Optical Communication is Viable
While optimum solutions are not currently available to fully resolve challenges with the scaled use of optical communication (OC) technology in military communication, key barriers are mitigable through appropriate measures at the network design and operations levels. Ground-based OC terminals could be designed in ways to limit potential atmospheric disruption by being positioned at higher altitudes or where more favorable climatic conditions exist. Fade mitigation techniques and adaptive optics on the other hand aim to resolve the disruptive impact of atmospheric factors through stabilizing sub-optimum connections. Finally, the application of efficient modulation formats for OC within a mega constellation can make data exchange possible at ranges, speeds and scales not possible with legacy radiofrequency (RF) technology while ensuring reliability of services.
Wireless Radiofrequency Communication vs Optical Communication
As radio waves diffuse at vast distances, communication using legacy RF technology must contend with transmission delays and resultant reliability concerns that can jeopardize decision-making for commanders and warfighters at the speed of relevance. Transporting high volumes of data using RF requires compression whereas others limitations such as antenna size, power requirements and frequency bands restrict the application of RF communication in smaller platforms such as nano-satellites and miniature drones. As the Air Force expands space-based intelligence, surveillance, tracking and reconnaissance (ISTAR) and command, control and battle management (C2BM), a more reliable means of sharing data remotely in real-time than what RF technology can provide is necessary.
Future reliance on space-based data transmission, high-definition imagery and video streaming services for the Air Force requires an improved communication capability for high throughput space-to-space and space-to-ground links. OC technology, which operates at a higher frequency of the electromagnetic spectrum than RF, provides a revolutionary opportunity to extend communication ranges to vast distances while ensuring low latency for data porting in space-to-space and space-to-ground feeds. By providing higher bandwidth and network availability, including for warfighting platforms operating remotely, OC will be vital in enabling more effective military operations as well as deep space missions more broadly.
OC modules, which require less volume, weight, and power than RF technologies currently used for wireless communication also allow for further miniaturization and will contribute to making satellites smaller as well as faster and less costly to deploy. As the Air Force expands the deployment of new space-based capabilities, OC will be key therefore in efforts to minimize cost per effect at a service lifecycle level. Despite its comparative advantages however OC technology is not a straightforward swap-out alternative to traditional RF communications technology. As OC technology advances, the Air Force must address technical obstacles to the effective adoption and integration of OC into existing and planned future capability, beginning with the challenge of accurately pointing light beams to moving targets at distances of 750-1200 kilometers.
Making Optical Communication Technology Work
Space-to-ground broadcasting with OC is challenging owing to atmospheric aberrations distributed along path of light beams, which cause turbulence and trigger beam spreading and wander. Signal capture by receiver terminals can be impacted severely as a result of beam wander caused by, for example, cloud deflection and other weather patterns. It is vital to achieve the precision necessary to broadcast from long distances in sub-optimal conditions where even fractional deviations of a degree can result in light beams missing target receiver terminals. Adaptive optics and more advanced fade mitigation techniques under development such as speckle optimization aim to resolve high-fidelity wave scenarios where speckle and beam spreading effects occur. Control systems using advanced algorithms on the other hand will make possible interaction between transmitter and receiver modules to stabilize connections through physical maneuvering.
It is however at the network design level that the comprehensive solution lies to making OC work better. Stretching across low earth orbit (LEO) and geostationary earth orbit (GEO), a mega constellation with built-in redundancy will provide coverage of any location on earth at any given time, or via relay links that can, and create multiple options for data routing. Relay terminals in GEO permanently positioned above ground-based receiver terminals make possible space-to-space links beyond the line-of-sight would receive and aggregate data packets from multiple satellites in LEO before distributing data to earth in a single space-to-ground downlink to one or more receiver terminals through optical connections or potentially broadcasted with 5G. Effectively harnessing the notion of a mesh network, which provides the topology to connect nodes directly, dynamically and in a non-hierarchical manner, can therefore provide the space and ground infrastructure design to best exploit OC for military communication.
