Beam Ray Tracing for Wireless LANS
project here was initiated by an interest in providing an open source
GPL tool that will allow installers of wireless LANS to simulate the
strength of one or more
Points in an arbitrary
building. This will help the installer to decide how many Access Points
are needed, and where they should be sited without the need for
extensive and costly site mapping.
The project has a range of challenges, particularly in the mathematical description of the building topology. Obtaining useful electromagnetic properties of building materials is also difficult, and will continue to be so as these properties can vary immensely between very similar materials (particularly wood). The tool will provide representative values for common materials.
In beamtracing, a geometric tree of 3D beams emanates from sources and from reflections at, and transmissions through, walls in a building. This tree is used to trace back from a large number of potential receiver points to the sources, allowing the signal strength to be determined accurately (in the mathematical sense) at the receiver points. In raytracing, rays emanate from a source and the program attempts to find those that reach (usually) a single point of view or camera. Beam tracing thus can be more efficient where the number of receiver points is large, however the geometric computational algorithms are non-trivial.
The only thing currently preventing the application from giving useful results is the completion of the coding of the electromagnetic model. The current state of the application provides a display of signal strengths throughout the building, but only the free space loss is included in the model. Reflections and transmissions are given by fixed coefficients independent of incidence angle and material properties of the walls. There are some minor computational problems to be fixed, and in addition it only seems to work on my 64-bit machine, not on a 32-bit PC - interesting.
Documentation: (OpenOffice 2.0 Format)
The solid lines are the original walls, and the dotted lines are transparent walls added by the topological partitioning. There is no legend yet. The colours range through the rainbow from red at highest signal strength to blue as the lowest. White represents signal strength below the lowest threshold.
In the first image the back reflection from the wall on the left of the source can be seen to enhance the lower part of the signals near the source.
The second one below shows an odd linear artefact parallel to the walls (upper right). These are results of reflections from the horizontal corners between walls and floor or ceiling.
This one has the source very close to a wall (but not coincident).
This one shows missing beams (bottom left) when the source is on a wall, in this case a transparent one. This is due to a bug in the geometry algorithms (see above).
Timing measurements done on a 2.8GHz Xeon CPU, 512MB DDR2 memory system. Smaller resolutions failed due to lack of memory (excessive paging occurred).
Warning: this author uses another popular PC operating system sparingly and on an emergency basis only. All software is developed on and for Linux, which is the only OS worth spending time and effort on (well - maybe OSX also). Note however that he considers this other OS to have a well defined place with non-technical users, where Linux and other open-source software still have yet break in, if they ever do.
Contact: My email address can be constructed from the username "ksarkies" and the ISP DNS address internode.on.net in the usual way.