MIMO-UWB propagation channels

The use of ultra-wide bandwidth, while keeping a low power spectral density, is a promising approach for high-data rate communications as well as low-power communications and geolocation. The use of multiple antenna elements at transmitter and receiver (MIMO) can further increase data rate, system robustness, and precision of localization. The ultimate performance of MIMO-UWB systems is determined by the propagation channels they operate in. This paper provides an overview of the state-of-the-art in UWB-MIMO channel measurement and modeling. The most popular technique for measuring UWB-MIMO channels is based on vector network analyzer sounding of the channel, together with the use of virtual arrays. Data are frequently evaluated by application of high-resolution parameter estimation methods in (relatively narrowband) subbands of the considered bandwidth; though interference-cancellation based techniques in the delay domain are popular as well. The most frequently used channel models are either generalized Saleh-Valenzuela models (where directional information has been added), or geometry-based stochastic channel models. We find that in general, the angular power distribution can depend on the considered frequency range of the UWB signal. This, together with the frequency dependence of antenna elements and array patterns, leads to frequency-varying correlation and capacity of UWB-MIMO propagation channels.