# Comprehensive Survey on VLC in E-Healthcare: Channel Coding Schemes and Modulation Techniques
## 6 Future Directions and Challenges
### 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.