This section will provide a tutorial on the many different transmission technologies used to provide broadband services. Because wireless broadband technologies likely will become an increasingly significant option, this section will also provide an introduction to basic radio spectrum management.*
5.3.1 Spectrum Management
While key wire-based technologies operate using closed circuit copper or glass conduits, wireless broadband transmission technologies use radio spectrum, a shared resource with physical characteristics that require attention to the potential for excess demand and interfering uses. Typically governments manage the allocation and assignment of spectrum with an eye toward reducing the likelihood of both interfering use of the same frequency and insufficient capacity to meet current and future demand for specific services, such as wireless broadband.
Governments manage this shared public resource by acting as a “traffic cop of the airwaves” who determines what uses can be made for specific blocs of spectrum and who can use specifically assigned frequencies through licensing. These potentially intrusive management strategies originated when spectrum users had limited technological means to avoid causing interference to other users of the same frequency. Rather than risk the potential for harmful interference, governments typically identify a specific use for a range of frequencies and assign specific frequencies solely to one user. When multiple users receive authorization to use the same frequency from a National Regulatory Authority, the potential for interference is deemed minimal primarily based on the geographical separation of the licensed users.
This allocation of spectrum blocs by service and assignment by specific user has occurred in both intergovernmental forums such as the International Telecommunication Union (“ITU”), and unilaterally in specific national spectrum policies. For example, the ITU, a specialized agency of the United Nations, decided long ago which frequencies nations should use for commercial radio and television broadcasting. Individual governments have a sovereign right to determine whether to accept the global consensus on such spectrum allocations and how to assign usage rights. Generally nations implement the consensus spectrum allocations decisions made at the ITU, but they can vary the terms and conditions under which operators secure spectrum usage rights. Even as many nations support commercial use of broadcast spectrum by private operators some nations, including developed nations such as the United Kingdom, continue to have government entities as the sole national broadcaster, or as a subsidized alternative to commercial broadcasting.FIGURE 5.8Spectrum Allocations in Blocs
Source: United States National Telecommunications and Information Administration, United States Frequency Allocation Chart (2011), available at http://www.ntia.doc.gov/files/ntia/publications/spectrum_wall_chart_aug2011.pdf
Wireless Broadband Spectrum Management
Wireless broadband operators need large amounts of spectrum so that they can provide very fast transmission of feature rich content, such as full motion video, to ever increasing numbers of subscribers with growing demand for service. Because all useable spectrum already has a specified use, governments can accommodate growing demand for wireless broadband spectrum only by reallocating blocks of spectrum with already specified uses. This means that existing or prospective users of spectrum authorized to use specific frequency bands, may lose that right, or face the need to share access, a process that requires coordination based on location of the spectrum use, or the implementation of techniques designed to support multiple, non-interfering use by two or more nearby operators.
High bandwidth requirements and rising demand for wireless broadband combine to support the use of radio spectrum at very high frequencies. These frequencies, measured in the billions of cycles per second, termed GigaHertz (“GHz”), only recently have become available as scientists invent ways use spectrum that increasingly has characteristics of visible light energy. Useable radio spectrum lies on a continuum with sound energy at the low end and infrared and light waves at the high end. Low radio frequencies have some characteristics like sound such as the ability to penetrate walls and other obstructions. Very high frequencies have some of the characteristics of light such as the ability to bounce off obstructions. Having only recently made allocations of the highest usable frequencies, governments can more easily accommodate the vast demand for wireless spectrum at these high frequencies in light of the possibility that at least some frequency bands have few current government and commercial users.
Very high spectrum also has transmission characteristics, known as propagation, which supports many broadband uses. For example, these frequencies, like light, lose power quickly and on a predictable and measureable basis. Wireless broadband operators can use the same frequencies at nearby locations without interference thereby making it possible to accommodate lots of simultaneous uses in the same region. This efficient frequency reuse can occur, because very high frequencies do not travel long distances, a characteristic much more likely to occur at lower frequencies. At lower frequencies signals with the same transmission power travel farther and thereby have the potential to interfere with more users operating on the same frequency over a larger expanse of terrain.
The likely growing demand for wireless broadband service can generate a shortage, unless governments respond by reallocating additional spectrum. Candidates for such reallocation generally represent underused spectrum that results from an initial overly generous allocation, or because usage patterns have changed. Spectrum reallocation decisions typically generate conflicts, because no incumbent user group will welcome the need to operate more efficiently, possibly having to satisfy all requirements with a net reduction in available spectrum capacity. Governmental spectrum users will invoke national security and cost concerns over any loss of available spectrum, while incumbent private users also will complain about incurring higher costs and inconvenience.
All spectrum has value, but that triggering the greatest demand logically also has the greatest value. Governments may try to extract some of this value by auctioning off the most desirable spectrum designated for the most attractive services that include wireless broadband. While some spectrum auctions have accrued limited returns, ones allocating mobile radiotelephone service and next generation broadband networks have generated up to several billions of dollars for national governments.
Because spectrum scarcity is all but inevitable for broadband applications, governments likely will try to reallocate additional spectrum by forcing some users to make do with less. This freeing up of spectrum can occur when new digital technologies make it possible for operators to:
- send signals using less total bandwidth;
- carry multiple calls and data sessions over the same channel;
- compress signals so that content can travel using narrower channels;
- increase the speed by which traffic reaches an end user; and
- use new techniques that avoid causing interference even by users in close proximity using the same frequency.
