Transmitter:
Transmitter is the first component in this block diagram. Using this system we can generate the messages which is to be sent through this system.
Encoder:
Encoder is the second element in the communication system. It performs the encoding of the given data, which means that this system converts the messages in the form of  symbols for transmission purpose. In this system, a sequence of characters are created in a special format for an effective transmission. This encoding system is used for security purpose.
Noisy Channel:
This is the third block in the block diagram of communication system. Noisy channel is nothing but the medium through which the message is transmitted. Messages are conveyed through this channel. Different channels have different strengths and weaknesses. Each channel has its own frequency and different applications have different operating frequencies.
Decoder:
Decoder is used to decode the encoded message and retrieve the actual message. Decoding must be done correctly . If this part is not performed well then the message which is received might not be correct
This encoding and decoding will be very help full in military and mobile communications.
Receiver:
This is the final block in block diagram of communication system. This can be said as the target to which the information need to be delivered.