What is handover? What are the different types of handovers?

A handover is defined as the change of the currently used radio channel (signaling or traffic) to another radio channel during an existing and active connection between a mobile station (MS) and base station (BTS). The handover procedure is always initiated by the network.

There are two criteria to categorize handovers:

1. What entity is executing the handover, i.e. which is the source BTS and which is the target BTS during handover?
2. Are the system clocks of the source cell and the target cell of a handover finely synchronized?

The first criterion gives handover types as "intra-cell handover" and "inter-cell handover".

The second criterion gives handover types as "synchronized handover", "non-synchronized handover", "pre-synchronized handover" and "pseudo-synchronized handover". The support of first three is mandatory in the MS. The pseudo-synchronization case is optional in the mobile station and this can be commanded only to a MS that can support it, as indicated in the classmark. The "Synchronization Indication" information element in "Handover Command" message indicates which type of handover is to be performed.