NTN Mobile Frequency Feud: IMT and NTN Frequency Factions Lock Horns, but Who Will Win?

The World Radio Congress 2023 (WRC-23) has come to a close with many wins for the satellite industry, yet the contentious issue of satellites using International Mobile Telecommunications (IMT) spectrum (i.e., cellular spectrum) for Non-Terrestrial Network (NTN)-mobile services is still unresolved. The primary proponent for using standard cellular smartphones, Starlink, is now poised to introduce low data rate connectivity to smartphones using cellular spectrum (1910 – 1915 Megahertz (MHz) and 1990 – 1995 MHz bands (PCS G Block) in 2024 (text) and 2025 (voice and calling) ahead of startups Lynk and AST Space Mobile. Championing the use of satellite spectrum (n255 (NTN 1.6 Gigahertz (GHz)) and n256 (NTN 2 GHz) is the newly formed Mobile Satellite Services Association (MSSA) that is supported by Mobile Satellite Services (MSS) operators Viasat, TerreStar Solutions, Ligado Networks, Omnispace, and Yahsat.

Factions are now forming as the race to connect devices via satellite heats up. Many questions remain at the forefront, and the use of IMT or satellite frequencies remains at the center.

Using IMT/cellular or satellite Radio Frequencies (RFs) for NTN-mobile services will become increasingly contentious in the lead-up to WRC-27 and WRC-31. As these factions and their respective technologies evolve, the stakes at WRC-27 and WRC-31 will be higher than ever as the legality of using IMT bands by satellite systems comes under scrutiny. Nevertheless, time is on the side of a potentially radical shift for both industries.

Therefore, it is critical to understand the players involved in this market and the factions that are starting to form.

• LEO Long-Term Evolution (LTE): Initiated by Low Earth Orbit (LEO) startups Lynk and AST Space Mobile, and popularized by industry behemoth Starlink, these operators use a modified network using terrestrial LTE spectrum to connect unmodified LTE phones from LEO satellites. In this way, all devices, including those without modems supporting NTN bands or antennas, are supported and therefore “unmodified” by not using additional components. Despite this, wideband signals, except for text messages or voice in a few Kilobits per Second (Kbps), cannot be transmitted directly from a LEO satellite to a standard mobile cellular phone due to the insufficient link budget. AST SpaceMobile has shown with recent tests, however, that a downlink to an unmodified smartphone with a 14 Megabits per Second (Mbps) data rate is possible with a specialized satellite with a 693-square-foot (64 Square Meters (m2)) antenna array. While this may be a “quick and dirty” approach, it has technical limitations and can only be achieved by LEO satellites, limiting access to this strategy by Geostationary Orbit (GSO) market incumbents. In this way, Starlink’s Direct-To-Cell (DTC) has yet to be commercially launched, but will represent the largest player in this category by being a first mover and essentially having the only access to the market, except for Iridium and Amazon. Furthermore, players that fall into this category do not yet appear to be organized for a common cause, although this may change in the future.
• MSSA: The group aims to develop a global ecosystem using L- (1 – 2 GHz) and S-band (2 – 4 GHz) spectrum already licensed for MSS for direct-to-device connectivity, integrating satellites into consumer mobile devices. This faction supports the use of NTN handsets and devices via standards-based solutions using n255 (NTN 1.6 GHz) and n256 (NTN 2 GHz) from LEO for 5G NTN. They also support connectivity of IoT devices via the IoT NTN standard, which uses the n255 and n256 bands alongside the Narrowband Internet of Things (NB-IoT) or LTE-M protocols from LEO and GSO satellites. Members of this faction, like Inmarsat, have already started to support standards-based solutions in the market, incorporating chipsets supporting NTN and Terrestrial Network (TN) bands. With the former standard, 5G NTN modems and enhancements on the device help establish a more substantial link budget and unlock Mbps data rates.
• Proprietary: Globalstar remains steadfast in its strategy with Apple to remain with a proprietary solution. While this strategy helped Globalstar become the first provider in the NTN-mobile market, many industry players, like Iridium, are dropping proprietary solutions in favor of open standards solutions. Proprietary solutions are still holding strong in the Chinese smartphone market, with players like Huawei and ZTE; however, even Chinese companies are showing an interest in standards-based solutions. In the long run, proprietary may only serve certain companies, like Apple and Globalstar, but has the potential to unlock a variety of solutions, from low data-rate narrowband texting and calling to potentially higher data rate applications, like Internet applications.

While the pursuit of a low-cost, no-spectrum strategy by the LEO LTE group enables fast go-to-market, there are significant potential long-term consequences. The expansion of the required spectrum by both satellite and cellular industries is constant. If Starlink (and Amazon) pursue a change in the way satellite systems and IMT spectrum can be used, there could be a case against satellite operators requiring so much spectrum for services—a blow, particularly for existing satellite incumbents much like the potential Equivalent Power Flux Density (EPFD) limits revision. However, this is not all bad, as this synergy between IMT and satellite could help unlock a new wave of ubiquitous connectivity with lower costs to access. However, this means rewriting the rules of the old system and potentially introducing a new standard for both industries.

While leveraging a standards-based or proprietary approach remains at a crossroads, companies could still opt for a hybrid solution similar to what Iridium is doing for its NTN-mobile service, Project Stardust. In this case, Iridium is updating its network protocols that then can be uploaded to the constellation, and to standards-based NB-IoT for both voice and data. Iridium will not shed its proprietary support, and still plans to support both proprietary and standardized mobile and IoT services. This strategy could work well for Iridium and allow it to support more devices in an NTN ecosystem. While the company exclusively controls 7.775 MHz of L-band spectrum, the company could potentially offer LEO LTE connectivity using IMT spectrum in the future. This option is more difficult for GSO operators, as leveraging the IMT spectrum may not be enough for satellites in their orbital regimes to connect with unmodified devices due to the link budget. Nevertheless, the evolution toward Software-Defined (SD) satellites, multi-application payloads, and the introduction of Artificial Intelligence (AI) payloads could help GSO systems overcome these challenges.

ABI Research sees LEO LTE and standards-based (MSSA/Iridium) systems as having divergent evolution paths that will impact each other's market potential. At this time, as the use of IMT spectrum by satellites comes under review and standards are specific to satellite spectrum, The 3rd Generation Partnership Project (3GPP)-based connections and devices are projected to win out in the long run.