Channel encoder and decoder :
Channel Encoder :
After converting message or information signal in the form of binary sequence by the source encoder, the signal is transmitted to the channel. The channel acts as noise and interference to signal being transmitted. Therefore, errors are introduced in the binary sequence received at the receiver. To avoid these errors channel encoding is done. The channel encoder acts as some redundant binary bits to the input sequence.
Example: The code word from the source encoder is 3- bits long and one redundant bit is added in channel encoder. If it an even parity then the number of 1’s in the encoded word remain even. At the receiver if odd number of 1’s are detected then reciver comes to know that there is an error in the receiver signal.
Channel Decoder :
The channel decoder is able to detect errors in the bit sequence and reduce the effects of channel noise interference. The extra bits/ redundant bits which are added by the channel encoder. Rather there are used by the channel encoder to detect and correct errors.
Digital Modulator And Demodulator :
Demodulator maps the input binary sequence of 1’s and 0’s to analog signal waves. If one bit at a time is to be transmitted then the digital modulator signal is S1(t) to transmit binary value zero(0) and S2(t) to transmit binary value one(1).
Communication Channel :
The connection between transmitted and receiver is established through communication channel the communication can take place through wire lines, wireless, fiber optics channel……
Some of the communication problems associated with the channels are:
- Signal Attenuation
- Noise and interference
- Multipar distortion.