Distinguished%20Faculty%20Lecture%20Wireless%20Communications%20and%20the%20Pleasures%20of%20Engineering%20David%20M.%20Pozar%20Electrical%20and%20Computer%20Engineering%20December%201,%202003

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Distinguished Faculty LectureWireless
Communications and the Pleasures of
EngineeringDavid M. PozarElectrical and
Computer EngineeringDecember 1, 2003
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James Clerk Maxwell (1831 1879) Scottish,
Professor of physics, Kings College (London) and
Cambridge University. Formulated the theory of
electromagnetism from 1865 to 1873.
His work established the theoretical foundation
for the development of wireless
communications. "From a very long view of the
history of mankind - seen from, say, ten thousand
years from now - there can be little doubt that
the most significant event of the 19th century
will be judged as Maxwell's discovery of the laws
of electrodynamics. The American Civil War will
fade into provincial insignificance in comparison
with this important scientific event of the same
decade." Richard Feynman, Lectures on Physics,
Vol. II
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Timeline of Wireless Communications Development .
. .
2003 - US cellular subscribers exceed 150M
Guglielmo Marconi (1874-1937) development of
wireless telegraphy trans-Atlantic 1901
Prof. H. Hertz (1857-1894) experimental
validation of Maxwell 1886-1888 at Karlsruhe
Martin Cooper, Motorola, develops first handheld
cellular phone in 1973
1920
2000
1900
1880
1980
1960
1940
1860
KDKA Radio -1920
Two-way mobile radio services 1960s 1970s
Prof. J. Maxwell (1831-1879) theory of
electromagnetism developed in 1865
1983 - Cellular AMPS service in Chicago
First television broadcast -1928
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Wireless Communications Theory 101
1. How does the radiated power density decrease
from a transmitting antenna ? 2. What is
electrical noise, and what is its effect on
wireless communications ?
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Consider an imaginary sphere of radius R
enclosing an antenna that radiates a total power,
P. The total power passing through this sphere
is given by the area of the sphere multiplied by
the power density radiated by the antenna. From
energy conservation, the total power radiated
must not depend on radius. Thus the power density
must vary as,
This is known as the inverse square law Received
power decreases as the inverse square of distance
between transmitter and receiver.
assuming an isotropic antenna
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• Random electrical noise is generated by
• thermal energy
• electric equipment (motors, vapor lamps,
  ignition systems, )
• lightning
• stellar sources
• interstellar background radiation

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Cellular Telephone Systems

• The need for mobile communications . . .
• In 1976 only 545 users in New York City had Bell
  System mobile telephones, with 3,700 customers on
  a waiting list. Nationwide, 44,000 users had ATT
  mobiles with 20,000 people on five to ten year
  waiting lists.
• An ATT marketing survey for US cellular
  telephone market in early 1980s less than
  900,000 users by year 2000 (actual figure in
  1998 was over 60 million)
• The technical challenges . . .
• power requirements (talk time, safety, weight)
• processing electronics required for base
  stations
• very limited frequency spectrum

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Radio Spectrum US Frequency Allocations . . .
AM Radio
TV 2-4
FM Radio
TV 7-13
TV 5-6
TV 21-36
TV 38-69
Cell
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Some current US radio spectrum allocations . .
. Cellular telephone (824-849, 869-894 MHz)
50 MHz PCS (1710-1785, 1805-1880 MHz) 150
MHz GPS (1227, 1575 MHz) 41 MHz FM Radio
(88-108 MHz) 20 MHz WLANs (2.400-2.484
GHz) 84 MHz Broadcast TV (54-72, 76-88,
174-216, 470-890 MHz) 492 MHz
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• The cellular radio concept . . .
• Many small cells (1 8 mile diameter) with
  low power transmitters
• Each cell has a base station that communicates
  with users within that cell
• Frequency reuse among seven nonadjacent cells
  (represented by same colors)
• Resolves problem of limited radio spectrum
• Actual cell coverage does not conform to the
  ideal plan shown below

