Wireless Communications and
Global WANs
ISOM 591
April 10, 2000
Wireless
 Unguided
media for which an antenna
radiates electromagnetic energy into the
medium (air) and another antenna acts as the
receptor
 directional (point to point) and
omnidirectional (like radio)
 the dish is the most common type of
microwave antenna
 a series of microwave antennas can be used
Wireless
 Major
applications include long distance
telecommunications (long distance
international links), point to point trunks
between telephone exchange offices,
television distribution, direct broadcast
satellite (ex: DirecTV), closed circuit TV,
VSATs, and data links between LANs
 in international telecom, used to bypass the
local telephone company
Wireless: General Applications
 microwave
provides high capacity links in
many established and emerging networks
 geosynchronous orbiting satellites, low
orbiting satellites
 analog cellular phones
 digital cellular phones promise more clarity
and more capacity
 wireless PCS (personal communication
systems)
Advantages of Microwave
Transmission
 Common
frequencies are in the range of 2
to 40 GHz, thus this has high frequency,
high bandwidth, and a high potential data
rate
 global access to information for a mobile
workforce
 mobility within the workplace and home
 ability to overcome environmental obstacles
–
cable is often impractical
Limitations of Microwave
Transmission
 Attenuation
(repeaters or amplifiers need to
be placed 10 to 100 km apart)
 interference (ex: weather, airplanes)
–
disruption of radio frequency transmissions
 security
is a concern
 transmissions areas overlap
 expensive and limited availability
Wireless Regulatory Issues
 FCC
and/or licensing permit required for
microwave and satellite transmissions
 sections of the electromagnetic spectrum are
assigned by the FCC
–
television, radio, cellular phones, ham radio,
military communication systems
 other
bands of the spectrum may be used
without license or permit
 ITU issues licenses and allocates frequency
bands
Microwave and Satellite
Transmission
 microwave
–
–
–
transmission
form of radio transmission using ultra high
frequencies in the gigahertz range, wide
bandwidth
line-of-sight, subject to interference by planes,
rain, etc.
microwave towers used to refresh and
retransmit signal
Microwave and Satellite
Transmission
 satellite
–
–
–
–
–
links
a communications satellite is basically a microwave
relay station, linking two or more ground-based
microwave transmitter/receivers
transponders amplify and retransmit data to earth
the C band 4-6 GHz and the Ku band 14-16 GHz
are set aside for the exclusive use of satellites
leasing equipment for a private ground station costs
between $3500 and $8000 per month
the footprint is what the satellite can see from
22,300 feet
Satellites
 satellites
simply reflect and amplify signals
transmitted to them
 the transponder provides this function and
the typical unit is equivalent to 36 Mhz of
bandwidth
 a transponder receives a signal, amplifies it,
and transmits it to Earth
 signal to the satellite is called an uplink,
from a satellite is called a downlink
Satellites
 cross-strapping
allows a satellite to receive
a signal on one frequency and transmit it on
another
 the size of the footprint (area covered by the
signal) can be controlled
 intersatellite links can allow carriers to
transmit signals between satellites
 satellites can be characterized by their orbits
Geosynchronous Satellites
 geosynchronous
(or geostationary)
rotating at the same angular speed as earth
– a stationary target for signals uplinked by Earth
stations
 footprint or coverage is about 1/4 to 1/3 of the earth
 a single satellite can be used to satisfy demand from
many nations
 a 4 degree spacing required to keep satellites from
interfering with one another, thus the number of
satellites is limited
–
Geosynchronous Satellites
delay for signals travelling at the speed of light
(186,00 miles/sec) to the satellite and back would
be 2*22,300/186,000 = 0.24 sec.
 latency or delay a real problem in data
transmission

–
transaction-oriented applications and associated
protocols with a large number of requests and responses
result in too many roundtrips
 Useful
for broadcasting over large areas
VSAT
 very
small aperture terminals which use
geosynchronous satellies to provide the
communication backbone
 a VSAT consists of a small satellite
communications antenna and electronics
which allow the location to access the
satellite
 http://www.ge.com/capital/spacenet/vsatcen
t/what-is.com
VSAT
 the
satellite connects the VSAT location to a
central hub facility which routes data to the
appropriate location
 each VSAT connects to a hub, a
communications earth station
VSAT
a
typical antenna is 6 feet in diameter and
can be mounted on the customer’s roof or
on a pole
 the VSAT is the indoor electronics
component which connects to the router
 the VSAT encodes the data, and transmits
via the outdoor components to the satellite
Low Earth-Orbiting Satellites
inexpensive satellites which orbit the earth about
200 to 700 miles above the surface
 signal is stronger than that of the geosynchronous
satellites
 coverage can be localized so less spectrum can be
consumed
 services include personal communication services,
radiodetermination service (location services like
GPS), two-way messaging, paging, fax, data

Low Earth Orbiting Satellites
(LEOs)
 for
orbits closer to earth, less power is
needed
 these are not geosynchronous and orbital
speed relative to earth is increased
 footprints are smaller
 thus, a constellation of satellites is needed
to provide services like cellular
LEOS: “Teledesic / Iridium:
Internet in the Sky”





