Visible Light Communication in 5G

Introduction Owing to the increasing demand for wireless data communication, the available radio spectrum below 10 GHz (centimeter wave communication) has become insufficient. The wireless communications industry has responded to this challenge by considering the radio spectrum above 10 GHz (millimeter-wave communication). However, the higher frequencies f mean that the path loss L increases according to the Friis free-space equation ( L α f 2 ), i.e., moving from 3 to 30 GHz would add 20 dB signal attenuation or, equivalently, would require 100 times more power at the transmitter. In addition, blockages and shadowing in terrestrial communication are more difficult to overcome at higher frequencies. As a consequence, systems must be designed to enhance the probability of line-of-sight (LoS) communication, typically by using beamforming techniques and by using very small cells (about 50 m in radius). The requirement for smaller cells in cellular communication also benefits network capacity and data density. In fact, reducing cell size has without doubt been one of the major contributors to enhanced system performance in current cellular communications. The cell sizes in cellular communication have dramatically shrunk (35 km in the second generation (2G), 5 km in the third generation (3G), 500 m in the fourth generation (4G), and probably about 50 m in the fifth generation (5G) [1] and 5 m in the sixth generation (6G). This means that, contrary to general belief, using higher frequencies for terrestrial communication has become a practical option. However, there are some significant challenges associated with providing a supporting infrastructure for ever-smaller cells. One such challenge is the provision of a sophisticated backhaul infrastructure. It is predicted that a capacity per unit area of 100 Mbps/m2 will be required for future indoor spaces, primarily driven by high-definition video and billions of Internet of Things (IoT) devices. Achieving this with low energy consumption will be critical if the potential of “green” communication is to be realized. The goal of connectivity will require swathes of new spectrum, and energy harvesting will be needed to prevent exponentially increasing energy consumption for wireless communications. The available optical spectrum dwarfs that available in the radio frequency (RF) region, and can be accessed using low-cost optical components and simple (compared with radio frequency (RF) baseband processing.