lightpointe canobeam free space optics historical paper

7/21/2019 LightPointe Canobeam Free Space Optics Historical Paper

1/646 | BROADBAND PROPERTIES | www.broadbandproperties.com | APRIL 2006

TECHNOLOGY

We get a lot of calls fromdevelopers at their witsend, looking for quicksolutions to nasty little

FTTH problems. High on our list ofquick fixes is free-space optics (FSO),especially for covering short distances,

1000 feet or less. We know that theselaser infrared devices are often used overdistances of a mile or more. But our read-ers are most interested in bridging shortgaps where laying fiber would be costly orinconvenient.

How does one design a building foreasy installation and maintenance? Whatsituations should be avoided? What worksand what doesnt? How much power willbe required? For indoor use, what kindof glass should it sit behind? What kindsof structures and construction cause themost trouble; for example, concrete orsteel?

We asked a lot of FSO suppliers. Mostof what follows was supplied by CanonsCanobeam staff, which has an activetechnician training program that helpsanswer these questions.

First, the good news: Given a goodvantage point, FSO units can be set upquickly, and with no FCC licensing. Most

companies products can be installedoutdoors, but they can also be installedindoors behind glass.

Like fiber, FSO is protocol-indepen-dent; it transmits any higher-layer proto-col including Ethernet, SDH, ATM andTCP/IP. Like fiber, FSO can transmit upto multi-gigabit speeds, especially over afew hundred feet. Canobeam pioneeredauto-tracking, which automaticallymoves the beam (within limits, describedbelow) in response to vibration or move-

ment of the building upon which thedevices are placed. All Canobeam FSOmodels include auto-tracking, as do

most devices from competitors.Building movement can occur even on

a clear, calm day as metal and masonryexpand and contract. ere is a tradeoffbetween bandwidth and the ability to

autotrack, especially at the maximumlink distances the vendors advertise. eCanobeams auto tracking system, for

instance, can compensate for up to 2.4degrees of movement. At a range of 500meters, this is equivalent to an area of 20meters. e tracking allows vendors tofocus the infrared laser beam more pre-

cisely. At 1 kilometer the Canobeamstransmitted beam has a 1-meter diameter.FSO systems without tracking require

We get a lot of calls from developers

at their wits end, looking for quick

solutions to nasty little FTTH problems.

High on our list of quick fixes is

free-space optics, especially for

covering short distances

Accommodating Free-Space Optics with good installation and building designA BBP Staff Report

Figure 1. First page of typical site survey form.


2/6APRIL 2006 | www.broadbandproperties.com | BROADBAND PROPERTIES | 47

closer to a 5-meter beam diameter at thisdistance. ats only 1/25ththe power onthe receivers sensor.

Fog is a bigger problem than rain forFSO devices, unless the downpour is in-tense; fog scatters the infrared laser beam.Rain tends only to partially block it.

Interfaces

Various models of FSO devices havedifferent available interfaces, even fromthe same vendors. Usually, the correctinterface has to be specified. For in-stance, the Canobeam DT-110 TP hasan RJ-45 twisted-pair connector for Cat.5 100BaseT copper cable.

e maximum cable length back to thenetwork switch, router or other equip-ment is 100 meters. ats generous,

but sometimes difficult to set up. Also,connection to this interface requires anEthernet switch port configured for 100Mbps full duplex.

e RJ-45 interface is passive, unlikean Ethernet port on a switch or a rout-er, and will not auto-negotiate with anauto-sensing network device. ats nota problem, but network devices do haveto be set accordingly.

Canobeam and many competitorshave an extra 10BaseT connector for

network management via the highlystandardized simple network manage-ment protocol (SNMP).

For Fiber

e DT-110 MM has a multi mode fi-ber interface with an SC connector thatallows the FSO device to be as much as2 km away from the nearest networkequipment. For 100Base FX, (Fast Eth-ernet over fiber) the Ethernet switch portconnected to the Canobeam must alsobe configured for 100 Mbps full duplex.e DT-110 SM has a single mode fiber

interface with an SC connector.Some devices, like the Canobeam DT-

130 LX, accept either multi mode orsingle mode fiber optic cabling with SCconnectors. ese should meet the IEEE802.3z standard for Gigabit Ethernet LX

interfaces. For multi mode 1000Base LXconnections, you should consult withthe switch or router manufacturers op-eration and installation guidelines.

