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

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/vsatcent/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-to-multipoint 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 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 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

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