1、 Recommendation ITU-R SM.2097-0 (08/2016) On-site accuracy measurements of a fixed DF system SM Series Spectrum management ii Rec. ITU-R SM.2097-0 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by
2、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 performed by World and Regional Radiocommunication Confere
3、nces 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 be used for the submission of patent statements and
4、 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 found. Series of ITU-R Recommendations (Also available
5、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, radiodetermination, amateur and related satellite servi
6、ces 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 SNG Satellite news gathering TF Time signals and fre
7、quency 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, 2016 ITU 2016 All rights reserved. No part of this publication may be reproduced, by any means whats
8、oever, without written permission of ITU. Rec. ITU-R SM.2097-0 1 RECOMMENDATION ITU-R SM.2097-0 On-site accuracy measurements of a fixed DF system (2016) Scope This Recommendation provides guidance on standard methods of testing the bearing accuracy of a fixed direction finder in its final environme
9、nt and reporting results. It may serve as part of a site acceptance test for monitoring services after the installation on site. Keywords Direction finder accuracy, on-site measurement, realistic environment Related ITU Recommendations, Reports Recommendation ITU-R SM.2060 Report ITU-R SM.2125 NOTE
10、In every case the latest edition of the Recommendation/Reports in force should be used. The ITU Radiocommunication Assembly, considering a) that ITU-R has published the typical specifications for direction finding (DF) accuracy1 in the ITU Handbook on Spectrum Monitoring (Edition 2011); b) that the
11、ITU Handbook on Spectrum Monitoring (Edition 2011) refers to Report ITU-R SM.2125 Parameters of and measurement procedures on H/V/UHF monitoring receivers and stations, which defines the DF accuracy and provides some relevant test procedures; c) that the specification of DF accuracy strongly depends
12、 on the test procedures applied; d) that performance data in specifications of DF equipment usually reflects ideal test conditions and does not include the influences of obstructions, reflections and disturbing RF signals at the final installation site; e) that the accuracy of a DF system on site ma
13、y be strongly influenced by these environmental conditions2 as well as the nature of the signal (signal strength, signal modulation including phase and time variant signals, signal duty cycle, signal polarization and signal duration), and the integration time of the DF; f) that, depending on task re
14、quirements, one or more of these specific conditions may be more or less important, and in some cases, can be omitted; 1 For purposes of the discussion in this Recommendation, “DF accuracy” is considered being the accuracy of a DF systems bearings to signals coming in from the horizon, with no consi
15、deration of signals arriving at other elevation angles such as skywave. 2 In actual operating environments, multipath conditions can be simple or complex; they may be static or time-varying, and they will be different for different surrounding environments. These conditions will also change for diff
16、erent DF antenna heights at the same location. 2 Rec. ITU-R SM.2097-0 g) that the site and installation of the DF system may directly impact its accuracy and suitability to fulfil certain monitoring tasks, recommends that the test procedures in Annex 1 should be used to determine and report the set
17、of DF accuracies of a DF system installed at its final site. Annex 1 1 Introduction This Recommendation proposes general test procedures that can be used to evaluate the DF accuracy of a radio direction-finding system in its realistic RF environment. While the DF accuracy indicated by a manufacturer
18、 in the data sheet is a measure of performance under clean, controlled receiving conditions (as described in Recommendation ITU-R SM.2060), the tests described in this Recommendation are intended to evaluate the DF accuracy in the RF environment in which that particular DF system is installed. This
19、environment is expected to include influences from the surrounding buildings, obstructions, reflections from nearby and moving objects and, in some cases, the presence of strong RF signals. Performance measurements in clean, controlled environments give good results for DF accuracy comparisons. Howe
20、ver, if the system does not perform adequately in an operational environment, its utility is degraded. Therefore, it is recommended to apply well-defined test procedures for fixed site installations for DF accuracy analysis in real operational environments, especially as a component of the acceptanc
21、e tests of a system. It is obvious that the DF accuracy, when measured in the actual operational environment, may be worse than the value stated in the data sheet, which is due to the usually negative effects of the operational RF environment. However, whether the DF errors measured on site may be (
22、partly) compensated for (e.g. correction tables) depends on the system design. It should be noted that the DF accuracy results measured with the methods described in this Recommendation are unique to the specific DF installation and cannot simply be transferred to other DF systems, even of the same
23、type, in different RF environments. It should also be noted that this procedure is not intended to be a complete site acceptance test. Though it may form the basis of a site acceptance test, there are usually more detailed requirements specified by the user based on their coverage and performance go
24、als. Two tests are recommended: (1) Tests using a test transmitter whose frequency and location can be controlled and which will transmit CW signals at a level that is adjusted to provide an SNR of 20 dB or more at the system under test, and (2) Tests using signals from existing known broadcast stat
25、ions and other transmitters with known, fixed locations (termed “targets of opportunity”) which may be of varying modulation types and signal levels, with the provision that only signals from targets of opportunity will be used that have an SNR of at least the minimum value specified by the manufact
26、urer of the system under test. Rec. ITU-R SM.2097-0 3 2 Measurement setup The DF system should be tested in operational conditions at the actual location where the system will be used by the procuring administration. “Factory operational tests” may be an acceptable alternative, but should be done un
27、der conditions that are as close as possible to the expected conditions where the system will be deployed. Determination of the coverage area for test Prior to the DF accuracy tests, an analysis should be completed to determine the coverage area from test transmitters to be deployed, and from known
