Comprehensive Survey on VLC in E-Healthcare: Channel Coding Schemes and Modulation Techniques

Abstract

The integration of information and communication technologies in the field of healthcare has generated a positive transformation in the traditional way of providing patient care, optimizing medical services, and streamlining healthcare operations. Traditionally, healthcare systems have relied on radio frequency (RF) signals for data transmission. However, the conventional RF wireless network faces ever-increasing challenges, such as spectrum shortage and a congested frequency spectrum. Moreover, issues such as interference, security vulnerabilities, and potential health risks associated with prolonged exposure to RF electromagnetic radiation complicate its application in healthcare environments. To address these challenges, visible light communication (VLC) systems, which offer dual functionalities, data transmission, and illumination, have emerged as a promising complementary solution to traditional RF-based options. VLC provides secure, high-speed data communication that is immune to RF interference, making it particularly suitable for healthcare settings. This research examines the advancements in e-health systems that utilize VLC technology, considering various modulation and channel coding techniques, with a focus on evaluating the effectiveness and limitations of these techniques to determine their impact on overall performance.

1. Introduction

The field of e-healthcare has experienced significant growth, due to its ability to enable remote patient monitoring, telemedicine consultations, and efficient exchange of medical data among healthcare professionals. Wireless communication technologies are increasingly being integrated into medical body area networks, to enhance flexibility and convenience for caregivers and patients. However, traditional solutions that rely on RF technologies face several challenges, including electromagnetic interference with precision medical equipment [1,2], saturation of the radio spectrum, and limited bandwidth. VLC emerges as an innovative alternative that utilizes white light-emitting diodes (LEDs) for both information transmission and illumination. In this context, VLC offers distinct advantages over RF communications, operating in a different part of the electromagnetic spectrum with wavelengths between 380 and 750 nm and frequencies ranging from 430 to 790 THz—10,000 times larger than the entire RF spectrum [3]. This frequency range is safe for human exposure, does not interfere with sensitive electronic devices, and is not licensed, providing abundant free bandwidth. Additionally, the VLC is energy-efficient, as it uses LEDs for communication and lighting [2,4].

VLC exhibits substantial promise within medicine, offering significant advantages to healthcare professionals and patients. Several prevalent applications of VLC in the medical domain include patient monitoring, indoor navigation and positioning, interactive dissemination of patient information, intercommunication between medical devices, medical imaging, communication during surgical procedures, and data transmission on wearable devices [2,5]. By integrating VLC technology into medical body area networks, healthcare providers can enhance flexibility and convenience for caregivers and patients in various medical applications. This integration leads to improved patient care, streamlined operations, and greater overall healthcare efficiency. In addition, patients benefit from a more seamless and interactive healthcare experience [6,7,8,9]. One of the primary applications of VLC technology is the real-time transmission of patient data from medical sensors, such as heart rate monitors, blood pressure monitors, and oxygen saturation sensors. VLC systems also enable the reception of location-based information and access to medical records, treatment plans, educational content, and entertainment options. Furthermore, VLC technology facilitates the transmission of high-resolution medical images, such as X-rays, magnetic resonance imaging (MRI), and computerized tomography (CT) scans, from imaging devices to display screens or viewing stations used by healthcare professionals within hospital settings [10,11].

The use of VLC technology in healthcare systems presents some significant challenges. For light signals to be transmitted effectively, there must be an unobstructed path between the transmitter and the receiver, as the light must propagate in a straight line. Ambient light interference can degrade signal quality, affecting the accuracy and reliability of data transfer. In VLC, signal attenuation can occur, due to factors such as distance, material properties, or environmental conditions, with indoor environments being the most critical. Maintaining a high signal-to-noise ratio (SNR) is critical for reliable data transmission, which can be challenging in specific medical settings [12]. To overcome these obstacles, ongoing research and development efforts focus on improving VLC technology. Recent advances in signal processing techniques and standardization efforts suggest that VLC has the potential to become a more robust and reliable communication solution for patient monitoring in the medical field [13]. Hence, the current analysis and identification of reviews are grounded in the findings and methodologies of previous researchers. These reviews show the progress made in designing and implementing a medical healthcare information system, using emerging wireless VLC technology, implemented with visible LEDs within the transmitter module [14].

The system under analysis employs an optical modulation method to transmit medical and healthcare information. However, a thorough review of the existing literature reveals a scarcity of publications related to the use of channel coding techniques in VLC, particularly in hospital settings, despite the importance of efficiently utilizing this technology for two fundamental reasons: first, to ensure that patients are not adversely affected by the use of the technology, and second, to ensure that data transmission occurs appropriately. Currently, some radiation therapy interventions involve electromagnetic radiation (EMR), which affects both the dermal and internal physiological systems of patients. Radiotherapy is a therapeutic intervention used in the medical field, in which high-energy electromagnetic waves, such as X-rays or gamma rays, are employed to specifically target and eradicate malignant cells within the human body. Although cancer treatment can be effective, it can also induce adverse effects on the skin and internal organs of patients. The occurrence of these adverse effects depends on the type of treatment used and the unique characteristics of the patient. The effects are closely monitored and managed by medical specialists, to mitigate any potential harm to the patient.

The remainder of the work is structured as follows. Section 2 of this paper discusses the effects of electromagnetic fields (EMFs) on health, and a table presents the findings of various researchers on the effects of EMFs on healthcare and their impacts on different applications. Section 3 analyzes modulation techniques for VLC in e-healthcare systems. Channel coding schemes for error correction in VLC are explored in Section 4. Section 5 presents the integration of VLC in healthcare scenarios. Section 6 describes future directions and challenges. Finally, Section 7 presents the conclusions of the work developed.

