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Complex model of fso links

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Complex model of fso links

  1. 1. COMPLEX MODEL OF FSO LINKS Otakar WilfertBrno University of Technology Pforzheim, July 2007
  2. 2. Outline1 Introduction (definition and history)2 Design of FSO links and their parameters3 Steady model of the FSO link4 Statistical model of installation site5 Complex model6 Conclusion
  3. 3. Basic characteristics of laser radiation high directivity - high concentration of optical power TX θ ≈ 10 −3 radLaserdiode high monochromatic wave - high concentration of information g(ν) Δν Δν <10 −3 ν ν possibility of quantum state transmission - high degree of security during transmission
  4. 4. Definition Free-Space optical link (FSO link) transmits an optical signal through the atmosphere. Optical power is concentrated to one or more narrow beams and optical wave can be divided into several optical channels.(Their application is suitable in situations where the use ofoptical cable is impossible and desired bit rate is too highfor a microwave link).
  5. 5. Wave and space divisionof optical signal transmitting lenses Transmitting transceiverλ1 FO λ1, λ2, …λ2 λ1, λ2, … λ1, λ2, … WDM Coupler: λ1, λ2, …: λ1, λ2, … receiving lense Receiving transceiver λ1 λ1, λ2, … λ2 λ1, λ2, … WDM : : 4 beams N-optical channel 2.5 Gb/s in each channel Fully: N x 2.5 Gb/s
  6. 6. History of optical communicationBell’s „photophone“ - Washington, Franklin ParkThe first device in the history whichtransmits message by optical beam ”FROM THE TOP FLOOR OF THIS BUILDING WAS SENT ON JUNE 3, 1880 OVER A BEAM OF LIGHT TO 1325 L STREET THE FIRST WIRELESS TELEPHONE MESSAGE IN THE HISTORY OF THE WORLD. THE APPARATUS USED IN SENDING THE MESSAGE WAS THE PHOTOPHONE INVENTED BY ALEXANDER GRAHAM BELL INVENTOR OF THE TELEPHONE.“
  7. 7. Bell regarded his photophone as: “the greatest invention I have ever made; greater than the telephone”. source (Sun) Principle of Bell’s „photophone“ modulator mirror receiverBell’s „photophone“ publication: Alexander Graham BELL, Ph.D., "On the Production and Reproduction of Sound by Light", American Journal of Sciences, Third Series, vol. XX, n°118, Oct. 1880, pp. 305- 324.
  8. 8. A.G. BELL and S. TAINTER, Photophone patent 235,496granted 1880/12/14 Charles Alexander Summer Tainter Graham Bell Authentic drawing of „photophone“ details
  9. 9. However, the radio communications demonstrated by Marconi (in 1895) had got bigger progress.Development of optical communications in free space was made possibleby achievements of semiconductor optoelectronics, fiber optics and lasertechnology. Theodor Harold Maiman (invention of laser 1960) fotodiodesAleksandr Mikhailovich Nikolai Basov laser diodeProkhorov (1916 - 2002) (1922 - 2001) (development of laser diodes - 1962)
  10. 10. 1966 Kao and Hockham pointed out that long-distance communication by fiber is possible Charles K. Kao (born in 1927)Kao a Fleming in 2004(Princeton University) Today: 0,1dB/km (in spectral window 1550nm)
  11. 11. Bell’s laboratory “today”: Scientists and engineers from Bell Labs demonstrated (New Jersey) optical link working in free space: Range 4,4 km, Bit rate 10 Gb/s, Wavelength 1550 nm Link design includes fiber elements (EDFA, WDM, fiber couplers etc.)Prototype of multichannelsFSO link (demo picture of progress) From history to present day Photophone
  12. 12. Advantages:the narrow beams guarantee high spatial selectivity sothere is no interference with other linkshigh bit rate of communication (of 10 Gbit/s)enables them to be applied in all types of networksoptical band lies outside the area of telecommunicationoffices, therefore, a license is not needed for operationthe utilization of quantum state transmissionpromises long-term security for high-value data
  13. 13. Disadvantages:9 availability of FSO link depends on the weather9 FSO link requires a line of site between transceivers9 birds and scintillation cause beam interruptionsFor reliability improvement number of new methods isapplied: 1. Photonic technology 2. Multi beam transmission 3. Wavelength and space division 4. Beam shaping 5. Auto-tracking system 6. Microwave backup 7. Adaptive optics 8. Polygonal (mesh) topology
  14. 14. Simplified drawing of the FSO transceiver (example)
  15. 15. FSO link network integration Network element FSO FSO Network elementTransceivers of FSO link are generally protokol transparent FSO link substitutes optical fiber
  16. 16. FSO links arrangementinto ”mesh“ topology
  17. 17. Unprofessional activity in area of FSO linkRonja = Reasonable Optical Near Joint Access “Ronja an User Controlled Technology (like Free Software) project of optical point- to-point data link. The device has 1.4km range and has stable 10Mbps full duplex data rate. Ronja is an optoelectronic device you can mount on your house and connect your PC, home or office network with other networks.“ ? BER, ? availability, ? reliability,http://ronja.twibright.com ? dynamic, ? power margin, …
  18. 18. Some realizations Laser transmitter (3 beams) Transmitter with LED (1 svazek) Receiver with PIN photodiode
  19. 19. Czech professional activity in the area of FSO links ORCAVE - FSO link of the Czech company Miracle Group  2 laser beams  auto-tracking system  range 2.0 km @ BER = 10-9  wavelength 1550 nm  management system  monitoring system etc.
