GSM congestion

[Jerry]

Dear all,

I am in stuck to set the criterias to select the congested cells to upgrade in our networks.

Say cells 100A and 201B have Traffic and TCH congestion rate as followings. What cells I should upgrade first? These two cells have same config 2 TRX.

Cells	avg Traffic (Erl)	avg TCH congestion
100A	21	15%
201C	17	45%

What the other factors I should consider to set up the criterias to sort out the cells list to upgrade?

It is very appreciated if you have any documents about this.

[vipbinh]

2 cell are high rate Erl/Trx, if you check online all TCH may busy.
See more about HR, avaiable of number TCH, number of congestion call...

[Ericsson_RND]

Good question Jerry, If these two cells are configured with 2 TRX per each and based on company criteria for control channels, it should be at least carrying 20.5 erlange.

This mean that 201C capable to carry additonal erlang, please check firts if Half rate subject and increase it for both, then monitor congestion.

May be there are some related subject which case to increase congestion on 201C.

BR//E*******_RND

[Jerry]

Thanks for your comments.
@vipbinh, TCH availability is fine (100%), HR activated 100%.
@E*******_RND
3 TS are configured for BCCH, SDCCH and EDGE, so there are only 13 TS for TCH, with HR activated we have 26 channels ~ 18.38 Erl.
Cell 100A get congested is congested as over utilization. cell 201C is congested as short avg holding time or more call attempts, look fine too.

Is there any way to estimated demand traffic for each cells. I think that will give the picture to calculate the volume of est traffic for each cells than we could sort out the cells list.

[johnnymuss]

in order to improve your KPis on BSC level,you must choose the worst cells(wheigted in term of CNRELCONG)

[Mdaf]

Hello, check the number of blocked calls, not the rate, anyway another way is to check which cell will have higher new traffic after performing the upgrade, its calculated as following, if busy hour blocking is hihger than 25% assume the blocking to be 25% if its less than 25% use the blocking value,
Total new traffic= current traffic/(1-Busy Hour Blocking)
extra traffic after upgrade is total new traffic- current traffic, ie
for cell 100A Total new traffic = 21/(1-0.15) = 24.75Erl
extra new traffic = 24.75-21=3.75 erlangs, say its 4 erlang now go to erlang table and check how many TS needed for the 4 erlangs.
for cell 201c total new traffic= 17/(1-0.45) = 31 erlang, extra new traffic = 31-17 = 14 erlang
so basically cell 201c will have higher traffic if upgraded:
question: where did I get this formula!!!
Believe me i took it from some one and its not documented but it works, anyone can try it from a cell that had blocking and blocking was solved after adding extra TRXs you will find this formula is really good!!! just try it.
when its not accurate? its not accurate if you have GSM & DCS on same cell (inner zone and outer zone) because allocating resources to inner zone depends on coverage so some resources might not be allocated because of level criteria and the outer zone is congested so call will be blocked.
why if the blocking is higher than 25% i use 25% this is because this blocking is fake since subs are trying to attempt many times, why 25 why not 35??? its imperial and we get it after tuning it on different cells!!

Dear all,

I am in stuck to set the criterias to select the congested cells to upgrade in our networks.

Say cells 100A and 201B have Traffic and TCH congestion rate as followings. What cells I should upgrade first? These two cells have same config 2 TRX.

Cells	avg Traffic (Erl)	avg TCH congestion
100A	21	15%
201C	17	45%

What the other factors I should consider to set up the criterias to sort out the cells list to upgrade?

It is very appreciated if you have any documents about this.

[peanut]

@Mdaf:

The formula you are used is deduced from the following equations:

Offered Traffic = Blocked Traffic + Carried Traffic
Blocked Traffic = Blocking Rate * Offered Traffic

So Offered Traffic wich is the expected traffic can be deduced as Carried Traffic / (1 - Blocking rate)

BR,

[peanut]

@Mdaf:

Dear,

you had suggested to use 25% as an upper limit to use for the formula of offered traffic, but you didn't use it in you calculations

is it just a mistake?

BR,

[peanut]

@ Jerry:

As many bro suggested, you need to check some points before going ahead for a TRX extension:

1. TCH availability
must be 100%
2. TS configuration
make sure that the configuration is normal (number of SDCCH)
3. HR utilisation
make sure that the HR traffic is at least 60% of Total traffic (60% is just a commonly used threshold, but you can use you proper threshold)
if not try to change HR parameter
4. 1800 load managment
make sure that 1800 TRX if any are used 100%
if not try to balance load between 900 & 1800

Then you can use the expected volume of traffic as calculated by Mdaf to put a priority to the cells.

BR,

[peanut]

@ jerry:

Cf the following thred for traffic engineering may be helpfull

http://www.finetopix.com/showthread.php?31975-Traffic-Engineering-in-GSM

BR,