# A Novel Multi-User Codebook Design for 5G in 3D-MIMO Heterogeneous Networks
## 6 Simulation Results  
Consider a two-layer 3D-MIMO heterogeneous network consisting of the macrobase station, a micro base station, and multiple users, where the serving base station is a micro base station. Let the serving base station is \(T_{0}\) collaborate with other micro base stations and macro base stations that greatly interfere with user terminals. At this time, the interference of the user terminal can be eliminated as much as possible. This heterogenous network simulation environment is built by MATLAB, and the improved 3D codebook is brought into the process of system performance analysis. The simulation curve of the closed-form solution of the system performance analysis illustrates the impact of various performance parameters and the improved 3D precoding scheme on system performance. The main simulation parameters are shown in Table 1.  
Figure 6 shows how the network throughput varies with the base station density. The proposed 3D MIMO codebook scheme is compared with perfect CSI condition for feedback bits of 4 and 6 respectively. The simulation results are consistent with the analysis results. As the base station density increases, the throughput gradually increases. It can be seen that proper adjustment of the base station density can increase system throughput and optimize system performance. Moreover, as the base \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Description** & **Settings** \\ \hline \(N_{t}\) & Number of micro base station antennas & 4 \\ \(N_{M}\) & Number of macro base station antennas & 8 \\ \(\rho\times\sigma^{-2}/dB\) & Transmitter SNR & 20 \\ \(\alpha\) & Path loss index & 4 \\ \(d_{k}\) & The distance between the specific user and its serving base station & 1.5 \\ \(\beta_{k}/dB\) & The threshold for receiving the SINR for the specific user & 1 \\ \(n\) & Macro BS transmit power/Micro BS transmit power & 2 \\ \(\lambda\) & Micro BS density & 0.9 \\ \(\lambda_{M}\) & Macro base station density & 0.8 \\ \(B/\text{bit}\) & Feedback Overhead & 18 \\ \(\sin\varphi_{k}\) & Quantization Error & 0.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation Parameters. station density increases, the impact of system performance caused by incomplete CSI becomes more serious. Furthermore, the system throughput curve when the base station receives perfect CSI is plotted as a comparison, indicating that the more feedback bits, the better the system performance. Figure 7 compares 3D DFT precoding scheme when the number of feedback bits is 4 bits and 6 bits, respectively, and perfect CSI, the BER of the system varies with the SNR of the base station transmitter. Simulation results show that as the number of feedback bits increases, the system's BER decreases. Figure 6: Throughput comparison of the proposed 3D MIMO codebook scheme for feedback bits of \(B=4\), 6 bits with perfect CSI conditions. Figure 7: The relationship between the BER and SNR for the proposed 3D DFT Scheme for a different number of feedback bits. Figure 8 compares the use of DFT precoding schemes in 2D and 3D environments, respectively, under the BER, and in the 3D-MIMO channel model, the performance difference between the improved precoding scheme and the DFT precoding scheme proposed in this paper in terms of system BET. The traditional DFT precoding scheme is not suitable for vertical dimension codebooks in a 3D environment in which the base station employs both planar and planar antenna arrays due to the problem of adjustable dynamic range and vertical distribution of the vertical dip and tilt angle, and this paper considers horizontal emission jointly. The 3D codebook is constructed by angle and vertical down-tilt, so the performance of the improved precoding scheme proposed in this paper is better. Figure 9 shows the Cumulative Distribution Function (CDF) curves for different codebook schemes.