- This topic has 17 replies, 1 voice, and was last updated 12 years, 12 months ago by amkam.
5th October 2007 at 11:55 #49343deep_kGuest
i m working with ZTE BSS and Ericsson switch.
i m facing a problem of handover delay described as follows:
I am latched to a particular cell( serving cell ) the Rx level is say : 85 dBm on hopping and the next best neighbour’s Rx lev is 60 to 65 dBm but still the handover is not attempted . As a result of which the quality gets affected. Its not like the handover is not happening ( thoroughly checked it is defined )………… it is happening but with a difference of over 15 dBm ( serving and next best neighobur )
At times the difference in the serving and next best neighbour is around 25 dBm but still the handover doesn’t take place…..i mean to say it happens after the level difference being 25 dBm.
My running parameters for handover control are as follows:
BTS preprocessing : 4
Sample count window : changed from 4 (default value) to 2 ( other systems i think it is Hreq ave )
Weight : 2 ( other systems i think it is Hreq t )
N(n) values = 3
P(p) values = 2
Handover margin : 6dBm
Handover Access minimum on power level : changed from -80 dBm (default value) to -95 dBm
Handover Access minimum on power budget level : changed from -80dBm (defalut value ) to -88dBm
after doing the above changes still the handovers are happening with a difference of over 15 to 18 dbm (serving and next best neighbour )
this problem is not in a particular site ….it is in whole network of around 50 sites
I don’t have DL pwr control in my network …….only UL pwr control
any suggestions will be ( highly )appreciated
rgrds5th October 2007 at 12:01 #49344deep_kGuest
Is it some parameter problem ?
Is it a software problem in BSC?
any suggestions ………..??
rgrds5th October 2007 at 16:11 #49345IndranilGuest
Pls give ur valuable consent regarding the problem6th October 2007 at 05:25 #49346asoGuest
dear deep K
did you check the priority for Handover.
thanks9th October 2007 at 12:55 #49347Gito PrastomoGuest
Hi,have you checked the hcs parameter for each cells and neighbour?Please check the hcs/priority layer.9th October 2007 at 17:51 #49348ArpanGuest
Make preprocessing 0 and then try…18th October 2007 at 04:57 #49349deep_kGuest
apologies to be late !
the handover priority is the standard one ,,,,, i.e
1. quality / interference
2. Rx level
3. TA ( distance )
4. PBGT handover
Can I change the priority ….. I don’t know ??….. pls suggest
i changed the bts preprocessing from 4 to 2 ( with sample count being 2 only )…….. there was an improvment in the handover but the no: of handovers increased by 40 to 50 percent ….. and the overall Handover success rate got degraded.
if changed to 0 it will create havoc ….in the field .
i will check the hcs parameter ..
hcs means ( hierarchy cell structure …… i suppose and the corresponding priority )
i would be thankful if u could pls elaborate it a little bit more….. like how does it affect the network…. i don’t have dual band network…..it is only 900 GSM
rgrds18th October 2007 at 05:51 #49350asoGuest
I don’t mean priority that you mentioned these are the cause for Handover which i meant by Handover priority there is feature that make the handover for cell in lower which mean if there are three cells , normally the priority is the same for all but when I want to make handover harder for one of them i will change the priority to lower then the handover for the harder cell will be executed and this feature in my network is cell wise18th October 2007 at 11:32 #49351RamiGuest
Check HCS and PBGT HO.
Good Luck18th October 2007 at 18:59 #49352PixGuest
sorry for my late reply !! i didn’t see this thread. I hope Deep K is still around ? The problem is interesting.
In my opinion, your parameters should be alright, if each parameter looks like it is around the default value. The only why the HO is not taking place might be because the PBGT HO is not allowed :
what is the frequency band of the serving and target cells ?
what is the cell type / layer of serving and target ?
other possibility : the target cells are congested (check the QoS Stats : incoming HO congestion). It seems highly improbable if that happen on 50 cells ! 🙂
finally, still about the traffic : maybe the target cell is in “HIGH” load, while the serving cell is in “LOW” load. That might delay the execution of the PBGT HO by 10dB.
