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In this paper, we report the results of a field measurement campaign carried out inside a pedestrian tunnel at 24 GHz in two conditions, namely, empty tunnel scenario and busy tunnel scenario with pedestrian movement. The experiment measures the fading effects of various groups of pedestrian crowds using directional antennas at the transmitter and receiver for millimeter-wave radio communications. Having presented and analyzed the measurement data in several diverse scenarios, we have further investigated human scattering effects in the crowded pedestrian tunnel and performed ray-tracing simulation for an empty pedestrian tunnel condition. Because tunnel is an enveloped scenario that is not bound by any geographic areas, the results of this study can be applied to a wider scenario like other pedestrian tunnels across the globe. Above all, these findings contribute towards ensuring wireless connectivity for everyone even in a remote scenario like underground passages.

This paper investigates the impacts that open-trench drains make on the accuracy of radio propagation prediction in an urban city environment. Compared with conventional prediction styles that assume the ground to be flat, in this paper, we have considered for the first time the real scenario in many Asian cities to make open-trench drains inclusive in radio propagation modeling. The aims of this paper are twofold. First, to scrutinize one narrow L-shaped structure, modeled after an open-trench drain, by means of comparing ray-tracing simulation results with the actual field measurement results at 2.4 and 5.8 GHz. Second, to compare one city model built without and with the inclusion of open-trench drains for running ray-tracing simulation in yielding radio propagation prediction results. The findings from this paper are especially beneficial to the improvement of mobile communications in extraordinary environments such as open-trench drains, caves, coal mines, underground passageway, and others. Besides, they provide a unique insight into how the presence of the open-trench drains may affect radio wave propagation in an urban city environment.

Radio propagation modeling and prediction play an important role in the understanding of electromagnetic (EM) wave propagation in complex environments, as well as in the design of wireless communications and radar systems.

A fundamental approach in the optimal design of wireless communication systems is a proper comprehension of radio wave propagation through wireless channels. As wireless communications become more ubiquitous, new propagation environments emerge and the propagation mechanisms therein are being constantly investigated. The objectives of this chapter are twofold: firstly, to give a succinct review of new and emerging complex environments that require fine-tuning of the propagation models since traditional propagation models that simplify the propagation environment by ignoring the small and fine structures are no longer valid for such complex environments and, secondly, to recount the fundamental concepts of radio propagation modeling and its significance, as well as the basic propagation mechanisms and ray-tracing image method. These fundamental working principles of ray-tracing image method can be utilized both for indoor and outdoor environments because these two settings are governed in essence by the same propagation mechanisms.

Digital terrain elevation data (DTED) is usually represented in raster form where the elevations are given at each cell (or point) in a regular grid. Raster forms are simple and widely used for radio propagation modeling. But a raster form does not explicitly have some key terrain features which are important to propagation modeling, such as peaks and ridges. In this paper, we propose a vector form terrain model which directly represents three-dimensional terrain structures (e.g., ridges) and can provide more accurate description of the propagation environments. It can also improve the accuracy for the calculation of diffracted field due to mountainous structures. The advantages and drawbacks of the vector form terrain model are discussed.

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.

Emerging homeland security applications require low-cost and rapid installation of HF radar systems in challenging terrain environments. One example concerns hills with natural slope and surface irregularity and roughness. In this letter, through the investigation of radio-wave propagation in such an environment, we examine the effect of the slope and surface roughness of the terrain on the performance of HF radars. It is shown that the slope and surface irregularity affect the effective electrical spacing between array elements and cause beamforming and scanning errors, which lead to misdetection of targets. It is also shown by an investigation of an actual HF radar site in the area of Koko Head in Hawaii that scattering from surface roughness of the terrain adds extra error to the phase difference between antenna array elements (~30°), hence degrades the radar performance further.

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.

Digital elevation models (DEM) or digital terrain elevation models (DTED) are widely used in radio propagation simulation and prediction. The resolution of DEM's is getting higher and higher with the latest resolution of centimeters generated by LIDAR (light detection and ranging). These high resolution DEM's provide more realistic representation of the environments and will enhance the accuracy of propagation modeling results. But they also have some drawbacks. First, the storage of high resolution DEM's will cost large computer disk space and slowdown the I/O process. Second, not all propagation scenarios need high resolution DEM's depending on the frequency and range. Third, the DEM's do not explicitly have the three dimensional (3D) information about topographic structures, such as ridges, which is physically important in diffracted field calculations. For example, 3D ridges are key contributors of diffracted field in certain mountainous regions. But many widely used and DEM-based methods (e.g., knife-edge models) ignore the 3D features. Our previous work has shown that the orientation and interior angle of a ridge can cause 3dB difference in path loss prediction for a single ridge. For two ridges, the difference is almost doubled.

As wireless communication becomes more ubiquitous, there is a steadfast growing need to accumulate the propagation knowledge in small radio cells because they can increase the capacity of radio networks and overcome radio spectrum crowding. For these small radio cells that are intended to cover mainly indoor or very small outdoor areas their base station antennas are usually mounted inside a building or below rooftop level in an outdoor environment. In such scenarios when the lower base-station antennas are used, various objects that exist in that particular environment may affect radio propagation significantly so their effects should be studied.

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.