2. Effects of Electromagnetic Fields (EMFs) on Health

The terrestrial electromagnetic environment has been significantly altered by technological advancements, with electromagnetic waves posing potential risks due to excessive radiation exposure. EMR is categorized by frequency into extremely-low-frequency-EMF and radiofrequency radiation. Studies have explored the health effects of EMFs, focusing on humans and rats. For example, exposure to pulsed microwaves at 3 GHz, 5.5 GHz, and 9.4 GHz in the workplace has been linked to genetic and cellular alterations, with oxidative stress identified as a key mechanism for DNA and cell damage [15,16].

Study [17] investigated the formation of reactive oxygen species (ROS) in L929 cells after exposure to 900 MHz RF radiation, with and without a carcinogen (MX), concluding that 900 MHz RF does not induce oxidative stress. Similarly, ref. [18] found no significant oxidative stress in mouse macrophage cells exposed to RF radiation modulated by FMCW and CDMA, suggesting no carcinogenic link. Research on mobile RF use [19] also found no increased cancer risk, even for long-term users. Additionally, experiments have shown that 2450 MHz microwave radiation does not cause significant DNA damage or crosslinks in cultured cells [20]. Other studies have focused on oxidative damage in rat brains from 900 MHz microwaves [21] and on cardiovascular mortality related to extremely low-frequency magnetic fields in Swiss railway workers [22], with no significant health risks found. While RF radiation can affect patients’ health, most studies, including those on gamma and X-ray radiation in healthcare, indicate limited evidence of significant risk [23].

The use of RF wireless technology in healthcare raises concerns about electromagnetic interference (EMI), which can affect medical devices, such as pacemakers, and can compromise patient safety [24,25]. Health Canada has called for stricter EMC standards to mitigate these risks. RF waves are also used in medical imaging and therapy, including CT scans, X-rays, and cancer treatments [26]. This study explores the interactions between EMR and living beings and EMR’s potential clinical applications. The authors in [27] provided a detailed analysis of the benefits and risks of EMR, along with safety recommendations for healthcare professionals and communications professionals, to address potential hazards. EMF shows promise in treating disorders such as cancer, kidney stones, and brain conditions, although its use presents challenges, including adverse effects, such as hair loss [28,29]. Non-ionizing EMR has been used in cancer treatments to eliminate micro-organisms [30]. A review comparing electromagnetic field therapy (EMFT) and ultrasound (US) for wound healing highlights the need for more quantitative studies to validate these methods [31].

Table 1. Several EMF applications in healthcare systems with observations identified in previous works.

SI. No	EMF Applications	Healthcare Systems	Health Effects	Ref.
1	7 mT, 50 Hz MF for 3 h, ferrous chloride (FeCl2, $10\mathsf{\mu }\mathrm{g}/\mathrm{mL}$), melatonin (0.5 or 1.0 mM).	Rat peripheral bloodlymphocytes in alkaline comet assay.	Melatonin ameliorates the effect of simultaneous exposure to FeCl2 and MF, resulting in significant DNA damage.	[32]
2	EMF ranges 980, 950 MHz, 200 KHz modulation, 5 w, and 500 ppm toluene applied for two weeks.	MN assay on lymphocytes.	When microwave (mW) radiation was combined with toluene it resulted in significant cytogenetic effects. However, neither MW radiation alone nor toluene alone caused these effects.	[33]
3	Minimum range of EMF used.	Small area of forearm skin in10 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.	[34]
4	Two hours per day for 6 months. Frequencies (900 MHz, 1800 MHz and 2100 MHz).	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]
5	Medium-frequency EMF.	General medical examination, cardiological, and family history surveys have been conducted for MF broadcast and radio link station workers.	MF broadcast and radio link station workers, which included general medical examinations, cardiological assessments, and surveys on family history.	[36]
6	EMF ranges like 700 MHz. ContinuousRF-EMF, 25.2–71.0 V/m, 5–15 min.	Slices of rat hippocampus were examined, using evoked field potential measurements.	Reported level of neuronal excitability increase.	[37]

summarizes various healthcare applications of EMF.

Finally, in the context of healthcare applications, it has been discovered that melatonin administration reduces DNA damage from simultaneous exposure to FeCl₂ and magnetic fields (MF) at 7 mT for 3 h [32]. EMF exposure at various frequencies, including 980, 950, and 2100 MHz, has been linked to oxidative stress and DNA damage in some cases, though the results are inconsistent [33,35]. Some studies suggest minimal health risks from low-level EMF exposure, while others report increased neuronal excitability at 700 MHz [37]. In contrast, VLC-based systems, which use LEDs for optical data transmission, provide a safe, cost-effective alternative for healthcare environments where RF is restricted.

3. Modulation Techniques for VLC in E-Healthcare Systems

Modulation techniques are crucial in determining the efficiency, data rate, and power consumption of VLC systems, particularly in healthcare applications where reliability and data transmission security are essential. This section provides an in-depth analysis of different modulation techniques, such as on–off keying (OOK), pulse amplitude modulation (PAM), quadrature amplitude modulation (QAM), and orthogonal frequency-division multiplexing (OFDM). We will evaluate their suitability for healthcare settings by considering factors such as data rate, power efficiency, and resistance to noise and interference.

3.1. 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.

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. The proof-of-concept OOK-based VLC system demonstrates that even at longer distances (up to 15 m), transmission quality remains acceptable, as evidenced by the low EOP values reported.

Despite its advantages, OOK has limitations. It is particularly vulnerable to noise and interference, especially in hospital environments where ambient light sources and reflections may affect signal clarity. This can increase BER, particularly in non-line-of-sight (NLoS) conditions or at longer distances. Furthermore, OOK’s spectral efficiency is lower compared to more advanced modulation schemes, such as OFDM, which can handle higher data rates and mitigate intersymbol interference (ISI). Therefore, in situations where high data throughput and noise resilience are required, alternative modulation techniques may be better suited.

