Page 18 - GuideFWA

where, htx and hrx are the TX and RX antenna heights and ? is the wavelength.

2.1.2.4 Formulae

• For the transmitter path two simple equations have to be taken into account:

P’L (dBm) = P’max (dBm) + G’tx (dB) - L’mask (dB) (2)
where,

G’tx (dB) = G’txant (dBi) - L’txant (dB) - L’txfeeder (dB) (3)

• For the receiver path some more complex calculation should be made:

The fundamental philosophy that has been adopted is that the effect of interference can be

modelled (at least for our purposes) as an increase in received interference power. The primary

interference metric agreed is the rise in the noise floor D, i.e. the increase in noise+interference

power compared to the original noise+interference power:

D = (N + Iact + Iext) / (N + Iint) (4a)
or, in dB, (4b)

D’ = 10 log(N + Iact + Iext) - 10 log(N + Iint)
where,

N = an equivalent noise power in the receiver and includes allowance for receiver
implementation and, sometimes, fading threshold as well as pure thermal noise.

Iint = the internal (expected) interference power from the victim system itself - both same
cell/sector and adjacent cell/sector, before any external interference is applied

Iact = the internal (expected) interference power from the victim system itself - both same
cell/sector and adjacent cell/sector, after any external interference is applied. Note that in

same cases Iact = Iint

Iext = the incremental external interference power received from the interfering system
If we assume that interference is a single event, that is assuming only a worst case of single

interference, it can be assumed that Iact = Iint. Then re-writing (4a):

D = 1 + Iext / (N + Iint) (5)
In other hand, a fundamental relationship between C and I and N can be modeled as:

M = C / (N+I) (6)

where

C = the received carrier power level on the channel

N = an equivalent noise power in the receiver (as before defined)

I = the same-channel received interference power

M = the specified minimum carrier-to-noise+interference ratio needed to guarantee the

specified performance. M is colloquially referred to as the C-to-I (C/I) ratio.

then, this basic relationship can be applied to our analysis, assuming a C value equal to Cref

(minimum operative RX level) and I value equal to Iint, as follows

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

or,

8