# SIC-Free Based Indoor Two-User NOMA-VLCP System
## 2 System Module and Optimization Algorithm
The BER of user 2 is more strongly affected by Gaussian white noise, from the Lambertian radiation model, the noise power shows a negative correlation with the distance of the signal transmission. Therefore, in this system, reducing the transmission distance of high-speed signals appropriately can decrease the BER and improve communication performance. As illustrated in Figure 6b, the BER of user 2 is the lowest directly beneath the LED in the receiving plane. Moving towards the center point of the receiving plane, the BER gradually increases until it reaches its maximum at the edge point of the receiving plane. Figure 6c,d show the BER of each user in the indoor environment. With the two figures, the position change has less effect on the BER of low-speed signals, while for high-speed signals, it is more affected by the superimposed noise. Therefore, the overall distribution of the BER of high-speed signals in the receiving plane follows a similar trend to that in Figure 6b. From a comprehensive analysis of Figure 6, as the signal transmission height increases, the SINR of the received signal for each user decreases, resulting in diminished BER quality. Simulation results show that the BER of each user in the receiving plane is lower than the error correction limit of FEC coding, which demonstrates that the system has anti-interference characteristics. Figure 7 illustrates that the BER decreases as the SNR increases for both the proposed VLCP system and the conventional VLCP system discussed in this study. The BER in the conventional VLCP system decreases more sharply due to the effect of error propagation (EP), a result of the SIC model employed. As SNR increases, the BER of user 1 declines, reducing EP's impact on user 2's signal judgment and thus lowering user 2's BER. Conversely, the proposed AFT-based VLCP system eliminates EP between users, and communication performance is primarily governed by SINR. In this system, user 1 exhibits a higher BER than user 2, particularly in high-SINR scenarios, where the BER of user 1 exceeds that of the conventional system. This is due to the absence of a SIC module, as the AFT-based method does not suppress user 1's signal during decision-making, nor does it improve user 2's SINR. Consequently, as SNR increases, the SINR for both users stabilizes under fixed power allocation, leading to minimal BER variation. Notably, the AFT-based system  
Figure 5: Comparison of localization performance of different algorithms (**a**) CDF of system positioning error (**b**) mean position error versus SNR. demonstrates superior anti-interference capabilities compared to the SIC-based VLC system and maintains reliable communication even under low-SNR conditions. Since the system uses a single-LED multi-PD structure, the multi-LED NOMA-VLCP structure is analyzed, including the communication performance and positioning performance of the system. In terms of communication performance, the increased number of LEDs can provide higher total transmission power and more signal paths, thereby improving the channel gain and signal-to-noise ratio at the receiving end, which is helpful in solving the problem of different signal strengths. Since the system is a non-SIC system, the addition of LEDs may aggravate the interference between multiple users, resulting in an increase in the bit error rate (BER) of remote users. The signal interference within the cell can be reduced by optimizing the power allocation and multiplexing scheme. Figure 6: System BER simulation (**a**) 2.5 m height, BER for user1 (**b**) 2.5 m height, BER for user2 (**c**) 3 m height, BER for user1 and (**d**) 3 m height, BER for user2. Figure 7: BER with different channel SNR. (**a**) low SNR. (**b**) high SNR. The positioning part of this system uses a single LED positioning solution. Since the receiver structure parameters are known, the relative position of the center PD and the LED is obtained by the ratio of the received signal strength. Adding LEDs is not very applicable to the current system.