## 8 Overview of VLC Emerging over the Last Few Years and Its Future Prospects  
As discussed in the Introductory section of this paper, visible light communication is wireless communication technology in which visible light is used to modulate the baseband signal. Light-emitting diodes (LEDs) are preferred to realize VLC systems as they offer multiple exciting benefits over traditional light sources in terms of cost, efficiency, energy consumption and lifetime. VLC is thought to be a future technology that has the potential to be used in the indoor environment for data transmission with the advantages of minimum security threats. Extension of bandwidth and increasing data transmission rates are the two of the main challenges faced by the researchers working in the field of VLC. The use of an efficient light source is an important consideration and an accomplishment of a VLC system. Phosphor-converted white LEDs are advantageous as they have less modulation complexity, but they perform poorly when it comes to the efficient utilization of the spectrum. We need to integrate LEDs of all three primary colors if spectrum utilization is to be maximized, but this results in modulation complexity and an increase in cost. If some low cost methods are developed that can help in the fabrication of full-color LEDs incorporating all three primary colors, we can realize a low-cost VLC system with efficient spectrum utilization. Besides white LEDs, dual- or multi-color emitting devices have also been used as VLC transmitters. Furthermore, instead of a single device, arrays of LEDs are also being utilized in VLC technology, which provides benefits in terms of higher output optical power. Solutions like this are also needed to be taken into account, and LED arrays with multi-color  
Figure 18: (**a**) Photoluminescence (PL) spectra of nanorod LEDs with and without Ag NPs at room temperature and 10 K; (**b**) J–V characteristics of the nanorod LEDs with and without Ag NPs; (**c**) frequency response of the nanorod LED with and without Ag NPs; (**d**) modulation bandwidth of the two LEDs as a function of the injection current density. [39] Figures reproduced with permission from Optical Society of America. emission should also be investigated for VLC applications. Transmission distance is another concern associated with VLC technology. VLC systems realized until now lack the advantage of long-distance transmission and reception of data. Factors hindering long-distance transmission in VLC should be investigated thoroughly and addressed accordingly. Use of better quality light sources like lasers can also contribute somehow to the improvement of VLC systems. Researchers working in the field of VLC are continuously exploring the ways to maximize bandwidth and enhance transmission speeds of VLC systems. Separating slow-responding components of the light from transmitted signals can help in increasing the bandwidth, as reported by [98]. The use of an appropriate modulation scheme is also crucial, for example, OFDM can account effectively for degradation factors, multipath fading and inter-symbol interference, and, hence, high transmission speeds can be attained. Equalization is something that can also contribute to the improvement of bandwidths for VLC systems. Photodetectors are the commonly used tools for the purpose of detection in the field of VLC. Other kinds of detectors should also be explored, as photodetectors are usually very prone to the noise signal. At the moment, there is still no strong agreement about how and where VLC could effectively be used for future wireless communications technology. In addition, the transmission distance is constrained as the distance increases, leading to a significant decrease in optical power. To improve the transmission distance for an efficient device application, high-performance and low-cost transmitter and receiver modules or chips need to be designed, and equalizer optimization and hardware design for OFDM modulation schemes are essential.