Video Transmission
`
`T e lepho ne
`S e rv ic e
`
`In te rn e t
`S e rvice
`
`To other head ends
`operated by same company
`
`FIGURE 27.6
`H ybrid fiber/coax.
`
`same fiber. Typically signals would be transmitted downstream at 1550 nm and upstream
`at 1310 nm.
`So far we’ve assumed that the same programs are broadcast to all subscribers. One trend
`in the cable industry is to direct some programs to specific subscribers, a practice called
`narrowcasting. Narrowcasting can be combined with broadcasting by transmitting the two
`sets of signals at different wavelengths, as shown in Figure 27.7.
`
`Narrowcasting
`directs programs
`to specific
`subscribers.
`MASIMO 2014
`PART 11
`Apple v. Masimo
`IPR2020-01526
`
`

`

`m Chapter 27
`
`FIGURE 27.7
`Broadcasting and
`narrowcasting
`with hybrid
`fiber/coax.
`
`1550-nm
`H igh-P ow er Transm itte r
`(b ro a d ca stin g to all
`nodes)
`
`1310-nm T ransm itte r
`N a rro w ca st to N o de 1
`
`1310-nm T ransm itte r
`N a rro w ca st to N o de 2
`
`1310-nm T ransm itte r
`N a rro w ca st to N o de 3
`
`131 0-n m T ransm itte r
`N a rrow ca st to N o de 4
`
`Identical signals can be broadcast to all nodes by splitting signals from one powerful
`transmitter at the head-end, shown emitting at 1550 nm in Figure 27.7. This can save
`money because one 100-mW transmitter generally costs less than 10 10-mW transmitters.
`Other signals can be narrowcast by directing the output of one lower-power and lower-cost
`transmitter to a specific node. Figure 27.7 illustrates this process with four 1310-nm trans-
`mitters, each directing signals to a separate node. Narrowcasting is natural for services directed
`at individual customers, such as video-on-demand programs, telephone, or data transmission.
`It also allows cable companies to target specific advertising to certain groups of customers. For
`example, a cable company might direct an advertisement for a local Mercedes dealer to the
`affluent side of town, and an advertisement for a used-car dealer to a poor neighborhood.
`Cable Modems and Telephone Service
`Data channels delivered from the head-end provide downstream data for cable modems.
`Standard cable modems are really nodes on an Ethernet local-area network. You share that
`network capacity with your neighbors. The number of households connected depends on
`the system design and the number of people who subscribe to the service.
`The distribution nodes receive downstream data and distribute those among one or
`more Ethernet networks on the cable. If the node serves 500 homes but only 2% have cable
`modems, it may deliver data to all 10 of you through one local-area network. If 60% of
`subscribers sign up for cable modems, the cable company typically would arrange its cables
`to split its 300 customers among 20 or 30 LANs.
`Like other LANs, cable modems can carry data all the time without tying up a phone line.
`Although the network is shared, downloads can reach peak speeds in the megabit range as long
`
`A cable modem is
`a node on
`Ethernet
`distributed from a
`cable node.
`
`

