Advantages: High link capacity (bit rate> 1 Gbs) with respect to RF/MW technologies Reduced costs for installation and maintenance with respect to optical fiber technologies Highly directional beams and larger robustness with respect to the risk of interception and intereference Optical frequencies not subject to spectrum regulation with less bureaucratic costs Effective low cost modulation schemes such as BASK (i.e., On-Off Keying, OOK) Beam FSO Beam RF Disadvantages: High attenuation along the line-of-sight between TX and RX due to particulates, such as aerosols, fog, rain and/or snow Significant fading due to atmospheric turbulence causing strong scintillation and possibly to accidental obstacles and volatiles Need of hybrid (FSO + RF/MW) links to guarantee high availability larger than 95% (up to 99.9%) EuCAP2011 - F.S. Marzano et al., Free space optical link in urban area at 1550 nm
Larger than 2.5 Gbit/s Applications: Point-to-point link between buildings in urban environment Optical communications between space and Earth and inter-satellite Penetration to inaccessible areas where RF cable and optical fibers are useless Distribution of digital connectivity in LAN areas where cable/fiber installation are costly Objectives Description of an urban FSO highcapacity link at 1550 nm Channel modeling of FSO link at 1550 nm due to weather effects Preliminary results by comparing measurements/predictions EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 3
Introduction FSO high-capacity urban link at 1550 nm Location and geometry FSO trans-receivers Meteorological instrumentation Weather effects on FSO links Fog and precipitation (rain and snow) FSO link budget FSO urban link data examples Measurements Case studies Conclusions EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 4
Simulation and experimentation activity in joint collaboration with ISCOM and both University of Rome La Sapienza on optical propagation and University of Rome Tre on QoS and Broadband Access. Roman Test Bed site made by: 1) 4 Sona beam 1250-E heads 2) 1 Meteo station and Rain gauge 3) 1 Disdrometer (drop size distribution) 4) 1 Visibilimeter 5) 1 Videocamera 6) 1 MMW radiometer Towards a full operative Wireless Wired test bed.olt:opticalline Termination, VO: Video Overlay, OH: Optical Head, ONT: Optical Network Termination, R: Router. EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 5
Site: Rome, EUR area across an artificial lake Vegetation and close to high traffic road Triangle geometry: A: Viale America, ISCOM building (25 m high) B: EUR Fungo Tower (50 m high) C: Viale Boston, Dept Commerce Building (25 m high) Link A-B: about 800 m; Link C-A: closed loop by optical fiber and 850 FSO FSO heads: 2 SONAbeam at 1550 nm in A and B EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 6
Site: EUR Fungo tower at 50 m Agreement with EUR SpA SONAbeam 1250-E head for A-B Radio link to ISCOM building in A Power load: 50 W FSO Undergoing characterization: FSO link B-C (Tower-Roof2) EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 7
SONAbeam 1250-E Supporting OC-3/STM-1, OC- 12/STM-4, Fast Ethernet, Gigabit Ethernet (1.25 Gbps) or datarate transparent transmission and offers the added reliability of clock datarate recovery (CDR) Managed over Ethernet and it is IP addressable EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 8
Meteo station at site A 1 station ptq (pressure, temp., humidity) 1 raingauge and 1 anemometer Disdrometer & Visibilimeter Particle size spectrum using a laser at 830 nm Fog density and visibility Installed on spring 2012 Radiometer at mm-wave (90 GHz) Integrated water vapor and cloud liquid Lab. development to be completed within 2012 Video camera FSO link video-monitoring (VIS+NIR channel) Visibility estimation through image processing EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 9
Video camera AXIS P1344-E Sonabeam1250-E Switch mediaconverter POE mediaconverter mediaconverter Router Server Laboratories Client EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 10
