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transmitters outside the 5-km radius are ignored, the results will somewhat understate the
interference at the lower tail of the distribution.
• Since a UPCS transmitter near one side of the building will “see” the FWA transmitters over
only about 180° rather than the full 360°, the adjustment factor for K was taken as ? = 0.5 .4
• Distributions for both rmin = 10 m and rmin = 100 m were computed to verify the insensitivity
of the lower tail to rmin .
• For purposes of computing the CDF of I min , it was assumed that N = 120 channels.
• Only downlink cochannel interference was considered. Interference from the fixed terminals
was ignored, as was adjacent-channel interference.

5.1.1.3.3 Discussion of Results
Figure 5.1 shows the CDFs of I and I min , from the Monte Carlo computations with 100 000
samples. Note the lack of sensitivity of the lower part of the distribution to rmin . This is simply
because nearby interferers correspond to high receiver interference levels, and hence to the upper
portion of the distribution. Note also that the distribution of I min derives from the lower tail of
the distribution of I. For example, the 99th percentile of the CDF of I min corresponds to the
same value of the abscissa x as the 3.76% point on the distribution of I, since

1 - (1 - 0.99)1 120 = 0.0376 . Therefore, rmin is unimportant (within limits) in determining the

interference power on the least-interfered channel. Stated another way, coexistence of FWA and
UPCS systems using DCA cannot be assessed on the basis of the minimum separation, except for
extreme cases in which front-end overload might result.

On the probability scale used for the ordinate in Fig. 5.1, a Gaussian distribution would appear as
a straight line, so the distribution of I min (in dB) is nearly Gaussian, which allows its mean and
standard deviation to be estimated directly from the plot. The median is about - 65.6 dBm. The
standard deviation appears to be roughly 0.5 dB, so I min can effectively be regarded as a constant
with a value of - 65.6 dBm.

4Locations near the corners of the building will see interference over more than 180°.

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