`

`Video Transmission
`
`as too many other users don’t try to download at the same time. Access speeds also can be
`limited by traffic jams at other points on the Internet, not just by the cable modem’s capacity.
`Cable networks also can transmit telephone signals in digital form, with special hardware
`converting the digital signals to analog form so you can use standard telephones over the
`cable network. The signals are transmitted in the same way as cable modem signals.
`Evolving Cable Networks and Bandwidth
`Interactive services such as telephone, cable modems, and two-way video increase the demand
`on distribution nodes. Present nodes are very efficient at distributing identical signals to sev-
`eral hundred subscribers. They are less efficient in distributing different services to each of
`those subscribers. The more bandwidth each subscriber needs, the more serious the problem.
`One way to enhance the bandwidth per subscriber is to split nodes so each one serves
`fewer households. Splitting nodes also can extend fiber farther into the community and
`closer to the home. Such extensions will be needed if cable networks are to compete with
`fiber-to-the-curb and fiber-to-the-home telephone networks for home users who want
`broadband net access.
`Both cable and telephone networks are installing fiber closer to homes as they strive to
`offer voice, broadband data, and video services. Convergence won’t make the two networks
`identical, but it will make them look more alike.
`
`HDTV and Cable
`
`The introduction of H D TV poses problems for cable systems, but it may also offer some
`opportunities.
`The HDTV broadcast standard at least nominally solved the technical problem of fitting
`the broader-bandwidth high-definition signal into the same channel slot as NTSC analog
`signals. Broadcast HDTV squeezes 19.2 Mbit/s into a 6-MHz slot, so cable companies can
`simply transmit the signal in broadcast format. Cable carriers can provide the needed
`interfaces between digital signals and analog sets— and digital sets and analog signals— by
`installing new set-top boxes.
`However, most cable companies don’t have extra slots available for HDTV channels to
`use. They would have to turn off other channels to make room for them, and they don’t
`have much incentive to do that as long as only a few people have HDTV. Another factor
`slowing the spread of H DTV has been a lack of available programs. The people who care
`most about video quality usually subscribe to cable or satellite services, so they face a choice
`of quality of images in HDTV versus quantity of programs on cable.
`The cable industry won’t have to replace its existing network because most of the
`changes are in the transmitter and receiver equipment. But it will have to pay for the new
`transmitters needed for HDTV signals, and for the new set-top boxes to convert the signals
`into the proper format for subscribers. The changeover will take time, and cable companies
`will lag behind broadcasters, who are much further along in the switch to HDTV.
`The issues of restrictions on the copying of digital programs remain unsolved. The
`entertainment industry wants to ban copying, but the cable companies don’t want to annoy
`
`Cable can
`trcnsmit HDTV in
`standard 6-MHz
`channels.
`
`

`

`Chapter 27
`
`Small, light, and
`durable fiber
`cables are
`valuable for
`portable systems.
`
`customers who pay for premium services partly so they can record movies at odd hours and
`time-shift them to more convenient times.
`Stay tuned for interesting times.
`
`Other Video Applications
`
`Cable television is the largest-volume video application for fiber optics, but there are many
`other cases where fiber is used for video transmission. Table 27.4 lists a sampling of
`important applications, with brief descriptions. Most involve point-to-point transmission.
`Transmission requirements vary widely for these systems. Although many require high
`transmission quality, security video systems must be low in cost. Although metal cables can
`do some of these jobs, fibers offer benefits of lighter weight, smaller size, higher signal
`quality, longer transmission distances, immunity to electromagnetic interference, better
`durability, and avoidance of ground loops and potential differences.
`Small, light, and flexible fiber cables offer important benefits where portability is
`important, such as in remote news gathering and when covering special events. Many
`systems use rugged cables and connectors developed to meet rigid military specifications
`for durability. Whenever cables are strung anywhere, they are vulnerable to damage.
`Wireless systems often cannot meet quality requirements, especially for broadcasting.
`Fiber transmission also offers more subtle advantages, notably avoiding the need to
`adjust transmission equipment to account for differences in cable length. Television studio
`amplifiers are designed to drive coaxial cables with nominal impedance of 75 LL However,
`actual impedance of coaxial cables is a function of length. As cable length increases, so does
`its capacitance, degrading high-frequency response if the cable is longer than 15 to 30 m
`(50 to 100 ft). Boosting the high-frequency signal, a process called equalization, can com-
`pensate for this degradation, but proper equalization requires knowing the cable’s length
`and attenuation characteristics. Compensation also becomes harder with cable lengths over
`300 m (1000 ft) and is impractical for cables longer than about 900 m (3000 ft). There is
`no analogous effect in optical fibers, so operators need not worry about cable length.
`
`Table 2 7 .4 Other video-transmission applications for fiber optics
`
`Application
`
`Requirements
`
`Special Notes
`
`Electronic news
`gathering, special-
`event coverage
`Security video
`Studio and production
`transmission
`Feeds to and from
`remote equipment
`(e.g., antennas)
`
`Light, durable cable to
`link mobile camera
`to fixed equipment
`Vary; low cost important
`High-quality link inside
`studio
`High transmission quality
`
`Wireless an
`alternative, but
`quality is lower
`Often low resolution
`1.5 Gbit/s for HDTV
`
`

