Handover types
How to choose the most optimal for your case?
What is the handover?
The handover is a process of handing over the tracking from one submap to another in large indoor positioning systems.
Learn more about maps, submaps, service zones, handovers:
- Basics about submaps, service zones, and handover zones – video intro to building large maps consisting of many submaps
- Building submaps (PDF, Video Part 1, Video Part 2) – detailed practical guidance on building large maps consisting of multiple submaps
Let’s discuss the basics of handovers based on the map consisting of two submaps: Submap 1 comprised of the Beacons 2 and 3, and the Submap 2 comprised of the Beacons 3 and 4:
- Beacon 3 belongs to both submaps
- Blue and light-blue rectangles – service zones for corresponding submaps
Types of soft handovers
Type I
- In this handover type, the location data is obtained from the “old” submap/service zone as long as possible
- Only when the “old” service zone is over, the tracking continues in the “new” submap/service zone
- The handover is soft but not very soft because there is a jump since the submaps are always slightly misaligned
- Another, more important part is that when the handover happens, we only hope there is a good tracking in the “new” service zone, but until we hand over there, we don’t know. But when we hand over, it may be already too late
- We still couldn’t extend the tracking anyway, if there is no proper tracking in the “new” submap/service zone for whatever reason. However, we could prepare ourselves somehow, if we knew that before the handover happens
Type II
- In this handover type, the location data is obtained from the “old” submap/service zone as long as possible
- Only when the “old” service zone is over, the tracking continues in the “new” submap/service zone
- The handover is soft but not very soft because there is a jump since the submaps are always slightly misaligned
- Another, more important part is that when the handover happens, we only hope there is a good tracking in the “new” service zone, but until we hand over there, we don’t know. But when we hand over, it may be already too late
- We still couldn’t extend the tracking anyway, if there is no proper tracking in the “new” submap/service zone for whatever reason. However, we could prepare ourselves somehow, if we knew that before the handover happens
Why do we need submaps at all? Why can't we have one large map?
It is possible, in theory, to have one large map and not to split it into submaps. We even practiced it many years ago. However, the tracking won’t be as good as with submaps. For example:
- One stationary beacon B2 – from the far – will report a distance L1 to the mobile beacon Mx
- Another group of stationary beacons (B3-B6) – much closer to the beacon Mx – will report other distances and coordinates that conflict with the data from B2
- Whom to trust? How to interpret the conflicting data?
Many of these issues are solved automatically when submaps with service zones are introduced, because:
- We typically know what stationary beacons have the line of sight where
- We may define the service zones so that hint or even directly command to the system whom to listen where, thus, eliminating “minority reports” that can be misleading
In very short: submaps with service zones:
- Simplify the building large and very large maps
- Make the process more controllable and predictable
- Provide more robust tracking at the same time
However, we need to handle handovers.