Low-Earth-Orbit Satellite Broadband

Low-Earth-orbit satellite broadband delivers internet access through satellites orbiting relatively close to Earth. A satellite constellation is a coordinated group of satellites that provides coverage as individual satellites move across the sky; their shorter distance from users reduces propagation delay, the time signals take to travel.

Why a low orbit reduces latency

Low Earth orbit extends to approximately 2,000 km above Earth's surface, whereas a geostationary satellite orbits at approximately 35,786 km. Radio signals travel at roughly the speed of light, so the much shorter journey to and from a LEO satellite reduces transmission delay.

• Latency is the delay in communication, not the amount of data a connection can carry per second.
• Lower propagation delay makes interactive applications such as video calls and online services more responsive than they would be over a comparable geostationary satellite connection.
• Total latency also includes processing, routing and congestion delays; low orbital altitude alone does not guarantee a fast connection.

How data travels through the network

A user's satellite terminal exchanges radio signals with a satellite overhead. The satellite connects this traffic to terrestrial networks, either through a ground gateway or, where available, through other satellites.

• A ground gateway links the satellite network to terrestrial internet infrastructure, which carries traffic to its destination.
• Some constellations use inter-satellite links, including laser links, to relay traffic between satellites before sending it to a suitable gateway.
• The return traffic follows the same basic chain in reverse, although the network may select a different route.

How constellations maintain continuous coverage

Unlike a geostationary satellite, a LEO satellite does not remain above the same location. Multiple satellites distributed across orbital planes therefore work together to maintain continuous coverage within the network's service area.

• As one satellite moves out of view, the network performs a handover, transferring the user's connection to another available satellite.
• Tracking antennas, including electronically steered antennas, maintain links as satellites move across the sky.
• Overlapping coverage and coordinated routing help preserve connectivity during satellite changes.

What determines actual broadband performance

LEO systems can serve places where laying terrestrial cables is difficult, but performance depends on more than orbital height.

• Bandwidth is shared among users, so available capacity and congestion affect speeds.
• Terminals need a sufficiently clear view of the sky; obstructions and weather-related signal attenuation can disrupt links.
• Gateway availability, routing choices and terrestrial backhaul influence end-to-end performance.