- This topic has 14 replies, 1 voice, and was last updated 5 years, 6 months ago by Neeraj.
3rd April 2008 at 07:14 #51748trucduGuest
I want to know, what are the reasons
of Random Access Failure. I have cell near the sea and Cssr values are very bad and RACH Failure values are very high. What can I do? Thanks for helping.4th April 2008 at 13:31 #51749pixGuest
CSSR values should not be impacted by RACH failures (depending on which formula you use for CSSR)
RACH failure might be due to the use of ABIS over SATELLITE, is it your case ?
otherwise, you should check BCCH/BSIC couples, and also TCH/BSIC couples
finally, it might be due to electromagnetic interference : are there military radars around, or military ships ? what about alarm systems ?
the only way to know : perform an ABIS trace on this BTS.
pix5th April 2008 at 10:20 #51750IbrahimGuest
Basically, there are two CSSR’s formula:
1. Radio CSSR that takes only TCH & SDCCH resources under consideration.
2. CSSR_Immediate that is the multiplication of immediate assignment by Radio CSSR. So, RACH failuer would not have an impact on the 1st one, but it does for the 2nd one.
Ibrahim16th June 2008 at 14:52 #51751MKTGuest
RACH failure might be due to the use of ABIS over SATELLITE
How does it goes?
Can you explain it pix.
Regards16th June 2008 at 16:09 #51752pixGuest
for alcatel vendor, the access failure are due to abis satellite (and not “might be due”)
for other vendors, i don’t know.
it is due to delay : the 1st channel request is answered by an immediate assigmnment from the BTS, but in the meanwhile the MS has already requested a 2nd channel request.
The 1st Channel Req is answered (no ffailure), but the second is NOT answered –> failure
for other vendor i don’t know how it works, possibly they will not “count” this kind of failures, even if they occur.
pix16th June 2008 at 20:41 #51753peyoGuest
is your cssr formula like:
rach_success_rate * tch_assignment_success_rate* (1-sdcch_drop)*100
do you have access to Maximum value for Timing advance ? if yes what is the value?16th June 2008 at 21:35 #51754pixGuest
maximum value of timing advance is 64 (35km).17th June 2008 at 06:51 #51755MKTGuest
MS sends an access request to BTS over RACH. BTS receives that request. And further action starts….
BTS and BSC will now talk and then..
IMM_ASS will be send by the BTS to MS over AGCH.
You mean to say that time between sending the RACH and getting IMM_ASS is more then the repeat request time for RACH. And hence the MS sends the second request.
I have one doubt in this….
1. Can’t we change/modify the time between the successive RACH requests. If yes, then case is over as per the theory you gave for RACH failure.
2. If MS is sending a RACH request and BTS is easily receiving that request then,
how can you say that it is a case of request failure or RACH failure. The failure actually is in the assignment. So don’t you think that we should term this as AGCH failure?17th June 2008 at 16:07 #51756pixGuest
1/ the MS timer is internal, it cannot be set at BSS level.
2/ a channel request shall be answered with an Imm Assignment. The 2nd ch req. is actually answered with an imm assignment (sorry, i didn’t make that clear in my previous reply)
But this I.A. is not received by the MS (MS is already on a SDCCH).
It is therefore counted as a SDCCH assignment failure due to radio problems, in alcatel systems. In other systems, i don’t know if it is counted, and if it is, i don’t know how it is counted.18th June 2008 at 05:27 #51757MKTGuest
So, we can say that
due to delay on A-bis, we can have
SDCCH ASSIGNMENT FAILUE.
I don’t think that we have the RACH FAILURE counter incremented by this.
Regards..18th June 2008 at 07:56 #51758pixGuest
i’m talking about alcat. systems : we don’t have RACH failure indicators. Only sdcch assign failure.21st February 2010 at 13:34 #51759LvinGuest
i have some cell have low random access success rate between(20 to 60)% it must over (98 %)our system ericsson and two bands (900 and 1800 )MHz.
i dont know what is the problem!
i chnaged the frequencies and BSIC.
please help me to solve them
thank you very much…22nd February 2010 at 11:17 #51760SHELDONGuest
Check your MAXTA and TALIM settings. If they’re too low, you can have RACH failures. Also check for faulty TRXs.
Matthew25th February 2010 at 12:56 #51761LvinGuest
according to what i change the MAXRET , TALIM and ACCMIN?
are Urban and city area the same?how much the range of these parameters for urban and city center?
because i checked BSIC and BCCH for the they are correct.
thank you very much for reply
our system ericsson-900 and 1800 GSM bands.2nd September 2015 at 13:45 #51762NeerajGuest
i am getting #DIV/0 in SD DROP & Random Access Success Rate.
Can you have any solution or suggestion