船舶自动识别与公共通信的电磁兼容性
technical report U.S. DEPARTMENT OF COMMERCENational Telecommunications and Information Administration Electromagnetic CompatibilityBetween Marine Automatic Identificationand Public Correspondence Systemsin the Maritime Mobile VHF Band Robert L. SoleBrent BedfordGary Patrick U.S. DEPARTMENT OF COMMERCEWilliam Daley, Secretary Greg Rohde, Assistant Secretaryfor Communications and Information April 2000 Executive Summary The Coast Guard funded the National Telecommunications and Information Administration(NTIA) toperform electromagnetic compatibility(EMC)tests between an ITU-R M.825-3(Characteristics Of a Transponder System Using Digital Selective Calling Techniques for Use withVessel Traffic Services and Ship-to Ship Identification) based Automatic Identification System (AIS)operating on 12.5 kHz channels and Public Correspondence (PC) Systems operating on 25 kHzchannels.The tests were performed between January 17-28, 2000 in and around an AIS basestation communications tower located at Point Ala Hache, La. by NTIA, SETA Corporation, andCoast Guard personnel.AIS is a shipborne transponder-based navigation safety system that serves as the foundation for the Vessel Traffic Service (VTS) being established in New Orleans and elsewhere by the CoastGuard under the Ports And Waterway Safety System (PAWSS) project. AIS is based on technicalstandardsestablished by the International Telecommunication Union(ITU).Thecurrentimplementation in New Orleans is based on ITU-R Recommendation M.825-3. This will be updatedin the future to the standard for Universal Shipborne AIS, ITU-R M. 1371 (Technical Characteristicsfor a Universal Shipborne Identification System Using Time Division Multiple Access In the VHFMaritimeMobileBand).Transponders that are fully compliant with ITU-R M. 1371 are not currently available.AIS facilitates the efficient exchange of data between ships and between shore stations and ships.AIS responds to the mariners’ need for timely, relevant and accurate information (including data onships position, speed, etc) delivered in an unobtrusive manner. AIS requires dedicated frequenciesin order to operate safely and reliably.AIS requires duplex channels for ship-to-shore and shore-to-ship digital data transmissions and simplex channels for ship-to-ship operations. Frequencies selected for AIS must come fromAppendix 18 of the International Radio Regulations (between 156.025-157.425 MHz and 160.625-162.025 MHz).Of the 35 duplex channels listed in Appendix 18 of the ITU Radio Regulations, only nine remain for consideration for potential AIS operations in the United States due to past U.S. regulatorydecisions.These nine 25 kHz duplex channels are currently utilized within the VHF marine PublicCorrespondence (PC) Band, and designated as channels 24, 84, 25, 85, 26, 86, 27, 87, and 28. Toobtain additional AIS frequencies, the U.S. must utilize techniques outlined in ITU-R M. 1084-3(Interim Solutions for Improved Efficiency In The Use of the Band 156-174 MHz by Stations In theMaritime Mobile Service) regarding the use of 12.5 kHz interstitial channels that are interleavedbetween existing 25 kHz wideband channels.AIS and Public Correspondence systems both use duplex channels in the maritime mobile VHF band for communications between a mobile unit and a base station, which results in fiveinterference scenarios occurring between the two systems. The four interference scenarios testedwere: 1) an AIS base station causing interference to a PC mobile radio receiver; 2) a PC basestation causing interference in a AIS transponder receiver; 3) an AIS transponder causinginterference in a PC base station receiver; and 4) a PC mobile radio causing interference to an AISbase station receiver.At a minimum, 12.5 kHz of frequency separation was used in all testsscenarios between the interfering transmitter and victim receiver. In addition, 25 kHz, 37.5 kHz, 50 kHz and 62.5 kHz frequency separations were also tested. Tests at 25 kHz and 50 kHz frequencyseparations are not be applicable since they would require that wideband Public Correspondenceto operate on interstitial channels.These tests were performed to obtain additional results toestablish data trends. A fifth test scenario would be required to determine compatibility betweenship-to-ship AIS and PC operations, and this was not tested due to the unavailability of suitableequipment. This fifth scenario represents a co-site concern with both AIS and PC systems operatingon the same ship.The inability to test the fifth scenario does not alter the conclusions orrecommendations given in this report.Analyses of the results of the four test scenarios offer general guidelines for determining compatibility between AIS operations on interstitial 12.5 kHz channels and Public Correspondenceoperations on wideband 25 kHz channels.Analyses of the test results show that, since AIS and PC systems both offer service to mariners on ships and would employ base stations with transmissio