Star Wars: SpaceX vs AST SpaceMobile

A celestial battle between the two companies and their telco partners, who are all going pew-pew over out-of-band emissions.

Oct 20, 2024

The race to put cell phone towers in space is on, and two companies are going head-to-head to dominate low-earth orbit.

SpaceX and AST SpaceMobile plan to provide Supplemental Coverage from Space (SCS) to eliminate dead spots in the cellular terrestrial networks of telecom providers and provide internet connectivity where none currently exists. But the battle has come down to a key technical spec: Out of band emissions. In this post, we will look at what this metric means and what everyone is fighting over.

Here’s a top-down view of this post:

Direct-to-Cellular Technology
Key Companies in the Space
Power Flux Density and Out-of-Band Emissions
SpaceX’s proposed specification
Opposition from AST SpaceMobile partners
Shots fired
Hurricane Helene and Milton
Where are we now?

Read time: 14 mins

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Direct-to-Cellular Technology

One could argue that most of us take internet connectivity for granted. The infrastructure needed for wireless communications includes cellular towers, backhaul networks, fiber optic cables over land and sea, all strategically placed to provide the lowest latency and highest signal-to-noise ratio to a radio device. It is sometimes easy to forget the engineering marvel we slip into our pockets, and the communication networks all around us.

In the course of evolution of telecommunications, it has only made sense to develop this immense infrastructure in densely populated areas — the urban centers of activity. Building infrastructure takes time and money, and the more the users, the more sense it makes from an economic standpoint. While the internet has become a centerpiece of human society, bringing people together, tearing them apart, toppling governments and creating trillion dollar companies, nearly 2.5 billion people still lack internet access.

One way to provide access to everyone in the world is to put a cell phone tower in orbit, in what is called Direct-to-Cell (sometimes, Direct-to-Device or D2D) technology. The idea is to beam internet connectivity to anyone in the world without the need for local internet infrastructure being built out, or being subject to the socio-political gyrations of the land. The idea is not to replace terrestrial networks, but merely augment it from space by providing connectivity where none exists. This is called Supplementary Coverage from Space, or SCS. The potential market for direct satellite-to-phone service is enormous, and is worth billions of dollars in the future if data speeds from satellite can even match a reasonable level of wireline internet service.

In February 2024, the Federal Communications Commission (FCC), in a bold move, proposed a regulatory framework that allows satellite operators and terrestrial service providers to collaborate and enable extended network coverage from space. Since the connection is directly from satellite to cellphone, SCS requires that satellites use the spectrum usually allocated for terrestrial service. The key requirement for space and terrestrial networks to coexist is that they should not interfere with each other.

Frequency bands allocated for SCS: Source: FCC (https://docs.fcc.gov/public/attachments/DOC-400678A1.pdf, Appendix C)

