LESSON 2-Discrete Source Encoding

Keywords: Source types, Discrete source coding, Kraft inequality

1.      Source classes

About Figure 1.1 in LESSON1, the source encoder converts the sequence of symbols from the source to a sequence of binary digits, preferably using as few binary digits per symbol as possible.

Thus, we first distinguish between three important classes of sources:

• Discrete sources, which is a toy source and we will begin with it. The output is a sequence of symbols like ABCDEFG.
• Analog waveform sources. The output, in the simplest case, is an analog real waveform, for example, a speech waveform.
• Discrete-time sources with analog values (analog sequence sources).

 

2.      Discrete Sources coding

 

 

　　2.1 The Kraft inequality for prefix-free codes:

　　

The Kraft inequality [17] is a condition determining whether it is possible to construct a prefix-free code for a given discrete source alphabet X = {a1,... ,aM } with a given set of codeword lengths {l(aj ); 1 ≤ j ≤ M}.