted rays, and hybrid rays. There is a good agreement between the measurement and the simulation results.

Modeling three-dimensional terrain in urban propagation environment using geospatial data in cyberspace

The wide spread of geospatial data in cyberspace provides a great opportunity for establishing more accurate three-dimensional (3D) propagation environments which are crucial for propagation modeling using ray-tracing methods. Many government agencies such as NASA and USGS (U. S. Geological Survey), and military and commercial companies have developed their own databases for housing the geospatial information which are accruing exponentially. Some of these data are free and others are not and may be very expensive.

Utilizing an interactive full 3D ray tracing software package for radio propagation in drain

In this paper, we proposed to utilize an interactive full 3D ray tracing software package to run numerical simulation for a partially open drain structure, whose presence can be readily seen in many Asian cities. Previous research finding on this topic concentrated on the field measurement works. The reported measured results have served as a useful initial experimental basis for further numerical studies to be conducted, upon finishing which, can be taken together with the measured results to better describe the propagation characteristics in the partially open drain structures. The remaining paper describes an intervention to adopt ray tracing approach, which is widely regarded as a highly promising procedure for providing accurate and site-specific means, to obtain simulation results for a partially open drain structure.