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3.1 General
Satellite communications
3.1.1 The INMARSAT system, which employs geostationary satellites and operates in the 1.5 and 1.6 GHz band (L-band) provides ships fitted with ship earth stations with a means of distress alerting and capability for two-way communications using direct-printing telegraphy and radiotelephone. L-band satellite EPIRBs are also used for distress alerting. The INMARSAT SafetyNET system is used as a main means to provide MSI to areas not covered by the NAVTEX system.
3.1.2 A polar-orbiting satellite system, operating in the 406 MHz band using satellite EPIRBs (COSPAS-SARSAT system), provides one of the main means of distress alerting and determining the identity and position of the ship in distress or its survivors in the GMDSS.
Terrestrial communications
3.1.3 With terrestrial communications, DSC forms the basis of distress alerting and safety communications. Distress and safety communications following a DSC call can be performed by radiotelephony or direct-printing telegraphy or both.
Long-range service
3.1.4 Use of HF provides a long-range service in both the ship-to-shore and shore-to-ship directions. In areas covered by INMARSAT it can be used as an alternative to satellite communications and outside these areas it provides the only long-range communication capability. Frequencies have been designated in the 4, 6, 8, 12 and 16 MHz bands for this service.
Medium-range service
3.1.5 MF radiocommunications provide the medium-range service. In the ship-to-shore, ship-to-ship and shore-to-ship directions 2187.5 kHz will be used for distress alerts and safety calls using DSC, and 2182 kHz will be used for distress and safety traffic by radiotelephony, including SAR co-ordinating and on-scene communications. 2174.5 kHz will be used for distress and safety traffic by direct-printing telegraphy.
Short-range service
3.1.6 VHF provides short-range service on the frequencies:
� 156.525 MHz (channel 70) for distress alerts and safety traffic calls using DSC, and � 156.8 MHz (channel 16) for distress and safety traffic by radiotelephony, including SAR co-ordinating and on-scene communications. There is no short-range direct-printing telegraphy service on VHF.
Frequencies used in the GMDSS
3.1.7 Frequencies used in the GMDSS communications system allocated by ITU WARC-Mob-87 are given in annex 9.3 (RR Art. N38).
3.2 INMARSAT system
Introduction
3.2.1 INMARSAT grew put of an idea that originated within IMO in 1966. Following extensive study by IMO experts an international conference was convened which, after three sessions on 3 September 1976, unanimously adopted the Convention and Operating Agreement on the International Maritime Satellite Organization (INMARSAT). According to its Convention, INMARSAT is "to take provision for the space segment necessary for improving maritime communications, thereby assisting in improving distress and safety of life at sea communications".
3.2.2 The INMARSAT system has three major components: the space segment provided by INMARSAT, the coast earth stations (CESs) provided by INMARSAT signatories and ship earth stations (SESs).
3.2.3 The nerve centre of the system is the operations control centre (OCC), located at INMARSAT's headquarters in the United Kingdom. The OCC is responsible for controlling the INMARSAT system operation as a whole. Operating 24 hours a day, it co-ordinates a wide range of activities. The OCC also arranges the commissioning of SESs upon application by the shipowner.
Space segment
3.2.4 Four satellites in geostationary orbit 36,000 km above the equator cover four ocean regions, namely AOR-E (Atlantic Ocean Region-East), AOR-W (Atlantic Ocean Region-West), IOR (Indian Ocean Region) and POR (Pacific Ocean Region), and provide near-global coverage. The current status of the INMARSAT system and coverage is given in annex 4 of the GMDSS Master Plan (see annex 5 of this publication).