3.2. Pulse Amplitude Modulation (PAM) and Quadrature Amplitude Modulation (QAM)

PAM and QAM are widely used in VLC systems, due to their ability to transmit higher data rates compared to simpler modulation schemes like OOK. Both PAM and QAM encode multiple bits per symbol, allowing for more efficient use of bandwidth and increasing data throughput [42].

PAM varies the amplitude of each pulse to encode information. For example, in 4-PAM, four distinct amplitude levels are used to represent two bits of information per symbol. In VLC systems, PAM is particularly attractive because it offers a good trade-off between power efficiency and data rate. PAM can achieve higher data rates than OOK by transmitting more bits per symbol, but it comes at the cost of increased complexity and susceptibility to noise, especially in environments with high ambient light interference. This trade-off makes PAM suitable for applications where moderate-to-high data rates are needed but power consumption remains a concern, such as in wearable medical devices or remote health-monitoring systems [43].

In healthcare environments, where devices such as patient monitors or diagnostic equipment may be required to transfer large amounts of data, PAM provides a feasible solution, due to its higher spectral efficiency. However, the implementation of PAM requires more precise control over transmission power and detection sensitivity, as errors due to noise or distortion can degrade performance more than with simpler modulation schemes. Error correction techniques and adaptive modulation schemes can help mitigate these challenges, making PAM a practical solution in environments where data integrity is critical.

QAM further improves upon PAM by modulating both the amplitude and phase of the light signal. This dual-modulation approach allows QAM to transmit even more bits per symbol compared to PAM. For example, 16-QAM uses 16 distinct combinations of amplitude and phase to encode four bits per symbol. This results in significantly higher data throughput than PAM or OOK, making QAM a strong candidate for high-bandwidth VLC applications, such as the transmission of medical images, video feeds, or other data-heavy applications in healthcare [44].

QAM is commonly used in VLC systems where high spectral efficiency is required. However, like PAM, QAM is also more susceptible to noise and interference, due to its reliance on amplitude modulation. The complexity of the signal constellation in higher-order QAM schemes (e.g., 64-QAM, 256-QAM) requires sophisticated receivers capable of accurately detecting small changes in both amplitude and phase. This makes QAM better-suited for applications where high-performance hardware is available and the VLC link is relatively free of interference [45].

In the context of healthcare, QAM’s higher data rate can support bandwidth-intensive applications, such as real-time monitoring of multiple patients, telemedicine, or the transmission of high-resolution medical imaging data between devices. For instance, in a hospital environment, QAM could be used to transmit large sets of diagnostic data between diagnostic devices and central servers for analysis, or to transmit real-time video feeds for telemedicine consultations.

3.3. Orthogonal Frequency-Division Multiplexing (OFDM) and Advanced Modulation Techniques for Improved Efficiency

OFDM is widely used in VLC, due to its ability to handle high data rates and mitigate ISI through the use of multiple subcarriers [46]. It is especially effective in environments where multipath reflection can degrade signal quality, such as hospital rooms with numerous reflective surfaces [47]. In particular, a study utilizing differential carrier offset orthogonal frequency-division multiplexing (DCO-OFDM) demonstrated the effective transmission of data in indoor environments using VLC [48]. OFDM’s advantage lies in its ability to divide the data stream into multiple lower-rate streams transmitted simultaneously, making it suitable for applications that require reliable, high-speed data transmission, such as the transmission of high-resolution medical images or video feeds in real time.

Variations of OFDM, including ACO-OFDM, DCO-OFDM, and PAM-DMT, have demonstrated high power efficiency and low complexity, making them practical for VLC systems in healthcare environments where both data integrity and low power consumption are critical [49,50]. ACO-OFDM reduces the peak-to-average power ratio (PAPR) by clipping the negative portion of the signal, making it ideal for low-power medical devices, such as wearable health monitors, where continuous real-time data transmission is required. This modulation scheme simplifies hardware implementation while maintaining sufficient data integrity, making it a good fit for real-time monitoring applications. DCO-OFDM, which adds a DC bias to make the signal positive, is suitable for higher-data-rate applications, like medical imaging or telemedicine, though it requires more power, due to the added bias.

PAM-DMT, combining pulse amplitude modulation with discrete multi-tone transmission, offers a balanced solution by enhancing power efficiency and spectral efficiency. It is particularly useful for longer-range VLC communication in hospitals, where data such as patient vitals need to be reliably transmitted across larger distances [50]. These OFDM variations ensure robust communication in healthcare settings, where signal integrity and low interference are essential for the reliable operation of multiple medical devices. By offering a range of trade-offs between data rate and power efficiency, ACO-OFDM, DCO-OFDM, and PAM-DMT are well-suited for diverse healthcare applications, from wearable technology to high-bandwidth hospital communication networks.

In this sense, several advanced modulation techniques, including HACO-OFDM (hybrid asymmetrically clipped optical OFDM), LACO-OFDM (layered asymmetrically clipped optical OFDM), AAO-OFDM (asymmetrically amplified optical OFDM), and ALACO-OFDM (adaptive layered asymmetrically clipped optical OFDM), offer significant improvements in spectral and power efficiency compared to traditional OFDM schemes [51,52,53,54]. These techniques enhance data throughput by efficiently utilizing available bandwidth while maintaining low power consumption, which is essential in environments like healthcare, where both energy conservation and high data rates are vital. HACO-OFDM and LACO-OFDM specifically improve spectral efficiency by clipping parts of the signal while maintaining a low peak-to-average power ratio (PAPR), allowing for effective transmission without the need for complex receivers.