Key Players in the Space

Starlink + T-Mobile: SpaceX launched the first six satellites with direct-to-cell capability earlier this year in January 2024 on a Falcon 9 rocket. Since then, SpaceX has had 17 launches each with 13 satellites with direct-to-cell capability, with over 220 such satellites in orbit presently. VP of Starlink Michael Nicolls has hinted that over 300 satellites would be required in orbit before cellular services can be launched. In August 2022, T-mobile announced a partnership with Starlink to expand its network coverage via Starlink satellites. They would initially provide text-only services and then expand to voice and data as more satellites are placed in orbit. Since then they have announced partnerships with Rogers in Canada, Optus in Australia, One New Zealand, KDDI in Japan, Salt in
Switzerland, and Entel in Chile & Peru.
Source: Starlink
AST SpaceMobile (ASTS) + AT&T + Verizon + Worldwide Providers: AST SpaceMobile is a Texas-based company founded in 2017 solely to provide broadband connectivity from space. Last month, they launched five of their “Bluebird” satellites on SpaceX rockets with massive 700 sq. ft. antennas that are the largest communication antenna arrays in orbit, with their planned next generation antennas being about three times bigger. At the moment, the company is still testing these satellites in a 15 minute window twice a day. To reach continuous coverage across the United States, dozens more such antennas are needed in orbit.
After collaborating since 2018, AT&T partnered with ASTS in May 2024 to provide space-based broadband directly to cellphones in their network. About two weeks later, Verizon signed a partnership agreement with ASTS to augment their networks with space coverage. Several other providers worldwide such as Vodaphone, Rakuten Mobile and Orange are also working with ASTS to enhance their networks. With backing from telcos and investors alike, ASTS is poised to be a big player in space-communications technology (ASTS is up +300% YTD).
It is important to note that ASTS has already demonstrated the first ever space-based voice call over satellite by placing a call from Midland, TX to Rakuten in Japan using a Samsung Galaxy S22. Vodaphone claims to be the first too, but the call to Japan seems to be a few months earlier. It appears that ASTS satellite technology already allows download rates of about 20 Mbps. We will have to wait and see how well ASTS networks actually perform when deployed for public use.
Source: AST SpaceMobile
There are some other companies in the space involved in direct-to-cellular technology that are worth a mention.
- Lynk Global: Lynk is a Virgina-based company founded in 2017, that launched three cell towers in space so far, and have signed agreements with 25 mobile network operators covering 41 countries, and is currently actively testing satellite to cellphone connections.
- Omnispace: Omnispace is a Washington DC-based company focused on direct-to-cell mobile service, and satellite IoT solutions. Earlier this year, they announced a collaboration with MTN, Africa’s largest mobile network operator to expand cellular coverage for underserved areas.
- Skylo: Skylo’s main focus is to utilize existing spectrum, cellular devices and satellite coverage to enable always-connected IoT devices for businesses conducted in remote locations such as deep-sea oil and gas operations, mining, or supply chain monitoring. By using existing low cost infrastructure, Skylo’s solutions are much cheaper than using traditional non-terrestrial networks. They currently use satellites already in place by Viasat and Ligado. Recently, Verizon has teamed up with Skylo to offer direct-to-cell text messaging.
- Project Kuiper: Amazon’s direct competition to Starlink, but their focus is on providing internet to satellite dish terminals on the ground, and not unmodified smartphones. Kuiper plans to launch 3,236 satellites by mid-2026, but they are far behind SpaceX having launched just two satellites into space so far. Their continued FCC approval hinges on them launching 1,600 satellites by August 2026. Where there are rumors that Amazon will get in on direct-to-cell service, they are not a competitor to Starlink, AST SpaceMobile or others at this time.

Out-of-Band Emissions and PFD

As mentioned earlier, the key to making this technology work is to ensure that the space-based radio emissions do not interfere with the already existing terrestrial networks. To achieve this, the FCC in its 160-page document, specifies the maximum radio emissions allowed from space-based operators as an out-of-band emission (OOBE) specification as follows (emphasis mine):

In consideration of the record, and in line with our goal to create a simple requirement, we adopt an aggregate out-of-band PFD limit of -120 dBW/m2/MHz for the 600MHz, 700MHz, 800MHz, and PCS 1990-1995 MHz bands.

Here PFD stands for Power Flux Density, and it is important to understand what this means.

Imagine an antenna radiating in space with a transmit power of Pt. Now, draw a sphere of radius R around the antenna. Loosely speaking, power flux density or PFD is the radiated power normalized to the surface area of this sphere and is given by

$PFD = \frac{P_t}{4\pi R^2}$

The power is expressed in decibels over Watt (dBW) normalized to a 1 MHz spectrum bandwidth, resulting in the PFD units of dBW/m2/MHz. The FCC also defines the radius of the sphere when the satellite is placed in low-earth orbit as

We also specify that this PFD limit will apply at 1.5 meters above ground level, a height frequently associated with terrestrial device usage that has been used by the Commission when developing interference protection criteria for other wireless services.