Ok, i think that’s about it. All other problems might be due to software issues : are the cells in same BSC, same LAC ?
To pursue the investigation, I propose you to do something during drive-tests : try to make HO from cell A to cell B (drive slowly, in order to give time to the BSC to make the averaging) : at what rxlev difference does it happen ?
Then, drive in reverse gear (:)) from cell B to cell A. When is the HO occuring ?
Ho… check also your PBGT equation. It might take other parameters into account, such as the MS TX POWER MAX, the BTS TX POWER MAX, or some PING PONG FEATURE. As said earlier, check the impact of traffic load, it might add some extra-margins to the HO_MARGIN.
Good luck, and again, sorry for the late reply.
Regards,24th October 2007 at 11:31 #49353deep_kGuest
i was waiting for u
i am always around here…..
i will check up with ur suggestions and revert back.
rgrds24th October 2007 at 15:03 #49354pixGuest
i’m glad you were still around… if you have time, answer my questions (especially the cell layers and cell types).
Regards,26th October 2007 at 07:02 #49355deep_kGuest
how r u?
here I am !
to dear aso and rami as well:
power budget handovers are allowed only
i have my network in GSM 900 only. There is no other band. But a few sites are co- located with CDMA sites. I know that CDMA downlink will interfere with GSM uplink , but ….. could this be the sole reason for the delay . The delay happens even when the site is not co-located with the CDMA site.
Cell type is : macro-cellular for all the sites.
Cell layer for serving and target both : Same layer of the home cell
( the other options in the NCellLayer are : upper layer of home cell and lower layer of home cell and the last one is udefined )
You are quite correct about the Qos that…. may be the target cell is highly congested or loaded but it is not a sector specifc problem …….. its random and occurs anywhere .
the drive test part is yet to be checked with your suggestion . I will revert back after i get it done.
i have a doubt about the corresponding power control parameters’ settings …….. if u wanna have a look i will send them in next thread.
rgrds26th October 2007 at 08:00 #49356pixGuest
ok, send all the parameters that are used in your power budget equation, i can have a look.
can you also write down the equation ?
in my vendor’s system :
AV_RXLEV_NCELL(n) – AV_RXLEV_PBGT_HO
– (BS_TXPWR_MAX – AV_BS_TXPWR_HO)
– (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)
– PING_PONG_MARGIN(n, call_ref)
with window level averaging: A_PBGT_HO
and then the PBGT HO is detected if :
PBGT(n) > HO _MARGIN(0,n) + OFFSET_HO_MARGIN_INNER
and AV_RXLEV_PBGT_HO < RXLEV_LIMIT_PBGT_HO and EN_PBGT_HO = ENABLED That's a lot of parameters to check...5th November 2007 at 14:27 #49357deep_kGuest
sorry , i couldn’t get the equation u asked for ….!
instead we did some power control parameter changes namely :
1. In power survey parameter:
sample count for Pc UL lev , Pc DL lev, Pc UL qual , Pc DL qual was changed from 6 to 4 and the corresponding weight is 2 only (pervious value )
2.Power adjustment threshold parameter
The N(n) values changed from 4 to 3 adn P(n)values from 3 to 2
the following thresholds were changed :
increase UL level 22 to 24
increase DL level 26 to 28
decrease UL level 30 to 34
decrease DL level 34 to 38
increase UL qual 2 to 3
increase DL qual 2 to 3
decrease UL qual 0 to 1
decrease DL qual 0 to 1
this increase and decrease is for Power inc or dec
3. In handover control parameters the following thresholds were changed :
HO UL level 15 to 22
HO Dl level 15 to 25
HO UL qual 4 to 3
HO DL qual 4 to 3
In addition to it we enabled on fast averaging parameter .
Now there is an improvement in the handover delay . Now there is no drag as earlier .