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COMMUNICATION SYSTEM EECB353

Chapter 1

INTRODUCTION TO COMMUNICATION SYSTEMS

Dept of Electronic & Communications Engineering

Universiti Tenaga Nasional

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INTRODUCTION TO COMMUNICATION SYSTEMS

Chapter Outline:

1.1 The Block Diagram of Communication System

- Definition

- Main Components

- Mode of Communication

1.2 SNR, Bandwidth & Rate of Communication

1.3 The Electromagnetic Frequency Spectrum

1.4 Modulation

- Continuous-wave Modulation

- Pulse Modulation

Reference:

Frenzel, Chapter 1

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“How do you want to send data/information to someone

who is far from you?”

Communication System History • 1837 – Samuel Morse invented telegraph. • 1858 – First telegraph cable across Atlantic (Canada – Ireland) • 1876 – Alexander Graham Bell invented telephone. • 1988 – Heinrich Hertz introduce electromagnetic field theory. • 1897 – Marconi invented wireless telegraph. • 1906 – Radio communication system was invented. • 1923 – Television was invented. • 1938 – Radar and microwave system was invented for World War II. • 1950 – TDM was invented. • 1956 – First telephone cable was installed across Atlantic. • 1960 – Laser was invented • 1962 – Satellite communication • 1969 – Internet DARPA • 1970 – Corning Glass invented optical fiber. • 1975 – Digital telephone was introduced. • 1985 – Facsimile machine. • 1988 – Installation of fiber optic cable across Pacific and Atlantic. • 1990 – World Wide Web and Digital Communication. • 1998 – Digital Television.

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Definition : Communication is the transmission of information from a source to a user via some communication link.

“If the information that you want to send is your voice, how to make sure that what you are saying is understood by your friend?”

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POSSIBLE SCHEMES

SOURCE ANALOG DATA

OR

DIGITAL DATA

COMMUNICATIONS

SYSTEM ANALOG DATA

OR

DIGITAL DATA

DESTINATION ANALOG DATA

OR

DIGITAL DATA

NUMBER OF POSSIBLE SCHEMES = 32

• AAA

• AAD

• ADA

• ADD

A

A D

A D A D

D

A D

A D A D

• DAA

• DAD

• DDA

• DDD

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COMMUNICATIONS SYSTEMS EXAMPLES

MODEM MODEM DIGITAL DIGITAL ANALOG

ANALOG ANALOG

IP

GATEWAY

IP

GATEWAY

WAN/LAN (DIGITAL)

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ANALOG ANALOG ANALOG

RADIO

STATION

AAAIR FREE SPACE

COMMUNICATIONS SYSTEMS EXAMPLES

ANALOG ANALOG CODEC CODEC

DS1

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2. Main Components of Communication System:

(i) Input message can be:

Analog – continuous signal i.e value varies continuously eg. human

voice, music, temperature reading

Digital – discrete symbol i.e value limit to a finite set eg. data

Figure 2: Analog Vs Digital Signal


Figure : Analog signals (a) Sine wave “tone.” (b) Voice. (c) Video (TV)

signal.


Analog signals is a smoothly and continuously varying voltage or

current. Examples are:


Digital Signals

– Digital signals change in steps or in discrete increments.

– Most digital signals use binary or two-state codes. Examples are:

Figure: Digital signals (a) Telegraph (Morse code). (b) Continuous-wave (CW) code.

(c) Serial binary code.

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(ii) Input Transducer:

A device that converts energy from one form to another.

Convert an input signal into an electrical waveform.

Example: microphone converts human voice into electrical signal

referred to as the baseband signal or message signal.


WHAT IS BASEBAND ?

•Without any shift in the range of frequencies of the signal

•The signal is in its original form, not changed by modulation.

•Baseband is the original information that is to be sent.

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(iii) Transmitter (Tx):

Modifies or converts the baseband signal into format appropriate for

efficient channel of transmission.

Example: If the channel is fiber optic cable, the transmitter converts the

baseband signal into light frequency and the transmitted signal is light.

Transmitter also use to reformat/reshape the signal so that the channel

will not much distorted.

Modulation takes place in the transmitter.

Modulation is a process of putting information onto high frequency

carrier for transmission.


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(iv) Channel:

Physical medium through which the transmitter output is sent.

Divided into 2 basic groups:

• Guided Electromagnetic Wave Channel – eg. wire, coaxial cable,

optical fiber

• Electromagnetic Wave Propagation Channel – eg. Wireless broadcast

channel, mobile radio channel, satellite etc.

In the channel, transmitted signal is attenuated and distorted due to

distortion, noise and interference etc.

Signal attenuation increase along with the length/distance of channel.

This results in corrupted transmitted signal received by receiver, Rx


Transmission Medium (Guided)

Twisted pair

– Unshielded Twisted Pair (UTP)

– Shielded Twisted Pair (STP)

Coaxial

Fiber Optic

Waveguide

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(v) Receiver

Receiver decodes the received signal back to message signal – i.e it

attempts to translate the received signal back into the original message

signal sent by the source.

Reprocess the signal received from the channel by undoing the signal

modification made by transmitter and the channel.

Extract the desired signal from the received signal and convert it to a

form that suitable for the output transducer.

Demodulation takes place in the receiver, to remove the high frequency

carrier and to recover the baseband signal.

(vi) Output transducer

Convert electrical signals to its original waveform.


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Transceivers

A transceiver is an electronic unit that incorporates circuits that both send and receive signals.

Examples are:

• Telephones

• Fax machines

• Handheld CB radios

• Cell phones

• Computer modems

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Mode of Communication (based on information flow):


Transmitter Receiver

Transmitter

Receiver

Receiver

Transmitter

Transmitter

Receiver

Receiver

Transmitter

AND

OR

Simplex: One way

Full Duplex: Two way simultaneously

Half Duplex: Either Tx Or Rx

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Mode of Communication (based on number if devices)

Transmitter Receiver Point to point (ie: Telephone, walkie talkie)

Point to multi-point @ Broadcast (ie: TV, satellite)

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1.2 SNR, Bandwidth & Data Rate

1. Signal to Noise Ratio (SNR):

SNR is defined as the ratio of signal power to noise power. Usually

represented in dB.

The dB value is calculated by taking the log of the ratio of the measured

or calculated power (PS) wrt a reference power (PN) level.

SNR of 10, 100 and 1000 correspond to 10dB, 20dB, and 30dB,

respectively.

dBm is a dB level using a 1mW reference.

Example - Convert 1mW to dBm

n

s

P

P

Wpowernoise

Wpowersignal

)(

)(dB

RV

RV

P

P

outn

ins

n

s

/

/log10log10

2

2

SNR = SNRdB

Decibel

decibel is a relative unit of measurement used frequently in electronic communications to describe power gain or loss

Equation 1 is commonly referred to as the power ratio form for dB.

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(Eq. 2)

(Eq. 1)

(Eq. 3)

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