International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 2

Number 3

September 2008

263

GMDSS as a Data Communication Network for

E-Navigation

K. Korcz

Gdynia Maritime University, Gdynia, Poland

ABSTRACT: In paper the functional requirements and the radiocommunication services of Global Maritime

Distress and Safety System (GMDSS) in respect of the E- Navigation has been described. Some aspects of the

improvement of GMDSS equipment and the utilization of the improved GMDSS as a data communication

network for E-Navigation has been presented. The items relating to technical improvement of the GMDSS

which should be considered as one of the discussion on the strategy plan of E-Navigation was given.

1 INTRODUCTION

For realizing the full potential of E-navigation, the

following three fundamental elements should be in

place:

1 Electronic Navigation Chart (ENC) coverage of

all navigational areas;

2 a robust electronic position-fixing system (with

redundancy); and

3 an agreed infrastructure of communications to

link ship and shore.

It is envisaged that a data communication network

will be one of the most important parts of the E-

Navigation strategy plan.

In order to realize efficient and effective process

of data communication for E-Navigation system, the

existing radio communication equipment on board

(GMDSS), as well as new radio communication

systems should be recognized.

2 REVIEW OF GMDSS

In 1988, the Conference of Contracting Govern-

ments to the 1974 SOLAS Convention on the Global

Maritime Distress and Safety System (GMDSS)

adopted amendments to the 1974 SOLAS Conven-

tion concerning radiocommunications for the

GMDSS. These amendments entered into force on

1 February 1992.

The basic concept of the GMDSS is that search

and rescue authorities ashore, as well as shipping in

the immediate vicinity of the ship in distress, will be

rapidly alerted to a distress incident so they can

assist in a coordinated search and rescue operation

with the minimum delay. The system also provides

for urgency and safety communications and the

promulgation of maritime safety information (MSI).

2.1 Functional requirements

The GMDSS lays down nine principal communi-

cations functions which all ships, while at sea, need

to be able to perform:

1 transmitting ship-to-shore distress alerts by at

least two separate and independent means, each

using a different radiocommunication service;

2 receiving shore-to-ship distress alerts;

3 transmitting and receiving ship-to-ship distress

alerts;

264

4 transmitting and receiving search and rescue

coordinating communication;

5 transmitting and receiving on-scene

communication;

6 transmitting and receiving signals for locating;

7 ransmitting and receiving maritime safety infor-

mation;

8 transmitting and receiving general

radiocommunication from shorebased radio

systems or networks;

9 transmitting and receiving bridge-to-bridge

communication.

2.2 Radiocommunication services

The following radio services are provided for the

GMDSS (Fig. 1):

− DSC - Digital Selective Calling;

− INMARSAT Satellite System;

− SATEPIRB - SATellite Emergency Position

Indicating RadioBeacon;

− SARTs - Search And Rescue Transponders;

− NAVTEX System;

− NBDP - Narrow Band Direct Printing;

− RTF - Radiotelephony;

− DMC - Distress Message Control;

− navigational equipment (for support).

Other elements of GMDSS to be showed in Fig. 1

mean as follows:

− CES - INMARSAT Coast Earth Stadion;

− SES - INMARSAT Ship Earth Station;

− LUT - COSPAS/SARSAT Local User Terminal;

− RCC - Rescue Coordination Centre.

CES

SES

SATEPIRB

DSC

VHF

NBDP

RTF

VHF

NAVIGAT.

EQUIPMENT

SARTs

NAVTEX

DMC

INMARSAT

COSPAS/

SARSAT

LUT

RCC

SAR

NBDP

DSC

RTF

NAVTEX

Fig. 1. Radio services of GMDSS

As a potential data communication elements for

E-Navigation following GMDSS radio services

should be recognized: DSC, INMARSAT, NBDP

and NAVTEX.

2.3 DSC specification

Digital selective calling (DSC) is designed for

automatic station calling and distress alerting. Each

call consists of a packet of a digitized information.

DSC calls can be routed to all stations, to an

individual station or to a group of stations.

The system is used by ship and coast stations in

the MF, HF and VHF maritime communication

bands.

The system is a synchronous system using

characters composed from a ten bit error-detecting

code. The first seven bits are information bits. The

last three bits are used for error-detection. Each

character is sent twice but separated in time and a

message check character added at the end of the call.