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Cellular base station and connection to publicly
switched telephone network
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Cellular Telephone Operation (AMPS) . . . Mobile
transmit band 824-849 MHz, divided into 832
channels, 30 kHz wide Mobile receive band
869-894 MHz, divided into 832 channels, 30 kHz
wide Communication between mobile unit and base
station uses four channels FCC forward
control channel (base to mobile) RCC reverse
control channel (mobile to base) FVC forward
voice channel (base to mobile) RVC reverse
voice channel (mobile to base) Each base station
is assigned a single FCC/RCC pair, and 59 FVC/RVC
pairs. Mobile unit scans all possible FCC
channels, selects strongest signal. Mobile unit
responds over RCC with Mobile Identification
Number (MIN) Mobile requesting a call sends
request and number over RCC Base responds by
assigning an FVC and RVC to mobile for voice For
a call to a mobile, MTSO sends request via base
station FCC
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Call Handoff . . . As mobile phone moves from one
cell to an adjacent cell, the FCC signal from
first cell will decrease, while FCC from second
cell is increasing. When FCC of second cell is
larger, the call will be handed off from first
to second cell, with a new assignment of FVC and
RVC.
This is one reason why cell phone use is
discouraged on airplanes.
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Why is cellular coverage sometimes very poor ?
building, vehicle, or other reflector
multiple paths (multipath) can lead to
cancellation of signal at phone
cellular user
base station
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Earth-Orbit Communications Satellites
photo courtesy of Dr. Fred Dietrich, Loral
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Artists rendering of Earth-orbit satellites . . .
courtesy of Professor Kurt Manheim, Loyola Law
School
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Characteristics of Some Recent Satellite Systems
Satellite System Purpose Parent Company Number of satellites Orbit Cost Completion Date Current Status
Iridium Voice Motorola 66 LEO 5B 1998 bankrupt 1999 (1)
Globalstar Voice Loral/Qualcomm 48 LEO 4B 1999 bankrupt 2002 (2)
Teledesic Data McCaw/Gates 840 (1994) 288 (1997) LEO 9B ? not completed suspended
DBS Direct TV Hughes (and others) 2 GEO 175M (each) 1993 2.1B revenue (2001)
(1) Iridium assets acquired for 25M, limited
service restarted 2001, DoD primary customer. (2)
Globalstar assets acquired for 55M, continuing
with limited service.
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Photograph of main mission antenna panel for
Iridium satellite. Each of the 66 Iridium
satellites employs three of these antennas, at
cost of about 200,000 each.
photo courtesy of Raytheon Company
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Communications Satellite Launches - Actual vs.
Forecast
abstracted from Wired Magazine, data from FAA
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Can extraterrestrials receive our television
broadcasts ?
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No
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(No Transcript)
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• Wireless systems of the (not too distant) future
  . . .
• Wireless solutions to the last mile problem
• High data rate wireless local area networks
  (Gigabit, with QoS and security)
• Ultra Wideband networking (short distances, high
  data rate)
• Wireless Personal Area Networks (PDAs, cameras,
  printers, )
• Mesh Networks (adaptive routers, sensor
  networks)
• Wireless phone subscribers will continue to
  outpace land line users
• A new generation of GPS satellites with improved
  accuracy
• . . . and others, as yet unimagined

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• Engineering . . .
• From the Latin, ingeniatorem one who is
  ingenious at devising
• Engineering unfortunately shares the same root
  as the word engine
• Application of scientific and mathematical
  principles to practical problems
• Engineering education is broadly-based in math,
  science, economics, ethics, . . .
• But successful engineering requires intuition
  about problems and solutions
• The engineering process begins with a desire -
  James Adams
• Engineering creativity produces original ideas,
  new approaches, radical designs
• Most engineering developments are incremental,
  but some are disruptive
• Originating a new idea may be glorious,
  implementing that idea is much harder
• Experimentation is often required, and failure
  is common
• It is difficult to foresee how a new technology
  will be used
• Being ingenious at devising is a fundamental
  characteristic of humans . . .

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Children are natural-born engineers . . .
Mike Pozar, ingeniously devising a transportation
system, circa 1987
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• The End
• Some suggested reading . . .
• The Science of Radio, Paul Nahin, 1996
• The Evolution of Untethered Communications,
  National Research Council, 1997
• The Soul of a New Machine, Tracey Kidder
• Flying Buttresses, Entropy, and O-Rings The
  World of an Engineer, James Adams
• The Existential Pleasures of Engineering, Samuel
  Florman

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(some additional slides follow)
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• Are cellular telephones safe ?
• Some background information
• Radio and microwave radiation (non-ionizing) is
  a known health hazard
• Proven biological hazards of RF radiation are
  due to thermal effects
• Best measure of RF internal exposure is the
  Specific Absorption Rate (SAR) W/kg
• FCC/FDA limits peak exposure to 1.6 W/kg of
  tissue, averaged over any 1 gram
• European limits are less restrictive, specifying
  1.6 W/kg averaged over 10 grams
• FCC limits power density at 869 MHz to 0.58
  mW/cm2
• FCC/FDA limits handset power to 600 mW newer
  phones run at about 125 mW
• Base station power typically 5-10 W
• Worst-case exposure from 50 tower, 50 channels,
  is about 0.14 mW/cm2
• Exposure levels decrease quickly with distance
  (inverse square law)
• A proven hazard of cellular phones using while
  driving

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• Many safety studies of non-thermal RF effects
  have been performed, and more are ongoing. A
  recent heavily-referenced review states,
• The epidemiological evidence for an association
  between RF radiation and cancer is found to be
  weak and inconsistent, the laboratory studies
  generally do not suggest that cell phone RF
  radiation has genotoxic or epigenetic activity,
  and a cell phone RF radiationcancer connection
  is found to be physically implausible. Overall,
  the existing evidence for a causal relationship
  between RF radiation from cell phones and cancer
  is found to be weak to nonexistent.
• from Cell Phones and Cancer What Is the
  Evidence for a Connection?, J. E. Moulder, et
  al, RADIATION RESEARCH vol. 151, pp. 513531,
  1999.
• Radiation Oncology, Medical College of
  Wisconsin.
• An 800M lawsuit brought by a 43 year-old
  neurosurgeon against several cell-phone
  companies, alleging that his brain tumor was
  caused by cell phone use, was dismissed in US
  District Court in Maryland in 2002. The Court
  ruled that there was no reliable scientific
  evidence linking cell phone use to brain cancer.

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Bandwidth vs. Data rate . . . Contrary to
current parlance, these are not equivalent. Data
rate (C bits/sec) for a given bandwidth (B Hz)
and signal-to-noise ratio (S/N) is given by the
Shannon Channel Capacity theorem
Depending on the signal-to-noise ratio, S/N, we
may have C ? B, (traditional radio systems,
e.g., 100 MHz ? 100 Mbps) C lt B (GPS, Ultra
Wideband radio, e.g., 5 GHz ? 100 Mbps) C gt
B (DBS, other high-data-rate systems, e.g., 100
MHz ? 400 Mbps)
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Wireless Network Standards
slide courtesy of Dr. Dev Gupta, Newlans, Inc.