1、 Recommendation ITU-R BT.1893-1 (10/2015) Assessment methods of impairment caused to digital television reception by wind turbines BT Series Broadcasting service (television) ii Rec. ITU-R BT.1893-1 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient an
2、d economical use of the radio-frequency spectrum by all radiocommunication 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 perfor
3、med by World and Regional Radiocommunication Conferences and Radiocommunication 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
4、 be used for the submission of patent statements and licensing declarations 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 fou
5、nd. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/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, rad
6、iodetermination, amateur and related satellite services P Radiowave propagation 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
7、SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2015 ITU 2015 All rights reserved. No part of th
8、is publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R BT.1893-1 1 RECOMMENDATION ITU-R BT.1893-1 Assessment methods of impairment caused to digital television reception by wind turbines (Question ITU-R 69-1/6) (2011-2015) Scope This Recommendation p
9、rovides methods to assess the potential impairment caused to digital television reception by wind turbine installation consisting of a single or multiple machines. NOTE 1 Recommendation ITU-R BT.805 provides “Assessment or impairment caused to analogue television reception by a wind turbine”. The IT
10、U Radiocommunication Assembly, considering a) that severe degradation of television reception can be caused by reflections from moving objects such as the blades of a wind turbine; b) that these effects are particularly serious because the impairment caused can be quasi-permanent, being reduced only
11、 during periods when the wind turbine is not rotating; c) that it is important to have available a simple method for calculating the potential impairments which could be caused by the installation of any proposed wind turbine; d) that reflection cancellation techniques are being investigated and tha
12、t these may offer some amelioration of the impairment caused by wind turbines; e) that reflected signals may have different effects on digital television signals; f) that reflected signals may have different effects depending on the digital modulation systems; g) that wind turbine blades are typical
13、ly made of composite materials which have different reflection coefficients than metal; h) that the design of wind turbine blades may include additional elements that may also impact televisions signals; i) that scattering from wind turbine pylons must also be taken into account; j) that the locatio
14、n of wind turbines and their scattering patterns have an impact on the level of impairment in the vertical and horizontal plane; k) that the number of wind turbines at a location will have an impact on scattering patterns, noting a) that Report ITU-R BT.2142 provides an extensive analysis of the eff
15、ect of the scattering of digital television signals from wind turbines; b) that the method given in Annex 1 is a simplified version of the complete analysis in Part A of Report ITU-R BT.2142; c) that Report ITU-R BT.2142 provides an in depth explanation of the method given in Attachments 2, 3 and 4
16、that addresses issues identified in further recommends 1, 2 and 3 of Recommendation ITU-R BT.1893-0 on the impact of pylon scattering, the effect of rotating blades, non-metallic blade composition, and the elevation pattern for scatter, 2 Rec. ITU-R BT.1893-1 recommends 1 that the method given in An
17、nex 1 may be used to assess the potential interference from a single wind turbine to digital television reception; 2 that the method given in Annex 2 may be used to obtain a channel model to characterize multipath propagation in the presence of multiple wind turbines1 in the UHF broadcasting band; 3
18、 that the method given in Annex 3 may be used to develop an assessment of the potential interference from a wind farm to digital television reception (DVB-T), encourages administrations to draw the attention of the relevant authorities in their countries to this Recommendation. Annex 1 Simplified mo
19、del of impairment caused to television reception by a wind turbine Figure 1 shows the plan view of the wind turbine problem of backscatter. At any receiving location, R, the wanted field strength is FSR. At the wind turbine site, WT, the field strength is FSWT. It is assumed that the receiving locat
20、ion is at distance r (m) from the blade2 of the wind turbine. A “scattering coefficient”, , which includes the free-space path loss for the path from the wind turbine site to the receiving location, may be defined as: grA where: s i nc o sc o ss i n c)( 02 Wgand: W : mean width of the blade (m) : wa
21、velength (m) A: blade area (m2) 0: angle of the incident signal at the blade : angle of the scattering signal from the blade. 1 Sites with multiple wind turbines are commonly referred to as “Wind Farms”. 2 This analysis assumes that the wind turbine blades are metallic and approximately triangular.
