1、STD-CEPT ERC REPORT 2b-ENGL 3994 M 2326414 0035327 4oY ERC REPORT 26 7 European Radiocommunications Committee (ERC) within the European Conference of Postal and Telecommunications Administrations (CEF“) %. x.- .-._.- COMPATIBILITY STUDY BETWEEN MOBILE SATELLITE SERVICE IN THE 1610-1626.5 MHz BAND AN
2、D RADIO ASTRONOMY SERVICE IN THE 1610.6-1613.8 MHz BAND Brussels, June 1994 STD-CEPT ERC REPORT 2b-ENGL 1774 II 2326434 0035328 340 CONTENTS 1. Introduction 2. In band interference from MES to stations of Radio Astronomy 2.1. In band interference for one user 2.2. In band interference for a density
3、of users 3. Required out of band emission limit 4. Interference fromdownlink MSS 5. Operational sharing techniques 6. Conclusion hx 1 : European Radio Astronony sites operating in the band 1610.6-1613.8 MHz Annex 2 : Detailed calculations P.1 P.1 P-1 P.2 P.3 P.4 P.4 P.5 Copyright 1994 the European C
4、onference of Postal and Telecommunications Administrations (CEPT) _ STD-CEPT ERC REPORT Zb-ENGL 3994 M 232b434 O035329 287 II ERC REPORT 26 Page 1 COMPATIBILITY STUDY BETWEEN MOBILE SATELLITE SERVICE IN THE 1610-1626.5 MHz BAND AND RADIO ASTRONOMY SERVICE IN THE 1610.6-1613.8 MHz BAND 1. INTRODUCTIO
5、N WARC-92 (RR 731 E) allocated the band 1610-1626.5 MHz on a primary basis to the Mobile Satellite Service (MSS) in the earth-to-space direction (uplink) and the band 1613.8-1626.5 MHz on a secondary basis to the MSS in the space-to- earth direction (downlink). This report presents the results of th
6、e study concerning the sharing between Radio Astronomy service and MSS. The band 1610.6-1613.8 MHz is used by radio astronomers to observe the spectral line of the hydroxyl molecule near 1612 MHz, which is considered to be among the most important lines below 275 GHz. The radioastronomy service is p
7、rotected by footnote 733E stating that “harmful interference shall not be caused to stations of the radioastronomy service using the band 1610.6-1613.8 MHz by stations of the radiodetermination service and mobile-satellite services (RR 2904 applies)“. 15 stations of radioastronomy are likely to use
8、this band in Europe and, consequently, require protection from MSS (see annex 1). Characteristics for MSS are not fully determined for the moment. Both TDMA and CDMA access techniques and both GSO and non GSO satellites are considered in calculations, with technical data already available. MSS syste
9、ms are referred to by name for ease of identification. According to RR731E, the MES maximum EIRP should be -15dBW/4kHz when sharing with systems operating under RR732 and -3dBWl4 IrHz elsewhere. Por the time being, only Iridium project intends to use secondary status downlink allocation in the band
10、1616 MHz to 1626.5 MHz. 2. IN BAND INTERFERENCE FROM MES TO STATIONS OF RADIOASTRONOMY see annex 2 for detailed explanations 2.1. In-band interference (1610.6-1613.8 MHz) for one user considerine: different propagation models The aim of this section is to assess the required separation distances bet
11、ween a radio astronomy observatory and a Mobile Earth Station. IT-R Recommendation 769 gives the maximum level of interference at a radio astronomy observatory (-262 dBW/Hz in 20 kH2). Separation distances are calculated assuming interference for 10% of the time. This percentage is stemming from WT-
12、R report 696 and is also recommended in the draft recommendation of Study Group 7 about “the protection of the Radio Astronomy service in the frequency bands shared with other services“. Unless specified, the MES antenna height has been assumed as 1.5 m and the radio observatory antenna height as 30
13、 m. STD-CEPT ERC REPORT Zb-ENGL 1994 Required path loss Spherical diffraction Extrapolation ofOkumuras model EPM 73 (dB) I 2326434 GLOBALSTAR ODYSSEY IRIDIUM INMARSAT INMARSAT CDMA TDMA 198.8 194.3 212.9 201.0 218.0 98 km 91 km 118km 101 km 126 km 226 km 187 km 413 km 247 km 513 km 169 km 130 km 379
14、 km 191 km 509 km 0035330 TT9 I Tropospheric scatter O“ 1.5 m antenna height 1“ ERC REPORT 26 Page 2 196 km 160 km 328 km 215 km 380 km 119 km 90 km 232 km 135 km 280 km An internationally agreed propagation model for interference prediction exists in ITU-R 452-5. This involves several propagation m
15、echanisms. For a time percentage of 10% and distances greater than approximately 100 km, the tropospheric scatter mechanism is dominant. For shorter distances, diffraction dominates. It is therefore judged that these models should determine the required separation distances. However, as there are al
16、so other models in use, separation distances for two other models are included for comparison. It can be noted that required separation distances vary considerably, depending on the propagation model. Tropospheric scatter 15 m antenna height The following 4 propagation models are used (see annex 2,
17、sections 1 and 2 for explanations) : O“ 203 km 165 km 335 km 222 km 388 km 1“ 124 km 95 km 239 km 140 km 287 km - spherical diffraction, using ITU-R Recommendation 526; - extrapolation of Okmuras model; - EPM 73 model (EPM for Empirical Propagation Model); - tropospheric scatter using ITU-R Recommen
