Multiple-Input Multiple-Output (MIMO) technology is expected to form the root of many wireless networks. MIMO measurement systems will therefore be needed to provide knowledge about MIMO channels. A radio-wave propagation measurement system for wideband, multichannel MIMO measurements at 5.3 GHz has been developed by Veli-Matti Kolmonen, Jarmo Kivinen, Lasse Vuokko, and Pertti Vainikainen at Helsinki University of Technology (TKK) in Espoo, Finland.
The wideband MIMO radio channel measurement system that is presented can measure the wave vector in both ends of the radio channel. The system covers three-dimensional (3D) directions and two orthogonal polarizations of the waves in both receive (Rx) and transmit (Tx) using 32 X 32 channels without excessive hardware complexity in the 5.3-GHz frequency range. To estimate the direction of departure (DoD) and direction of arrival (DoA), conventional Fourier processing is used. Such processing is based on the phasing of adjacent elements and the weighting of the element signals.
The researchers' goal was to enable the estimation of the DoD and DoA as quickly as possible—including polarization. Due to the limited MIMO matrix size, microwaves switches are used at both the Tx and Rx. Their experiments delve into the hardware realization of the high-power switch, group geometries, mechanics, and more. They conclude with measurements and analysis of their findings. The resulting measurement system can measure directional data including polarization in both ends of the link with relatively small-size antenna groups that have both semispherical and planar shapes. See "5.3-GHz MIMO Radio Channel Sounder," IEEE Transactions on Instrumentation and Measurement, August 2006, p. 1263.