The so-called Digital Dividend* provides an example of how digital transmission techniques make it possible to accommodate incumbent operators’ bandwidth requirements using less total spectrum. When broadcast television operators convert from analog to digital transmission, governments typically can “refarm” portions of the frequency band allocated by reassigning all incumbent users into a smaller range of usable channels thereby freeing up spectrum for new uses.* Digital transmissions reduce the potential for harmful interference between the signals of two or more television broadcasters, because the signal weakens (attenuates) quickly after serving a predictable geographical area. Analog signals on the other hand degrade more slowly making it possible for signal reception and interference to occur over farther distances from the transmitter. By relocating all broadcasters onto more closely aligned channels governments can free up spectrum and reallocate it for wireless broadband use.
Spectrum conservation also can take place through the use of transmission formats that facilitate shared use by several simultaneous users of the same frequency channel. By using smart transmitters and receivers, equipped with digital signal processing technology, many nearby operators can identify unused spectrum and operate at very low power. Before transmitting, smart radios can identify actual existing users nearby, or consult a data base of known users.
Additionally governments can permit use of allocated, but sparsely used spectrum thereby permitting unlicensed uses in these geographically dispersed “white spaces.”* NRAs typically allow white space use only if it does not cause interference with licensed operators, and other users having a higher access priority. Governments also can identify spectrum for shared use by unlicensed, low powered devices such as Wi-Fi routers that provide wireless access to broadband services. However excessive use of unlicensed spectrum leads to what economists call “the tragedy of the commons”* when no one can productively use a shared resource due to overuse that becomes apparent when users encounter congestion and interference.
Because governments cannot typically remedy all types of existing or anticipated spectrum scarcity, carriers have to employ many types of spectrum conservation techniques. Section 5.7.2 will identify many strategies used by wireless broadband carriers.
220.127.116.11 Reference Documents and Case Notes
Radio spectrum has different value based on the specific amount of bandwidth available, propagation characteristics, allocated uses and demand. For example, spectrum allocated for wireless mobile services such as cellular radio and broadband, can generate billions of dollars in a competitive auction. On the other hand some spectrum has little value, because of limited demand, or because a legislature or National Regulatory Authority has decided that the public should have access on a free and unlicensed basis as is the case for Wi-Fi spectrum. Spectrum scarcity occurs when demand exceeds supply and a government cannot quickly add to the inventory of available spectrum allocated for a specific use.*
5.3.2 Fiber Optic
Increasingly widespread installation of flexible, fiber optic cables as thin as one strand of hair constitutes one of the major telecommunications transmission media for broadband networking. Glass strands coated (“doped”) with trace amounts of rare earth elements such as erbium provide a medium that can guide extremely fast pulses of laser light beams across significant distances without the need for reamplification (“regeneration”) of the signal. Very narrow, high frequency light energy can travel great distances, because this type signal can “refract” or bounce from one edge of a glass cable to the other without quickly degrading or weakening as happens when electrons travel through copper wires. While a copper medium generates friction and resistance to the conduction and transmission of electrons, the glass medium offers far less obstruction to the transmission of laser signals.
Carriers using fiber optic cables can transmit vast amounts of broadband traffic, not only because single strands have wideband capacity and fast transmission speeds, but also because many pairs of cable (for two-way, simultaneous upstream and downstream “duplex” traffic) can be bundled together and then encapsulated with plastic and metal cladding for structural support. Dense Wave Division Multiplexing makes it possible for multiple laser beam (“optical carrier”) transmissions to take place via a single cable strand using different, non-interfering lightwave frequencies.
While the technology of fiber optic cable refraction and transmission involves complex science, the use of lasers in compact disk (“CD”) and digital video disk (“DVD”) players can provide insights on how the cables operate. If you were to examine the operation of CD and DVD players, you would see an apparently constant illuminating red or blue light, which you should examine only from a distance and at an angle. The light source actually turns on and off in very quick succession matching the on and off sequence of data transmissions which can be reduced to a series of ones and zeros. CD and DVD players use the laser beams to “read” the digital signal streams imbedded in the disk. The concept of different operating frequencies are represented by the red laser beam used by lower frequency and lower capacity CD and first generation DVD players, as well as the higher frequency and higher capacity “blue ray” laser frequency used by current generation DVD players.
