# Comprehensive Survey on VLC in E-Healthcare: Channel Coding Schemes and Modulation Techniques
## 3 Modulation Techniques for VLC in E-Healthcare Systems
### On-Off Keying (OOK)  
OOK is one of the most fundamental modulation techniques in VLC, where the intensity of the light source is modulated to represent binary data. In this scheme, the light is turned on to represent a binary '1' and off to represent a binary '0'. Its simplicity and low power requirements make it highly suitable for low-cost and low-power applications, such as in healthcare environments where data transmission of vital signs is needed without high computational complexity. A recent study explored the use of OOK in a low-cost VLC transceiver system designed for intensive care (IC) medical environments. This system, employing Manchester-based OOK signals, was designed to prevent the spread of emerging diseases by reducing the need for physical connectivity in highly sterile environments. The study used the eye opening penalty (EOP) metric to characterize the system's performance in varying conditions, including LED bias current, modulation frequency, link distance, and signal pattern [38]. The experimental results demonstrated excellent performance, with an LED bias current of 400 mA, a signal frequency of 1 MHz, and a VLC transmission distance of 2.5 m. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**SI. No** & **EMF Applications** & **Healthcare Systems** & **Health Effects** & **Ref.** \\ \hline \multirow{4}{*}{3} & \multirow{4}{*}{Minimum range of EMF used.} & \multirow{4}{*}{Small area of forearm skin in 10 female volunteers is assessed.} & Exposure to radiation from mobile phones (MPs) has been suggested to have an impact on protein expression in human skin samples, potentially leading to health effects. \\ \cline{3-5}  & & & There was a significant increase in DNA damage in the frontal lobe of the rat brain, especially in the 2100 MHz group. & The results indicated that the higher the frequency of RFR, the greater the observed DNA damage and the increase in oxidative stress. & [35] \\ \hline \multirow{4}{*}{5} & \multirow{4}{*}{Medium-frequency EMF.} & General medical examination, cardiological, and family history surveys have been conducted for MF broadcast and radio link stations & MF broadcast and radio link assessments, and surveys on family history. & [36] \\  & & & & \\ \cline{1-1} \cline{3-5}  & & & & \\ \cline{1-1} \cline{3-5}  & & & & \\ \cline{1-1} \cline{3-5}  & & & & \\ \cline{1-1} \cline{3-5}  & & & & \\ \cline{1-1} \cline{3-5}  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._To further validate the system, critical medical parameters such as heart rate, oxygen saturation, pulse rate, respiration rate, temperature, and non-intrusive blood pressure were transmitted over VLC links of varying distances (1.5, 5, and 15 m). The results showed EOP values of 0.89 dB, 0.96 dB, and 2.67 dB, respectively, which indicate minimal signal degradation even at greater distances. These findings illustrate that OOK can be an effective modulation scheme in healthcare applications, particularly in IC environments where reliable and low-cost communication is critical [39]. However, while OOK offers simplicity and power efficiency, it is inherently limited in environments with high noise and interference, such as hospital rooms where ambient lighting may cause signal disruptions. In these cases, more advanced error correction or modulation schemes may be required, to ensure data integrity over longer distances or in high-interference environments [40]. OOK is a highly attractive option for VLC systems in healthcare settings, due to its ease of implementation and power efficiency. Its low complexity allows for straightforward transmission of critical medical data, such as heart rate and oxygen saturation, without the need for significant signal processing [41]. This simplicity is especially beneficial in intensive care units (ICUs), where minimizing potential contamination from physical connections is a priority.