Global mobile satellite communication: SpaceX fails and calls for exemption
- by heise online
- Oct 24, 2024
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Size does matter
, the company that operates the Starlink satellite service, is fighting for a special permit from the US regulatory authority, the Federal Communications Commission (FCC), to offer mobile services for smartphones from space via Starlink satellites. Representatives of the company are also playing hardball in an attempt to negotiate better radio conditions for themselves so that they can offer gigabit internet. The dispute begins in the USA and at first glance only concerns SpaceX, the FCC and local network operators. However, many of the FCC's decisions in the past have been groundbreaking for other regulatory authorities. It is therefore likely to have consequences for all terrestrial mobile network operators on the planet, and therefore also for all mobile phone users.
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It has long been technically possible to supply cell phones via satellite; depending on the design and approval of the FCC, low-flying satellites (Low-Earth Orbit, LEO) use a radio band normally used on Earth, so that standard LTE and 5G smartphones can be connected. The satellites act as intermediaries between smartphones and the mobile network operators' ground stations.
Although SpaceX has been offering global internet via its Starlink satellites for several years, this has so far required stationary terminals with antennas the size of a tablet or towel. Now SpaceX wants to use a new generation of satellites to supply ordinary cell phones as soon as possible. To this end, the company is cooperating with T-Mobile, the US subsidiary of Deutsche Telekom. SpaceX has already launched over 200 satellites specially designed for mobile phone operation into orbit. According to Starlink employee Michael Nicolls, over 320 such satellites will be required for public operation in the final stage.
However, while SpaceX's Falcon rockets have been launching 13 new Starlink V2 mini satellites into orbit with each flight for several months, the development of the radio coverage is apparently not going as planned. In a document submitted to the FCC in September 2016, SpaceX promised "gigabit speeds for every user in the final rollout". However, the current Starlink technology apparently does not deliver this. This is clear from an application submitted by SpaceX to the FCC. In it, SpaceX demands significantly better framework conditions exclusively for itself than the FCC provides for such services.
Reckoning without the regulator
In retrospect, SpaceX's 2016 announcement seems premature, as the FCC only set the framework conditions for supply from space in April of this year (PDF, 160 pages). These also include decisive limits for coexistence with terrestrial mobile networks. Accordingly, satellite spurious emissions in the mobile radio bands at 600, 700, 800 and 1990 MHz must not exceed the limit of -120 dBW/m2/MHz(out-of-band emissions, OOBE). Among themselves, mobile network operators call this globally accepted limit "the -120 limit".
Depending on the altitude of the earth's orbit (GEO, MEO, LEO), satellites cover different areas. However, the services are largely intended to cover the whole world. The high-altitude platform systems (HAPS), on the other hand, only cover cities or small regions and fly twice as high as commercial aircraft.
It is this limit that enables a narrow allocation and therefore efficient use of the radio spectrum. Although regulatory authorities allocate a frequency band of a certain width to each service, it is technically impossible to make the signal disappear completely at the exact channel or band limit. Depending on the quality of the transmitter and the filters, it flattens out more or less steeply at the edges, so that interfering spurious transmissions always leak into neighboring areas. To ensure that services still function there, regulatory authorities set the maximum level of spurious emissions and transmission system operators must comply with the limit value.
SpaceX now claims that the limit is too strict and leads to reduced data rates, making satellite technology unusable for voice and video communication. In order to meet the FCC's requirements, SpaceX would have to halve the Starlink transmission power, which would greatly reduce the data rate. Experts therefore expect Starlink mobile satellites to deliver 100 Mbit/s at best.
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SpaceX goes on to say that "blanket limits for all bands from 600 to almost 2000 MHz are inappropriate". Two 5 megahertz narrow bands from 1910 to 1915 MHz and from 1990 to 1995 MHz are reserved for Starlink, and "frequency-specific limits make sense" precisely for these bands. According to the company's own calculations, -110.6 dBW/m2/MHz is sufficient there, i.e. around nine times the FCC limit. This would allow Starlink to offer gigabit speed and still avoid interference with neighboring bands. As an example, the company cites the 1895 to 1910 MHz and 1975 to 1990 MHz bands used by its cooperation partner T-Mobile; these would not be affected by Starlink.
