EDA Focus November 2009: Case study of Urban Propagation

Wireless InSite® allows RF communications engineers to accurately analyze the impact of the physical environment on the performance of wireless communication systems. The software provides a broad range of site-specific predictions of propagation and communication channel characteristics in complex urban, indoor, rural and mixed path environments. Most of these results are derived from accurate solutions to the underlying EM wave propagation problem determined by the UTD (Uniform Theory of Diffraction) and FDTD (Finite Difference Time Domain) methods.

Remcom’s XFdtd® is a full wave three dimensional electromagnetic solver based on the FDTD method. Complicated CAD objects with thousands of parts may be imported into XFdtd and combined and edited within XFdtd using the internal graphical editor. RF designers can import an electromechanical CAD file, improve the design using XFdtd, then export the revised CAD file to reduce design time. Applications include microwave, radio frequency (RF), antennas, scattering, biological EM including Magnetic Resonance Imaging (MRI) and Specific Absorption Rate (SAR), photonics, packaging, Electromagnetic Compatibility (EMC), and electromagnetic behavior of specialized materials.

Many applications require detailed knowledge of antenna performance as deployed in a realistic setting. To solve such problems the complementary capabilities of XFdtd and Wireless InSite are highly effective and easy to use. For example, consider the design of a simple outdoor wireless system to be used in Chicago (if desired an indoor/outdoor system can also be easily studied). Such systems are rapidly being used for cellular, WiFi, and emergency services. We have selected several city blocks in Chicago and shall demonstrate how Remcom’s tool can be used. The gain pattern for the array antenna will be computed using XFdtd while the coverage will be found using Wireless InSite.

Using XFdtd’s modern interface and effective efficient workflow, a simple six-element array with a single excited element can be readily constructed using the XFdtd GUI or using XFdtd’s scripting language. In fact, using the scripting language allows the user to relate the frequency to the size, spacing, and geometry of the array as well as the computational mesh. Extremely complex antennas with specialized material and novel geometries are equally easy to model using XFdtd’s powerful flexible CAD editor and import capabilities.

Remcom’s relentless pursuit of rapid high fidelity computations is born out in XFdtd’s XStream® GPU computational technology, which computes both the simulation and the far zone in just a few seconds. Even much larger problems compute unimaginably fast with speed improvements compared to CPUs as much as 300X for the simulation and 900X for the far zone.

XFdtd’s powerful data analysis capability allows the user to effortlessly view the results, post-process the results into new and novel forms, and even, via custom scripting, optimize the design. Once the results satisfy the user, the pattern is exported for use with Wireless InSite in a general purpose format.

Figure 1: Far zone pattern for an array antenna in XFdtd

The next step in the communication network design uses Wireless InSite. The user has the option of computing the coverage for the area of interest or integrating the Wireless InSite tools into a commercial or their own network simulator by directly accessing the Wireless InSite model APIs. For rapid computations using a network simulator, the Wireless InSite Real time API provides computations in milliseconds. For deeper high fidelity analysis of propagation and channel characteristics, the user may prefer to use Wireless InSite’s full 3D ray tracing model.

For this discussion, Wireless InSite’s 3D model will be used. Wireless InSite makes working with complex urban building, terrain, and map data a breeze. The user simply imports all of the data for Chicago. Wireless InSite’s GUI synthesizes all the data into a complete picture of the situation. If necessary, the user may modify the building materials for any of the buildings in the scene. Wireless InSite’s innovative intelligent building processor reduces computation time by analyzing each building and subtly and unnoticeably altering its shape to optimize computation time and fidelity.

Selecting and placing the transmitter and orienting the antenna are quickly accomplished. As we are interested in the coverage of the proposed transmitter and its location, we cover the streets in the area of interest (825m x 860m) with a 5m meter spaced grid of receivers (~31,000) each near the ground.

Figure 2: Wireless InSite display of Chicago

Using Remcom’s full 3D ray tracing model to find the ray paths the paths between the source and any receiver are computed. While more interactions are possible, this example shows the results for ten reflections and two diffractions. The ray tracing shoots rays in all direction 0.5 degrees apart, reflecting them off surfaces and diffracting them off corners as they propagate through the scene. Remcom’s relentless pursuit of computational speed for high fidelity results makes computing the results for this example swift and easy.

Figure 3: Path loss and ray paths in Wireless InSite

To help understand the propagation mechanisms, ray paths can be displayed to any receiver location. More importantly, the signal loss and channel characteristics determine the performance of any proposed systems. Thus, an important and useful feature in Wireless InSite is the ability to graph the delay path profiles and angle of arrival. The results can be aggregated for the entire area to gain an understanding of the system performance. This comprehensive set of high fidelity data and tools allow the user to deeply understand the channel characteristics of the area and assist in determining performance of any proposed communications system.

Figure 4: Wireless InSite view of antenna pattern, rays, and loss

Figure 5: Delay spread in Chicago

Through this example, the effective and powerful capabilities of Remcom’s tools are clear. Remcom tirelessly endeavors to provide tools that transform the workflow, productivity, and creativity of electromagnetic engineers as is evident in the design and performance of XFdtd and Wireless InSite.

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