Coast earth stations
3.2.5 The CESs provide the link between the satellites and terrestrial telecommunications networks. Currently, all CESs are owned and operated by telecommunications carriers. A typical CES consists of a parabolic antenna about 11 m to 14 m in diameter, which is used for transmission of signals to the satellite at 6 GHz and for reception from the satellite at 4 GHz. The same antenna or another dedicated antenna is used for L-band transmission (at 1.6 GHz) and reception (at 1.5 GHz) of network control signals. The type of communication service provided varies depending on the CES. A CES designated for each ocean area for each communication service (i.e. telephone, direct-printing telegraph, etc.) services as a network co-ordination station (NCS) which assigns communication channels, on demand, to SESs and other CESs and monitors signals transmitted by these stations.
Ship earth stations
3.2.6 The requirements for the SESs in the GMDSS can be met by INMARSAT SESs capable of two-way communications, such as INMARSAT-A, INMARSAT-B and INMARSAT-C SESs. Performance standards for SES equipment are given in annex 3-4.
INMARSAT-A SES
3.2.7 An INMARSAT-A SES consists of two parts, above-deck equipment (ADE) and below-deck equipment (BDE). The ADE includes a parabolic antenna, about 0.85 m to 1.2 m in diameter, mounted on a platform and stabilized so that the antenna remains pointed at the satellite regardless of ship motion. It also includes a solid state L-band power amplifier, an L-band low-noise amplifier, a duplexer and a low-loss protective radome. The BDE consists of an antenna control unit; communications electronic used for transmission, reception, access control and signalling; and telephone and telex equipment.
3.2.8 The new generation of INMARSAT-A equipment currently being produced by manufacturers is smaller and easier to use than earlier models. ADE is now available weighing less than 50 kg, making it suitable for installation on most types and sizes of vessel and yachts. Many of the current systems are modular in design and allow the addition of optional equipment such as facsimile, data and slow-scan television, etc. Some BDE has a microcomputer with a visual display unit (VDU), alphanumeric keyboard, hard-copy printer and modem. The computer can be used to prepare telex messages with the ease of modern word-processing equipment. Messages can be compressed, edited and transmitted directly from the screen or stored for later transmission. In some models, the computer memorizes the satellite's co-ordinates and CES tariffs and automatically routes the call in the most economical way.
3.2.9 With additional facilities, users have modified their terminals to allow automated vessel reporting. Those involved in vessel management on shore can dial the ship at any time of the day or night and automatically receive information as to its position, heading, etc., as well as data on its cargo and operation - all without disturbing or distracting the crew. A distress message generator is normally built into a terminal (mostly a software modification) for storage of basic essential vessel information and automatic transmission in a distress situation.
INMARSAT-B SES
3.2.10 The INMARSAT-B SES is a digital complement of INMARSAT-A SES developed to replace INMARSAT-A SES equipment in the future. It provides the same communications services as an INMATSAT-A SES.
INMARSAT-C SES
3.2.11 INMARSAT-C SESs are small, lightweight terminals designed for two-way message communication. INMARSAT-C SESs cannot be used for radiotelephone communications; they operate at 600 bit/s and provide access to the international telex/teletex networks, electronic mail services and computer databases. This low-powered terminal with its omnidirectional antenna and light weight is a practical solution for reach of all mariners. It will enlarge the user community by providing equal access to existing and emerging satellite services to all seafarers.
3.2.12 Additionally, an INMARSAT-C SES can serve as back-up for an INMARSAT-A SES on large ships and also fulfill a potentially vital role as a fixed or portable transmitter/receiver for use on board ship or in survival craft. The omnidirectional antenna characteristics are particularly valuable for a vessel in distress as the SES continues to operate even when the vessel is listing severely. As with the INMARSAT-A SES, a distress message generator can be included in the terminal software for storage of basic essential vessel information and automatic transmission in a distress situation.
Enhanced group call receiver
3.2.13 The INMASRSAT EGC receiver is a dedicated piece of equipment for reception of information by INMARSAT EGS service. It has been designed to enable automatic continuous watch on international SafetyNET MSI broadcasts and commercial INMARSAT FleetNET messages, such a subscription to news services, etc. An EGC capability can be added to INMARSAT-A, INMARSAT-B and INMARSAT-C SESs or it can be stand-alone receiver with its own antenna. Annex 3-5-2 gives the performance standards for EGC receivers.
