Drop Call Rate Optimization, How to identify and finding root cause for Optimization solution on GSM and UMTS Network

Drop call rate is Main KPI that very important in RF Optimization. Drop Call  indicate how connection between Handset and Network become discontinue and causing bad experiences on user experiences because the call is release suddenly. In this paper I will share everything I know related drop call rate both on GSM and UMTS Network. Based on my experience the root cause of Drop Call Rate can be listed as follow:
- Hardware Problem.
This problem is very critical related to all KPI including Drop Call rate. If the problem is coming from hardware, percentage of drop call rate would be very high(usually more than 1 %) and you have to replace bad module with good module. For example in GSM Network you have to check and make sure TRX module such as GRFU/CU or Combiner/Duamco working properly. To make sure the problem was coming from hardware or bad module, you can identify by trying Swap module first. For example: if the problem high drop call rate is occurred in sector-1, you can swap TRX Module sector-1 to sector-2 and Combiner from sector-1 to sector-3. If the problem move to other sector then indicate the problem is coming from that module. For example in the above case if the problem move to sector-2, so the problem is TRX Module(GRFU/CU) or if the problem move to sector-3 then the problem should be Combiner/Duamco. In UMTS Network also same, if the problem is coming from hardware then you have to identify what module the problem is. You can identify the problem by swap WRFU Module. If the problem high drop call happened in one site/NodeB, you can try swap GTMU(Transmission module). Beside defect module the problem can be occurred due to wrong or bad installation such as Semirigid connection, Cross feeder problem or etc(especially for new site)
- Frequency Interference. 
Frequency interference is include in problem that can impact to high drop call rate because the Noise(Interference Signal) is very high and affecting to Carrier( primary Signal) and also affect to bad vice quality. To overcome the problem in GSM network you have to re-tune/ change Frequency that suspected Interference especially on BCCH Frequency for RF Hoping cells. As we know in GSM there area 2 type of Frequency Interference that called Co-Channel Interference(Same Frequency) and Adjacent Interference( Difference 1 Frequency  channel). Sample for Co-channel Frequency : Frequency Cell A=  Cell B = 670 with close location of cell each other. Sample for Adjacent Interference : Frequency Cell A=670 and Cell B=671 or 669 and the position of cells is close each of other. The solution in GSM network for interference is retune or change Frequency for one of the cells to avoid interference. in UMTS network the frequency interference also can occurred and indicated by bad Ec/No(Quality).Different with GSM, to overcome Interference in UMTS network is commonly solved by Change Antenna Tilt or reduce CPICH Power to avoid Coverage overlap. The other solution to reduce Drop call rate in UMTS Network is by making fast IRAT handover to GSM Network. In Huawei implement by Changing Parameter IRAT Handover 2D/2F.
- Overshooting Cells
Overshooting cell can be the one that causing high drop call rate in the network.To overcome this issue you have to change tilt configuration of Antenna, for example change Mechanical Tilt  from 0 to 2. Overshoot is common problem for both GSM and UMTS that causing drop call due to bad RX level in the edge of Coverage or bad RSCP and Ec/No in UMTS Network. The solution is same for both GSM and UMTS that is change Antenna configuration tilt/Down tilt.
- Missing neighbor.
Missing neighbor also will causing High drop call rate in your network. You have to check and make sure relation of the cells is complete and  no missing neighbor. The solution is same for both GSM and UMTS, you have to make sure no missing neighbor to avoid high drop call rate.
- Wrong Parameter Configuration
Wrong parameter configuration will causing high drop call rate in your network. Make sure to check all parameter and configure accordingly.In GSM there is parameter related drop call rate KPI such as : RLT(Radio Link Timeout), You can set by increase RLT to reduce drop call but will affect to Customer Experiences because release call is too long even when radio environment is poor and conditionally should be released. The other solution to reduce drop call related parameter is by adjust HO Parameter to make fast handover to a good cells in surrounding closest cells such as adjust PBGT, RXLEVMIN to target Cells. Making fast HO to a good cells can be implemented on both GSM and UMTS Network. You have to find out parameter related Radio Link and HO parameter in your vendor you are working for because the Parameter name would be different but in same Idea That is Radio Link Time out and Handover Parameter.
- Power or Transmission Problem
Power problem can make high drop call rate in the network. You have to make sure no power problem by check the alarm and Cell Availability.If the problem occurred you need to follow up the problem to Field Maintenance Team to fix it.
Transmission problem also can make drop call rate very high and affecting to your KPI. You need to check alarm related transmission and make sure also cell availability is stable. If you found transmission problem the you have to follow up the problem to Transmission Team to check and fix it.
- Contour Problem(Hilly/Rural Contour)
Bad contour can be the one that causing high drop call rate especially if your network in Hilly or Rural area. Check and identify your cells by drive test to make sure the problem is causing by contour or check the coverage by Simulation. If the problem is bad contour then you have to  adjust tilt of the cell or re-azimuth make sure coverage continuous.
- Discontinuous Coverage
If your coverage discontinue due to lack of site then you need to propose new site to your operator. Discontinue coverage also can occurred due to wrong antenna configuration such as over tilt. You need to check tilt configuration of the antenna and make sure no over tilt that causing coverage become discontinue.

Thanks for visiting my blog and hope can help your network problem related Drop Call Rate Optimization on GSM and UMTS Network

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