CITM805 - Free Space Optics

8/14/2019 CITM805 - Free Space Optics

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CITM805:

SPECIAL TOPICS IN ITProfessor Robert Hudyma

Ryerson University

Brian OrlottiMike Warren

Farhan Yousaf

980979207981656705981676125

Free Space Optics (FSO)

Using “Free Air” As Fiber



Table of Contents

1.0 Introduction________________________________________________________________________________ 1

2.0 Technology Overview ________________________________________________________________________ 2 2.1 Factors Affecting FSO Performance ____________________________________________________________ 3 2.2 Advantages of FSO __________________________________________________________________________ 3 2.3 Disadvantages of FSO________________________________________________________________________ 4 3.0 Analysis of Deployment Options _______________________________________________________________ 5 4.0 Business Case Scenario _______________________________________________________________________ 7 5.0 Conclusion _________________________________________________________________________________ 7 6.0 Annotated Bibliography ______________________________________________________________________ 8 7.0 Additional Sources _________________________________________________________________________ 11 8.0 Appendix _________________________________________________________________________________ 11



Free Space Optics (FSO)

1.0 Introduction

Free Space Optics may sound like a new buzz-word-enabled technology that seems tohave very outer-space connotations, but in reality it’s an old technology that was originallydeveloped by the military over 30 years ago. In technical terms, Free Space Optics is anoptical wireless, point-to-point, line-of-sight high bandwidth broadband solution with datarates ranging from 1 Mbps to over 1.25 Gbps that provides the best solution to the “last-mile” needs of bandwidth hungry applications created due to the convergence of telecommunications and data communications. What makes this technology so special isthe compelling economic advantages and the relative speed and ease of deploymentwhen compared to typical fiber or copper connectivity.

Most people think that optical communication is only possible through a fiber. However,

light can be made to travel through air as its medium for a lot less money than with typicalfiber optic deployments.

The term Free Space Optics (FSO) may be slightly misleading, as a more precise andself-describing terminology could have been “fiber-free” or “fiber-less” optics. Nonetheless,we will stick with the industry standard terminology of FSO through out this paper.

It is worth mentioning that one of the three leading players in the FSO market is fSONA1,based out of Richmond, British Columbia.

1 Please see Appendix A for a press release on fSONA’s product offerings.



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2.0 Technology Overview

This technology uses powerful infrared beams to transmit data through the air betweentransceivers, or link heads that are typically mounted on rooftops or behind windows. Itworks over distances of several hundred meters to a few kilometers depending onatmospheric conditions.

The transceiver works in the electro-magnetic spectrum above 300 GHz (which includesinfrared) that is unlicensed worldwide and does not require the payment of spectrum feesto any governmental bodies. The radiated power, however is subject to limitationsestablished by the IEC60825-1 standard established by International ElectrotechnicalCommission (IEC). In the United States, the governing body is The Center for Devicesand Radiological Health (CDRH) which is part of the Food and Drug Administration (FDA).Currently, the IEC60825-1 standard is being ratified and CDRH is expected to adopt thenew revised standard. So in the near future there will be a single worldwide standard for these devices. The lasers in these devices work at one of two wavelengths, 850nm or 1550nm. The former, 850nm lasers are much less expensive (around 30$) than the1550nm variety which cost around $1000. For short or moderate distances, the 850nmlasers suffice given the price differential. However, the 1550nm beams that are of longer wavelengths are allowed to operate at higher power (almost twice the amount of 850nm)because this boosts “link lengths” by factor of at least 5. One reason why 1550nm can beoperated at higher power is that the infrared radiation at this wavelength tends not to reachthe retina of the eye and is mostly absorbed by the cornea2. Therefore, for long distances,high bandwidth, and poor propagation conditions like fog, 1550nm lasers are a no-brainer choice. Following diagram illustrates the inner workings of a typical FSO transceiver:

2Please see Appendix B for a whitepaper on Lasers and Eye Safety.



