259
1 INTRODUCTION
The focus of maritime communications and GMDSS
networks these days is concentrated towards satellite
communications and IP networking. Many things
have changed from even a few decades ago, when
radiotelegraphy and radio telex were main method of
ship to shore and vice versa radiocommunication
systems, so oceangoing ships are now effectively
expanding computer LAN over satellite networks.
However, VHF, HMF and HF radio communication
systems continue to provide huge support for
upgrading the GMDS network.
Of course, the driver for all these changes in
distress Search and Ressque (SAR) operations was the
establishment of the GMDSS network in the early
1990’s, which still uses VHF and HF Digital Selective
Calls (DSC), VHF radiocommunication systems and
NAVTEX transmissions. After the GMDSS operator
onboard ships sends an DSC alert, then it switches to
the radiotelephone distress and safety channels and
conducts onscene communications with other ships,
SAR forces and shore stations. The problem is that
these channels are often plagued by interference and
that some new and most reliable solutions should be
proposed. Here will be shortly introduced new VHF
and MF radio systems able to improve radio
Communication, Navigation and Surveillance (CNS)
requirements for the GMDSS network [01, 02, 03].
Alternative Maritime Radio Solutions for Enhanced
GMDSS Network
D
.S. Ilcev
University of Johannesburg (UJ)
, Johannesburg, South Africa
ABSTRACT: This paper introduces novel alternative maritime radio solutions for the improved Global
Maritime Distress and Safety System (GMDSS) network and equipment within the Very High Frequency (VHF),
Medium Frequency (MF) and High Frequency (HF) Ship Radio Station (SRS) terminals. Since its foundiing in
1959, International Maritime Organization (IMO) and its member states, in close co-operation with the
International Telecommunication Union (ITU) and other international organizations, notably the World
Meteorological Organization (WMO), the International Hydrographic Organization (IHO), the International
Mobile Satellite Organization (IMSO) and the Cospas-Sarsat partners, have striven to improve maritime distress
and safety radiocommunications, as well as general radiocommunications for operational and personal
purposes. This paper also reviews concept of the GMDSS network, an overview of new propsed by author
maritime VHF Data Link (VDL), maritime Radio Automatic Dependent Surveillance-Broadcast (RADS-B), an
maritime GNSS Augmentation VDL-Broadcast (GAVDL-B). In addition, the type of the current radio Maritime
VHF Data Exchange System (VDES), Maritime MF-band Navigational Telex (NAVTEX), and Maritime MF/HF-
band Navigation Data (NAVDAT) are also described in this paper.
http://www.transnav.eu
the
International Journal
on Marine Navigation
and Safety of Sea Transportation
Volu
me 16
Number 2
June 2022
DOI: 10.12716/1001.16.02.08
260
2 MARITIME VHF DATA LINK (VDL)
The aim of this section is to present a new proposed
marine VHF Data Link (VDL) similar to aeronautical
VDL, which can be applied in the future for the CNS
service within the GMDSS network in the Sea Area
A1. The new VDL service has to improve GMDSS
solutions in coastal navigation, inland waters,
approaching to anchorage and inside of the harbors as
new solution with 3 main objectives:
1. To provide a more reliable and effective ships
communications system based on efficient and
higher rate digital transmission over VHF radio
including International Ship and Port Facility
Security Code (ISPS) system in harbors;
2. To improve R-AIS basic functions for ships
collision avoidance; and
3. To enhance GMDSS network, Ship Traffic Control
(STC) and Ship Traffic Management (STM)
through the VDL network, together with the
proposed RADS-B network.
Figure 1. Maritime VDL Radio System for Enhanced
GMDSS Network –Source: Ilcev
The ship's VDL system will be similar to R-AIS
with the task of improving its capabilities and
functionality, the configuration of which is shown in
Figure 1. A major improvement of R-AIS requires the
installation of VDL transponders onboard ships for
improved STC and CTC in coastal waters,
approaching anchorages and seaports. In the same
way, similar VDL installations will be able to control
the movement of land vehicles and rails within
seaports. Both ships and vehicles transporters can be
integrated with GNSS receivers that can receive
navigation signals from GPS or GLONASS satellites
and resend them via VHF Coast Radio Stations (CRS)
terminals to STC and STM operational centres.
