Cryptography Reference
In-Depth Information
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Figure 5.1
A communication system.
a sequence of bits. In analog communication, however, the object can be a
signal represented by a continuous waveform.
•
The
channel
is the medium over which the objects prepared by the encoder
are actually communicated or transferred.
•
The channel may be subjected to
noise
. This noise, in turn, may cause some
objects to be modified or disturbed.
•
The
decoder
operates on the output of the channel and attempts to associate a
message with each object it receives from the channel.
•
Similar to the source, the
destination
can be a person or machine. In either
case, it receives the messages that are communicated or transferred.
Ta b l e 5 . 1
The Entities of a Communication System with Their Input and Output Parameters
Entity
Input
Output
Source
Message
Encoder
Message
(Input) object
Channel
(Input) object
(Output) object
Decoder
(Output) object
Message
Destination
Message
The entities of a communication system with their input and output parameters
are summarized in Table 5.1. Note that the objects mentioned earlier are divided into
(input) objects that are input to the channel and (output) objects that are output to
the channel.
The ultimate goal of information theory is to provide mathematically precise
answers to many practically relevant questions in information processing, such as
how you can optimally (i.e., most efficiently) compress and transmit information or
information-encoding data. Against this background, information theory can only be
applied if the question can be modeled by stochastic phenomena.
