Ray tracing and imaging techniques in urban pico and micro cell wave propagation modelling

Cellular networks show a steadily increasing number of subscribers. During "rush hours" high blocking rates have already been observed in densely populated regions. To increase the network's capacity in such areas, base stations with antennas below roof-top level and limited cell radii are used. For these urban pico or micro cells wave propagation effects along street canyons are often dominant. The need for an accurate wave propagation model to calculate the contribution of those signal paths arises. This paper introduces a new deterministic algorithm which is able to calculate multiple diffracted and reflected paths using imaging techniques. Emphasis is put on the efforts made to reduce the problem's complexity since a straight forward application would suffer from enormous computing time and memory requirements and not be feasible for urban micro or pico cells. The new imaging approach is opposed to a simple ray tracer, which is restricted to diffraction phenomena. Comparisons with DCS1800 measurements show notable improvements of the field strength prediction and indicate that signal paths consisting of a combination of diffraction and reflection are important contributions to the received signal. From the evaluation it can be concluded that even for base station heights above the mean building height in NLOS (non-line-of-sight) situations considerable signal power propagates along around building paths.