Model Digital Communication System :
The source and destination points are separated through a communication channel
* Discrete information source :
- Source : These are the letter, digits or special charectar available in the information source.
- Source Alphabet Probability : Each source alphabet from information source has independent occurrence rate in the sequence.
Example: Letter or words (a, e, i, o, u) occurs frequently in the source.
- Symbol Rate: It is the rate at which the information source generates source alphabet and represented in symbol/ sec unit.
- Information Rate: This parameter defines the average information content of the symbols. Entropy describes the average information content per symbol, it is defined in terms of bits / symbols.
The source information rate is the product of symbol rate and source entropy
information rate = Symbol rate * source entropy
(bits/sec) = (Symbol /sec) * (bits/symbol).
Source encoder and decoder:
The symbols produced by information source converted into digital form (binary 0, 1). The group of bits is called a code word.The source encoder asigns code word to the symbols.
- Block Size: It describes the maximum number of different code words which can be represented by the source encoder.
Example: The block size of 8- bits will be
28 = 256 code words.
Code word Length : This is the number of bits used to represent each word .
- Average Data Rate: The source encoder assigns multiple number of bits to each input symbols.
Example: If we consider that the symbols are given to the source encoder at the rate of 10 symbols/sec and the length of code word is 8- bits then the output data from the source encoder is
Data rate = 10*8
= 80 bits/sec.
At the receiver side the decoder is used to perform the reverse operation of source encoder. Here it converts the binary output of the channel decoder into a symbol sequence.