The substantial capital expenditures required to install fiber optic cables support their use primarily for high capacity transmission projects often covering long distances. Operators seek to spread the cost to acquire rights of way and install wires within ductwork over a large pool of users. While the services provided via fiber optic cables may be priced on an average cost basis, the installation costs of such facilities are distance sensitive, i.e., the total cost increases incrementally as the length of the cable installment grows. However, once installed fiber optic cables provide great opportunities to scale up and increase overall transmission capacity simply by activating additional cable pairs, or by using multiple frequencies of light in each cable. Except for instances where operators cannot economically justify the cost of installing cables most long haul carriage of broadband traffic takes place via fiber optic facilities.FIGURE 5.9Fiber Optic Cable Elements
Source: United States Dept. of Transportation, Highway Administration. Fundamentals of Telecommunications, available at http://ops.fhwa.dot.gov/publications/telecomm_handbook/chapter2_01.htm
18.104.22.168 Reference Documents and Case Notes
For a primer on how fiber optic cable operate see:
- Matt Burns, Techcrunch.com, A Clever Video Primer On Fiber Optic Cables, available at http://techcrunch.com/2011/06/22/a-clever-video-primer-on-fiber-optic-cables/
- Youtube videos, available at http://www.youtube.com/watch?v=llI8Mf_faVo
- Tutor Vista, Optical Fibres, available at http://www.youtube.com/watch?v=aqazAcE19vw
- Australian Broadcasting Corp., How Optical Fibre Works, available at http://www.abc.net.au/news/2011-05-31/how-optical-fibre-works/2737088
- Fiber-to-the-Home Council, Advantages of Optical Access, available at http://www.broadbandproperties.com/2007issues/feb07issues/ftthprimer_feb.pdf;
- OECD, Fibre Access: Network Developments in the OECD Area”, OECD Digital Economy Papers, No. 182, OECD Publishing (2011), available at http://dx.doi.org/10.1787/5kg9sqzz9mlx-en
For background on how Dense Wave Division Multiplexing works see:
- Columbia University, High Performance Communication Networks (EC/TC)
- Dense Wave Division Multiplexing, available at http://www.ee.columbia.edu/~bbathula/courses/HPCN/chap04_part-3.pdf
- Gerald P. Ryan, The Applied Technologies Group, Dense Wavelength Division Multiplexing, available at https://aresu.dsi.cnrs.fr/IMG/pdf/dwdm_ciena.pdf
- Fiberoptic.com, DWDM - Dense Wavelength Division Multiplexing, DWDM systems,available at http://www.fiberoptic.com/adt_dwdm.htm
Kansas City Gigabit Test and Demonstration Project
After inviting localities throughout the United States to submit proposals Google selected Kansas City, in the states of Missouri and Kansas to serve as the first site for the construction of a metropolitan wide broadband network operating at speeds in excess of 1 Gigabit per second (“Gbs”). Goggle hopes that this test and demonstration project will show how the private and public sector can partner to expedite widespread access to next generation networks capable of delivering service at bitrates well in excess of what the fastest networks currently can provide.
For background on the Google Fiber — Kansas City Gigabit Test and Demonstration Project see:
- Geek.com, How Google Fiber Will Work, available at http://www.geek.com/articles/chips/how-google-fiber-will-work-20120726/
The Australian National Broadband Network
Determining that it should expedite the availability of affordable and ubiquitous broadband service, the Government of Australia has underwritten the development of a wholesale broadband network with the goal of serving every resident in the country. The venture will provide direct fiber connections to 93 percent of the population at speeds of up to 100 megabits per second (“Mbps”) with the most remote residents served by terrestrial wireless and satellite technology providing bit transmission rates of up to 12 Mbps. The network will provide business with up to 1 Gbps downstream and 400 Mbps upstream service.
For background on Australia’s National Broadband Network see:
- NBN Co. World Wide Web site; available at http://www.nbnco.com.au/
- Government of Australia, Department of Broadband, Digital Communications and the Digital Economy, National Broadband Network World Wide Web site, available at http://www.dbcde.gov.au/broadband/national_broadband_network
- The Coalition’s Plan for Fast Broadband and an Affordable NBN (April, 2013) (proposing modifications that will reduce the cost of the NBN), available at http://www.malcolmturnbull.com.au/wp-content/uploads/2013/04/Broadband.pdf
- Background Papers, available at http://www.malcolmturnbull.com.au/wp-content/uploads/2013/04/Background.pdf
- International Telecommunication Union, Case Study, Toward Universal Broadband Access in Australia, available at http://www.itu.int/ITU-D/asp/CMS/Docs/Australia_broadband_case.pdf
- Carnegie Mellon Heinz College, Max Booker, ed., An Analysis of the national Broadband Network (April, 2012),available at http://www.heinz.cmu.edu/download.aspx?id=3164
Satellites perform a vital role in the broadband ecosystem, particularly for nations located far from coastal connections to transoceanic fiber optic cables and major population centers served by them. From a vantage point located 22,300 miles above earth communications satellites can provide a signal relay service covering as much as one third of the earth’s surface. By operating as a “bent pipe” satellites can receive “uplinked” signals from earth and relay (“downlink”) them back down to locations within a large “footprint,” or signal contour. Satellite technology has made a reality to something envisioned by science fiction author Sir Arthur C. Clarke. He predicted the use of an artificial satellite located at a specific orbital location where the speed of the satellite relative to the earth’s orbital speed made the satellite appear motionless.FIGURE 5.10Communications Satellites Operate as "Bent Pipe"
Source: Viterbi Voices Blog site (July 18, 2012), available at http://viterbivoices.usc.edu/emily/summer-at-boeing/
These geostationary satellites are located in a narrow orbital arc where the earth’s gravitation pull is offset by the centrifugal force created when the satellite was launched. Because communications satellites primarily are subject to the earth’s gravitation pull, they are termed geosynchronous. Communications satellites also operate in a geostationary mode when their orbital speed matches that of the earth and the satellites operate above the equator. At this location satellites appear to hover, motionless thereby eliminating the need for receiving dish antennas on earth to track a moving target. Such earth station equipment costs less when they can “lock in” on a satellite operating in a single location.