Photovoltaic panel Anemometer Stevenson screen Current Regulator Datalogger Combilog Batteries DC-DC converter MOXA NPort IA5450A Rain Gauge Inverter Visibilimeter-disdrometer PSW100 EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 11
Introduction FSO high-capacity urban link at 1550 nm Location and geometry FSO trans-receivers Meteorological instrumentation Weather effects on FSO links Fog and precipitation (rain and snow) FSO link budget FSO urban link data examples Measurements Case studies Conclusions EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 12
Optical link: Free space (vacuum): Channel extinction: EuCAP2011 - F.S. Marzano et al., Free space optical link in urban area at 1550 nm
Absorption: part of the optical beam energy is captured by gas molecules (water vapor, carbon dioxide, ozone) and medium particulates (aerosols, hydrometeors), if present. Optical windows: 850 nm and 1550 nm Scattering: interaction between beam photons and medium particles causing the deviation of the optical beam: Aerosols (1-20 m size, solid) Fog (1-20 m size, liquid) Rain (0.1-8 mm, liquid) Snow (0.1-10 mm size, ice-air) Turbulence: random variability of temperature and humidity, inducing refractivity fluctuation and eddy cascade in the inertial energy range, causes signal scintillation in amplitude and phase. Beam wander can be also associated to refractivity variability. EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 14
N p (r): particle size distribution (PSD), i.e. # particles per unit volume and radius r size. W p : liquid water content due to sphere-equivalent particles. N p e r r e e r 3 e N ( r) Ne e e 10 Wp 4 4 p re e 4 re e 4 Units: [m -3 mm -1 ] e 3 Wp r pn 4 3 0 3 Units: [g cm -3 ] p ( r) dr e 3 4 1 1 Radiation fog: related to the ground cooling by radiation, it appears when the air is sufficiently cool and becomes saturated. Advection fog: is formed by the movements of wet and warm air masses above colder maritime or terrestrial surfaces [Gebhart et al., 2005]. Class Advection Fog Radiation Fog W p r e [g m 3 ] [mm] 0.0W p 0.4 0.019r e 0.02 1 0.0W p 0.02 0.001r e 0.00 6 N e [adim] [adim] e [mm 1 ] 2.93.1 5.210 7 N e 3.010 11 5.9 e 6. 1 1.05.0 1.410 10 N e 3.510 1 4.0 e 8. 5 0 N(r) [m -3 mm -1 ] 10 x 108 Fog Distribution Function 9 8 7 6 5 4 3 2 1 AF <W p > RF <W p > 0 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 radius [mm] EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 15
Extinction coefficient Parametric models : V = visibility [km], λ = wavelength [nm] V% transmission of air drops to percentage of clear sky λ 0 = reference wavelength (550 nm) q = scattering spatial distribution coefficient Formulas from [Kim et al., 2001]: rm e 10log10 r N r dr e( ) p( ) rm e extinction cross section e _ fog db/km Other parameteric models: - [Kruse et al., 1962] - [Al Naboulsi et al., 2004]: ADVection and RADiation fog 10log V V 1.6 1.3 q 0.16V 1.34 V 0.5 0 % V 50 km 0 V 0.5 km q 6 km V 50 km 6 km V 50 km 0.5 km V 1 km e [db/km] e [db/km] 300 250 200 150 100 50 Adv. fog Rad. fog 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 300 250 200 150 100 50 Extinction Coefficient W [g/m 3 ] Extinction Coefficient Advection Fog Radiation Fog Kruse m. Kim m. ADV m. RAD m. 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 V [km] EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 16
Rain can be categorized according to raindrops mean diameter D 0 in light (D 0 <1mm), medium (1mm<D 0 <2mm) and heavy (D 0 >5mm) [Straka et al., 2000]. Raindrops can have radii up to 8 mm (breakdown with oblate shapes). e [db/km] 160 140 120 100 80 60 40 20 Light Rain Medium Rain Heavy Rain Extinction Coefficient Empirical model: R = Rain Rate [mm/h] a=1.076, b=0.67 [Carbonneau et al., 1998] Physical model: W p Class r e e [g m 3 ] [mm] [adim] [adim] [mm 1 ] Light Rain 0.0W p 1.0 0.3r e 1.5 1.04.0 3.5N e 1.310 7 2.0 e 7.0 Medium Rain 0.0W p 1.2 0.5r e 2.0 1.04.0 3.7N e 2.510 6 2.0 e 7.0 Heavy Rain 0.0W p 8.0 0.7r e 3.0 1.04.0 2.3N e 5.410 6 2.0 e 7.0 e _ rain ar N e b e [db/km] 0 0 1 2 3 4 5 6 7 8 100 90 80 70 60 50 40 30 20 10 Light Rrain Medium Rain Heavy Rain Carbonneau m. W [g/m 3 ] Extinction Coefficient 0 20 40 60 80 100 120 140 160 180 200 R [mm/h] EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 17
