- This topic has 7 replies, 1 voice, and was last updated 12 years, 8 months ago by pix.
5th May 2008 at 08:25 #52337new engineerGuest
can any body explain for detail expalnation for C/I and C/A and what is the threshold by example in order to see in TEMS it is come from adjacent frequency or co frequency5th May 2008 at 10:50 #52338pixGuest
i forgot about the details, but i remember the help (F1) of TEMS is very detailed about this. They give the method of calculation of C/A and C/I.
i remember that the C/I is not the real C/I though, it’s just an approximation.
C(co)/I > 9dB is needed in order to have good voice quality (above 12dB is even better)
C(adj)/I > -9dB in order to have god voice quality (> -6dB, even better)5th May 2008 at 12:48 #52339new engineerGuest
would you please give more detail about C/A let say I have BCCH 20 and adjacent BCCH is 19 what must be the Rxlevel difference between them it is -9db in this case the sdjacent BCCH some times will be stronger as you make by equation C-A>=-9 is it write?????????5th May 2008 at 20:06 #52340pixGuest
BCCH(serving) = -70dBm
the maximum value of an adjacent frequency should be -61dBm (-9dB difference)
if the adj is -65dBm, then it’s totally fine.
if the adj is -60dBm, then it’s bad.
yes, the adjacent frequency is stronger than the serving frequency. it’s a very useful characteristic for frequency planning with multilayer (umbrella / micro)6th May 2008 at 05:26 #52341new engineerGuest
thanks alot and just one more Question about the last sentence(it’s a very useful characteristic for frequency planning with multilayer (umbrella / micro)) what do you mean by this would you please give me more information?25th June 2008 at 12:13 #52342lotfiGuest
anyone has a detailed doc about C/I, C/A and interference probability ? I’m exactly searching for curves : interference probability = f(C/I) and interference probability = f(C/A)
thanks for help6th September 2008 at 17:41 #52343learnerGuest
Why C/A is -ve value whereas C/I is positive value?7th September 2008 at 06:31 #52344pixGuest
C/A = rxlev(serving cell) – rxlev(adjacent channel)
with adjacent channel = a channel which is adjacent to the serving channel by -1,-2,-3, +1, +2, +3 offset. (depends o your configuration)
C/I = rxlev(serving cell) – rxlev(cochannel)
with cochannel = same frequency as serving cell.
they can all be +ve or -ve ! but it happens that in a gsm network, only the cochannel interference are very dangerous. So frequency planning needs to pay particular attention to C/I, and keep it as high as possible.
for C/A, it can be negative since it won’t affect voice quality.