Signal transmissions from satellites travel long distances and generate a large footprint on the surface of the earth. An unconcentrated satellite signal can cover as much as one-third of the earth’s surface making it possible for a single source of content to reach many receivers located within the footprint. This point-to-multipoint capability makes satellites well suited for content delivery targeted for access by many simultaneous users, e.g., video and television relay, but the distance from earth results in some negative factors when used for Internet access by individuals and for point-to-point communications between two people as occurs in telephone calls. The time it takes to send and receive traffic from distant satellites results in comparatively more delay than what occurs using terrestrial options. Such latency can present problems for traffic that frequently switches between sender and receiver, videogames. Also without increasing signal strength by narrowing the size of the footprint, or using higher powered transmitters satellites require large earth station dish antennas and other equipment having significant bulk and expense.*FIGURE 5.11Satellite Point-to-Multipoint Service
Source: Deha Telekom, available at http://www.deha.net.tr/satellite_vpn.html
Despite their limitations, satellites perform a vital role in extending the geographical scope and reach of broadband access to areas where a business case does not support private venture investment in very high capacity fiber optic cable, or terrestrial wireless services. Satellites may provide the only viable, “gap-filling” broadband distribution technology to the most remote and least populated locations in the world. Additionally networks using many small, low cost satellite earth stations can serve users located in remote areas as well as places where the terrain makes terrestrial services comparatively more expensive, or infeasible, e.g., a chain of islands, and communities situated in remote desserts, mountaintops and valleys. Users in these remote areas can access broadband satellites using Very Small Aperture Antenna (“VSAT”) earth stations operating as a geographically dispersed network. A star topology VSAT network combines a central hub earth station with many smaller terminals. A mesh network eliminates the need for a central hub. Another broadband network access option in remote areas combines the use of VSATs with a terrestrial network such as wi-fi or Wi-MAX.
In light of ever-increasing consumer demand for high speed, high capacity broadband service, satellite operators have begun to launch satellites with much more available bandwidth optimized for data services. These High Throughput Satellites (“HTS”) have greater size and overall transmission power than previous satellite generations. They also use many small and steerable, “spot beam” transmitting antennas that can concentrate signals to cover a smaller portion of earth thereby making it possible to use receiving dishes with a diameter of 1-3 meters.
Satellites have significant disadvantages compared to fiber optic cables rendering them a more expensive option for point-to-point broadband transmission services. Satellites only can offer a fixed amount of bandwidth while a few fiber optic cable pairs can transmit the total capacity of all available communications satellites. Satellites have a usable life of about fifteen years and cannot easily be repaired should a malfunction occur. On average one out of every ten satellites launches fails and a single satellite typically costs $300 million or more to construct, insure, launch and track. Additionally the large distance between satellites and users results in longer transmission time (latency) than what it takes to send and receive via a terrestrial network. For two way traffic, such as voice and some kinds of Internet traffic that involve frequent changes in who transmits and who receives, such latency can present a problem.
Despite these cost disadvantages, satellites offer comparatively greater cost savings for point-to-multipoint applications, such a video content distribution, because activating an additional receiving point within the satellite footprint has low costs, primarily the installation of a relatively inexpensive receiving antenna and associated electronics.
Basic Technical Elements of Satellites
Satellites provide a broadband signal relay function requiring them to have onboard all the electronics needed to receive content and resend it back to earth. The receiver/transmitter (“transceiver”) function requires radios, tuned to satellite frequencies—typically at the very high GigaHertz (“GHz”) range—and capable of both receiving and transmitting content. To power these radios, satellites need a constant source of electrical power. The primary source comes from solar energy collected by panels that cover much of the satellite’s exterior. However, because the moon occasionally blocks access to solar energy in an eclipse, satellites also must have rechargeable batteries on board.
Satellites operate in a number of extremely high frequency bands for two primary reasons. Because of the distance between earth-based users and satellites (ranging from a few hundred to 22,300 miles) transmissions must use very narrow signals to achieve a direct line of sight link to a tiny, distant target. For downlinking from the satellite even a very narrow beam expands as the signal travels down toward earth. Extremely high frequencies transmit with very narrow amplitude and therefore have the desired propagational characteristics. Also satellites require substantial blocs of radio spectrum. National Regulatory Authorities could identify new previously unused extremely high frequency bands for which satellites could make the first practical use.
Multinational and national spectrum managers use alphabetical letters to identify the frequency bands allocated for satellite use. The C-band and Ku-band represent the major frequency band used by most communications satellites, with the later used Ka-band offering more spectrum for data and broadband service. Satellite frequency bands typically have different allocations for spectrum used to “up-link” to a satellite and for spectrum used to “down-link” from the satellite. Generally the uplinking bands operate at higher frequencies than the downlinking bands. For example the C-band uplinking frequencies range from 5.925 GHz to 6.425 GHz with the downlinking frequencies at 3.7 to 4.2 GHz.
