1. Wireless Communications and Global WANs
ISOM 591
April 10, 2000

2. 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

3. 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

4. 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)

5. 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

6. 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

7. 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

8. 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

9. 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 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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!

20. 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-to-multipoint service like video distribution, broadcast and news services
medium for international telecommunications

21. 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

22. International Satellites: Technical and Logistical Factors
Technology
cost-effective ways to make use of higher frequencies
signal reception
Geography and climate
work around rainfall

23. International Satellites: Technical and Logistical Factors
spectrum 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. INTELSAT approximately $1 billion revenues in 1997
200 countries and nations served
20 satellites
voice, data, video services provided

30. 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.

31. INTELSAT
currently manages a fleet of 20 high-powered 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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