Distributed Approach to Satellite Direct-to-Cell Connectivity in 6G Non-Terrestrial Networks

Satellite direct-to-cell (D2C) connectivity considers the communication between satellites and low-cost handheld devices on Earth. It represents one of the most challenging aspects of the integration between terrestrial and non-terrestrial networks. Low Earth orbit (LEO), sub-6GHz bands, and large aperture satellite antennas are the key to enable D2C connectivity. The industry is tackling the problem with a conventional approach, consisting of the design of very large reflectors or phased arrays. This article proposes a new way to face the problem: the distributed approach. A satellite base station (BS) is decomposed into several small platforms in a so-called swarm configuration to form a sparse phased array. The use of small satellites promises cost-effective solutions, while distributed satellite systems (DSSs) increase the fault tolerance, and thus the reliability, of the entire constellation. This article compares the performance of conventional and distributed approaches under different conditions. It shows that distributed approaches outperform conventional ones even under unfavorable conditions and pessimistic assumptions. Important tradeoffs are derived showing the flexibility of distributed approaches. Finally, major research aspects for exploiting the full potential of the distributed approach are highlighted.