MIMO channel emulator based on reverberation chambers

Multiple Input Multiple Output (MIMO), based on channel diversity, is a promising technique for increasing the performances of a communication. Nevertheless, the improvement will be strongly dependent on the propagation characteristics. If, for example, a ground to train communication is established in a tunnel, experiments described in the first part of the paper, show that at large distance, MIMO only slightly increases the capacity, contrary to what happens at short distance from the transmitter. This is due to a degeneracy of the transfer matrix H related to the propagation in a guiding structure. It is thus interesting to test communication equipments with laboratory setups, able to reproduce not only urban and rural environment but also environments like a tunnel leading to a degenerated H matrix. In this work, a new experimental setup for emulating MIMO channels is thus proposed. The system is composed of two mode stirred reverberation chambers, each one generating Rayleigh environments, which are coupled together with a rectangular waveguide. The transmitting antenna array is placed in one chamber whereas the receiving antenna array is placed in the other one. Depending on the dimension of the guide (i.e. its cut-off frequency), it is shown that one can control the order of the channel diversity. Hence, this setup could not only be used to perform tests of MIMO communication systems in perfectly defined environments but also under reproducible conditions.