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2.1 Factors Affecting FSO Performance

There are functional limits to any emerging technology, and optical wireless systems areno exception.

The challenges affecting FSO in terms of reaching 99.999% availability (also known as the

five nines) manifest themselves as environmental phenomena that vary significantly fromone area to another. Without delving into too much micrometeorological definitions andtheory, we will discuss two major factors:

1. Attenuation: Adverse Weather Conditions

The greatest loss mechanism is caused by fog particles3. The affect of fog is entirely

analogous to attenuation that is suffered by traditional RF wireless systems due torainfall. However, this technology is relatively unaffected by rain or snow. This effect isdealt with by simply increasing the transmitted power.

2. Swaying Buildings

Another hurdle in the way of deploying free-space optics links on tall buildings or towers is sway due to wind or seismic activity; storms and earthquakes can alsocause enough movement to affect beam aiming. This problem is dealt with in twoways, beam divergence and active tracking4.

2.2 Advantages of FSO

Free-Space Optics (FSO) holds many distinct advantages over other high-speedcommunications technologies. The fact that FSO uses Terahertz (THz) infrared lasersrather than electrical signals to send packetized data allows for immense bandwidth. FSOequipment currently supports speeds ranging from OC-3 (155 Mbps) to 1.25 Gbps. Somevendors have demonstrated links running as high as 3 Gbps.

FSO equipment also benefits from simplicity and rapid deployment time. FSO gear consists mainly of laser terminals which are installed on rooftops or mounted in windows.This is a massive advantage over another technology traditionally seen as bridging the“last mile” -- fibre optics. Fiber Optic installations have proven to be extremely time-consuming because of the need to negotiate right-of-way permits and to physically dig tolay the cable. FSO equipment can be setup within days, as opposed to months or evenyears for fiber.

FSO’s simplicity and rapid installation provides its greatest advantage; low cost. With noright-of-way permits to secure, and no digging required, FSO can offer ultra-high datarates at a very low price. US telecom giant Qwest recently began installing FSOequipment from LightPointe at a cost of about US $8,000 per link5

. With fiber-opticinstallations running from the hundreds-of-thousands to the millions of dollars, FSO holdsan incredible advantage.

3 Referred to as Mie scattering in micrometeorological terms4

This technique was effective during an earthquake in Seattle, where Terabeam had its equipment continue tooperate without a link break-down.5 Greene, Tim. (2001). Qwest tries out free-space optics service. Retrieved March 9th, 2002 from Network World

website: http://www.nwfusion.com/edge/news/2001/125510_09-24-2001.html



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FSO also holds some additional advantages over fiber, microwave, and other technologies. FSO terminals are strictly physical layer devices. As such, existing protocols(Ethernet, TCP/IP, ATM, etc.) require no modifications and no additional software isrequired. Also, FSO terminals use laser diodes and photodetectors similar to those used infiber optic equipment (DWDM MUXes, hubs, NIC’s, etc). This allows use of off-the-shelf equipment and easy integration with existing fiber installations. In addition, FSO

communicates in the Terahertz frequency band—which is currently unregulated. Becauseof this, FSO eliminates the need for expensive spectrum licenses (from CRTC or FCC).

2.3 Disadvantages of FSO

Although FSO holds a great deal of promise, there are several drawbacks which must beaddressed if it is to gain wide acceptance.

FSO uses high-frequency lasers to transmit data and, as such, is a Line-Of-Sight (LOS)technology. LOS systems require an unobstructed signal path from sender to receiver.Interruption of a laser signal can come from several sources. As discussed previously,these include:

Inclement weather (rain, snow, fog)

Building sway (due to winds)

Transient obstructions (flocks of birds, locust swarms, etc.)

To deal with transient obstructions, FSO laser nodes are designed to automatically reducepower (so the beam may travel through the object) to 1 percent until the obstruction hascleared6.

Another drawback of FSO is that of limited range. FSO’s gigabit-per-second speeds canonly be provided reliably over a distance of 1-2 kms. This can be addressed however,

through proper network design. FSO links can be arranged in mesh or ring topologies todecrease link distances and provide multiple transmission paths.

