# SIC-Free Based Indoor Two-User NOMA-VLCP System
## 2 System Module and Optimization Algorithm
As the number of iterations increases, the system's SINR converges and its positioning accuracy improves. This optimization scheme incorporates a compensation factor to balance the emphasis on positioning accuracy and SINR. Owing to the use \begin{table}
\begin{tabular}{c c c} \hline \hline
**Symbol** & **Parameter Name** & **Value** \\ \hline \(R_{1}\) & User1 rate & 1 Mbps \\ \(R_{2}\) & User2 rate & 20 Mbps \\ \(m\) & Order of Lambertian emission & 0.6461 \\ FOV & The field of view of PDs & 70\({}^{\circ}\) \\ \(P_{t}\) & The emitting power of LED & 10 W \\ \(A\) & Area of photodiode & 0.04 cm\({}^{2}\) \\ \(\alpha\) & Photodiode tilt angle & 20\({}^{\circ}\) \\ \(T_{s}(\Psi)\) & Gain of optical filter & 1 \\ \(G(\Psi)\) & Gain of concentrator & 1 \\ \(h\) & Height between the LED and the receiver & 2.5 m and 3 m \\ \(l\) & The horizontal distance between PD\({}_{i}\) and PD\({}_{0}\) & 0.012 m \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. Figure 2: Power superimposed signal (**a**) Time domain characteristics (**b**) Frequency domain characteristics. of random data during the optimization process, which estimates the user's SINR and positioning errors, the target optimization function exhibits fluctuations within a specific range. As a result, the overall optimization function fluctuates constantly with the increase in the number of iterations, and the minimum positioning error during the iteration process is 2.01 cm. The positioning performance of the proposed system is shown in Figure 4, where Figure 4a,b show the positioning results in the receiving plane when the device is deployed in an environment with a height of 2.5 m and 3 m, respectively. Comparing Figure 4a,b, increases in height from 2.5 m to 3 m result in a smaller effect on the positioning error. The simulation results indicate that the proposed system achieves a positioning error of each user within 10 cm, where the average positioning error of user 1 is 4.50 cm and that of user 2 is 4.12 cm at a height of 2.5 m. In the environment with a height of 3 m, the average positioning error of user 1 is 4.62 cm and the average positioning error of user 2 is 5.74 cm. Figure 5a demonstrates that the proposed VLCP system can significantly reduce the average positioning error of multi-users. The average positioning error of the proposed VLCP system in this letter is 4.31 cm, and the lower 0.9 quartile of the positioning error is 5.43 cm. In comparison, the average positioning error of the traditional VLP system is 11.9 cm, and the lower 0.9 quartile of the positioning error is 16.7 cm. To investigate the positioning capability of the system under poor channel conditions, we compared the positioning accuracy of the proposed system with that of the conventional system as a function of the SNR, as shown in Figure 5b. Figure 4: Positioning performance of the VLCP system (**a**) at a height of 2.5 m and (**b**) at a height of 3 m.  
Figure 3: Optimization process of PSO algorithm (**a**) objective function optimization process (**b**) optimization curve of SINR and positioning error. The simulation results in Figure 5 indicate that the proposed system's positioning error remains under 6 cm even under lower SNR conditions, demonstrating its good anti-interference characteristic. Compared to VLCP systems equipped with SIC, this system implements the AFT mechanism and does not exhibit EP. Here, user positioning accuracy is primarily influenced by the SINR. Therefore, the system can provide high-precision positioning services for indoor devices. In the 5 m \(\times\) 5 m \(\times\) 2.5 m environment, the BER of user 1 and user 2 are represented in Figure 6a,b, respectively. For user 1, BER in the receiving plane remains relatively stable within a certain range. Additionally, for low-speed signals, the impact of inter-user interference from high-speed signals on communication performance is more significant than that of additive Gaussian white noise.