1、 Report ITU-R F.2106-1(11/2010)Fixed service applications using free-space optical linksF SeriesFixed serviceii Rep. ITU-R F.2106-1 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommun
2、ication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radioc
3、ommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing decl
4、arations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Reports (Also available online at http:/www.itu
5、.int/publ/R-REP/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propaga
6、tion RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management Note: This ITU-R Report was approved in English by the Study Group under th
7、e procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2011 ITU 2011 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rep. ITU-R F.2106-1 1 REPORT ITU-R F.2106-1 Fixed service applications using free-s
8、pace optical links (Question ITU-R 245/5) (2007-2010) TABLE OF CONTENTS Page 1 Introduction 5 2 Description on system configuration and basic parameters . 5 2.1 Explanation of parameters 5 2.1.1 Transmitter side 5 2.1.2 Receiver side 6 2.2 System configuration 7 2.3 Basic system parameters . 9 3 Fre
9、e-space propagation characteristics relating to the link design . 10 3.1 Clear-sky propagation . 10 3.2 Effect of fog 11 3.2.1 Estimation of fog attenuation using atmosphere visibility . 11 3.2.2 Detailed analysis on aerosol attenuation (fog) . 11 3.3 Effect of rain . 13 3.4 Snow attenuation 15 3.5
10、Ambient light attenuation . 16 3.5.1 Solar trajectory . 16 3.5.2 Solar power at the receiver . 17 3.6 Scintillation effects . 17 3.7 Other factors . 18 4 Applications in the fixed service 18 4.1 General features 18 4.2 Basic application examples . 19 4.3 Real deployment examples . 20 5 Link design c
11、onsideration . 21 5.1 Link margin 21 5.1.1 Beam diameter . 22 2 Rep. ITU-R F.2106-1 Page 5.1.2 Geometrical attenuation . 22 5.1.3 Molecular absorption . 23 5.1.4 Received level 23 5.1.5 Beam wavefront errors and intensity profile homogeneity 24 5.1.6 Margin for the unit distance . 24 6 Deployment of
12、 FSOL in specific climatic areas . 25 7 Consideration on the operational aspect . 25 7.1 Propagation times . 26 7.2 Transmitted data confidentiality . 26 7.3 Guidelines for implement FSOL 27 7.3.1 FSO installation process . 27 7.3.2 FSO alignment process example 28 7.4 Multi FSOLs . 29 8 Summary . 3
13、0 Annex 1 Examples of the link budget . 31 1 Example of the link budget . 31 2 Example of FSO availability prediction . 32 2.1 Some link margin 32 2.2 Availability and Quality of Service 33 2.2.1 Example of minimum visibility calculation . 33 2.2.2 Example of weather statistical data 34 2.2.3 Exampl
14、e of a link availability calculation 35 2.2.4 Example of availability according to the link distance 36 Annex 2 Comparison between ITU-R Recommendations and “FSO prediction” QoS Software (Experimentation in France) . 37 1 Introduction 37 2 FSOL field test . 38 2.1 Site and equipment characteristics
15、38 2.2 Link design . 39 2.2.1 Engineering data 39 Rep. ITU-R F.2106-1 3 Page 2.2.2 Field data 39 3 Simulation software 40 3.1 Capture data window 40 3.2 Report window 40 3.3 Profile window 41 4 Results comparison . 41 4.1 Comparison FSO prediction versus FSO and France weather station 42 4.1.1 Aeros
16、ol attenuation (fog) . 42 4.1.2 Other attenuation 44 4.2 QoS comparison and availability FSO versus ITU-R Recommendation . 46 4.2.1 Comparison of QoS FSO versus Recommendation ITU-R F.1668 . 46 4.2.2 Comparison of FSO availability versus Recommendation ITU-R F.1703 47 4.3 Comparison of FSOL availabi
17、lity versus FSO prediction software . 48 5 Conclusion 49 Annex 3 Direct fibre coupling FSO terminals and their radiocommunication application . 49 1 Introduction 49 2 Terminal description . 50 3 RoFSOL application . 52 3.1 RF-optic I/F unit . 53 Objective This Report provides a response to Question
18、ITU-R 245/5 concerning free-space optical links for fixed service (FS) applications. The following sections present equipment characteristics, possible FS applications as well as technical and operational aspects of the free-space optical transmission (see Notes 1 and 2). NOTE 1 The free-space optic
19、al transmission discussed in this Report focuses on systems for outdoor use. NOTE 2 Free-space optical connection between a hub station and mobile/nomadic terminals serving as wireless local area network is outside the scope of this Report; however, a fixed link between hub stations is covered by th