3.2.14 An EGC receiver is required in the GMDSS for all ships which proceed beyond coverage international NAVTEX service (regulation IV/7.1.5)
INMARSAT services Ship-to-shore distress alerting
3.2.15 The INMARSAT system provides priority access to satellite communications channels in emergency situation. Each SES is capable of initiating a "request" message with distress priority (INMARSAT priority-3 call). Any "request" message with a distress priority indication is automatically recognized at the CES and a satellite channel is instantly assigned. If all satellite channels happen to be busy, one of them will be pre-empted and allocated to the SES which initiated the distress priority call. The processing of such calls is completely automatic and does not involve any human intervention. The CES personnel, however, are notified of the reception and passing through of a distress priority message by audio-visual alarms.
3.2.16 To ensure the correct treatment of distress priority requests, the NCS in each ocean region automatically monitors the processing of such calls by all other CESs in that region. In the event that any anomalies in processing are detected, the NCS will take appropriate action to establish the end-to-end connection. In addition, the monitoring NCS also checks the CES identity contained in the distress priority message and automatically accepts the call if an identity of a non-operational CES has been detected (which may happen due to operator error aboard the vessel in distress).
3.2.17 The distress priority applies not only with respect to satellite channels but also to the automatic routeing of the call to the appropriate RCC. Each CES in the system is required to provide reliable communication interconnection with an RCC; these national RCCs are known as associated RCCs. The means of CES-RCC interconnection may vary from country to country and include the use of dedicated lines or public switched networks. Thus, any distress priority request message received at the CES is automatically processed and passed to the associated RCC. Some CESs, due to national considerations, pass distress priority messages to special operators, who are responsible for the subsequent routeing of the call to the appropriate RCC, or provide an opinion which allows the shipboard operator to contact any RCC when a satellite channel has been assigned on the distress priority basis.
3.2.18 The initiation of a distress priority message in most SESs is made simple for ship crew members by provision of a "distress button" or code in the SES. On activation of this button, the equipment instantaneously transmits a distress priority message. This single operation, a push of the "distress button", provides automatic, direct and assured connection to a competent rescue authority, thereby avoiding the need for the SES operator to select or key the telex or telephone number of the RCC an eliminating possible human error. The establishment of this end-to-end connection, being completely automatic and on a priority basis, takes only a few seconds.
3.2.19 INMARSAT has issued technical guidelines to manufacturers for a distress message generator (DMG), which consists of SES software to transmit automatically, after the connection has been established, the distress message in standardized format that provides information on the vessel's identification, its position and the particular emergency.
3.2.20 The procedure described above is the primary means of ship-to-shore distress alerting in the INMARSAT system. It should be noted, however, that INMARSAT SES-equipped ships can also contact any RCC of their choice by following the calling procedure for routine calls. In this case, the complete international telephone/telex number has to be selected.
3.2.21 A major benefit of the INMARSAT distress priority system is that it eliminates the need for dedicated frequencies to be allocated for distress and safety communications. Distress messages made through the INMARSAT distress priority system are sent trough the general communication channels on an absolute priority basis to ensure an immediate connection.
Shore-to-ship distress alerting
3.2.22 Shore-to-ship alerting to groups of ships with INMARSAT-A, INMARSAT-B or INMARSAT-C SESs but without INMARSAT SafetyNET capability can be performed in the following modes:
1 "All ships call" - Calls to all ships in the ocean region concerned. It should be noted, however, that due to the large coverage zones of geostationary satellites such alerting is not very efficient, although it my be justified under exceptional circumstances;
2 "Geographical area calls" - Calls to ship navigating in a defined geographical area. Each satellite coverage region is subdivided into smaller areas, and the boundaries of these areas are based on NAVAREAs each having a unique two-digit area code. SESs will automatically recognize and accept geographical area calls only if the correct code has been input by the SES operator; the system requires the periodic manual input of appropriate area codes; or
3 "Group calls to selected ships" - This service is provided by a number of CESs in the operator-assisted mode and allow alerting of a predetermined group of vessel. This service could be very useful for alerting, for example, SAR units.
