## 5 Cost and Energy Evaluation
No commercial VLC products are currently available, which makes a comparison on the basis of cost and power consumption difficult. Consequently, we develop a criterion to illustrate the potential comparison between the three systems. For the hybrid VLC-Wi-Fi system and the proposed full-duplex VLC system, the cost of the SPU, which is typically used for commercial telecommunication system implementation and is based on the Texas Instrument \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Architecture** & **Specification** & **Signal Processing Power** & **Approximated Cost (USD S)** \\ \hline
1 & 1 Core & 100 W & 120 \\
2 & 2 Core & 100 W & 200 \\
3 & 4 Core & 200 W & 300 \\
4 & 8 Core & 400 W & 400 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Architecture of different signal processing units (SPUs) with their approximated power consumption and cost [34]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Device** & **Consumption in 1 h (kWh)** & **Cost per Year (USD S)** \\ \hline LCD TV & 0.346 & 466.65 \\ HDTV set-top box & 0.021 & 28.32 \\ Apple iMac & 0.108 & 145.66 \\ Video player & 0.028 & 37.76 \\ Gaming console & 0.016 & 21.58 \\ Linksys WLAN & 0.011 & 14.84 \\ D-LINK switch & 0.01 & 13.49 \\ Belkin ADSL2 + Modem & 0.005 & 6.74 \\ Incandescent lamp (60 W Mirabella) & 0.053 & 71.48 \\ Energy-saving LED lamp & 0.009 & 12.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Average household electronics power consumption and yearly cost. LCD: Liquid crystal display; HDTV: high-definition television; WLAN: wireless local area network; and ADSL: asymmetric digital subscriber line. digital signal processing (DSP) board series C6000, is approximated [34]. The computation of the device cost and power consumption includes the cost of maintenance and electricity used in the long run. The indoor VLC environment simulation model is taken from [29]. Other simulation parameters are discussed in Section 6. The calculation of the cost and power consumption of the first system, which uses simple LED lighting with Wi-Fi, is done using the following equations:  
\[Cost=No\_LED_{R}\times No_{LED_{N}\times LED_{cost}}+WiFi_{cost} \tag{10}\]  
\[Power=No_{LED}\times LED_{power}+WiFi_{power} \tag{11}\]  
In the above equations, \(No\_LED_{R}\) is the number of LED lights replaced during the length of the simulation, \(No\_LED_{N}\) is the total number of LEDs used in a specific room, \(LED_{cost}\) is the cost of LEDs used, \(WiFi_{cost}\) is the cost of Wi-Fi equipment and the internet connection used, \(LED_{power}\) is the power consumption of the LEDs, and \(WiFi_{power}\) is the power consumption of both the Wi-Fi access point and the router. The calculation of the cost and power consumption of the second system, which is a hybrid VLC-Wi-Fi system, is done using the following equations:  
\[Cost=No\_LED_{R}\times No_{LED_{N}\times LED_{cost}}+SPIU_{cost}+WiFi_{cost} \tag{12}\]  
\[Power=No_{LED}\times LED_{power}+No_{LED}\times SPIU_{power}+WiFi_{power} \tag{13}\]  
In the above equations, \(SPIU_{cost}\) is the cost of the SPU and \(SPIU_{power}\) is the power consumed during the operation of the SPU. Here, the \(SPIU_{power}\) is multiplied by the number of LEDs used because the LEDs are connected to the GPIO register of the SPU and consequently, will draw power according to the number of LEDs that are attached. The method of connecting the LEDs to the GPIO register can vary. For example, they can be connected such that each GPIO will entertain one LED, which is an expensive solution. Alternatively, an array of LED lights that serves one room can be connected to a specific GPIO, which would allow the whole home to be covered using only one SPU. As mentioned earlier, if there are 32 VLC sub-carriers, then by using a simple one-core and four GPIO register-based SPU, a total of 128 users or devices or both can be entertained.