20、is Report. 4 Rep. ITU-R F.2106-1 Abbreviations AAC Automatic attenuation control APD Avalanche photo diode ATM Asynchronous transfer mode ATPC Automatic transmission power control EAM Electrical absorption modulator E/O Electrical to optical conversion FDDI Fibre distributed data interface FOV Field
21、 of view FSO Free-space optics FWHM Full width at half maximum FSM Fast steering mirror FSOL Free-space optical link IDU Indoor unit LD Laser diode LAN Local area network LoS Line of sight LED Light emitting diode LIDAR Light detection and ranging ODU Outdoor unit O/E Optical to electrical conversio
22、n O/R Optical to radio conversion PD Photo diode PDH Plesiochronous digital hierarchy QoS Quality of Service R/O Radio to optical conversion RoFSOL Radio on free-space optical link RTC Rseau tlphonique commut (Switched Telephone Network) Rx Receiver SDH Synchronous digital hierarchy SMF Single mode
23、fibre STM-1 Synchronous transport mode level-1 Tx Transmitter WDM Wavelength division multiplexing Rep. ITU-R F.2106-1 5 References ITU-R Recommendations Recommendation ITU-R F.1668 Error performance objectives for real digital fixed wireless links used in 27 500 km hypothetical reference paths and
24、connections. Recommendation ITU-R F.1703 Availability objectives for real digital fixed wireless links used in 27 500 km hypothetical reference paths and connections. Recommendation ITU-R P.1814 Prediction methods required for the design of terrestrial free-space optical links. Recommendation ITU-R
25、P.1817 Propagation data required for the design of terrestrial free-space optical links. ITU-T Recommendations ITU-T Recommendation G.640 Co-location longitudinally compatible interfaces for free space optical systems. ITU-T Recommendation G.692 Optical interfaces for multichannel systems with optic
26、al amplifiers. ITU-T Recommendation G.694.1 Spectral grids for WDM applications: DWDM frequency grid. ITU-T Recommendation G.694.2 Spectral grids for WDM applications: CWDM wavelength grid. ITU-T Recommendation G.984.5 Enhancement band for gigabit capable optical access networks. 1 Introduction Rece
27、ntly free-space optical links (FSOLs) are becoming attractive transport media for short-range fixed wireless applications. FSOL has the following advantages: broadband transmission is available; transmit/receive equipment is compact; there is almost no need for coordination to avoid interference bet
28、ween FSOLs. Therefore, in order to expand its current and future applications, technical and operational aspects of FSOL need to be addressed through theoretical analyses as well as experimental approaches as described in this Report. 2 Description on system configuration and basic parameters 2.1 Ex
29、planation of parameters 2.1.1 Transmitter side 2.1.1.1 Emission area, AeEmission area, Ae, is the surface of the transmitting window expressed in square metre (m2). The emission area is a parameter used for the determination of a laser safety class. 2.1.1.2 Emission power, PeEmission power, Pe, is t
30、he optical power transmitted through the Emission area, Ae, expressed either in dBm or in mW. It is one of the other parameter used for the determination of the laser safety class and used to calculate the link margin. The power measurement should be performed outside the FSO and as close as possibl
31、e to the FSO emission windows. If possible, the measurement 6 Rep. ITU-R F.2106-1 should be performed transmitting “0” and “1” with equal probabilities of occurrence. The power is the averaged value of the high level value (“1” bit) and of the low level value (“0” bit). For safety reason, it is nece
32、ssary to determine the accuracy of the power measurement, e.g., Pe= 10 dBm 1 dB. Also for safety reasons, if the terminal has an automatic divergence adjustment, the Peis defined for the minimum divergence value, and, for the terminal with Automatic Transmit Power Control (ATPC), the maximum Pevalue
33、 is the maximum value of the emission power. For terminals having a multibeam system, the Peon each Aeand the total (sum of the beams mW) should be indicated. The total is the sum of all the Pefor each emission terminal when all beams converge and this parameter is used for safety reason. The distan
34、ce between two Aewith the beam divergence should also be indicated. For terminals having a holographic optical diffuser to achieve a super-extended source, in order to provide a high level of diffusion transmission efficiency with a controlled diffusion area, and increase the transmission efficiency
