Digital Signal Processing Reference
In-Depth Information
Receive window blocks
out unwanted noise and
interferer energy.
Pulse power compressed in
a short period of time.
T
on
T
off
time
second layer of interferer suppression needed
analog frontend
digital backend
pulse-based receive unit
RX gate is equivalent to
the band-preselect filter in
a narrowband system.
Linearity requirements of
front-end are relaxed.
Figure 5.3.
In the pulse-based radio concept, the transmitted energy is compressed
in short pulses. This allows the receiver to block interferer power when
no pulse is expected to arrive.
receiver (while maintaining the transmitted symbol rate) does not improve the
reliability of the wireless link. This is caused by the fact that if the receiver
takes multiple samples within the period of a single transmitted symbol, the as-
sumption of independently fading samples does not hold any longer. Combin-
ing the energy of several resolved multipath components will thus not reduce
the effects of fading in order to produce a more reliable signal. Concluding,
Equation (4.6) does not apply for dependent fading signals.
Apart from a better multipath resolvability in indoor channels with a short
delay spread, the concept of using short pulses instead of a continuous-time
modulated system has some additional advantages. In a pulse-based radio sys-
tem, the transmitted energy is compressed in a short period of time (Figure 5.3).
This implies that, if the receiver is aware of the period between two consecu-
tive transmitted pulses, it can anticipate on this by only allowing rf-energy
from the antenna to enter the front-end when a pulse is expected to arrive.
This technique can be easily extended for a rake receiver architecture: only
when a certain multipath component is expected to arrive at the antenna, the
front-end is activated. For the remaining time, all rf-signals arriving at the
antenna terminal are blissfully ignored. The result is that a receiver which
employs this
gating
or
windowing
technique, will be less susceptible to the
increased channel background noise caused by the large input bandwidth of
