comm introduction

Student will learn:

• The basic elements that related with a communication system

• Introduction to signals, medium, analog systems and digital systems.

• Energy and Electromagnetic Waves.

• Electromagnetic Spectrums and Allocations.

• Simplex, Duplex and Half Duplex.

Communication:• A basic process of exchanging information.• To convey thoughts, ideas and feelings to one

another.• Through spoken words, body movements and

facial expressions.• Later, through written letters, news papers and

books.• Nowadays, through many electronic devices.

• Eg.: telephones, emails, sms, mms, video streaming etc.

• Started before 3000 B.C. - Egyptians develop hieroglyphics.

• 1834 – Gauss & Weber build the electromagnetic telegraph.

• 1844 – S. F. B. Morse patent the telegraph.

• 1876 – A. G. Bell develops and patent telephone.

• 1895 – Marconi demonstrates wireless telegraphy.

• 1926 – Baird & Jenkins demonstrate the television.

• 1933 – E.H. Armstrong invents FM (Frequency Modulation).

• 1937 – A. Reeves conceives PCM(Pulse Code Modulation).

• 1954 – Colour TV broadcasting begins.

• 1962 – First satellite communication.

• 1969 – Internet is invented.

• 1975s – PC(Personal Computer) come into use.

• 1981s – Modems become widespread.

• 1983 – First cellular telephone system become operational.

• 1989 – GPS is use for commercial and personal applications.

• 1989 – www is invented.

• 2000s – Era of digital signal processing.

Transmitter (Tx)

Noise

Receiver (Rx)

Communications channel or medium

Human message input (voice, code, pictures, data, etc.)

Message for human application

Information source

Destination

Figure 1.1 : The basic elements of communication system.

Collection of electronic devices or circuits that convert the information into a signal that is more suitable for transmission over a given transmission medium. Eg. Microphone or microwave radio transmitter.

Transporting signal from the TX to the RX. Eg. Pair of wires that carry voice signal from a microphone to a headset.

Collection of electronic devices or circuits that accepts the transmitted signal from the transmission medium and converts them back to their original form. Eg. Earphone or complex electronic receiver.

Random, undesired electrical energy that enters the communication system via the communication media (i.e. inserted between TX and RX) and interferes with the transmitted message.

Figure 1.2 : Basic transmitter block diagram.

Signal source Base band converter

Modulation and power

amplification

Transmission (Electromagnetic

Field)

Subsystem synchronization

Amplification and

demodulation

Base band inverter

Synchronization system

Base band processing

Electromagnetic field

Figure 1.3 : Basic receiver block diagram.

• Electronic communication: – Transmission, reception and processing of information between

2 or more locations using electronic circuit.• Information:

– Analog or digital signal that had been converted to electromagnetic energy.

• Base band converter: – To convert the signal source into base band waveform for the

carrier signal before transmission.– Analog or digital system.

• Subsystem synchronization: – Synchronizing connection between the TX and RX for recovery

processes.

• Transmission impairments : – Any undesired effect on the signals while traveling

from the transmitter to the receiver, such as noise, attenuation, interference and other losses caused by the atmosphere or the medium itself.

• Attenuation : – Drop in signal power due to distance travel by the

signal.• Interference :

– Noise signal that has the same frequency as the information signal.

Digital and Analog signal

Message signals can be in two forms:

•Analog signals

Analog information source produces messages that defined on a continuum (transition of one language to another).

Eg. Microphone.

•Digital signals

Digital information source produces a finite set of possible messages.

Eg. Telephone touchtone pad.

Signal with interference

DEK 3233 COMMUNICATION ENGINEERING

1717

Analog Signal:• Components of Speech• Characterized by data whose values vary over a continuous

range.• Frequency range (of hearing) 20 Hz-20 kHz.• Speech 100Hz-7kHz.• Easily converted into electromagnetic signal for transmission.• Sound frequencies with varying volume converted into

electromagnetic frequencies with varying voltage.• Limit frequency range for voice channel ~ 300-3400Hz.

1818

Digital Signal:– From computer terminals etc.– Constructed with finite number of

symbols. – Eg. Binary numbers, morse code, ASCII

code etc.– Bandwidth depends on data rate

• Guided – coaxial cable, twisted pair, fiber optic, waveguide.

– The medium is more important.

• Unguided– wireless (terrestrial, spacewave, free space, earth wave).

