Wireless Communications and Global WANs

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 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

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 • http://www.ge.com/capital/spacenet/vsatcent/what-is.com

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