Page 15 - GuideFWA

2.1.1. Methodology

The methodology described here has been generally agreed by all the Interference Experts Group
participants. However, there were some disagreements, in these cases the different approaches
are also described.

The methodology is based on the following assumptions:
• The basic threshold parameter to analyse the interference is the Rise In The Noise Floor which

occurrs when external interference appears.
• This methodology calculates:

• the required minimum signal attenuation in the air interface,

• and by applying the chosen propagation model, the corresponding minimum distance .

for each scenario between a single interfering TX and victim RX device.
• The methodology assumes that both victim and interferer are operating at the closest possible

adjacent channels.
• This methodology only uses emissions due to the modulation mask and does not consider

other emissions such as out-of-band emissions, spurious emissions, etc.. For the calculations
these masks have been extended beyond the immediate channel from the carrier. The
emissions due to modulation were chosen as highest priority.
• This methodology does not take into account the probability of interference.
• The methodology uses the following steps:

1. Calculate the maximum level of the interfering TX at the antenna output. To do that, it
is assumed that TX is working at the adjacent carrier to the victim system, at
maximum power and with the two TX antenna alignments relative to the victim RX
position.

2. Calculate the maximum level of the interfering signal which can be tolerated at the
victim RX antenna. The interference is calculated when the RX is working at the
minimum operating threshold level, , and assuming a specific Rise in the Noise Floor.
Two RX antenna alignments relative to the interfering TX position have been
assumed.

3. The Path Loss difference between above two values gives the required isolation in the
air interface. Then, propagation model is applied to obtain the required minimum
separation distance between interfering TX and victim RX devices.

• The above calculations assume only one single interfering signal. There was a disagreement
within the group about this matter. The two main views were:
a) The effect of any other interfering signal is negligible.
b) The effect of multiple interfering signals needs to be considered. Due to shortage of
time, this approach was not investigated.

• The group could not agree on whether to include or not include Rayleigh fading margin for the
wanted signal in the calculation. Both approaches have been used.

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