Received Position, Velocity and Time (PVT) data
from ships and vehicles within VHF coverage will be
processed and displayed on radar like a VDL display
unit. In the opposite direction, the ship traffic
controller may send PVT to all ships outside seaports
and in particular to all ships and land vehicles within
the seaport, and manage their movement in a safer
manner [04, 05, 06, 07, 08].
3 MARITIME RADIO AUTOMATIC DEPENDENT
SURVEILLANCE-BROADCAST (RADS-B)
The Radio Automatic Dependent Surveillance-
Broadcast (RADS-B) communication mode has been
developed for aeronautical applications, but can also
be used for maritime applications, the configuration
of which is illustrated in Figure 2. This system can
uses radio transmissions from ships, approximately
once in a while, to provide PVT and other data that
have been detected and captured by onboard ships
sensors, such as not-augmented Global Navigation
Satellite System (GNSS) receiver (GPS or GLONASS),
Automatic Radar Plotting Aid (ARPA) or
Gyrocompass.
The RADS-B VHF CRS terminal uses a non-
rotating omnidirectional radio antenna to receive VDL
messages transmitted from ships in a certain ocean
area. The maritime RADS-B network has been
proposed as a multiple use surveillance technique for
harbour terminals, approaching to anchorage, sea
passages and coastal waters in range of VHF CRS
terminals and is also applicable to STC, STM and
ship-to-ships data transmitting OUT and receiving IN
surveillance, known as an Internship RADS-B for
enhanced collision avoidance.
The RADS-B transmission is “line of sight” based
surveillance and requires CRS terminals to receive
data and transmit to STC and STM operational
centres. A single CRS can provide coverage out to
approximately 250 Nm for coastal enroute, terminals
and seaport area surface surveillance. This RADS-B
communication network can be integrated with
Ground Surveillance Radar (GSR) installations and
provide additional surveillance capabilities. In ordet
to improve ships surveillance and traffic control in the
seaport area, this new system will require a special
RADS-B transceivers integrated with GNSS receivers
installed onboard ships and land vehicles [02, 04, 09,
10, 11].
Figure 2. Maritime RADS-B System for Enhanced GMDSS
Network –Source: Ilcev
261
4 MARITIME GNSS AUGMENTATION VDL-
BROADCAST (GAVDL-B)
The GNSS-1 network is integral part of all
applications where mobile CNS solutions play an
important role in the development of modern
configurations for enhanced STC and STM, and in
particular for improved GMDSS shipborne facilities.
In the GNSS-1 satellite network are integrated the US
GPS and the Russian GLONASS, while the Chinese
BeiDou or Compass and the European Galileo are
included in the GMSS-2 network. The GNSS network
provides standardized PVT information via VDL to
oceangoing ships for more precise navigation and
enhanced collision avoidance in global scene, which
scheme is shown in Figure 3. The VDL system in the
core GNSS constellations broadcast a timing signal
and a data messages for differential correction of GPS
and GLONASS signals. Shipborne not-augmented
GNSS receivers use these signals to calculate their
range from each satellite in view and also calculate 3-
D position and precise time.
Figure 3. Maritime GAVDL-B System for Enhanced GMDSS
Network – Source: Ilcev
In this way, the current radio navigation system
can be replaced by a modern GNSS solution that will
be capable to guide ships in more safe way. As stated
above, the GAVDL network is providing GNSS data
via GPS and GLONASS satellites for Ground
Monitoring Stations (GMS) known as Reference
Stations (RS), which provide determination of
integrity, correction information, processing facility
and precise accuracy with position errors below 1
meter, and forward them to Ground Control Station
(GCS) or Master Station (MS). The GCS terminal
augments primary GNSS constellations by providing
Very High Speed (VHS) ranging, integrity and
correction information. Accordingly, GCS receives
GPS measurements from GMS and calculates clock
and ephemeris corrections for each monitored GPS
satellite, ephemeral information for each GEO
satellite, and Ionosphere Grid Points (IGP) at an
altitude of 350 km above the Earth's surface.