These advanced modulation schemes are particularly well-suited for high-performance healthcare applications, where low latency and high spectral efficiency are critical. In real-time patient monitoring systems, for example, the ability to transmit high volumes of data—such as vital signs or imaging data—quickly and efficiently is crucial for timely medical interventions. Additionally, in telemedicine, where high-quality video and data streams must be transmitted with minimal delay, the power efficiency of AAO-OFDM and ALACO-OFDM ensures that these high-bandwidth services can be delivered reliably without overloading the system or requiring excessive power consumption. These advanced schemes allow for robust, high-speed communication in healthcare settings, making them ideal for applications that demand both performance and efficiency [51,52,53,54].

On the other hand, recent research has explored the use of VLC for long-range transmission and imaging applications. For example, a study used low-resolution cameras and intensity modulation/direct-detection orthogonal frequency-division multiplexing (IM/DD-OFDM) to estimate distances between vehicles, showing high-speed data transfer even in challenging underwater environments [55]. Such techniques, when adapted to healthcare, could enable long-range data transfer in large hospital facilities or remote monitoring scenarios.

Further studies have demonstrated high-speed underwater VLC, achieving 1.45 Gbit/s over a 4.8-m channel using a blue-light laser diode (LD) [55]. Although this setup is designed for underwater communication, similar approaches could be adapted to healthcare for robust data transmission in challenging environments, such as those with high interference or when long-range communication is necessary.

3.4. Modulation Techniques for MIMO Approaches in VLC

Multiple-input multiple-output (MIMO) techniques have been shown to significantly enhance the data rate and spectral efficiency in VLC systems, which is particularly beneficial in healthcare environments where multiple devices may need to communicate simultaneously [56]. In VLC, MIMO uses multiple LEDs and photodiodes to transmit and receive data across multiple channels, effectively multiplying the available data throughput. For example, spatial multiplexing (SMP) has been used to improve performance in VLC systems using imaging receivers, resulting in significant improvements in signal reception and data transmission [57,58,59]. These techniques are particularly useful in healthcare settings where large amounts of data, such as high-resolution medical images, need to be transferred quickly and efficiently.

Additionally, the use of imaging receivers with specialized lenses, such as convex or fish-eye lenses, plays a crucial role in improving the performance of MIMO VLC systems. These lenses focus the incoming light more precisely onto the photodetectors, which helps maximize the received signal’s intensity and reduce signal loss. By using these lenses, the light beam can be better concentrated, allowing for more efficient use of the available light and improving the overall quality of the received signal. This is particularly beneficial in environments where light reflections or diffusions might otherwise scatter the signal, such as in healthcare settings where equipment and personnel may obstruct direct line-of-sight communication. Specialized lenses enable the VLC system to maintain high performance even in challenging conditions, ensuring that data such as patient monitoring information or medical imaging can be transmitted reliably across the hospital or clinical environment [58,59].

A study specifically examining GSM, QCM, and DCM modulation techniques with convex lens-based image receivers demonstrated substantial improvements in SNR and BER when using these specialized lenses [60]. The lenses’ ability to focus light more accurately onto the photodetectors enhanced signal reception and contributed to more stable data transmission, especially in multi-user scenarios where multiple VLC systems operate simultaneously. These improvements in SNR and BER are critical for applications that require high data integrity and minimal interference, such as real-time patient monitoring or the transfer of large medical datasets like MRI scans or X-rays. By using convex or fish-eye lenses, the system can effectively handle larger volumes of data with fewer errors, ensuring reliable and efficient communication in complex healthcare environments. This highlights the potential of integrating imaging receivers with advanced lens technology, to optimize further the performance of MIMO VLC systems in medical and other high-demand settings.

3.5. Modulation Techniques in IEEE 802.15.7-2018 Standard and Their Adaptation to E-Health Environments

The IEEE 802.15.7-2018 standard for VLC outlines several modulation schemes, including OOK, OFDM, variable pulse position modulation (VPPM) and color shift keying (CSK) [61,62]. These modulation techniques are designed to optimize communication for various applications, balancing data rate, power efficiency, and robustness against interference—factors critical for VLC systems in healthcare environments.

In this sense, VPPM combines the benefits of pulse position modulation (PPM) with the ability to control the intensity of light, making it a highly flexible modulation technique [63]. In VPPM, the position of the pulse is varied to encode the data, while the intensity of the light can be adjusted for dimming control. This dual capability allows VLC systems to perform data transmission and lighting functions simultaneously, which is particularly valuable in healthcare settings where the intensity of the light must be carefully managed for patient comfort and medical procedures.

For example, in environments such as operating rooms or ICUs, VPPM can ensure that lighting conditions are optimal for medical personnel while maintaining continuous data transmission for patient monitoring devices. VPPM also offers better noise and interference resistance compared to OOK, making it more suitable for healthcare environments where lighting conditions and ambient light sources may vary. This modulation technique can be used in systems where low-to-moderate data rates are sufficient, such as transmitting patient vitals (e.g., heart rate, temperature, and oxygen levels) to monitoring stations without interrupting the visual experience of the room lighting [64].

On the other hand, CSK is a more advanced modulation technique specified in the IEEE 802.15.7-2018 standard that encodes data by varying the color of the transmitted light [65]. By using different wavelengths of light, typically red, green, and blue (RGB) LEDs, CSK can transmit multiple bits of information simultaneously by altering the color combinations. This modulation scheme is highly spectrally efficient, as it leverages the color properties of LEDs without requiring significant bandwidth. The basic transmission scheme using CSK modulation can be seen in Figure 1:

In e-health applications, CSK could be particularly useful for transmitting larger datasets or more complex medical information, such as medical images or real-time video for telemedicine. Because CSK uses multiple wavelengths, it can achieve data rates higher than those of OOK or VPPM, making it suitable for bandwidth-intensive applications. For example, in a telemedicine scenario where high-resolution video and diagnostic data need to be transmitted with minimal latency, CSK can provide the necessary data throughput while still allowing the lighting system to function at its regular capacity [2,61].