`

`Video Transmission
`
`What Have You Learned?
`
`1. Video signals encode continuous changing pictures and sound. They are
`transmitted in standard formats and require considerably more capacity than
`voice or digital data.
`2. Analog NTSC video displays 30 analog 525-line frames a second with interlaced
`scanning. Each NTSC channel requires 6 MHz of broadcast spectrum. PAL and
`SECAM are interlaced scanning systems that each second show 25 analog frames
`of 625 lines each. These formats are decades old.
`3. Computer displays need progressive scanning to show text clearly, not the
`interlaced scanning of NTSC, PAL, or SECAM. Progressive scanning demands
`more bandwidth and faster electronics.
`4. Digitized video signals can be compressed by a factor of 75 without seriously
`degrading quality.
`5. Digital television standards cover both high-definition (HDTV) and standard-
`definition (SDTV) video. The H DTV formats have 720 or 1080 lines and a
`wide-screen format.
`6. Digital television broadcasting is being phased in to replace analog broadcasts in
`the United States, but the change probably will take much longer than had been
`planned.
`7. Video signals can be broadcast from a ground station to serve a local area.
`Microwave transmission from direct broadcast satellites can serve a much larger
`area; customers need satellite dishes and converters.
`8. Modern cable television systems now carry dozens of analog NTSC video
`channels over fiber-optic and coaxial cables; the fiber runs from the head-end to
`distribution points or optical nodes. Coaxial cables run from those points to
`homes. Customers need set-top converters to access premium channels.
`9. Hybrid fiber/coax systems transmit NTSC video to subscribers at 50 to 550 MHz.
`Digital services are transmitted to optical nodes at 550 to 750 MHz, and signals
`from subscribers return at 5 to 40 MHz. Each optical node serves about 500 homes.
`10. Hybrid fiber/coax can deliver services including Internet connections, telephony,
`and subscription video services. Internet connections via cable modem work like
`local-area networks.
`11. Hybrid fiber/coax can be upgraded by splitting optical nodes to serve fewer
`subscribers.
`12. Video transmission generally is over single-mode fiber at 1300 or 1550 nm.
`13. Small, lightweight fiber cables are valuable for portable news gathering and
`sports event coverage.
`14. HDTV signals are compressed to a digital rate of 19.3 Mbit/s, which can be
`broadcast or transmitted through cable in a signal that fits into the same 6-MHz
`band used for analog channels.
`
`

`

`15. Digital cable and DVDs are compatible with analog television sets; HDTV is not.
`Analog televisions will have to be discarded or equipped with adapters when
`television transmission is all-digital. The adapters can be installed in cable decoders.
`
`What's Next?
`
`In Chapter 28 you will learn about the role of fiber optics in vehicles and other mobile
`communications for civilian and military applications.
`
`Further Reading
`
`Analog television: http://www.ntsc-tv.com/
`Walter Ciciora, James Farmer, and David Large, Modern Cable Television Technology: Video,
`Voice and D ata Communications (Morgan Kaufmann, San Francisco, 1999)
`Digitaltelevision.com: http://www.digitaltelevision.com/
`Gary M. Miller, M odern Electronic Communication, 6th ed. (Prentice Hall, 1999). See
`Chapter 7 on television.
`Ken Nist, An H D TV Primer: http://www.hdtvprimer.com
`
`Questions to Think About
`
`1. Analog-to-digital conversion generates lots of extra bits, so it isn’t fair to say that
`a 25-megabit HDTV frame contains only 2.8 times more information than an
`NTSC frame digitized to give 9 megabits. It’s fairer to compare the number of
`lines of resolution and the width of the screen. Using those guidelines, how much
`more information does a 1080-line HDTV image contain than a 525-line NTSC
`image? Remember that the HDTV image has a 16:9 aspect ratio, while the NTSC
`image is only 4:3. (Hint: calculate the number of picture elements or pixels.)
`2. The highest resolution possible for digital television is 1080 lines by 1920 pixels,
`in 60 interlaced frames per second. The lowest is 480 lines by 640 pixels in 24
`progressive scans per second (corresponding to a digitized movie). How do the
`numbers of pixels per second compare? (Note that multiple bits encode each
`pixel, so this is not the data rate.)
`3. Digitizing voice and video both produce data streams with much higher
`numbers of bits per seconds than the bandwidth in hertz. Compare the ratios of
`bits per second per hertz for voice and video. What might cause the difference?
`4. A broadcast transmitter in a hybrid fiber-coax system generates output power of
`10 dBm (10 mW). Analog receivers require an input power of 5 ptW (—23 dBm)
`for adequate signal-to-noise ratio. If the transmission loss between head-end and
`distribution node is 10 dB (not counting the splitter), and system margin is
`
`

