Wireless, cellular and
personal communications
introduction
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Text books/references


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Wireless communications, principles and
practice 2nd edition by Theodore S.
Rappaport
Wireless communication by R. Blake
Wireless communication by William Stallin
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Grading policy
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
Sessional=20%
Midterm=30%
Final=50%
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Award of Sessional Marks
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


Quiz =5%
Assignment=5%
Presentation=5%
Class participation=5%

(Can have positive as well as negative weightage)
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Historical Background




1864. Maxwell predicted the existence of
electromagnetic wave (radio wave).
1887 Hertz demonstrated the existence of
radio wave.
1901 Marconi realized first across Atlantic
wireless transmission (England to Canada)
1906 First radio broadcast (AM radio)
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Historical Background


1946: AT&T introduced first mobile telephone
service using line of sight analog FM radio
transmission, 120 kHz per voice channel,
limited to 50 miles from base, operatorassisted dialing
Mid-1960s: AT&T’s IMTS (Improved Mobile
Telephone Service) uses 30 kHz voice
channels, narrowband FM and direct dialing
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Historical Background (cont)

First generation analog cellular telephony



late 1940s: AT&T develops cellular concept for
frequency reuse
1971: AT&T proposes High Capacity Mobile
Phone Service to FCC
1979: US standardizes it as AMPS (Advanced
Mobile Phone System)in 800-900 MHz range
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Historical Background (cont)

First generation analog cellular telephony



1983: AT&T launches AMPS in Chicago 1985:
Nordic Mobile Telephone (NMT 450) in
Scandanavia, Total Access Communications
System (TACS) in UK, C450 in W. Germany
Total six incompatible analog cellular systems in
Europe
Motivated Europe to accelerate 2nd generation
digital cellular
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Historical Background (cont)

Second generation digital cellular

1989: Europe standardized Global System for
Mobile Communications (GSM)
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1992: GSM is launched
1990: Japan standardized Japanese Digital
Cellular (JDC) now called Personal Digital
Cellular (PDC)
1990: Europe standardized Digital Cellular
System at 1800 MHz (DCS 1800, recently
renamed GSM 1800)
1993: DCS 1800 launched
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History (cont)
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1992: TIA / IS-54 TDMA (Digital AMPS) is
deployed in US
1996: TIA/IS-95 CDMA in US
1995: Personal Handphone System (PHS) in
Japan, first widespread low-tier PCS, is hugely
successful
1996: AT&T and Sprint offer PCS in major US
cities

Smaller cell sites (0.25 km vs traditional 1-8 km),
smaller/lighter portable handsets, cheaper
access pointsBZUPAGES.COM
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History (cont)
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1998: ITU begins to study proposals for 3rd
generation cellular
mid-2000s: UMTS, IMT-2000, W-CDMA,
cdma2000, EDGE,...
2010-?: 4th generation?

Self organizing, ad hoc?
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Multimedia Requirements
Delay
Packet Loss
BER
Data Rate
Traffic
Voice
Data
Video
<100ms
-
<100ms
<1%
10-3
0
10-6
<1%
10-6
8-32 Kbps
Continuous
1-100 Mbps
Bursty
1-20 Mbps
Continuous
One-size-fits-all protocols and design do not work well
Wired networks use
this approach, with poor results
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Wireless Performance Gap
LOCAL AREA PACKET SWITCHING
100 M
Ethernet
100,000
10,000
FDDI
Ethernet
1000
100
User
Bit-Rate
(kbps)
WIDE AREA CIRCUIT SWITCHING
ATM
10,000
wired- wireless
bit-rate "gap"
1000
1st gen
WLAN
Polling
2nd gen
WLAN
Packet
Radio
ISDN
wired- wireless
bit-rate "gap"
28.8 modem
9.6 modem
9.6 cellular
2.4 modem
1
2.4 cellular
14.4
digital
cellular
32 kbps
PCS
.1
.1
.01
100
User
Bit-Rate
(kbps)
10
10
1
ATM
100,000
1970
1980
YEAR
1990
2000
.01
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1970
1980
YEAR
1990
2000
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Spectrum
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Radio Frequency (RF)
 1MHz to 1GHz (general classification, not absolute)
 100 MHz to 1GHz (more widely used definition)
 Applications: AM radio, FM radio, TV, some cellular telephone
systems, etc.
Microwave
 1 GHz to 300 GHz (general)
 1 GHz to 100 GHz (more widely used)
 Most cellular telephone systems, wireless LAN, Satellite, etc.
Trends towards use of higher frequencies
 Maximum bandwidth » 10% of carrier frequency
 More users and higher data rate
 More difficult to design leading to more $$ of investment
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STANDARDS: MOBILE
TELEPHONE SYSTEMS
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1st generation: analog voice
Example: Advanced Mobile Phone Service (AMPS)
2nd generation: digital voice and narrowband
data


