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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
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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.
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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
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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
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• 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.
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• 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.
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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