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Following on from their webinar last year, “Is Satellite Direct to Handset Really Dead? Here are the Real Opportunities for 5G NTN”,  TTP’s Peter Kibutu and Paul Tindall explore what 2025 and beyond has in store for D2D

Direct-to-device (D2D) satellite communications has become a focal point in the drive to ubiquitous connectivity for mass-market handset devices. There are two flavors of D2D; the established MSS (mobile satellite services) operators looking to extend their current offerings, adopting new 5G NTN (non-terrestrial network) standards to deliver D2D to next generation handset devices. Then there are the new entrants such as Starlink and AST Space Mobile, who are accelerating plans to deploy large LEO constellations that reuse terrestrial mobile spectrum, targeting the customer base with existing, unmodified devices.

Although these approaches differ in their choice of air interface waveform and business models, they share the common goal of extending ubiquitous connectivity to locations that have limited coverage.

A D2D strategy based on mobile network operator (MNO) spectrum has a promising business case as it lowers the barrier to entry to a large market of existing devices. However, it faces complex regulatory challenges which arise from spectrum sharing and the potential to cause interference with the existing terrestrial services. In the United States, the FCC’s “Supplementary Coverage from Space” framework grants permission for satellite operators to reuse terrestrial spectrum, if they respect the non-interference requirements.

Europe remains cautious due to high terrestrial coverage and spectrum congestion, requiring exclusion zones that reduce the ability of D2D to provide service in small coverage gaps and along the many national boundaries. Consequently, D2D on MNO spectrum is ideal for extending coverage to large un-served areas in sparsely populated areas like the U.S., Canada, and Australia, as well as developing regions with limited cellular deployments. The leading D2D operators have made tremendous progress over the last year, with Starlink launching over 400 satellites and AST SpaceMobile with five satellites in space. Recently Starlink announced the start of beta D2D messaging services with T-Mobile, and AST SpaceMobile made a revolutionary video call with Vodafone. Starlink intends to launch data and IoT type of services in 2025 with voice following later.

MSS operators using dedicated satellite spectrum avoid MNO interference challenges, making deployment easier. In this camp there are those using legacy satellite waveforms to deliver services, examples include Globalstar’s partnership with Apple for SOS messaging and Iridium’s partnership with Qualcomm that fell through due to lack of support from the handset ecosystem.

On the other hand, some MSS operators are taking a more forward-looking approach, launching 5G NTN based D2D services. Viasat, in collaboration with Skylo, is deploying 5G NTN NB-IoT messaging services via Geostationary Orbit (GEO), with chipsets from MediaTek, Sony, and Qualcomm, supported by handsets from companies like Google and Samsung. Terrestar Solutions Inc. from Canada has also recently announced they have started the deployment of 5G NTN NB-IoT services over their existing GEO satellite.

The mass adoption of 5G NTN D2D services has been slow mainly because the basic voice, data and messaging services we are accustomed to, are only feasible through a Low-Earth Orbit (LEO) constellation. There is uncertainty over subscribers’ willingness to pay for GEO-based messaging services beyond SOS mainly due to the poor user-experience.  The LEO constellation link budget is much better than GEO and will enable 4G type of services to be delivered directly to handsets, which will be a game changer.

With the more recent push from 3GPP releases focusing on NTN, we are seeing more interest in “regenerative” LEO architecture with inter-satellite links, which will provide the ability to deliver a better class of services and open up more revenue generating use cases as compared with the traditional bent-pipe satellite architectures.

New 5G NTN services require optimized handsets for satellite links to provide the enhanced performance needed to deliver a 4G type of service and user experience. At TTP, we encounter persistent engineering trade-offs in both satellite network and handset design. A key challenge is the need for high EIRP (effective isotropic radiated power) to maintain a strong link budget. However, SAR (specific absorption rate) regulations limit transmission power, reducing link margins. Modern handsets integrate multiple wireless technologies (Wi-Fi, Bluetooth, NFC), leaving little space for high-gain satellite antennas. As a result, power-hungry amplifiers are necessary to achieve high EIRP, leading to overheating.

Engineers must carefully balance space, antenna gain, and power consumption to comply with both SAR and EIRP requirements. Terrestar Solutions Inc. has recently announced the ‘Sat Companion’, a snap-on device for existing smartphones developed in collaboration with TTP and Bittium that addresses these issues and enables 5G NTN direct-to-mobile communication over a GEO link.

Another bottleneck is the integration with terrestrial networks that will enable NTN operators to use MNOs as a route to market for their services. Although the 5G architecture can, in principle, treat satellite access like any other 5G radio node, there are many unresolved questions around roaming agreements, authentication paths, security and user-plane optimization. Some operators may choose a light-touch solution — treating D2D as a subset of roaming, while others prefer deeper integration to achieve a more seamless user experience. Either way, it is only through large-scale commercial trial deployments that the industry can verify these approaches for reliability and scalability.

MSS operators will initially focus on messaging and IoT via GEO and small LEO constellations. Satellite fallback for emergencies and low-bandwidth use is advancing, driven by Apple and Skylo’s satellite messaging in standard handsets. This is expected to become a common feature among major handset vendors. As larger 5G NR NTN LEO constellations emerge and satellite-optimized 5G handsets become available, mass adoption of enhanced broadband D2D services will follow.

The momentum for widespread commercial D2D services is undeniable, and TTP believes that AST SpaceMobile and Starlink are well ahead of the MSS operators. Over the course of the year, we expect to see more partnership agreements between MNOs and players like Starlink and AST SpaceMobile, to start testing their services, with some regulators allowing for commercial services. We also expect to see the MSS operators take up the challenge and start commercial deployment of 5G NTN services on existing satellites and one or two announcements for a potential global LEO network.

The progress of adoption of 5G NTN NR broadband services over LEO in Ku- and Ka-bands is also gaining traction as demonstrated in the recent announcement by Eutelsat and Mediatek. Eutelsat was the first satellite operator to demonstrate 5G NTN working on a commercial Ku-band deployment using a commercial chipset from MediaTek, paving the way for future 5G NTN constellations.

The path forward is clear: if the technical pieces come together, D2D will become transformative, finally addressing coverage gaps that have long been out of reach of terrestrial infrastructure.

Peter Kibutu is 5G NTN Market lead at TTP, specializing in advising our clients on the business and technical aspects of 5G NTN broadband and D2D satellite communications, with over 18 years of experience in waveform system design, modeling and implementation.

Paul Tindall is a Senior Consultant at TTP, specializing in 5G Non-Terrestrial Networks, with over 40 years of experience in software architecture, system design, and turning complex technologies into robust, real-world products.

TTP supports satellite operator clients in designing optimized 5G NTN networks as well as satellite compatible handset devices.