(Source: http://rfoptimization-tips.blogspot.com)
This chapter is part of previous post about Common question about RF Optimization.In This post I would like to share about 2G theory and concept that I ask to RF Guys that promoted to become RF Optimization Engineer. May be this post also use full for you especially for RF Engineer who will promoted also to become Optimization guy or just for your reference to improve your knowledge about basic RF Optimization. Here are the question that I made for RF Team and also the Best Answer I got from the Winner.
1. What do you know about interference?
Interference definition from Wikipedia:"interference is a phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude. Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency"
Good Answer from RF Team:
Interference is RF Condition when Primary signal(Carrier) disrupted by other Signal that have same frequency or gap +-1 value of Primary frequency. There are 2 type of Channel interference: Co-channel interference and Adjacent Interference.
- Co-channel Interference is interference caused by the use of the same frequency by a cell carrier and also another cell and its antenna facing each other. Example : Cell A with frequency 642 facing cell B with same frequency 642 too.
- Adjacent Interference is interference when Primary cell interfered by other cells with have frequency value gap +-1 from Primary cell. Example: Cell A with frequency 642 interfered by Cell B with frequency 641 or Frequency C with frequency 643
2. How to improve Voice Quality in 2G?
There area many ways to improve voice quality such as: Clearing frequency interference, Hardware problem solving, transmission problem clearance, TRX Layering Priority and Increase Full rate setting. Buat Answer from RF Team is to the point--->>Increase Full rate Setting(Reduce Half rate) by setting TCHBISYTHRESHOLD and AMRTCHHPRIORLOAD for cells with low TCH Utilization.Of course this is correct answer because we are in Huawei Project :D. Increase Full rate also great impact to reduce drop call rate and improve VQI(Voice Quality Index) in 2G Huawei network
3.What is different between Cell selection/reselection and Handover?
Good Answer from RF team:
- Cell selection is The condition when UE camp on a Cell during start up from Switch Off
- Cell reselection : The condition when UE re-camp to other cell from a cell in Idle Mode because of UE moving
- Handover: The condition when serving cell change from a cell to other cells during connected mode because of UE moving.
4. What do you know about CRO?
Good answer from RF team:
CRO: Cell reselect Offset
Coefficient that functioned to make a cell aggressive serving(dominant) or not dominant. When PT=0,Increasing this value will make serving cells aggressive(increasing traffic).When PT=31,increasing this value will make serving not dominant
5. In order to increase TCH traffic(erl),PT setting to zero(PT=0).What is the setting of CRO? Increase or decrease?
Correct answer: Increase value of CRO(cell reselect offset)
6. Please explain how to do traffic sharing in 2G?
Good answer from RF Team:
- Audit neighbor cells and do physical tuning.
- Make Faster/Easier Handover to neighbor cells for cells with high traffic to the lowest traffic. Ex: decrease value of: HOM(Handover margin),etc
-Make difficult handover from other cells to the highest traffic cells(ex: Increase HOM)
-Idle Setting parameter: Increase value of CRO for low traffic cells(PT=0)
7. What do you know about Power Control in GSM?
Good Answer from RF Team:
Power control is used to save power consume of MS/BTS. Power in MS/BTS will decrease in certain threshold when signal is considered as a Good and increase when considered as a bad.Power control is also used to reduce frequency interference.
8.There are 1 TRX in a cell in Hoping mode that not used power control but use Full power.Which one of TRX?
Correct Answer: TRX BCCH(TRX:0)
9. What is the benefit of Handover?
Good Answer from RF Team: Handover keep a call connected while user moving and continuing conversation between user.Handover also reduce interference and avoid cells overload.
10. What do you know about PBGTMARGIN?
PBGTMARGIN( Power Budget Margin) is Handover margin parameter in adjacent level that used to make faster or delay of handover to keep good mobility.
11. If you found TCH Blocking, what are your action to optimize TCH Blocking rate?
Good Answer from RF Team:
- Check for channel allocation, check SDCCH utilization, if found low SDCCH Utilization(<<60%) then need to convert SDCCH to TCHFR
- Check hardware problem(get measurement TCH availability from statistic), if found degraded the need to escalate hardware problem to Field maintenance Team
- Check Timing advance, if found High TA need to do physical Tuning(down tilt)
- Check Neighbor relation, make sure doesn't missing any relation that causing handover problem and impact to congest on a cell.
- Check Half Rate Parameter (TCHBUSYTHRESHOLD/AMRTCHHPRIORLOAD ex. in Huawei), adjust HR setting if needed--->reduce value of TCHBUSYTHRESHOLD/AMRTCHHPRIORLOAD.
12. How Many MCS used in EDGE ?
Correct Answer: 9 MCS
