On the design of an optical wireless link for small cell backhaul communication and energy harvesting

The outdoor deployment of small cells (SCs) in heterogeneous cellular networks for mobile communications is advantageous from both the capacity and the power consumption point of view. In practice, however, the network operators are limited by the high costs associated with the provisioning of backhaul communication and power supply to the SCs. This paper addresses these operational challenges by using optical links at the same time for high-capacity backhaul and wireless power supply. In particular, we present an experimental design of an optical wireless link for energy harvesting (EH). Our system consists of (i) a high-brightness white light-emitting diode (WLED) with an output luminous flux of 2200 lm, and (ii) an amorphous silicon (a-Si) solar panel. The distance of the experimental link ranges from 0.5m to 5m. The visible-light EH from the solar panel is negatively affected by the Lambertian radiation pattern of the WLED. In order to increase the collimation of the source light, we use three optical elements - a spherical lens, a reflector, and a parabolic mirror. The latter is shown to achieve a gain of 28.4 dB in EH over a distance of 5 m compared to the non-collimated case.