Wireless Communications and Global WANs ISOM 591 April

Wireless Communications and Global WANs ISOM 591 April 10, 2000

Wireless u Unguided media for which an antenna radiates electromagnetic energy into the medium (air) and another antenna acts as the receptor u directional (point to point) and omnidirectional (like radio) u the dish is the most common type of microwave antenna u a series of microwave antennas can be used

Wireless u Major applications include long distance telecommunications (long distance international links), point to point trunks between telephone exchange offices, television distribution, direct broadcast satellite (ex: Direc. TV), closed circuit TV, VSATs, and data links between LANs u in international telecom, used to bypass the local telephone company

Wireless: General Applications u microwave provides high capacity links in many established and emerging networks u geosynchronous orbiting satellites, low orbiting satellites u analog cellular phones u digital cellular phones promise more clarity and more capacity u wireless PCS (personal communication systems)

Advantages of Microwave Transmission u Common frequencies are in the range of 2 to 40 GHz, thus this has high frequency, high bandwidth, and a high potential data rate u global access to information for a mobile workforce u mobility within the workplace and home u ability to overcome environmental obstacles – cable is often impractical

Limitations of Microwave Transmission u Attenuation (repeaters or amplifiers need to be placed 10 to 100 km apart) u interference (ex: weather, airplanes) – disruption of radio frequency transmissions u security is a concern u transmissions areas overlap u expensive and limited availability

Wireless Regulatory Issues u FCC and/or licensing permit required for microwave and satellite transmissions u sections of the electromagnetic spectrum are assigned by the FCC – television, radio, cellular phones, ham radio, military communication systems u other bands of the spectrum may be used without license or permit u ITU issues licenses and allocates frequency bands

Microwave and Satellite Transmission u 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 u 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 u satellites simply reflect and amplify signals transmitted to them u the transponder provides this function and the typical unit is equivalent to 36 Mhz of bandwidth u a transponder receives a signal, amplifies it, and transmits it to Earth u signal to the satellite is called an uplink, from a satellite is called a downlink

Satellites u cross-strapping allows a satellite to receive a signal on one frequency and transmit it on another u the size of the footprint (area covered by the signal) can be controlled u intersatellite links can allow carriers to transmit signals between satellites u satellites can be characterized by their orbits

Geosynchronous Satellites u geosynchronous (or geostationary) rotating at the same angular speed as earth – a stationary target for signals uplinked by Earth stations u footprint or coverage is about 1/4 to 1/3 of the earth u a single satellite can be used to satisfy demand from many nations u a 4 degree spacing required to keep satellites from interfering with one another, thus the number of satellites is limited –

Geosynchronous Satellites u 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. u 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 u Useful for broadcasting over large areas

VSAT u very small aperture terminals which use geosynchronous satellies to provide the communication backbone u a VSAT consists of a small satellite communications antenna and electronics which allow the location to access the satellite u http: //www. ge. com/capital/spacenet/vsatcen t/what-is. com

VSAT u the satellite connects the VSAT location to a central hub facility which routes data to the appropriate location u each VSAT connects to a hub, a communications earth station

VSAT ua typical antenna is 6 feet in diameter and can be mounted on the customer’s roof or on a pole u the VSAT is the indoor electronics component which connects to the router u the VSAT encodes the data, and transmits via the outdoor components to the satellite

Low Earth-Orbiting Satellites u inexpensive satellites which orbit the earth about 200 to 700 miles above the surface u signal is stronger than that of the geosynchronous satellites u coverage can be localized so less spectrum can be consumed u services include personal communication services, radiodetermination service (location services like GPS), two-way messaging, paging, fax, data

Low Earth Orbiting Satellites (LEOs) u for orbits closer to earth, less power is needed u these are not geosynchronous and orbital speed relative to earth is increased u footprints are smaller u thus, a constellation of satellites is needed to provide services like cellular

LEOS: “Teledesic / Iridium: Internet in the Sky” u u u Teledesic, Motorola, Boeing, Mc. Caw, 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), Global. Star (Qual. Comm) Not exactly a success story!

International Satellites u no single location or route needs to generate a sufficient volume of traffic to justify its investment since such a large area is covered u Satellites can be used for point-tomultipoint service like video distribution, broadcast and news services u medium for international telecommunications

International Satellites u until the middle 1980 s, only the US, the European Space Agency, and the former Soviet Union had satellite launching technology u recently, China, Israel, Japan, Norway, Australia, to name a few, have launched satellites u lifetime expectation is about 15 years u satellites and submarine cables are complementary media

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

International Satellites: Technical and Logistical Factors u 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

International Satellites: Technical and Logistical Factors u 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 u “open skies” to encourage all technically, financially, and legally qualified applicants to provide satellite services u advocates transborder use of domestic satellites and international competition from private ventures

Satellite Policies: The US u US initiatives include creating a new category of carrier (private carrier) that is relatively free of regulation u this gives users the freedom to negotiate service contracts rather than the government issuing service tariffs

INTELSAT u established in 1964 as satellite technology moved from military to commercial applications u goals are to provide universal service and global connectivity at rates averaged over densely and sparsely populated areas u more than 140 member countries

INTELSAT u nations signed INTELSAT and Inmarasat agreements and treated these organizations as diplomatic organizations like the ITU and the United Nations u exempt from taxes, officers and employees immune from lawsuits u in 1965, launched the world’s first commercial communications satellite, connecting North and South America with Europe and Africa

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

INTELSAT u each country member designates one or more companies to resell Intel. Sat’s services in their country u 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 u currently manages a fleet of 20 highpowered satellites that send telephone, television, and data transmissions from around the world u held a monopoly on international satellite traffic until the 1980 s u many regional satellite networks in Asia, South America, and elsewhere u commercial satellite competitors like Pan. Am. Sat

INTELSAT u 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 u changing global customer base (allowing more resellers to buy directly from Intel. Sat) and an increase in competition

INTELSAT u members oversee its operations via a board of governors comprised of member country reps u 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 u expanded their sales and marketing intranet to include customers u Intel. Sat Business Network (IBN) provides customers with technical and sales information u can determine coverage, tranmission capacity available, which firms have dishes to receive and send transmissions u can find out what the tariff is and what to charge their customers

Satellite Applications u 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 u work sites in remote areas can use the Immarsat (International Maritime Satellite Organization) satellite to gain access to the global phone system

Satellite Applications u Direc. TV – Hughes and USSB – the Direc. TV 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 u new satellites are streamlined in size, weight and capacity u privatized from government to private ownership u renovated and relaunched u retrieved by space shuttle – – Asia. Sat-1 brought back to earth INTELSAT VI was retrofitted in space