Book: Wireless Receiver Design for Digital Communications
ISBN: 9781891121807
Publisher: SciTech Publishing
Year: 2012
There have been two paradigm shifts since we wrote the first edition of this book. The
first major shift is that the world is now full of digital signals. Commercial television
and radio have changed from analog to digital formats. Cellular telephone signals are
digital, and even video baby monitors transmit digital signals. I’m not sure you can even
find an analog signal on the air anymore. In a way, this is sad. In the “either you get a
perfect signal or you get nothing” world of the digital broadcast, our children will never
know the distinct pleasure of watching a snowy ultrahigh frequency (UHF) broadcast
or listening to a crackling AM radio station after it has traveled from the other side of
the nation.
The second paradigm shift since the publication of the first edition is the availability
of inexpensive digital processing power. As of this writing (early 2011), processing power
is essentially free. In the past, radio receivers performed filtering and demodulation in
the analog world. Many old-school receivers performed demodulation using analog techniques
that were finicky and required large amounts of circuit board real estate. Control
functions such as automatic gain control (AGC) and automatic frequency control (AFC)
were realized in the analog world using individual diodes, operational (op) amps, resistors
and capacitors. Today, it makes technical and economic sense to perform these functions
in the digital domain.
We find ourselves in a world where the receiver is primarily a downconverter whose
sole purpose is to translate the signal of interest to a frequency and power level that is
suitable to be sampled by an analog-to-digital converter (ADC). Similarly, transmitters
convert the user’s information into complex waveforms using digital signal processing
(DSP) techniques. A digital-to-analog converter (DAC) then converts these signals to the
analog domain. The transmitter’s remaining task is to convert the modulated signal to its
final frequency and power level.
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