6Allen, Doug. (2001). The Second Coming of Free-Space Optics. Retrieved March 9

th, 2002 from Network

Magazine website: http://networkmagazine.com/article/NMG20010226S0007



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3.0 Analysis of Deployment Options

Free Space Optics have in fact been used for over a decade in very limited use (Allen,Network Magazine), however their prevalence in end-user solutions has only just begun.The “Last Mile Problem” afflicting fiber optic technology seems to be easily solved with aFSO solution. Without expensive rights of ways, building permits and the actual installation

process of digging up roadways, FSO usually repays itself within one year (Allen, NetworkMagazine). Current FSO technologies offer transmission rates of up to 2 Gbps

7, with

faster systems still under development. Lucent’s OpticAir DWDM (dense wave divisionmultiplexing) promises further increases in speed to 2.5 Gbps or more (Lucent).

FSO is seen as a major player in connecting smaller and medium sized businesses withtrue broadband access in the OC-3 range (155 Mbps) and above which currently do nothave a fiber connection. FSO can be used to provide both Internet and private, corporatenetwork access.

FSO links have been available in the past but were rejected by customers and providersdue to perceived instability and reliability of the system (Allen, Network Magazine).However, successes of FSO in specialized applications (such as television production8 have proven that the technology is ready to be adapted for business applications, offeringclose to mission-critical levels of reliability. Mesh connections can also be developed for multi-site links and to increase the number of available paths in case of a disruption to onelink site.

In-house uses of FSO can be either for a primary link or a backup system to ensureconnectivity if the primary link (fiber or otherwise) fails. It can also be used in disaster-recovery situations. After the September 11 attacks on New York, Terabeam installedFSO access for customers such as Merrill Lynch, who had lost connections betweenoffices due to the destruction of Verizon’s telecom facilities located near the World TradeCenter (Kagan, Washington Post). The quick deployment of the FSO connection allowedthe company to resume business much faster than if it waited for the fiber links to be

restored.

FSO systems can also be teamed up with microwave equipment to provide a fail-safe,completely wireless solution for connectivity.

FSO providers in major cities (at least now) tend to be smaller, niche-driven companiessuch as AirFiber, with its OptiMesh connection system (see Appendix C). In such asystem, a central hub transceiver creates a mesh connection with transceivers onneighboring building’s roof tops.

In addition, major telecom service providers have begun to jump on the FSO bandwagon,and are now offering their own services to business clients. Qwest started offering such aservice in Denver in September 2001 (Green, NetworkWorld Fusion). Qwest’s service is

roughly equivalent to OC-3, at 155 Mbps. While this is not cutting edge technology, the

7OrAccess claims speeds of 10Gbps, but there is insufficient evidence of this speed being achieved in real-world

business conditions.8 See Lucent article regarding HDTV site broadcast transmissions to central hub.



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service provides bandwidth that is more than sufficient for small to medium sizedbusinesses, for either WAN or Internet connectivity9.

Local loop connections from service providers would consist of a hub transceiver (preferably at high elevation to maximize customers in the line of sight) and customer transceivers either mounted in windows or on building rooftops.

However, the primary drawback of service provider FSO is that it only can servecustomers who are close enough to their central hubs. The provider would have to rentand invest in equipment for many additional roof-top locations if access is to be providedto secondary locations, and this is when FSO starts to lose its cost advantage comparedto fiber.

3.1 Costs of Deployment

When choosing to deploy Free Space Optics connectivity solutions, customers canchoose either an in-house solution (provided through a FSO vendor) or one that ispurchased through a service provider. While some service providers are now offering pre-packaged and transparent FSO solutions to enterprise customers, there is currently

insufficient information on pricing available to the general public. It is our assumption thatthis lack of information is caused by telecom providers not specifically marketing FSOsolutions, but transparent solutions where FSO may be employed.

In-house solutions are only really justified when the organization has two buildings withinthe range of the FSO system, such as the Merrill Lynch example.

