Pilot aided channel estimation for 3D MIMO-OFDM systems with planar transmit antennas and elevation effect

Three-dimensional (3D) channel with elevation effect and planar antennas employed at the base station are two factors to be considered when researching 3D multi-input multi-out (MIMO) technique. Based on 3D channel, this paper first addresses pilot spacing constraints in frequency, time and the vertical direction of spatial domain for orthogonal frequency division multiplexing (OFDM) systems with multiple antennas. Then, three kinds of 4D pilot pattern for systems employing planar transmit antennas in 3D channel is designed. Through utilizing channel correlation in spatial domain, the transverse and vertical, pilot overhead can be reduced substantially. What´s more, this paper verifies the performance of different 4D pilot patterns and cascaded low-dimensional Wiener filters in mean square error (MSE) sense. Numerical results show that diamond-shaped 4D pilot pattern is recommended. It is also shown that the channel estimation in spatial domain, the transverse or the vertical, cannot be decomposed out of 4D channel estimation unless the big performance degradation is acceptable.