  20. 20. ORCAVE - structural design 2 laser beams  auto-tracking system  installation receiver optical system  management system
  21. 21. Commercially obtainable FSO linksBasic characteristicsExamples of commercially obtainable FSO:Canon (Japan): CANOBEAM DT 50CBL (Germany): Air LaserLight Pointe (USA): Flight Spectrum 155/2000Optical Access (USA): TereScope-OptiLink TS155/DST/CDSONA Optical Wireless (Canada): SONA beam 155-MLight Pointe (USA): Flight Strata (Parameters of selected FSO follow)
  22. 22. Producer, type Canon (Japan) CBL (Germany) CANOBEAM AirLaser DT 50 Bit rate 25 Mb/s to 155 Mb/s 1.25 Gb/s 125 Mb/s Application: a) Fast Ethernet, ATM etc. Gigabit Ethernet, b) Fast Ethernet Range: a) 100 m to 2 km 1 km b) 2 km Wavelength 785 nm 850 nm Class of laser 3B! 1 M IEC (eye safety) Optical dynamic range ? 30 dB of receiver 36 dB Interface (fibre): a) multimode multimode b) singlemode Backup N Y Remote control Y Y Auto-tracking system Y N Number of beams/ 1/1 4/1number of receiving apertura
  23. 23. Producer, type LightPointe (USA) Optical Access (USA) FlightStrata 155 TereScope-OptiLink TS155/DST/CD Bit rate 1.5 Mb/s to 155 Mb/s 10 Mb/s to 155 Mb/s Application: a) Fast Ethernet, ATM etc. Ethernet, ATM etc. b) Range: a) 0 m to 2 km 2.2 km @ 10 dB/km b) 1 km @ 30 dB/km Wavelength 850 nm 785 nm Class of laser 1 M IEC 3B! (eye safety) Optical dynamic range ? ? of receiver Interface (fibre): a) singlemode multimode b) singlemode Backup N N Remote control Y Y Auto-tracking system Y N Number of beams/ 4/4 3/1number of receiving aperture
  24. 24. Producer, type SONA (Canada) Ideal (?) SONAbeam 155-M Cost-effective, reliable Bit rate 125 Mb/s to 155 Mb/s High bit rate (10 Gb/s) High secure Application: a) Fast Ethernet, ATM etc. Transmission of data, b) video and high-value data Range: a) 200 m to 2 km Terrestrial: 500 m b) Satellite: 30 000 m Wavelength 1550 nm WDM Class of laser 1 M IEC Eye safety (eye safety) Optical dynamic range 36 dB Availability of 99.99% of receiver (?) Interface (fibre): a) multimode multimode b) singlemode Backup N Y Remote control Y Y Auto-tracking system N Y(?) Number of beams/ 4/1 4/4(?)number of receiving aperture +APC
  25. 25. Summary of availability improvement methods(Pav = 99.9%)9 (!) the utilization of only photonic elements9 the utilization of WDM and EDFA9 (!) multi-beam and multi-aperture transmission9 “eye safety“ wavelength (1550 nm)9 greater aperture of transmitting system9 “auto-tracking“ system (ATS)9 adaptive power control (APC) for exclusion of saturation9 optical beam shaping (OBS) for obtaining of top-hat beam9 the utilization of adaptive optics for reducing of power losses9 (!) “mesh“ topology and less distance between transceivers9 (!) microwave backup
  26. 26. Modeling of FSO link Laser beam (without atmosphere) Wave equation is 2 starting point ∇ E(x, y, z)+ k 2 E(x, y, z) = 0 2 2 x +y ⎛ π⎞ w0 − jk − j⎜kz+ϕ ( z )− Gaussian beam (laser beam) is one of its solutions E(x, y,z) = E0 e 2q( z ) e ⎝ 2⎠ w(z) Utilization of matrix (ABCD law) Gaussian beam is fully characterized 1 = 1 −j 2 by complex parameter Aq1+ B q(z) R(z) kw 2 (z) q 2= Cq 1+ D Radius curvature of wavefront vs. range Beam width vs. range 5 6 4.5 4 5 3.5 4 3R/z0 2.5 w/w0 3 2 2 1.5 0.5 1 1 θ 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 z/z0 z/z0
  27. 27. Optical wave Optical intenzity Optical power GG GG G P(z,t) =∫ I(x, y,z,t)dxdy E(r,t)×H(r,t) =I(r) =I(x, y,z) time S Fast optical changes in time Slow (modulation) changes in time 2 2 ⎡ ⎤ w0 2 −2x 2+y Optical intensity distribution w (z) in Gaussian beam w(z) ⎥ I( x, y,z) = I 0 ⎢ e ⎣ ⎦ 1 1 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6I/I0 0.5 I/I0 0.5 0.4 0.4 0.3 0.3 0.2 0.2 e -2 0.1 0.1 0 0 -3 -2 -1 0 1 2 3 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 x/w0 z/z0
  28. 28. Laser beam 1 0.9 0.8 0.7Optical intensity distribution 0.6in Gaussian beam I/I0 0.5 0.4 0.3 0.2 0.1 e-2 0 -3 -2 -1 0 1 2 3 x/w laser diode beam Speckles in beam spot
