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TRANSMISSION FUNDAMENTALS
SOME HISTORICAL BACKGROUND
 THE WIRELESS TELEGRAPH WAS INVENTED IN 1896 BY
MARCONI
 IN 1901 TELEGRAPHIC SIGNALS WERE SENT FROM CORNWALL
TO NEW FOUNDLAND, ABOUT 3200 KM
 COMMUNICATION SATELLITES WERE LAUNCHED IN THE 1960S,
COULD HANDLE ONLY 240 VOICE CIRCUITS, TODAY 1/3 OF ALL
VOICE TRAFFIC AND ALL OF THE TELEVISION SIGNALS
BETWEEN COUNTRIES
 SEE THE MILESTONES BELOW
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CELLULAR REVOLUTION
 IN 2002 THE NUMBER OF MOBILE PHONES WORLDWIDE
OUTNUMBERED FIXED-LINE PHONES
 TECHNICAL INNOVATIONS: SMALL, LIGHT, LONGER BATTERY
LIFE, BETTER USE OF A FINITE SPECTRUM, PRICES HAVE
DROPPED, ACCESS TO INTERNET, DIGITAL CAMERA, GPS, ETC
 IN MANY AREAS MOBILE PHONES ARE THE ONLY WAY TO
PROVIDE PHONE SERVICE
BROADBAND
 GRAPHICS, VIDEO AND AUDIO NEED BROADBAND
 DATA RATES FROM 2 MBPS to OVER 100 MBPS
 EXAMPLE: WIRELESS LAN HAS DATA RATES UP TO 54 MBPS
SOME FUTURE TRENDS
 USE OF FREQUENCY SPECTRUM THAT DOES NOT REQUIRE
LICENSING
 SUCH FREQUENCY BANDS ARE INDUSTRIAL, SCIENTIFIC AND
MEDICAL (ISM) BAND NEAR 2.4 GHZ
 Wi-Fi (WIRELESS-FIDELITY): REFERS TO 802.11-COMPATIBLE
PRODUCTS THAT HAVE BEEN CERTIFIED AS INTEROPERABLE
BY THE Wi-Fi ALLIANCE
 WiMAX: SIMILAR TO Wi-Fi BUT HAS A RANGE UP TO 40-50 KM
WHILE Wi-Fi CAN COVER SEVERAL HUNDRED METERS.
 ZigBee: LOW DATA RATE, SHORT DISTANCE, LOW POWER
CONSUMPTION, VERY LOW COST, FOR SENSORS
 ULTRAWIDEBAND: HIGH DATA RATES OVER SHORT
DISTANCES
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TIME DOMAIN CONCEPT
 AN ELECTROMAGNETIC SIGNAL CAN BE EITHER ANALOG OR
DIGITAL
 ANALOG: SMOOTH VARATION OVER TIME, NO
DISCONTINUITIES
 DIGITAL: A CONSTANT LEVEL FOR SOME PERIOD OF TIME AND
THEN CHANGES TO ANOTHER CONSTANT LEVEL; DISCRETE
LEVELS
 SIMPLEST SORT OF SIGNAL: A PERIODIC SIGNAL
s(t + T) = s(t)
-∞ < t < ∞
where T is the period of the signal. If not periodic then aperiodic.
 The fundamental analog signal is the sine wave. It is presented bythree
parameters: peak amplitude (A), frequency (f) and phase (Φ)
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 The peak amplitude is the maximum value of the signal over time, the
frequency is the rate at which the signal repast and phase is a measure of
the relative position in time within a single period over a signal
 AN ELECTROMAGNETIC SIGNAL IS MADE UP OF MANY
FREQUENCIES, CAN BE SHOWN BY FOURIER ANALYSIS
 FREQUENCY COMPONENTS OF A SQUARE WAVE IS SHOWN
BELOW
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ANALOG AND DIGITAL DATA TRANSMISSION
 SIGNALS ARE ELECTRIC REPRESENTATIONS OF DATA
 TRANSMISSION IS THE COMMUNICATION OF DATA BY THE
PROPAGATION AND PROCESSING OF SIGNALS
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 THE ACOUSTIC FOR HUMAN SPEECH AND MUSIC IS SHOWN
BELOW
 BELOW: A SEQUENCE OF VOLTAGE PULSES AND THE
RECEIVED VOLTAGE
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CHANNEL CAPACITY
 DEFINITION: THE MAXIMUM RATE AT WHICH DATA CAN BE
TRANSMITTED OVER A GIVEN COMMUNICATION PATH
 WE RELATE FOUR PARAMETERS: DATA RATE, BANDWIDTH,
NOISE AND ERROR RATE
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 DATA RATE: THE RATE, BITS PER SECOND, AT WHICH DATA
CAN BE COMMUNICATED
 BANDWIDTH: THE BANDWIDTH OF THE TRANSMITTED SIGNAL
AS CONSTRAINED BY THE TRANSMITTER AND THE NATURE OF
THE TRANSMISSION MEDIUM, GIVEN IN HZ.
 NOISE: AVERAGE LEVEL OF NOISE OVER THE COMUNICATION
PATH
 ERROR RATE: NUMBER OF ERROR BITS IN RELATION TO THE
TOTAL NUMBER OF BITS
NYQUIST BANDWIDTH
CHANNEL IS NOISE FREE    C = 2B log2 M
C = CHANNEL CAPACITY
B = BANDWIDTH
M = NUMBER OF DISCRETE VALUES
SHANNON CAPACITY FORMULA
CHANNEL IS NOT NOISE FREE    C = B log2 (1 + SNR)
SNR = SIGNAL POWER / NOISE POWER
THE SIGNAL-TO-NOISE RATIO IS OFTEN GIVEN IN DECIBEL
SNRdB = 10 log10 (SIGNAL POWER / NOISE POWER)
A HIGH SNR WILL MEAN A HIGH-QUALITY SIGNAL
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EFFECT OF NOISE ON A DIGITAL SIGNAL IS SHOWN BELOW
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THE ELECTROMAGNETIC SPECTRUM AND FREQUENCIES AT WHICH
VARIOUS GUIDED MEDIA AND UNGUIDED TRANSMISSION
TECHNIQUES OPERATE
MULTIPLEXING
DEFINITION: CARRY MULTIPLE SIGNALS ON A SINGLE MEDIUM
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TWO MULTIPLEXING TECHNIQUES ARE IN COMMON USE:
FREQUENCY DIVISION MULTIPLEXING, FDM
TIME DIVISION MULTIPLEXING, TDM
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GENERIC DESCRIPTION OF A SYNCHRONOUS TDM SYSTEM