## 6 Result and Analysis
### Multi-User Full-Duplex Visible Light Communication System Performance Analysis  
To simulate the performance of the proposed system, two main parameters were investigated, namely, the data rate and the bit error rate (BER). The simulation environment was identical to the one set up in [29]. The room dimensions were \(5~{}\mathrm{m}~{}\times~{}5~{}\mathrm{m}~{}\times~{}3~{}\mathrm{m}\). The LED lights were deployed on the ceiling in a circular scheme to ensure optimized ROPD at the receiving plane. The receiving plane was set to an average height of \(0.8~{}\mathrm{m}\). The system considered both LOS and NLOS signals to improve the system performance. In a VLC system, the dominant and most reliable signal path is an LOS path, however, as it is sometimes unavailable, the NLOS or the diffused path is considered. The power level of the NLOS path is significantly lower than that of the LOS path, however under certain conditions, it is strong enough for the receiver to successfully detect the correct signal. The resulting data were simulated for an average of five users and ten smart devices. As mentioned earlier, the downlink section is based on an ACO-OFDM scheme while the uplink section is based on a simple OOK scheme implementation. Figure 5 shows the BER simulation results of the downlink and uplink sections of the proposed scheme along with the respective data rates. From Figure 5a, it can be seen that the BER performance of the proposed system for user and smart home devices is similar. The performance of the proposed system is compared to a simple OOK-based implementation of the same system for downlink transmission. It can be seen that the ACO-OFDM performs better than simple OOK implementation, which is due to the inherent advantages of ACO-OFDM and the added orthogonal Walsh codes used to avoid multi-user interferences. For uplink transmission, the performance of the proposed system is similar to that of a typical OOK system. This is an acceptable result as there are limited power resources present to achieve high SNR and the performance was sufficient to ensure reliable data transmission. While the use of OFDM instead of OOK for uplink will improve the data rate, the robustness, and the performance of the system, the main parameters under consideration were cost, energy consumption, and power consumption. As a result, the significant increase in cost of hardware required for OFDM made OOK a more favorable option. The results in Figure 5 show that an acceptable performance is achievable with the current implementation. With the current cost of hardware, the VLC system deployment will become very expensive, as a stronger SPU would be required and by looking at Table 2, the cost of SPU doubles as the number of cores and memory is increased. Please note that the system performance is not compared with the other two systems that were earlier mentioned as they utilize different techniques and resource allocation methods, consequently any comparison would be unfair. Further, the aforementioned systems are compared in terms of cost, energy, and power consumption to the proposed system in Section 6.2. Figure 5: Simulation of the proposed system: (**a**) bit error rate (BER) performance of the proposed system and (**b**) data rate against the number of users. OFDM: orthogonal frequency-division multiplexing; and SNR: signal-to-noise ratio. Figure 5b shows the downlink and uplink rates. The data rate for user devices and smart devices are shown in red and green respectively. The uplink data is shown in blue. From the figure, it can be seen that the user data rate is higher than the device data rate because smart devices do not consume a large amount of data while the user engages in data intensive activities such as streaming videos and surfing the internet. The uplink has the slowest rate but this is acceptable as in a smart home environment downlink is utilized more than uplink.