VoIP services over satellite constellations

Satellite constellation - TeleDynamics blog

Anyone interested in the latest news about telecommunications has been hearing about Starlink, a satellite internet constellation currently being deployed into low earth orbit (LEO) by SpaceX. This network aims to deliver high-speed internet connectivity to any location on the planet — a particularly beneficial development for those in rural or remote areas.

In this article, we examine this space-age internet service provider and evaluate its viability for services such as VoIP, video and other time-sensitive communications applications.

Traditional communications satellites

Communications satellites have typically been deployed in what is known as a geostationary orbit or geosynchronous equatorial orbit (GEO) at about 22,200 miles from the surface of Earth. The advantage of such an orbit is that the satellite remains stationary in the sky as viewed from any location on the surface of Earth.

This is extremely convenient but does introduce some drawbacks. Among other problems, voice and other real-time services are typically at a disadvantage simply due to the inherent delay introduced by the distance a signal must travel to and from the satellite itself.

Alternatively, we can place a communications satellite into low earth orbit (LEO), typically less than 1,200 miles above Earth’s surface. This resolves the delay issue and other complications associated with GEO but introduces additional challenges.

In particular, a satellite in LEO is not geosynchronous — it will orbit Earth typically 12 to 16 times a day, traveling at around 17,000 mph. From any particular location on Earth, that satellite would only be visible for a few minutes as it streaks across the sky, which makes continuous coverage of any area tough to achieve.

Satellite constellations have been developed to resolve the difficulties introduced by LEO. Only recently has the technology become available, the cost sufficiently low, and companies become tenacious enough to make such an endeavor viable.

What is a satellite constellation?

A satellite constellation is a group of artificial satellites operating as a unified system. They are deployed in such a way so that, at any time, at least one satellite is visible in the sky over any specific location on Earth, ensuring continuous coverage. The following animation highlights this.

satellite constellation orbiting around Earth

Paulsava, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

This constellation consists of 20 satellites, and there are always between 5 and 10 satellites visible over a particular location, as indicated by the red dots and lines linked to an example location. Consequently, from any spot on the planet, you will have visibility of at least one satellite at any time without the need for any earthbound telecom infrastructure beyond a satellite transceiver.

Satellite constellations are typically deployed in orbital shells, consisting of satellites that orbit at the same fixed altitude. This creates an imaginary sphere or shell of a specific radius.

All satellites that belong to an orbital shell will always be found on the surface of that imaginary sphere. The diagram above depicts such an orbital shell. Some constellations can consist of several orbital shells at varying altitudes, resulting in even more satellites visible from the ground.

How satellite constellations work

Satellites are responsible for receiving a signal from the ground (uplink) and relaying it back to the ground (downlink) at a different location to be further routed to its intended destination. They are part of a more extensive telecom infrastructure that connects end devices to services.

Unlike traditional communications satellites that use GEO, LEO satellite constellations involve satellite-to-satellite signaling, creating a meshed communications configuration. Any uplink from a particular point on the planet may go through several satellite hops before reaching the downlink to a base station on Earth.

All this messaging occurs in a system where dozens or even hundreds of satellites continually move, dynamically handing off communications links from one to another. That means a satellite must constantly be aware of its location relative to Earth's surface and its continually moving neighbors.

Current status of Starlink

Various companies worldwide operate several communications satellite constellations. None are as ambitious and wide-ranging as Starlink. At the time of writing, Starlink had five orbital shells ranging in altitude from 547 to 577 km (340 to 359 miles), with a total of 3,717 satellites deployed, of which 3,122 are operational.

Nearly 12,000 satellites are scheduled to be deployed, possibly increasing to over 42,000 before the decade's end. This is significant given that all other communications satellite constellations currently have under 1,000 active satellites.

As of December 2022, Starlink had over one million active subscribers and has received regulatory approval in more than 40 countries. For up-to-date statistics about Starlink's current status, see Jonathan's Space Pages.

Starlink's performance

According to Starlink's documentation, the network's performance consists of downlink speeds ranging from 40 to 220 Mbps and uplink speeds ranging from 2 to 10 Mbps. One can expect latency within the range of 25 to 50 ms for stationary installations (mobile hardware has higher latency).

These performance specifications are exceptional, considering that this is a satellite communications network and that signaling may pass through multiple satellites before returning to the ground.

However, we must remember that these values are almost certainly the latency that Starlink's infrastructure contributes to the total delay you may experience, which will be larger. We should add to the value of 25 to 50 ms the typical latency that other networks along the full communications path may add.

These networks may include the internet and the network of the service you are communicating with. Furthermore, as stated in the Starlink documentation: "Users may experience higher latencies in regions that are far from Starlink ground stations or during periods of high load on their user terminal."

VoIP services over satellite internet constellations

Now that we've covered the technologies and infrastructure used to support and deliver internet connectivity over a satellite constellation such as Starlink, let's look at the implications of using VoIP services over such an ISP. Note that we are explicitly examining OTT VoIP services over satellite internet constellations.

Today, a satellite constellation cannot guarantee the quality of service in the same way a traditional landline ISP can. The primary reason is that it has yet to deploy its full infrastructure.

Performance is a function of the number of satellites, the number of subscribers, and the traffic load at any particular location at any time. To keep their subscribers as evenly distributed as possible, Starlink limits the number of subscribers per unit area on the Earth for regions of high population density.

Any subscribers who sign on above this limit within an area will essentially be offered "best effort" service, which means that their traffic is not guaranteed to conform to specific benchmarks.

On the other hand, the level of service of Starlink, although not equal to landline ISPs, is quite respectable. If VoIP communications are not mission-critical for your business, then the service is still a viable supplier of internet connectivity for use with VoIP services.

So, what's the verdict? Well, it depends. If Starlink's advantages outweigh the possible occasional degradation in VoIP services for your business, then the service is sufficient for your needs. If your business depends almost exclusively on high-quality, highly available VoIP services, consider an alternative option, if available.

One word of warning, however. As the network develops, network capabilities have been observed to waver because the factors affecting network performance have yet to stabilize. It may take several years for the whole infrastructure to be mature enough to offer the same level of quality and availability as landline ISPs.

Future developments

To connect to the Starlink constellation, you must have a Starlink user terminal, which is essentially a specialized transceiver with an antenna. In cooperation with T-Mobile, Starlink will begin to offer cellular satellite service sometime in 2023, allowing T-Mobile customers to connect directly to Starlink's satellites from their existing mobile devices.

Initially, this will be a backup service if terrestrial cellular coverage is impossible. Voice services, texting, and low-bitrate data connectivity (2-4 Mbps) will be available directly to mobile user devices without the need for specialized terminal equipment.

This and similar developments, along with the planned increase in the number of satellites, will improve performance, boost the number of services the infrastructure can support and enable connectivity that can meet even the greatest network needs.

Conclusion

The space age is upon us. Satellite constellations that deliver broadband connectivity to any location on the face of the earth are a reality. Although unsuitable for those requiring extreme availability and robustness for time-sensitive applications such as VoIP and video communications, they are sufficient for many of today's personal and business needs. They will only continue to improve in the years to come.