Some manufacturers, such as Cisco,require a special mode-conditioningpatch cable when connecting to theirmulti mode LX interfaces. Withoutthe patch cable, a high bit-error countcould be possible due to receiver over-saturation. e type of fiber governsthe maximum length of the fiber cable

between the Canobeam and the net-work equipment. e maximum speci-fied by Canobeam is 550 meters for62.5/125 or 50/125 micron core MMFcables and 10 km for 9.5 micron coreSMF cables, for instance.

Installation

ese devices are meant to be profes-sionally installed by experienced tech-nicians. But before you bring them in,you can do a preliminary site survey touncover obvious problems.

Obstructions to line of sight

Figure 2. Recommended transmission distances are calculated under conditions of morethan 99.5 percent reliability based on actual visibility data in Tokyo, Japan. All distancesexpressed in meters. ese values are calculated by transmission margin, beam divergence,Gaussian intensity distribution of light and are different from Canobeams recommendedtransmission distance described in specifications. Visibility distances are approximate.Actual transmission distance should be considered with scintillation, backlight noise ,and another factors.

1. E.J. McCartney, Optics of the Atmosphere, J. Wiley & Sons, New York, 1976.2. T.S. Chu and D.C. Hogg, Effects of precipitation on propagation at 0.63, 3.5, and10.6 Microns, Bell Syst. Tech. J., 47, pp. 723-759, 1968.

Figure 3. Canobeam FSO mounted on the edge of a roof; its beam will not be affected by

heat or venting from the roof itself.



Transmission distance

Mounting and stability Network equipment specifications/

connectivity

Canon requires that installers fill out asite survey checklist (Figure 1) and sub-mit it with photos to the company beforeinstallation.

Detailed issues include:

New building construction near-by: Construction cranes and otherconstruction equipment can tempo-rarily block the line of sight. So canplanned new construction itself.

Growing trees.

Vehicular traffic: FSOs must be

mounted high enough so that atruck or other tall vehicle does notinterrupt the link. To pass underInterstate highway bridges, a truckmust be less than 14 feet high.

Nesting birds: Do not install anFSO device where the lens is adja-cent or near a flat surface where nest-ing birds could block the beam.

Exhaust vents and chimneys:Vented hot gasses (although invis-ible), as well as steam and smoke inthe optical path, can cause link in-terruptions.

Scintillation or hot air can oc-cur frequently over asphalt-covered

roofs, parking surfaces or any otherdark surfaces. Transmission distur-bances will occur when the FSOsoptical path traverses these types ofsurfaces. To protect the beam fromscintillation effects, avoid install-

ing over any heat-generating surfacewhenever possible. If there is no al-ternative path, the FSOs must beinstalled as high above the surfaceas possible to minimize the heat ef-fects.

Building maintenance personnel:Mount far away from maintenanceand window cleaner staging areasand high-traffic areas. Ask mainte-nance personnel where temporarymaintenance gear may be placed,

and the frequency with which win-dow cleaning is performed. For

window installations, the customermay want to request window clean-ing during non-business hours or onselect days. Optionally, a second pairof devices can back up a primarypair blocked by window cleaners orbuilding maintenance personnel.e backup pair must be installedfar from the primary pair.

Attenuation effects due to win-dow glass for devices mounted in-doors.When an FSO is installedbehind window glass, the beammay be attenuated depending onthe glass characteristics (tinting/re-flective, number of window panes).e angle the beam makes withthe window is critical the deviceshould be approximately 5 degreesfrom perpendicular to the glass sur-face. If the FSO is perpendicular to

the glass, the devices own light willbe reflected back into its receiver,causing over-saturation. Installingbehind glass at glancing angles willcause increased attenuation.

Another issue is orientation of thebeam direction. If instal led East-West itis possible one of the FSO devices couldgo into Sun Protection mode. isoccurs for Canobeam devices whensunlight enters the receiver within 0.3

degree of the beam transmitted by theother FSO in the pair. Should this oc-cur, the device will shut down the re-

Scintillation or hot air can occur

frequently over asphalt-covered roofs,

parking surfaces or any other dark

surfaces. Transmission disturbanceswill occur when the FSOs optical path

traverses these types of surfaces. To

protect the beam from scintillation

effects, avoid installing over any heat-

generating surface whenever possible.

