1. The station moves out of the range of BTS or a certain antenna of a BTS respectively .The received signal level decreases continuously until it falls below the minimal requirements for communication .The error rate may increase due to interface , the distance to the BTS may be too high etc. All these effect may diminish the quality of the radio link and make radio transmission impossible in near feature .
2. The wired infrastructure may decide that the traffic in one cell is too high and shift some MS to other cells with a lower load .Handover may be due to load balancing .
The handover are four type
1. Intra-cell handover
2. Inter-cell , Intra-BSC handover
3. Inter-BDC , intra-MSC handover
4. Inter-MSC handover
TYPES OF HANDOVER IN GSM SYSTEM
To provide all necessary information for a handover due to weak link , MS and BTS both perform periodic measurement of the downlink and uplink signal quality respectively. Measurement report are sent by the MS about every half-second and contain the quality of the current link used for information as well as the quality of certain channels in neighboring cells(BCCH). Handover is of two type Soft handover and hard handover. In hard handover MS can only talk with a single BTS at a time when changing from one cell to other . But in soft handover MS can talk old and new BTS simultaneously .Soft handover is used in CDMA technology while Hard handover is used in GSM technology. The procedure for handover is given below.
INTRA-MSC HANDOVER
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