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(ITU) ﻟﻼﺗﺼﺎﻻﺕ ﺍﻟﺪﻭﻟﻲ ﺍﻻﺗﺤﺎﺩ ﻓﻲ ﻭﺍﻟﻤﺤﻔﻮﻇﺎﺕ ﺍﻟﻤﻜﺘﺒﺔ ﻗﺴﻢ ﺃﺟﺮﺍﻩ ﺍﻟﻀﻮﺋﻲ ﺑﺎﻟﻤﺴﺢ ﺗﺼﻮﻳﺮ ﻧﺘﺎﺝ (PDF) ﺍﻹﻟﻜﺘﺮﻭﻧﻴﺔ ﺍﻟﻨﺴﺨﺔ ﻫﺬﻩ .ﻭﺍﻟﻤﺤﻔﻮﻇﺎﺕ ﺍﻟﻤﻜﺘﺒﺔ ﻗﺴﻢ ﻓﻲ ﺍﻟﻤﺘﻮﻓﺮﺓ ﺍﻟﻮﺛﺎﺋﻖ ﺿﻤﻦ ﺃﺻﻠﻴﺔ ﻭﺭﻗﻴﺔ ﻭﺛﻴﻘﺔ ﻣﻦ ﻧﻘﻼ ً◌ 此电子版（PDF版本）由国际电信联盟（ITU）图书馆和档案室利用存于该处的纸质文件扫描提供。 Настоящий электронный вариант (PDF) был подготовлен в библиотечно-архивной службе Международного союза электросвязи путем сканирования исходного документа в бумажной форме из библиотечно-архивной службы МСЭ. © International Telecommunication Union XVII A.R DUSSGLDORF 21.5 - 1.6 1990 CCIR XVIIth PLENARY ASSEMBLY DUSSELDORF, 1990 INTERNATIONAL TELECOMMUNICATION UNION QUESTIONS OF THE CCIR, 1990 VOLUME XV SG 1 SPECTRUM MANAGEMENT TECHNIQUES SG 12 INTER-SERVICE SHARING AND COMPATIBILITY SG 5 RADIO WAVE PROPAGATION IN NON-IONIZED MEDIA SG 6 RADIO WAVE PROPAGATION IN IONIZED MEDIA SG 7 SCIENCE SERVICES INTERNATIONAL RADIO CONSULTATIVE COMMITTEE Geneva, 1990 CCIR 1. The International Radio Consultative Committee (CCIR) is the permanent organ of the International Telecommunication Union responsible under the International Telecommunication Convention "... to study technical and operating questions relating specifically to radiocommunications without limit of frequency range, and to issue recommendations on them../7 (Inter­ national Telecommunication Convention, Nairobi 1982, First Part, Chapter I, Art. 11, No. 83)? 2. The objectives of the CCIR are in particular: a) to provide the technical bases for use by administrative radio conferences and radiocommunication services for efficient utilization of the radio-frequency spectrum and the geostationary-satellite orbit, bearing in mind the needs of the various radio services; b) to recommend performance standards for radio systems and technical arrangements which assure their effective and compatible interworking in inter­ national telecommunications; c) to collect, exchange, analyze and disseminate technical information resulting from studies by the CCIR, and other information available, for the development, planning and operation of radio systems, including any necessary special measures required to facilitate the use of such information in developing countries. * See also the Constitution of the ITU, Nice, 1989, Chapter 1, Art. 11, No. 84. COVERING NOTE GENERAL SECRETARIAT INTERNATIONAL TELECOMMUNICATION UNION Subject: ADDENDUM No. 2 Geneva, 6 September 1993 VOLUME XV-1 CCIR XVIIth PLENARY ASSEMBLY DUSSELDORF, 1990 Study Group 7 Add the following new Questions*: - Question ITU-R 201/7, page 151 - Question ITU-R 202/7, page 152 - Question ITU-R 203/7, page 153 - Question ITU-R 204/7, page 154 * These Questions were adopted between March and M y 1993. Union internationale des telecommunications Place des Nations 1211 GENEVE 20 Suisse-Switzerland-Suiza Q. ITU-R 201/7 151 QUESTION ITU-R 201/7 TWO-WAY TIME TRANSFER THROUGH COMMUNICATION SATELLITES (1993) The ITU Radiocommunication Asembly, considering a) that the theoretical accuracy and stability of the two-way exchange of timing signals through communication satellites has great promise; b) that the experimental results on the short-term time stability are consistent with theory; c) that sufficient experience for long-term time stability studies has not yet been obtained; d) that systematic variations in the delays of the transmitting and receiving elements for this technique need to be better understood and documented; e) that there is not an agreed-upon method for quantifying the time accuracy, the time stability and the frequency comparison capability of this technique; f) that many of the world timing centres are implementing this technique because of its apparent potential, decides that the following Question should be studied 1. What are the performance levels that can be achieved in practice when using the two-way satellite time transfer technique with respect to the following: the long-term time stability of this technique; the time accuracy of this technique; the frequency comparison capability of this technique; and comparisons of the performance of the two-way technique with similar results from alternative methods, such as use of GPS satellites? 2. What are the causes and cures for systematic delay variations that may be perturbing this technique? 3. What standard data format, if any, can be agreed upon and implemented for comparison between the different timing centres? 