18、dation 452-5, with O“ or 1“ additional elevation angles. Calculations have also been computed assuming an antenna height of 15 m to simulate a MES on a ship. It should be noted that the higher required path loss for TDMA systems is balanced by a lower probability of finding a MES transmitting in the
19、 RAS receiving bandwidth. Moreover, footnote 731E states that a MES should produce an EIRP lower than -15 dB(W/4kHz) in part of the band used by systems operating in accordance with the provisions of RR 732 and -3 dB(W/41IHZ) in any other part of the band. 2.2. In-band interference for a density of
20、users In this section, a density of 0.004 users per square miles (0.001545 users per square kilometre) during peak loading hours is taken into account, based on commercial market surveys. This figure is obviously not valid for a MES on a ship and, consequently, this case has not been computed. STD.C
21、EPT ERC REPORT 26-ENGL 1994 I 2326434 0035333 935 1111 O“ elevation angle 1 O elevation angle ERC REPORT 26 Page 3 GLOBALSTAR ODYSSEY IRIDIUM INMARSAT INMARSAT CDMA TDMA 266 km 285 km 257 lun 279 km 279 km 158 km 176 km 150 lun 171 km 171 km ITU-R Rep 1126 describes the way to calculate separation d
22、istances between the radio astronomy observatory and the mobile services : the interfering signal received at a Radio astronomy observatory is assumed to be the sum of the contributions of users located in concentric rings 10 km large around the observatory. Given the distances considered, only trop
23、ospheric scatter model is used. In order to calculate final separation distances for interference for approximately 10% of the the, path losses for the first three rings are calculated assuming interference 10% of the time and for 50% for the other rings. For CDMA systems, calculations are made on 5
24、0 rings (500 km more than the required separation distance). For TDMA systems, calculations are stopped when the maximum number of users for one channel and one spot beam is reached (8 users for the INMARSAT system 4 users for the IRIDIUM system), without exceeding 50 rings. See annex 2 section 3 fo
25、r detailed explanations. Required separation distances for a land MES (antenna height 1.5 m) are given in the following tables: Using a density of users and taking the probability of interference in the radio astronomy band into account leads to more homogenous required separation distances between
26、TDMA and CDMA systems. However, calculated values are in some cases (e.g. TDMA systems) lower than when considering a single user. The reason is that in the above calculations, users are assumed to be uniformely distributed. This means for instance that the average number of users in the frst ring i
27、s very much less than one. Calculations carried out with a single user assume that there is one user at the edge of the coordination area, regardless of the probability of such an event. However, the assumption of an uniform distribution of users is not sufficiently reliable and, consequently, the p
28、rovisional separation distance should be based on the methodology (single user or density of users) which gives the greatest separation distance. 3. MAXIMUM REQUIRED OUT-OF-BAND EMISSION IN ORDER TO AVOID INTERFERENCE FROM A MOBILE 1 KM AWAY FROM A RADIO ASTRONOMY OBSERVATORY. In this section, a mob
29、ile terminal channel is assumed to operate next to a radio astronomy observation (1610.6 - 1613.8 Miz). The aim of the following calculations is to evaluate the maximum out-of-band emissions from the operating MES to prevent interferences to the radio astronomy service. For this calculation, the MES
30、 is assumed to be not closer than 1 km from the radio astronomy observatory (this assumption is based on the size of a radio astronomy site). Using a free space propagation model, the maximum acceptable out-of-band emissions from the MES in any radioastronomy channel is then -129 dE!(W/4lrHz) i.e. -
31、10 dBW/3kHz). STD-CEPT ERC REPORT 26-ENGL 1774 I 232b414 0015332 871 1111 ERC REPORT 26 Page 4 If out-of-band emissions in the band 1610.6-1613.8 MHz are higher than this value, the MES should not emit in a given area around the radio astronomy observatory. For the out-of-band level to be low enough
32、, the required separation distance can be computed using the Okumura-Hata propagation model valid for a distance smaller than 100 km The relation between out-of-band level and the separation distance is given in the figure below. 80 70 60 50 Out ofband 40 emission level (dB(pW13kHz) 30 20 10 O -1 o
33、O 10 20 30 40 50 60 70 80 90 100 Separation distance (km) (assuming OKUMURA propagation model) 4. INTERFERENCE FROM DOWNLINK MSS The only calculation which can be made is to give the maximum EIRP of the satellite in the 1610.6 - 1613.8 MHz band in order to protect the radio astronomy service. Calcul