Any Regional Satellite Augmentation System
(RSAS) as a civilian mobile safety-critical network that
supports the regional or wide area augmentation
through the use of GEO satellites only to broadcast the
augmentation information received from GCS
terminal. However, in the case of GAVDL system, a
Local VHF Augmentation System (LVAS) is used here
for ranging, monitoring and transmission of GAVDL
signals to oceangoing ships. In the reverse direction,
ships can send their GNSS augmented signals derived
from GPS or GLONASS receivers directly via VHF
CRS to STC stations. The STC processor will process
received PVT data, displayed it on the screen like a
radar display and use it for enhanced collision
avoidance. In that manner, at the request of ship
navigation officers, the operator in SCS can send them
PVT data of nearby ships or the navigator can use data
reporting and polling service and pools this data
himself [02, 04, 05, 09, 10, 11].
5 MARITIME VHF DATA EXCHANGE SYSTEM
(VDES)
The new VHF Data Exchange System (VDES) network
was developed by the International Association of
Maritime Aids to Navigation and Lighthouse
Authorities (IALA) to address the emerging signs of
data transmission channel overload in the AIS (VDL)
band and at the same time provides more wide and
unhindered data exchange for the maritime
community. The initial concept of VDES includes the
function of an AIS (R-AIS), Application Specific
Messages (ASM), VHF terrestrial and satellite
communication segments.
The VDES radio network is one of the potential
elements of maritime E-navigation, which will
exchange ASM transmission, thereby arranging
operation of numerous applications to ensure safety,
security, efficiency and protection of shipping and
environment. In the future, this modern network will
have a significant positive impact on the Maritime
Safety Information (MSI) network, including
Navigation Assistance Services (NAS) and the Vessel
Traffic Management System (VTMS) for oceangoing
ships.
Therefore, VDES network has been developed with
the purpose of resolving problems regarding AIS
channel congestion and efficiency degradation.
Namely, today AIS is being used beyond the
identification and tracking ships. More precisely,
besides standard AIS data reports include the
following features: static, dynamic and voyage related
data; there are also general data exchange on maritime
VHF band; data transmission between ships and
satellite communication satellites; AIS-based Aids to
Navigation (AIS-AtoN), AIS-SART, and AIS-EPIRB
applications; Application Specific Messages (ASM),
and since recently Maritime Service Portfolio (MSP).
Due to some of existing analogue channels of
maritime VHF band have been relocated to AIS. The
use of additional channels and digital VHF system
will improve AIS services, thus in parallel modernize
GMDSS network and support development of
Maritime Cloud and e-Navigation. Within the context
of e-Navigation, in the short term, mandatory
reporting from ships might be encapsulated into
ASM.
On the other side, MSP will cover a number of
Vessel Traffic Service (VTS) related and other
information services. The scope of the MSP concept is
to align maritime networks with the need for
information and communication services in a clearly
defined operational area. Therefore, the maritime VTS
network will play a central role in the coordination of
262
MSP information (i.e., information service, traffic
organization service, ship navigation assistance
services, ships security and the like).
Figure 4. New Concept of VDES/AIS Network – Source:
Ilcev
In Figure 4 is illustrated the new concept of an
integrated VDES/AIS Network, which consists an
VDES/AIS space segment, ground segment integrated
with GES and VHF GRS terminals, and users segment
containing SRS/SES terminals and AIS/SART beacons.
The VDES/AIS Network provides satellite and VHF
radio VDES/AIS links, inter-ship (ship-to-chip)
communications, and AIS/SART signals. Thus, AIS
signals can be received by the R-AIS receiver, and
SART signals can be received by the onboard ships
radars.
In this context, it should be pointed out that the
new VDES will provide two-way communication at
considerably higher data rate than previously used
AIS systems. Within the VHF maritime frequency
band (156.025-162.025 MHz), VDES integrates AIS
with ASM and MSP to enhance smooth distribution of
maritime data, including extensive meteorological
and traffic data.
By enabling VDES to use a satellite platform,
global data exchange between ships and the shore via
satellites, will be provided in the future. It is also
expected that future ship VDES transceivers will be
combined with S-AIS into a single device. Thus, WRC-
15 recognized that the VDES satellite component is
necessary to expand the system from coastal coverage
to global one, and recommend the further research for
future developments.