The lettered satellite spectrum also identifies frequency bands that support different types of service, in part based on signal propagation characteristics. The L-band offers spectrum at the lowest frequencies now used by satellites. These lower frequencies make it possible to for consumers to use very small, lightweight handsets to communicate with satellites. Satellites operating in low earth orbit (“LEO”), only a few hundred miles above earth, can receive comparatively weaker signals than ones operating in geostationary orbit 22, 300 miles above earth. Mobile satellite service ventures, such as Iridium and Globalstar operate in the L-band. Other L-band services include satellites used primarily for maritime, aeronautical and mobile applications like that offered by Inmarsat. Additionally global positioning satellite (“GPS”) services operate in the L-band. These satellites operate in Middle Earth Orbit (“MEO”), about 12,500 miles above earth, and transmit with at high power making it possible for mobile handset manufacturers to install a very small module capable of receiving GPS signals.
The S-band and X-band generally provide spectrum for government satellites including frequencies used for defense, intelligence and some remote sensing applications. S-Band is also used for satellite phone and TV broadcasting in some countries.
The Ka-band provides and increasingly used frequency band for the latest generation of communications satellites, particularly ones providing broadband access such as High Throughput Satellites. At Ka-band frequencies (17.3-30 GHz) satellite operates need to consider the potential for rain, fog and smog to weaken and interfere with signals. Ka-band satellite operators can increase the transmission signal strength. Alternatively some Ka-band operators, e.g., o3B, use MEO orbiting satellites that can combine high transmission power with shorter distances to earth to ensure reliable service.
The frequency range of transceivers is limited by the amount of total weight the satellite can support. Typically satellites have several hundred MegaHertz (“MHz”) of bandwidth which is measured in terms of transponders each having about 36 MHz of capacity. Satellites double their transponder capacity through the process of polarizing signals, in the same manner as coated sunglasses block certain solar frequencies while allowing other frequencies through. Satellite receivers and transmitters are able to use signals polarized horizontally and vertically using the same frequency without significant interference.
Operating at such a great distance from earth, satellites need to amplify both received and transmitted signals. A two step process provides the necessary amplification (“gain”). First satellites use parabolic antennas that collect received signals from all angles of the curved circular surface. Similarly they aggregate transmitted signals across the same surface when transmitted back to earth. The collection and aggregation of signal strength provides a natural, non-electronic amplification in much the same way as ears and eyes collect and concentrate sound and light respectively. Satellites collect both received and transmitted signals at a single focal point known as the feed horn. Additional signal amplification takes place electronically in both receivers and transmitters.
Satellites also need systems to manage the steep variation in temperature caused by direct exposure to the sun and the absence of such exposure. Heat sinks are used to draw away heat and reduce the temperature of sensitive electronic components. Satellites also need onboard ways to keep the satellite in its proper orbit (“on station”) and properly pointed down toward earth (proper “azimuth setting).” To achieve ongoing stability, including the elimination of vibration to antennas and other sensitive components, satellites use internal motors or gyroscopes that spin internally, or at external locations lacking proximity to sensitive components. So called spin-stabilized satellites combine internal gyroscopes and exterior spinning to achieve stabilization. One way to visualize this process is to examine washing machines that have an interior basin that spins at high speeds to draw away water from cleaned clothing in what is commonly called the spin cycle. As the interior basin spins the exterior vibrates less. For spin stabilized satellites the external spinning and interior gyroscope spinning makes it possible for other parts of the satellite to operate without vibration and instability.FIGURE 5.15
Source: Samsung, available at http://www.samsung.com/latin_en/consumer/home-appliances/washers-dryers/washing-machine/WA11V5WDP/XAPFIGURE 5.16Spin-stabilized Satellite
Source: Astronautix.com, available at http://www.astronautix.com/craft/hs376.htm
The now dominant satellite design uses long wings and an interior spinning motor to control the three major axis of flight: yawl, pitch and roll. Satellites of this type are termed three-axis stabilized. Satellite carriers prefer this design, because it can provide more bandwidth using a much larger payload than spin stabilized spacecraft.
Satellites also need the ability to rise to geostationary orbit from a lower, temporary position reached by using large capacity thrusters attached to the rocket launcher. Satellites also may have to change orbital parking places (“slots”) and to make minor adjustments in their location and earth pointing orientation or attitude. Small thrusters located on the satellite provide short bursts of propulsion to place and return a satellite to its proper location and orientation relative to earth. Most satellites use a gas fuel known as hydrazine to control their position or attitude. Because satellites have only a fixed amount of fuel on board, often station keeping is the first operational element of a satellite to fail. Such satellites tend to wobble in orbit and can continue to provide service, albeit less reliable. New generations of satellites will use electric propulsion instead of gas power thereby reducing their weight and extending useable life. Satellites also have on board processors to receive and respond to instructions issued from earth and to send down information about their current health and operating conditions (“telemetry”).FIGURE 5.18Satellite Components
Source: University of Texas, TOPEX/Poseidon, available at http://www.tsgc.utexas.edu/spacecraft/topex/compo.html
Basic Technical Elements of Satellite Receivers
Satellite receivers (“earth stations”) combine many of the same elements contained in satellites to process and convert signals into useable content. Outdoors a parabolic antenna (“dish”) must have an unobstructed “line of sight” to the desired satellite downlink transmission. Most communications satellites hover 22,300 miles above the equator so earth stations located north must point south and earth stations south of the equator must point north. Dish antennas located close to the equator have a more advantageous “look angle” toward the satellite, because the signal from the satellite will traverse less of the earth’s atmosphere, as it points upward at a more direct angle. Likewise the dish can avoid more obstructions, because it can be pointed well above the horizon pointing upward instead of across the horizon. A satellite antenna located on the equator would point straight upward while dishes near the north and south pole have to point only a few degrees above the horizon.