Exact pricing (aside from eBay) is not available for in-house solutions offered by vendorssuch as Air Fiber and Terabeam, who instead encourage potential customers to call tospeak with a salesperson – possibly to avoid competitors from being knowledgeable abouttheir pricing strategy. However, in the Network Magazine article, AirFiber is quoted asproviding a price of $20,000 for a complete solution to link two buildings, presumably at155Mbps. The actual installation of a FSO system usually takes four hours or less by two

technicians (AirFiber).

In contrast, Network magazine reports that a similar capacity link provided by fiber opticswould cost over $200,000 to install, plus leased line charges from the telco provider. Inaddition, fiber installations have a lead time of between four months to a year, while FSOcan by deployed in two days or less.

9 Research on eBay has shown that such a FSO equivalent to the one Qwest offers subscribers (~155 Mbps)

costs less than $6000 USD in capital expenses if installed by the customer.



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4.0 Business Case Scenario

Although FSO services are now beginning to be offered by telecom providers and FSOspecialists in major metropolitan areas, there is no such system that integrates FSO andWAN capabilities. The service would be somewhat similar to AirFiber’s OptiMesh system(see Appendix C), however with links to service access points in other cities and to the

Internet. Additionally, the service would be marketed differently

What we propose is a series of interconnected FSO providers that offer WAN connectivityto organizations that have locations in more than one of the service areas. Linking theaccess points would be a high-speed fiber backbone leased from a major telecomprovider. This would provide a truly integrated service to customers, reducing both costsand complexity in their connectivity needs. Plus, the mesh connection would provideredundant connections in case of problems with one link.

FSO links could be used to transmit both data and voice (VOIP) over a VPN to other locations that are also connected via FSO. For example in conjunction with a VOIP-compatible PBX, this could increase call-centre personnel efficiency by routing calls to thelocation that has a lower holding time.

Such a service does not necessarily have to be marketed as a FSO service. Mostcustomers are concerned only with pricing, speed and reliability, not the actually method of transmission.

5.0 Conclusion

The lower overall cost and particularly quick deployment speed makes FSO a veryattractive option, but not for all customers. The ideal FSO customer has two locationswithin 1km of each other and has a completely unobstructed line of sight. For fringeapplications where the distance is close to the maximum supported by the transceiver or with poor line of sight/poor weather conditions, the savings in costs may well be offset by

lower speed and decreased reliability that FSO would offer in such installations.



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6.0 Annotated Bibliography

1. Allen, Doug. (2001). The Second Coming of Free Space Optics. Network Magazine,March 2001

Free Space Optics, or FSO links have actually been used since the late 1980s, but are

only now gaining popularity for business applications. Why? In the past, perceivedreliability problems and limited installation sites had stifled demand for FSO. But now, it iscoming back into focus a solution for the all-important “Last-mile problem” of proving fiber-class broadband connections to business customers premises.

Allen introduces prominent vendors and service providers such as LightPointe, AirFiber and Terabeam. There is also discussion of the current technical specifications of FSOsystems and their capabilities, and which types of applications are good and not sopromising uses for FSO. Also raised is the point that major telecom providers are nowconsidering FSO as a service delivery option, resulting in huge projected increases in FSOequipment sales during the next five years.

The article brings together a balanced viewpoint on both the good and bad points of FSO

applications, including possible health implications. Some FSO vendors have claimed thattheir lasers emit low levels of power that are not harmful but the author challenges them toprove these claims. Regulation also comes into play, although currently the frequenciesthat FSO utilizes (in the terahertz range) are not regulated, they may become regulated if the technology gains widespread acceptance and congestion occurs.

2. Greene, Tim. (2001). Qwest tries out free-space optics service. Retrieved March 9th,

2002 from Network World website: http://www.nwfusion.com/edge/

news/2001/125510_09-24-2001.html

Qwest Communications, a well known service provider in the states is using free-spaceoptical gear to supplement its point-to-point broadband service offerings, bringingcorporate users high-speed connections that previously were impractical. As an emergingtechnology, Qwest’s adoption is critical in the success of this new technology. It will take atleast several other companies to adopt this technology before one can be reasonably sureof its long term survivability.