  29. 29. Model of power budgetThe basic arrangement of the FSO link γ tot TX TXA RXA attenuation αtot RXsource detector P m,TXA L 12 P m,RXA Psat,RXA p(t) data (OOK modulation) P dynamical Pm,TXA ≈ 1/2 Pimp,TXA range Δ P0,RXA t All power levels are “mean” value w.r.t. modulation noise floor Pm,TXA - mean power radiated through TXA; TXA - output aperture Pm,RXA - mean power received on RXA; of the transmitter; αtot - total attenuation; RXA - input aperture γtot - total gain; of the receiver; L12 - distance between TXA and RXA;
  30. 30. Power balance equation and power level diagram atmosphere beam transmitter receiver Power level diagram P [dBm] Pm,TXA α 12 10 α~ atm αatm −γtot 0optical -10power Psat,RXA saturation δ ~ -20 P m,RXA “clear” atm. -30 Pm,RXA real situation random Δ M -40 P0,RXA sensitivity Power balance equation Pm,TXA - α12 + γtot - ~atm - αatm = Pm,RXA
  31. 31. Link marginGraph of link marginM (L12) M(L 12 ) =Pm,PD (L12 ) −P0,PD Stationary model of the link by itself Link margin is possible to utilize for: increasing of range, increasing of link immunity against weather
  32. 32. Atmospheric phenomenaTransmission of „clear“atmospheremeasured at sea level L12 = 1km; Δλ = 1,5nm Areas applied
  33. 33. Atmospheric phenomena Components of αatm  1. Absorption, scattering and refraction on gas molecules and aerosols (fog, snow, rain) (slow variations)(λ = 785 nm) visibility attenuation State of the atmosphere [km] [dB.km-1] < 0.05 > 340 Heavy fog 0.2 - 0.5 85 - 34 Middle fog 1.0 - 2.0 14 - 7.0 Weak fog or heavy rain 2.0 - 4.0 7.0 - 3.0 Haze 10 - 23 1.0 - 0.5 Clear
  34. 34. Atmospheric phenomenaComponents of αatm  2. Beam deflection (diurnal variations) (temperature or mechanical deformation of consoles)  3. Short-term interruptions of the beam (short pulses) caused by birds, insect, 1e4 1e3 1e2 10 (7th floor, filmed from a distance of 750m) 1 0 00:00 06:00 12:00 18:00 00:00 29/09/2000
  35. 35. Atmospheric phenomenaComponents of αatm  4. Fluctuation of optical intensity (noise-like) caused by air turbulence f [Hz] time of day  5. Background radiation
  36. 36. FSO testing link Bit rate: 155 Mb/s Range : 750m Single beam On-line monitoring: - BER - power levels - meteorological data In operation since 1999
  37. 37. Measurements on testing link turbulence, birds, …Bit error rate (BER) a)% Error free sec. (EFS) b) c)Received power (Pr) fog
  38. 38. Results processing -statistical model of installation site 100 PDF of random atmospheric attenuation (histogram) 10 (measured in Autumn) 1 0.1 0 -5 0 5 10 15 20 25 30 35 αatm [dB/km] 102 Exceedance probability function of atmospheric attenuation This is probability that atmospheric 101 attenuation exceeds given value 100 0 5 10 α 15 20 atm [dB/km] 25 30 35
  39. 39. Synthesis of stationary model of the linkand statistical model of installation siteModel of the link:link margin vs. range Availability of the link - complex model (model of the given link in selected installation site) 100Model of installation site:probability that 10atmospheric attenuation 1 λ = 850 nmexceeds given value 0,1 0,01 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 Koeficient útlumu [dB/k m]
  40. 40. Complex model of FSO link 1 0.01 MS=90dB Brno 0.8 0.1 MS=70dB 0.6 1 Milesovka 0.4 10 0.2 100 0 20 40 60 80 100 120 140 160 180 M1 [dB/km]Nomogram for unavailability of link assesment
  41. 41. Monitoring of atmospheric phenomena in selected sitesSelected Czech Republicsites: Prague (750m) Brno (950m) FSI Milesovka hill (Donnersberg) FEKT- Long-term monitoring ofoptical power and BER- Meteorological sensors
  42. 42. Conclusion9 FSO links are a suitable technology for the ”last mile” solution in the frame of access network9 The utilization of the FSO links is requested namely in situations where the use of an optical cable is impossible and desired bit rate is too high for a microwave links9 FSO links are flexible, simple and full-value (in terms of quality of transmission) license-free instrument of network communication technologies

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