Page 215 - GuideFWA

5.1.1.2 Model and assumptions

The FWA system is assumed to serve a traffic density of ? FWA Erlangs/km2 using a network (or
multiple networks, if there are multiple operators) of elevated base stations which communicate
via the DECT air interface with fixed terminals. These fixed terminals are also elevated (e.g.,
rooftop- or poletop-mounted) and oriented to provide a line-of-sight path to a base station. The
UPCS systems are assumed to be deployed indoors, primarily in office buildings.

5.1.1.2.1 Propagation Model

The propagation model used here is the “two-slope” model adopted by the PCC.III Interference
Experts Group [19], which is:

? ??? 4p r ??? 2
?? ?
L(r) = ??????? r = rb with rb = 4ht hr (5.1)
4p r 2 ? 2 r = rb ?
?rb ?
?

where r is the distance between transmitter and receiver, ? is the wavelength (0.156m for a 1920

MHz carrier), and ht and hr are the respective elevations of the transmit and receive antennas.
The attenuation into the building which houses the UPCS system is assumed to be 15 dB.3

5.1.1.2.2 Power Output, Antenna Elevation, and Gain

From [19], the RF power output of the DECT FWA transmitter is assumed to be 24 dBm, and the
antenna gain is assumed to be 12 dB with a 120° azimuthal beamwidth for a “macro” FWA base
station, and 10 dB with an omnidirectional (in azimuth) antenna for a “micro” FWA base. The
elevations for the macro and micro bases are assumed to range from 20-80 meters and 20-40m
respectively, with respective reference levels of 40m and 20m.

5.1.1.2.3 Average Number of FWA Transmissions per Channel

Consider a UPCS receiver centered on a circle of radius d. The average active number of FWA

( )transmissions d2 r2 , where rmin is the minimum possible
within that circle is p - min ? FWA

distance between the FWA transmitter and the UPCS receiver. If there are N FWA channels

(frequency/timeslot combinations), then the average number of transmissions within the circle

per channel is

( )K = p d2 - r2 ? FWA . (5.2)
min

N

For purposes of computing interference, K must be adjusted to account for antenna directivity

and orientation, as well as the fact that a UPCS receiver near one side of the building will tend to

be more sensitive to transmissions originating on that side. Thus, Keff = ?K is the effective

3The 15dB figure for external wall attenuation is taken from ETR 310 [23] page 32. 201

Inter-American Telecommunication Commission