The FSO gear will be used in customer networks where traditional options such as opticalfiber are unavailable or would take too long to install. Gaining permits and rights of way torun fiber can take months, whereas free-space lasers can be set up rapidly, mounted onrooftops or inside windows. Broadband wireless had been considered the front-runner toaddress fiber unavailability, but licensing and funding problems with wireless carriersslowed this market. In the meantime, the price of FSO gear has dropped dramatically,making it more attractive. Qwest will use equipment from LightPointe that reaches1.25GBps, but for now, will run the equipment at 155MBps.

According to John Griffin, CEO of LightPointe, an OC-3 free-space link that cost $25,000to $30,000 two years ago now costs $8,000 per link, indicating the improvement in bothtechnology and price structures.

Qwest is building fiber networks in 25 cities outside its home states where it is thepredominant local exchange carrier. The provider says FSO is being used in at least onecorporate user's network supported by Qwest, but it would not identify the customer.



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3. Kagan, Jeff. (2001). Free-Space Optics Come to Rescue of NY Firms. RetrievedMarch 9

th2002 from Washtech website: http://washtech.com/news/jkagan/12899-

1.html

In the aftermath of the September 11 attacks, the ramifications in terms of human life andinfrastructural are staggering. Services providers like AT&T, WorldCom, and Sprint, and

equipment makers like Lucent, Nortel, ADC and Alcatel worked virtually round the clock torestore the services and put their customers back into business. Imagine not having anyconnectivity between your various offices, and how this would affect your daily operations.In particular, one company, Merrill Lynch could not function at all and needed to bereconnected to its offices immediately.

Executives and engineers from a young start-up company, Terabeam, based out of Seattle Washington, flew in to the rescue the very next day. Within a week they had asingle 1-gigabit link up and running, connecting Merrill Lynch buildings in lower Manhattanand Jersey City.

4. Lucent Corporation, Lucent Technologies teams with ABC Sports to transmit uncompressed HDTV signals during Super Bowl XXXIV HD broadcast , Retrieved

March 9th

, 2002 from Lucent website:http://www.lucent.com/press/0200/000203.nsa.html

During the last Super Bowl event, ABC Sports used Lucent’s WaveStar OpticAir system totransmit uncompressed HDTV signals from a remote camera to a mobile production truck,built and outfitted by Panasonic and located at the Georgia Dome. ABC used Lucent’stechnology to transmit so-called “beauty shots” during the event’s HDTV broadcast. TheHD camera was positioned on a building one-mile away from the stadium, and providedimages of Georgia Dome and the Atlanta skyline. Utilizing the high-bandwidth of thistechnology enabled ABC to minimize the number of times the video signal had to becompressed, resulting in much high-quality transmission of the video and for re-broadcastover satellite for worldwide distribution.

Until now, ABC was required to apply for FCC licenses to transmit the video signals over alocal radio frequency, which can be not be costly but also have a limited maximumcapacity of 155 MBps whereas transmission of these HDTV signals require a transmissioncapacity of nearly 1.5GBps. Thus, ABC needed to compress the signals before they weretransmitted from the camera to their mobile production trucks, resulting in lower imagequality (due to lossy compression schemes) as these same images were then re-compressed for satellite transmission. Lucent’s WaveStart OpticAir transmission capacityis a whopping 2.5GBps, enough to satisfy virtually any media driven demand with room tospare.

5. Mullen, R.A, H.Wildebrand, et al. (No date). Wireless Optics Protection of Fiber viaSONET Ring Closure. Retrieved from LightPointe Communications. Inc. website:http://www.lightpointe.com

A free-space laser link closes an otherwise all-fiber SONET ring, demonstrating for the firsttime the feasibility of using wireless optics as a backup to fiber in an applicationdemanding the highest levels of statistical availability and sub-50-ms protection-restoraltimes. This experiment demonstrates that protocol-transparent wireless optical links canbe readily internetworked with industry-standard fiber-based protection protocols toachieve SONET restoral times in the event of a fiber cut.



