Different approaches are possible to enable Direct-to-Handset (DTH) satellite connectivity. For instance, there’s the approach by T-Mobile and SpaceX and by Apple and Globalstar. AST SpaceMobile is taking yet another approach.
What differentiates these approaches is the way they access spectrum.
- AST chose to be nimble so the DTH service fits within the existing mobile coverage and spectrum allocation.
- T-Mobile and SpaceX chose to operate in a slice of spectrum that T-Mobile will dedicate to DTH services.
- Apple and Globalstar look to implement DTH in MSS frequencies which bypasses the service provider.
Three radically different approaches with different trade-offs in balancing the technology, cost and commercial requirements.
| AST | Globalstar | SpaceX | |
|---|---|---|---|
| Spectrum | In-fill MNO spectrum | MSS spectrum | Dedicated slice of MNO spectrum |
| Technical Complexity | Very complex antenna, resource and traffic management | Low complexity | Average-to-high complexity |
| Modification to Phone | No change | Support for MSS spectrum in uplink (L-band) and downlink (S-band) | No change |
| Regulatory Requirements | Modification of spectrum allocation tables to include mobile satellite service | Largely approved at global scale; limited to no new approvals required | Modification of spectrum allocation tables to include mobile satellite service |
| MNO Partnership | Essential | Not required: over-the-top | Essential |
Citadels in the Sky
AST has taken the approach to fit the satellite coverage within the service area of the Mobile Network Operator (MNO). This also implies a high degree of coverage selectivity to avoid interference to adjacent-area license holders. Therefore, AST is building a giant phased-array antenna that’s capable of forming hundreds of pencil-shaped beams.
The test antenna it launched into space on September 10, 2022 has a surface area of 693 sq. ft. (64.4 m). Each pencil-shaped beam illuminates a small cell on Earth measuring about 24 km in diameter. This allows the satellite to selectively cover the desired areas, while staying away from adjacent-license service areas to prevent co-channel interference.
The approach has the advantage of providing coverage selectively with “surgical precision”. This is necessary to be compatible with global spectrum allocations considering the multitude of licensees and service area sizes.
The disadvantage of the design is in the size of the antenna and how it will hold up in space. Just as critical is the software that controls and manages resource allocations and traffic routing; which could become very complex, especially as satellites are traveling at a speed of 7.5 km/sec. Thus, AST assumes more technical risk in order to partially reduce commercial risk, which nevertheless still exist.
Need a Blanket
SpaceX will use T-Mobile’s 1900 MHz PCS spectrum for which it holds a nationwide license. The duo called on collaboration with other MNOs which is critical: they need global footprint in a select few frequencies. MNOs will need to dedicate a slice of spectrum for SpaceX DTH service.
The advantage of this approach is that it reduces the pressure on the antenna design and associated resource and traffic management software. However, SpaceX and T-Mobile will need the buy-in from global MNOs. Anyone who dealt with MNOs knows the high risk associated with such business plan.
Going Their Own Way
Apple and Globalstar are going their own way by completely decoupling from MNOs. The duo will provide global coverage using Globalstar’s MSS spectrum in the L and S-bands. There may be some regulatory approvals to secure in some locations, but by far these should be easier than the case of AST and SpaceX where regulators need to update the Frequency Allocation Tables to add satellite mobile spectrum. Additionally, it would be easier to size the constellation for the targeted economics than the other constellations.
The question around Globalstar is for how long the service will remain restricted to Apple. Apple funded the R&D and is financing the new generation of Globalstar’s satellite. Hence, it is likely that the service will remain proprietary to Apple.
Concluding Thoughts
The three approaches provide different user experiences and cost structures. The main challenge in DTH is compensating for the weak RF capabilities of the mobile handset which limit range. But when it comes to modeling profit and loss, the question centers on revenue. DTH is a new market segment for emergency services and connectivity in areas where none exist. It is not a replacement for fixed wireless access because DTH has low throughput by comparison.
DTH is also not a solution to “connect the unconnected” because by definition one needs to have a subscription with an MNO to use this service (in the case of Apple-Globalstar, the users need iPhones!).
Originally published by Frank Rayal as How the Different Direct-to-Handset Satellite Constellations Stack Up
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