Wireless network research company Signals Research Group (SRG) published some of the results from its recent tests of T-Mobile’s new satellite messaging service, running through SpaceX’s Starlink satellites.
The firm highlighted a few noteworthy takeaways:
- The connections are 4G LTE, not 5G.
- They run over a tiny slice of T-Mobile’s spectrum holdings: 5MHz of spectrum in Band 25 (1952.5MHz).
- There’s very little delay between the messages being sent and received. According to SRG, "in many cases, the delivery time was largely comparable to a terrestrial text messaging service. In a few instances, the delivery time wouldn’t suffice if the text message read, ‘Help, a Grizzly bear is chasing me,’ but if that is what the message reads, then the sender’s days on earth are already numbered."
- There doesn’t appear to be much interference between SpaceX’s satellites and T-Mobile’s terrestrial cell towers – an early concern in the sector. "I decided to really stress test the service from inside my house, a mere 1.5 miles from the nearest T-Mobile cell site, which offers great Band n25 5G coverage (e.g., the same exact radio channel used by Starlink)," SRG’s Michael Thelander wrote on social media. "Despite the 40-45 dB difference in signal strength between Starlink (LTE) and 5G in the same 5MHz channel at my house, the messages always got delivered / received, even when placing the phone on a basement stairway banister located in the middle of my house."
The findings are important because SRG conducts its tests using professional wireless network testing equipment from the likes of Rohde & Schwarz and Accuver. Indeed, the firm has a lengthy history of running detailed networking tests on emerging wireless technologies, from open RAN to dynamic spectrum sharing.
"To summarize, the service worked with RCS messaging and basic SMS, even while testing under conditions where it was not designed to work and where a normal person would never want/need to use it," according to SRG’s report. "The time intervals we measured generally exceeded what is typical with terrestrial texting (we did these tests as well for comparison purposes), but the times were fast enough that it wouldn’t have an impact on a typical user experience. Reliability is also extremely important, and, in that regard, the reliability was consistent with terrestrial text messaging. Implementing voice and low bandwidth data services that require a continuous connection will likely require enhancements, most likely involving 5G NTN (already standardized and being further enhanced in future 3GPP releases), but the writing on the wall is promising."
T-Mobile, for its part, recently began offering a test of its satellite messaging services to T-Mobile, AT&T and Verizon customers, with an eye on a commercial launch in July.
A fast-moving industry
News on the phone-to-satellite front isn’t slowing down. Just today Verizon said it successfully completed its first video call over AST SpaceMobile’s satellites, and AT&T said it successfully conducted another such call. Eutelsat said its OneWeb network tested 5G connections on its low-Earth orbit (LEO) satellites with Airbus and MediaTek.
Meanwhile, Mavenir said it successfully completed a voice over NB-IoT (Narrowband Internet of Things) call in NTN (Non-Terrestrial Networks) mode with Canada’s Terrestar Solutions. The two companies are working to launch direct-to-device (D2D) services across Canada in the coming months.
The reason there’s so much noise on the D2D front is because the service promises to potentially increase the revenues wireless network operators can squeeze out of their customers. For example, T-Mobile could charge as much as $20 per month for its satellite messaging service with SpaceX.
That tantalizing prospect is pushing companies like AST SpaceMobile, Globalstar and other D2D players to launch dozens of new satellites in support of their various offerings.
However, SpaceX remains far in the lead in terms of the number of D2D-capable satellites it operates. The company today counts 477 such satellites in orbit that support T-Mobile’s satellite messaging service.
SpaceX of course has an advantage in that arena given its core business of building and launching rockets.