| The deployment of Personal Communication Services (PCS) systems envisions using microcells having low base station antennas in a cluttered urban building environment at UHF frequencies. Radio propagation in these microcells can be modeled using ray tracing technique and the Uniform Theory of Diffraction (UTD). In order to efficiently account for many classes of rays, the Vertical Plane Launch (VPL) algorithm was developed to approximate a full 3D ray trace for site specific propagation prediction. The VPL technique employs the standard shoot and bounce ray method (SBR) in the horizontal plane, while using a deterministic approach to find the vertical displacement of the ray paths. The VPL approach accounts for specular reflections from vertical surfaces and diffraction at vertical edges and approximates diffraction at a horizontal edges by restricting the diffracted ways to lie in the plane of incidence. Compared to the full 3D SBR method, that handles at most 1 or 2 diffraction for any edge orientation, the VPL approach can treat many multiple forward diffraction at horizontal edges, which is known to be a dominant propagation mechanism in various environments. The VPL method was validated with measurements made in Rosslyn, VA for street level and rooftop antennas in a heterogenous building environment. The comparison of the predictions with the measurements shows that an average error of approximately 2dB and a standard deviation of the error of about 8 dB can be achieved with the VPL method. |
