On the design of a free space optical link for small cell backhaul communication and power supply

The concept of small cells (SCs) is widely acknowledged for its significant benefits in energy efficiency and capacity of heterogeneous cellular networks. However, a large scale outdoor installation of SCs is limited by cost factors. Therefore, wireless backhaul communication and wireless power supply to SCs could significantly reduce deployment costs. The focus of this paper is on the investigation of the use of free space optical (FSO) links for power transfer to SCs in an indoor environment. In particular, an experimental design of a red light link for wireless power transmission (WPT) and energy harvesting (EH) is presented in the absence of ambient light. The transmitter includes up to five laser diodes (LDs) with a typical output optical power of 50mW per LD. Light collimation is achieved by the use of aspheric lenses. The receiver comprises a crystalline silicon (c-Si) solar panel placed at 5.2m from the optical transmitter. The use of five pairs of LDs and lenses results in a maximum harvested power of 10.4mW. This study shows that the number of optical transmitters required for the generation of an electrical power of 1W (demanded for the operation of a SC) from the solar panel is estimated to be 110.