Page 256 - GuideFWA

Prob{I < x}effects on the total interference. The Monte Carlo analysis also shows that even with the case
where the PCS receiver can only be interfered by DECT transmitters located no further than 1 km
of distance, the interference level impinges upon the PCS receiver is still several tens of decibels
higher than its affective receiver noise floor(see Equation (17.8)). For example, the mean values
of the received interference for R=1, 5, 10, 15 km cases are 85, 71, 62 and 56 dBm respectively.
This corresponds to a rise of 38, 52, 61 and 67 dB, respectively, in the receiver noise floor for IS-
136. An increase on the receiver noise floor means less sensitivity in the receiver RF frond end
which will result in the reduction on the service quality(QoS) and the service coverage area.

To analyze the adjacent channel interference for different service areas, a computer simulation
with R=5 km is performed and the results are illustrated in Figure 17.3. It is clear from the
results that the interference received by PCS receiver antenna is proportional to the FWA serving
traffic density and has similar probability density functions in different service areas.

Compare the simulation results shown in Figure 17.3 and the value of the affective noise floor
we notice that even in the area with very light traffic, e.g. rural area, 99% of the time that the IS-
136 BS receiver suffers significant increases in its receiver noise floor caused by the out-of-band
DECT FWA transmissions. Consequently, unless additional isolation between DECT FWA and
PCS IS-136 is provided, the Grade-of-Service(GoS) of PCS systems will be greatly sacrificed.
In the study of how the wider frequency separation might affect the received interference, a
scenario assuming an one MHz guard band is inserted into the DECT FWA is simulated. The
simulation results show that the average interference received at IS-136 receiver in the business
area drops about 22 dB.

1
0.9
0.8
0.7
0.6
0.5 Bussiness Area
0.4 Rural Area
0.3 Urban Residential
0.2 Bussiness Area with
0.1 1MHz Guard Band

0

Interference, dBm

Figure 17.3 Interference CDF for varied service areas

It is a common practice and beneficial to calculate the rise in receiver noise floor while
evaluating the receiver performance degradation caused by external interference. Results of the
rise in receiver noise floor for IS-95 CDMA BS and IS-136 TDMA BS in the business area with
the maximum receivable range R = 5 km are provided in Figure 17.4. In each case, total of
100,000 “snap shots” are taken during the simulations.

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