Handover in GSM is very important to keep continuous of call communication. In this note I would like to share about GSM handover and how to optimize Handover Success Rate(HOSR) in GSM Network based on my knowledge and experiences. Sorry I don't tell you based on document because too much reference. You can refer to your document in your vendor if you want to learn detail based on document.
- Handover definition
Handover meaning call moving between cells to continue conversation and prevent drop call on the Network. Handover also purposed to improve services performances and reduce congestion in the cells.
-Types of handover in GSM
Based on reason type of handover in GSM can be classified as below
1. Emergency Handover : Timing Advance(TA) Handover, Bad Quality Handover,RxLevel Drop handover and Interference Handover
2. Load Handover
3. Normal Handover: Edge Handover, Layer Cell Handover and Power Budget(PBGT) handover
4. Fast Moving Handover
5. Overlaid/Underlaid Handover
Based on location type of Handover can be listed as follow:
1. Intra cell handover : Handover that happened between channel/ TRX in one cell
2. Inter cell Handover : Handover that happened between cell(ex: HO from cell A to Cell B)
3. Intra BSC Handover: Handover between cells in same BSC(ex: HO from cell A to Cell B, A and B located in same BSC)
4. Inter BSC Handover:Handover between cells in different BSC(ex: HO cell A to Cell B, A and B located in different BSC)
5. Handover Inter MSC: Handover that happened between cells but different MSC
For the details about handover process,protocol and rule of each handover type, you can refer to your document in your vendor. In this paper I just want to share step by step how to optimize Handover Success Rate to improve your KPI based on what usually I do. Lets follow below step to optimize Handover.
Step 1: Killing Hardware issue
Hardware issue always the first step to check. As I said before in this blog, to improve all KPI Such as CSSR, Drop Call Rate, HOSR, TCH Blocking,etc always to make sure first no hardware issue occurred. Your next action will be useless if hardware issue occurred in your cells. To identify hardware issue in the cells related handover you can generate measurement related Incoming Handover.After generate measurement you will find which cells have high handover failure.
You can check related cells that have high handover failure and low HOSR and troubleshoot one by one. To troubleshoot hardware issue you can collaborate with FM(Field Maintenance) Team. Make sure no TRX faulty or Combiner problem or event connector problem. If the problem suspected only one cell/sector in 1 site, you can try swap each module to other sector and let see if the problem move to other sector.If the problem happened in all sector in 1 site then you can try swap transmission module(GTMU, IDU, ODU) to other site and let see if handover Incoming failure move to other site. Don't forget to check by drive test to make sure no cross feeder problem occurred in the site.
Step 2: 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. Change Frequency of the cells(retune) if you found cells suspected frequency interference.
Step 3: 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
Step 4: 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.
Step 5: 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.
Step 6: 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).You can minimize congestion by adjust half rate setting in the cells(ex:TCHBUSYTHRES and AMRTCHHPRIORLOAD in Huawei) or Traffic sharing to other cells by parameter or physical optimization
Step 7: 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.You can refer to your document in your vendor to change specific parameter but keep in mind the idea is to reduce handover fail to specific cells and increase successful attempt to specific targeted cells.For example if you have cell with low handover Success rate(HOSR) due to high attempt to targeted congestion cell or problematic cells, you need to adjust HO PBGT margin or increase RXlevmin to target cell. This idea is purposed to improve HOSR KPI based on statistic to achieve agreed KPI target.
Thanks for reading my note about Handover in GSM, hope can help your daily optimization activity to improve your GSM handover Success rate.
- Handover definition
Handover meaning call moving between cells to continue conversation and prevent drop call on the Network. Handover also purposed to improve services performances and reduce congestion in the cells.
-Types of handover in GSM
Based on reason type of handover in GSM can be classified as below
1. Emergency Handover : Timing Advance(TA) Handover, Bad Quality Handover,RxLevel Drop handover and Interference Handover
2. Load Handover
3. Normal Handover: Edge Handover, Layer Cell Handover and Power Budget(PBGT) handover
4. Fast Moving Handover
5. Overlaid/Underlaid Handover
Based on location type of Handover can be listed as follow:
1. Intra cell handover : Handover that happened between channel/ TRX in one cell
2. Inter cell Handover : Handover that happened between cell(ex: HO from cell A to Cell B)
3. Intra BSC Handover: Handover between cells in same BSC(ex: HO from cell A to Cell B, A and B located in same BSC)
4. Inter BSC Handover:Handover between cells in different BSC(ex: HO cell A to Cell B, A and B located in different BSC)
5. Handover Inter MSC: Handover that happened between cells but different MSC
For the details about handover process,protocol and rule of each handover type, you can refer to your document in your vendor. In this paper I just want to share step by step how to optimize Handover Success Rate to improve your KPI based on what usually I do. Lets follow below step to optimize Handover.
Step 1: Killing Hardware issue
Hardware issue always the first step to check. As I said before in this blog, to improve all KPI Such as CSSR, Drop Call Rate, HOSR, TCH Blocking,etc always to make sure first no hardware issue occurred. Your next action will be useless if hardware issue occurred in your cells. To identify hardware issue in the cells related handover you can generate measurement related Incoming Handover.After generate measurement you will find which cells have high handover failure.
You can check related cells that have high handover failure and low HOSR and troubleshoot one by one. To troubleshoot hardware issue you can collaborate with FM(Field Maintenance) Team. Make sure no TRX faulty or Combiner problem or event connector problem. If the problem suspected only one cell/sector in 1 site, you can try swap each module to other sector and let see if the problem move to other sector.If the problem happened in all sector in 1 site then you can try swap transmission module(GTMU, IDU, ODU) to other site and let see if handover Incoming failure move to other site. Don't forget to check by drive test to make sure no cross feeder problem occurred in the site.
Step 2: 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. Change Frequency of the cells(retune) if you found cells suspected frequency interference.
Step 3: 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
Step 4: 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.
Step 5: 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.
Step 6: 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).You can minimize congestion by adjust half rate setting in the cells(ex:TCHBUSYTHRES and AMRTCHHPRIORLOAD in Huawei) or Traffic sharing to other cells by parameter or physical optimization
Step 7: 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.You can refer to your document in your vendor to change specific parameter but keep in mind the idea is to reduce handover fail to specific cells and increase successful attempt to specific targeted cells.For example if you have cell with low handover Success rate(HOSR) due to high attempt to targeted congestion cell or problematic cells, you need to adjust HO PBGT margin or increase RXlevmin to target cell. This idea is purposed to improve HOSR KPI based on statistic to achieve agreed KPI target.
Thanks for reading my note about Handover in GSM, hope can help your daily optimization activity to improve your GSM handover Success rate.
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