The direct-to-device (D2D) satellite communication market is emerging as a highly competitive field, exemplified by the ongoing debates around out-of-band (OOB) power flux density (PFD) regulations. Satellite operators using terrestrial mobile spectrum as a secondary application must adhere to strict PFD limits, which impacts the performance capabilities of D2D services, with significant commercial implications for market players.
The SpaceX predicament
A prominent example is SpaceX, which has deployed over 240 D2D satellites and plans to launch commercial services in partnership with T-Mobile. These services will initially include text messaging and emergency alerts, with plans to expand to voice and data as the constellation grows. However, SpaceX’s D2D constellation does not meet the -120 dBW/m2/MHz PFD limit required under the FCC’s SCS framework. To comply with this limit, SpaceX would need to reduce its transmit power by approximately half (3.1 dB), potentially limiting the capacity and coverage of its D2D services—particularly for high-SNR services like voice and data. To address this, SpaceX has requested a waiver to operate with a modified OOB PFD limit of -110.6 dBW/m2/MHz.
The stance of MNOs
Conversely, AT&T and Verizon, backing AST SpaceMobile, contend that emissions from SpaceX’s satellites could reduce adjacent-channel capacity by an estimated 15%-18%. They base this calculation on an edge spectral efficiency of 0.5 bps/Hz with an interference-to-noise ratio of -6 dB. They further assert that satellite interference would prevent reliable voice calling near the cell edge. This issue primarily impacts channels adjacent to T-Mobile’s PCS Block G, including AT&T’s PCS Block C and Dish’s PCS Block H, and is particularly concerning to MNOs in rural areas where coverage is stretched. It’s noteworthy that low-band spectrum (e.g. 600/700/800 MHz), which is typically deployed in rural areas for its range, is unaffected by satellite interference from SpaceX’s PCS Block G service. Joining AT&T and Verizon in objecting to SpaceX’s plans, a coalition of seven European operators—including Orange, Telefonica, and Vodafone—has taken the unusual and extraordinary step of urging the FCC not to relax the OOB PFD limits.
Various approaches in D2D
In contrast to SpaceX, AST SpaceMobile has adopted a different satellite design, utilizing larger antennas (64 m² compared to SpaceX’s ~25 m²) to generate narrow, targeted beams that minimize interference. This spot-beam approach effectively reduces interference and enables SCS to operate in smaller licensed service areas. However, it also increases satellite costs, thereby raising the financial profitability threshold for AST SpaceMobile’s constellation. [See our analysis of AST SpaceMobile technology here.]
Concluding thoughts
The PFD dispute largely centers on limiting SpaceX’s capacity to provide voice and data services (e.g., web browsing, social media, IoT connectivity) through D2D satellites. These services will only become available after SpaceX deploys 1,500 satellites, with a final target of 7,500. SpaceX estimates that maintaining the current OOB PFD limit would reduce its capacity by 20%. Given this impact, any subsequent FCC reduction in the OOB PFD limit is critical. Each passing month heightens the risk of deploying more satellites with a suboptimal design to support planned real-time services within current regulatory constraints, making a quick resolution advantageous for SpaceX.
Conversely, AST SpaceMobile and its MNO partners aim to impede SpaceX and T-Mobile’s ability to provide real-time services in order to carve out a unique niche in the market. AST SpaceMobile offers a peak data rate of 30 Mbps, which surpasses SpaceX’s planned speeds. However, this higher speed comes at a cost: AST’s satellites are more expensive and technologically sophisticated than those of SpaceX. If the FCC lowers the PFD limit, operators with spectrum licenses adjacent to the SCS band may lose capacity and coverage. Given that operators depend on sub-1 GHz spectrum in rural and remote areas, it is makes sense to concentrate SCS services in higher frequency bands.