Electronic communication systemTransfer info from one place to another Is the transmission, reception and

processing of information between two or more locations using electronic circuits

3 main components of communication system:TransmitterChannelReceiver

Transmitter – circuit/device which converts original source info to a form more suitable for transmission

Medium/channel – provides means of transporting signal between transmitter and receiver

Noise – unwanted signals that interfere with the info signal

Receiver – circuit/device which accepts transmitted signals and converts them back to their original form

Two types: Guided propagation Free propagation

Signal = set of information/data represented by mathematical functions of time

System will process a set of signals (i.e. inputs) to produce another set of signals (i.e. outputs)

1. Continuous-time and discrete-time signals

2. Analog and digital signals3. Periodic and non-periodic signals4. Even and odd signals

Continuous-time signal: Specified at every value of time t. Represented by x(t).

Discrete-time signal: Specified at separate values of time. Represented by x[n].

Continuous-time signal

Discrete-time signal

Binary signal Is a type of digital signalHas only two possible levels (‘high’, or ‘low’)

Periodic signal: Signal that repeats itself over a time period T. Otherwise, it is non-periodic

A continuous-time periodic signal satisfies the condition x(t) = x(t ± T), where T is the period

A discrete-time periodic signal satisfies the condition x[n] = x[n + N], where N is the period

Relationship between period, T and frequency, f:

frequency, f = T

1

Even SignalA signal that is identical to its reflection

about the originSymmetric about the vertical axisx(-t) = x(t), or x[-n] = x[n]

Odd signalSymmetric about a line midway between

the vertical axis and the negative horizontal axis and passing through the coordinate origin

Signal is zero at the origin, and -x(-t) = x(t) or -x[-n] = x[n]

Decibel (dB) – to define power ratios, voltage ratios or current ratios

Note:Power levels P1 and P2 must be in same

units+ dB power gain - dB power loss (attenuation)0 dB unity power gain (i.e. P1 = P2)

2

110log10P

PdB

Given P1/P2 = 100. Convert this absolute power ratio to dB

Convert 23 dB to absolute power ratio

Decibel milliwatt (dBm) – a unit of measurement to indicate the ratio of a power level with respect to a fixed reference level i.e. 1 mW

mW

PdBm

1log10 10

Convert 200 mW to dBm