Figure 4. Heavy post mount clears the parapet.



ceiver, interrupting the optical path.e Canobeam can take up to 6 min-utes to recover and resume transmit-ting. is exists to protect the receiver.

us, if possible, avoid an installationwhere sunlight could enter the receiverlens at the same angle as the laser beam.is is a rare condition, but could occur

even at high noon if the two devices areinstalled so that one is at an extremelyhigh elevation.

If the situation is unavoidable, installa wall-like sunshade behind the devicein the direction of the sun, to block thesunlight from entering the opposite re-ceiver.

Transmission Distances

It sounds obvious, but distancesshould be checked carefully, on a site

plan or map, or with a rangefinder.Less obviously, FSO devices haveminimum as well as maximum trans-

mission distances. For the CanobeamDT series, for instance, the a llowableranges are:

DT-110: 20-500 meters (65ft. to .31mi.)

DT-120: 100-2000 meters (328ft. to1.24mi.)

DT-130: 100-1000 meters (328ft. to.62mi.)

Excessive light input can occur if de-vices are too close. When that happens,FSO devices go into sun protection modeto protect the receiver. e Canobeamdevices have a Low power position forshort distances.

Longer distances are always possible,especially in dry climates. But system re-liability tends to suffer as distances are

extended beyond manufacturers limits.Some vendors are also overly optimisticabout range.

Mounting

Even with built-in auto-tracking, FSOdevices should always be mounted on arigid frame or surface. Auto-tracking ex-ists to compensate for movement from

wind, temperature, and other environ-mental factors, not to make up for a loosemount. To achieve as rigid a mount as

possible, consider the following mount-ing recommendations:

Mount with penetrating mounts toa concrete or masonry structure (asteel structure is a second option ifa concrete or masonry mount is notpossible).

Mount to a solid, stable platform withpenetrating mounts (the mounts arebolted to the rooftop) wherever pos-sible. Some rooftop environments

may not permit penetrating mounts.A platform or tripod weighed downby heavy concrete or masonry blocks,

Figure 5. Indoor mount. Note how the FSO is tilted a bit, relative to the glass. See text for details.


5/6APRIL 2006 | www.broadbandproperties.com | BROADBAND PROPERTIES | 51

or sandbags, is an option where pen-etrating mounts are not possible. Ingeneral, the mounting frames shouldbe metal, not wood. Wood warpsand shrinks enough to cause align-ment problems over time.

Corners are typically the stron-gest rooftop location on which tomount.

Identify potential sources of vibra-

tion such as HVAC equipment, el-evator headhouses and other enclo-sures with compressors or motors.

Avoid instal ling the equipment inthese locations. It is often temptingto do so, because such devices typi-cally have an existing electrical con-nection that could be used to powerthe FSO.

With a pole mount or pedestalmount installation, the lowest pos-sible mounting position is always

the best option. If a high mount isnecessary to avoid a hot surface oran obstruction, take care to properlybrace the mounting brackets to en-sure complete rigidity. A 3 to 4-inchdiameter pole is recommended to

provide maximum stability.

Also, attach an FSO on the roof edgeclosest to the direction of the transmissionbeam. is helps keep the beam away fromheat-emitting dark surfaces or exhaustvents. Raising the mount helps avoid theseissues, if the closest edge is unsuitable. Useonly installation materials and methodscapable of supporting four times the maxi-mum expected load, to allow for wind andother forces.

Typically, a mount then fits betweenthe FSO device and the mounting frameor pole, to allow fine-tuned aiming adjust-ments. For the Canobeam products, theCanon FA-100 Tilt/Swivel Head bolts di-rectly to Canobeam DT-100 Series unitsto allow for vertical and horizontal adjust-ments during alignment. Included withthe FA-100 are four screws to attach themount to the DT-100 Series unit and fourmore to attach to mount adaptors (de-scribed below). e FA-100 has separatelocking bolts next to each center axis boltand circular cutouts on the bottom of theunit for swiveling action and lockdown.

Another popular mount, the PelcoAH2000, has shared center axis/lock-ing bolts. Pelco (www.pelco.com andmany independent distributors) alsosells a wall mount, the WM3026, madeof heavy aluminum. It supports a maxi-mum load of 300 pounds. e PelcoPM2010 Pedestal mount has a height

of 10 inches and is compatible with theFA-100 Pan/tilt head. e Pelco PP200Parapet mount mates directly with theFA-100 Tilt/Swivel mount in order tomount a Canobeam to the inside of aparapet. e maximum load for themount is 175 lbs.

