# AI-Driven Pilot Overhead Reduction in 5G mmWaveMassive MIMO Systems
## 3 Results
### Random Forest Regression NNSVD with 64 Tx/16 Rx Antennas  
In this section, we change the parameters of the simulation to study the effect of this change on the system, proving that the proposed system is valid for all possibilities through changing the antenna numbers and the modulation technique used. These changes were carried out with the RFR-NNSVD technique since it was shown to be the most effective pilot overhead reduction technique in our work. First, we changed the transmitter and receiver antenna numbers and studied the same parameters to observe the effect of this change. The baseline configuration of 16 transmitter (Tx) and 4 receiver (Rx) antennas was chosen for computational feasibility while maintaining a focus on pilot overhead reduction. To address scalability, an additional configuration with 64 Tx/16 Rx antennas was simulated. This setup aligns more closely with the requirements of m-MIMO systems and demonstrate the robustness of the proposed methods under varying antenna densities.  
Figure 19 shows the pilot overhead after changing the number of antennas. It is clear that the pilot overhead size increased from 63 at \(-\)10 dB with Tx = 16 and Rx = 4 to 160 at the same SNR, and it decreases as SNR increases to reach 154 at 30 dB. Although there is an increase in pilot overhead size, this is the normal behavior of the system since as the number of antennas increases, the number of spatial channels that need estimation also increases. This typically requires more pilot symbols to estimate the channel accurately. And although the number of antennas are multiplied by 4, the pilot overhead size is less than multiplication by 4 from the previous result (160 is less than 63 \(\times\) 4), leading to the conclusion that the proposed system optimizes the pilot overhead size by a ratio less than what is expected.  
The BER of the system is shown in Figure 20. The results show that the BER for the increased number of antennas is enhanced, showing a decrease in BER at \(-\)10 dB from  
\begin{table}
\begin{tabular}{c c c c} \hline  & **PO Reduction** & **BER Reduction** & **SE Improvement** \\ \hline RFR-NNSVD & 82.14\% & 82\% & 250\% \\
[7] & 17\% & NA & 17\% \\
[8] & 43.24\% & NA & 43\% \\
[9] & 80\% & NA & 85\% \\
[10] & NA & 10\% & 20\% \\
[11] & NA & 15\% & 25\% \\
[12] & NA & 20\% & 35\% \\ \hline \end{tabular}
\end{table}
Table 2: Comparison of RFR-NNSVD parameters with those of all previous works.  
Figure 19: RFR-NNSVD pilot overhead vs. SNR for Tx = 64 Rx = 16.  
\(1.05\times 10^{-4}\) in the previous antennas combination to around \(3\times 10^{-5}\) at the same SNR level, reaching \(2\times 10^{-5}\) at 30 dB. Also, the accuracy of the system is shown to be high at about 98% when comparing the predicted and the actual BER. This coincides with the theory that the increase in Tx and Rx antenna numbers leads to improved spatial diversity, reducing the likelihood of fading and improving beamforming gain since a system with more antennas can focus energy on the desired directions, leading to reduced interference and thus improving BER [25].  
As for the SE in the modified antennas system shown in Figure 21, it is obvious that the system yielded the anticipated result, showing an increase of SE at 30 dB from \(40\;\mathrm{bps/Hz}\) in the older antenna configuration to reach almost \(70\;\mathrm{bps/Hz}\) in the increased antenna number configuration. This is due to the increased data rate transmission caused by increasing the antenna numbers and thereby significantly increasing the SE of the system. Of course, this increase in SE can be offset by the increase in pilot overhead, but as seen in Figure 19, the pilot overhead size did not increase linearly as the number of antennas increased, minimizing the effect of the pilot overhead increase and still leading to a significant increase in SE, which was discussed in [26].  
Figure 21: RFR-NNSVD SE vs. SNR for Tx = 64 Rx = 16.  
Figure 20: RFR-NNSVD BER vs. SNR for Tx = 64 Rx = 16.