In the immediate vicinity of the antenna satellite earth stations have electronic components that process and amplify the weak signal that has traversed 22,300 miles and been concentrated at the feed horn located above the center of the parabola. The GigaHertz frequencies used to transmit content are converted to lower frequencies so that cheaper and more effective amplification can take place. A device known as a block converter/low noise amplifier performs the frequency conversion and amplification process. The signal subsequently travels via a closed circuit low loss wire and is attached to the antenna terminal of a receiver. Inside the receiver the signal may undergo additional frequency conversions and filtering. Additionally the desired content is detached from the radio frequency carrier, a process known as demodulation. The now stripped off content is delivered to a proper device for consumption, e.g., a computer terminal, radio receiver, or television set.FIGURE 5.19Satellite Receiver Components
Source: DAE Notes, available at http://www.daenotes.com/electronics/communication-system/satellite-communication#axzz2Gdng89bH
Satellite Orbits and Footprints
Satellites operate in several orbital locations, based on their function and target audience as does the size of the transmission contour (“footprint”) received on earth. For maximum coverage and connectivity communications satellites operate in the geostationary orbital arc and use unconcentrated “global beams.” By concentrating the downlink beam size, satellite operators can increase the strength of the received signal available in a smaller geographical area. Satellites operating in geostationary orbit typically have global beams for maximum coverage, plus concentrated beams, having a smaller footprint, but making it possible for users within the smaller coverage area to install smaller receiving antennas. As a satellite footprint decreases in size the strength of the received signal increases making it possible to use smaller antennas. Concentrated footprints of geostationary satellites can cover an entire hemisphere, with about half the coverage as a global beam, a zone within one hemisphere, with about one quarter the coverage of a global beam, or as small a coverage area as a single metropolitan area (a “spot beam”). Geostationary orbiting satellites can more readily provide broadband services using spot beams, because the higher signal strength supports the needed wideband link and users can transmit and receive content using the smallest possible earth stations.
Satellites operating in orbits closer to earth are better equipped to provide broadband services, because of the lower signal delay and the ability to generate adequate signals for use by small, even handheld devices. Satellites located closer to earth than 22,300 miles lose their geostationary orbital status. This means that they become moving targets orbiting in known locations that must be tracked and monitored from earth. Several existing and planned broadband satellite venture have designed a network using satellites in middle earth orbit (“MEO”), a location where satellites can still operate without the risk of being pulled back to earth by gravity. MEO broadband networks require more operating satellites, because the closer proximity to earth reduces the footprint size. However this closer location makes it possible for subscribers to communicate with these satellites using small, lightweight devices.FIGURE 5.20Three Major Types of Satellite Earth Orbits
Source: U.S. Army Information Systems Engineering Command, Automated Information Systems (AIS) Design Guidance Long-Haul Transmission Systems, available at http://www.fas.org/spp/military/docops/army/lhaul/Lhfinweb.htmFIGURE 5.21Satellite Footprint Map
Source: Google Maps Mania, Satellite Coverage Map, available at http://googlemapsmania.blogspot.com/2008/07/satellite-coverage-map.html
Coordinating Satellite Use
Because of the potential for interference and the duty to share scarce resources, nations using satellites must coordinate their use of both satellite orbital locations and frequencies. The International Telecommunications Union (“ITU”) provides a multinational forum for conflict avoidance through the process of registering future uses and conflict resolution by providing a forum for parties to negotiate ways to avoid actual or anticipated interference. Invariably conflicts will occur, because only a relatively small number of satellites can share the geostationary orbital arc and demand for satellite services continues to grow.
Nations generally coordinate the use of satellite orbital slots through an ITU notification process that favors the first filed registration. This process may create incentives for prospective satellite operators to register uses prematurely and to increase the anticipated number of orbital slots required. The ITU has sought to reduce such “paper satellite” registrations and to impose deadlines for operators to launch and operate a satellite.