22、However, typically blades are fibreglass or other composite materials which results in 6 to 10 dB less scattering than metallic blades. Rec. ITU-R BT.1893-1 3 The maximum value of this scattering coefficient due to a blade in the vertical position occurs when both the incident and scattering directi
23、ons are normal to the blade and is given by: rAmax FIGURE 1 B T . 1 8 9 3 01-W T (w i n d t u rb i n e )R (r e c e i v e r)T ra n s m i t t e r 0rIn the case of a free-space path, of length r (m) between the wind turbine and the receiving location, the unwanted field strength may be calculated as: F
24、SWT 20 log The scattering coefficient only accounts for backscatter from the blades. It must be noted that the metallic support pylon also contributes significant static backscatter. Forward scatter from the blades may be significant, but has a lower amplitude than backscatter and is more complicate
25、d to calculate. Forward scatter from the pylon is minimal. It should also be noted that scattering pattern changes by at least 10 dB as the blades rotate. For full analysis, refer to Report ITU-R BT.2142. The receiving antenna directivity discrimination as a function of (as shown in Fig. 1) is given
26、 in Recommendation ITU-R BT.419 and this should be applied to determine the ratio of the wanted to unwanted signal for any specific receiving location. An example of the use of this method is given in Attachment 1. 4 Rec. ITU-R BT.1893-1 Attachment 1 to Annex 1 Example of use of simplified assessmen
27、t method As shown in Fig. 1 of Annex 1, identify the point of any receiver location, near the site of a proposed wind turbine. As a first step, calculate or, preferably, measure the field-strength values, FSR, at the various receiver locations. It is unlikely to be necessary to extend the investigat
28、ion area to more than about 10 km from the proposed wind turbine site (or sites, if there are multiple turbines). However, if there are special circumstances, for example buildings which are screened from the wanted transmitter but which are line-of-site to the wind turbine, then the area may need t
29、o be extended. Calculate or, preferably, measure the field strength, FSWT, at the wind turbine site, near the height of the centre of rotation of the blades. For each of the receiving points, R: calculate the scattering coefficient, , for the path between the wind turbine and the receiver; calculate
30、 the unwanted field strength using FSWT 20 log ; calculate the wanted field strength FSR; calculate the wanted-to-unwanted signal ratio, taking account of the receiving antenna directivity discrimination; using the information of Attachment 2, assess the potential impairment to digital television re
31、ception given the calculated wanted-to-unwanted signal ratio at the receiving point. The results of the study may then be presented in the form of a map showing the areas/locations where reception impairment may occur. It should be noted that the process is more complicated if there are multiple win
32、d turbines on a given site as there are then several possible sources of impairment at each receiving location. Report ITU-R BT.2142 provides example predictions for a large wind farm. Annex 2 Channel model to characterize signal propagation in the presence of a wind farm in the UHF broadcasting ban
33、ds Introduction It should be noted that the channel model is independent of the television standard, and as such, it can be used to estimate the potential impact of a wind farm on any television service provided in the UHF band. The channel model for propagation in the presence of wind turbines is a
34、 Tapped-Delay Line model with a number of paths, with: corresponding delays; Rec. ITU-R BT.1893-1 5 mean amplitudes, and Doppler spectrum associated to each path to account for the variability caused by the rotation of the blades. In the channel model, all these components are adaptable to the parti
35、cular features of any case under study. More precisely, these parameters are specified for each reception location in the coverage area of a potentially affected transmitter. To do so, a digital terrain database can be used to divide the coverage area into small grids of a given size (pixel). For ea
