1、 Rec. ITU-R S.1558 1 RECOMMENDATION ITU-R S.1558 Methodologies for measuring epfdcaused by a non-geostationary-satellite orbit space station to verify compliance with operational epfdlimits (Question ITU-R 236/4) (2002) The ITU Radiocommunication Assembly, considering a) that the World Radiocommunic
2、ation Conference (Istanbul, 2000) (WRC-2000) adopted a combination of single-entry validation, single-entry operational and, for certain antenna sizes single-entry additional operational equivalent power-flux density(epfd) limits, all of which are now contained in Article 22 of the Radio Regulations
3、 (RR), and also adopted the aggregate limits in Resolution 76 (WRC-2000), which apply to non-geostationary-satellite orbit fixed-satellite service (non-GSO FSS) systems to protect GSO networks in parts of the frequency range 10.7-30 GHz; b) that the operational epfdlimits were adopted by WRC-2000 to
4、 protect operational GSO FSS networks from interference levels which may result in severe degradation in performance; c) that operational epfdlimits were also adopted by WRC-2000 to protect operational GSO FSS networks employing adaptive coding from interference levels which may result in loss of ca
5、pacity, which is considered a severe degradation; d) that Resolution 137 (WRC-2000) invites the ITU-R to develop, with the aim of completion by 2003, measurement methods which may be used by administrations to verify compliance of an individual non-GSO FSS system with these operational limits; e) th
6、at, as a consequence of those measurements, a non-GSO system causing interference may have to reduce its epfdpower levels towards the affected GSO earth station to meet the single-entry operational epfdlimits unless otherwise agreed by the concerned administrations; f) that compliance of a non-GSO F
7、SS system with the single-entry operational epfdlimits is not subject to verification by the ITU-R; g) that the determination of whether a non-GSO FSS system is exceeding the operational epfdlimit into an operating GSO earth station would be made by individual administrations and their GSO network o
8、perators; h) that the worst-case occurrences of events exceeding the operational limits are likely to be of short duration (from a fraction of a second to a few seconds) with a repeat period ranging from several days to weeks, depending on the orbital characteristics of the non-GSO system; j) that t
9、he loss of synchronization or severe degradation may be used as a trigger for the application of a methodology for checking whether the operational limits are met; 2 Rec. ITU-R S.1558 k) that a reliable means of measuring the actual interference corresponding to the epfdproduced by a non-GSO FSS sys
10、tem into the operational GSO earth station experiencing interference would assist administrations and operators in determining whether a non-GSO system is exceeding the operational epfdlimit; l) that measurement procedures have inherent accuracy and operational limitations which have to be taken int
11、o account during the measurement process, noting a) that regulatory procedures are being developed to enable the quick resolution of any proven instance of the operational epfdlimits being exceeded; b) that Recommendation ITU-R S.1527 has been developed enabling the identification of satellites belo
12、nging to a particular non-GSO system; c) that Recommendation ITU-R S.1554 has been developed in order to assess the overall accuracy of epfdmeasurements, recommends 1 that the methodologies described in Annex 1 be used by individual administrations and their GSO system operators to determine if non-
13、GSO FSS interference exceeds the operational epfdlimits into an operating GSO earth station. NOTE 1 Other measurement methods may be identified. In due course it may be appropriate to add such methods to this Recommendation. ANNEX 1 1 Introduction This Annex provides methodologies to enable the meas
14、urement of the power flux-density (pfd) level emitted from a non-GSO space station incident at the antenna aperture of an operational GSO earth station receiver sharing the same frequency bands. This level can then be compared with operational epfdlimits provided in RR Article 22 to determine whethe
15、r the non-GSO space station is exceeding these limits. These limits should be met in order to comply with RR No. 22.5I and also to protect GSO FSS links from suffering loss of synchronization or degraded performance1due to the passage of non-GSO satellites close to or within the main beam of the GSO
16、 earth station antenna. Three methods have been identified, each having advantages and disadvantages. Details of each method are provided in Sections 2, 3 and 4. One or more of these methods can be invoked if a loss of synchronization or degraded performance occurred at a GSO earth station at an une
17、xpected time (i.e. not obviously caused by a high rain or scintillation fade, a sun outage event, a terrestrial interference source such as radar, or an event caused by equipment failure and/or associated switch-over). The GSO satellite operator would then _ 1This includes protection of GSO FSS syst
