Page 19 - GuideFWA

N+Iint = Cref / M = Cref / CIR (7b)

Then substituting (N + Iint) in (5):

D = 1 + Iext / (Cref / CIR) (8)

And from this equation, the maximum external interference level allowed by the receiver can be

deduced:

Iext = Cref * (D - 1) / CIR (9a)
I’ext = C’ref - CIR’ + 10 log(100.1 D’ - 1) (9b)

Finally, it is also necessary to define what is the Cref value. There is a disagreement within the
Experts group regarding “Rayleigh fading margin”. If the approach is to include fading, then the

value of Cref should be the Receiver Sensitivity with Rayleigh Fading (as indicated in section
2.2.2). If the approach is to remove fading, the value of Cref should be the Receiver Sensitivity
with No Fading (as indicated in section 2.2.2).

Therefore two equations are obtained for the receiver path (note that RX antenna effects have

been already included):

- Including fading margin in calculations: (10a)
P’R (dBm) = RX’sensitivity w Fading (dBm) - (C’/I’) + 10log(100.1D’-1) - Grx (10b)

- Excluding fading margin in calculations:
P’R (dBm) = RX’sensitivity w/o Fading (dBm) - (C’/I’) + 10log(100.1D’-1) - Grx

in both cases:

G’rx (dB) = G’rxant (dBi) - L’rxant (dB) - L’rxfeeder (dB) (11)

• Final formulae:

According to point 2.1.2.3 and the above formulae (2) and (10a, 10b), the final power calculation

should comply with the following rule:

L’ (dB) = P’L (dBm) - P’R (dBm) (12)

and then, the minimum required distance can be calculated by (1a) and (1b) assuming a single

interferer.

2.1.3. Probability Estimation

This methodology does not take into account the probability of interference. The Group has
discussed this issue, but no agreement on how to assess the probability has been reached.

2.1.4. Other Considerations

• All the systems considered in the analysis include a set of mechanisms to avoid interference.
These mechanisms have not been considered in the quantitative calculation performed. These
mechanisms are Power Control, Frequency Hopping, Intracell and Intercell handover,
Dynamic Channel Allocation, etc.

• The methodology does not highlight some other issues, such as: cell radius of victim and
interferer systems, site engineering, etc

• The Experts Group has implemented the methodology in an Excel Spreadsheet tool, which
allows anyone to perform the calculation in an easy way by simply inputing basic parameters
(involved systems, desired guard-band, desired desentization parameter, option to include or

Inter-American Telecommunication Commission 9