22.214.171.124 Reference Documents and Case Notes
For a primer on how satellites work see:
- Boeing, Corp. What Is A Satellite? available at http://www.boeing.com/defense-space/space/bss/about/What_is_a_Satellite_2006.pdf
- Bruce A. Henoch, Satellite Technology Basics, available at http://www.sia.org/Stratos-Henoch-SatelliteBasicsIWCE2007.pdf
- INTELSAT, A Practical Introductory Guide on Using Satellite Technology for Communications (2010), available at http://www.intelsat.com/wp-content/uploads/2013/01/5941-SatellitePrimer-2010.pdf
- For background on the satellite industry and its market segments see: State of the Satellite Industry, available at http://www.sia.org/wp-content/uploads/2012/05/FINAL-2012-State-of-Satellite-Industry-Report-20120522.pdf
Geostationary Orbiting Satellites
International Telecommunications Satellite Organization
INTELSAT was established by national governments in 1965 to operate the world’s first global communications system. The organization first operated as a cooperative, but later privatized into a commercial venture. INTELSAT operates geostationary orbiting satellites, including ones 22,300 miles above the equator in slots located between continents to maximize geographical coverage and connectivity.*
International Maritime Organization
Inmarsat was organized in 1979 to provide service to maritime users. This organization operated as a cooperative using spectrum allocated specifically for maritime applications. Nations participating in Inmarsat subsequently amended the treaty level management document to authorize the organization to serve aviation (“aeronautical”) and land-based users. Inmarsat subsequently privatized and now provides broadband services via geostationary satellites.*
Middle Earth Orbiting Satellites
O3b proposes to use Medium Earth Orbit (“MEO”) satellites, located approximately 8,000km away from Earth to provide voice and data service primarily to users in lesser developed nations situated near the Equator. The network will use Ka frequencies (20-30 GHz) in an orbital constellation that emphasizes service to users located 45 degrees north and south of the Equator. The venture’s name refers to the other three billion people on earth who lack access to advanced telecommunications services due to geography, political instability and economics.*
Low Earth Orbiting Satellites
The Iridium satellite networks uses 66 low earth orbiting satellites to provide voice and data service primarily to users in locations where reliable terrestrial service does not exist. Because the Iridium satellites operate close to earth their footprints are small thereby requiring a larger number in the constellation of satellites to provide global coverage. Iridium satellites are interconnected and cross-linked so they can communicate with nearby satellites in adjacent orbits.*
Using Satellites for Broadband Service
While satellites lack the capacity of terrestrial networks such as fiber optic cables, their large geographical coverage makes it possible to provide broadband service to users in many widely dispersed locations that may never qualify for terrestrial broadband network service. Recently launched satellites in the Ka-band (20-30 GHz) offer high power and large bandwidth making it possible for offer broadband service at speeds exceeding 10 megabits per second.*
For background on High Throughput Satellite (“HTS”) see:
- Steve Schuster, High Throughput Satellites Benefit Military and Medicine, Via Satellite magazine web site (May 24, 2013); available at: http://www.satellitetoday.com/publications/st/feature/2013/05/24/high-throughput-satellites-benefit-military-and-medicine/
- Intelsat General Corp., Defining High Throughput Satellites (HTS) (March 26, 2013); available at: http://www.intelsatgeneral.com/blog/defining-high-throughput-satellites-hts
- Harris Caprock: http://www.kafactcheck.com/hts.php
- Via-Sat web site: http://www.viasat.com/
- iDirect site: http://www.idirect.net/; and
HNS site HN and HX system description:
Gilat SkyEdge system description:
Satellite Industry Reports and Forecasts
- For a comprehensive report and forecast on the commercial satellite industry, see United States Federal Aviation Administration, 2012 COMMERCIAL SPACE TRANSPORTATION FORECASTS (May, 2012); available at: http://www.faa.gov/about/office_org/headquarters_offices/ast/media/2012_Forecasts.pdf.
- For a complete list of satellites and their transmission footprint, see http://www.satbeams.com/footprints.
Microwave technology offers low cost solutions to broadband requirements mostly for non-residential applications. For many decades it provides point-to-point analog services using very high frequencies* that can provide first and last kilometer services for local and long distance telephone companies, as well as business users. Microwave radio offers long haul transmission using a chain of repeater transmitters, each transmitting over a distance of up to 50 kilometers.
Microwave transmissions have proved quite reliable and cost effective service, largely because ample spectrum makes it possible to transmit a large volume of traffic over such networks. Operators can achieve efficient scale which makes it possible to spread the costs of constructing towers and installing the necessary electronics over a large user base.
While microwave frequencies operate in bands that favor line of sight, directional transmissions, they also can provide point-to-multipoint services spanning an entire contour of 360 degrees. Recent examples of such “omni-directional” service include wireless fidelity (“Wi-Fi”) that provides short range broadband access to multiple portable devices and Worldwide Interoperability for Microwave Access (“WiMAX”) service offering broadband access with signal contours extending out for up to 15-20 kilometers.
Microwave radio networks use parabolic antennas, much like that installed for satellite communications. However the antennas are pointed across the horizon in the direction of a transmitting antenna located on a tower or rooftop installation some distance away. Like satellite communications microwave radio transmitters need an unobstructed “line of sight” link to the next transmitting antenna in a network chain. Microwave networks contain a relatively simple combination of receivers and transmitters typically located at high vantage points to avoid obstruction by buildings and terrain. Transmitters contain a number of subsystems that include multiplexing, the combining of many different channels of traffic, encoding and modulating signals, alignment of traffic onto the proper transmitting frequency, signal amplification and filtering for spectrum control. Receiver functions include filtering, down-conversion of frequencies for easier processing and amplification, demodulation, decoding, and demultiplexing.
Microwave radio can provide a cost-effective, land-based solution particularly for terrain not favoring inexpensive underground ductwork installations, e.g., swampy, rocky and sandy locations. Similarly microwave radio can operate in urban locales, including the central business district, where tall buildings provide an ideal vantage point for line of sight transmission and reception above all obstructions. Because microwave networks do not require the installation of below ground ducts, or closely spaced above ground poles, installation can occur on a relatively short timetable. Placing transmitting and receiving antennas at high vantage points also prevents most service disruptions, like that caused by cuts in wires.
