Handover from WCDMA to GSM:
As and when the signal strength in WCDMA system falls below a given threshold, the WCDMA network orders the mobile terminal to perform GSM measurements. Typically, the mobile terminal is instructed to send a measurement report when the quality of a neighboring GSM cell exceeds a given threshold and the quality from WCDMA is unsatisfactory.
In fact UTRAN initiates handover when received measurement report message indicates that all the conditions to do handover is fulfilled—for instance when MT moves outside the coverage area of
WCDMA system or when MT enters to a full WCDMA cell.
- UTRAN asks the target BSS to reserve resources.
- Target BSS prepares a handover command message (to MT), which includes the details of the allocated resources (This GSM message, which is sent to the mobile terminal via the WCDMA radio interface, is transferred within a container that is transparently passed on by the different network nodes)
- Next step is to move to the target GSM cell. MT after receiving command message, based on the parameters included in command message establishes the new connection in GSM cell.
- After successfully establishing the connection MT sends a handover complete message to BSS.
- Afterwards GSM network initiates to release WCDMA radio connection.
Handover from GSM to WCDMA:
Like the same, when the signal strength in GSM system falls below a given threshold, the network orders the dual-mode mobile terminal to perform WCDMA measurements by sending the measurement information message. The message contains information on neighboring WCDMA cells and the criteria for performing and reporting measurements.
When the criteria to WCDMA handover have been met:
- BSS initiates the allocation of resources for the WCDMA cell (BSS also sends the WCDMA capabilities of mobile terminal to UTRAN)
- As soon as the resources of the WCDMA target cell have been allocated, UTRAN compiles the handover to UTRAN command message, which typically includes the identity of the pre-defined configuration for the service in use.
- Afterwards Handover to UTRAN message is sent to the mobile terminal through the CN (core network) and BSS.
- When the mobile terminal receives the handover-to-UTRAN command message it tunes to the WCDMA frequency and begins radio synchronization.
- Mobile station sends handover-to-UTRAN complete indication when the handover is successfully done.
- When all the process is accomplished GSM resource is released.