Internet of Things (IoT) via Satellite

In “Massive IoT” applications terminals are deployed in large quantities and thus are under cost and resource constraints. Such constraints include size of the terminal, bill of materials, energy budget for battery-powered devices, permitted transmit power and antenna performance. Typically the amount of data transmitted by each terminal is small and transmissions occur infrequently. Thus, even if the spectral efficiency of the satellite link may be low, each terminal only consumes a small fraction of the available satellite bandwidth.

For most antennas, the beam width is indirectly proportional to the size of the antenna, i.e. a small footprint antenna has limited gain and directivity, thus produces a “wide” beam. This results in unwanted emissions toward adjacent satellites in the GEO arc and other LEO or HEO satellites or terrestrial receivers. Therefore, to mitigate such harmful interference into other systems, direct-to-satellite IoT terminals need to comply with defined power spectral density (PSD) masks. Depending on beam width and pointing accuracy, such PSD masks significantly limit the permitted transmit power, link efficiency, system capacity and the number of IoT terminals in the network.

Fraunhofer IIS has devised a novel solution addressing the efficient use of spectrum and maximizing system capacity in such PSD limited scenarios, considering terminal and antenna type and pointing accuracy. Furthermore, a waveform implementing such concepts has been developed and is available in simulation.

“Critical IoT” applications and aggregation nodes in hybrid terrestrial-satellite systems demand for dependable, low latency and high-throughput connections. These requirements are similar to those for high-throughput satellite (HTS) broadband, but with the additional challenges of using smaller antennas or operating in a LEO or HEO satellite infrastructure. Therefore, additional aspects like low signal-to-noise (SNR) link budgets and time variant channels (variable frequency shifts and path delays) have to be considered when selecting and tailoring the communication standard.

For professional equipment and broadband applications, DVB-S2X is the latest in the “DVB-” series of satellite communication standards. For IoT applications, DVB-S2X provides unique advantages by supporting very low signal-to-noise ratio (VL-SNR) operation down to -10 dB and a low-overhead super-frame structure. Especially the DVB-S2X super-frame format 4 provides a flexible extension with VL-SNR payload header (PLH) tracking. This allows robust synchronization and signal decoding under variable channel conditions.

Fraunhofer IIS was actively involved in the development, specification and validation of DVB-S2X. DVB-S2X solutions and IP are available at Fraunhofer IIS for specific markets, including IoT.

Hybrid terrestrial-satellite systems require both in-depth understanding of terrestrial IoT and satellite communication. While it may appear attractive to use the same technology and waveforms for terrestrial and satellite communication, competing requirements and technical constraints – low power and low cost terrestrial communication in “unlicensed” bands below 1 GHz vs. PSD constraint and highly regulated satellite communication at frequencies above 10 GHz – favor a hybrid solution, optimized for “terrestrial” and “satellite”.

In addition to satellite communication, Fraunhofer IIS is also heavily engaged in providing technology, intellectual property and solutions for terrestrial IoT networks. This includes wireless sensor networks using s-net® technology and the wireless IoT solution MIOTY.

High-throughput satellite (HTS) applications require the use of high gain antennas, perfectly pointed toward the satellite of interest. Active antenna tracking and beam repointing is compulsory whenever the ground terminal or the satellite moves, e.g. for terminals used in LEO or HEO constellations or for mobile terminals used on GEO satellites. Active beam pointing capabilities are also highly advantageous to simplify installation of fixed terminals operating on GEO networks.

Size and complexity constraints prohibit the use of mechanically steerable reflectors or electrically steerable phased arrays for “Massive IoT” applications. On the other hand, throughput requirements for IoT are low compared to HTS use cases, allowing compromises on antenna gain and directivity. This favors the use of multibeam antennas that provide adequate gain and beam steering capabilities while keeping antenna size, number of radiating elements and complexity of the excitation network low.

Fraunhofer IIS offers different multibeam antenna solutions and intellectual property for licensing.