18、ems employing adaptive coding from loss of capacity. Rec. ITU-R S.1558 3 determine, via ephemeris data whether an in-line or near in-line event had occurred at the location of the site incurring the loss of synchronization and communicate the results of the measurement to the non-GSO operator concer
19、ned. It is expected that the occurrence of in-line or near in-line events will be rare and it is essential that either the methods described in Sections 2, 3 and 4 are fully automated or that the time of a repeat occurrence can be accurately determined. The method in Section 2 is a procedure for ide
20、ntifying that there may be a loss of synchronization or severe degradation problem and that the operational epfdlimits may be exceeded. If it is judged that the problem may be due to peak interference from a non-GSO system, Method 2 or 3 may be employed to measure the peak epfdlevel. Method 1 requir
21、es a minimal use of staff and equipment resources. More detailed methods are presented in Sections 3 and 4. These can either be used as standalone methods of determining the epfdmore accurately or as a follow-on procedure from the method in Section 2. None of these methods assume the presence of a d
22、edicated non-GSO pilot signal. In Section 3 the interference level is measured in frequency bands between adjacent carriers which have suffered loss of synchronization or degraded performance1. These methods assume that the interfering traffic carrier is sufficiently broadband to include both the af
23、fected carrier and the guardband between it and the adjacent carrier, and that the carrier sideband level is sufficiently attenuated to be able to measure the interference power level in the guardband. The method is also valid for the case where multiple carriers, of the non-GSO system in frequency
24、division multiple access (FDMA), span both the affected carrier and the guardband. If the non-GSO carrier is sufficiently broadband or there are multiple non-GSO carriers in FDMA, the effects due to Doppler frequency shift on the non-GSO carrier are minimized. The preferred realization of this appro
25、ach uses a reference earth station (e.g. a carrier system monitor (CSM) earth station). The key advantage of using the CSM earth station is that it avoids the need to know the gain of the affected earth station receive chain. Section 4 contains some techniques which make use of auto- and cross-corre
26、lation techniques to derive the interference level from a measurement of the non-GSO carrier in the presence of the affected GSO carrier when the non-GSO carrier level is well below the GSO carrier level. The choice of which technique in Section 4 to use depends on the level of the a priori knowledg
27、e of the non-GSO satellite signal being separately available. These techniques are more complicated for the GSO operator to carry out because they are accomplished at the centre frequency of the GSO carrier. Calibration is an important factor in assessing the overall accuracy of each of these techni
28、ques. Recommendation ITU-R S.1554 includes some information on this matter. 2 Method 1: A rapid technique based on loss of synchronization The following method is a simplified procedure for identifying a possible exceedance of the operational epfdlimits. This technique is sufficient to show that the
29、 operational limits may have been exceeded in the case where a loss of synchronization in the operating GSO carrier has _ 1This includes protection of GSO FSS systems employing adaptive coding from loss of capacity. 4 Rec. ITU-R S.1558 occurred. More comprehensive measurement procedures may be requi
30、red to accurately determine the epfdlevels generated by the non-GSO system into the operational GSO earth station antenna. The following steps will lead to a determination of whether the operational limits have been exceeded by a non-GSO system. Step 1: Record the date and coordinated universal time
31、 (UTC) of the loss of synchronization as accurately as possible, as well as the duration of the loss of synchronization under clear sky and nominal operating conditions (see Note 1) (no sun outage, no switch-over, equipment failure etc.). Step 2: Correlate the time of the loss of synchronization wit
32、h the presence of the non-GSO satellite close to or within the main beam of the GSO earth station antenna by using the ephemeris data (see Note 2) of the non-GSO and GSO satellite systems. Step 3: Verify the C/N of the GSO carrier during clear sky conditions and verify the C/N threshold at which los
33、s of synchronization of the demodulator (see Note 3) occurs to ensure that there are not any technical problems with the earth station. Step 4: Compute the epfdreceived at the antenna aperture during the synchronization loss in Step 1 using: the link budget of the GSO carrier, the C/N synchronizatio
