cse350 lec2 data transmission
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CSE 350
Lecture 2: Data Transmission
Maheen Islam
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Terminolo 1
Receiver
Guided medium
. . ,
Unguided medium
e.g. air, water, vacuum
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Terminolo 2
No intermediate devices
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Direct link
Multi-point
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Terminolo 3
One direction e. . Television
Half duplex
Either direction but onl one wa at a time
e.g. police radio
Full duplex
Both directions at the same time
e.g. telephone
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Fre uenc , S ectrum and Bandwidth
Continuous signal Various in a smooth wa over time
Discrete signal
Maintains a constant level then changes to another constantlevel
Periodic signal
a ern repea e over me Aperiodic signal
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Continuous & Discrete Si nals
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Periodic
gna s
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Sine Wave Peak Am litude A
maximum strength of signal volts
Frequency (f)
Rate of change of signal Hertz (Hz) or cycles per second
Period = time for one repetition (T)
Phase ()
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Var in Sine Waves
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Wavelen th
Distance between two points of corresponding
= vT
c = 3*108 ms-1 (speed of light in free space)
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Fre uenc Domain Conce ts
Components are sine waves
made up of component sine waves
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FrequencyComponents
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Frequency
omain
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S ectrum & Bandwidth S ectrum
range of frequencies contained in signal
Absolute bandwidth
width of spectrum
Effective bandwidthOften just bandwidth
Narrow band of frequencies containing most of the energy
DC Component
Component of zero frequency
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Si nal with DC Com onent
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Data Rate and Bandwidth
frequencies
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Analo and Di ital Data Transmission
Entities that convey meaning
Electric or electromagnetic representations of data
Communication of data by propagation and processing
of si nals
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Data
Continuous values within some interval
Digital
e.g. text, integers
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Acoustic S ectrum Analo
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Si nals Means b which data are ro a ated
Analog Continuously variable
Various media
wire, fiber optic, space Speech bandwidth 1 Hz to 7kHz
Telephone bandwidth 300Hz to 3400Hz
Digital
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Data and Si nals
analog signals for analog data
Modem
Compact Disc audio
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Analog Signals Carrying Analog and
g a a a
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Digital Signals Carrying Analog and
g a a a
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Analo Transmission
May be analog or digital data
Use amplifiers to boost signal
so amp es no se
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Di ital Transmission
Integrity endangered by noise, attenuation etc.
Repeater receives signal
xtracts t pattern
Retransmits
Attenuation is overcome Noise is not amplified
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Advanta es of Di ital Transmission Di ital technolo
Low cost LSI/VLSI technology Data integrity Longer distances over lower quality lines
Capacity utilization Hi h bandwidth links economical High degree of multiplexing easier with digital techniques
Security & Privacy
ncryption Integration Can treat analo and di ital data similarl
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Transmission Im airments
Analog - degradation of signal quality-
Caused by
enua on an a enua on s or on
Delay distortion
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Attenuation Signal strength falls off with distance
Depends on medium
Received signal strength:
must be enough to be detected
must be sufficiently higher than noise to be receivedwithout error
Attenuation is an increasing function of frequency
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Dela Distortion
Propagation velocity varies with frequency
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Noise 1
receiver
Due to thermal agitation of electrons
Uniforml distributed
White noise
Signals that are the sum and difference of original
frequencies sharing a medium
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Noise 2
A signal from one line is picked up by another
Irregular pulses or spikes
Short duration
Hi h am litude
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Channel Ca acit
In bits per second
Bandwidth
Constrained by transmitter and medium
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Re uired Readin