35、 with a class 1 (following the IEC 60825-1 standard 4) configuration; the Pebased on Aeshould be indicated. 2.1.1.3 Beam divergence, Bdor The beam divergence, Bd, is the maximum value of the angles between the beam central axis corresponding to the maximum power density and the direction correspondi
36、ng to a power density 3 dB lower. This value is important for the determination of the laser safety class and to calculate the link margin. The value can be expressed as half angle or full angle, but should be noticed; and the unit is usually expressed in milliradian (mrad). In case of adjustment di
37、vergence, the minimum and the maximum values should be indicated. 2.1.1.4 Wavelength, Waor The wavelength, Waor , is the central wavelength and its full width at half maximum (FWHM). The central wavelength value is also important for laser safety class calculation. The unit should be in nanometres (
38、e.g.: = 849 2 nm). If there is a wavelength division multiplexing (WDM) transmission, it could be easier to indicate the spectral range. 2.1.1.5 Laser safety class The FSO terminal safety class follows the IEC 60825 normative reference and has to be controlled by a certified laboratory. The 1 or 1M
39、safety class for FSO terminal should be preferred. 2.1.2 Receiver side 2.1.2.1 Receiver area, ArReceiver area, Ar, is the complete receiver area or surface through the receiver window and the unit can be measured in metres squared (m2). 2.1.2.2 Sensitivity, SrSensitivity, Sr, is the minimum optical
40、level with a considered data quality transmission (for instance, BER should be better than 106; i.e., BER 106). The unit should be dBm and the measurement should be achieved close to the FSO receiver window. Rep. ITU-R F.2106-1 7 If the terminal has multi-receiver windows, Sron each Arand the total
41、sensitivity should be indicated. If the terminal has a reception system formed by micro-sphere doped, A, by doping element, A, according to the resonance wavelength of the incidental beam, B, interfaced with a laser transmitter, C, with definite wavelength and adjustable power offering an energy con
42、tribution in link at the frequency of resonance of the doping elements contained in the micro-spheres; the terminal, D, sensitivity, Sr, will be the sensitivity of such a system with the same considered data quality transmission (Fig. 1). FIGURE 1 Terminal with micro-sphere 2.1.2.3 Saturation sensit
43、ivity, Ss Saturation sensitivity, Ss, is the maximum optical level with a considered data quality transmission (for instance, BER should be better than 106; i.e., BER 106); with and without automatic attenuation control (AAC). The unit should be in dBm and the measurement should be achieved closer t
44、o the FSO receiver windows. If the terminal has multireceiver windows, Sson each Arand the total saturation sensitivity should be indicated. The difference between the saturation sensitivity (with AAC if any) and the sensitivity gives the dynamic range. 2.1.2.4 Field of view, Fv The Field of view (F
45、OV), Fv, is the angle between the central axis and the 3 dB value angle detection. The value can be expressed as half angle or full angle, but has to be mentioned; and the unit can be expressed in milliradian (mrad). 2.1.2.5 System loss, AsysThis element shall be used as an indication and it is not
46、used for laser safety class and link margin calculation, due to the emission and receiver measurement points. The unit should be in dB. 2.2 System configuration Basic configuration of a FSOL for the FS applications is illustrated in Fig. 2. 8 Rep. ITU-R F.2106-1 FIGURE 2 Basic configuration of FSOL
47、In many FSOLs, the function of electrical/optical (E/O) conversion or optical/electrical conversion (O/E) is performed using a laser diode (LD) or a light emitting diode (LED) in the transmitter (Tx) and using a photo diode (PD) or an avalanche photo diode (APD) in the receiver (Rx), respectively. R
48、ecently, some systems have implemented the WDM technique in which more than one optical carrier can be accommodated in a couple of transmitter and receiver to increase the link capacity 1, 2. Many types of the FSO equipment use the intensity modulation of transmitting laser beam to send binary data
49、in both directions through a transmitter/receiver couple at each end. The equipment is used for point-to-point, bilateral links and used in line of sight (LoS) conditions. Another type of equipment to make WDM technology, such as fibre amplifiers and WDM components available in the FSOL configurations have been recently demonstrated where free-space optical beam should be coupled into a single mode fibre (SMF) with a good efficiency 3. Since the effective aperture of the SMF is very small,
