1、 Rep. ITU-R M.2027 1 REPORT ITU-R M.2027*Engineering guidance for operators to upgrade shore based facilities to operate the Global Maritime Distress and Safety System in the A1, A2 and A3/A4 sea areas (2001) 1 Overview In order to establish a new A2, A3, or A4 sea area it is necessary to gain some
2、knowledge of how the propagation conditions vary. A2 coverage is by groundwave, which is stable, enabling the extent of the service area to be confirmed by measurement before committing capital expenditure, which is recommended by the IMO. A3 and A4 coverage is by skywave which depends upon the cond
3、ition of the ionosphere which varies with solar activity. Since this follows an 11-year cycle, the extent of the service area cannot be confirmed by performing a new measurement study, and administrations wishing to join the HF shore station network may require methods to verify feasibility and size
4、 the equipment required in order to confidently establish a project budget. The extent of the sea areas A2, A3, and A4 are specified by the IMO in Annex 3 to their resolution A.801(19), and 3.4.1 of this Report provides charts for rapid assessment of the extent of the A2 sea area using this data, an
5、d also guidelines to enable administrations to make their own assessment of potential A3 and A4 coverage using HF prediction software in the context that each shore station is a member of a community of HF stations working together to provide the required grade of service. Section 2 defines the func
6、tional requirements, and describes the equipment required. Section 3 defines single sideband (SSB) carrier/noise ratio and useable signal level, outlines the grades of service, presents performance criteria, reviews the software tools available and provides guidance on determination of receive range
7、s and transmitter power require-ments. Section 4 covers site engineering issues: including selection of good receive sites, isolation between sites, protection of watch frequencies, station earthing and lightning protection. 2 The Global Maritime Distress and Safety System (GMDSS) 2.1 Statutory requ
8、irements The GMDSS came into force in February 1992 under the international convention for the Safety of Life at Sea (SOLAS) amended in November 1988 and is intended for setting up a global communications network to support search and rescue activities from land, air and sea for rapid rescue for shi
9、ps in distress. _ *This Report should be brought to the attention of the International Maritime Organization (IMO). 2 Rep. ITU-R M.2027 The GMDSS allows shore based search and rescue (SAR) authorities as well as ships in the immediate vicinity of the ship in distress to be rapidly alerted to the dis
10、tress incident so that they can assist in coordinated search and rescue operations with a minimum delay. The GMDSS substantially expands the SAR communications coverage to the global sphere using the VHF, MF and HF bands as well as satellite communication systems using digital selective calling (DSC
11、) which allows a ship in distress to rapidly transmit information on its situation to a shore-based coast station in a simple, secure way. The coast station that has received a distress alert can easily access the ship for SAR communications. In addition, the GMDSS NAVTEX system provides automatic b
12、roadcasting of maritime safety information, navigational and meteorological warnings and SAR information to all ships in a coastal area of up to 500 nautical miles offshore. Full GMDSS coverage is provided by dividing the oceans of the world into four different areas in which ships are expected to o
13、perate: Area Definition of sea area Means of coverage Typical range Al An area within radiotelephone coverage of at least one VHF shore station, in which continuous DSC alerting is available Permanent VHF coverage Within line-of-sight of antenna, extended when ducting persists Short range 15 to 30 n
14、autical miles offshore A2 An area, excluding sea area A1, within radiotelephone coverage of at least one MF station, in which continuous DSC alerting is available Permanent MF coverage Groundwave propagation over the horizon with some patches fading at night Medium range 100 to 300 nautical miles of
15、fshore A3 An area, excluding sea areas A1 and A2, within which the elevation of an INMARSAT geostationary satellite is 5 or more Alternative to INMARSAT Using skywave propagation on 5 HF bands Long range Mainly between latitude 70 N and latitude 70 S A4 An area outside sea areas A1, A2, and A3 Prima
16、ry HF coverage Shared between network of participating shore stations by skywave on 5 HF bands Long range Beginning north of 70 N south of 70 S 2.2 Operational requirements 2.2.1 Basic operator functions Shore-based coast stations providing ships at sea with VHF, MF or HF radiocommunication services
17、 for use with the GMDSS have to incorporate the following functions. Rep. ITU-R M.2027 3 Reception of distress alerts. The shore station is required to keep continuous watch for distress alerts transmitted from ships using DSC. The distress alert identifies the ship in distress, its position, the na
18、ture of the distress, the type of assistance required and the time of recording of the information. Transmission of acknowledgement. The shore station which has received a distress alert is required to send back an acknowledgement signal to the ship in distress, to cease any transmission which may i
19、nterfere with distress traffic, and to continue to watch distress traffic. Re-transmission of the distress alert. The shore station is required to have the means to re-transmit the received distress alert to all the ships navigating in the vicinity of the ship in distress. Dissemination of maritime
20、safety information. To support SAR operations, shore-based coast stations are expected to disseminate maritime safety information including navigational and meteorological warnings and other urgency and safety messages. The NAVTEX information is transmitted on 518 kHz by means of narrow-band direct
