DCR analysis

RAN
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1

Hello experts.
I’m new in the industry. I need your support please. I’m facing issues with some 2G cells and 3G cells experiencing a high drop call rate. On what should I base myself to effectively carry out the root cause analysis such that it should meet the threshold?

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as 1st step - make sure all necessary neighbours defined, and also having correct parameters.
2nd - check Timing Advance KPIs;
3rd - check parameters related to handover…

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This is for LTE, but may help:

A call drop in LTE means that a user’s ongoing session is dropped requiring the user to initiate a new connection to resume services.

Causes:
Radio Induced Drops.
MME Induced Drops.

  1. Radio Induced Call Drops.
  • DL RLC Retransmissions.
  • Optimization ( Due to Quality and Coverage).
  • Hanover Execution Failure and Optimization.
  • Drop due to No Response.
  1. MME Induced Drops:
  • Uplink RLC Retransmission Issue.
  • Optimization.
  • N310 PDCCH Decoding Failures. (N310 indicates an interval of 200 PDCCH decoding failures).
  • Handover Drop due to MME.

How Do You Calculate Call Drop Rate.?

It is Possible by Drive Test.

  1. Call drop rate = Number of call drop times/Number of call setup success times.
  2. Number of call setup success times + 1:
    After the Alerting message is received.

What is Call Drop Problem?

If your cell phone has a damaged antenna, you may experience poor cell phone Reception, Data loss and Frequent dropped calls, Radio Coverage.

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In the core network, 2G/3G are using circuit switch method, but 4G above are using packet switch method. 2G/3G are using hard handover, 4G above are using soft handover. Thus their MME functions are very different. DCR debugging in MAC above layer shall be very different.

In radio access layer (PHY+MAC), they are also using very different technologies. In 2G/3G, for TDD, timing advance parameter is very important. But for FDD in particular with CDMA technologies, timing advance is not so important, while the adjacent cell/user interference, near far effect (power control) is very main concern. Moreover, in 4g LTE, there are more mechanism to handle VoLTE optimization to tackle DCR, for example, TTI bundling, RLC segmentation, adaptive modulation and coding plus HARQ.

In a word, 2G/3G and 4G’s DCR handling should be very different and require very different domain knowledge.

5

As you mention 2G and 3G, it is important to check also power and tilt be tune specially on 2G with common BCCH feature.
You can check that there is no huge diffrence on master and slave band to avoid drop and asfr.
Also make sure that you are not restricting UE power!

6

For 2G you need to check the alarms, Interference, HSN, MAIO,TA, neighbors etc and the cause of call drop;
Either it is due to radio link failure, LAPD failure or HO failure. Then take necessary actions to resolve the DCR.

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