BLOS Communications

Beyond Line of Sight Comms

BLOS communications are essential for a wide range of military activities and operations. These include connecting in-theater forces with distant command centers, location and data sharing, C2 (command and control) of long-range UAVs (unmanned aerial vehicles), precision firing, and co-operation between airborne assets and ground troops.

BLOS (beyond line of sight) communications refers to a particular subset of NLOS (non-line of sight communications, where the obstacles that stand in the way of long-range electromagnetic wave transmission and reception are the curvature of the Earth or significant amounts of terrain such as mountains.

A number of different methods may be used to achieve effective BLOS communications:

BLOS Radio

HF (high-frequency) radio links may utilize troposcatter systems, which rely on the scattering effect of transmitted signals in the lowest part of the atmosphere known as the troposphere. Only a small amount of the original energy will be scattered in the direction of the receiver, so these systems require directional antennas and precise pointing systems to minimize signal loss. This makes them less suited for communications with highly mobile or unstable platforms such as aircraft and naval vessels.

Satellite Communications

SATCOM (satellite communications) may be used, either as a direct datalink or a way to extend the range of tactical UHF and VHF radios. Radio-over-IP (RoIP) technology may be used to convert the voice signals and data normally sent over radio waves into a form that can be transmitted via SATCOM. While data rates and latency may be better with SATCOM-based BLOS solutions, they do require satellite network availability and resources. SATCOM signals may also be more vulnerable to interception and jamming than modern troposcatter systems.

Repeater Stations

Another method of achieving BLOS communications involves the use of repeater stations to extend the overall distance. These repeaters may be fixed ground sites, and HALE (high altitude long endurance) UAVs and HAPS (high-altitude pseudo satellite) platforms may also be used.