The usage of the millimeter wave (MMW) band in the 5th generation (5G) networks relies on beamforming to compensate the strong path-loss suffered at higher frequencies. To exploit the beamforming implemented by multiple antenna devices, proper algorithms to estimate the channel need to be designed. In this work we propose a novel channel estimation method for MMW systems where both transmitter and receiver are equipped with fewer radio frequency chains than antennas and implement hybrid analog-digital beamforming.
First, we define a training sequence which includes a set of analog and digital beamformers to probe the channel. Then, we develop an algorithm which estimates the channel parameters directly rather than the multiantenna channel matrix and it is based on the two dimensional (2D) discrete Fourier transform (DFT) of the received training samples. Numerical results show the effectiveness of the proposed channel estimation method even in low signal to noise ratio (SNR) conditions.