Characterization of multipath clusters with ray-tracing in urban MIMO propagation environments at 2 GHz

For the design of MIMO (multiple input multiple output) systems, channel models are required that properly describe the behavior of the physical channel. The propagation environment around a mobile station (MS) and a base station (BS) is a multipath environment. Multipath components can be grouped together into so called clusters. We define a cluster as a group of paths with similar directions of departure or arrival in azimuth and elevation and similar time delay of arrival. A 3D deterministic ray-tracing tool is used to calculate the double-directional MIMO channel. The advantage of deterministic ray-tracing in contrast to measurements is that ray-tracing offers the possibility of detailed characterization of all multipaths and investigation of the propagation effects without any constraint concerning the antenna or the measurement equipment. A new automatic procedure to identify clusters in azimuth, elevation and delay at the transmitter and the receiver from ray-tracing data is presented. Based on the ray-tracing simulations, we propose a new iterative procedure to extract multipath clusters. The extracted parameters show clearly that, in macrocellular environments, the number of MS-clusters is much greater than the number of BS-clusters. The presented cluster characteristics help to parameterize MIMO channel models and to make simulation results more realistic.