3.2.23 As long as they are not engaged in traffic, SESs accept all incoming messages without any differentiation of priority.
Shore-to-ship distress alerting through the INMARSAT SafetyNET system
3.2.24 The EGC receiver can be an integral part of an SES or a completely separate unit and it ensures a very high probability of receiving shore-to-ship distress alert messages. When a distress priority message is received, an audible alarm will sound and it can only be reset manually.
3.2.25 Accessing the INMARSAT SafetyNET service by RCCs requires arrangements similar to those needed for shore-to-ship distress alerting to a standard SES. Those RCCs unable to obtain a reliable terrestrial connection to a coast earth station can install an INMARSAT SES at the RCC. The RCC would then transmit the distress alert via the SES to a CES, where it would be relayed by means of broadcast over the INMARSAT SafetyNET system. See section 3.7 and annex 4-3 for further details of the INMARSAT SafetyNET system.
Search and rescue co-ordinating communications
3.2.26 For the co-ordination and control of SAR operations, RCCs require communications with the ship in distress as well as with units participating in the operation. The methods and modes of communication (terrestrial, satellite, telephone, telex) used will be governed by the capabilities available on board the ship in distress as well as those on board assisting units. Where those ships are equipped with an SES, the advantages of the INMARSAT system for rapid, reliable communications including receipt of MSI can be exploited.
3.2.27 A reliable interlinking of RCCs is important for the GMDSS, in wich a distress message may be received by an RCC thousands of miles away from where the assistance is needed and it may not be the RCC best suited to provide the necessary assistance. In this case prompt relay of the distress message to the appropriate RCC is essential and any communications means, whether landlines, terrestrial radio networks or satellite links, must be used.
3.2.28 To increase the speed and reliability of inter-RCC communications, some RCCs have installed SESs providing them with the capability of communicating via the INMARSAT system. These facilities are useful for long-distance interconnection of SAR organizations, especially when dedicated lines or public switched networks are unavailable or unreliable.
On-scene SAR communications
3.2.29 On-scene communications are those between the ship in distress and assisting vessels, and between SAR vessels and the OSC or the CSS, and are normally short-range communications made on the VHF or MF distress and safety frequencies in the GMDSS. However, INMARSAT SES-fitted ships could, if necessary, use satellite communications as a supplement to their VHF and MF facilities.
Promulgation of MSI (via INMARSAT SafetyNET services)
3.2.30 In the INMARSAT system, promulgation of MSI is performed by means of the INMARSAT SafetyNET system. Although an INMARSAT-A, INMARSAT-B or INMARSAT-C SES can receive the SafetyNET broadcasts, if uninterrupted receipt of important MSI is required when the SES is engaged for other communications, then it is essential to have a dedicated EGC reception capability for such broadcasts. Alternatively, an EGC receiver can be installed as a separate unit. Details of the INMARSAT SafetyNET service are given in annex 4-3.
General communications
3.2.31 The INMARSAT system provides ships at sea with the same types and quality of modern communications as are available ashore. The capability for direct-dial, automatic connection without delay using high-quality multi-mode communications is provided by SES. Teleprinters, VDUs and telephone sets, as well as facsimile machines and data equipment, can serve as peripheral equipment to SESs.
3.2.32 The quality and availability of general radiocommunications offered by the INMARSAT system permit a ship's master to rapidly consult and seek assistance on any matter, whether of safety or commercial nature. High-quality general communications are therefore a valuable asset to safety at sea as well as to the efficient operation of the ship.