Teledesic, Motorola, Boeing, McCaw, Gates, Matra Marconi
Space (France and UK)
world’s first network to provide fiber-like access to telecom
services including linking enterprise computing networks,
broadband Internet access, videoconferencing and other digital
needs
licensed in March 1997 by FCC and in November, 1997 by the
ITU, service to begin in 2003
other projects under development include Odyssey (TRW),
GlobalStar (QualComm)
Not exactly a success story!
International Satellites
 no
single location or route needs to generate
a sufficient volume of traffic to justify its
investment since such a large area is
covered
 Satellites can be used for point-tomultipoint service like video distribution,
broadcast and news services
 medium for international
telecommunications
International Satellites
 until
the middle 1980s, only the US, the
European Space Agency, and the former
Soviet Union had satellite launching
technology
 recently, China, Israel, Japan, Norway,
Australia, to name a few, have launched
satellites
 lifetime expectation is about 15 years
 satellites and submarine cables are
complementary media
International Satellites:
Technical and Logistical Factors
 Technology
–
–
cost-effective ways to make use of higher
frequencies
signal reception
 Geography
–
and climate
work around rainfall
International Satellites:
Technical and Logistical Factors
 spectrum
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use and management
spectrum planning and frequency allocation by
the ITU
incumbents must share allotted frequencies
with newcomers
traffic needs motivate migration from C-band
earth stations to the higher frequency Ku-band
some reservations of slots
International Satellites:
Technical and Logistical Factors
 politics
–
–
–
national regulatory policies can promote or
restrict use, demand, and availability
some nations (US, UK, Canada, Australia and
Japan) have liberalized policies while most
countries maintain monopolistic control for
basic switched satellite services
satellite-delivered messages have great social
implications and impact
»
uncensored broadcasts from the West
Satellite Policies: The US
 “open
skies” to encourage all technically,
financially, and legally qualified applicants
to provide satellite services
 advocates transborder use of domestic
satellites and international competition from
private ventures
Satellite Policies: The US
 US
initiatives include creating a new
category of carrier (private carrier) that is
relatively free of regulation
 this gives users the freedom to negotiate
service contracts rather than the government
issuing service tariffs
INTELSAT
 established
in 1964 as satellite technology
moved from military to commercial
applications
 goals are to provide universal service and
global connectivity at rates averaged over
densely and sparsely populated areas
 more than 140 member countries
INTELSAT
 nations
signed INTELSAT and Inmarasat
agreements and treated these organizations
as diplomatic organizations like the ITU
and the United Nations
 exempt from taxes, officers and employees
immune from lawsuits
 in 1965, launched the world’s first
commercial communications satellite,
connecting North and South America with
Europe and Africa
INTELSAT
 approximately
$1 billion revenues in 1997
 200 countries and nations served
 20 satellites
 voice, data, video services provided
INTELSAT
 each
country member designates one or
more companies to resell IntelSat’s services
in their country
 works like a wholesaler, most of its
customers are carriers who resell services to
end users
–
–
authorized local resellers (signatories) invest in
INTELSAT and receive profits
long distance carriers like AT&T and BT, international
broadcasters like CNN and BBC, international
manufacturers, news wire services, banks, etc.
INTELSAT
 currently
manages a fleet of 20 highpowered satellites that send telephone,
television, and data transmissions from
around the world
 held a monopoly on international satellite
traffic until the 1980s
 many regional satellite networks in Asia,
South America, and elsewhere
 commercial satellite competitors like
PanAmSat
INTELSAT
 in
1992, major organizational changes were
made to move toward the
commercialization of the group
–
six additional satellites have been transferred to
a spinoff company, New Skies satellites, started
in 1998, with and IPO in 1999
 changing
global customer base (allowing
more resellers to buy directly from IntelSat)
and an increase in competition
INTELSAT
 members
oversee its operations via a board
of governors comprised of member country
reps
 600 person staff in Washington, D.C.
–
–
–
engineers who control and maintain the
satellites’ geostationary orbits
a team who assist users
marketing group
INTELSAT: Using an Extranet
to Communicate with Customers
 expanded
their sales and marketing intranet
to include customers
 IntelSat Business Network (IBN) provides
customers with technical and sales
information
 can determine coverage, tranmission
capacity available, which firms have dishes
to receive and send transmissions
 can find out what the tariff is and what to
charge their customers
Satellite Applications
Globalstar is a low orbiting earth satellite network
– 48 satellites in orbit covering 70 degrees north
and south of the equator
– acts as a communications network to ground
stations which connect the user to the land
network
– this means you can roam the globe with your
cellular phone
 work sites in remote areas can use the Immarsat
(International Maritime Satellite Organization)
satellite to gain access to the global phone system

Satellite Applications
 DirecTV
–
–
–
–
Hughes and USSB
the DirecTV satellite circumvents cable and broadcast
TV to offer interactive television directly to subscribers
programming is transmitted as digital video with 16-bit
stereo and audio, compatible with NTSB and HDTV
a back channel operates over a modem to make home
shopping and interactive games available to the
subscriber
Maintaining the Satellite System
 new
satellites are streamlined in size,
weight and capacity
 privatized from government to private
ownership
 renovated and relaunched
 retrieved by space shuttle
–
–
AsiaSat-1 brought back to earth
INTELSAT VI was retrofitted in space