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Hi All,
We have implemented Synthesized Freq Hopping in our Nokia GSM network, but the quality on hopping TRXs has really degraded after activating hopping.
Our plan is:
Freq 1-17 BCCH
18 Guard Band
19-24 MA ListHSN for every site is unique, and MAIOs are 0,2,4 for sectors one, two and three respectively.
MAIO Step is 1 for all cells.All cells have two 900 TRXs.
Could the degradation be due to some feature which has to be implemented? Or some feature which needs to be activated? I remember implementing exactly the same plan in another network once, and it worked perfectly fine.
Please help!!
hi,
dangerous minds,
your MA list = 6 frequencies ??
As you have read in the several posts about SFH, SFH must obey a rule :
# TRX / # freq < 12% In your case : # TRX / 6 < 12% how many "hopping" trx per cell do you have ? Based on your MAIO planning, I'd say 3 hopping TRX per cell. 3/6 = 50% You are way higher than the threshold, and you will therefore face awfully poor KPIs due to terrible interference. regards pixHi DangerousMinds,
before BB was used? or non hoping, also what is the configuration this is crutial ,
just for information, keep in mind in BB if u are using bcch trx hopping and u convert to sfh, in this case bcch frequency becomes critical u need a good bcch plan than.
hi,
dangerous minds,
1, Pls try to edit your current Freq. Plan carefully(as brother said).
2,before implementing the SFH, you have to make sure that the azimuths of all sites are unique(standard) and it is a must for implementing SFH.
3,you have to make sure that there is no overshooting.
4, try to balance your available freq. band between bcch and hopping channels(MA list).thank you
MFHi,
Thanks for your inputs!
Previously there was no hopping in the network. Sites are on grid. Configurations are 2/2/2 900 TRXs per site, which means that we have 1 BCCH and 1 hopping TRX per cell.
Should we increase the MA List to achieve better quality? How many frequencies ideally?
We have given adjacent HSNs (HSN=10 for one site, HSN=11 for neighboring site), could that be an issue?
dangerous minds,
One hopping TRX per cell would ideally require 10 frequencies in the MA-List.
In the worst case, 9 frequencies, with very agressive downtilts.
6 frequencies are way too low, unless you push voice traffic on the BCCH TRX preferentially, so that you ensure that “hopping” TRXs are never all loaded at the same time (within a certain area). Difficult to ensure that, isn’t it ? So go for MA list = 10 frequencies (or even 11 if you can !).
Adjacent HSN are not an issue. Just ensure your MAIO in the hopping TRXs of one BTS are set to 0, 2, 4.
Thanks pix,
Yeah I guess you are right, I will re implement the whole thingy.
But here’s a dilemma: we implemented hopping on 1800 band also..
One Hopping List, 36 frequencies,
MAIOs 0,8,16 for three sectors
Different HSN for every site..And KPIs still went bad !!
I was thinking that with this huge band, we’d see improvement but there was degradation. Not as much as 900, but still everything went down, instead of going up…
hi dangerous minds,
the 1800 trx should not be interfered… could you share the values of the KPIs ? (Call Drop Rate, SDCCH Drop Rate, HO Quality %, HO Interference %, TCH Assignment Success Rate)
(before and after activation)
Before SFH1x1, you were doing BBH?
Are you pushing the TCH allocation on the BCCH TRX or on the hopping TRXs ?
What is the congestion rate at busy hour in your area ?
I hesitate between an interference problem (too much traffic, not enough downtilt, poor terrain conditions) or a parameter problem (wrong tch allocation, handovers are not pushing traffic where they should, MS ends up in a cell with low coverage while other cells are providing better coverage).
Because you have a dual band network, the parameter mistake could easily happens, especially with low capacity cells. You must manage “nominal” situations, which already rather difficult, but also “busy hour” situation, by using advanced traffic sharing algorithms (FDR, traffic ho, etc).
Your answers to my questions above might help 🙂
Regards
pixThanks Pix,
There was no major degradation in KPIs DCR, SD Drop etc.
Only the UL/DL Quality HO%, which increased from about 5% to 9%Also, hopping was deactivated before this change.
No priority has been given in terms of shifting traffic to hopping or nonhopping trxs, but generally emphasis is on pushing traffic on 1800, which is now all hopping.Congestion rate is around 3% at Busy Hour.
I am looking into the parameters, I think i am going to go ahead with three hopping lists (1 x 3) instead of one on the 1800 (1 x 1), and see the effect.
Minds,
No major degradation = no degradation at all ?
Only Qual HO are degraded ?
You know that when you enable frequency hopping, you must also tune your HO QUALITY threshold by “+1”.
Instead of 4, you should use 5.In ALU system, it is done automatically : an offset “Offset_Hopping_HO” is added to both thresholds “L_RXQUAL_DL_H” & “L_RXQUAL_UL_H”
Maybe in your system, you should do it manually.The TRX1800 are all hopping..? there is no BCCH in 1800 ? So that’s the inner zone of a multiband cell ? (trx900 = outer zone, trx1800 = inner zone ?)
regards,
pixInteresting!
Yes, by degradation I mean you can see maybe a slight dip in HOSR, CSSR etc but thats not very noticeable. But when you look at Qual HO%, you see a clear degradation. I think we will set this Quality HO threshold ourselves (from present 4 to 5)
All 36 frequencies on 1800 are hopping. Different HSN for different sites, and MAIOs 0,8,16 yet even C/I from the drive test has gone bad …
I am beginning to think frequency hopping is not that good a technique after all!
Hi,
What about Intra Cell Handover. Is it activated? Could that be the reason for degrading Qual HO and increasing congestion? Just checking, as I know Intra Cell HO is not suitable in hopping mode.
Regards,
RexDear DangerousMinds,
Why dont you try 1×3 on 1800? I think it is bound to give you some improvement if you use 12 freq per sector. (Worked on 2 networks with 11 freq. per sector and KPIs were fine). Let us know your future observations regarding parametric check too.
Regards
Hi,
Yes, Intracell HO is enabled.Should I disable it? You mean intracell HO between 900 and 1800, right? Because there is this AMR Intracell HO also.
Also, yes i have gone ahead with 3 Hopping lists on 1800, 12 per sector, and awaiting results. I have also increased the 900 hoppin list from 6 to 9.
With this configuration, I think I should also set the preference for call setup to hopping TRX?
Is there any other hopping plan that I can try?
Thanks/
Hi DangerousMinds,
disable Intracell Ho first for one-two days and see what happens.
Regards,
Rex
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