Snow can be considered an aggregate of air and ice (Dry Snow) or air, water and ice (Wet Snow). Large aggregates can reach D20-50mm, while density rages from 50 to 900 kg m -3 [Straka et al., 2000]. Graupel (0.5mm<D<5mm) coexist often with Small Hail (5mm<D<20mm) and are indistinguishable. The density of Graupel/Small Hail can range from 100 to 900 kg m -3 [Straka et al., 2000]. e [db/km] Extinction Coefficient 40 35 30 25 20 15 10 5 Graupel/Smal Hail 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 W [g/m 3 ] Physical model: W p Class r e e [g m 3 ] [mm] [adim] [adim] [mm 1 ] Graupel 0.0W p 1.5 0.8r e 2.5 0.00.0 4.010 2 N e 1.010 4 3.0 e 3.0 Small Hail Dry Snow 0.0W p 1.0 0.7r e 1.0 0.00.0 1.510 1 N e 6.510 4 3.0 e 3.0 Wet Snow 0.0W p 1.0 0.7r e 1.0 0.00.0 2.010 1 N e 1.610 4 3.0 e 3.0 N e EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 18
Power scintillation index P Under strong scintillation, PSI is non linearly dependent on the range (aperture averaging, saturation) Rytov parameter 0 Proportional to structure constant C n 2 (average 10-14 m -2/3 ) and L 11/6 (weak scintillation) Scintillation fade A fade Outage probability p B under log-normal PDF of received power (Henninger and Wilfert, 2010) EuCAP2011 - F.S. Marzano et al., Free space optical link in urban area at 1550 nm
Introduction FSO high-capacity urban link at 1550 nm Location and geometry Specifications Weather effects on FSO links Fog and precipitation (rain and snow) Turbulence FSO link budget FSO urban link data examples Measurements Path attenuation prediction Conclusions EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 20
FSO link margin P Rx : received power in vacuum S r : minimum power for requested BER Urban link in Rome at 1550 nm C 2 = n 10-14 m -2/3 Scintillation fade A fade =1.25 db R=0.1 mm/h Rain extinction A rain =0.2 db Outage prob.: 10-2 ; L = 1 km; Assumptions: S r =-34 dbm; W T =320 mw; D lens =10 cm; BW=1 mrad; A sys =0.5 db Vacuum Link Margin M link = 39.1 db Expected Link Margin M link = 37.6 db EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 21
Measured data FSO link between A and B sites Range=800 m Meteo and raingauge data available EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 22
Estimated visibility and specific attenuation from parametric relation converting FSO attenuation into visibility (Kruse model) from 2012-01- 20 to 2012-02-05 Note: - Diurnal cycle - Normalized atten. EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 23
Measured power and specific attenuation on 19-21 October 2011 Heavy rain (day 20) Note: -Average power in clear air not constant - Sporadic peaks due to the transit of birds EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 24
EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 25
Measured power and specific attenuation on 2-4 Feb 2012 EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 26
FSO attenuation prediction using the parametric model 25 Precipitation 6 Rain specific attenuation prediction at 1550 nm rain [mm/h] 20 15 10 5 Predicted Specific attenuation Rain [db/km] 5 4 3 2 1 0 0 5 10 15 20 25 30 35 40 45 50 time [h] 0 0 5 10 15 20 25 30 35 40 45 50 time [h] 90 Received power [W] 5 FSO Measured average path attenuation at 1550 nm 80 4.5 70 60 50 40 30 20 Measured Path attenuation [db] 4 3.5 3 2.5 2 1.5 1 0.5 10 0 5 10 15 20 25 30 35 40 45 50 time [h] 0 0 5 10 15 20 25 30 35 40 45 50 time [h] EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 27
A urban link at 1550 nm has been set up in the Roman urban area; ancillary meteorological instrumentation is now almost completed. Channel modeling taking into account rain, for, snow extinction; multiple scattering and and turbulence effects are being taken into account. Systematic measurement campaign initiated at the beginning of 2012 and still on going. A diurnal FSO trend is noted and needs to be carefully filtered removed in order to extract meteorological effects. EuCAP2012 - F.S. Marzano et al - Characterization of Hydrometeor Scattering Effects and Experimental (...) 28