Handover Success Rate (HOSR)

In cellular telecommunications, the terms handover or handoff refer to the process of transferring an ongoing call or data session from one channel connected to the core network to another channel.

The HOSR is the ratio of the number of successful handovers to the number of handover requests. The major purpose of handover is to guarantee call continuity, improve speech quality, reduce cross interference in the network, and thus provide better services for mobile station (MS) subscribers.

Types of GSM handover

Within the GSM system there are four types of handover that can be performed for GSM only systems:

• Intra-BTS handover:   This form of GSM handover occurs if it is required to change the frequency or slot being used by a mobile because of interference, or other reasons. In this form of GSM handover, the mobile remains attached to the same base station transceiver, but change the channel or slot.
• Inter-BTS Intra BSC handover:   This form of GSM handover or GSM handoff occurs when the mobile moves out of the coverage area of one BTS but into another controlled by the same BSC. In this instance the BSC is able to perform the handover and it assigns a new channel and slot to the mobile, before releasing the old BTS from communicating with the mobile.
• Inter-BSC handover:   When the mobile moves out of the range of cells controlled by one BSC, a more involved form of handover has to be performed, handing over not only from one BTS to another but one BSC to another. For this the handover is controlled by the MSC.
• Inter-MSC handover:   This form of handover occurs when changing between networks. The two MSCs involved negotiate to control the handover.

Hardware issue
Hardware issue always the first step to check, always to make sure first no hardware issue occurred. To identify hardware issue in the cells related handover you can generate measurement related Incoming Handover.
Clearing Frequency Interference
Frequency interference will take effect to all KPI in GSM including Handover Success Rate. You have to make sure no Co-channel /Adjacent channel Interference. Retune theFrequency of the cells if you found cells suspected frequency interference.

Neighbor list checking and external discrepancy fixing
Check neighbor list in the cells and make sure no missing neighbor. You need to remove unnecessary relation and add necessary relation. Make sure head to head cells have relation (no missing). Your Handover will improve if neighbor list configure properly. Don’t forget to check external neighbor value and make sure no discrepancy with existing such as: LAC,BSIC,BCCH and RAC
Coverage Checking
Coverage will take effect to Handover performances. You need to make sure no coverage issue, No overshooting cells and coverage is continuous. Propose add site if needed to improve coverage or physical optimization(Down tilt/Up tilt/re-azimuth) to improve your coverage.
Check BA List
BA list indicate your neighbor list. Too many measurement frequencies in the active BA list will make you handover bad and you need to remove unnecessary relation.
Check for Congestion Problem
Handover Success Rate will be also influenced by congestion on target cells. Make sure no congestion on target cells to improve your HOSR(handover Success Rate).Do the parameter tuning or Traffic sharing to other cells by parameter or physical optimization
Parameter Handover Optimization
The final step to improve Handover Success Rate is Parameter tuning. You need to change some parameter related handover to improve HOSR. The idea is to reduce fail of handover to specific cells and increase successful attempt to several targeted cells. Some parameter can be adjusted such as: PBGT margin, RXLevmin Cell etc.