Although additive noise has nothing to do with useful signals, it always exists and interferes with useful signals, which inevitably harms communication. The sources of additive noise in the channel can usually be divided into two aspects:

1, Man-made noise Man-made noise comes from other irrelevant signal sources, such as external signal, switch contact noise, industrial point macro-pure mode fire radiation shielding, slow shooting, etc.

2. Natural noise Natural noise refers to various electromagnetic wave sources existing in nature, such as lightning, lightning strikes, electrical storms in the atmosphere and various universes.