In reality, the power flux density also depends on effective isotropic radiated power (EIRP), polarization losses, and antenna gain.

The FCC believes that any emission from space within a terrestrial communication spectrum that is below -120 dBW/m2/MHz is acceptable and will not cause interference or loss of service quality for existing terrestrial networks.

SpaceX Disagrees With OOBE Specification

In a filing with the FCC in September 2024, SpaceX explains that the OOBE limit of -120 dbW/m2/MHz is too strict and will cause reduced data rates that will render direct-to-cellular technology useless for voice and video communications. This is because SpaceX would have to reduce in-band transmit power by half to meet the specified emission limits which adversely affects the data rate of the communication channel (due to the Shannon-Hartley theorem).

The argument is that it is unreasonable to have a “blanket” OOBE spec across all SCS frequency bands which span from 600 MHz to nearly 2000 MHz. Compared to ASTS, which primarily uses 698—960 MHz for its satellite services, Starlink uses the PCS G bands at 1910—1915 MHz and 1990—1995 MHz, which is why they argue that a different, “frequency-specific”, requirement be established to ensure fairness between the operators offering services at different bands.

SpaceX proposes a different specification for Starlink satellites that operate at PCS G band (emphasis mine).

SpaceX states that complying with section 25.202(k)(1), which the Commission adopted earlier this year and which establishes an aggregate OOBE limit of -120 dBW/m2/MHz, would be “overly restrictive” on SpaceX’s currently proposed SCS network, and requests a waiver to permit an aggregate out-of-band emissions in the United States at a PFD of -110.6 dBW/m2/MHz for the PCS G block based on the interference threshold of -6 dB I/N.

They claim that -110.6 dBW/m2/MHz is sufficient to have no interference with existing terrestrial networks at PCS bands, and that this limit has shown to not interfere with T-mobile’s own PCS C bands at 1895—1910 MHz and 1975—1990 MHz. SpaceX provides the following table to show how the new limits would provide excellent satellite service in the US while the old limits would result in degraded area coverage.

AT&T, Verizon and European Telcos Oppose SpaceX

Since the proposed limit by SpaceX allows nearly nine times more emissions than the FCC’s proposed limit, AT&T and Verizon filed statements with the FCC saying that their network throughput in the PCS C bands would be degraded by up to 18% if this waiver is granted to SpaceX.

They argue that SpaceX has made simplistic assumptions on polarization loss that will not hold true in a variety of real world scenarios, and that SpaceX’s proposed limit still fails the -6 dB interference-to-noise ratio requirement established by the International Telecommunications Union (ITU). AT&T and Verizon say that SpaceX has not exactly demonstrated why they cannot meet the proposed FCC limits, although doing so will most often reveal proprietary design information.

Impact of increasing the OOBE PFD limits according to AT&T. Source: FCC filing (https://www.fcc.gov/ecfs/document/1081242986780/1).

On September 30, 2024, a group of seven European telecom companies including Vodafone, Orange, and Telefonica, threatened the FCC with a lawsuit stating that the relaxed OOBE spec would undermine their service quality considering that mobile networks in Europe are designed to work in smaller countries with closer neighbors, compared to the US, and asking that the FCC deny SpaceX’s request for a waiver.

They go on to say that the -120 dBW/m2/MHz limit is actually the “best case” scenario, which can be interpreted as the bare minimum emission levels that can be tolerated. They state their concern that when multiple satellites go online in orbit, their simultaneous operation and increased emissions are a substantial cause for concern.

Shots Fired

A few days later, SpaceX filed a response to the opposition by both American and European telecom companies saying that,

AST is now taking its misinformation campaign overseas by recruiting its European investors and partners to parrot its talking points and harm competition there as well.