The classes of emission, frequency shifts and

modulation rates are as follows:

− F1B or J2B 170 Hz and 100 Bd for use on MF

and HF channels. When frequency-shift keying is

effected by applying audio signals to the input of

single-sideband transmitters (J2B), the centre of

the audio-frequency spectrum offered to the

transmitter is 1700 Hz.

− Frequency modulation with a pre-emphasis of 6

dB/octave (phase modulation) with frequency-

shift of the modulating sub-carrier (G2B) for use

on VHF channels; the modulation rate is 1200

Bd; frequency-shift is between 1300 Hz and 2100

Hz, the sub-carrier being at 1700 Hz.

Technical characteristics and operational proce-

dures for the use of DSC equipment are described in

the following documents:

− Recommendation ITU-R M.493 ‘Digital selective

calling system for use in the Maritime Mobile

Service’.

− Recommendation ITU-R M.541 ‘Operational

procedures for the use of digital selective-calling

(DSC) equipment in the Maritime Mobile

Service’.

2.4 INMARSAT specification

At present Inmarsat system provides not only a range

of services and equipment types to cover GMDSS

requirements.

Inmarsat A provides two-way direct-dial phone

connection as well as fax, telex and data services at

rates between 9.6kbps up to 64kbps. Inmarsat A

265

services will cease to be supported on December 31,

2007.

Inmarsat B was first maritime digital service,

launched in 1993, and remains a core service for the

maritime industry. It supports global voice, telex, fax

and data at speeds from 9.6kbps to 64kbps, as well

as GMDSS - compliant distress and safety functions.

Inmarsat B is recommended for the any of the

following applications:

− Data transfer

− Internet

− E-mail

− Fax

− SMS text

− Voice

− Crew calling

− Encryption

− Videoconferencing

− Remote monitoring

− Weather updates

− Telemedicine

− GMDSS

Inmarsat C is one of the most flexible mobile

satellite message communication systems, it has the

ability to handle commercial, operational and

personal messages just as easily as distress and

safety communications.

It offers two-way, store-and-forward packet data

communication via a lightweight, low-cost terminal.

Inmarsat C is recommended for the any of the

following applications:

− E-mail and messaging

− Fax and telex

− SMS text

− Remote monitoring

− Tracking

− Chart and weather updates

− Maritime safety information

− GMDSS

− SafetyNET and FleetNET

Inmarsat Fleet service provides both ocean-

going and coastal vessels with comprehensive voice,

fax and data communications. At present the Fleet

range of services includes:

− Fleet 77

− Fleet 55

− Fleet 33

Inmarsat Fleet's high-quality Mobile ISDN and

cost-effective IP-based Mobile Packet Data Services

offer unparallel connectivity for access to e-mail and

the Internet, weather updates, video conferencing

and vessel monitoring systems.

Fleet 33 offers global voice as well as fax and a

choice of data communications at up to 9.6kbps.

Fleet 55 offers global voice and high-speed fax

and data services at up to 64kbps.

Fleet 77 is Inmarsat's most advanced maritime

service, providing global voice and high-speed fax

and data services at up to 128kbps. It fully supports

the GMDSS and includes advanced features such as

emergency call prioritization, as stipulated by IMO

Resolution A888 (21). Fleet F77 also helps meet the

requirements of the International Ship and Port

Facility Security (ISPS) code, which enables the

cost-effective transfer of electronic notices of arrival,

crew lists, certificates and records.

Inmarsat Fleet series are recommended for the

applications showed in Table 1.

2.5 NBDP specification

The Narrow Band Direct Printing – NBDP

(radiotelex) systems employs error correction in the

form of ARQ (Automatic Retransmissions Request)

and FEC (Forward Error Correction). The technical

details of the error correction are defined by the ITU-

R in Recommendation M.476 and the Recommen-

dation M.625. Radiotelex is also known as Telex

Over Radio (TOR).

Table 1. Applications of Inmarsat Fleet series

Teleprinters of the (international) telex networks

use CCITT ITA-2 code (International Telegraph

Alphabet Code) for communications. Each keyboard

character is transformed to a five-element code of

constant duration. This code is able to provide 32

combinations only but the use of the 'shift' key

enables a further 26 combinations to be available.

