Atec Rohde-Schwarz-SFQ Series - Manual (Page 11)

TV Test Transmitter R&S ® SFQ 11
The pure Doppler profile is suitable for the
simulation of mobile reception. Mobile
reception means that the receiver is mov-
ing or the signal is reflected by a moving
object. The assumed speed of movement
can be varied over a wide range. More-
over, the direction of movement can be
defined with reference to the transmitter
site. Special profiles have been developed
for the reproducible simulation of com-
plex scenarios. The profiles are based on
the WSSUS (wide sense stationary uncor-
related scattering) model and are recom-
mended by the relevant DVB and DAB
bodies (MOTIVATE, COST 207, EUREKA
147). Rayleigh fading, for example, simu-
lates a radio field with many strongly
scattered partial waves uniformly distrib-
uted and arriving at the mobile receiver
from all directions. Rice fading simulates
the same situation as Rayleigh fading, but
with a variable, discrete component
received via a direct path. Lognormal fad-
ing simulates slow variation of the receive
amplitude; together with Rayleigh fading,
Suzuki fading is obtained. With different phases in the individual
paths, RF power may be reduced through
cancellation and, more frequently,
increased through addition of the paths.
Therefore, with the fading simulator
switched on, the maximum RF level is
reduced to avoid overloading. To configure a complete channel simula-
tion model, a large number of parameters
has to be set for each of the 6 or 12 paths:
on/off, profile, loss, delay, speed/Doppler
frequency, direction, discrete component,
local constant for lognormal. To provide
for comparable, reproducible measure-
ments, international bodies recommend
the use of defined channel models, for
example typical urban, rural area, hilly
terrain, difficult RA250 (difficult rural
area, 250 km/h). The fading simulator
offers the recommended as well as fre-
quently used channel models as pre-
defined setups for convenient testing. All
parameters can be modified to match the
requirements of a given task.
Following the fading simulator, all paths
are combined for modulation. Simulation
may cause a considerable change of RF
power. Depending on the settings of the
FADING POWER parameter (MULTIPATH
or MAIN), the R&S SFQ displays the total
power of all paths involved or the power
of the main path. The C/N ratio is set
according to the two power models.
DVB-T spectrum with constant phase (phase 0 degree, delay 0 µs/0.45 µs, 2 paths) and regular TU50 fading (typical urban, 50 km/h, 6 paths)