21、printing (NBDP) telegraphy in forward error correction (FEC) mode. 2.2.2 Functional roles played by shore-based facilities Although arrangements differ from country to country, shore-based facilities generally comprise radio stations and SAR forces under the supervision of one or more rescue coordin
22、ation centres (RCC), and rescue missions commonly employ facilities from more than one country, calling for a high degree of international cooperation. Annex 2 of document COM33/2/3 (July 1987) Input from IMO subcommittee on Life Saving Appliances, Search and Rescue to IMO subcommittee on Radiocommu
23、nication concerning SAR communications on Long Ranges in GMDSS, describes how the search and rescue operations are coordinated by the international RCC community with direct assistance from shore-based radio facilities, and lays out some basic guidelines for international cooperation. The shore stat
24、ion nearest to the reported distress position should acknowledge the alert. Other shore stations receiving the alert should acknowledge if the nearest station does not appear to respond, which may be due to the variability of HF skywave communications. The shore station which acknowledges the alert
25、is then expected to establish and maintain communications with the casualty until relieved by the affiliated RCC which bears responsibility for all subsequent coordination of SAR measures, unless and until responsibility is accepted by another RCC better able to take action. 2.2.3 Initial operator r
26、esponse to a distress alert The loss of life resulting from any accident or disaster is reduced by the speed of response from the rescue service. The prime directive should therefore be to enable the shore station operator to implement the fastest possible response, summarized as: recognizing the na
27、ture of the distress and notifying the affiliated RCC; establishing initial contact with the distressed vessel or task force; accepting responsibility for and initiating transmission of the DSC acknowledgement; patching the RCC through by radio to the distressed vessel or task force if required. The
28、 operator response software should be designed to immediately invoke an appropriate human response, minimizing the amount of time which the operator should spend correlating data, deciding 4 Rep. ITU-R M.2027 what action to take, and performing subsequent actions like dialling telephone numbers and
29、setting up equipment. The ships crew-member raising the alert has the option to request the use of NBDP for follow-on communication, mandatory if in A4 waters. The operator workstation should therefore be equipped to double as an NBDP chat-mode terminal. 2.3 Equipment required for distress response
30、2.3.1 Basic equipment required for short-range communication (A1) A country with an extended coastline may need a number of VHF base stations for effective radio coverage, as shown in Fig. 1, in which one RCC supervises a number of geographically based subsystems, each with its own operator. As a ca
31、ll may be picked up by more than one base station, each subsystem would use a voting system to decide which base station to use, and these would be linked between sites to decide which operator would be responsible for overlapping calls. Rap 2027-01SSSSSSRCCRemote VHF base stationShore radio station
32、Signal voting linkSSFIGURE 1Typical system covering a complete coastlineFigure 2 depicts the basic equipment required in each subsystem to provide a response to an A1 distress alert, showing 10 remote VHF base stations under the control of a single DSC processor and operator. 2.3.2 Basic equipment f
33、or medium-range communication (A2) Figure 3 shows the basic equipment required for providing a response to an A2 distress alert, configured to enable the transmission of the distress acknowledgement and provision of manual response using SSB radiotelephony to be accomplished using a single transmitt
34、er. Rep. ITU-R M.2027 5 Rap 2027-02LineinterfaceReceiverTransmitterCH70watchCH16receiver/transmitterVHF antennasDSCprocessorOperator GMDSSworkstationTelephone interfaceTelephone interface10-channel operatorcontrol panelTelephone patch panel10 remote sitesFIGURE 2Basic GMDSS A1 subsystemLineinterface
35、ReceiverTransmitterA short whip receive antenna is connected to a crystallized A2 watch receiver and an operational receiver via a multi-coupler. The watch receiver output is connected to DSC processor modem input, the modem audio frequency and PTT outputs being connected to the transmitter via an i
36、nterface panel to enable the DSC acknowledgement to be routed to the transmitter when required. The interface panel enables the operator to establish a radiotelephony circuit with the ship, and provide the necessary connection to the RCC, and to maintain control of the transmitter and receiver. The
37、transmit antenna is a vertically polarized tuned monopole antenna, capable of launching a groundwave for A2 response. The size of transmitter required will depend upon the antenna efficiency, which depends upon the antenna length, and the size of the earth mat, and for output powers below 500 W it w
38、ould be possible to combine the transmitter and the operational receiver into a single transceiver. More information on antenna efficiency is given in 4.5.1.3 below. 6 Rep. ITU-R M.2027 Rap 2027-03OperatorworkstationLogprinterTuned verticalmonopole transmitantennaEarthmatDSC channel processorOperato
39、r interface panelControlControlTransmitterOperational receiverCrystalized A2watch receiver2 187.5 kHzTelephonepatch unitTelephoneline to RCCReceivewhipantennaFIGURE 3Basic GMDSS MF DSC systemMulticouplerThe transmitter and operational receiver can be set to the appropriate mode and frequency by the
40、DSC processor, either directly, or indirectly via the operator workstation. Additional equipment which may be used, but is not shown, include modems to enable the equipment to be installed on separate sites, and a call logger to enable the radiotelephony messages and DSC signals to be recorded. 2.3.