SpaceX accuses ASTS of being a “meme-stock” whose investors continue “their scorched-Earth campaign to hamstring competing direct-to-cellular operations.” SpaceX claims that ASTS is already violating the emission spec because a -120 dBW/m2/MHz limit at 1990—1995 MHz (where Starlink operates) actually translates to a -130 dBW/m2/MHz requirement at 698—960 MHz (where ASTS operates) for a -16 dB interference-to-noise ratio.

It is hard to see this argument as anything other than mudslinging because any existing violations of emission limits would only cause the FCC to tighten the limits further, not loosen them as SpaceX is requesting.

This month, AT&T released a report that analyzes the impact of the proposed loosening of OOBE limits in the Tuscon, AZ area and concludes that T-mobile’s analysis is flawed and ignores critical interference scenarios for SCS applications stating,

T-Mobile did not take into account the impact of SCS OOBE interference in those network service areas that experience inter-cell interference values less than -94 dBm/MHz – an omission that assumes away a significant portion of the impact of the proposed alternative OOBE limit.

Hurricanes Helene and Milton

Amidst this dispute, a marketing opportunity (and a genuine chance to help) rains from the sky in the form of hurricanes Helene and Milton which pummel the east coast of the US destroying communication lines. SpaceX is quick to provide direct-to-cell coverage for text messages by having the FCC provide temporary authority for coverage. Starlink’s text message only service via the T-mobile network could be construed as indirect evidence that their degraded interference issues have stopped them from providing at least voice coverage in disaster times.

While SpaceX provided 30 days of free access to the Starlink direct-to-cell service, users quickly found out that they need to pay $400 for the hardware. Elon Musk then wrote on X that terminals would work without the need for payment, but people still had to pay to get access. It could be that the infrastructure to provide selective access did not roll out effectively in time for victims of Helene, and one could be cautious about chalking it out to deception on Musk’s part. It is more likely that he was trying to actually help in this situation. Regardless, free subscribers in disaster zones were moved automatically to a $120/month plan after the 30 day grace period.

Sadly for ASTS, their five BlueBird satellites were still not in orbit for them to provide any sort of meaningful coverage during disaster times, resulting in a missed opportunity to provide even temporary satellite service to future paying customers.

Where are we now?

The request to change the OOBE spec for PCS G band provides the optics of moving the goalpost because SpaceX’s engineering team could not meet the required specifications. We will have to wait and see how the FCC handles SpaceX’s request for a waiver. It is instructive to know that the FCC has a history of denying SpaceX requests however — for example, when Starlink wanted to use several spectrum bands for mobile service, or when the FCC denied $885 million in funding to Starlink citing that they were a nascent technology.

Several online discussions on this topic opine that SpaceX was late to the direct-to-cell game, and they are using their existing satellite designs initially meant for ground terminal-based satellite service. While it is possible that a complete hardware redesign might alleviate the emissions issue for SpaceX, doing so takes time and resources.

It is quite possible that full-sized Starlink v2 or even v3 satellites will provide improved radio performance in orbit compared to the current generation, but that depends on the Starship rocket being ready in time to launch the increased payload of new generation satellites. Currently, SpaceX has been launching “V2 Mini” satellites on the Falcon 9 rocket due to delays in the Starship program.

In contrast, ASTS has been seemingly been building up this technology from the ground up for several years. Their focus has been solely on providing direct cellular service from space, and is a popular contender considering how many operators in both Europe and America have signed contracts with them.

It is hard to currently predict who will win this race to space. But maybe there doesn’t have to be one. More likely, there is room for enough players in the direct-to-cell market — a piece of the pie for everyone — when the total addressable market is the entire planet. It will be interesting to watch SpaceX/Starlink, ASTS and even other players like Lynk Global, Omnispace, Viasat, Ligado, and Skylo, make direct-to-cell technology a reality.

Thanks to friend of the newsletter Aram Akhavan for putting this story on my radar. Connect with me on X, LinkedIn or reply to this email if you have cool stuff to share.

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