Why digital communication is suitable for long distance?

The digital communication is more reliable and secured as compared to analog communication system due to some following reason

• Long distance communication:

In analog communication system, the signal travels over a longer distance it amplitude   reduces due to attenuation and received signals becomes distorted.
In digital communication systems, repeaters are introduced between the source and destination.
Repeaters separate out the signal from noise and regenerate the signal which is free from noise.
Due to use of repeater noise performance is much better than analog communication system.

• Effect of noise:

In digital communication the information is transmitted in term of 0’s and 1’s, so receiver check only 0’s and 1’s numbers the shape. Thus no distortion is received signal.
In analog communication systems, information is in amplitude so it is necessary to maintain the shape of signal. But due to interference introduced in the transmitted signal and shape of received signal distorted.