Unmanned Aerial Vehicle-based Spatial Mode Diversity Free-Space Optical System for Reducing Link Failure During Flood Recovery Communications

Communications is an important lifeline during natural disasters such as floods. In the event where many conventional base stations spanning several cities are damaged, such as during the massive flood in December 2021, a complementary, high-bandwidth wireless access technology is required for recovery communications, to expedite communications to the flood-stricken area. Free space optics (FSO) is an attractive solution for this, whilst ensuring minimal disruption in unaffected areas. Free space optics provides high data bandwidth and rapid deployment, without spectrum licensing costs.

Several UAV-based FSO strategies have previously been developed for recovery communications between base stations for recovery communications, focusing on downlink scheduling, and placement of FSO transceivers, divergence angle or hybrid RF/FSO links. An unveiled challenge to UAV-based FSO systems is to maintain a high SNR between the base station and UAV-based FSO relay. This is largely unattainable, due to minute but rapid UAV propeller and body movements, which result in fluctuations in the beam alignment and water scattering from flood waters. Consequently, this leads to frequent link failures. To address this issue, spatial mode diversity is proposed for improving the rate of link failure from UAV movements.