Co-channel Interference (C/I)
Cellular networks are more often limited by problems caused by interference rather than by signal strength problems. Co channel interference is caused by the use of a frequency close to the exact same frequency. The former will interfere with the latter, leading to the terms interfering frequency (I) and carrier frequency (C).
The GSM specification recommends that the carrier to interference (C/I) ratio is greater than 9 decibels (dB).
This C/I ratio is affected by the following factors:
- The location of the MS
- Local geography and type of local scatters
- BTS antenna type, site elevation and position
Using TEMS investigation tool, the C/I ratio can be observed and the highest show best values. Generally above 15.00 are considered as best.
Adjacent channel interference (C/A)
Adjacent frequencies (A), that is frequencies shifted 200 kHz from the carrier frequency (C), must be avoided in the same cell and preferably in neighboring cells also. Although adjacent frequencies are at different frequencies to the carrier frequency they can still cause interference and quality problems.
