Optimal allocation of feedback bits for 3D MIMO systems

In this paper, the optimal feedback bits allocation scheme between horizontal channel quantization and vertical channel quantization is proposed in three-dimensional (3D) multiple-input multiple-output (MIMO) systems with limited feedback. The proposed scheme aims to allocate more bits to quantize the channel dimension with stronger gains. The feedback bits allocation is studied by comparing the gains of horizontal channel and vertical channel. The optimization model is built in the form of minimizing the differences between limited feedback and ideal feedback under the condition of fixed bits. The optimum result of feedback bits allocation is obtained by strict derivations. The system level simulation results show that the 3D MIMO systems with optimal bit allocation can achieve higher spectral efficiency than equal bit allocation, the accuracy of which is then verified by the theoretical analysis.