Common question about RF Optimization

Hi RF engineer,

This month I was assigned by Manager to make some question for RF Team related Job position upgrade from RF to Optimization Engineer. Here I would like to share some question test that I made for RF Team  just for your reference to expand your Optimization knowledge.

2G DT Analysis Part:
1. When you perform drive test in the field then you found dropped Call suddenly. What are the root cause possibility of dropped call and how to solve it?

Good Answer

• Root Cause of Dropped Call:

1. Hardware Faulty
2. Frequency Interference(Co-channel or Adjacent)
3. Neighbor relation problem(missing Neighbor)
4. Low Signal Strength
5. Failed during HO process

• Drop call solution 

1. Hardware Troubleshooting
2. Clearing Frequency Interference
3. Fix Missing Neighbor
4. Antenna Tuning(Physical Optimization)
5. Change Parameter(HO Parameter, RLT,Timer,etc)

2. When you analyze log file you found too many handover failure. What is the root cause of handover failure and what is your action to solve handover failure?

Good Answer

• Root Cause and solution to solve handover failure:

1. TRX module faulty on target cells----> Need to fix TRX Module
2. Missing neighbor---> Fix neighbor relation
3. Congestion on target cells----> Upgrade TRX or HR threshold setting on target cell or Change HO parameter threshold to target cell
4. Frequency interference between source and target cells---->Change Frequency 
5. Far distance between cells----> Antenna tilt optimization or Propose new site to improve coverage

3. When perform Monthly drive test you found too much bad quality(RxQual>>5).  What is the root cause and solution to improve bad quality?

Good Answer

• Root Cause and solution to improve Bad Quality:

1. Interference problem(Co-channel/adjacent/external)----> Fix Interference problem by change frequency(BCCH/TCH) and find out source of external interference then report to Frequency Department regulation(DEPKOMINFO in Indonesia).
2. Hardware problem such as Bad TRX module, Combiner or Crossfeeder/installation problem------>> Fix hardware problem by troubleshooting proposal to FLM Team
3. Bad Level and low signal strength----> Change Antenna Tilt or propose new site to improve coverage

4. When you are positioned as Optimization Engineer, there are complain about Can't make a call. What is the root cause of Can't make outgoing call and what is the solution?

Good Answer

• Root Cause and solution of complain Can't make outgoing call

1. LAC CI didn't yet registered on Core side----->Check and register LAC CI on Core.
2. SDCCH Blocking on the cell-------->Add SD channel
3. Hardware problem(ex: TRX Module faulty or Combiner problem)------> Fix hardware problem
4. Low Coverage--------> Change Antenna tilt or propose new site to improve coverage.

5. What is the different of RXLevel, RXQual and SQI?

Good Answer

• RXLevel: Receive signal level by MS in dBm, where athe lowest value mean the lowest Level, the greatest value means the greatest level
• RXQual: Receive quality of signal by MS from the BTS which have rage from 0-7. The lowest value mean the best quality, the highest value mean the lowest Quality.
• SQI: Speech Quality index, Quality of Speech during dedicated call which range from -20 to 30. The highest value mean the best Quality of speech, The lowest value mean the bad one

6. During perform drive test you found low throughput. What is root cause of low throughput?

Good Answer
The root cause of low throughput:

• Interference problem(bad C/I)---> Clear frequency interference
• High Traffic------> Traffic sharing or change antenna tilt configuration
• Transmission capacity limitation---------> Upgrade Transmission(increase ABIS Capacity)
• Resource blocking(TRX Capacity issue)-------->Upgrade TRX

7. What is mean and root cause of Low signal strength? give some solution
Good Answer
Low signal strength mean low of the received signal level  by MS
Root cause and Solution:

• Hardware Faulty-------> Fix hardware issue
• Cell down-------->Fix cell down and make it up
• Output power problem---> Check setting of TRX Power and fix it.
• Antenna direction problem------->Change Antenna direction
• Over tilt of Antenna configuration-------> Change Antenna tilt(Up tilt)
• Missing neighbor relation-------> Fix missing neighbor
• Site location-----> Adjust Antenna tilt or propose new site to improve Coverage thus improve signal strength.

8. What is the trigger of  Handover?
Good Answer
Trigger of Handover: Level, Quality, Power Budget , Timing Advance.

9. What is the root cause and solution of Call block?
Good Answer
The root cause and solution of Call Block:

• SDCCH Blocking-----> Add SD channel
• TCH Blocking--------> Setting HR threshold, Upgrade TRX,Channel redimensioning
• Hardware faulty-------> Fix hardware issue
• High Traffic and congestion---->Review setting of HR threshold, Upgrade TRX or Traffic sharing
• Low RX Level--------> Improve Coverage by change antenna tilt or propose new site

2G Theory and Concept

You might also Need to know:
- TCH Block Rate Optimization Tips in Huawei GSM
- 2G Voice Quality improvement by TRX Layering Priority
- TBF Drop Improvement tips in Huawei GSM
- GPRS Packet Data Access Rate(PDASR) Improvement in Huawei GSM