Physical Layer

Fourier Analysis

The French mathematician J.B. Fourier proved that any reasonably behaved period function, g(t) with period T can be constructed as the sum of a number of sines and cosines:

$$g(t)=\frac{1}{2}c+\sum _{n=1}^{\mathrm{\infty }}{a}_n\sin (2\pi nft)+\sum _{n=1}^{\mathrm{\infty }}{b}_n\cos (2\pi nft)$$

Where $f=\frac{1}{T}$ is the fundamental frequency, $a_n$ and $b_n$ are the sine and cosine amplitudes of the $n_{th}$ harmonics, and c is a constant.

Transmission Medium and Physical Layer

Classes of Transmission Media

+ Transmission media

• Guide wired
  • Twisted-pair cable
  • Coaxial cable
  • Fiber-optic
• Unguided wireless
  • Free space

Guided Transmission media

• Guided media, which are those that provide a conduit from one device to another.
• Include twisted-pair cable, coaxial cable, and fiberoptic cable.

Twisted-pair

• A twisted pair consists of two insulated copper wires, typically about 1 mm think.
•