Digital Signal Processing Reference
In-Depth Information
synchronize
BPF
PA
baseband section
transmit
window
LO
QPSK radio TX section
window alignment control
LPF
LNA
digital backend
receive
window
LO
QPSK radio RX section
= wideband signals are present
Figure 5.7.
Instead of focussing on the generation/demodulation of pulses, a pulse-
based radio must be considered as a regular qpsk receiver with an ex-
tension layer decoupling symbol rate from multipath resolvability.
window opens again. The same procedure is repeated exactly the same way at
receiver side, where the antenna signal is only gated to the receive chain at the
moment a pulse is expected to arrive.
In contrast to the transmitter, the receiver has no clue about the moment when
the receive window must be activated. Finding the exact timing is part of the
synchronization procedure and will be discussed in the next section. Leaving
the synchronization aspect aside, consider the remaining part of the receive
chain. As explained earlier, maintaining a wide bandwidth needed to represent
the short pulses along the entire receive chain is a real kiss of death for low-
power applications. One part of the demodulation process, which is the band-
width compression of the pulses, should be performed as soon as possible after
the rf-signal has passed the receive window switch. This time, fortunately,
the explanation takes longer than the actual implementation. The bandwidth of
the rf-pulses can be compressed to a baseband signal by an ordinary low-pass
