Sharing between satellite orbit systems

Viasat CEO, Mark Dankberg, shares his insights on satellite orbits with ITU News Magazine

Mark Dankberg Headshot Landscape

The following article was featured in ITU News Magazine with permission to reshare.

By Mark Dankberg, Chairman of the Board and CEO, Viasat

Countries invest in satellites for many reasons, including national security, sovereign control, and to connect their people. For most of them, satellite communications will be their most significant participation in the space economy.

In the coming months, however, a few large operators for non‑geostationary‑ satellite orbit (non‑GSO) systems seek to change long‑standing spectrum sharing rules in a way that would impact tens of billions of dollars of satellite investments, with consequences for all countries. The largest non‑GSO operators seek to reduce interference protection for geostationary‑satellite orbit (GSO) system operators, claiming non‑GSOs are superior and merit regulatory precedence. But GSOs and non‑GSOs are both just orbits, both using the same payload technology.

To draw a parallel, terrestrial wireless coverage depends on tower locations. For satellites, orbits are like tower locations.

GSOs provide a large and constant field of view and are more economical for regional operators. A constant field of view makes GSO much more financially attractive for virtually all applications, including high‑speed data, and much better for broadcasting.

Because non‑GSOs are closer to the Earth and their field of view is smaller, the coverage provided by each satellite is less. It may require dozens, hundreds, or thousands of satellites to provide the same service to a region that a single GSO provides. Non‑GSO operators must therefore be global because the limitations of their orbits demand it.

The technologies currently used

An orbit only defines the location of satellite towers. Payload technology defines capability.

While the same technology can be used in both GSOs and non‑GSOs, GSOs have demonstrated more advancements in technologies such as ground‑ based beam forming, large deployable antennas, efficient high‑power buses, and thermal management.

GSO and non‑GSO systems have both used fixed‑feed spot beams, electronically steered spot beams, software defined on‑board processing and routing, adaptive modulation and coding, multi‑band user and feeder link architectures, and satellite‑to‑satellite links. Satellites in both orbits can use ground terminals with the latest phased arrays. But only GSOs can use simple, very inexpensive, fixed terminals.

Hundreds of millions of homes worldwide depend on free‑to‑air TV provided by GSOs. This happens through receive‑only terminals on sides of buildings in densely‑populated neighbourhoods, without the 360‑degree view of the sky required by most non‑GSOs.

New GSO systems will offer similarly inexpensive “OTT streaming terminals” that can bring the latest Internet entertainment and information services to those homes on similar terms.

Service speeds

The shorter signal propagation paths used by non‑GSOs — because they are closer to the Earth — does not mean higher transmission speeds.

Service speeds depend on power‑flux density (PFD) on the ground, terminal size and gain (G/T), and the interference received from other users of the same spectrum at different look angles. Thermal link budgets yield the same downlink data rates for GSOs and non‑GSOs with equivalent terminal size and PFD

Spatial seperation
The first large non‑GSO operators are unfortunately seeking to exploit the lack of competition and deploy numerous small terminals. These increase interference potential, require very large spatial separation, and thus pre‑ empt future non‑GSO competition.

GSO orbital slots define the spatial separation among operators and enable the type of spectrum sharing that allows access to space by any nation on Earth.

Both non‑GSO and GSO operators need spatial separation, along with the associated spectrum re‑use and interference protection. Spread spectrum technology and innovative coordination agreements can enable GSO systems to use terminals just as small — while preserving equitable access.

Rules for sharing spectrum

Rules for sharing spectrum in non‑geostationary orbits are nascent, and the largest non‑GSO systems could exploit that void by deploying many very small terminals. This would pre‑empt prospective new non‑GSO operators using the same spectrum, as well as taking spectrum and look‑angles away from GSO operators.

Nations need to understand the implications of these dynamics and act now, at the national level, to ensure access to space.

Spectrum sharing rules, including spatial interference protection and PFD, amount to “rules of the road” that allow all nations to participate in space. When it comes to sharing spectrum with GSOs, the principles of interference protection are expressed in terms such as equivalent power‑flux density (EPFD) and inline events.

These rules have enabled decades of non‑GSO and GSO innovations. Reducing GSO interference protection would not only undermine innovation for GSOs, it would also limit, or even completely deny, spatial protection and look angles to future non‑GSOs.

Safeguarding the New Space Age for all

Viasat, a global communications company with a long‑term vision for global satellite development, urges all ITU Member States to get the facts on how the changes advocated by the largest non‑GSO systems would change the rules of the road.

Changes that purport to improve non‑GSO services would adversely affect GSO satellites and constrain the ability of all nations to participate in the high‑speed, bandwidth‑rich, multi‑orbit New Space Age.

The proposed changes would benefit only the largest and richest few — while constraining the rest of us not only in non‑GSO, but in what should be an exciting GSO future as well.