On the other hand microwave network operators need to coordinate their use with other operators to avoid congestion and interference, especially in urban locales. Additionally some equipment, located in remote and hard to reach places, will need maintenance and a source of electric power that may not be generally available in the area. Operators also need to consider propagation factors including the potential for rain and snow to cause signal fading and weakening.FIGURE 5.23Microwave Point-to-Point Communications
Source: TEMS Investigation, Wireless Networking, Part Five, available at http://pathloss40.blogspot.com/2010/11/wireless-networking-part-5.html
Microwave Backhaul and Middle Mile Services
Microwave radio networks can provide long, medium and short haul carriage of broadband traffic. Long haul applications typically substitute for fiber optic and copper based networks, because hostile terrain conditions necessitate wireless tower-based operation instead of transmissions underground, or via closely spaced poles. Short haul carriage includes the first and last kilometer access to private networks, such as a dedicated network for retailers, banks and other financial service providers, manufacturers, etc. Recently some stock market traders have installed dedicated, private microwave networks, because they can provide slightly faster opportunities (lower “latency”) to receive the latest share price information and to execute trades.*
For medium distances microwave radio networks provide essential links between facilities of users and network operators. So-called middle mile services provide a link between the geographically separate factories and other installations of users within a region. A single business venture may have the need to link many different factories, office building, warehouses, and campuses within a region. Each facility can communicate with all others via the short haul first and last kilometer microwave radio facilities interconnected with other microwave facilities designed to transmit at farther distances.
Microwave radio also provides essential “backhaul” functions for networks including satellite and terrestrial wireless networks. Many traffic receiving facilities are situated in remote locales that must be interconnected with network management facilities typically located at a central point, often in a city or suburb. Microwave backhaul networks receive and deliver traffic originating at remote tower sites like those providing cellular radio telephone service. The towers that provide service to cellphones and smartphone also contain parabolic antennas to send voice and broadband data traffic to a central facility, commonly referred to as the Mobile Telephone Switching Office (“MTSO”) for onward delivery to other networks, including the Internet “cloud.”FIGURE 5.24Wireless Backhaul
Source: New Tech Observer, Wireless Backhaul Technology Improves by Ten Fold (April 9, 2012), available at: http://www.newtechobserver.com/2012/04/wireless-backhaul-technology-improves.html
126.96.36.199 Reference Documents and Case Notes
For background on microwave backhaul see:
For a comparison of microwave and fiber optic cable backhaul see:
For an analysis of fixed and mobile network technology options see:
- OECD, Fixed and Mobile Networks Substitution, Complementarity and Convergence, available at http://dx.doi.org/10.1787/5k91d4jwzg7b-en
For background on the design of wireless networks see:
- Book chapter from Wireless Networking in the Developing World, a free book about designing, implementing, and maintaining low-cost wireless networkshttp://wndw.net/pdf/wndw2-en/ch11-casestudies.pdf
Copper metal has provided a closed circuit medium for telecommunications since the onset of telegraph and telephone service in the late 1800s. Wireline communications exploit the electron conductivity of copper and its historically moderate price. While far from ubiquitous wireline copper networks typically serve all areas with high and moderate population density and many more remote areas have qualified for universal service subsidies that extend the geographical reach of service. Copper has provided a cost-effective way to route voice, data, and video traffic via above-ground wires attached to poles and through underground ductwork. Wireline service costs increase with the distance served by a network, but carriers may average costs.
For many years copper wireline networks have provided both first and last kilometer service as well has long haul transmission. The conventional wireline Public Switched Telephone Network (“PSTN”) uses narrow gauge copper wire pairs to form a “local loop” connection between individual subscribers and a nearby telephone company switching facility. Telephone companies provide highly reliable service using direct current to power the local loop at short distances not requiring electronic amplification. For onward delivery from the initial switching facility, commonly referred to as the End Office or Central Office, telephone companies aggregate traffic by multiplexing so that larger capacity trunk line and inter-office channels handle many simultaneous calls. Telephone networks have evolved over time to incorporate digital transmission technologies and increasingly efficient routing and multiplexing of traffic.
Copper wires of higher thickness (“gauge”) and more insulation and support (“cladding”) can provide a closed circuit medium for the delivery of video content. Cable television networks use coaxial cables to offer many channels of video content through a locality or metropolitan area. Cable television operators provided the first truly broadband, two-way networking capability to residences. They started offering one way retransmission of a few broadcast stations, so called Master or Community Antenna Television. Cable operators later expanded the bandwidth available from the coaxial cable to provide many additional channels, installed an upstream channel and provided each subscriber with an address so that individual subscribers could request and receive specialized content, e.g., pay per view, video on demand, premium programming.
Both the PSTN and cable television networks have been retrofitted so that they can provide broadband, Internet access. While next generation networks primarily will use wireless and fiber optic connections, currently most residential broadband access comes from two copper-based networks: 1) Digital Subscriber Line (“DSL”) service provided by telephone companies and 2) cable modem service provided via cable television networks discussed in Section 5.7.1.