Digital Signal Processing Reference
In-Depth Information
Standardization and backward compatibility
Most of the complexity of the pulse-based radio
system is located at receiver side. For a possible
standardization procedure, this implies that the
actual specifications of the physical layer in the
osi
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model can be kept at a very basic level,
with the synchronization procedure probably
being the most complex aspect of the standard.
With most of the work pushed to the receiver,
the system designer is free to choose the com-
plexity of the implementation, without loosing
compatibility with the standard itself. For exam-
ple, an outdated and basic version of the pulse-based radio receiver with only
limited hardware resources will be able to communicate with a highly perform-
ing and scalable multi-antenna receiver. Also, the scalability and flexibility of
pulse-based radio is much better than this of the ofdm transceiver: based on
the actual quality of the signal and properties of the channel, the receiver can
decide to reduce the number of active receive units to save power. In fact, the
receiver is completely free to change the number and duration of the receive
slots, which is something that is completely unique to the pulse-based radio
system. This trend is even taken a step further in the digital back-end of the
receiver. The processing effort that is put in the issr algorithm is entirely up to
the discretion of the receiver. If an error is detected later on in the data process-
ing chain, the receiver can schedule some extra cycles of the issr algorithm,
without interrupting the transmitter for this.
With the same flexibility, the receiver is free to completely unplug the issr
module from the chain if the signal quality allows for it. And since the trans-
mitter does not play an active role in the reconstruction process, a designer
has the freedom to tweak the issr algorithm and implement better performing
solutions. Also at the hardware level, there are a lot of opportunities to push
down the costs of hardware. At receiver side, there is indeed an increased need
for chip area which is due to the parallel setup of the pulse-based system, but
some building blocks can be reused. For example, the local oscillator and pll
are shared among all receive units (even the transmitter) as they all operate in
the same frequency band. The addition of an extra auxiliary receive unit only
requires an extra mixer circuit,
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a quadrature baseband variable gain amplifier
and a dedicated analog-to-digital converter.
TX
Complexity located
at receiver side.
RX
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osi model: Open Systems Interconnection Basic Reference Model. This seven layer model provides an
abstract description of a generalized computer or network protocol architecture [Zim80].
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The mixer cannot be shared among different receiver chains for reasons of in-band switching noise.
