Introduction: Challenges in 5G+HetNet Integration

The current developments in the fifth generation and beyond (5G+) mobile networks focus on moving from the increasingly congested radio frequencies (RF) to higher frequency bands such as millimeter wave (mmWave), Terahertz, and Visible Light bands. Among these high frequency options, visible and infrared lights represent a strong candidate owing to the widely deployed lighting systems. Due to their distinct wave propagation characteristics, efficient integration of RF with such high frequency bands is needed for better reliability and high throughput. This introductory chapter presents an overview on RF and light (optical)-based wireless networks. This chapter highlights existing research efforts along with the limitations that should be addressed from planning and operational perspectives to enable a smooth integration of RF and optical networks in mobile environments.