Exploitation of reciprocity in measured mimo channels

In this work we study the feasibility of relative calibration to exploit channel reciprocity in a multipleinput multiple-output (MIMO) time division duplex (TDD) system. As an extension to the work of Guillaud et al. (2005), where the method was only applied to SISO and SIMO channels, real two-directional channel measurements were performed using the Eurecom MIMO Openair Sounder (EMOS). The setup considered here is more realistic, since a faster repetition rate, synchronization of transmitter and receiver over the air, and frequency offset, are accounted for. One of the major findings in the paper is a modification to the system model that correctly describes the non-negligible phase drift present in the measurements. We demonstrate that in a single-user MIMO channel and for low signal-to-noise (SNR) ratios, the relative calibration method can increase the capacity close to the theoretical limit.