`

`Video Transmission
`
`10 dB, how many nodes can this transmitter support? How many could you
`serve by reducing the system margin by 3 dB?
`5. You need narrowcast transmitters for the same system. What power level do they
`require if system margin, receiver sensitivity, and cable loss are the same?
`6. You need to lease capacity on a metro network to transmit one channel of
`studio-quality H D TV from a studio to a television transmitter. The network
`operator has four types of transmitters available, which operate at rates to OC-3,
`OC-12, OC-48, and OC-192. Which one offers the capacity you need without
`too much excess?
`
`Chapter Quiz
`
`1 . What is the analog bandwidth of one standard NTSC television channel?
`a. 56 kHz
`b. 1 MHz
`c. 6 MHz
`d. 25 MHz
`2. How many lines per frame do standard analog European television stations show,
`and how many full frames are shown per second?
`a. 525 lines, 25 frames per second
`b. 625 lines, 25 frames per second
`c. 625 lines, 30 frames per second
`d. 1125 lines, 25 frames per second
`3. The H D TV standard in the United States transmits 19.3 Mbit/s after digital
`compression. How much compression is used, and what would the data rate be
`without it?
`a. 4-to-l compression, 80 MHz
`b. 10-to-l compression, 200 Mbit/s
`c. 13-to-l compression, 270 Mbit/s
`d. 75-to-l compression, 1500 Mbit/s
`e. none of the above
`4. What key development made the quality of analog fiber-optic transmission
`adequate for cable television trunks?
`a. highly linear distributed-feedback lasers
`b. inexpensive single-mode fiber
`c. dispersion-shifted fiber
`d. digital video compression
`e. optical amplifiers for 1550-nm systems
`
`

`

`Chapter 27
`
`5. What is the most important advantage of fiber optics over coax for distributing
`cable television signals from head-ends to optical nodes?
`a. Fiber optics are hard to tap, so they reduce signal piracy.
`b. Fiber repeater spacing is much longer, avoiding noise and reliability
`problems with coax amplifiers.
`c. Fiber can be extended all the way to subscribers.
`d. Fiber cables are less likely to break.
`
`6. How are analog video signals distributed to subscribers on present cable
`
`television systems?
`a. All subscribers receive the same signals, which require set-top decoders to
`show premium services.
`b. Signals from set-top controls are used to switch designed signals to the
`home.
`c. Equipment at the head-end switches selected services to each subscriber.
`d. One pair of optical fibers runs directly from head-end to home.
`7. What must cable systems change to transmit H DTV signals instead of NTSC
`analog video signals?
`a. All coaxial cable must be replaced with fiber-optic cable reaching homes.
`b. Analog transmitters and set-top boxes must be replaced with digital
`versions.
`c. Only the transmitters at the head-end must be changed to HDTV
`format.
`d. Only the set-top boxes and the cable type must be changed to H DTV
`format.
`e. No changes are necessary because cable transmission has always been
`digital.
`8. What frequencies are used for signals from the subscriber to the head-end in
`hybrid fiber-coax?
`a. 50 to 550 MHz
`b. 0 to 1 GHz
`c. 550 to 750 MHz
`d. 5 to 40 MHz
`e. none of the above
`9. How do cable modems work on hybrid fiber/coax networks?
`a. They switch signals directly from the head-end to individual subscribers.
`b. They transmit signals in one direction only.
`c. They function like a local-area network, addressing high-speed signals to
`one of many subscriber terminals served by the same network.
`
`

`

`Video Transmission
`
`d. They digitize video images for videoconferencing but cannot be used for
`other purposes.
`e. They are incompatible with hybrid fiber/coax.
`10. Which format is used for digital television displays?
`a. 1080 lines, 1920 pixels, 60 interlaced frames per second
`b. 1080 lines, 1920 pixels, 30 progressive scan frames per second
`c. 720 lines, 1280 pixels, 60 progressive scan frames per second
`d. 480 lines, 640 pixels, 60 interlaced frames per second
`e. all of the above
`1 1 . How many analog video channels are required to transmit a full H DTV digital
`signal?
`a. 1
`b. 2
`c. 4
`d. 5
`e. 6
`1 2. A fundamental difference between cable-television and telephone networks is that
`a. cable networks can’t carry two-way telephone traffic.
`b. only cable networks can carry high-speed data.
`c. cable networks do not use circuit switching.
`d. only cable networks use single-mode fiber.
`e. there are no differences left.
`
`

