LTE RACH SR formula

4G LTE
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1

Hi Experts,
Is this formula accurate for LTE RACH SR?

([L.RA.Dedicate.HO.Msg3Rcv] + [L.RA.GrpA.ContResolution] + [L.RA.GrpB.ContResolution])
/
([L.RA.Dedicate.HO.Att] + [L.RA.GrpA.Att] + [L.RA.GrpB.Att])

Vendor is Huawei.

2

Yes, correct.

3

Then threshold should be ~95-98%?

4

CB RACH SR =
([L.RA.GrpA.ContResolution] + [L.RA.GrpB.ContResolution])
/
([L.RA.GrpA.Att] + [L.RA.GrpB.Att]) * 100%

CF RACH SR =
[L.RA.Dedicate.HO.Msg3Rcv] / [L.RA.Dedicate.HO.Att] * 100%

RACH SR often not too high as RRC / ERAB SSR.

5

Currently is about 78% but I’m not observing any other negative impacts.
At least on basic KPIs.

6

Increase cellradius to 20 Km on particular cells with low success rate and you will see improvement.
Negative impacts are UE battery draining from Msg1 that do not reach eNodeB so are not counted in your stats.

7

I see.
Can this increase be done even in a dense urban environment?
Increase of cell radius I mean…

8

Yes. If cell is overshooting it doesn’t matter if dense urban or not.
You need a large cellradius for it.
This will boom your Traffic but will also degrade some KPIs like Accessibility and Drop Rate.

9

I got you. Thanks for the tip!

10

Another issue for reduced cellradius is users not having service.
UE camp on the cell due to acceptable RSRP and eligible cell but cannot pass RACH due to cellradius. You should see them failing in stats.

11

RACH issue almost caused by: small cell-radius and weak uplink coverage.

12

And overshooting cells I would say, not enough downtilt.

13

Good point too, actually I had some RSI conflict which caused UE restriction to access.

14

If I’m not wrong, by cell radius you mean PRACH cyclic shift for RACH.

15

No. cellradius is distance based.
Here are failing counters due to cellradius:

  • L.RA.ExceedRadiusContention.Resp Number of times a cell sends Random Access Response messages after contention-based exceeding-cell-radius preamble receptions
  • L.RA.eMTC.ExceedRadiusContention.Att Number of times preambles for contention-based exceeding-cell-radius random access are received from eMTC UEs
  • L.RRC.SetupFail.Rej.ForbidAc Number of times the eNodeB sends RRC Connection Reject messages because of UE access beyond the cell radius
1 Like
16

Ok, any parameter there in system to define cell radius?

17

Is cellbased.

18

Not seen such parameter for Nokia.

19

In Huawei it can be defined through MOD CELL.

20

In my understanding cell radius calculated by link budget only.