 This topic has 24 replies, 1 voice, and was last updated 9 years, 5 months ago by fanz.

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BhupendraGuest
Dear All,
i need your help.. Pls clear what is the relation in GSM Spectrum & TRX? Like… we got 4.4 MHz GSM spectrum i.e 22 ARFCN. Now how many TRX in a BTS can be occupied?… i am very confused…
RnzeitGuestBhupen,
TRX in a BTS depends on BTS capcity and TS assigned for the BTS!
Example: For SIEMENS 240XL you can have 12 TRX and can extend by adding a COAMCO(4TRX).but depends on E1.
ThanksTimzGuestI 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.
BhupendraGuestYea TIMZ, u r right..
i got the answer also…
in 22 ARFCN, Say 10 ARFCN will be used for BCCH, 1 as Guard Band and remaining 11 for TCH.
If we take hopping in 3/3/2 configuration BTS then 3 ARFCN will be used for BCCH TRXs (1 per sector) are non hopping & remaining 5 TRX will be in hopping mode. For these 5 TRX there will be 5 frequencies at a time, these 5 frequencies should not be adjacent so keeping gap of atleast 1 ARFCN the total requirement is 10 ARFCN.
That is the reason why we can not go beyond 3/3/2 configuration with 4.4 MHz spectrum (in hopping case).Pls revert if i m not correct…
Thanks
BhupiPixGuestBuphendra,
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 available11 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.pramod kumarGuesthi…. i want to know that if gos is 2% than how many traffic putup a site in 2,2,2 trx configuration
and one trx will take how many erlangs if gos is 2%PixGuestTo 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.micky1GuestHi PIX,
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.pls elaborate.PixGuesteach 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.micky1GuestHi Pix,Can u pls explain the same for SFH 1*3 whose threshold value for RF load is much higher,pls provide max confg.of trx in such case,also try to elaborate it with an example.
rgds,
micky.aravindGuesthi 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.
pixGuestmicky,
you cans earch the forum for 1×3, you’ll find plenty of answers.
cheers
pixMonica voda..GuestMicky,
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.PixGuestMonica,
That’s it ! Just one clarification (but you didn’t say anything wrong : i just want to make it clear for readers):
the total bandwidth needed is 33 frequencies for hopping TRXs (that’s 11 ARFCN per sector, as you said).
natashaGuestHi 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.. 
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