Measurement and modeling of wireless propagation channels for MIMO

Summary form only given. The ultimate performance limits, as well as the performance of practical systems, of any wireless system is limited by the radio propagation channels that the system is operating in. It is thus critical that we understand the channel properties that are relevant for MIMO systems: directional and delay properties of the multipath components. Any such understanding must be based both on the understanding of the physical propagation processes and actual measurements; furthermore, it is very helpful to have good channel models that can be used to test the performance of algorithms and systems. These aspects are treated in the tutorial. We start out with an introduction of spatial sounding techniques that form the basis for spatial channel measurements and spatial channel characterization. We present new measurement results of the directional channel properties as seen from the base station and from the mobile terminal jointly (double-directional propagation characteristics). Both indoor and outdoor scenarios are treated. We explain how these measurement results can be utilized and included in spatial channel models, which are required for the design and development of adaptive antenna and MIMO systems. A classification of MIMO models, including their "why?" and "for what?" are given. Then, the various methods to model the MIMO channel are discussed. The relative merits and shortcomings of measurement-based stochastic models, relying on parameter estimation techniques; of geometry-based parametric models, approximating a radio environment by geometry, but adding stochastic processes; and of deterministic models (ray-tracing or measured) are highlighted. Finally, a review on standardized MIMO channel modeling are given. It includes the models of 3GPP/3GPP2 for outdoor environments, the IEEE 802.11n models for indoor environments, and the COST 273 model, which is valid for all environments