In Multiple Input Multiple Output (MIMO) systems, spatial correlation plays an important role. The level of correlation cannot be determined based on antenna characteristics without knowing the propagation characteristics. Therefore, a new Over-the-air (OTA) testing methodology is needed in order to take into account both antenna and propagation characteristics in the system setup when testing multi-antenna devices. 

MIMO-OTA device testing with anechoic chambers emulates complex spatial- temporal propagation environments at the device location in a realistic and repeatable way by using a radio channel emulator connected to a circular array of probes (multiple cluster) or to an array of probes on one side of the chamber forming a single spatial cluster model. Both configurations are referred to as the Multi-probe technique. This technique addresses the need to generate precise spatial channel models at the device location for the evaluation of MIMO antenna and handset performance. Wide band cellular propagation channels exhibit the cluster behavior which can be taken into account by emulating the Spatial Channel model within the anechoic chamber. The clusters are then simultaneously mapped to the probes so that the sum of the trans-mitted signals at the DUT location is as defined in the model. These measurement-based channel models include all dimensions of the radio channel (time, frequency, space and polarization). Each cluster is split between several probes to enable angular spread. As a result the geometry based environment of the channel model is accurately reproduced within the anechoic chamber.

The primary goal of the MIMO OTA measurement system is to be able to compare Multi-antenna/MIMO devices and algorithms based on their throughput performances when tested against spatial channel models. All critical parts of the mobile terminal design (antennas, RF front-end, baseband processing) are tested in an end-to-end configuration. This document aims to present all the most relevant technical features of the MVG StarMIMO system relative to the MIMO OTA measurement technique with anechoic chambers.
Download：www.mvg-world.com/en/system/files/application_note_mimo_2015.pdf