Wireless Optical Link Design and Fog Loss Measurements

Abstract

Deployment of 5th generation of mobile networks leads to an increasing demand for high-speed access interfaces. The challenge of finding an alternative to fiber optics used now as a link between the centralized radio controllers and the radio heads can be overcome by implementation of wireless optical communication technology. However, despite of many advantages of this technology, weather conditions impede its reliable operation. Being relatively immune to rain and snow, traditional wireless optical systems of near-infrared wavelengths suffer from atmospheric turbulence and especially fog.

To explain interruptions of operation of wireless optical links in fog, an experimental setup consisting of a mid-infrared (9.2 µm) quantum cascade laser (QCL) link, a near-infrared (1.55 µm) laser link, and a visible (0.532µm) laser link was built during the project.

Droplet size distributions at different fog stages were deducted from direct extinction of multi-wavelength signals. This allows to better understand fogs dynamics and their influence on link losses that can help to develop more reliable solutions of wireless optical technology.

Comparison of standard telecom diode laser and mid-infrared QCL beams loss in dense fog conditions proved that QCL could be considered as an effective source of signal for wireless optical links.