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# C/I for GSM

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bpong
Guest

can anyone confirm if C/I= 12dB for GSM?
can I interpret that if I got a wanted signal at -90dBm, the interference cannot be higher than -102dBm?

Arindam
Guest

Hi,
In GSM the acceptable value of C/I is 12dB or higher. Allthough some vendors say that with hopping even 9dB or higher can be acceptable.

This means if your serving frequency (C) should be at least 12dB higher than the interferer(I).

So if you have a serving ARFCN at -90, then the interferer should be at -102 or lower.

bpong
Guest

Does the interferer (I) mean co-channel ARFCN or adjacent channel?

Arindam
Guest

When you’re talking about C/I, it means co-channel. For adjacent channel , the relevant parameter is C/A.

Arindam
Guest

The term “I” indeed is the co-channel interferer. When we are talking about adjacent channel interference, the relevant parameter is C/A.

bpong
Guest

What’s the C/A value for GSM, offset at 1 channel & 2 channels away?

Arindam
Guest

Usually the recommended value of C/A is 3dB. This is an Ericsson recommended value.

bpong
Guest

Is it so low, 3dB? I thought it should be around 50-60dBc.

Arindam
Guest

Hi,
I am afraid it is not 50-60. May be ,you could give me your mail id, I can send you a document dealing with C/A and C/I.

bpong
Guest

I just read the GSM spec.
C/A @ 200khz = 9db

AliShah
Guest

Can anyone tell me the range of C/A in GSM ???? please……… m much confused

pix
Guest

h,

C/A is just the C/I with I = the adjacent freq.

an ok value is C/A > -9dB, for speech purposes.

You can find all the thresholds you need in 45.003 i believe.

regards
pix

gm
Guest

When predicting C/Ic=9dB for the purpose of frequency planning, one must keep in mind that a prediction is a prediction. In reality, the measured value can be higher or smaller with a probability of 50%. Theoretical mathematical calculation can show more details. Therefore it is better to predict a value higher than 9dB, at least 12dB or 18dB or more.

gm
Guest

9dB is for speech.. EGPRS can require a C/I up to 30dB ! (mcs9)

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