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I am working on simulating a satellite constellation and I keep coming across the term "handover". My general understanding is that a handover is when a ground station switches its connected between two satellites, presumably because one of them is no longer visible and the new one has just come into view. However, this seems to imply a simultaneous transition between the two satellites (i.e. one leaves the visibility windows just as the other enters it). Can a handover technically occur when a single satellite enters/leaves the ground stations view? If so, the every satellite would require two handovers during its connection to the ground network. But this definition is still a bit confusing because a handover implies that the connection is being transferred elsewhere, while with a single satellite the connection would simply be turned off/on.

I have searched everywhere online for a comprehensive definition on this, but I haven't been successful. Thank you!

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  • $\begingroup$ it's a general communications term and so likely not on topic here, see e.g. the Wikipedia article. $\endgroup$
    – Erin Anne
    Nov 10 at 20:31
  • $\begingroup$ As the satellites fly overhead, you want to be talking to the one that's directly above you - you'll get the best bandwidth. So, even though there might be multiple satellites in the network you could potentially communicate through, switching you periodically to the one that's mostly overhead will keep the bandwidth from changing very much. $\endgroup$
    – Steve
    Nov 13 at 18:04
  • $\begingroup$ hughes.com/resources/insights/satellite-broadband/… $\endgroup$
    – Steve
    Nov 13 at 18:06
  • $\begingroup$ Also, see this answer about the OneWeb constellation. Specifically the "window blinds" portion. This arrangement of satellite beams means that even as a single sat is flying overhead, you're handing-over to another channel on the same satellite (and presumable a different physical antenna on the satellite itself). space.stackexchange.com/a/54568/12742 $\endgroup$
    – Steve
    Nov 13 at 18:08

2 Answers 2

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This might become clearer if you can think in terms of what the ground station is there to do and what assets it has to do so. Its a resource management issue.

e.g. if the number of antennas the ground station has, combined with the number of frequency slots the can manage, exceeds the number of satellites in view then it clearly won't cope with all the potential traffic and so some co-ordination will be necessary, either amongst which satellites are connected or with other ground stations to spread the load.

In a satellite constellation the chances are the owners dreamed up the design of the constellation and then began to wonder how many ground stations they would need. Scaling the ground resources to fit the satellite constellation could well involve having to make switch change-overs.

That wiki article mentioned by Erin Anne, has a helpful first paragraph but after that dives straight into the assumption that it is all about telecommunications.

It is worth checking if the context of any given article is really always as you have described, i.e. two satellites and one ground station, rather than the other way around e.g. determining the sequence of ground station availability so as to work out which ground station is nominated as the primary link for a given satellite. The problem could be specified either way around.

It is also quite plausible that the shape of the resource problem will vary according to whether one is considering command access, telemetry reception, instrument down link reception or communications traffic.

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In general, handovers happen when a device that has single upstream connection switches between access points that are serving multiple devices each.

  • In mobile telephones, your phone does a handover when it switches between base stations.
  • In satellite internet access, your user terminal switches between satellites.
  • For a satellite's own link to internet, the satellite switches between ground base stations.

The critical part of handover is that the upstream network needs to know how to route data towards the downstream terminal. So the terminal needs to inform the network "Hey, the route to me will change!" after it has determined what the new connection will be. Sometimes the decision comes from the network as "Hey, move to base station X on frequency Y now!", but the end result is the same: coordinated handover to ensure uninterrupted communication.

If the satellite completely leaves the coverage area, there is no handover of its upstream connection because there is nowhere to change to. The user terminals connected to that satellite may be able to handover to another satellite to maintain their connections.

Satellite handovers are special in that they need to regularly switch both their upstream and downstream connections as they move along their orbit. There will be separate handovers on each connection, with the satellite acting different roles in them.

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