28、broadcast stations and other transmitters with known locations (termed “targets of opportunity”). A suitable target of opportunity must have stable output power, and be capable of providing sufficient SNR for the duration of the test. Simulation tools can be used to analyse coverage based on the req
29、uired transmitter power, frequency, modulation and location. This analysis will aid in planning the test transmitter locations and selecting targets of opportunity. Test transmitter output power considerations For controlled test transmitters, a CW signal should be transmitted at sufficient power to
30、 provide a received SNR of 20 dB or more, but by mutual agreement between the administration and the manufacturer, signals with the minimum SNR at which specified accuracy is achieved (as documented by the manufacturer) may be used. For targets of opportunity, the transmitted modulation types and si
31、gnal levels will necessarily be used, but signals with a received SNR that is less than the minimum specified by the manufacturer will not be used. Test transmitter and antenna considerations Test equipment should be prepared for the field evaluation/testing. This equipment includes transmitters to
32、generate signals over the frequency range of interest and with power appropriate to achieve the desired received SNR. The test equipment (including transmitter, transmitting antennas, etc.) should be calibrated to ensure valid data. To most accurately simulate operational conditions, it is recommend
33、ed that omnidirectional antennas be used with the transmitters. However, if mutually agreed, a directional antenna may be used for tests with a specific objective. These cases should be noted in the test results. Test transmitter locations Test equipment should be placed in a vehicle with a global p
34、ositioning system and with appropriate power source (the test vehicle); the vehicle will drive to locations along roads in the calculated coverage area, to obtain at least eight well-distributed azimuth values within 360 degrees (two per quadrant).3 The test points should have line of sight to the D
35、F. The difference between any two adjacent test angles should be no less than 30 degrees. Where it is not practical to have this distribution of transmitter locations, other distributions are allowed, preferably keeping to a two-point-per-quadrant distribution, as long as the area of interest is cov
36、ered. A minimum of 8 test points should be used. The 8 test points should be at different distances from the DF system location ranging from close-in to the outer limit of the range of coverage. The test point with the longest distance should be at the limit of coverage to maintain a 20 dB SNR. For
37、the short distance test point, it is sufficient to only be in the far field. The test points may be selected by administrations. Also, by mutual agreement between the manufacturer and administration, 3 This would be the optimum situation for a DF system which covers 360 degrees. There may be reasons
38、 to modify this in cases where the DF is intended to cover fewer quadrants. 4 Rec. ITU-R SM.2097-0 additional test points may be used, so that the administrations get a better understanding of the performance of the system in their environment. Test transmitter frequency selection The selected frequ
39、encies should be well distributed within the frequency range. However, they should be adequately separated (in frequency) from those of the “targets of opportunity” identified above so that the bearing result for the test transmitter signal is not influenced by the signal of an adjacent target of op
40、portunity4. The methodology used for selecting test frequencies can follow Recommendation ITU-R SM.2060 (The final number of test frequencies may be limited by license restrictions or other factors). Test transmitter modulation settings The test should be performed with unmodulated (CW) carriers usi
41、ng the test transmitters as well as targets of opportunity as noted earlier. Targets of opportunity should include analogue and digital signals with modulation types typical of the signals to be received by the installed DF system, and typical of the operational environment.5 If the test is being pe
42、rformed with unmodulated carriers, the DF bandwidth should be set to a value in line with Recommendation ITU-R SM.2060. If the test is performed using a signal with analogue or digital modulation, the DF bandwidth should be adjusted according to the signal bandwidth. Reporting of the test settings A
43、ll the test settings (test signal level in V/m, test signal type, DF bandwidth, test point angle, test distance, antenna types, etc.) should be noted in the report. 3 Measurement procedure The test vehicle should be driven to the first location. The global positioning system should be used to determ
44、ine precise location, from which the true bearing from the DF system to the test transmitter is calculated. The test transmitter azimuth relative to the DF station (true azimuth) should be established with an accuracy of at least 0.1 RMS or a tenth of the estimated DF accuracy, whichever alternative
45、 is more restrictive, considering a confidence level of 95%. The signal level of the test transmitter should be adjusted to make sure the field strength of the transmitted signal, as received at the DF antenna, has an SNR of 20 dB or more, unless it has been agreed between the administration and man
46、ufacturer to test at an SNR equivalent to the minimum signal strength advertised by the manufacturer at which specified accuracy is achieved. In addition, before switching on the test transmitter, it has to be verified that the selected frequency is “free” which means that no other signal is being r
47、eceived at the DF site. Then the azimuth reading of the DF system is noted and entered into the data tables. The test should be repeated for the different frequencies. After all measurements at one location have been 4 In practice, this may be difficult to achieve with certain signals or certain mod
48、ulation types, where multiple signals occupying the same frequency range may be present. Care should be taken to avoid these situations or some exception note may be needed. 5 By mutual agreement between administrations and manufacturers, testing of certain types of modulated signals may be specifie
49、d. Rec. ITU-R SM.2097-0 5 completed, the Test Vehicle should move to the next location, and the measurement procedure repeated. This procedure is repeated until measurements have been made at all required azimuths6. In addition to the measurements of the test transmitter, the indicated bearings on the selected “targets of opportunity” are performed and the results are entered in the table, together with the calculated true bearings. For target of opportunity tests, the received SNR and the signal modulation are entered in the table. Table 1 is an example of such a result table; one
