## 5 Cost and Energy Evaluation  
To deploy a multi-user full-duplex VLC system in the market, it must be both cost and power efficient. The proposed system is compared with two other systems that are commercially available and have been widely reviewed in the existing literature. The first system is the traditional Wi-Fi system that is currently one of the most widely used wireless systems in the world. The second system is the hybrid VLC-Wi-Fi system that is currently being widely studied and researched [34]. In this system, the downlink transmission can either be carried out using VLC or Wi-Fi but the uplink transmission is always based on Wi-Fi technology. This design was aimed at resolving issues that affect uplink transmission in VLC systems and ensures uninterrupted connection for the user or device. In this section, we compare the proposed system to the aforementioned systems and present analysis of the simulations results in Section 6. The architecture of the two systems is described as follows. The simple Wi-Fi system consists of a router with a wireless access point. The router is connected to the wide area network (WAN) and using RF radiation, transmits and receives data. A simple Wi-Fi system is shown in Figure 4a. On the other hand, a hybrid VLC-Wi-Fi system utilizes both technologies to achieve a robust system performance. The downlink transmission can be based either on VLC or Wi-Fi, while the uplink transmission is based on Wi-Fi. The hybrid system is depicted in Figure 4b. Figure 4c shows the depiction of the proposed system. In order to implement a VLC system, the use of signal processing unit (SPU) is essential. The nature and scope of the signal processing required depends on the size of the home and the number of users. This study presents different types of SPUs, whose architecture differ based on processing power, cost, and power consumption. Since VLC systems are yet to be commercially available, unlike Wi-Fi systems,  
Figure 4: (**a**) Traditional Wi-Fi model; (**b**) hybrid VLC-Wi-Fi model; and (**c**) proposed full-duplex multi-user VLC system. PD: photodiode. the initial installation cost that is included in the simulation and the results is an approximate value. As is the case when any new product is launched, the initial equipment price will be high when VLC is launched but as it becomes more common, the price will also decrease substantially. This is similar to what was observed when Wi-Fi was initially introduced in 1999. In this study, the SPUs with different architectures are used and comparatively studied. The architecture of SPU can differ with respect to the number of cores and general-purpose input-output (GPIO) registers it offers. This can significantly affect the processing speed and power consumption of the whole system. As the number of cores increase, the performance of the unit increases but the cost and power consumed also increase and vice-versa. Thus, the SPU has to be carefully designed to ensure optimum balance. Table 2 presents several SPU architectures with different cost, power, and processing power. Since this paper is related to smart home technologies, architecture 1 will be used for simulation purposes. Both hybrid and full-duplex VLC systems use the same architecture and the results and analysis are given in Section 6. As per Table 2, architecture 1 has one core and four GPIO registers. This is the most basic, low cost, and power-efficient processing unit. Since the number of sub-channels is not yet defined in the VLC standard, it is safe to assume that there are 32 sub-channels. Therefore, with the architecture 1 processing unit, \(4~{}\times~{}32~{}=~{}128\) users and devices can be accommodated. This is more than enough for a smart home application. Table 3 provides the power consumption of an average American household. The table only shows devices that have the potential to use VLC in the future. The performance evaluation of the three systems in terms of device cost and power consumption against data throughput is carried out.