GSM TCH expansion

[vadb]

Hi,

I was wondering if there is a way to approximate the required number of TCH on a cell knowing the current traffic, congestion level and available TCH. I was thinking about using the erlang B formula using the congestion % and the number of configured channels to determine the offered traffic and then use the erlang formula again to calculate the required TCH to serve that offered traffic with a 2% GoS. Is this the right way to do this? I'm getting extremely high TCH requirements.

The other option is to consider that the lost-traffic is equal to the percentage of congestion, so, a 50% congestion would mean approximately a 50% increase in traffic.

How do you decide how many additional TRXs to add?

Thanks in advance.

[bdplanner]

is ur carried traffic/offered traffic > 100% and also have congestion?

[vadb]

Hi Amit.Kumar,

I'm not sure if I follow what you're saying. I'll give an example of the situation:

I have a cell with 20 Erl of carried traffic with 13 TCH-FR (26 TCH-HR) and 75% of TCH congestion. How can I determine the number of additional TCH needed to carry all the offered traffic (20 Erl + the lost traffic) with a GoS of 2%?.

Regards.

[bdplanner]

may i ask what is the formula for tch congestion? we use the following huwei counters to determine congestion in a cell and add/remove trx accordingly.sometimes we go for half rate penetration




TR373:Cell Availability(none)


K3004:Traffic Volume on SDCCH(Erl)


K3014:Traffic Volume on TCH(Erl)


K3034:TCHH Traffic Volume(Erl)


CR3557:Traffic Volume on TCHs (Underlaid Subcell)(Erl)


CR3558:Traffic Volume on TCHs (Overlaid Subcell)(Erl)


K3041:TCH Congestion Rate (Overflow)(none)


SDCCH Congestion (including reattempt)(%)


K3016:Configured TCHs(none)


K3006:Configured SDCCHs(none)


AR3017A:Mean Number of Dynamically Configured Channels (TCHF) (900/850/810 band)(none)


AR3017B:Mean Number of Dynamically Configured Channels (TCHF) (1800/1900 Band)(none)


AR3018A:Mean Number of Dynamically Configured Channels (TCHH) (900/850/810 band)(none)


AR3018B:Mean Number of Dynamically Configured Channels (TCHH) (1800/1900 Band)(none)


TCH Congestion(%)


R3007A:Number of Initially Configured Channels (TCHF) (900/850/810 band)(none)


R3007B:Number of Initially Configured Channels (TCHF) (1800/1900 Band)(none)


CR300B:Number of Initially Configured Channels (TCH)(none)





also for tch congestion we use the following formula. Your TCH congestion seems to be too high



TCH Congestion

({100}*[CA312:Failed Assignments (Channel Unavailable)])/([CA310:Assignment Requests]+([H3301W:Outgoing External Inter-Cell Handover Requests (Directed Retry) (900/850/810-900/850/810)]+[H3301X:Outgoing External Inter-Cell Handover Requests (Directed Retry) (1800/1900-1800/1900)]+[H3301Y:Outgoing External Inter-Cell Handover Requests (Directed Retry) (900/850/810-1800/1900)]+[H3301Z:Outgoing External Inter-Cell Handover Requests (Directed Retry) (1800/1900-900/850/810)]+[H3101W:Number of Outgoing Internal Inter-Cell Handover Requests (Directed Retry) (900/850/810-900/850/810)]+[H3101X:Number of Outgoing Internal Inter-Cell Handover Requests (Directed Retry) (1800/1900-1800/1900)]+[H3101Y:Number of Outgoing Internal Inter-Cell Handover Requests (Directed Retry) (900/850/810-1800/1900)]+[H3101Z:Number of Outgoing Internal Inter-Cell Handover Requests (Directed Retry) (1800/1900-900/850/810)]))

[karim]

Hi,

I assume another 15 Erl will solve your congestion problem if I correctly got your point.


Regards,
Karim

[vadb]

Hi,

Amit.Kumar, I would have to check the formula on Monday, I'm not really sure right now, but I think is a simpler formula.

Karim, you agree that the lost traffic is aproximately equal to the congestion level?.

Thank you both.

Regards.