Furthermore, CSK’s ability to modulate data through color changes rather than intensity adjustments makes it less sensitive to ambient light interference, ensuring a more stable communication link in environments like hospital wards or emergency rooms. This capability allows CSK to be applied in scenarios where both lighting and communication are critical but must not interfere with each other.

4. Channel Coding Schemes for Error Correction in VLC in E-Healthcare Scenarios

The implementation of channel coding in VLC systems applied in e-healthcare scenarios plays a critical role in ensuring reliable data transmission by detecting and correcting errors. As VLC systems are often subject to noise, interference, and signal degradation—particularly in indoor environments with multiple sources of ambient light or reflections—error correction mechanisms are essential for maintaining the integrity of transmitted data. Various coding schemes, such as Reed–Solomon (RS) codes, convolutional codes, low-density parity check (LDPC) codes, and polar codes, have been explored for their effectiveness in error correction and their trade-offs in complexity and performance.

In the general framework of error control coding, redundant bits are added to the data stream to help identify and correct errors. A typical encoder divides the input message into blocks of size ‘k’ bits and replaces each block with a codeword of length ‘n’ bits, thus introducing ‘n–k’ redundant bits. This redundancy enables the detection of transmission errors and, in some cases, allows error correction at the receiver, improving the BER of the system [66,67,68].

4.1. Reed–Solomon and LDPC Codes in VLC

RS codes are block error correction codes that are particularly effective in correcting burst errors that occur in sequences, due to noise or interference. RS codes have been applied to VLC systems to maintain robust communication in environments prone to sudden signal degradation, such as indoor spaces where lighting conditions can fluctuate. RS codes perform well in scenarios with high SNR requirements, as they correct multiple errors within a block. However, the high computational complexity of RS decoding can limit their application in real-time, low-latency scenarios, such as e-health systems, where patient monitoring data must be transmitted and received quickly.

LDPC codes, on the other hand, offer a more efficient alternative, with lower decoding complexity, while maintaining strong error correction capability. LDPC codes utilize a sparse parity-check matrix, enabling iterative decoding algorithms that rapidly converge to correct errors. In VLC systems, LDPC codes have been found to strike a balance between performance and complexity, making them suitable for applications that require high data rates and reliability. For example, in water-to-air VLC systems (W2A-VLC), the combination of RS and LDPC codes has been shown to significantly reduce the BER and frame error rate (FER), demonstrating improved communication reliability over noisy channels, even with varying transmitter–receiver distances [69].

Moreover, recent advances in VLC systems have introduced coding schemes designed specifically to address flicker mitigation and dimming support, which conventional forward error correction (FEC) codes may not handle effectively. One such approach combines polar codes (PCs) with a Knuth balance code and enhanced prefix coding, to achieve flicker-free transmission while improving efficiency [70]. This scheme reduces computational complexity by eliminating lookup tables and generating minimal redundancy, which increases energy efficiency. The proposed coding structure offers significant improvements in transmission efficiency, particularly for dimming values of 75% (or 25%) and 87.5% (or 12.5%), compared to standard polar codes or polar codes with run-length limited (RLL) encoding. Furthermore, the scheme exhibits superior BER performance compared to traditional approaches, making it ideal for real-time VLC applications where flicker-free, energy-efficient communication is critical [71]. This integration of polar codes with optimized flicker and dimming support represents a significant step forward in the development of practical VLC systems, especially for healthcare settings where reliable real-time data transmission is essential.

4.2. Turbo Codes and Polar Codes

Another powerful coding scheme employed in VLC systems is the turbo code, which is designed to approach the Shannon limit, in terms of error correction performance. Turbo codes are iterative codes that combine two or more convolutional codes in parallel, separated by an interleaver. In the context of VLC, turbo codes have been implemented to improve indoor data communication. For example, a study using MATLAB simulations version R2022a showed that turbo codes significantly reduced BER compared to uncoded systems, demonstrating their potential to improve the reliability of VLC systems even in high-interference environments [72]. This improvement was further validated by hardware implementations, which confirmed that reliable data transmission over distances up to 5 m indoors is achievable with turbo codes, making them suitable for applications in e-health, such as real-time patient monitoring.

Polar codes, introduced as the first class of codes to achieve channel capacity, have also gained traction in VLC systems. Polar codes use channel polarization techniques to divide the channel into “good” and “bad” sub-channels, transmitting data over the more reliable sub-channels, to optimize error correction. A novel application of polar codes in RLL coding has been proposed, to further improve BER performance and mitigate flicker in VLC systems [73,74]. In RLL decoding, frozen bit indices are used to generate RLL codes, improving the resilience of VLC systems against flicker—a significant concern when LEDs are used for both illumination and data transmission in healthcare environments. The advantage of polar codes lies in their scalability; as the code length increases, so does their ability to approach the Shannon limit, making them highly efficient for both short-range and long-range VLC communication.

4.3. Advanced Coding Techniques for Dimmable VLC Systems

Dimmable VLC systems present a unique challenge, as they must balance the dual functions of data transmission and lighting control. This is particularly important in environments such as hospitals, where lighting conditions directly affect patient care and comfort and where data transmission must be both reliable and adaptable to varying levels of light intensity. To address this, advanced coding techniques are designed to support both flicker mitigation and dimming control while maintaining high transmission efficiency.

