GMS RACH Failure in E******* system

[tokybaz]

Hi all.

How to improve GSM RACH Failure in E******* system?

I may activate xrange even the traffic is not so far, but activating XRANGE damages capacity...

Could you please advise? Thks.

[Ghost78]

Hi;

activating xrange feature, will recover the subscribers droped due exessive timing advance, I don't think this will help to improve RACH failures, please, can you tell me how many timeslots are configured as BCCH, what is the value of parameters MAXRET, AGBLK, and TX.

B.R

[tokybaz]

Usually, XRANGE works fine, but we have problem on capacity.

Only 1 timeslot is configured as BCCH.
MAXRET = 4, AGBLK = 1 and TX = 32.

Thanks in advance for your help.

[Ghost78]

ok;

the configuration is fine, but tell me now about the following points, after that we can tune some parameters:
- site rural or urban
- ACCMIN parameter value.
- transmission over MW links or other.
- from MRR what is the distribution of traffic, what is the percentage of samples for TA>55.
- is there any site can share traffic with this cell, means existance of sites in the area served by this cell.

B.R

[tokybaz]

ok, thks.

- Site is rural
- ACCMIN = 104
- Transmission is over MW link
- TA > 55 is less than 0.5%
- There is no site to share traffic with.

Could you find what to do on those sites ? Thks.

[Ghost78]

Hi;

Since it's rural site, we can not modify neither ACCMIN nor CRO; I suggest to reduce TX to 10; RACH restransmission delay will be shorter, also, try to configure one additional CCCH for this cell.

Bytheway, is this cell situated in the middle between two LACs.

B.R

[tokybaz]

Hi,

Thks for your suggestion. I'm going to test TX and CCCH.

This cell is also situated in the middle between two LACs.

BR.

[Ghost78]

Ok;

if it is border cell, increase CRH parameter, you can put it 10, this will decrease the reselection from the neighbour LAC cells, hence decreasing in term of Location updates.

B.R

[tokybaz]

Hi Ghost78,

After setting TX and CCCH as you suggested, I still have bad RACH Success rate (with the same trend hourly).
What do you propose for me?

BR.

[oswe]

im not so keen on E--- system but I saw an MRR report which can show you UL/DL imbalance. i didnt have time to compare with other cells but if you check perhaps this can explain your failure. thanks god our customer doesnt involve RACH kpis´s they are awful.