3.2.33 The following are examples of INMARSAT services: � Telephony � Direct-printing telegraphy � Facsimile � Slow-scan television � Automatic data collection from ships (see section 3.2.9)
L-band satellite EPIRBs
3.2.34 L-band satellite EPIRBs operating through the INMARSAT system can be used as means of alerting by ships operating in sea areas A1,A2, and A3 as an alternative to 406 MHz satellite EPIRBs, mentioned in section 3.3.
3.2.35 The basic concept of the INMARSAT L-band satellite EPIRB system. The distress signal transmitted from the float-free satellite EPIRB on the dedicated channel in the 1.6 GHz frequency (L-band) is relayed by an INMARSAT satellite to CESs equipped with the appropriate receiver and processor equipment.
3.2.36 The L-band satellite EPIRB provides for rapid distress alerting (in the order of 10 minutes with 1 W output power radiated by an EPIRB), coverage up to � 70� latitude, 20 simultaneous alerts within a 10-minute time frame and the possibility of manual or automatic entry and update of position information to the satellite EPIRB. The satellite EPIRB can be activated either manually or automatically, by floating free from the sinking ship.
3.2.37 After activation, the satellite EPIRB transmits the distress message containing the ship station identity, position information and additional information which could be used to facilitate rescue. The transmission is repeated on a pre-selected duty cycle. Additionally, unless an integrated electronic position-fixing device is included which provides position updates, a built-in 9 GHz SART is activated for locating purposes. Annexes 3-3-3 and 3-3-4* give detailed technical characteristics of L-band satellite EPIRBs.
3.2.38 After being relayed by the satellite, the distress signal is down-converted at the CES to the specified intermediate frequency to be transferred to the computer-aided multi-channel receiver for satellite EPIRB identification and message decoding.
3.2.39 After the signal channels are identified, they are assigned to processor channels where the incoming signal plus noise is superimposed in the memory. Having accomplished the necessary number of superpositions, which results is 2 ~ 3 dB improvement of signal-to-noise ratio for every frame, the memory is read out and the usual procedures, such as bit and frame synchronization, evaluation of the error-correcting code and the message print-out, are performed.
3.2.40 The distress message is then forwarded to an associated RCC for appropriate action.
3.3 COSPAS-SARSAT system
Introduction
3.3.1 The COSPAS-SARSAT system is a satellite-aided SAR system designed to locate distress beacons transmitting on the frequencies 121.5 MHz or 406 MHz. It is intended to serve all organizations in the world with responsibility for SAR operations whether a distress occur at sea, in the air or on land.
3.3.2 COSPAS-SARSAT is a joint international satellite-aided SAR system, established by organizations in Canada, France, the United States and the former USSR.
3.3.3 The COSPAS-SARSAT system has demonstrated that the detection and location of distress signals can be facilitated by global monitoring based on low-altitude satellites in near-polar orbits. It has been used successfully in a large number of SAR operations world-wide.
3.3.4 Unless, as an alternative, a ship is provided with an L-band satellite EPIRB, the carriage of float-free satellite EPIRB operating on the frequency 406 MHz in the COSPAS-SARSAT system is mandatory on all SOLAS ships (regulation IV/7.1.6.1).
General concept of the system
3.3.5 The basic COSPAS-SARSAT system concept is given in figure 6. There are present types of satellite beacons, namely emergency locator transmitters (ELTs) (airborne), EPIRBs (maritime) and personal locator beacons (PLBs) (land). These beacons transmit signal that are detected by COSPAS-SARSAT polar-orbiting satellites equipped with suitable receivers/processors. The signals are then relayed to a ground receiving station, called a local user terminal (LUT), which processes the signals to determine the beacon location. An alert is then relayed, together with location data and other information, via a mission control centre (MCC), either to a national RCC, to another MCC or to the appropriate SAR authority to initiate SAR activities.
3.3.6 Doppler shift (using the relative motion between the satellite and the beacon) is used to locate the beacons. The carrier frequency transmitted by the beacon is reasonable stable during the period of mutual beacon-satellite visibility. The frequencies currently in use are 121.5 MHz |