However, the use of the VDES network can
potentially provide local VTMS, however VDES may
also include the concept of deploying the space
(satellite) segment for global coverage. The space
segment of the system can be used for VTMS
transmission in remote areas [Recommendation ITU-R
M.2092-0, 2015]. Insufficient study and proposals of
the issue for sharing and comparability between the
new developed satellite segment of the VDE system
and the existing services in the same and adjacent
frequency ranges caused the operating frequency
range to not be determined at the World
Radiocommunication Conference in 2015 (WRC-2015).
As a result, VDES as a whole is still not a complete
functional system. As part of the 2015 IGC, the ITU
approved the standard for VDES in the form of
Recommendation ITU-R M.2092-0 [PP, 2015].
Only the issue of satellite segment approval for
VHF (VDE) data exchange channels remains
unresolved. Approval of this issue is one of the goals
of the 2019 World Radiocommunication Conference
(WRC-2019). The study of the vacant frequency ranges
156.0125-157.4375 MHz and 160.6125-162.0375 MHz
will mainly concern interaction with existing mobile
services, primarily for land and sea mobile services, as
well as services within adjacent lower (from 154 MHz
up to 156 MHz) and high (from 162 MHz to 164 MHz)
frequency ranges. The concept of a VDES will be
developed under agenda item 1.9.2 at WRC-19:
1. Amendments to the ITU Radio Regulations and
new spectrum allocations to the mobile two-ways
satellite service, preferably in the VHF- bands
156.0125 to 157.4375 MHz and 160.6125 to 162.0375
MHz of Appendix 18, are established to create
conditions for the operation of the VDES, while
ensuring that this segment does not impair the
operation of existing VDES terrestrial segments,
ASM, S-AIS and does not impose any additional
restrictions on existing services in these and
adjacent frequency bands referred to in d) and e) of
the section, recognizing ITU Resolution 360 (Rev.
WRC-15).
2. Among other applications, the use of VDES must be
considered in all kinds of future VTMS
dissemination mechanisms.
In this context, it should be noted that the new
VDES will provide two-way communication at
considerably higher data rate than previously used
AIS systems. Within the VHF maritime frequency
band (156.025-162.025 MHz), VDES integrates AIS
with ASM and MSP to enhance smooth distribution of
maritime data including extensive meteorological and
traffic data. By enabling VDES to use a satellite
platform, a global data exchange between ships and
shore via satellites, will be enabled. It is also expected
that future ship VDES transceivers will be combined
with AIS into a single device. The WRC-15 recognized
that the VDES satellite component is necessary to
expand the system from coastal coverage to global
one, and recommend that further research is to be
done in order to decide on the further development of
satellite VDES, during the upcoming WRC-19.
The new VDES network will undoubtedly support
developing concepts of Maritime Cloud and e-
Navigation, where VTS will play a key role in
enabling team work between the crew and the
personnel ashore. This service will make a shift from
ship-to-ship, shore-to-ship, or VTS-centric navigation
and relieve considerably seafarers in the future. Also,
this will open the whole panoply of ICT jobs ashore
dealing with navigation, meteorology, hydrographs,
ecology, and provide path towards ashore assisted
navigation and autonomous ships [02, 07, 08, 11, 12,
13, 14, 15].
263
6 MARITIME MF-BAND NAVIGATIONAL TELEX
(NAVTEX)
In SOLAS regulation IV/12.2 is stated: “Every ship,
while at sea, shall maintain a radio watch for broad-
casts of maritime safety information on the
appropriate frequency or frequencies on which such
information is broadcast for the area in which the ship
is navigating”. The radio watch can be maintained
via NAVigational TEleX (NAVTEX) an international
Narrow Band Direct Printing (NBDP) telex for
transmitting MSI, such as navigational (NX) and
meteorological warnings (WX), and other maritime
safety-related messages emitted by hydrographic or
meteorological offices, Rescue Coordination Centre
(RCC), etc.
