Transmission Media Notes from the University of zambia.pptx

Wireless Communication
Networks and Systems
1st
edition, Global edition
Cory Beard, William Stallings
© 2016 Pearson Education, Ltd.
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Cory Beard and William Stallings, All Rights Reserved
CHAPTER 2
TRANSMISSION
FUNDAMENTALS
TRANSMISSION FUNDAMENTALS 2-1

ELECTROMAGNETIC SIGNAL
• Function of time
• Can also be expressed as a function of
frequency
– Signal consists of components of different
frequencies

TIME-DOMAIN CONCEPTS
• Analog signal - signal intensity varies in a smooth
fashion over time
– No breaks or discontinuities in the signal
• Digital signal - signal intensity maintains a constant
level for some period of time and then changes to
another constant level
• Periodic signal - analog or digital signal pattern that
repeats over time
s(t +T) = s(t)-∞ < t < +∞
• where T is the period of the signal

2.1 ANALOG AND DIGITAL WAVEFORMS

• Aperiodic signal - analog or digital signal pattern that
doesn't repeat over time
• Peak amplitude (A) - maximum value or strength of
the signal over time; typically measured in volts
• Frequency (f)
– Rate, in cycles per second, or Hertz (Hz) at which the
signal repeats

• Period (T) - amount of time it takes for one repetition
of the signal
– T = 1/f
• Phase (ϕ) - measure of the relative position in time
within a single period of a signal
• Wavelength (λ) - distance occupied by a single cycle
of the signal
– Or, the distance between two points of corresponding phase
of two consecutive cycles

2.2 EXAMPLES OF PERIODIC SIGNALS

SINE WAVE PARAMETERS
• General sine wave
– s(t ) = A sin(2πft + ϕ)
• Figure 2.3 shows the effect of varying each of the
three parameters
– (a) A = 1, f = 1 Hz, ϕ = 0; thus T = 1 s
– (b) Reduced peak amplitude; A=0.5
– (c) Increased frequency; f = 2, thus T = ½
– (d) Phase shift; ϕ = π/4 radians (45 degrees)
• Note: 2π radians = 360° = 1 period

2.3 s(t) = A sin (2πft + ϕ)

TIME VS. DISTANCE
• When the horizontal axis is time, as in Figure 2.3,
graphs display the value of a signal at a given point in
space as a function of time
• With the horizontal axis in space, graphs display the
value of a signal at a given point in time as a function
of distance
– At a particular instant of time, the intensity of the signal
varies as a function of distance from the source

FREQUENCY-DOMAIN CONCEPTS
• Fundamental frequency - when all frequency
components of a signal are integer multiples of one
frequency, it’s referred to as the fundamental
frequency
• Spectrum - range of frequencies that a signal contains
• Absolute bandwidth - width of the spectrum of a
signal
• Effective bandwidth (or just bandwidth) - narrow
band of frequencies that most of the signal’s energy is
contained in

2.4 ADDITION OF FREQUENCY COMPONENTS(T = 1/f)

FREQUENCY-DOMAIN CONCEPTS
• Any electromagnetic signal can be shown to
consist of a collection of periodic analog
signals (sine waves) at different amplitudes,
frequencies, and phases
• The period of the total signal is equal to the
period of the fundamental frequency

2.5 FREQUENCY COMPONENTS OF SQUARE WAVE

2.6 ACOUSTIC SPECTRUM OF SPEECH AND MUSIC

RELATIONSHIP BETWEEN DATA
RATE AND BANDWIDTH
• The greater the bandwidth, the higher the
information-carrying capacity
• Conclusions
– Any digital waveform will have infinite bandwidth
– BUT the transmission system will limit the bandwidth that
can be transmitted
– AND, for any given medium, the greater the bandwidth
transmitted, the greater the cost
– HOWEVER, limiting the bandwidth creates distortions

2.7 ATTENUATION OF DIGITAL SIGNALS

DATA COMMUNICATION TERMS
• Data - entities that convey meaning, or
information
• Signals - electric or electromagnetic
representations of data
• Transmission - communication of data by the
propagation and processing of signals

EXAMPLES OF ANALOG AND
DIGITAL DATA
• Analog
– Video
– Audio
• Digital
– Text
– Integers

ANALOG SIGNALS
• A continuously varying electromagnetic wave that
may be propagated over a variety of media,
depending on frequency
• Examples of media:
– Copper wire media (twisted pair and coaxial cable)
– Fiber optic cable
– Atmosphere or space propagation
• Analog signals can propagate analog and digital data

DIGITAL SIGNALS
• A sequence of voltage pulses that may be
transmitted over a copper wire medium
• Generally cheaper than analog signaling
• Less susceptible to noise interference
• Suffer more from attenuation
• Digital signals can propagate analog and
digital data

REASONS FOR CHOOSING DATAAND
SIGNAL COMBINATIONS
• Digital data, digital signal
– Equipment for encoding is less expensive than digital-to-
analog equipment
• Analog data, digital signal
– Conversion permits use of modern digital transmission and
switching equipment
• Digital data, analog signal
– Some transmission media will only propagate analog signals
– Examples include optical fiber and satellite
• Analog data, analog signal
– Analog data easily converted to analog signal

2.8 ANALOG AND DIGITAL SIGNALING OF ANALOG AND DIGITAL DATA

ANALOG TRANSMISSION
• Transmit analog signals without regard to content
• Attenuation limits length of transmission link
• Cascaded amplifiers boost signal’s energy for longer
distances but cause distortion
– Analog data can tolerate distortion
– Introduces errors in digital data

