Optimal feedback bits allocation based on 3D MIMO systems

In this paper, the optimal allocation scheme of feedback bits between horizontal channel quantization and vertical channel quantization is proposed in three-dimensional (3D) multiple-input multiple-output (MIMO) systems with limited feedback. The goal of the proposed scheme is allocating more bits to quantize the channel dimension with stronger gains. Through comparing the gains of horizontal channel and vertical channel, the feedback bits allocation is studied. 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 superior performance of proposed scheme is demonstrated by simulation results, which show that the 3D MIMO systems with optimal bits allocation scheme have higher achievable sum rate than equal bits allocation scheme.