# Low Power FPGA Implementation of a Smart Building Free Space Optical Communication System
## 2 Materials and Methods  
The proposed system has the computer placed as the data server. The FPGA is directly linked with each computer via a universal asynchronous receiver transmitter (UART). This interface implies the usage of a serial communication technique in which the data is sent into the FPGA for processing and modulation. Reduced Instruction Set Computer Five (RISC-V) is installed into the FPGA for managing the sent data. The modulated data is streamed from the FPGA, as shown in Figure 2, to the laser driver circuit at the transmitting terminal, where the signal is amplified and converted from an electrical signal to an optical one. The red laser source was selected as the transmitting module due to its low cost, adaptability, and high data rates endurance. Focally concentrated beams that can travel \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Trade-Offs** & **DSPs** & **FPGAs** & **GPUs** \\ \hline \multirow{4}{*}{Advantages} & \multirow{2}{*}{Sequential Algorithm Support.} & Parallel and Reconfigurable & Instrumentation Projects \\  & & Nature with high data & Support and video processing \\  & & throughput. & support \\ \cline{2-4}  & Low Developing Cost and free & Moderate ownership cost & Low Cost \\ \cline{2-4}  & \multirow{2}{*}{Short Developing Time for Image Processing Algorithms.} & High Energy Efficiency and & \multirow{2}{*}{High Performance with Only Parallel Processing} \\  & & Harsh Working Conditions & & \\ \cline{1-1}  & & Flexibility. & & \\ \hline \multirow{3}{*}{Disadvantages} & Not Suitable for High-Data & Need for Technical Skills to & \\ \cline{1-1}  & Throughput Apps and incompatible & Develop Reliable Designs and & & \\ \cline{1-1}  & & Long Development Time. & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: DSPs vs. FPGAs vs. GPUs [20]. long distances are also one of its landmarks, thus it is a gradable versatile light source. The channel is conceptually a free space line of sight (LOS) medium. Modulation schemes are one of the key factors that affect the performance of a communication system, given that the major drawback an FSO link can suffer from is a bad weather channel condition. Attenuation jeopardizing the quality of the received signal is the main driver of the transmitter specifications, including transmission configuration and the modulation scheme used. Originally, OOK is the simplest form a signal is modulated by where only one bit is sent in each clock cycle, where digital 1 is represented by full illumination, while digital 0 is represented when the laser is off [22]. The OOK is frequently plagued by spectral and energy efficiency issues. This sort of modulation approach also has amplitude distortion as a disadvantage. One way to overcome the drawbacks of OOK is using other modulation techniques such as Pulse Width Modulation (PWM) and Pulse Phase Modulation (PPM), where the amplitude interpretation is eliminated in the signal detection. Another \"optical compatible\" modulation technique that has shown a favored performance in the FSO system is IM. In IM, information is retrieved at the receiver side by detecting the intensity of received light, which is modulated as an information-carrying signal. Opposite to RF conventional communication that may include complex types of data, intensity-modulated signals are rather positive and real-valued [23]. Besides bypassing the OOK disadvantages, its simplicity and low-cost installation are other advantages of the IM technique. Reconfigurable algorithms can be established to pick the optimum modulation technique according to the type of data, transmission distance, and channel model. In this research, the implemented system initiated a study that compares the realization of OOK and IM schemes in terms of data rate since these two modulation schemes are the most commonly used in FSO implementations, and the fact that IM can be integrated with other modulation techniques that control the light intensity makes it an interesting approach for further optimization and modification.