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Examples: GSM, D-AMPS (AT&T), IS-95 (Interim
Standard-95) (Sprint)
2.5 generation: GPRS
3rd generation: digital voice and broadband data
Examples: WCDMA, cdma2000
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STANDARDS: MOBILE
TELEPHONE SYSTEMS contd…
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STANDARDS: MOBILE
TELEPHONE SYSTEMS contd…
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STANDARDS: MOBILE
TELEPHONE SYSTEMS contd…
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STANDARDS: MOBILE
TELEPHONE SYSTEMS contd…
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IS-95 (Narrowband CDMA)
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Code Division Multiple Access
All users Tx simultaneously using the same frequency and
same time.
Different codes are used to separate the signals from
different users.
CDMA

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Each user is assigned a unique code
The code is known at both transmitter (Tx) and receiver
(Rx)
All users Tx at the same frequency and time
Receiver uses codes to pick up desired signals
Also called spread sprectrum
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STANDARDS: MOBILE
TELEPHONE SYSTEMS contd…
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WCDMA (Wideband CDMA)
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cdma2000
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Also called UMTS (Universal Mobile Telephone System)
Proposed by Ericsson
Will mainly be used in European countries
Proposed by Qualcomm
Will mainly be used in North America
Both standards use CDMA

Only some detailed technical differences
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Basic concepts

In most wireless communication systems, the
wireless communication occurs between mobile
station (MS) and base station (BS)

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Downlink
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MS: Cell phone, wireless laptop, wireless PDA, etc.
BS: wireless access point, wireless router, etc.
Radio channel for transmission from BS to MS
Also called forward link
Uplink

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Radio channel for transmission from MS to BS
Also called reverse link
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Basic concepts contd…
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Simplex
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Half Duplex
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Communication occurs only in one direction E.g.
paging system
Tx can occur in either direction, but only one way
at a time E.g. Walki-Talki (police radio)
Full Duplex

Tx can occur at both direction simultaneously E.g.
Telephone. Two simplex
One Full
Duplex
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Basic concepts contd…
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Base station
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A fixed station a mobile radio system used for
radio communication with mobile stations. Base
stations are located at the center or on the edge
of a coverage region and consists of radio
channels and transmitter and receiver antennas
mounted on a tower.
Control channel

Radio channel used for transmission of call setup,
call request, call initiation and other beacon or
control purposes.
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Basic concepts contd…
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Forward channel
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Handoff
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Radio channel used for transmission of information from
the base station to the mobile
The process of transferring a mobile station from one
channel or base station to another.
Mobile station

A station in the cellular radio service intended to for use
while in motion at unspecified locations. Mobile station may
be hand held personal unit or installed in vehicles.
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Basic concepts contd…
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Mobile switching center
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Switching center which coordinates the routing of
calls in a large service area. In a cellular radio
system, the MSC connects the cellular base
stations and mobiles to the PSTN. An MSC is also
called mobile telephone switching office.
Reverse channel

Radio channel used for the transmission of
information from the mobile to base station.
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Basic concepts contd…
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Roamer
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A mobile station which operates in a service area
other than that from which service has been
subscribed.
Transceiver

A device capable of simultaneously transmitting
and receiving radio signals.
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Transmission
Fundamentals
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Electromagnetic Signal


Function of time
Can also be expressed as a function of frequency

Signal consists of components of different frequencies
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Time-Domain Concepts
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Analog signal - signal intensity varies in a smooth fashion
over time

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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
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Time-Domain Concepts
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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
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Time-Domain Concepts

