11.7 Handover Design inside Tunnels
Large tunnel systems often need to be divided into several cells, especially if it is a rail tunnel system over a large area. Therefore you need to plan an adequate handover zone between the overlap of the adjacent cells that will ensure a successful handover of the traffic.
There are some basic parameters and tricks that are essential for a successful design handover design.
11.7.1 General Considerations
HO Zone Placement
In a metro rail application it is worthwhile considering having the HO zone planned at the station area, preferably in a well-defined zone, with clear definition of the difference in level of the two cells at the centre of the platform. This approach will have several benefits:
- Slow moving traffic: a train fully loaded with mobile users will load severely the signaling for the two cells handing over all the calls. The network will have to hand over all the users in the traffic within a limited time window if the train is moving at high speed (relative of course to the planned handover zone). Therefore it is preferred not to do the handover at high speed; you need a margin for ‘retries’ (GSM) if the first handover fails.
- Capacity overlap: having the HO zone at the station means that there will be capacity overlaps from both cells at platform level where most passengers are placed. This helps in peak load situations as both cells will be able to carry the traffic (not for UMTS designs).
- Redundancy of the radio service: if one ...