One such advanced approach is the curved polar code methodology, which has shown notable improvements in transmission efficiency for dimmable VLC systems. Studies have shown that the coding gains achieved using this methodology exceed those of LDPC codes and polar codes with compensation symbols, offering gains of 1.4 dB to 2.8 dB, depending on the configuration [75]. This method allows VLC systems to maintain high data integrity while adapting to varying light intensities, making it particularly suitable for healthcare applications where both efficient lighting and reliable communication are essential.

Building on this, a new scheme involving shaped polar codes has been proposed specifically for dimmable VLC systems. The shaped polar codes scheme uses a precoder to control the dimming by adjusting the probability of 1 s in a codeword, directly correlating with the dimming value in OOK modulation systems. The simulation results for this approach reveal significant coding gains of about 2.5 dB and 2.8 dB compared to LDPC codes with compensation symbols and polar codes with compensation symbols, respectively. Furthermore, the shaped polar codes scheme maintains strong performance even at higher information rates, making it an ideal solution for applications requiring both high efficiency and adaptability to varying lighting conditions [74].

These advanced coding techniques represent a significant evolution in dimmable VLC systems. By improving error correction capability while providing flexible dimming control, they enhance the overall performance of VLC systems in real-world environments. In healthcare settings, where dimming and flicker-free lighting are critical for patient comfort and procedural accuracy, these advanced codes offer a promising solution for ensuring reliable, high-quality data transmission.

4.4. Run-Length Limited (RLL) Codes

Finally, RLL codes have been specifically designed for VLC systems to mitigate flicker and optimize error correction. By controlling the maximum and minimum run lengths of consecutive identical bits, RLL codes ensure that the light intensity changes frequently enough to prevent visible flicker while maintaining strong error correction capability. Recent developments in high-rate RLL codes, based on finite-state machines, have further improved the error performance of VLC systems, as demonstrated in simulations where these codes outperformed existing RLL schemes in both error correction and flicker mitigation [71]. The optimized minimum Hamming distance in these codes plays a critical role in reducing BER, making them highly effective for VLC systems used in healthcare, where even minor interruptions in data transmission can lead to incorrect patient monitoring.

In [75], a new RLL code, called 5B10B, was developed, which is not specified in the 802.15.7 standard, but is used instead of the well-known 8B10B code. This new code, in addition to preserving the desirable characteristics of traditional RLL codes for VLC, allows for improved error correction capability. Figure 2 presents a schematic diagram of the VLC system with RLL code.

5. Integration of VLC in Healthcare Environments

This section examines the pragmatic application of VLC systems within healthcare environments, taking into account the obstacles presented by diverse lighting conditions, patient mobility, and the coexistence of various wireless technologies. The healthcare sector has the potential to gain advantages from the implementation of secure and safeguarded conditions by employing VLC data transfer technology.

The aforementioned mode of transmission demonstrates characteristics that are favorable to users and environmentally conscientious, providing a practical and economically efficient resolution [76]. Within the context of VLC healthcare ICU monitoring systems, it is imperative to maintain a consistent emphasis on the health status of patients and to ensure the regular updating of their health information by medical professionals. Therefore, it is imperative to find a viable solution to tackling these issues, and VideoLAN Client VLC emerges as a highly promising technology for meeting these requirements [77]. Additionally, a separate research investigation examined the utilization of VLC wireless systems, presenting a novel conceptual framework for the integration of medical healthcare data. This study conducted a comparison of the energy efficiency of the visible-light-emitting diodes that were employed [78]. The mobile health-monitoring system, which is based on VLC technology, utilizes visible light as a medium for transmitting biological signals and patient data. Modifying the size of data packets has the potential to improve the dependability of transmitting information, hence enabling the feasibility of portable patient monitoring on mobile devices. The transmission of electrocardiogram (ECG) and photoplethysmogram (PPG) data facilitates the assessment of heart rate and blood pressure, with the aid of an emergency alert feature implemented on an Android platform. Real-time experiments demonstrate the simultaneous monitoring and evaluation of heart rate and arterial blood pressure. The technology utilizes a communication technique that does not pose any risks and a portable device, hence improving the safety and quality of healthcare services. There was a requirement for the integration of a user-friendly health monitoring system that facilitates the transmission of biological signals, real-time data signal transfer, alarms, data analysis, and implementation [79]. The study was conducted to analyze the overall performance of hybrid VLC-RF systems in e-health medical applications, specifically focusing on the implementation of the decode-and-forward relay technique. The system offers robust connectivity options that provide seamless access to patient information for hospitals and laboratories. Therefore, an examination of many factors about the cumulative distribution function (CDF) and probability density function (PDF) of the end-to-end SNR of the system was conducted, to derive the analytical equation for the BER of VLC and RF communication systems [80]. Moreover, it should be noted that VLC systems necessitate a continuous source of illumination to maintain network connectivity, which has the potential to disrupt the rest of the patients. The issue can be resolved by reducing the intensity of the light, which enables the transfer of data while maintaining the appearance of being switched off. Various levels of dimming facilitate efficient data transfer. Therefore, VLC technology demonstrates suitability for the transmission of medical information. VLC technology in medical settings provides effective wireless communication and illumination, using the benefits of LED technology, such as energy efficiency, robustness, and high luminosity. In the realm of e-health services, medical data transmission now relies on the utilization of existing RF networks. However, it is important to note that these networks present certain health concerns and have the potential to interfere with the proper functioning of medical devices. Consequently, limitations have been imposed on the usage of RF equipment, such as mobile phones, within hospital premises. The presence of adverse consequences necessitates the use of environmentally sustainable communication alternatives within healthcare facilities [80,81,82]. To address forthcoming healthcare demands, we propose the implementation of a flexible hybrid optical–radio wireless network that can provide robust wireless connectivity within healthcare facilities. The subsequent stages encompass the process of enhancing the criteria that are relevant to the environment and conducting tests on a hybrid network that is adaptable and created specifically for healthcare situations [12,83]. Scholarly investigations have placed significant emphasis on the constraints associated with various uplink systems. In order to optimize the utilization of the extensive range of wavelengths within the visible light spectrum, it is imperative to conduct a thorough evaluation at the system level, taking into account the limitations imposed by uplink and backbone considerations. A heterogeneous network would encompass a scalable, dependable, high-data-rate VLC network [82]. The identification of distinct finger movements is achieved by the utilization of the long short-term memory (LSTM) neural network, which is trained on the analysis of luminous transitions occurring between fingers. This study assesses the design and execution of a gesture recognition technique for a viable VLC system that operates at a distance of 48 cm. The system’s applications encompass various domains of human–computer interaction, such as healthcare, commerce, and home environments. Future endeavors encompass the augmentation of gesture diversity and the refinement of the system’s ability to identify individuals by their unique gesture signatures [84]. Furthermore, empirical study has demonstrated that the utilization of external synchronization is a viable approach in mitigating SDR clock drift, thereby showing the feasibility of attaining dependable higher-order modulation and coding schemes (MCSs), such as 64-QAM. The methodology employed facilitates rapid prototyping across a wide range of configurations. In order to strategize the expansion of research in challenging outdoor environments, it is proposed to employ specialized SDR synchronization solutions and implement pre-equalization or mapping techniques to optimize performance, given the limitations of the hardware [85]. The review explores potential applications, such as indoor positioning, patient monitoring, and medical device communication. The incorporation of VLC technology within healthcare settings has several advantages, encompassing precise indoor localization, streamlined data transmission, and enhanced patient surveillance. VLC employs LED technology for the purpose of data transmission, hence facilitating the monitoring of medical equipment and personnel and augmenting oversight. Enhancements can be made to enhance patient data security. Nevertheless, the successful integration of systems must take into account many problems, such as signal interference and the establishment of infrastructure, which necessitate careful attention.

