The satellite industry has adopted two primary approaches to connecting smartphones to satellites using 5G. The first approach utilizes MSS (Mobile Satellite Service) spectrum, as seen with the Globalstar-Apple collaboration. The second approach employs low-band terrestrial spectrum, such as the PCS band, which is being implemented by SpaceX and planned by startups like Lynk Global and AST Spacemobile.
In an earlier post, I expressed my view that the second approach might face challenges due to regulatory and implementation issues that could result in complex systems with limited performance in terms of capacity and throughput. I argued that higher frequency bands in the spectrum could be more suitable for improving cost and performance. This perspective is now gaining traction, especially among traditional satellite companies that are preparing for Non-Terrestrial Network (NTN) services within the 3GPP framework.
Consequently, the number of high-bands, including millimeter wave bands, designated by 3GPP for NTN is increasing, with the most recent development being the approval of the workplan to support the Ku band at the 3GPP meeting in Shanghai last June [Link]. Overall, while the current industry and regulatory focus remains on using MSS and terrestrial spectrum for NTN, the approach to leveraging satellite frequencies in the Ka and Ku bands for 5G/6G services is gradually advancing.
| Satellite Band | Downlink | Uplink |
|---|---|---|
| L band (GEO) | 1518 - 1559 MHz | 1626.5 - 1660.5 MHz and 1668 - 1675 MHz |
| L band (non-GEO) | 1613.8 - 1626.5 MHz | 1610 - 1626.5 MHz |
| C band | 3400 - 4200 MHz and 4500 - 4800 MHz | 5725 - 7025 MHz |
| S band | 2160 - 2200 MHz and 2483.5 - 2500 MHz | 1980 - 2025 MHz |
| Ku band | 10.7 - 12.75 GHz | 12.75 - 13.25 GHz and 13.75 - 14.5 GHz |
| Ka Band (GEO) | 17.3 - 20.2 GHz | 27.0 - 30.0 GHz |
| Ka band (non-GEO) | 17.7 - 20.2 GHz | 27.0 - 29.1 GHz and 29.5 - 30.0 GHz |
| Q/V band | 37.5 - 42.5 GHz 47.5 - 47.9 GHz 48.2 - 48.54 GHz 49.44 - 50.2 GHz | 42.5 - 43.5 GHz 47.2 - 50.2 GHz 50.4 - 51.4 GHz |
Competitive landscape
There are at least three classes of companies aiming to serve mobile users from space: MSS companies, startups and traditional satellite companies. These companies approach NTN services from different spectrum angles to provide their services.
The MSS-class, exemplified by the Apple-Globalstar partnership, is currently in the lead with live commercial service. In this scenario, the mobile phone includes a chip to communicate with a satellite using MSS spectrum. Therefore, no tie-up with a mobile network operator (MNO) is necessary, and regulatory barriers are low.
The startup-class, which includes SpaceX, has largely opted to partner with MNOs to share their terrestrial spectrum for satellite communications. This has prompted the inception of new regulatory frameworks, such as Supplementary Coverage from Space by the FCC. The third class is dominated by traditional satellite companies, such as Intelsat and Eutelsat, which are laying the groundwork to potentially compete in this segment by preparing to offer NTN services using their spectrum. As these companies face declining revenue from video and broadcast services, NTN services are seen as a potential solution to reverse such trends. Consequently, these companies have been pushing to include their frequency spectrum as part of the 3GPP approved frequency bands as a step toward enabling NTN services.
3GPP NTN frequency bands
The 3GPP has defined two classes of frequency bands for NTN. The first class is the 5G bands, driven by the personal connectivity use cases. The second class consists of LTE bands, primarily driven by IoT connectivity. These bands are identified in the table below. The S and L bands target handheld devices, while the Ka band targets high-gain, small aperture antennas, such as those used in fixed wireless access and on vehicles.
| Release | Band | Use case | Uplink | Downlink | Bandwidth | Notes |
|---|---|---|---|---|---|---|
| Rel-17 | n256 | 5G NTN | 1980 - 2010 MHz | 2170 - 2200 MHz | 2x30 MHz | FR1, S band, |
| Rel-17 | n255 | 5G NTN | 1626.5 - 1660.5 MHz | 1525 - 1559 MHz | 2x34 MHz | FR1, L band |
| Rel-18 | n254 | 5G NTN | 1610 - 1626.5 MHz | 2483.5 - 2500 MHz | 2x16.5 MHz | FR1, LS band |
| Rel-18 | n512 n511 n510 | 5G NTN | 27.5 - 30.0 GHz 28.35 - 30.0 GHz 27.5 - 28.35 GHz | 17.3 - 20.2 GHz 17.3 - 20.2 GHz 17.3 - 20.2 GHz | 2.5/2.9 GHz 1.65/2.9 GHz 0.85/2.9 GHz | FR2, Ka band |
| Rel-18 | 256 | LTE IoT | 1980 - 2010 MHz | 2170 - 2200 MHz | 2x30 MHz | S band |
| Rel-18 | 255 | LTE IoT | 1626.5 - 1660.5 MHz | 1525 - 1559 MHz | 2x34 MHz | L band |
| Rel-18 | 254 | LTE IoT | 1610 - 1626.5 MHz | 2483.5 - 2500 MHz | 2x16.5 MHz | LS band |
| Rel-18 | 253 | LTE IoT | 1610 - 1626.5 MHz | 1518 - 1525 MHz | 16.5/7 MHz | Extended L band |
| Rel-19 | TBD | 5G NTN | 12.75-13.25 GHz and 13.75-14.5 GHz 12.70-13.25 GHz and 13.75-14.5 GHz | 10.70 - 12.75 GHz 10.70 - 12.70 GHz | 1.25/2.05 GHz 1.3/2 GHz | Ku band proposal, exact frequencies depend on region |
I see these developments as a step towards enabling direct-to-device services in the future, despite the necessary work that remains at the ITU and regional/national regulatory levels.
Interference in D2D
One of the challenges in direct-to-device (D2D) communications is managing access to spectrum in a way that prevents interference. Satellites using terrestrial spectrum need to ensure that mobile networks are protected from interference. I have described the trade-offs in my earlier post. Here, I wanted to share this diagram from the 3GPP that clearly illustrates the different interference scenarios that could be experienced in D2D NTN communications:
- i1: Downlink terrestrial network 5G to uplink NTN 5G
- i2: Uplink NTN 5G to downlink terrestrial network 5G
- i3: Uplink NTN 5G to uplink terrestrial network 5G
- i4: Uplink terrestrial network 5G to uplink NTN 5G
The deployment model and interference scenarios bring back memories of small cell deployments. Small cells are low-power nodes operating under a macrocell layer of high-power nodes, causing high cell-boundary interference problems that contributed to the demise of the concept as a scalable capacity solution. In NTN, the scenario is somewhat reversed. Even as satellites transmit at high power similar to, if not more than macrocells, propagation losses are significant due to the long distance. Controlling cell-boundary interference is critical to the success of in-band NTN solutions. I mention this as several regulators are currently considering their frameworks for D2D NTN services.