DIGITAL TRANSMISSION
• Concerned with the content of the signal
• Attenuation endangers integrity of data
• Digital Signal
– Repeaters achieve greater distance
– Repeaters recover the signal and retransmit
• Analog signal carrying digital data
– Retransmission device recovers the digital data from
analog signal
– Generates new, clean analog signal

ABOUT CHANNEL CAPACITY
• Impairments, such as noise, limit data rate that
can be achieved
• For digital data, to what extent do impairments
limit data rate?
• Channel Capacity – the maximum rate at
which data can be transmitted over a given
communication path, or channel, under given
conditions

2.9 EFFECT OF NOISE ON DIGITAL SIGNAL

CONCEPTS RELATED TO CHANNEL
CAPACITY
• Data rate - rate at which data can be communicated
(bps)
• Bandwidth - the bandwidth of the transmitted signal
as constrained by the transmitter and the nature of the
transmission medium (Hertz)
• Noise - average level of noise over the
communications path
• Error rate - rate at which errors occur
– Error = transmit 1 and receive 0; transmit 0 and receive 1

NYQUIST BANDWIDTH
• For binary signals (two voltage levels)
– C = 2B
• With multilevel signaling
– C = 2B log2
M
• M = number of discrete signal or voltage levels

SIGNAL-TO-NOISE RATIO
• Ratio of the power in a signal to the power contained
in the noise that’s present at a particular point in the
transmission
• Typically measured at a receiver
• Signal-to-noise ratio (SNR, or S/N)
• A high SNR means a high-quality signal, low number
of required intermediate repeaters
• SNR sets upper bound on achievable data rate
power
noise
power
signal
log
10
)
( 10
dB 
SNR

SHANNON CAPACITY FORMULA
• Equation:
• Represents theoretical maximum that can be achieved
• In practice, only much lower rates achieved
– Formula assumes white noise (thermal noise)
– Impulse noise is not accounted for
– Attenuation distortion or delay distortion not accounted for
 
SNR
1
log2 
B
C

EXAMPLE OF NYQUIST AND
SHANNON FORMULATIONS
• Spectrum of a channel between 3 MHz and 4
MHz ; SNRdB
= 24 dB
• Using Shannon’s formula
 
251
SNR
SNR
log
10
dB
24
SNR
MHz
1
MHz
3
MHz
4
10
dB






B
  Mbps
8
8
10
251
1
log
10 6
2
6






C

EXAMPLE OF NYQUIST AND
SHANNON FORMULATIONS
• How many signaling levels are required?
 
16
log
4
log
10
2
10
8
log
2
2
2
6
6
2







M
M
M
M
B
C

CLASSIFICATIONS OF
TRANSMISSION MEDIA
• Transmission Medium
– Physical path between transmitter and receiver
• Guided Media
– Waves are guided along a solid medium
– E.g., copper twisted pair, copper coaxial cable, optical fiber
• Unguided Media
– Provides means of transmission but does not guide
electromagnetic signals
– Usually referred to as wireless transmission
– E.g., atmosphere, outer space

UNGUIDED MEDIA
• Transmission and reception are achieved by
means of an antenna
• Configurations for wireless transmission
– Directional
– Omnidirectional

2.10 ELECTROMAGNETIC SPECTRUM OF TELECOMMUNICATIONS

GENERAL FREQUENCY RANGES
• Microwave frequency range
– 1 GHz to 40 GHz
– Directional beams possible
– Suitable for point-to-point transmission
– Used for satellite communications
• Radio frequency range
– 30 MHz to 1 GHz
– Suitable for omnidirectional applications
• Infrared frequency range
– Roughly, 3x1011
to 2x1014
Hz
– Useful in local point-to-point multipoint applications within
confined areas

TERRESTRIAL MICROWAVE
• Description of common microwave antenna
– Parabolic "dish", 3 m in diameter
– Fixed rigidly and focuses a narrow beam
– Achieves line-of-sight transmission to receiving antenna
– Located at substantial heights above ground level
• Applications
– Long haul telecommunications service
– Short point-to-point links between buildings

SATELLITE MICROWAVE
• Description of communication satellite
– Microwave relay station
– Used to link two or more ground-based microwave
transmitter/receivers
– Receives transmissions on one frequency band (uplink),
amplifies or repeats the signal, and transmits it on another
frequency (downlink)
• Applications
– Television distribution
– Long-distance telephone transmission
– Private business networks

BROADCAST RADIO
• Description of broadcast radio antennas
– Omnidirectional
– Antennas not required to be dish-shaped
– Antennas need not be rigidly mounted to a precise
alignment
• Applications
– Broadcast radio
• VHF and part of the UHF band; 30 MHZ to 1GHz
• Covers FM radio and UHF and VHF television

MULTIPLEXING
• Capacity of transmission medium usually
exceeds capacity required for transmission of a
single signal
• Multiplexing - carrying multiple signals on a
single medium
– More efficient use of transmission medium

2.11 MULTIPLEXING

REASONS FOR WIDESPREAD USE OF
MULTIPLEXING
• Cost per kbps of transmission facility declines with
an increase in the data rate
• Cost of transmission and receiving equipment
declines with increased data rate
• Most individual data communicating devices require
relatively modest data rate support

MULTIPLEXING TECHNIQUES
• Frequency-division multiplexing (FDM)
– Takes advantage of the fact that the useful
bandwidth of the medium exceeds the required
bandwidth of a given signal
• Time-division multiplexing (TDM)
– Takes advantage of the fact that the achievable bit
rate of the medium exceeds the required data rate
of a digital signal

2.12 FDM AND TDM

2.13 SYNCHRONOUS TDM SYSTEM

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