Hence, Figure 3 illustrates the prototype design of the medical healthcare system that uses VLC for data management and monitoring in the RF domain. These techniques offer a potential alternative to traditional wireless communication systems employed in healthcare facilities.

The work developed by [39] demonstrates the feasibility of a stable and low-cost VLC system based on Manchester-OOK for monitoring parameters using a multiparameter monitor in intensive care units (ICUs) in hospitals. Figure 4 shows an illustration of the conceptual idea of implementing VLC to monitor patients in hospitals. The data from the multiparameter monitor of patients in intensive care units is transmitted via lighting LEDs and collected by healthcare personnel smartphones, as well as by devices connected to computers located in a monitoring center.

6. Future Directions and Challenges

This paper provides a comprehensive analysis of e-healthcare systems based on VLC and concludes by identifying key areas for future research and development. While VLC offers significant potential for transforming wireless communication in healthcare environments, several challenges must be addressed to fully leverage its capabilities. This section highlights future research directions and the technical obstacles that need to be overcome for the successful implementation of VLC in e-healthcare systems.

6.1. Mitigating the Effects of Electromagnetic Interference (EMI)

One of the significant advantages of VLC over traditional RF systems is its immunity to EMI. Research has shown that exposure to EMF from RF systems can cause health issues, including damage to the nervous system, and other physiological effects [64]. VLC, which operates outside the electromagnetic spectrum used by RF systems, offers a safer alternative, especially in sensitive healthcare environments. However, future work should focus on further exploring the impact of VLC on human health, particularly in prolonged exposure scenarios. Furthermore, hybrid systems that combine the VLC and RF technologies could be developed to capitalize on the strengths of both, while mitigating their weaknesses.

6.2. Channel Coding Optimization

Another crucial area for future research is the optimization of channel coding schemes within VLC systems. Current coding schemes, such as RS, LDPC, and polar codes, have demonstrated strong error correction capability, but further improvements are needed, to enhance their performance under varying environmental conditions. Investigating new and advanced coding techniques tailored to the unique characteristics of VLC, such as flicker mitigation and dimming control, will be essential. Researchers should also focus on evaluating how distinct photodiodes perform under different lighting conditions and coding schemes. For example, combining photodiode performance analysis with optimized channel coding could result in better data integrity, especially in scenarios where the SNR is reduced, due to ambient light interference. The use of simulation tools, such as NI cDAQ programmed in LabView, as verified by previous studies, should continue to be used for physical system validation and to assess real-world performance [86].

6.3. Resource Allocation and Spectrum Efficiency

One of the significant challenges faced by VLC systems in healthcare environments is suboptimal resource allocation, which can lead to low multiplexing gain and poor spectrum efficiency. Efficient resource allocation is critical in settings such as hospitals, where multiple medical devices—such as patient monitors, infusion pumps, diagnostic imaging equipment, and wearable health devices—may be simultaneously communicating over the same VLC channel. If the available spectrum is not used effectively, this can result in interference between devices, reduced data throughput, and delayed transmission of critical health data, such as patient vital signs or real-time diagnostic information.

To address this challenge, techniques such as space–time block codes (STBCs) and spatial multiplexing (SMP) have been explored as methods to enhance spectrum efficiency and increase the data rate of VLC systems [87,88]. STBCs, in particular, are known for their ability to utilize multiple transmitter and receiver antennas to achieve diversity gain, improving the reliability of the communication link by mitigating the effects of fading and interference. SMP, on the other hand, leverages the spatial dimension of the communication system to send multiple data streams simultaneously, thus significantly increasing the overall data rate of the VLC system. SMP has been shown to improve the throughput of VLC systems in environments with high device density, such as healthcare facilities.

