Baseband communication is the simplest form of analog communication.
We use analog communication techniques for analog message
signals, like music, speech, and television. Transmission andreception of analog signals using analog results in an
inherently noisy received signal (assuming the channel addsnoise, which it almost certainly does).
The simplest form of analog communication is
baseband
communication .
We use analog communication
techniques for analog message signals, like music, speech, andtelevision. Transmission and reception of analog signals using
analog results in an inherently noisy received signal(assuming the channel adds noise, which it almost certainly
does).
Here, the transmitted signal equals the message times a
transmitter gain.
An example, which is somewhat out of date, is the wireline
telephone system. You don't use baseband communication inwireless systems simply because low-frequency signals do not
radiate well. The receiver in a baseband system can't do muchmore than filter the received signal to remove out-of-band noise
(interference is small in wireline channels). Assuming thesignal occupies a bandwidth of
Hz (the signal's spectrum extends from zero to
), the receiver applies a lowpass
filter having the same bandwidth, as shown in
[link] .
The receiver for baseband communication systems is quite
simple: a lowpass filter having the same bandwidth as thesignal.
We use the
signal-to-noise ratio of the
receiver's output
to evaluate any analog-message communication system. Assume that
the channel introduces an attenuation
and white noise of
spectral height
. The filter does not affect the signal component—we
assume its gain is unity—but does filter the noise,removing frequency components above
Hz. In the filter's output, the
received signal power equals
and the noise power
,
which gives a signal-to-noise ratio of
The signal power
will be
proportional to the bandwidth
;
thus, in baseband communication the signal-to-noise ratio variesonly with transmitter gain and channel attenuation and noise
level.