`

`

`

`Mobile Fiber-Optic
`Communications
`
`28
`
`About This Chapter
`
`The past few chapters have described the many applications of fiber optics in fixed
`telecommunication systems. Fibers also are used in a variety of mobile systems for civil-
`ian and military systems. Fiber cables can be used for remote control of robotic vehicles
`and guidance of tactical missiles. Fiber cables also are used inside vehicles ranging from
`battleships to private automobiles. This chapter briefly surveys these diverse applica-
`tions, explaining how and why fibers are used.
`
`Mobile Systems
`
`Mobile systems differ in important ways from fixed systems, with the details depending
`on the application. This leads to some constraints on system design.
`Some fiber-optic cables are used as tethers or connections for transmitting signals to
`and from moving objects. An example is a cable connected to a remotely operated ve-
`hicle that may venture into extreme environments where humans can’t go. These cables
`have to survive whatever environment they pass through, so they are specially designed
`for that environment. The requirements can vary widely. Cables that tether a robotic
`mini-submarine to its human operators in a ship have to be strong and rugged. In con-
`trast, the single fiber that connects to a fiber-guided missile during its brief flight must
`be light and flexible as well as strong, and is used only once.
`Connections inside vehicles generally are short, with the exception of those in ships.
`Links inside a plane or car run no more than tens of meters, and often only meters, so
`plastic or graded-index fibers are often used, although single-mode fibers are used in
`some places. Often these are miniature dedicated local-area networks that interconnect
`
`

`

`B Chapter 28
`
`Connections in
`vehicles generally
`are short.
`
`Vehicles are
`more hostile
`environments than
`offices.
`
`Military
`equipment must
`be rugged and
`repairable in
`the field.
`
`•
`Fiber-optic cables
`carry signals to
`C° n r*h‘ *i° ° IC
`
`the growing variety of electronic systems in the vehicle. Copper cables often can carry data
`the required distances, but fiber cables are lighter and smaller. The immunity of fiber to
`electromagnetic interference is a big plus in vehicles where electrical, electronic, and me-
`chanical systems are packed tightly together.
`Environmental requirements generally are much more stringent for equipment installed
`in a vehicle than in an office. Connections to your desktop computer don’t have to with-
`stand the constant vibration of a moving car or flying airplane. Some common fiber con-
`nectors that work perfectly well in an office building or telecommunications switching
`center can work loose in moving vehicles that are exposed to outdoor temperature
`extremes.
`Military equipment must meet special requirements for ruggedness and field repairabil-
`ity, and some must meet radiation-hardening specifications. Recent changes allow the use
`of some off-the-shelf commercial components that meet most military requirements.
`Military systems share some other common features with civilian aircraft and automo-
`tive systems. They tend not to adapt cutting-edge optical and electronic technologies.
`Design cycles and production cycles are usually much longer than for telecommunications
`or computer equipment. Many systems are critical for safety and have to pass stringent test-
`ing requirements. You can survive a system error on your personal computer, but you might
`not survive if your car’s computerized braking system froze when you stomped on the brakes
`in an emergency. The auto industry has different standards for entertainment systems and
`for safety-critical components. Military and civilian aircraft are designed to operate for a
`dozen years or more, so their control systems have to meet the same requirements.
`Automotive systems are supposed to last for many years, but also must be mass producible
`at low cost, which leads to long design lead times.
`This chapter will give you a brief overview of these special fiber systems, emphasizing
`how they resemble and differ from other fiber communications equipment.
`
`Remotely Controlled Robotic Vehicles
`
`When we think of remotely controlled vehicles, most of us think first of radio-controlled
`toys that zip across the floor until the batteries run down. Radio controls are cheap and
`simple, but limited. You can command your radio-controlled car to go faster, slower, for-
`ward, backward, or turn right or left— but not much more.
`Control of advanced robotic vehicles is a far more demanding job. The operator needs
`video transmission from a camera in the robot to see the local environment. Other envi-
`ronmental sensing information may also be needed, such as temperature and pressure read-
`ings- Signals must flow in the opposite direction so the operator can control the vehicle.
`Fiber-optic cables carry signals in both directions in a variety of remotely controlled vehi-
`cles, often sending two signals in opposite directions through a single fiber at different
`wavelengths. Although care must be taken to protect them, fiber-optic cables can work in
`places where radio signals cannot, including underwater and in electromagnetically noisy
`environments. Fiber cables can also be made quite rugged and special ruggedized connec-
`tors are made for military systems. Other fiber advantages include their ability to carry
`high-bandwidth signals over greater distances and their light weight.
`
`