ITA-2 code has no error detection or correction

possibilities. For that reason direct mode of telex

communication with ITA-2 code is seldom used.

The CCIR recommended code is a 7-unit

synchronous code. This code is able to provide 128

Fleet

Data transfer

Internet

E-mail and messaging

Fax

SMS text

Voice

Crew calling

Encryption

–

Videoconferencing

–

Remote monitoring

Weather updates

Telemedicine

GMDSS functions

–

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combinations but it uses only those bit combinations

having a ratio of 3 Mark bits to 4 Space bits to

represent valid characters. There are 35 of the 3/4

ratio combinations, allowing all 32 ITA-2 characters

to be represented. Each of the five-unit ITA-2

characters is converted to 7-unit code. The reco-

mmended code needs no start or stop bits because it

is synchronous. No error-detecting parity is required

because the Mark/Space ratio is constant. This

allows efficient transmission of messages, since all

character bits are used to determine the character.

The characteristics of ARQ communication can be

summarized as follows:

− it practically guarantees error-free data, assuming

reception is possible at all;

− automatic exchange of identities guarantees

connection with the requested station, also after

rephasing conditions;

− communication is possible between only two

stations at a time;

− this gives some limited protection against

unauthorised eavesdropping;

− the receiving station must have an operating

transmitter.

− The primary characteristics of FEC are folowing:

− a message may be transmitted to several receiving

stations simultaneously.

− it does not require transmitters at the receiving

stations;

− there is no acknowledgement of transmissions;

− there is no active error correction;

− there is no protection against eavesdropping.

2.6 NAVTEX specification

International NAVTEX (NAVigational TelEX)

service means the co-ordinated broadcast and

automatic reception on the frequency 518 kHz of

maritime safety information (MSI) by means of

Narrow Band Direct Printing (NBDP-FEC) tele-

graphy. The operational and technical characteristics

of the NAVTEX system are contained in Reco-

mmendation ITU-R M.540. Performance standards

for shipborne narrow-band direct-printing equipment

are laid down in IMO Assembly resolution A.525(13).

The principal features of NAVTEX service are as

follows:

− the service uses a single frequency (518 kHz) on

which coast stations transmit information in

English on a time-sharing basis to prevent mutual

interference; all necessary information is contained

in each transmission;

− the power of each coast station transmitter is

regulated so as to avoid the possibility of interfe-

rence between coast stations; Navtex trans-

missions provide a range of about 250 to 400

nautical miles;

− dedicated Navtex receivers are used on the board

of the ships; they have the ability to select

messages to be printed, according to a technical

code (B1B2B3B4) which appears in the preamble

of each message.

3 GMDSS ELEMENTS AS A DATA

COMMUNICATION SERVICES

3.1 Present situation

At present, taking into account above consideration,

the only GMDSS element which can be recognized as

a data communication system is Inmarsat, in particular

Fleet 77 and future FleetBroadband services.

Because Fleet F77 is IP compatible, it supports

an extensive range of commercially available off-

the-shelf software, as well as specialized maritime

and business applications. Fleet F77 also ensures

cost-effective communications by offering the choice

of Mobile ISDN or MPDS channels at speeds of up

to 128kbps.

Mobile ISDN is best suited for applications where

data throughput and speed are important, including:

−

videoconferencing;

−

store-and-forward video;

−

video streaming;

−

large data file transfer, including FTP and digital

images;

−

high quality digital voice;

−

secure voice and data communications;

−

electronic chart downloads;

−

anti-virus updates.

MPDS is more suitable for interactive, short-burst

data and web-based applications, such as:

−

e-mail;

−

Internet and private network access;

−

instant messaging;

−

universal messaging, including SMS;

−

office/management software applications

−

‘thin client’ applications;

−

electronic chart downloads;

−

real-time online weather/oceanographic infor-

mation;

−

vessel telemetry, SCADA and technical support

applications;

− telemedicine.

FleetBroadband is Inmarsat's next generation of

maritime services delivered via the Inmarsat-4

satellites. It is currently planned to be commercially

available in the second half of 2007. The service is

designed to provide the way forward for cost-

267

effective, high-speed data and voice communications

(Table 2). The proposed FleetBroadband service will

provide:

− simultaneous voice and data functionality;

− standard IP with speeds of up to 432kbps

(contended service);

− ISDN at 64kbps;

− streaming data up to 256kbps.

