#### CHAPTER 15 COMMUNICATION SYSTEMS

Rectangular waves

Digital signals are in the form of rectangular waves. This rectangular wave can be decomposed into a superposition of sinusoidal waves of frequencies ν0, 2ν0, 3ν0, 4ν0 ... nν0, where n is an integer extending to infinity and ν 0 is fundamental frequency equal to $\frac{1}{{\mathrm{T}}_{\mathrm{o}}}$.

To reproduce the rectangular wave shape exactly we need to superimpose all the harmonics ν0, 2ν0, 3ν0, 4ν0 .., which implies an infinite bandwidth.

However, for practical purposes, the contribution from higher harmonics can be neglected, thus limiting the bandwidth.

Received waves are a distorted version of the transmitted one. If the bandwidth is large enough to accommodate a few harmonics, the information is not lost and the rectangular signal is more or less recovered.