`

`Mobile Fiber-Optic Communications W
`
`Remotely controlled robots can go into places unsafe for humans. Robots can probe the
`radioactive parts of nuclear reactors to take measurements or make repairs, or to disassem-
`ble old reactors at the ends of their operating lifetimes. Robots can descend deep into the
`ocean or explore the surface of the moon or Mars. Robots can be scouts for armies, and
`they can even deliver weapons to their target (we call them guided missiles).
`Fiber-Optic Guided Missiles
`Guided missiles are essentially simple robots with deadly missions— to deliver bombs to
`their targets. One type of guided missile uses a ruggedized optical fiber to carry control signals
`to and from the launch site on the ground or a ship. The original version, called FOG-M for
`fiber-optic guided missile, was developed by the Pentagon, and gives a good idea how remote
`control through optical fibers works.
`As shown in Figure 28.1, a video camera in the missile sends images to a soldier who
`guides the missile to its target by sending control signals in the opposite direction. The mis-
`sile is preprogrammed to aim at the target, but the soldier provides fine guidance to make
`sure it hits the target. Images and control signals travel through a single bare ruggedized
`optical fiber that trails from the missile to the launcher. The soldier monitors the video im-
`age throughout the missile’s flight to home the missile in on its target, following it all the
`way to impact. This system enables the soldier to stay hidden out of sight because it does
`not require a line of sight to the target, unlike laser-guided bombs that require that the
`soldier be able to see the target. The fiber-guided missile is similar to a wire-guided missile,
`but the fiber has much greater bandwidth, so it can carry video signals or span longer
`distances.
`The components of the U.S. FOG-M system is shown in Figure 28.2. The missile con-
`tains a video camera, a fiber-optic video transmitter, a low-bandwidth receiver for control
`signals, and a special reel of fiber. One end of the fiber is fixed to the launcher, and remains
`behind when the missile is fired. As the missile flies toward its target, the fiber unwinds rap-
`idly from the reel, forming a long arc over the battlefield. The reel is a critical component
`because it must deploy the fiber at the right rate so as not to tangle or break the fiber. The
`
`G u id a n ce
`C o ntrol
`S ig n a ls
`
`Soldier safely under
`cover—watches
`video image sent
`through fiber.
`
`S in g le H igh-
`S tre n g th F ib e r
`
`Spool unreels
`fiber rapidly.
`Video camera
`looks ahead
`at target.
`E n em y
`Tank
`
`A fiber carries
`video images
`back to a soldie
`who guides the
`missile.
`
`Up to 60 km of
`fiber can be
`deployed from the
`missile.
`
`FIGURE 28.1
`A concealed soldier
`guides a FOG-M
`missile to its target.
`
`

`

`w Chapter 28
`
`FIGURE 28.2
`FOG-M
`components.
`
`W avelength
`S p littin g
`C o u p le r
`
`V ideo
`Display
`
`C o n tro ls
`
`C o n tro l S ig n a ls
`1550 nm
`
`1300 nm
`(V id eo)
`Reel holding
`fiber unwinds
`rapidly in flight.
`W a ve le n g th -
`S p littin g
`C o u p le r
`
`P ro p e lla n t
`a n d E n gine
`
`,
`
`1550-nm
`R e ce ive r of
`C o n tro l S ignals
`
`W a rhead
`
`single fiber carries signals in both directions: a video signal from the missile at 1300 nm
`and a control signal to the missile at 1550 nm.
`Raytheon developed an enhanced version of FOG-M with a range of 15 km, which
`could fly at altitudes to 300 meters. This design enabled it to hit the tops of armored vehicles,
`which are more vulnerable than the sides. Although test flights were successful, the Army
`cancelled the program in 2002.
`In a parallel program, the governments of Germany, France, and Italy sponsored devel-
`opment of their own fiber-guided missile called Polyphem. Designed to be fired from ships
`or the ground, it has a range to 60 km and uses infrared cameras, which were optional on
`FOG-M. Data from the missile reportedly can be transmitted at rates above 200 Mbit/s.
`Robotic Vehicles on Land
`Fiber-optic cables also can guide robotic vehicles on land. Military agencies have done
`extensive testing of unmanned ground vehicles that are remotely controlled in various
`ways, including by fiber. Radio signals have the obvious advantage of not requiring a
`physical connection to the vehicle. Cables have to be ruggedized because the robots are
`likely to run over them. However, fiber cables are immune to electromagnetic interference,
`electromagnetic pulse effects, and jamming that could block radio communications.
`Fibers also offer high bandwidth, so operators can obtain detailed information from the
`vehicle.
`The robots are intended for hazardous duty. For example, the Naval Sea Systems
`Command has developed the Remote Ordnance Neutralization System, which runs on
`pivoting tracks and has a robotic arm that can defuse explosives. A soldier can control the
`robot over a radio link or fiber cable, staying safely out of harm’s reach in case anything
`goes wrong. Similar robots could be used to detect and remove land mines, which continue
`
`Fiber cables can
`control robotic
`land vehicles.
`
`

