Page 253 - GuideFWA

R

PCS BS

DECT
FWA

Figure 17.1 PCS and FWA Overlapping Scenario

To estimate the interference intensity, first, we need to understand the statistical properties of the
radio traffics in FWA. In general, the call arrival rate per user is random and fairly small, but the

total average arrival rate from the entire population, ?, may be large and could be modeled as the
Poisson-distribution.

In characterizing the statistic model of the radio traffics and computing the distribution of the

emitted interference intensity, it is necessary to determine the expected number of the calls been

made simultaneously in the service area and how often other cases may occur. Applying the

mean traffic value K (in Erlang) to the Poisson formula, the probability that there are m radio

transmissions at a give time slot for a given frequency then can be found

P(m) = e-K Km (17.4)
m!

With the given parameters such as the transmitter and receiver antenna gains, Gtx and Grx,
transmitter output power Ptx and the propagation loss at distance dj, Lp(dj), we now are able to

calculate the interference level received by the PCS BS,

( )I j (dBm) = Ptx (dBm) - M (dBm) + 10 log10 Wpcs / Wfwa + Gtx (dBm) + Grx (dBm) - Lp (d j )(dBm)

(17.5)

where M is the attenuation for out-of-band transmission mask, Wpcs and Wfwa are the
measurement bandwidths of PCS and FWA systems, respectively. The minimum requirements
of several DECT unwanted RF emissions are listed in [25] including emissions due to
modulation, emissions due to transmitter transients, emissions due to intermodulation and
spurious emissions. For simplification purpose, we only consider the component of emissions
due to modulation. However, it is not suggesting that other unwanted emissions are insignificant
and can be ignored. The minimum requirements of emissions due to modulation are shown in
Table 1.1 on Page 1

From Table 1.1 we notice that the level of interference received by the PCS receiver is most
likely to be dominated by the emissions from the channel closest to PCS receiving band based on
the assumption that the channel assignments and transmitter’s location of DECT are uniformly
distributed. Thus, only the transmissions due to modulation from DECT band edge channel is

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