FD-MIMO system can support high-order Multi-
User MIMO (MU-MIMO), while fully exploiting the
elevation as well as the azimuth dimension, thereby
generating improved system throughput.
In full buffer system-level evaluations, it has been
found that 64-antenna-port FD-MIMO system
achieves 243% average-cell and 244% cell-edge
performance gain, compared to those of the
8-antenna-port legacy MIMO system. In order to
achieve the promising gain of FD-MIMO in practice,
we need accurate beam steering and tracking in
three Dimensions (3D).
To steer and track the MU beams toward serving
MSs, FD-MIMO BS should be equipped with multiple
transceivers (TRX) feeding 2D array elements,
in which the number of TRX doubles or even quadruples
compared to that of the conventional BS.
Having a large number of TRX poses new challenges,
such as antenna calibration and complexity
issues associated with Channel State Information
(CSI) acquisition and precoding.
On the other hand, high-order MU-MIMO introduces
another set of new challenges, such as scheduling
complexity and link adaptation. Furthermore, in Frequency
Division Duplex (FDD) systems, other new
challenges emerge such as pilot overhead, CSI estimation
complexity, CSI quantization and feedback
overheads.