Period (T ) - amount of time it takes for one repetition of
the signal
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T = 1/f
Phase () - measure of the relative position in time within
a single period of a signal
Wavelength () - distance occupied by a single cycle of
the signal

Or, the distance between two points of corresponding phase of
two consecutive cycles
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Sine Wave Parameters
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General sine wave


Figure 2.3 shows the effect of varying each of the three
parameters

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s(t ) = A sin(2ft + )
(a) A = 1, f = 1 Hz,  = 0; thus T = 1s
(b) Reduced peak amplitude; A=0.5
(c) Increased frequency; f = 2, thus T = ½
(d) Phase shift;  = /4 radians (45 degrees)
note: 2 radians = 360° = 1 period
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Sine Wave Parameters
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Time vs. Distance
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
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
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Frequency-Domain Concepts
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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
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Frequency-Domain Concepts
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
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
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Relationship between Data Rate
and Bandwidth
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The greater the bandwidth, the higher the informationcarrying capacity
Conclusions
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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
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Electromagnetic waves and
energy

All electromagnetic systems send information
from one point to another by transmitting
electromagnetic energy from the sender to
the intended receiver. This electromagnetic
energy can travel in various modes:

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
As a voltage or current through wires
As radio emissions through air
As light through optical fiber
In all cases it follows following law
Wavelength( )=
Velocity (c)
Frequency (f)
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Electromagnetic waves and
energy

Where “c” is the propagation velocity and it
depends on the medium through which it is
traveling.

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The fastest propagation velocity occurs in vacuum
and is symbolized by the letter “c”
C=3*10^8 m/s
What is the wavelength in vacuum for a
frequency of 1 million hertz?
What is the frequency when the measured
wavelength is 6 m?
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Electromagnetic waves and
energy
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The propagation velocity is less in any
medium other than vacuum.
In air the propagation velocity of
electromagnetic energy is about 95 to 98% of
the value in vacuum.
In wire it is anywhere from 60 to 85% of c,
depending on wire type, construction and
insulation.
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Data Communication Terms
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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
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Analog Signals
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
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
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Digital Signals
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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
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Analog Signaling
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Digital Signaling
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Reasons for Choosing Data and
Signal Combinations

Digital data, digital signal
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
Analog data, digital signal


Conversion permits use of modern digital transmission and
switching equipment
Digital data, analog signal

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
Equipment for encoding is less expensive than digital-toanalog equipment
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
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Analog Transmission
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
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
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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
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About Channel Capacity


Impairments, such as noise, limit data rate that
can be achieved
Channel Capacity – the maximum rate at which
data can be transmitted over a given
communication path, or channel, under given
conditions
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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
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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
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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)
signal power
( SNR) dB  10 log 10
noise power
A high SNR means a high-quality signal, low number of
required intermediate repeaters
SNR sets upper bound on achievable data rate
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Shannon Capacity Formula

Equation:

Represents theoretical maximum that can be achieved
In practice, only much lower rates achieved




C  B log 2 1  SNR
Formula assumes white noise (thermal noise)
Impulse noise is not accounted for
Attenuation distortion or delay distortion not accounted for
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Example of Nyquist and Shannon
Formulations


Spectrum of a channel between 3 MHz and 4
MHz ; SNRdB = 24 dB
B  4 MHz  3 MHz  1 MHz
SNR dB  24 dB  10 log 10 SNR 
SNR  251
Using Shannon’s formula
C  10  log 2 1  251  10  8  8Mbps
6
6
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Example of Nyquist and Shannon
Formulations

How many signaling levels are required?
C  2 B log 2 M
 
8 10  2  10  log 2 M
6
6
4  log 2 M
M  16
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Classifications of Transmission
Media

Transmission Medium


Guided Media



Physical path between transmitter and receiver
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
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Unguided Media


Transmission and reception are achieved by
means of an antenna
Configurations for wireless transmission


Directional
Omnidirectional
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General Frequency Ranges

Microwave frequency range





Radio frequency range



1 GHz to 40 GHz
Directional beams possible
Suitable for point-to-point transmission
Used for satellite communications
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
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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
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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
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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
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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
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Multiplexing
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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
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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
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Frequency-division Multiplexing
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Time-division Multiplexing
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