Fade Margin Calculation in GSM:
Cell area probability (CAP) is the percentage of the cell area that has signal strength greater than the receiver sensitivity.
CAP is dependent on the radio environment, primarily the standard deviation of the log normal faded signal (s) and the propagation loss constant (n).
The CAP is calculated using the following equation:
PCA=½ ( 1+ erf (a) + exp (2ab+1/b2)(1 – erf(ab+1/b)))
PCA = Cell area probability
A = Mfade/s
B = 10nLog10(e) / sÖ2
MFADE = Fade margin applied
s = Standard deviation of received signal
N = Propagation constant
Outdoor Fade Margin:
- The outdoor fade margin depends on the standard deviation of the lognormal shadowing and the propagation constant.
- The propagation constant depends on the environment and the frequency.
- For urban areas propagation constant varies from 2.7 to 5 , with a typical value of 5 for both 850 Mhz and 1900 Mhz.
- Standard deviation also varies on environment and frequency , and may vary slightly with frequency.
- The urban areas have higher standard deviation than rural areas.Typical value ranges from 5-12dB with a typical value of 8dB
- Outdoor fade margin can be calculated using a plot of the CAP equation.