Influence of diffraction coefficient and corner shape on ray prediction of power and delay spread in urban microcells

For a low base-station (BS) antenna located on one street, signals propagate into crossing and parallel streets by reflection and diffraction at corners of buildings. Therefore, in order to accurately predict the received signals, it is necessary to properly model the diffraction coefficient at the building edge and to accurately represent the shape and the electrical properties of the building near the corner. This paper compares ray-tracing predictions to measurements of received power and root mean square (rms) delay spread and shows the need for a diffraction coefficient having larger values than suggested by the commonly used heuristic diffraction coefficient. A new heuristic diffraction coefficient is proposed that has higher diffracted field strength in the deep shadow region and in the region between the two shadow boundaries. The proposed diffraction coefficient shows better agreement with measurements of both received power and delay spread compared to the commonly used heuristic diffraction coefficient. The influence of building shape near the corner and its electrical properties on the ray-tracing predictions are also presented. The shape is shown to have an important role in accurately predicting both received power and delay spread.