## 4 Numerical Simulation Analysis  
In this section, we verify the effectiveness of the proposed IAAM algorithm by analyzing the simulation results with different parameters and contrast with optimal pure digital precoding, fixed-sub-connected hybrid precoding, full-connected based OMP algorithm [8], SIC based algorithm [10], and sub-connected based Dynamic Connected (DC) algorithm [14]. The parameters of the channel model are set in Table 1. MATLAB R2018a is used for simulation, and the simulation results are based on 1000 random millimeter wave channel samples. Figure 2: Flow of IAAM algorithm. Figure 3 shows the spectral efficiency (SE) of different precoding algorithms with the increasing SNR. It can be seen from Figure 3 that, compa with other sub-connected based methods, the proposed algorithm has the highest spectral efficiency under the same SNR, and is close to the full-connected-based OMP algorithm. The fixed-sub-connected method has poor adaptability to channel conditions and thus has the worst performance. The DC algorithm has better performance than the fixed-sub-connected method because it adaptively allocates antennas, but it only optimizes the analog precoding, which only uses the phase characteristics. The SIC-based algorithm both optimizes the analog and the digital precoding, but its allocation of RF-antenna pairs is fixed, which means the channel characteristics are not fully utilized, so its spectral efficiency performance is only higher than the DC algorithm and the fixed sub-connection. The OMP algorithm is based on a fully-connected structure, which can obtain more beamforming gain from all antennas compa with the sub-connected one, but it also leads to more energy consumption from a large number of phase shifters in exchange. \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Value** \\ \hline Number of clusters N\({}_{\text{cl}}\) & 4 \\ Number of propagation paths per cluster N\({}_{\text{ray}}\) & 20 \\ Antenna array deployed & USPA \\ Azimuth Angle-of-Arrival (AoA) & \\ and Angle-of-Departure (AoD) & Uniform\([0,2\pi]\) \\ cluster angles distribution & 10\({}^{\circ}\) \\ Angular spread & 64 \\ Number of transmitter antennas N\({}_{\text{r}}\) & 4 \\ Number of RF chains N\({}_{\text{rf}}^{\text{t}}\) & 4 \\ Number of data streams N\({}_{\text{s}}\) & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. Figure 3: The average Spectral Efficiency versus SNR with N\({}_{\text{rf}}^{\text{t}}\) = 4. Then, we conducted a simulation analysis on the system energy efficiency of the proposed algorithm. The energy efficiency calculation formula of the hybrid precoding system is:  
\[\text{EE}=\frac{\text{SE}}{\text{P}_{\text{common}}\ +\text{N}_{\text{rf}}^{\text{t}} \text{P}_{\text{rf}}+\text{N}_{\text{t}}\text{P}_{\text{pa}}+\text{N}_{\text{ ps}}\text{P}_{\text{ps}}+\text{N}_{\text{sw}}\text{P}_{\text{sw}}+\text{P}_{ \text{o}}} \tag{22}\]  
where Pcommon, Prf, Ppa, Pps, Psw and Po are, respectively, the power of the transmitter, RF chain, power amplifier, phase shifter, switch, and the other circuit components, including baseband processor, filtering, etc. This article sets the simulation parameters as: Pcommon = \(\|\text{FB}\|_{\text{F}}^{2}\) W, Prf = 0.3 W, Pps = 0.05 W, Ppa = 0.3 W, Psw = 0.01 W, Po = 0.5 W [22]. Nsw and Nps are, respectively, the number of switches and the number of phase shifters, defined as follows:  
\[\text{N}_{\text{sw}},\text{N}_{\text{ps}}=\left\{ \begin{array}{cc}\text{N}_{ \text{t}}\text{N}_{\text{rf}}^{\text{t}}&\text{fully}\ -\ \text{connected}\\ \text{N}_{\text{t}}&\text{sub}\ -\ \text{connected}\end{array} \right. \tag{23}\]  
Figure 4 shows a comparison between the proposed IAAM algorithm and the fully-connected based OMP algorithm with the changes in the number of RF chains (N\({}_{\text{rf}}^{\text{t}}\)).