1 INTRODUCTION

The European Geostationary Navigation Overlay

Service (EGNOS) is Europe's regional satellite-based

augmentation system (SBAS). Today it improves the

performance of GPS and from 2025 will augment

Galileo as well. Since 2009 it is providing benefits in

different maritime applications such as general

navigation, especially in terms of increased accuracy.

EGNOS can provide multiple benefits to the

maritime and IWW service providers. The most

relevant ones are associated to three key features:

free of charge access, redundancy of signal sources

(Signal-in-Space (SiS) and EGNOS Data Access

Service (EDAS)), and the possibility of making use of

the Virtual Reference Station (VRS) concept. The

main advantage of a DGPS solution based on VRS

(using EGNOS messages as input, that is, EGNOS-

based VRS) with respect to traditional DGPS is that

corrections can be remotely generated for a specific

Support to Maritime and Inland Waterways Service

Providers for the Transmission of EGNOS Corrections

via IALA Beacons and AIS/VDES Stations

M. López

GSA, Prague, Czech Republic

M. Cano & R. Martínez

LG, Barcelona, Spain

C. Álvarez & L. Tavira

Indra, Barcelona, Spain

. Morán, V. Antón & J. Vázquez

ESSP SAS, Madrid, Spain

ABSTRACT: The use of SBAS corrections for navigation, in both coastal waters and inland waterways, has

already brought the attention of many European authorities, which are interested in its potential to

complement/replace their DGPS radio beacon networks.

The European GNSS Agency (GSA) has an active long-term trajectory working to foster the EGNOS adoption in

maritime through the launch of several actions whose results will pave the way for the provision of maritime

EGNOS services. In this line, GSA awarded the consortium ALG-Indra, ESSP and Alberding with the Specific

Contract GSA/OP/07/13/SC24 ‘Support to Maritime Service Providers for the transmission of EGNOS

corrections via IALA beacons and AIS/VDES stations’.

The main objective of this Specific Contract is to demonstrate the operational performance of the transmission

of EGNOS corrections converted to Differential GPS corrections over the existing transmission infrastructure

(AIS base stations/IALA beacons) in the Maritime and Inland Waterways (IWW) domains, while providing a

detailed cost benefit analysis of the solutions proposed. This service may complement the current GNSS

augmentation services exploiting synergies and benefiting from the current infrastructure and standards,

facilitating the adoption of EGNOS by maritime and inland waterways authorities. Furthermore, the service has

no impact at user level since the DGNSS corrections are transmitted over the existing infrastructure, in the same

format and implementing the same integrity mechanisms required for traditional IALA beacons ([1]).

This project will allow the maritime and IWW service providers to have a clear understanding about the

technical, operational and economic feasibility of the transmission of EGNOS corrections via IALA beacons and

AIS/VDES stations.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 13

Number 1

March 2019

DOI: 10.12716/1001.13.01.03

location without the need of having a physical

reference station at that location and ensure that the

quality of the corrections is not affected by local

errors (e.g. multipath/interference at transmitting

site). Also, there are a number of EGNOS-based

architectures that can be set-up to complement and/or

replace traditional DGNSS networks, adapting to the

specific operational scenario with a high degree of

versatility.

The European GNSS Agency (GSA) is fostering

the adoption of EGNOS V2 in maritime, with

different active lines of action for general navigation.

The current paper reports on the activities in the

frame of Specific Contract GSA/OP/07/13/SC24,

which aims at promoting the adoption of EGNOS in

maritime by supporting service providers to

implement and test the transmission of EGNOS

corrections through existing national

Administrations’ infrastructure (IALA beacons and

AIS/VDES stations). This will be achieved by

demonstrating the operational performance of the

transmission of EGNOS corrections converted to

Differential GPS corrections over the existing

transmission infrastructure in the Maritime and

Inland Waterways (IWW) domains, while providing

a detailed cost benefit analysis of the solutions

proposed.

This service may complement the current GNSS

augmentation services exploiting synergies and

benefiting from the current infrastructure and

standards. Furthermore, the service has no impact at

user level since the DGNSS corrections are

transmitted over the existing infrastructure, in the

same format and implementing the same integrity

mechanisms required for traditional IALA beacons

(i.e. [2]).

2 PROJECT STRUCTURE

The organizations involved in the project team are:

GSA (customer), ALG (prime contractor), Indra,

ESSP, and Alberding GmbH (subcontractors).

Additionally, several European maritime and inland

waterways authorities are actively contributing to the

project.

The project has been distributed in two phases:

 First phase – preliminary tests - (which lasted for 7

months and ended in April 2018) was aimed at

verifying the feasibility of using EGNOS as a

source for the Differential GNSS (DGNSS)

corrections to be transmitted via IALA beacons

and AIS/VDES stations. This was achieved by a set

of preliminary tests performed without signal

broadcast, but focused on the locations where

pilot projects were implemented in the second

phase of the project and with a configuration as

close as possible to the operational one. Also, the

same SW solution (provided by Alberding GmbH)

to be used for the real tests –pilot projects- was

used for the generation of the EGNOS-based

DGPS corrections (conversion from RTCA to

RTCM format) and the required integrity

verifications, ensuring the representativeness of

the preliminary tests. Due to the promising results

of this phase, GSA authorized the Consortium to

proceed to project phase 2 at the beginning of

April 2018.

