SOURCE AND ERROR CONTROL CODING

1.What is meant by encoder and decoder?

            The encoder adds redundant bits to the sender’s bit stream to create a codeword. The decoder uses the redundant bits to detect and/or correct as many bit errors as the particular error-control code will allow.

2.What is meant by error control code?

            A set of code-words used with an encoder and decoder to detect error, correct error, or both detect and correct error.

3.Define code word.

            The encoder blocks of ‘n’ bits is called as code word.

            Code word=Message bits + Redundant bits

4.What is meant by code efficiency?

            It is the ratio message bits in a block to the transmitted bits for the block by the encoder.

5.What are the types of error control coding?

            -Forward Error Correction

            -Automatic Repeat Request

6.What are the advantages and disadvantages of coding?

 Advantage:

            -Used to minimize the channel noise effect

Disadvantage:

            -Decoder circuits is complex

            -Addition of redundancy increases the transmission bandwidth

7.What are the types of parity check codes?

            -Even parity

            -odd parity

8.What are the advantage and disadvantages of linear block codes?

Advantage:

            -Easy to encode and decode

Disadvantage:

            -Can detect only two error

            -can correct only one error

9.What is meant by convolutional code?

            Convolution codes are widely used as channel codes in practical communication systems for error correction. The encoded bits depends on the current k input bits and a few past input bits.

10.What are the representation of convolutional encoder?

            -Code tree diagram representation

            -State diagram representation

            -Trellis diagram representation