In this chapter, we consider the basic functions performed by the physical layer. In particular, we consider the following:

- Signal classification
- Fourier analysis: Fourier series and Fourier transform
- Modulation and demodulation
- Sampling theorem
- Analog-to-digital conversion
- Channel sharing schemes
- Modems
- Guided and unguided transmission media
- Channel impairments.

Message signals are classified as either analog (or continuous-time) or digital (or discrete-time). Analog (or continuous-time) signals, which include speech, audio, and video, have an infinite number of values. Digital signals are predominantly binary in nature and thus are represented by two values: 0 and 1. These two values are called *binary digits*, or *bits*.

Signals found in communication systems are complex waveforms. However, in many instances, these waveforms can be analyzed as one or more sine waves of the form:

where *A* is the *amplitude* of the sinusoid, *f* the *frequency* in Hertz (Hz), and *ϕ* the *phase* in radians.

As mentioned in Chapter 1, a transmitter is required to convert signals into a form suitable for transmission over a channel. A key operation is to change the signal's frequency range to match the frequency range, or *bandwidth* (BW), offered by the channel. In some systems, the signal's frequency content (or *frequency spectrum ...*

Start Free Trial

No credit card required