36、ch of the center locations of these pixels, the parameters of the channel model for those specific conditions would be obtained, as explained below. This process is easily implementable in planning tools, and provides a fast overview of the potential degradation due to the wind farm. The adaptation
37、of the channel model to the particular characteristics of a case under study requires some input data, which is gathered in Table 1. Accordingly, the necessary parameters which are obtained from the input data of Table 1 are included in Table 2. TABLE 1 Input data to adapt the channel model to the s
38、pecific features of a case under study Type Description For each windturbinePosition Geographical coordinates, terrain height (m) Mast dimensions Vertical dimension of the mast (m) Lower and upper diameters of the mast (m); uppermost diameter of the mast (just below the nacelle) and the diameter of
39、the base of the mast (at ground level). Blades length l Longitudinal dimension of the blades (m) Maximum rotation rate, max Maximum rotation rate of the blades (rpm) Transmitter Position Geographical coordinates, including terrain height (m) Transmitter antenna pattern Transmitter antenna radiation
40、pattern Antenna height Above ground level height of the geometric centre of the antenna within the telecommunication tower where it is allocated (m) Frequency, f Working frequency within the UHF band (Hz) Power, Pt Maximum transmitter power (W) Receiver Position Geographical coordinates, including t
41、errain height (m) Receiver antenna pattern Receiver antenna pattern Receiving antenna height Height above ground level (m) 6 Rec. ITU-R BT.1893-1 TABLE 2 Data calculated from the input data of Table 1 Symbol Description RTx-WTi Transmitter to wind turbine distance (m) for wind turbine WT RWTi-Rx Win
42、d turbine WT, wind turbine to receiver distance (m) RTx-Rx Transmitter to receiver distance (m) GTx-WTi Radiation pattern gain of the transmitter toward i-th wind turbine (numerical with respect to isotropic antenna) GRx-WTi Receive antenna gain toward i-th wind turbine (numerical with respect to is
43、otropic antenna) GTx-Rx Transmitter antenna gain of toward the receiver (numerical with respect to isotropic antenna) GRx-Tx Maximum gain of the receive antenna (numerical with respect to isotropic antenna) r Mean radius of the mast (m), calculated as the arithmetical mean of lower and upper radii L
44、 Length of the slanted surface of the mast, which is a truncated right circular cone (m); it can be approximated to the vertical height of the mast r Bistatic angle in the horizontal plane (transmit antenna-wind turbine-receive antenna) measured as in plan view, for each wind turbine (radians) t Ang
45、ular position of the television transmit antenna in the vertical plane measured from the zenith, with respect to each wind turbine, taking as reference points the transmit antenna height and the half-height point of the mast (radians) r Angular position of the television receive antenna in the verti
46、cal plane measured from the zenith, with respect to each wind turbine, taking as reference points the half-height point of the mast and the receive antenna height (radians) Figure 2 shows a view of the general wind farm interference situation. Rec. ITU-R BT.1893-1 7 FIGURE 2 View of the general wind
47、 farm interference situation B T . 1 8 9 3 02-trrRec ei v erT ran s mi t t erW i n d t u rb i n eR WT 1- RxRTx-RxRT x- W T1Number of paths The number of paths is on a first approach, the total number of wind turbines of the wind farm, plus a static path corresponding to the signal from the transmitt
48、er. Depending on the results obtained for their delays and amplitudes, as explained in the following subsections, the number of paths may be reduced. Relative delays of the paths For each wind turbine, the relative delay i (s) of the scattered signal is calculated as a function of the distance diffe
49、rence between the direct path (television transmit antenna television receive antenna) and the path of the scattered signal (television transmit antenna wind turbine-television receive antenna) according to equation (1). (1) where: RTx-WTi : transmit antenna to i-th wind turbine distance (m) RWTi-Rx : i-th wind turbine to receive antenna distance (m) RTx-Rx : transmit antenna to receive antenna distance (m) c : speed of light (m/s). Mean amplitude of the paths The static path with relative delay zero (i.e. the
