Signal Processing - MATLAB Simulations for Radar Systems Design - page 619

Signal Processing

Chapter 13

13.1. Signal and System Classifications

In general, electrical signals can represent either current or voltage, and may
be classified into two main categories: energy signals and power signals.
Energy signals can be deterministic or random, while power signals can be
periodic or random. A signal is said to be random if it is a function of a random
parameter (such as random phase or random amplitude). Additionally, signals
may be divided into low pass or band pass signals. Signals that contain very
low frequencies (close to DC) are called low pass signals; otherwise they are
referred to as band pass signals. Through modulation, low pass signals can be
mapped into band pass signals.

The average power P for the current or voltage signal x () over the interval

( t 1 , t 2 ) across a 1Ω resistor is

t 2
∫

1

x () 2

--------------

P = d t

(13.1)

t 2 – t 1

t 1

The signal is said to be a power signal over a very large interval
, if and only if it has finite power; it must satisfy the following

x ()

Tt 2 = – t 1

relation:

T ⁄

∫

2

1
---

x () 2 0 < lim d t < ∞ (13.2)

T → ∞

– T ⁄ 2

Using ParsevalÓs theorem, the energy E dissipated by the current or voltage

signal x () across a 1Ω resistor, over the interval ( t 1 t 2 , ) , is