41、3 Basic equipment for medium- and long-range communication (A2/A3) Figure 4 shows the additional equipment required to the basic configuration in Fig. 3 for a second channel providing A3 coverage, comprising watch receivers and DSC modems to cover the five HF bands, operational receiver, transmitter
42、, and transmit antenna. Both transmitters connect to their own wideband conical monopole antenna suitable for initiating groundwaves for MF A2 coverage, and low angle skywaves for HF A3 coverage, and a transmitter crosspatch ensures that if one transmitter fails the remaining transmitter can be used
43、 on either Rep. ITU-R M.2027 7 service. Additional redundancy could be provided by doubling the number of watch-keeping receivers, providing two identical subsystems each capable of operating on either A2 or A3. Rap 2027-04WorkstationLogprinterDSC channel processorOperator interface panelTransmitter
44、Operational receiverConical monopoletransmit antenna(2-20 MHz)Telephonepatch unitReceivewhipantennaOperational receiverTransmitterTelephonepatch unitOperator interface panelConical monopoletransmit antenna(2-20 MHz)PSTNPSTNDSC channel processor16 804.5 kHz12 577.0 kHz8 414.5 kHz6 312.0 kHz4 207.5 kH
45、z2 187.5 kHzGMDSS watchreceiversFIGURE 4Basic GMDSS MF or HF DSC systemRS232 controlMulticouplerPSTN: public switched telephone networkLogprinterWorkstation8 Rep. ITU-R M.2027 2.3.3.1 Typical system providing full cover on A2, A3, and A4 Rap 2027-05AF and PTTswitch matrixor patch panelHF receiverHF
46、receiverHF receiverHF receiverHF transmitterHF transmitterHF transmitterHF transmitter16 804.5 kHz12 577.0 kHz8 414.5 kHz6 312.0 kHz4 207.5 kHz2 187.5 kHzWatch receiversTransmitter antennaswitchmatrixMulticouplerOperatorpanelDSCprocessorTelephonepatch unitVoiceloggerTo RCCControlMedium rangeoperator
47、MF A2LoadTransmitter antennasTuned monopoleConical monopoleLog periodicOther operatorsSupervisor(optional)AuxiliaryoperatorA1/A2/A3/A4Long rangeoperatorHF A3/A4Short rangeoperatorVHF A1To A1processorReceiver/transmitterCH16CH70VHF base stationsReceiverwhipantennaFIGURE 5Typical system providing full
48、 GMDSS A1, A2, and HF coverageRep. ITU-R M.2027 9 2.3.4 NAVTEX system The NAVTEX system can store broadcast messages in advance and automatically send them out on a pre-set broadcast timetable. The 518 kHz transmitter is designed to operate in the F1B mode in order to transmit NAVTEX information in
49、the FEC mode through the NBDP system. Rap 2027-06Changeovercontrol unitNAVTEXprocessorDummyloadACUFIGURE 6Basic NAVTEX systemEarthmatAntenna forGPS clockNAVTEX control andmessage preparationACU: antenna command unitTee antenna10 Rep. ITU-R M.2027 3 System planning 3.1 Planning objectives Shore-based GMDSS stations have to provide short-range, medium-range and/or long-range services using VHF, MF and HF bands, respectively. Whereas an A1 sea area may require a large number of VHF stations at intervals along the coastline, NAVTEX and A2 sea areas can
