As the MS (Mobile station) gets out of the service cell and goes into another service cell, the link between the former base station and the MS will be substituted for the link between the new base station and the MS. Handover, in mobility management, is mostly performed by RRC layer protocol in 3G.

According to the setup and release of radio link between MS and network, handover can be classified
  • Soft handover
    • Softer handover
  • Hard handover 
    • Intra-frequency hard handover
    • Inter-frequency hard handover
    • Inter-system handover (Between WCDMA and GSM)
The typical process of handover is measurement control --> measurement report --> handover decision--> handover implementation --> new measurement control.
In the phase of measurement control, the network informs UE (User Equipment) of the measurement parameters through the sent measurement control message. In the phase of measurement report, the measurement report message is sent to the network by UE. In the phase of handover decision, the network makes a handover decision according to the measurement report. In the phase of handover implementation, UE and the network go along the signaling procedure and make a response to signaling.

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