Radio propagation in smaller radio cells is significantly affected by the surrounding environments such as the geometry of buildings, terrain, foliage, and others. In this work, focus is given on radio propagation in environment where drains are present - both covered and partially open. Ray tracing method was utilized to examine the differences between the ground-reflected rays from these two scenarios at 900 MHz. Discussions are given to offer an insight into the propagation of radio wave in drains environment.

When diffraction of ridges is required for predicting radio signal in mountainous regions, the realistic shape of ridges is often simplified (e.g., as a knife edge or a wedge). Also, the ridge orientation is usually ignored and the EM waves are assumed to be normally incident on the ridge. As more accurate radio propagation prediction is needed for advanced wireless communications, it is necessary to take into account more realistic features of ridges. For example, the slopes and orientation of ridges should be considered as two key features since they directly affect the values of diffraction coefficients. In this paper we present methods to extract these features of ridges based on digital terrain elevation data. The effect of the ridge orientation on the diffracted field is then investigated.

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.

Modeling radio propagation over ocean surface is important for homeland security applications. Due to its fast simulation speed, the parabolic equation (PE) method is a good candidate for and has been used in such simulations for decades. Since PE method is based on paraxial approximation of wave equation, its accuracy is not guaranteed for short ranges and larger propagation angles. On the other hand, Finite Difference Time Domain (FDTD) method is well known as an accurate method in short range but not suitable for large regions (in terms of wavelengths). For homeland security applications, it is necessary to deal with both short and long range propagation problems and it is natural to integrate PE and FDTD for simulating such scenarios. To exploit the advantages of PE and FDTD, quantifying the ranges suitable for these two methods is important and practically useful. In this paper, we examine the accuracy of PE method as a function of range (in short range regime) for smooth/flat ocean surfaces.

Emerging homeland security applications require low-cost and quickly deployable HF radar systems. In order to overcome the significant costs/unavailability of land lease in coastal areas for fixed applications, deployment of HF radar systems in challenging terrain environments is necessary. One such environment is the hilltops which naturally have slope and roughness. In this paper, through the investigation of radio wave propagation in such environments, we examined the effect of the slope and roughness of the terrain on the performance of HF radars. It is shown that the slope of the terrain will affect the effective inter-element spacing of the array and causes beamforming and scanning errors. It is also shown that surface roughness of the terrain also changes the effective inter-element phase differences and hence array performance. While the effect of the slope could be very significant diffraction effects from surface roughness resulted in a much smaller error of about 18°.

In this work, propagation measurements in a multifloor indoor stairwell have been conducted at 2.4 GHz and 5.8 GHz. Two antenna polarizations, namely VV and HH polarizations in LOS and NLOS scenarios are considered. It is observed that in the propagation environment of an indoor stairwell, the antenna polarizations effect is only noticeable for LOS scenario. In cases where NLOS scenario dominates, both VV and HH polarizations give the similar results at 2.4 GHz and 5.8 GHz. Also, the sudden-power-drop phenomenon between the consecutive stair sections can be observed for both VV and HH polarizations at 2.4 GHz, but at 5.8 GHz it can only be observed for HH polarizations at a milder scale.

In this paper, we will first review the ray-tracing algorithms developed in our group; then examples of the exploitation of geospatial data for radio propagation and its benefits will be presented. We will discuss the techniques to extract three dimensional (3D) building structures in urban propagation environment using 2D images in cyberspace. Finally, a real-time ray tracer will be briefly described.

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.

A new method is introduced for the reconstruction of 3D building structures using single-view 2D image with controlling objects setup in Google Earth. The method is based on the theory of projective geometry and the aid of GE which provides means that make it possible to set controlling objects possible. Two types of building structures and their variations and combinations could be reconstructed. It is shown that the accuracy of the reconstruction is satisfactory based on observations of some test cases. The ray tracing method is used to calculate the received power in five routes in Rosslyn, VA. Comparison with the path gain obtained using a more accurate city model shows that the new model provides good results. More details and examples will be provided in the presentation.

This paper presents a new method of incorporating propagation models into wireless systems simulations. The multipath data for each transmitter-receiver pair in a realistic environment is calculated using the site-specific propagation modeling software developed at the University of Hawaii. Instead of fitting the multipath data into a statistical model, we directly use the data for the calculation of discrete channel impulse responses for each transmitter-receiver pair. The Doppler effects and the effects of pulse shaping filters on the calculation of discrete channel impulse responses are investigated. Finally, these channel impulse responses are employed in a CDMA system simulator to evaluate the output signal-to-noise ratio (SNR) and the corresponding bit error rate (BER).

A new method is proposed to calculate the field or power distribution in a rectangular region in wireless communication environments using the efficient ray-tracing algorithm developed by the authors. The region is divided into small cells according to the resolution requirement. Instead of checking all the cells for possible reception of the rays, we first check the interception of the ray with the rectangle. Then the cells hit by the ray can be determined and serve as the starting cells for a cell-scanning procedure that finds out all the cells illuminated by the ray tube. It is shown that the new method is very efficient

Two fast ray tracing procedures, one using space division with uniform rectangular grid and the other using unstructured triangular grid, are combined to cope with the complex propagation environments, such as micro-and pico-cells. Basically, unstructured triangular grids are employed for the calculation of outdoor propagation and uniform rectangular grids are used for indoor cases. The combined procedure has the advantages of the rectangular and triangular methods while overcoming their disadvantages. The new method is general, easy to implement and computationally efficient for many propagation environments.