The NAVTEX maritime radio system has been
developed to provide a low-cost, easy and automated
means of receiving MSI onboard ships in coastal
waters (about 200 nautical miles off shore, or
maximum up to 400 nautical miles by CES terminals).
The NAVTEX information may be relevant to all types
of ships to receive broadcasts that suit well their
particular needs, which provides automatic display or
printout from a dedicated receiver. This service means
the coordinated broadcast and on and automatic
reception on 518 kHz (MF) of maritime safety
information by means of NBDP telegraphy using
English language. There are two additional
frequencies for transmitting MSI within this system:
490 KHz (MF) and 4209.5 kHz (HF) for safety
messages in national languages.
The NAVTEX network is a part of GMDSS, which
is global communication system based upon
automated terrestrial and satellite telecommunication
sub-systems, to provide distress alerting and
propagation of MSI at sea. There are 24 active
NAVTEX transmission stations (A-X) and one backup
station (Z), i.e., in total, 25 stations within each
NAVAREA and/or METAREA. All NAVTEX stations
transmit in the period of 10 minutes every 4 hours
according to predefined timetable, and with limited
transmission power in order to avoid interference.
The NAVAREA radio network means particular
geographical sea area identified with the aim of
coordinating the broadcast of navigational warnings.
Figure 5. Current Concept of NAVTEX Network – Source:
Ilcev
Otherwise, METAREA meteorological messaging
service means a geographical sea area established for
coordinating the broadcast of marine meteorological
and warnings data for oceangoing ships. It is also
important to note that different NAVTEX navigation
messages are labeled with letters of English alphabet,
which concept is shown in Figure 5. In other words,
each NAVTEX message class carries a different topic
indicator symbol that allows the operator on board
the vessel to program the receiver and discard certain
classes of suspicious NAVAREA or METAREA data
that are not needed.
The maritime NAVTEX Network Management
System (NMS) provides the ultimate overview of the
site locations and simple network management of the
entire NAVTEX messaging system. It enables
monitoring and configuration of each individual
NAVTEX transmitter to avoid failed transmissions.
For a complete overview the system provides all
relevant data including message transmissions,
temperature and forward and reflected power
readings. In case of failure, the system offers visual
and audible alarms and ready redundant NAVTEX
transmiter. Transmitter works independently of
network functionality. It ensures messages can be sent
even if a reverse power fault is observed. The fail-safe
transmission is ensured by planned messages
generated by remote control at preselected times,
frequencies and output power.
The operator in the NAVTEX network can choose
to schedule messages within selected time-slots or
transmit urgent information immediately. All
messages are automatically transmitted and logged
and the interface is operated by either touch screen or
keyboard. Therefore, the operator cannot refuse
navigation and meteorological warnings, including
search and rescue information. Also, the receiver
cannot reject the item indicators related to the letters
A, B, D and L and they will always be printed and/or
displayed.
Basically, the NAVTEX network is a maritime
radiotelex system for transmission of navigation
meteorological information, which works at both MF
and HF- bands. It operates in the Forward Error
Correction (FEC) mode in which the source
(transmitter) sends redundant data and the
destination (receiver) recognizes only the portion of
the data that contains no apparent errors. This
broadcating system does not allow two-way
communication between two stations, ie it is used
only for broadcasting messages.
Thus, NAVTEX belongs to the systems known as a
telex Narrow Band Direct Printing (NBDP), which
refers to channel bandwidth of 500 Hz, and it is based
on Frequency Shift Key (FSK) modulation, while the
shift between carrier frequencies is 170 Hz, and data
rate is approximately 100 bit/sec. It communicates
with text messages rather than by voice. It is said that
NBDP was introduced in the GMDSS to help seafarers
whose first language was not English.
264
Figure 6. New Concept of NAVDAT Network – Source:
Ilcev
Because of such low data rate NAVTEX might be
treated as outdated, particularly within the context of
developing complex e-Navigation, so called system-
of-systems. Thus, NAVTEX cannot transfer large
amounts of data in real time for the needs of berth-to-
berth navigation, including possibilities of advanced
route exchange mechanism. Due to some technical
problems, the NAVDAT system was recently
developed with the intention of replacing the
NAVTEX syste [02, 07, 10, 12, 13, 15, 16, 17, 18].
