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The trend towards MEO (Medium Earth Orbit) satellites is gaining momentum with further growth in the segment very likely.
This shift has created a need for enhanced modems to better match the characteristics of this orbit. The University of Luxembourg, working with Newtec and O3b, has risen to the challenge and through ESA’s ARTES Advanced Technology Programme, developed a successful prototype.
MEO is becoming more popular – for good reason. This orbit has a coverage or ‘footprint’ of virtually the entire Earth – which is particularly well-suited not only for regional networks but also mobile users, such as on cruise ships that roam the globe.
Other perks of this orbit include a lower latency (useful for real-time applications in 5G networks) and reduced propagation loss, as MEO is closer to the Earth than geosynchronous orbit (GEO), the traditional orbit of choice for communications satellites.
While MEO satellites offer many benefits, the fact that they are ‘moving’ brings in novel aspects in terms of architecture, network management, and ground segment. The team had to navigate some new scenarios characteristic to MEO constellations in the conception of their ‘enhanced’ cost-effective modem, including ‘handover’ and ‘combining’ techniques – essential features of MEO ground segment operations.
Ground users see GEO satellites as stationary in the sky; however, they see MEO satellites as always moving with different rising and setting times. Typically, as a MEO satellite rises and comes into the user’s visibility another satellite is setting and disappearing from view. The handover window is a critical period where communication with the setting satellite is abandoned and a link established with the rising satellite.
Any break in this communication will necessarily disrupt services – for example a perceptible time-lag in a telephone conversation.
‘Make before you break’
The team were able to streamline the handover technique to make it seamless, so the satellite makes the link with the rising satellite on the horizon before breaking with its predecessor as it drifts out of sight.
Daniel Arapoglou, ESA Technical Officer
of the project explains: “The prototype guarantees a ‘smart’ handover ensuring that not a single data unit is lost and the quality of service is not impacted in a noticeable way.”
He adds: “The prototype exploits the availability of two antennas outside of the handover phase at any ground station through diversity combining. Contrary to existing products on the market, the combining of multiple reception streams in this prototype takes place inside the modem.”
The prototype successfully passed all the tests. Geert Adams, VP of R&D Programs and Competence Centers at Newtec says: “We are very happy to develop this know-how, it strengthens our Modem Product portfolio roadmap to support Non-GEO satcom satellite systems.”
“The project opens a number of avenues, both in terms of research and commercialisation; this first activity is the tip of the iceberg,” Bhavani Shankar, Research Scientist at the University of Luxembourg