For non-penetrating mounts, Cano-beam recommends the Rohn/RadianFRM 238 due to its low, 30-inch mastheight (www.criticaltowers.com). ismount is optimal for roofs with low or

no parapet. For non-penetrating instal-lations that require a mounting heightabove 30 inches, Canobeam recom-

Thin facades look much more rigid than

they really are. Canobeam reports one

customer who attached the FSO to a

false-wall facade on a rooftop constructedof thin metal beams. Even worse, the

angle of the facade directed wind directly

to the Canobeam and caused it to move

independently of normal building sway.

Figure 6. Canobeam swivel mount.

Figure 7. Pelco wall mount.

Figure 8. Pedestal mount.

Figure 9. Rohn/Radian FRM238 non-penetrating mount.



mends the Trylon 5.951.0049.005 (seewww.trylon.com).

Non-penetrating mounting adaptersdesigned to mate with the FA-100 Tilt/Swivel mount and similar products fromother vendors are available from HuttonCommunications (www.huttononline.com). ey can mount to either 2 3/8inch or 4 inch diameter masts.

FSO vendors say a common problem

with todays curtain wall construction isthat thin facades look much more rigidthan they really are. Canobeam reportsone customer who attached the FSO to afalse-wall facade on a rooftop constructedof thin metal beams. Even worse, the angleof the facade directed wind directly to theCanobeam and caused it to move indepen-dently of normal building sway. On windydays the link would become unstable even

with auto-tracking enabled.Another bad example involved an FSO

on plywood supports on top of a sag-ging floor in an abandoned building. ebuilding was subject to frequent vibrations

from trucks passing on the heavily traveledstreet adjacent to the building. e woodplatform and wood supports moved withthe vibrations and the sagging floor andaltered the original FSO alignment.

Another customer, rather than install-ing into the concrete ledge, chose to installon the railings. e horizontal u-channelthat supported the mount did not provideenough lateral stability because there wastoo much spacing between vertical railingsupports.

FSO units are sometimes combined withRF links because their availability tends tobe complementary; the radio tends to op-erate in fog when the FSO might not. eFSO handles rain well, while RF links of-ten fail under those conditions. But puttingeverything on one mast is not wise unlessthe mount is carefully designed for stabil-ity and ease of maintenance. If the RF an-

tennas have a large surface area, wind cancause additional mast movement. e FSOcould also be affected if any maintenance

work is performed on the antennas.e Canobeam (and all other FSOs

we checked) conforms to FCC Part 15(ICES-003) standards on electromagneticinterference. at is, they dont cause prob-lems. (For more information see www.fcc.

gov/oet/info/rules/part15/part15_7_12_04.pdf.) FSO devices themselves, however,may not perform adequately in environ-ments subject to strong electromagnetic

waves.For indoor installation, remember that

condensation tends to form on windowglass in winter and can attenuate thebeam. is not only reduces the transmis-sion range, but also can completely cut offtransmission. If condensation will be aproblem, install a defroster/defogger that

blows air on the window glass.Generally, glass windowpanes are not

perfectly flat. e imperfections in theflat glass can cause the window to actas a lens, changing the angle of the beamand affecting the transmission range. Old-er buildings can have imperfect glass. Inthese instances, as well as for tinted glass,do a transmission test to check.

Power and Other Connections

FSO units are not heavy power users.Most run on AC 100-240V, 50/60Hzand draw about 20 watts. Canon offersan optional 48 VDC power supply as

well. e bottom of the DT-100 serieshas a 1.57-inch (4 cm) cutout providedto pass power and network cabling tothe interior. For outdoor installations,the cutout should be sealed airtight tokeep any liquids or dust from enteringthe unit. Typically, this involves usinga weather-tight conduit adapter. For

Canobeam products, the adapter is (part# 134628-000) from Anixter (www.an-ixter.com, 224-521-8000). BBP

Figure 10. Growing trees can cause problems.

Figure 11. Conduit adapter.

For indoor installation, remember that

condensation tends to form on window

glass in winter and can attenuate the

beam. If condensation will be a

problem, install a defroster/defogger

that blows air on the window glass.

lightpointe canobeam free space optics historical paper

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