Digital Signal Processing Reference
In-Depth Information
Use spread spectrum
to avoid interference.
Modulation of pulse
characteristics.
Precision timer to
position the pulses.
Dedicated wideband
pulse shaping circuit.
pulse position
high-speed
PN-code
modulation
counter
pulse amplitude/
phase modulator
pulse generation
data in
circuit
TX section
RX section
energy detection
template estimation
decision
correlator bank
offset tracking
time
offset
multiphase clock
template
PN-code
generators
synthesizer
Recovery modulated
pulse information.
Active tracking offset
of individual pulses.
Optimization of the
template pulse shape.
Multiple parallel
pulse detectors.
Figure 5.8.
How not to build a pulse-based radio. Many pulse-based systems in
the literature [Kim08, Ded07, Lee04, O'D05] focus on the gener-
ation and detection of pulses. However, this approach tends to get
caught up in insignificant low-level details and secondary system
patches.
pointless to put endless effort in the realization of a pulse-generating circuit
(Figure 5.8) that perfectly fits into the spectral mask imposed by the fcc,then
only to forget about the original purpose or ignore new problems that emerge
from this approach.
One of the most challenging problems for the designer of a pulse-based
radio receiver is synchronization, i.e. trying to lock on a stream of pulses
(Figure 5.9). If the receive window is not aligned properly with the arrival time
of the pulses, the receiver is unable to 'see' the pulses. This issue is caused
by probably the most significant difference between time- and frequency-
domain based filtering techniques: a frequency domain filter does not require
an absolute phase reference in order to discriminate the signal-of-interest from
all other unwanted frequency components. This in contrast to a time domain
filtering method, which requires an absolute time reference. The window at
