P-CPICH and overshooting

[sakibd2k]

Hi all,

I want to clear some basic concept.
What is Pilot channel and how does cell is overshooting?
In response of the answer i will ask question after that.

Thanks

[riverstreamer]

Two docs:
CPICH Power Optimization (E*******)
A thesis on UMTS Dimensioning

[Blacktiger]

@riverstreamer : Hey Can You Upload to somewhere else.

Thanks in Advance.

[gc_sw]

common pilot channel power is a downlink channel broadcast by node b's with constant power and of a known bit sequence.

[sakibd2k]

HI Riverstreamer,

I actually unable to download those doc as i dont have enough
previlege and i get this message

you do not have permission to access this page. This could be due to one of several reasons:

Your user account may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.


SO what will i do to read those doc?

thanks

[coursekec]

Another great document on CPICH from E//

[sakibd2k]

" common pilot channel power is a downlink channel broadcast by node b's with constant power and of a known bit sequence"
i understand it thanks.
@gc_sw: So how will pilot pollution occur?
Is there any coverage hole thats the pollution? is that because of power is not uniform over the coverage area?

I cannot download the document yet untill i post enough . SO could have read the attached doc.

[sakibd2k]

hi ,

I just got pilot pollution related answer.
Pilot pollution is a type of co-channel interference in CDMA systems caused when the pilot code from a distant cell or base station is powerful enough to create an interference problem.

So why is that pollution is only with CDMA system?does not happen in GSM?

Thanks

[s52d]

hi ,

I just got pilot pollution related answer.
Pilot pollution is a type of co-channel interference in CDMA systems caused when the pilot code from a distant cell or base station is powerful enough to create an interference problem.

So why is that pollution is only with CDMA system?does not happen in GSM?

Thanks

Pilot pollution is if you have several (over 3) cells with simmilar signal strength - as a consequence, you have bad EcNo (your own best cell is weak - so all traffic on other cells are interferring), and a lot of unnecessary events when terminal tries to get 3 best cells into active set. It is quite likely you run out of power (drop) or you fail to change cells (drop) or your EcNo is too low (move to GSM) even if RSCP is good.

In ideal world, there is never more than 3 cells ;-). Overshooting means cell creates interference
where it should not. In order to detect, we do drive tests with PN scanner and do our analyzes.


In BSS, we try to separate BCCH on different frequencies, thus there is no interference.
Anyhow, yes we have BCCH pollution. If there are many cells, all with equall signal strength,
terminal can not pick best one - and it is quite likely to find some undefined neighbor relation and drop ;-).

Take your test phone to some high building, where you can see many BS antennas and there is no clear best server, and enjoy plenty of handovers and drops.

Worst case: take your TEMS into balloon and try making calls 800 m above big city.
You are out of main lobe for antennas close, in main lobe for far away... Pure fun!

Not many networks are optimized for interference free operation on 800 m high, so balloon pilots
prefer to use operators with low traffic and low number of base stations ;-)

BR
s52d

[banisha]

Guys, just clarify something for me. To find areas of pilot pollution I look how many scrambling codes are found in 5dB from top one Ec or from top one Ec/Io scrambling code?
So do I use Ec or Ec/Io to identify areas of pollution?

[s52d]

Guys, just clarify something for me. To find areas of pilot pollution I look how many scrambling codes are found in 5dB from top one Ec or from top one Ec/Io scrambling code?
So do I use Ec or Ec/Io to identify areas of pollution?

If we ignore slight difference in decoding/filtering, we can assume Io is same for all pilots.
Thus, you shall get same results. And indeed, in empty network they are same.

On the other hand, while Ec is constant for all pilots, Io is NOT: it depends on traffic.

It makes clear story for me.

BR
s52d

[banisha]

So if I have more than 3 SC in (Top1 Ec - 5 dB) range (including the top1), I have an area with pilot pollution?
That's how i thought, just wanted to check.
Thank you!

[cococrunch]

Hi Guys,

Do you have the script in Actix for filtering Pilot Pollution Plot? Thanks.

[intros]

Hello,
for more than 3 Sc in active set with similar levels will degrade your quality in that area. try electric tilt for distant servers from active set than reduce power.
You should remain with 2 SC in active set, and one of them should be best server. Clearing an area of pilot pollution is a tough task but not impossible!