`

`Mobile Fiber-Optic Communications m
`
`to take a heavy toll on civilians long after the wars are over. Other robots might fire
`weapons at dangerous targets.
`The high bandwidth of fiber cables makes it possible to consider using virtual reality
`techniques to remotely operate robotic vehicles. Sensors on the vehicle would scan the area,
`serving as the operator’s “eyes,” while other sensors would listen for sounds and “feel” the
`terrain. The sights, sounds, and feel would be conveyed to the operator— far from the
`vehicle— using screens, speakers, and perhaps virtual-reality gloves. The goal would be to
`keep the operator safe while feeling as if he or she were driving the vehicle.
`Remote-controlled robots could also serve many nonmilitary purposes in dangerous en-
`vironments. Robots could inspect the “hot” interiors of nuclear power plants or perform
`needed repairs inside the reactor. The robots could be left: inside the reactor permanently if
`they became contaminated. Specialized robots could be used to dismantle old reactors,
`without exposing people to the highly radioactive materials inside. Likewise, remotely con-
`trolled robots could clean up hazardous wastes. Scientists used a fiber-optic cable to control
`a multilegged robot as it climbed into a hazardous Antarctic volcano to collect data.
`
`Submersible Robots
`Radio links can substitute for cables in many land applications, but most radio waves don’t
`penetrate far into water. Cables or acoustic signaling are required to maintain contact with
`submerged vessels. Although crewed submersibles can operate without a continuous link
`to the surface, only cables can provide the transmission capacity needed to remotely oper-
`ate a sophisticated submerged vessel. Fiber cables are preferred because of their high band-
`width and durability.
`Hybrid fiber and electrical cables carry the signals and power needed to steer and accel-
`erate submerged vessels, as well as bring video signals and telemetry to the surface, where
`shipboard operators can monitor them.
`Fiber cables also allow operators aboard a submersible to control robotic vehicles that
`can be sent into small spaces or dangerous areas. The most famous example came when
`Robert Ballard’s team from the Woods Hole Oceanographic Institution discovered the
`sunken wreck of the Titanic in 1985. The scientists discovered the wreck with Alvin, a
`submersible that carried three people. However, they did not dare to explore the inside of
`the deteriorating wreck. Instead, they used a 250-lb robot, tethered to Alvin with a fiber-
`optic cable that carried control signals. It was this fiber-controlled robot that photographed
`details of the dark interior of the wreck. Ballard remains enthusiastic about the use of fiber-
`controlled robot submarines.
`
`Remotely
`controlled robots
`could clean up
`hazardous wastes
`and dismantle old
`nuclear reactors.
`
`Hybrid fiber-
`electrical cables
`carry signals and
`power to remotely
`operated
`submersibles.
`
`Fibers in Aircraft
`
`It was not too long ago that most aircraft were controlled by hydraulic systems. When the
`pilot moved a lever, it would cause hydraulic fluid to move a control surface (e.g., a wing
`flap), much as hydraulic brakes work in an automobile. Newer planes have fly-by-wire elec-
`tronic controls that send electronic signals to motors that move control surfaces. Modern
`aircraft— particularly military planes— also use many electronic systems and sensors,
`
`•
`Fibers can serve
`as ^le con^r°l
`networks^ for
`
`

`

`S Chapter 28
`
`New tactical
`aircraft use fiber-
`optic links.
`
`Fiber-optic aircraft
`l