Relation in GSM Spectrum & TRX _ urgent

I think what Bhupendra asked was how many TRX’s can be deployed per sector depending on the 22 ARFCN NOT the BTS Capacity. He’s worried of TIGHT frequency. In my case i work for an operator with 24 GSM 900 ARFCN and we are using maximum of 2 TRX’s per sector. We have many DCS Frequency where we use 6 TRX’s.

Buphendra,

The computation is actually more complex than this, but the results are the same. For the sake of sharing, here is the full explanation 🙂

If you want to use SFH 1×1, then you must apply a threshold of 12% :
22 ARFCN – 10 BCCH ARFCN – 1 Guard
= 11 ARFCN available

11 ARFCN * 12% = 1.3 (approx)
This magic number “1.3” means you should have an average of 1.3 hopping TRX per sector, therefore your max BTS config should be 2/2/3.

To remain below 2% GoS, a cell with 2TRX shall not exceed 8.2 erlangs.

Capacity of a BTS 2/2/2 = 3*8.2 erlangs

If cell with 2 TRXs exceed 8.2 erlangs, then the GoS will get greater than 2%

One TRX can accept up to 8 timeslots TCH, so that is 8 FR calls or 16 HR calls (and any possible mix in between)

When you talk about capacity of a cell with 2 TRXs, you cannot talk about the individual Erl. capacity of 1 particular TRX.
Erlang B Law doesn’t work this way. You must think at “Cell” level.

each sector can get 1 TRX “non hopping” (that carries the BCCH ts) + 1.3 TRX “hopping”.

In average, that’s 2.3 TRX / sector

a BTS with 3 sectors could have a config of 2/2/3, as long as the average number of TRX per BTS = 2.3 * 3 = 6.9, then you can do whatever mix you want.
1/1/5, 2/2/3, 1/2/4, etc.
of course it is much more manageable to have a regular BTS configuration.

hi guys,i am working in ericsson as a o&m engineer can anyone suggest me how to clear 2to 3 site downs i checked everything bts earthing,e1 path,power.i am not able to find how to clear this issue please help me.

Micky,
The threshold value for rf load for 1*3 is 30% with 11 ARFCN available (as explained earlier)–11*30%=3.3.this means you can have 3.3 hopping trx per sector,ie total of 10 trx.consider it as 9,+ 1 TRX per sector”non hopping” (that carries the BCCH ts)so max conf for SFH 1*3 will be 4*4*4, Pix correct it if i am wrong.

Hi PIX,
Can u pls explain the relation of ARFCN and physica channel,is it that 1 AFRCN is a carrier that has 8 time slots (ie TDMA frames) so with 22 ARFCN ie on 4.4 mhz spectrum,there are 22 ARFCN so the pysical channel with be 22*8=176 avaliable for a cluster.Now we have to map the logical channels on this physical channel,using reuse pattern,am i right?if i am wrong pls give correct explaination..