Abstract— Fast radio wave propagation prediction is of tremendous interest for planning and optimization of cellular radio networks. We propose a cube oriented 3D ray launching algorithm for both fast and accurate field strength prediction, particularly suitable for urban scenarios. Our model allows field strength prediction for a 5 km2 area with 5 meter resolution in about 8 sec with mean squared error of 7 dB. As urban environments cannot be completely described, we recommend a parameter calibration for different cities using measurement data from test runs.