Method and apparatus for implementing handover in a mobile communications system

DETAILED DESCRIPTION OF THE INVENTION In the invention, handovers due to cell loading are carried out in a centralised fashion in base station controller BSC.
Implementation of the invention thus requires implementation of the algorithm monitoring the EXIT CRITERIA triggering off the functionality and implementation of the target cell selection algorithm in the base station controller.
For example, such a situation where there is no free channel in a cell can be defined as the EXIT CRITERIA for triggering off a handover due to cell loading in a direction out of the cell.
In its simplest form the criterion may be defined to be the same for all cells subordinated to the base station controller.
Since better information about the load situation of cells is available to the base station controller than to the mobile services switching centre, the EXIT CRITERIA may also alternatively be defined as dynamic criteria.
An example of a criterion defined as a dynamic one is such a criterion which rules that at least so many channels should always be kept free in the cell that the connection setups requested in the connection setup requests received by the base transceiver station can be implemented through the base transceiver station.
Moving of load out of the cell is hereby started with the setting up of a new connection when the channels which are free at the base transceiver station are not sufficient for setting up the requested connection.
For example, such a situation where there are 3 free channels in a cell may be defined as the ENTRY CRITERIA.
In its simplest form the ENTRY CRITERIA is also the same for all cells subordinated to the base station controller.
One advantage compared with the state of the art is that when checking if the EXIT CRITERIA condition is fulfilled in the base station controller, such information on the target cell load is available for the comparison which is more up to date than in a comparison performed in the mobile services switching centre.
The ENTRY CRITERIA too may be defined to change dynamically e