Physical Layer - Data Signals

COMP211 Lectures 2021-11-15

Sine Waves

Sine waves can be made using the following function:

$$s(t)=A\sin (2\pi ft+\varphi )$$

Where:

• $A$ - Amplitude
• $f$ - Frequency
• $t$ - Time
• $\varphi$ - Phase
• $T$ - Period ($\frac{1}{f}$)

Any signal can be made of many sine components.

Frequency Domain Representation

• You can plot the frequencies of a periodic signal on a bar graph to represent the signal. (Discrete)
• Aperiodic signals have continuous frequency domain representations.

If a signal has a spectrum with a zero frequency component (direct current), this is used as a voltage offset.

Bandwidth

The bandwidth of a signal is the upper and lower limit of the frequencies that can be represented in the medium.

A higher bandwidth gives more definition to analogue signals.

Advantages of Digital

• Digital is lower cost.
• Data integrity is preserved over longer distances with digital data.
  • Repeaters can amplify the data without including line noise.
• High degree of multiplexing is easier with digital techniques.
  • Increases utilisation.
• Data is easier to encrypt.