Salt in the wound
The US network operators AT&T and Verizon strongly disagree with these statements. According to their own calculations, the limit demanded by SpaceX would reduce throughput in their networks by 18 percent. An increase in the -120 limit in the 1900 MHz band is out of the question. They also rubbed salt in SpaceX's wound: the company had not clearly explained why Starlink satellites could not comply with the FCC's limit without halving the transmission level.
SpaceX's idea has long since alarmed European network operators. A group including Telefónica and Vodafone is now threatening the FCC with a lawsuit if it gives in to SpaceX: "Any relaxation of the limits that affects the management of allocated spectrum would be grounds for claims for damages." The current -120 limit is the "minimum level of protection that mobile network operators need in order to continue to provide the promised quality of terrestrial services." In addition, even higher interference levels would threaten to affect terrestrial mobile network operators and their customers if further satellite systems of this type were to come into operation or if an operator were to launch additional satellites into orbit.
It is noteworthy that some of these network operators are themselves cooperating with AST SpaceMobile, a SpaceX competitor. AST itself is working on a service for cell phones and has so far launched five satellites into orbit and won several mobile network operators worldwide as customers.
Exchange of blows across borders
In early October, SpaceX continued to threaten the FCC with another notice: "AST's foreign investors and partners will stop at nothing to slow progress. AST and its investors continue their scorched earth campaign to obstruct competing direct-to-home links, even when their efforts mean Americans can't get reliable connectivity in emergencies and American satellite systems are at a competitive disadvantage in international markets."
The rebuttal is partly related to the damage caused by the recent hurricanes in the US. SpaceX wanted to offer Starlink-switched voice services for smartphones as a replacement until the destroyed mobile infrastructure was repaired. However, the FCC stuck to the -120 limit. As a result, Starlink only offered a messaging service.
The further tone of the SpaceX document to the FCC suggests a testy mood. David Goldman, Vice President of SpaceX writes, among other things: "Apparently not content with just harming competition in America, AST is taking its disinformation campaign abroad by recruiting European investors and partners to parrot its arguments and harm competition there as well."
Size does matter
Such statements shift the focus away from the technical problems that Starlink obviously has with compliance. Indirectly, you can get a rough picture: With antennas, it's the surface area that counts, the bigger the antenna gain. This gives the receiver a better signal, which means a higher data rate. When transmitting, the output power and thus the spurious emissions can be reduced for the same speed.
SpaceX has given the Starlink satellites intended for mobile communications antennas with a surface area of around 25 square meters. The first-generation AST satellites already surpass this: their first test satellite, BlueWalker 3, communicates via a 64 square meter antenna array. This makes it the largest LEO satellite. The housing behind the array antenna contains a modified mobile radio base. This covers an area of around 777,000 square kilometers using the giant antenna.
AST SpaceMobile demonstrated the first mobile phone call with BlueWalker 3 in internal test runs as early as 2023. AST recently followed up BlueWalker 3 with five new BlueBirds with improved technology and allegedly three times the antenna size. The entire constellation is expected to consist of 243 satellites at an altitude of 725 to 740 km. AST submitted an application for operation to the FCC in April 2020. The FCC has not yet made a decision, but has approved all the steps taken so far along the way. It remains to be seen whether the FCC will give in to SpaceX's request. The process has been dragging on for several months now and SpaceX has received several objections from mobile network operators.
Other companies around the world are also working on satellite systems that will cover the planet with mobile internet from orbit. These include Globalsat and Globalstar with Apple as the flywheel, as well as Iridium. Not all of them are designed for voice and data services. Apple and Globalstar have so far only planned text messaging for scenarios in which no terrestrial mobile radio is available. Of course, they require a modern iPhone, which has special technology on board for this mode of operation.
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