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additional loss due to propagation inside the building using (5.9) will be less than 1.9 dB, or less
than 3 dB, depending on which value is used for G.
Obviously, the specific numbers for additional loss will be different if other in-building
propagation models are used, but the distribution of the distance to the nearest exterior wall will
be unaffected, and it is clear than a significant fraction of the building’s occupants will tend to be
fairly near an exterior wall, which minimizes the effect of loss due to interior building
obstructions. The main point is that path loss inside a building cannot be assumed to
significantly reduce the effect of interference from the FWA transmissions. Moreover, UPCS in
office buildings will tend to be used by those employees at the upper strata of the management
hierarchy, who will also tend to have offices with windows; i.e., along the exterior of the
building. Hence, for both geometric and demographic reasons, UPCS usage will tend to be the
greatest toward the outer walls of the building, where the interference is the highest.
5.1.1.4.3 Synchronization and Frame Structure Issues
In calculating the distributions shown in Fig. 5.1, only downlink interference was taken into
account, and it was assumed that all FWA transmissions were frame-synchronized. However,
the UPCS systems will in general not be synchronized with the FWA systems. Even if a UPCS
carrier overlaps only a single DECT FWA carrier and has the same frame structure as DECT, the
UPCS timeslot will in general receive interference from first one FWA slot, then another. The
effect of the interference on the UPCS communication link will be determined by the maximum
of the interference on the two overlapping slots. This maximum will have a CDF given by:
{ ( ) } { } { }FImax (x) = Pr max I1, I2 < x = Pr I1 < x × Pr I2 < x = FI2 (x) (5.12)
The CDF of the least-interfered channel is then found from (5.8), but substituting FI2 (x) for
FI (x) . As shown in Fig. 5.2, the net result is to increase the effective interference on the least-
interfered channel by a little more than 1 dB. The implicit assumption is that the victim UPCS
receiver has a 10-msec frame, as does the DECT FWA system.
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