152 Q. ITU-R 202/7 QUESTION ITU-R 202/7 FREQUENCY SHARING AND PROTECTION BETWEEN SPACE VLBI AND OTHER SPACE RESEARCH SYSTEMS (1993) The ITU Radiocommunication Assembly, considering a) that there are requirements to use spacecraft for conducting very long baseline interferometry (VLBI); b) that space VLBI observations usually require wideband data transmission in the space-to-Earth direction; c) that space VLBI systems require precision up-link and corresponding down-link phase reference signals which need to be protected from interference; d) that there may be a potential for mutual interference when space VLBI systems are operated in die same frequency bands used by other space research systems, decides that the following Question should be studied 1. How do the technical and operating characteristics of space VLBI systems affect the feasibility of sharing with other space research systems? 2. Under what conditions and to what extent is it possible for space VLBI systems to share frequency bands with other space research systems? 3. What frequency bands are suitable for sharing between space VLBI systems and other space research systems? Q. ITU-R 203/7 153 QUESTION ITU-R 203/7 CHARACTERISTICS AND TELECOMMUNICATIONS REQUIREMENTS FOR SPACE VLBI (1993) The ITU Radiocommunication Assembly, considering a) that the angular resolution of measurements made by very long baseline interferometry (VLBI) techniques is limited by the distance between two observing stations; b) that, compared to the largest possible distance between two observing stations on Earth, this baseline distance may be substantially increased by locating one or more of the observing stations in space; c) that by conducting VLBI measurements which utilize spacecraft, it is possible to eliminate the limitations of ground-based observations caused by the absorption, path length fluctuations and noise contributions by the atmosphere; d) that space VLBI will eventually provide invaluable knowledge of physical parameters leading to highly accurate determination of: radiosources structure; deep-space navigation; geodynamics; astrometry; satellite's orbit parameters; e) that the transmission of wideband space VLBI data from space-to-Earth is required; f) that space VLBI systems require the transmission of highly accurate time/phase reference signals from Earth-to-space and space-to-Earth, decides that the following Question should be studied 1. What are the technical characteristics of space VLBI systems with regard to their requirements for telecommunication links? 2. What are the orbital characteristics of spacecraft engaged in space VLBI, as they may affect the utilization of radio-frequency bands and the feasibility of sharing (see Question ITU-R 202/7)? 3. Considering the effects of radio-wave propagation, and available techniques; what are the frequency bands most suitable for the precise time/phase transmission; what are the frequency bands and bandwidths most suitable for the wideband data transmission space-to-Earth? 154 Q. ITU-R 204/7 QUESTION ITU-R 204/7* SHARING OF THE BAND 1 675-1 710 MHz BETWEEN THE MOBILE-SATELLITE SERVICE AND THE METEOROLOGICAL-SATELLITE AND METEOROLOGICAL AIDS SERVICES (1993) The ITU Radiocommunication Assembly, recognizing a) that the World Administrative Radio Conference (Malaga-Torremolinos, 1992) (WARC-92) decided that, in the band 1 675-1 710 MHz, stations in the mobile-satellite service shall not cause harmful interference to, nor constraint the development of, the meteorological-satellite and meteorological aids services and the use of this band shall be subject to the provisions of Resolution No. 46 (WARC-92) (Footnote 735A (WARC-92) to the Radio Regulations); b) that Resolution No. 213 of WARC-92 "Sharing studies concerning the use of the bands 1 492-1 525 MHz and 1 675-1 710 MHz in Region 2 by the mobile-satellite service" resolves that studies be undertaken by the ex-CCIR to examine the operational and technical measures that would facilitate sharing; c) that this Resolution invites the ex-CCIR also to study as a matter of urgency the technical and operational issues relating to the sharing of these bands, noting a) that, as for the band 1 675-1 710 MHz, Recommendation ITU-R SA.514** and Reports ITU-R SA.395**, ITU-R SA.541**, ITU-R SA.851** and ITU-R SA.1121** contain some information on this matter, decides that the following Question should be studied 1. What are the operational and technical measures appropriate for preventing harmful interference to