Obtaining transmitter side channel state information in MIMO FDD systems

Channel state information (CSI) in systems with multiple antennas at both sides of the transmission link (multiple input multiple output, MIMO) is beneficial for many transmission schemes. However, a transceiver station can only estimate the channel transfer functions (CTFs) of the channels over which the received signals propagate which are different from the channels over which the transmitted signals will propagate in FDD systems. This paper shows a technique to obtain the CSI of the channels over which the transmitted signal will propagate based on the CSI of the channels over which the received signals propagate. By means of estimating the directions of arrival (DOAs) and times of arrival (TOAs), the shift of the previously estimated CSI to the CSI which cannot be estimated based on training signals can be calculated. The quality of the proposed algorithm depends on the quality of the parameter estimation. In scenarios with many scatterers the estimation of the DOAs and TOAs may not be precise enough or there may be paths with similar parameters which cannot be resolved. Thus, the proposed algorithm performs better in non-rich scattering environments.