Mumbai University > Electronics Engineering > Sem4 > Fundamentals of Communication Engineering

Marks: 5M

Year: Dec 2014

• The process of compression of the signal at the transmitter and expansion at the receiver is called as companding (compression and expansion).
• In companding, the higher amplitude analog signals are compressed preceding transmission and then expanded in the receiver.
• Companding is performed with the help of three functional blocks, which are Compressor, Uniform quantizer and Expander and the diagram in shown below in the Fig1.

• The compressor will compress the dynamic range of the signal so that high dynamic range signal can be passed through components of low dynamic range capability, the uniform quantizer will undergo the quantization process of the compressed signal and the lastly the expander will undergo expansion and invert the compression function to reconstruct the original signal.
• The expander has complementary characteristics as that of compressor so that the compressor input is equal to expander output in order to reproduce the signal at the receiver.
• The Fig2 below illustrates the input-output characteristics and curves of the companding process, and it can be seen that companding has linear characteristics.

• It helps in minimizing noise, distortion, interference and reduction in the levels of crosstalk.
• Companding helps in improving the dynamic range of the communication systems.
• Companding is used in telephony and other audio applications.