Network Coding and Wireless Physical-layer ... - Jacobs University

6 Chapter 2: Introduction to Digital Communication Systems and Networks
Binary
Source
Source
Encoder
Channel
Encoder
Digital
Modulator
Channel
Binary
Sink
Source
Decoder
Channel
Decoder
Digital
Demodulator
Figure 2.1: A basic digital communication system
To make the system secure, however, we need to insert two more blocks, which are
encryptor and decryptor, as shown in Fig. 2.2.
Binary
Source
Source
Encoder
Encryptor
Channel
Encoder
Digital
Modulator
Channel
Binary
Sink
Source
Decoder
Decryptor
Channel
Decoder
Digital
Demodulator
Figure 2.2: A secure digital communication system
A digital transmitter consists of four basic elements, which are a binary source, a
source encoder, a channel encoder, and a digital modulator, whereas a digital receiver is
composed of a digital demodulator, a channel decoder, a source decoder, and a binary
sink.
A binary source in the transmitter generates information to be transmitted, be it
audio, speech, or video data, in a binary representation.
Usually, this representation
is not the most economical one possible, i.e., it is possible to squeeze it into a shorter
string of 0s and 1s without reducing the amount of information, or reducing only some
insignificant amount of it. The source encoder is made for this task. It transforms the
data into another binary representation with less redundancy. These two blocks, however,
are not the focus of this thesis.
Our concern in the thesis ranges from the third block, the encryptor, to the ninth block,
the decryptor. Although the encryptor in Fig. 2.2 locates right after the source encoder,
it is not necessarily the case when we consider some new cryptographic technologies, for
example, physical-layer security and physical-layer secret-key generation, which will be
discussed in detail in Part III.