So if I have more than 3 SC in (Top1 Ec - 5 dB) range (including the top1), I have an area with pilot pollution?
That's how i thought, just wanted to check.
Thank you!

[hatemarslan]

hello
pilot pollution may you have one active set and detected neighbours with good rscp
solution : define this neighbours

[mrevans]

hey there, I have a question. How many of you play with the CPICH power when doing the Initial tunning?
I know that a good initial tunning you let the CPICH power and play with the electrical or mechanical downtilts and just as a last resource and in a very polluted and important area you might think of downgrade the cpich of some neighbors to have a dominant in that area. How often you play with this little dirty trick?

[s52d]

hey there, I have a question. How many of you play with the CPICH power when doing the Initial tunning?
I know that a good initial tunning you let the CPICH power and play with the electrical or mechanical downtilts and just as a last resource and in a very polluted and important area you might think of downgrade the cpich of some neighbors to have a dominant in that area. How often you play with this little dirty trick?

Dirty trick?
Yes, pilot power is one of the first parameters to touch a bit.

But, you do not want to go too far, just +/- 2dB: otherwise you might make too big difference
between UL and DL soft handover region.

BR
s52d

[mrevans]

thank you, we hired the initial tunning service to 3 vendors and they have very different styles to optimize the network. Some others says that the CPICH is the last thing you touch to optimize the network. Anyways i don't think one is wrong or right and sorry about the dirty trick (just a thought) :P.
The whole point is that now we have to make the initial tunning and i wanted to know how you guys have been dealing with all the problems overshooters, pilot pollution etc.

[s52d]

thank you, we hired the initial tunning service to 3 vendors and they have very different styles to optimize the network. Some others says that the CPICH is the last thing you touch to optimize the network. Anyways i don't think one is wrong or right and sorry about the dirty trick (just a thought) :P.
The whole point is that now we have to make the initial tunning and i wanted to know how you guys have been dealing with all the problems overshooters, pilot pollution etc.

Hi, optimizing is a bit of art, so you can expect different results from different people.
Even different people from same vendor might have different apporach.
Especailly if you give them different goals.

If you ask me to do perfect road coverage and ignore indoor (yes, some operators
request it this way) then network is perfect for TEMS in the car, but not for 99% of users.

After all neighbor relation is fixed, and parameter consistency confirmed,
there is time for antennas (RET is easy, otherwise somebody have to climb up),
and touching pilot a bit can help.

I even heard statement: our planning tool is SOOOO GOOD you do not need to
do any antenna tuning. And installers never made any mistake.
And cables never get swapped if you use OUR planning software ;-)

BR
s52d

[chiku]

differnce between pilot polution and too many server?

[s52d]

differnce between pilot polution and too many server?

In principle, none.

Terminology. Effect.
Pilot pollution: too many pilots, generating interference (polluton). Drop or H/O to GSM.
Too many servers: too many pilots, Ue can not pick best server; zillion of events, SHO failures, drop.

BR
s52d

Funny side:
For MBA manager:
Polluton is something we fix, we are green company.
Too many is good: we have good redundancy in coverage.

[mrevans]

Lol, green company! hahah that is a good one!

[Processor]

But i read from a document that an event qualifies as pilot pollution if the 4 or more cells are greater tha 100dBm.....Please how true is this.

Also does anyone have a querry in Actix that can give me the pilot pollution other than the one in spotlight?

[cococrunch]

"Too many servers" and "Pilot pollution" can be the same at some points but not all the time.
"Too many servers" is always true in "Pilot pollution" but "pilot pollution" is not always true in "Too many servers".

1. Pilot Pollution is GOOD COVERAGE BUT POOR EC/NO, say like >3 cells with >-95dBm or >3 cells with CPICH Ec/No within 5dB.
2. Too many servers can happen in poor coverage area but all servers <-100 dBm or so, this is not pilot pollution, this is POOR COVERAGE AND POOR EC/NO.
This is because the "Addition Window" is usually 4dB from strongest cell, so in poor coverage almost all nearby cells are within the window.

Recommendations for these 2 cases are different also,
1. Downtilt interfering cells.
2. Uptilt dominant/nearest cell if still can but usually New Site.

[Gambino8]

If Overshooting problem is detected, what is recommended if Electrical tilt is not an option? CPICH power decrease? How much must it be decreased?