34、ations have been made just for the Iridium system, which would normally transmit in the band above 1616 MHz. The maximum interfering signal coming from the MSS downlink must not exceed -262 dB(w/Hz) at the receiver of the radioastronomy observatory. Using a free space propagation model and a 0 dBi r
35、adio astronomy sidelobe antenna gain, this figure leads to a maximum average EIRP (in the adjacent radio astronomy 1610.6 - 1613.8 MHz band) of - 71.6 dB(W/4kHz) (IRIDIUM satellite height is 780 km). It is recognised that Iridium satellites could be seen in the main lobe of radio astronomy antenna f
36、or a very short time. This may be tolerated by the radio astronomy community. When considering all 4 time slots used, IRIDIUM average EIRF is 21.5 dBW/40kHz. The above figure leads to a maximum EIRP at the satellite antenna (in the adjacent radio astronomy 1610.6 - 1613.8 MHz band) of -83 dBc. 5. OP
37、ERATIONAL SHARING TECHNIQUES If coordination is to work, the mobile user must have some means of determining when a coordination zone has been entered, and some means of reducing the power flux density received at the radioastronomy observatory below the threshold for harmful interference. Two possi
38、ble solutions have been discussed, although neither system has yet been demonstrated in practice. In the fxst solution the mobile user carries position-determining equipment (e.g. GPS receiver) together with a regularly updated list of positions of those radio astronomy sites currently observing in
39、the 1612 MHZ band, and their required coordination zones. Emissions in the band 1610.6 - 1613.8 MHz are then inhibited whenever the mobile enters a coordination zone in accordance with section 2. A similar solution is not to allocate a channel in the radio astronomy band or in adjacent bands when th
40、e MES is in a spot beam which overlapps with the coordination area. Attention should be given to the accuracy of position-determining equipment (if worse than few kilometers). STD-CEPT ERC REPORT 2b-ENGL 1994 m 232b414 0035333 708 L111 GLOBALSTAR Land MES 158 km MES on a ship 203 km ERC REPORT 26 Pa
41、ge 5 ODYSSEY IRIDIUM INMARSAT INMARSAT CDMA TDMA 176 km 232 km 171 km 280 km 165 km 335 km 222 km 388 km in the second solution, the radio astronomy observatory has an omni-directional beacon transmitter. The beacon is activated only when radio astronomical measurements are being made, and the power
42、 level of the beacon is related to the size of the coordination zone required. Transmission from the mobile is inhibited in the band 1610.6 - 1613.8 MH2 whenever the mobile user detects the beacon. Two types of beacon have to be examined : - beacon in a nearby frequency band : in this case propagati
43、on losses are the same between the beacon and the MES receiver as between the MES transmitter and the radio astronomy observatory. But this solution requires a receiver and a transmitter in a nearby frequency band in the MES terminal which is technically difficult. - beacon operating in another freq
44、uency band than the MES : this case is technically easier but beacon path loss and MES path loss would be different. Therefore, assuming a propagation model for MES and a propagation model for the beacon, a coordination zone would have to be calculated in accordance with section 2. Because of the di
45、sadvantages of the second solution discussed above, the first solution is considered to be more realistic at the moment. 6. CONCLUSION A supplementary elevation angle of 1“ above the horizon at radio astronomy observatories or at MES antennas is realistic in most cases (trees 10 m high located 500 m
46、 away from the MES or hills 180 m high located 10 km away from the radio astronomy site) for a MES on land. No supplementary elevation angle should be taken into account for MESS on ships. For a MES on land, calculation should be made with a single user and a density of users, using tropospheric sca
47、tter 1“. Provisional separation distances should be based on the largest separation distance. For a MES on a ship, calculation should be only made assuming a single user and tropospheric scatter 0“. The following separation distances are found : Then it can be seen that maximum required separation d
48、istances range from 176 km for a CDMA MES to 280 km for a TDMA MES when operating on land. For a MES on a ship, distances range from 222 km for a CDMA MES to 388 km for a TDMA MES. If coordination is to work, the MES should carry position-determining equipment and the list of positions of radio astr
49、onomy sites and separation distances should be regularly updated. It should be noted that the propagation models used for the calculations do not take into account any terrain profile. Each radio astronomy site has its own terrain profile (forests etc.) which could be computed with an appropriate propagation model. Moreover propagation measurements could be undertaken around each radio astronomy site to validate the order of magnitude of the required separation distances. STD*CEPT ERC REPORT 26-ENGL 1774 111 232b414 0015334 b44 II ERC REPORT 26 Page 7 ANNEX 1 Table 1. Obs