7 MARITIME MF/HF-BAND NAVIGATION DATA
(NAVDAT)
The NAVDA MF radio system is designed for use in
the maritime mobile service operating in the 500 kHz
band for digital broadcasting of information relating
to maritime safety and security in the coast-to-ship
direction. The NAVDAT HF ship receiver
specifications are between 4 to 22 MHz maritime
band, such as: 4,226; 6 337.5, 8,443; 12,663.5; 16,909.5
and 22,450.5 kHz. The new concept of NAVDAT
network is shown in Figure 6.
The maritime NAVDAT System of Information
and Management System (SIM) provides the
NAVDAT message types 1 and n, and transmits them
via coast NAVDAT transmitters to the shipborne
NAVDAT receivers. The control and signalization
system provide a superior overview of site locations
and simple network management of the entire
NAVDAT system. In this way, special marine
NAVDAT receivers onboard oceangoing ships use the
MF and HF frequency bands to receive free any kind
of NAVDAT messages with possibility of encryption.
The international digital radio broadcast standard
Digital Radio Mondiale (DRM) is used for digital
radio broadcasting at MF and HF band. The DRM
standard is a proven technology that provides
superior coverage, improves signal fidelity (through
digital error correction coding), eliminates multi-path
interference (including sky-wave interference) and
thus extends coverage from sky-wave propagated
signals. Thus, the DRM system broadcasts are
implemented in both 16-QAM (Quadrature
Amplitude Modulation) and 64-QAM modulation
modes, depending on coverage requirements,
transmitter location, power and antenna height.
The NAVDAT radio system uses a time slot
allocation similar to the International Automated
Alert System known as Navigational Telex
(NAVTEX), which IMO can coordinate in the same
way. The NAVDAT system can also operate in Single
Frequency Network (SFN) mode. In this case, the
transmitters are synchronized in frequency, and the
data for transmission should be the same for all
transmitters. Thus, the digital NAVDAT 500 kHz
system provides broadcast transmission of any type of
message in the shore-to-ship direction with
encryption capability.
Any broadcast message must come from a secure
and managed source. Types of NAVDAT radio
messages for broadcast include, but are not limited to
the following particulars: 1) Navigation safety; 2)
Security Issues; 3) Data on piracy event; 4) SAR; 5)
Meteorological reports; 6) Pilot or port
communications; and 7) File transfer of the ship traffic
system. These messages broadcast information for
vessels, groups of vessels, or in certain areas of
navigation. Besides, these messages can be addressed
to a single vessel using the Maritime Mobile Service
Identity (MMSI).
These messages broadcast information for vessels,
groups of vessels, or in certain areas of navigation.
Besides, these messages can be addressed to a single
vessel using the Maritime Mobile Service Identity
(MMSI). The organization of the NAVDAT system is
determined by five factors that ensure the
performance of the following functions:
1. System of Information and Management (SIM) –
Collects and manage all types of information,
creates message files to be transmitted and creates
transmission programs in accordance with the
priority of message files and the needs of the
replay;
2. Coastal Network – Provides transportation of
message files from different sources to relevant
transmitters;
3. Shore Transmitter – Accepts message files from
SIM, converts message files to a signal with
Orthogonal Frequency Division Multiplexing
(OFDM) and transmits an RF ;
4. Transmission Channel – Transmits radio frequency
signals at 500 kHz; and
5. Ship Receiver – Ships NAVDAT receives and
demodulates an RF signal with OFDM modulation
mode, restores and sorts message files and makes
them available to the target equipment in
accordance with the application of the message
files [02, 07, 10, 12, 16, 18, 19].
8 CONCLUSION
The future enhanced GMDSS network has to provide
integration of radio and satellite CNS systems, which
have to ensure rapid automated alerting and Search
and Rescue (SAR) operations of ships in distress at sea
and inland waters. The main maritime systems,
networks and equipment that can be integrated into
the GMDSS infrastructure are the existing and new
projected Radio Distress and Safety Systems (RDSS)
and Satellite Distress and Safety Systems (SDSS).
265
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