Required Databases

An appropriate database for the propagation model considered is important for accurate prediction data.

The basis for any propagation model is a database that describes the propagation environment. Micro cell and indoor propagation modeling rely strongly on high-resolution geographical information. Most organizations are now using high-resolution databases of the building structures in the urban area with an accuracy in the range of 1-2m derived from aerial photography measurements. For urban propagation, it is essential to have accurate information at least about the average height of individual buildings, especially when base stations are operating close to rooftop height.

Figure 1. Building a database in vector format to describe the urban environment.

As micro cells are planned to increase the network capacity in urban areas, it is obvious to use building-focused databases. To get a more accurate description of wave propagation, the building data are stored in a vector format. Every building is modeled as a vertical cylinder with a polygonal ground plane and a uniform height above street level. With this approach, only the propagation environment including building vertical walls and horizontal flat roofs are considered. Also, the material properties (thickness, permittivity, conductivity) of the building surfaces can be taken into account, which is important for the calculation of the reflection and diffraction coefficients and also for the penetration into buildings. Figure 1 shows an example of a data base for buildings in vector format used in ProMan.

Considering the influence of database information on prediction accuracy, it is noted in Damosso1 that prediction errors in micro cells of up to 15 dB were attributed to database inaccuracies arising from poor resolution of the building data. Given the sensitivity to the terrain surface, the terrain profile should be considered for propagation modeling if the considered area is not flat. Therefore terrain databases in pixel format are required with resolutions about 20-30 m. This resolution is higher compared to terrain models.

1 E. Damosso, ed., Digital Mobile Radio: COST 231 View on the Evolution towards 3rd Generation Systems. Bruxelles: Final Report of the COST 231 Project, published by the European Commission, 1998