Table 2. FleetBroadband performance capabilities

_____________________________________________

FB250 FB500

_____________________________________________

Data

Standard IP Up to 284kbps Up to 432kbps

Streaming IP 32, 64, 128kbps 32, 64, 128, 256kbps

ISDN – 64kbps

Voice 4kbps and digital 3.1kHz audio

Fax Group 3 fax via 3.1kHz audio

SMS Standard 3G (up to 160 characters)

Antenna

Diameter from 25cm 57cm

Height from 28cm 68cm

Weight from 2.5kg 18kg

_____________________________________________

Users will have the choice of two products

(FB250 and FB500). Both will use stabilised,

directional antennas, which will vary in size and

weight. The above deck antennas will be smaller

than existing Fleet products used today. The whole

system is designed specifically for the marine

environment and will be rigorously tested to

Inmarsat’s exacting standards.

FleetBroadband supports an extensive range of

commercially available, off-the-shelf software, as

well as specialised user applications. It is ideal for:

− Email and webmail

− Real-time electronic chart and weather updates

− Remote company intranet and internet access

− Secure communications

− Large file transfer

− Crew communications

− Vessel/engine telemetry

− SMS and instant messaging

− Videoconferencing

− Store and forward video

3.2 General comments

The above considered GMDSS equipment (Fig. 1)

like Inmarsat system can be also used as a way of

data communication for the E-Navigation system,

provided that the GMDSS MF, HF and VHF

equipment is technically improved by means of:

− digitization of the analogue communication MF,

HF and VHF channels;

− application of high-speed channel to GMDSS;

− utilization of SDR (Software Defined Radio)

technology;

− adaptation of IP (Internet Protocol) technology to

GMDSS;

− integration of user interface of GMDSS equipment;

and

− any other proper technology for GMDSS

improvement.

This technical improvement of GMDSS equipment

may means the potential replacement of the conven-

tional equipment by virtual one. In this approach to

development of E-Navigation it is very important

that the integrity of GMDSS must not be jeopardized.

With respect to the communication aspects

required for E-navigation, the following should be

taking into account as well:

− autonomous acquisition and mode switching;

− common messaging format;

− sufficiently robust;

− adequate security (e.g. encryption);

− sufficient bandwidth (data capacity);

− growth potential;

− automated report generation;

− global coverage (could be achieved with more

than one technology); and

− the use of a single language, perhaps with other

languages permitted as options.

4 CONCLUSIONS

The improved GMDSS equipment can be an

effective way to increase the reliability of

E-Navigation data communication network.

This goal can be achieved as the result of the

work on two items:

− technical improvement of GMDSS equip-ment

taking into account the above chapter 3.2; and

− utilization of technically improved GMDSS

equipment as a data communication network for

E-Navigation.

− During this work it is necessary to first identify

user requirements and secondly, that the deve-

lopment of E-navigation should not be driven by

technical requirements. In addition, it is necessary

to ensure that man-machine-interface and the

human element will be taken into account

including the training of personnel.

The lessons learnt from the development and

operation of GMDSS and AIS should be taken into

account in the development of E-Navigation as well.

268

In consideration on GMDSS as a Data Communi-

cation Network for E-Navigation the sea area A1,

A2, A3 and A4 should be also recognized.

REFERENCES

Czajkowski J., Bojarski P., Bober R., Jatkiewicz P., Greczycho

J., Kaszuba F. & Korcz K. 2000. System GMDSS

regulaminy, procedury i obsługa, Wydawnictwo „Skryba”

Sp. z o.o., Gdańsk.

Czajkowski J. & Korcz K. 2000. The Problem of Generating

False Alert Signals with Help of Digital Selective Calling-

DSC in the GMDSS System. International Wrocław

Symposium on Electromagnetic Compatybility – EMC

2000, Wrocław.

Korcz K. 1995. Przepisy radiokomunikacyjne w morskiej

służbie ruchomej. Wydawnictwo Uczelniane Wyższej

Szkoły Morskiej, Gdynia.

Sub-Committee on Radiocommunications, Search and Rescue-

COMSAR11. 2007. Report to the Maritime Safety

Committee (MSC), International Maritime Organization

(IMO), London.