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By using the wireless optics as a back-up to fiber rather than as the primary link, end-users are normally protected from the unavoidable burst errors and outages that can ariseon a wireless optical link in the event of anomalously poor atmospheric visibility or unanticipated line-of-sight obstructions. While an all-fiber SONET ring operating over physically diverse paths is generally preferred, hybrid fiber/air rings operating over physically-diverse paths (fiber as one path and air as the other) will easily meet or exceed

existing Bellcore availability standards for SONET rings. The hybrid part-fiber, part-air ringadvantageously protects customers from fiber cuts (a.k.a. “backhoe fade”) and may bepreferable to over service via either an unprotected fiber spur or over a “collapsed” fiber ring made up of fiber segments sharing a common conduit. The experiment is performedat an OC-12 (622 Mbps) data rate in a point-to-consecutive point configuration whichdemonstrates the use of a relay site to work-around a line-of-sight obstruction.

6. Wildebrand, Heinz A. and Ghuman, Baksheesh S. (2001). Fiber Optics without Fiber .IEEE Spectrum, August 2001

In an industry where fiber optic cable is the standard for all your bandwidth woes, onecould never have imagined that the virtually the same bandwidth at a fraction of the costcould be provided with inexpensive equipment and using “free air” as the medium. It is no

wonder that even with the broad availability of fiber in urban centres, cost remains aformidable obstacle to overcome. Companies like 360 Networks have risen, and thencrumbled due to a huge saturation of the fiber bandwidth market.

Known within the industry as free-space optics (FSO), this form of deliveringcommunications services has compelling economic advantages. Although it only recently,and rather suddenly, sprang into public awareness, free-space optics is not a new idea. Ithas roots that go back over 30 years--to the era before fiber-optic cable became thepreferred transport medium for high-speed communication. In those days, the notion thatFSO systems could provide high-speed connectivity over short distances seemedfuturistic, to say the least. But research done at that time has made possible today's free-space optical systems, which can carry full-duplex (simultaneous bidirectional) data atgigabit-per-second rates over metropolitan distances of a few city blocks to a few

kilometers.

7. Wildberand, Heinz A. (2002). Free Space Optical Transmission Security. RetrievedMarch 9

th, 2002 from LightPointe Communications Inc. website:

http://www.lightpointe.com

Network security is one of the major concerns for any business or organizationtransporting sensitive and confidential information over the network. Such network securityconcerns involve the lowest network layer, typically referred to as the physical layer (layer one), as well as higher software layers of the networking protocols. Most of theinterception activity by outside intruders occurs within higher protocol software layers.Password protection or data encryption are examples of counter measures to protect thenetwork from outside and unwanted tampering. Intrusion of the physical layer itself can be

another concern for network operators, although it is a far less likely target for unauthorized access to networking data. This can be a threat if information is transportedover a copper-based infrastructure that can be easily intercepted, but Free-Space Optics(FSO) transmission is among the most secure connectivity solutions, regarding networkinterception of the actual physical layer.



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7.0 Additional Sources

AirFiber Corporation (2002). AirFiber OptiMesh. Retrieved from AirFiber website:http://www.airfiber.com/products

eBay Auctions (2002). Free Space Optics Wireless 155Mbps Laser Link . Retrieved from eBay

website: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2008684190

Terabeam Corporation (2002). Solutions for carriers. Retrieved from Terabeam website:http://www.terabeam.com/sol/car_700.shtml

8.0 Appendix

Appendix A: Press release on fSONA’s product offerings.

Appendix B: Whitepaper on Lasers and Eye Safety.

Appendix C: AirFiber’s OptiMesh system.

Please see accompanying CD for appendix items (PDF format) in folder \Appendix\.

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CITM805 - Free Space Optics