34、n loss threshold of the receiving demodulator and the G/T of the earth station. Step 5: Establish the times of subsequent non-GSO satellite passes and go back to Step 1 until the correlation between the event of non-GSO satellite pass close to or through the GSO earth station main beam and a loss of
35、 synchronization appears to be confirmed. Step 6: If there is correlation between the event of a non-GSO satellite pass and a loss of synchronization, and the calculation of the epfdmade in Step 4 shows that the non-GSO system is probably exceeding the operational epfdlimits, the GSO operator may de
36、cide to use a more comprehensive method to determine the epfdlevels generated by the non-GSO system into its operational earth station more accurately. The GSO operator may also decide to advise the non-GSO system operator that his system is causing a degradation to the GSO earth station. This metho
37、d contains inherent uncertainties not present in the other methods, i.e. uncertainty in the C/(N + I) at which a demodulator loses synchronization for a given bit rate, type of modulation and forward error correction (FEC), uncertainty in the C/N ratio during an in-line event, and variation in C/N t
38、hreshold, at which loss of synchronization occurs, with the duration of interference peak. However, when a loss of synchronization is recorded and correlated with ephemeris data, an in-line event can be assumed to have occurred. NOTE 1 It will be important to note the weather for the GSO earth stati
39、on location. NOTE 2 It is assumed that the non-GSO ephemeris data is available. NOTE 3 This can be done by checking the Eb/N0readout of the demodulator. 3 Method 2: epfdmeasurement technique using a calibrated reference earth station 3.1 Principle of the measurement procedure The measurement of the
40、epfdat an earth station requires the calibration of the receive earth station receive chain to provide a conversion factor that enables the translation of power measurements taken at an RF or IF point in the receive chain into an epfd value at the receive antenna aperture. The power level measuremen
41、t is made either in absolute terms or relative to some known reference Rec. ITU-R S.1558 5 level. The latter approach is used in the methods described in Section 3 through the cooperation of a well-calibrated reference earth station. This eliminates the need to know the precise antenna gain and rece
42、ive chain gain for the earth station under test. The standard approach for satellite system monitoring involves a power measurement using either a power meter, spectrum analyser or a digital signal processing (DSP) device. The measurements consist of four basic parts: gain calibration of the receive
43、 signal path; non-GSO interference plus noise measurement; noise power measurement to determine the earth station noise level; fade measurement using GSO beacon or telemetry channel. Several of these measurements have to be done in rapid succession, before the environment changes. Section 3 describe
44、s a preferred realization of this methodology which makes use of a well-calibrated reference earth station. This measurement procedure requires the cooperation of a well-calibrated GSO FSS earth station that, simultaneously with the affected GSO earth station, can accurately measure the equivalent i
45、sotropically radiated power (e.i.r.p.) of the GSO carrier and/or a GSO beacon signal. Most GSO FSS satellite operators have CSM earth stations that measure the e.i.r.p. of each operational carrier to ensure the satellite transponder is operating at its planned input and output back-off point. By acc
46、urately calibrating the peak e.i.r.p. of the wanted carrier at the satellite, the e.i.r.p. in the direction of the interfered with GSO earth station can be calculated. This procedure takes advantage of the accurate e.i.r.p. measurements of the CSM by calibrating the e.i.r.p. of the interfered with G
47、SO FSS carrier or a GSO beacon. The GSO beacon could be either one generated on the satellite or an unmodulated carrier inserted between the two carriers by an uplink earth station. If a reference earth station is not available, the affected earth station may be able to incorporate equipment to accu
48、rately calibrate the gain of its receive signal path. The following are the steps which could be undertaken in implementing this procedure: Step 1: Firstly, the GSO carrier level or beacon signal is monitored and the carrier-to-noise (CGSO/N) level is derived from a measurement of (CGSO+ N)/N using
49、a suitable power measuring device (see equation (1). This measurement can be carried out automatically and preferably shortly before and immediately following a measured burst of non-GSO interference. This level relates to the pfd incident on the antenna from the GSO satellite, which is easily calculated (see equation (2). The mathematical relationship between (I + N)/N ratio (Inon-GSO+ N)/N (dB) and I/N ratio (Inon-GSO+ N)/N (dB) is given in equation (1): = +110log10-1.0- NNIGSOnonGSOnonNIdB