However, the challenge lies in adapting these techniques to the specific characteristics of VLC channels, which differ from traditional RF channels, due to the requirement for line of sight (LoS) communication and the impact of ambient lighting conditions. In VLC systems, the light emitted by LEDs is used for both illumination and data transmission, and any obstructions in the LoS path can severely degrade communication performance. Therefore, future research should focus on developing dynamic resource allocation algorithms that can adapt in real time to changes in network traffic, user mobility, and environmental factors. These algorithms should be able to optimize the use of available spectrum resources while ensuring that high-priority data, such as real-time patient monitoring or emergency communication, is transmitted with minimal latency.

Additionally, research should investigate the use of multi-user MIMO (MU-MIMO) techniques in VLC systems. MU-MIMO allows multiple users to be served simultaneously over the same VLC channel by leveraging multiple transmitters and receivers to separate the data streams spatially. By using multi-user beamforming and precoding techniques, MU-MIMO can further improve the spectrum efficiency of VLC systems, particularly in high-density environments where multiple devices must operate concurrently [57,86]. Recent studies have shown that MU-MIMO VLC systems can achieve significant improvements in both spectrum efficiency and energy efficiency by optimizing the allocation of resources between users. These advancements could lead to more robust and efficient VLC networks in healthcare settings, enabling the simultaneous operation of numerous medical devices with high data demands.

Moreover, cognitive radio techniques could also be integrated into VLC systems, to optimize spectrum usage dynamically [55]. Cognitive radio can sense the environment and adapt its transmission parameters based on real-time spectrum availability, which can help minimize interference and maximize spectrum utilization. By applying cognitive radio principles to VLC, healthcare networks could become more flexible and resilient, especially in environments where bandwidth demands fluctuate throughout the day.

6.4. Environmental Impact on VLC Systems

Another key area of research lies in the assessment of the impact of environmental conditions on the performance of VLC systems. Although VLC is generally robust against many forms of interference that affect RF communication, certain environmental factors, such as fog, thermal turbulence, and precipitation, can still degrade VLC performance, particularly in outdoor or automotive applications. A multistage quadrature amplitude modulation (M-QAM) approach was employed in prior studies, to test the impact of these environmental conditions on the performance of VLC systems using ceiling lights and automotive lamps. Future research should expand on this work, to develop more resilient modulation schemes capable of adapting to changing environmental conditions [88]. This will be particularly important for healthcare systems that rely on VLC in both indoor and outdoor environments, such as for ambulance-to-hospital communication or emergency response scenarios.

6.5. Hybrid VLC-RF Systems for E-Healthcare

Although VLC offers several advantages, including immunity from electromagnetic interference and high data security, there are certain situations where RF technologies may still be required, particularly for long-range communication or through-wall transmissions [55,79,81]. Therefore, the development of a hybrid VLC-RF system could be an effective way to combine the strengths of both technologies. Hybrid systems would allow seamless communication in complex healthcare environments, enabling robust indoor VLC for high-speed data transmission, while RF could be used for long-distance communication or where direct line of sight is not possible. More research is needed to develop efficient handover mechanisms between VLC and RF technologies, to ensure uninterrupted service and optimize network performance in healthcare applications.

Figure 5 shows a diagram of a hybrid VLC-RF system consisting of a personal area network of real-time sensors, which allows remote monitoring of the patient’s health.

6.6. Energy Efficiency and Real-Time Processing

Another important challenge is the need to improve the energy efficiency of VLC systems, especially for use in portable or battery-powered healthcare devices. As real-time patient monitoring becomes increasingly critical in e-health systems, VLC-based solutions must be designed to support low-latency, energy-efficient communication [77]. Future research should focus on developing new coding and modulation schemes that minimize power consumption without compromising data transmission quality or speed. Furthermore, real-time processing capabilities must be enhanced, to ensure that data from multiple medical devices can be processed quickly and accurately, with minimal delay, in applications such as telemedicine or remote patient monitoring.

We can see that VLC presents exciting opportunities for revolutionizing wireless communication in healthcare; however, significant research efforts are still required to overcome challenges related to channel coding, resource allocation, environmental impact, and energy efficiency. Advanced coding techniques and hybrid VLC-RF systems offer promising solutions for enhancing system performance in complex healthcare environments. By addressing these challenges, future VLC systems can provide reliable, efficient, and safe communication in critical healthcare applications.

7. Conclusions

This paper presents a study on VLC technology, its development, modulation, and channel coding techniques, with a focus on applications in healthcare environments, and it is evident that this solution offers some advantages compared to RF-based solutions.

The analysis of studies on the various types of electromagnetic radiation and their potential effects on human health—including ionizing radiation such as X-rays and gamma rays, which have enough energy to cause damage to human tissues, and non-ionizing radiation, which includes radio waves and microwaves used in common devices like cell phones—suggests that prolonged exposure to high densities of nonionizing radiation could be associated with health risks, such as cancer. However, there is no definitive scientific consensus on these effects, and further studies are recommended. In addition, greater caution is required, particularly with exposure to higher frequencies, due to the potential long-term risks.

The use of VLC technologies for communication in healthcare environments offers some advantages over RF technology, mainly because medical devices, which are highly sensitive and delicate, do not suffer from electromagnetic interference while in a VLC environment.

The research places significant emphasis on the evaluation of a prototype vehicular and healthcare communication system, incorporating essential components, such as a transmitter, receiver, controller area network (CAN) bus, and various testing conditions.

The potential to revolutionize electronic healthcare is promising, through the introduction of VLC systems that incorporate appropriate modulation and channel coding algorithms. This analysis highlights the need to carefully choose appropriate schemes based on specific use cases in the healthcare field, and it emphasizes the ongoing importance of research and development in this area. By utilizing VLC technology, the healthcare industry could implement communication solutions that are efficient, secure, and reliable, ultimately leading to improved patient care and an enhanced healthcare experience.