– The bandwidth produced by the antenna is more important.

• Characteristics and quality determined by medium and signal.

• Key concerns are data rate and distance.

2020

Analog Communication System

• Analog communication system transfers information from an analog source to the intended receiver (sink).

• Both info and carrier are analog signals.• Advantages:

– A Simple system– Cheap

• Disadvantages:– Noise– Attenuation - high loss

2121

Digital Communication System• Digital communication system transfers information from an

digital source to the sink.• Original source info may be in digital or analog signal.• If analog signal = convert to digital pulses prior to transmission

& converted back to analog signal at the RX.

• Disadvantages:• More BW required• Synchronization required.

• Advantages: Digital technology

Low cost LSI/VLSI technology Data integrity

Longer distances over lower quality lines Capacity utilization

High bandwidth links economical High degree of multiplexing easier with digital techniques

Security & Privacy Encryption

Integration Can treat analog and digital data similarly

2323

• Electronic communication system send info from Tx to Rx by sending electromagnetic energy.

• Modes:– voltage, current, radio emission or light.

• Laws involved:– Wavelength -the distance traveled in time to complete one

cycle.– Velocity – the speed at which energy travels through the

medium.– Frequency – the number of oscillation or cycle per second

(hertz, Hz)

v = ƒ

2424

Radio wave, television wave, and microwaves are all types of electromagnetic waves.

They differ from each other in wavelength. Wavelength is the distance between one wave crest to the next.

Please refer to Maxwell’s Equation for more explanation.

2828

• It refers to the total span of frequencies and corresponding wavelengths used in communication systems.

• 10,000 Hz to billions Hz.

• Application depends on the frequency allocation.

• Eg. Submarines, AM broadcast, TV, Cellular phones, satellite systems etc.

Ultra High Frequency (UHF) * freq > 1GHz is known as microwaveTV land mobile communicationcellular phone militarycertain radar and navigation systemmicrowave and satellite radio systemamateur radio

Super High Frequency (SHF)•microwave and satellite radio system •radar•specialized form of 2-way radio

Extremely High Frequency (EHF)•seldom used in radio communication except in very sophisticated, expensive and specialized application

•satellite communication•Radar

* freq > 300 GHz are not referred as radio wave

• Infrared– refers to electromagnetic radiation generally

associated with heat– anything that produced heat generate infrared signal

eg : light bulb, human body– astronomy (to detect stars)– electronic photography– heat-seeking guidance system (weapon)– TV remote control

• Visible light– optical communication

• Bandwidth– Portion of the electromagnetic spectrum occupied by the

signal– Frequency range over which a receiver or other electronic

circuits operate.– Difference between the upper and lower limit frequency,

limits of the signal, or equipment operation range• Channel bandwidth

– Range of frequencies required to transmit the desired information

– i.e. an audio signal (3kHz) being modulated by a 1000kHz carrier signal using AM modulation

Example 1:• What is the bandwidth of HF signal?

Example 2:• How many times more BW does the UHF

band have than the VHF band?

Shannon’s Law: I = 3.32BW log10(1 + (S/N))

• I= information capacity, Unit: bits/second• C = information or channel capacity• BW = bandwidth (kHZ)• S = signal power (W)• N = noise power (W)

Example 3:

• Q. For a standard telephone circuit with signal-to-noise power ratio of 1000(30dB) and a bandwidth of 2.7kHz, determine the Shannon limit for information capacity

• A. 26.9 kbps

• Gain and attenuation often expressed in decibels, rather than ratio value (decimal)

• Decibel, dB unit of measurement originally created as a way of expressing the hearing response of human ear to various sound levels. A decibel is one-tenth of a bel.

• Using decibel, total gain or attenuation can be calculated by simply adding the gains and the attenuation expressed in decibel.

• Beside performing ratio operation, decibel is also used to expressed power in communication.

• A notation is added after the dB symbol,• dBW, dBm etc.

• For dBm, reference level = 1mW.• A larger unit, dBW has reference value of 1W.• dBm and dBW are decibel units used for expressing

power in communication.

4242

a) Simplex is one direction data communication.• e.g radio…• Communication is only from one direction.

b) Half Duplex is involving two directions but only one direction is allowed at a time.

c) Duplex is two direction communication.

Quiz:

Gives 2 examples of each data communication:– Simplex– Duplex– Half Duplex

The end