 Second phase – pilot projects - (lasting 10 months

and ending in January 2019) was aimed at

deploying and testing via four (4) pilot projects

the EGNOS-based solutions in various European

locations re-using as much as possible the

currently available infrastructure. Cost Benefit

Analysis were also developed and customized

(with the support of the corresponding

authorities) for the countries hosting a pilot

project. Additionally, a liability analysis was

performed in order to understand the regulatory

constraints that may apply to the proposed

solutions with the objective to achieve a

harmonized approach to be followed by Maritime

and Inland Waterways authorities.

A total of seven (7) European Maritime and

Inland Waterways (IWW) authorities have

contributed to the project, namely: CEREMA

(France), GLA (United Kingdom and Ireland),

Kystverket (Norway), MRCC (Latvia), Puertos del

Estado (Spain), RSOE (Hungary), and WSV

(Germany). Some of these authorities (MRCC,

Puertos del Estado, RSOE and WSV) have also

provided their infrastructure to host a pilot project to

demonstrate the operational performance of the

transmission of the EGNOS corrections. They have

also supported the project by providing information

to generate realistic cost benefit analysis and

reviewing their outcomes afterwards.

The paper focuses on the results achieved during

the second phase of the project, when real signal

broadcast was used.

3 TECHNICAL FEASIBILITY ANALYSIS

Four (4) European scenarios have been analysed and

the most suitable architectures to transmit the

EGNOS-based VRS differential corrections have been

selected, which can be either centralised or de-

centralised. A fair combination of both IALA

beacons and AIS/VDES stations as well as maritime

and IWW domains have been chosen. The duration of

the pilot projects has been six (6) months. Data has

been collected from both static and dynamic

receivers.

Figure 1. Pilot project locations and architectures/domains

4 EGNOS-BASED ARCHITECTURES

IMPLEMENTED IN THE PILOT PROJECTS

From the recommended EGNOS-based architectures

detailed in [1], the following have been implemented

in the pilot projects:

Table 1. Pilot projects domains and architectures

_______________________________________________

Scenario Domain Architecture implemented

_______________________________________________

Rota IALA maritime Hybrid centralised

Koblenz AIS inland AIS centralised

Budapest AIS inland AIS centralised

Riga AIS maritime AIS decentralised – external

source

_______________________________________________

4.1 Hybrid centralized architecture (IALA beacon in

Spain)

This solution combines a classical DGNSS station

deployed at each beacon site with a centralized

EGNOS based VRS solution. For the EGNOS-based

VRS solution (right chain in Figure 2), both the RS

and the IM stations are centralized in the “Central

Facility”, and therefore, the only infrastructure

needed at each beacon site is the communication lines

and the transmission equipment. Additionally, a

network of GNSS receivers is needed for the integrity

check. At least one receiver located within the

coverage range of each beacon transmitter and able to

transmit the GNSS raw data collected to the central

server shall be available.

On the other hand, it is noted that the network

approach results in high requirements concerning the

availability and quality of the communication links.

Figure 2. Hybrid Centralized Architecture: classical DGNSS

+ SBAS Based VRS (functional view)

As agreed with the Spanish Ports authority (PdE),

one of the GNSS receivers in the classical DGNSS

architecture (left chain in Figure 2) was also used to

monitor the signal and corrections transmitted by the

EGNOS based solution (right chain in Figure 2). Data

collected by this receiver was sent to the central

server for the integrity check.

4.2 AIS decentralized architecture – external source (AIS

station in Latvia)

In those AIS Base Stations where there is no access

(either via radio or serial connection) to the DGPS

messages provided by a IALA beacon, the

pseudorange corrections can be generated locally

using the EGNOS message (either obtained from the

EGNOS SIS or from the EDAS service).

DGNSS corrections are provided as input (via a

dedicated portFigure 4) to the AIS Base Station,

therefore, whether these corrections are received

from a traditional DGNSS stations or generated based

on EGNOS is completely transparent for the AIS Base

Station.

Taking this into account, it is not necessary to do

any change on the AIS Base Station, but just

implementing an external component that converts

the EGNOS wide area corrections in RTCA format

into local area corrections in RTCM. It is to be noted

that the SBAS message and the GPS ephemeris can be

obtained from an SBAS enabled receiver or from the

EDAS SISNeT service over the internet.

Figure 3. EGNOS-based AIS station: RS & IM block

diagram

In the Riga pilot, an SBAS enabled receiver was

used to obtain the EGNOS message. Hence, GNSS

observations collected by this receiver were used to

check the integrity of the data (note that the

observations were not used to generate the

differential corrections, and therefore, the same

receiver can be used for the corrections generation

and the integrity check).

The corrections generated by the RTCA to RTCM

converter were provided to the AIS Controller Unit in

Message Type 17 format (via the dedicated input

port).

4.3 AIS centralized architecture (AIS station in Germany

and Hungary)

This solution consists on generating the EGNOS-

based VRS streams in a central facility. Through the

AIS Service Manager (ASM), these corrections are

then routed and sent to each AIS base station. At very

high level, the architecture of this solution is depicted

in the following diagram:

Figure 4. EGNOS-based AIS centralized architecture

 Central Facility: The primary function of the

Central Facility is to compute the Pseudorange

Corrections for all the satellites above the

elevation mask. PRCs and ancillary information

(e.g. antenna location) are encoded into RTCM

10402.3 and transmitted to each beacon

transmitter site. The source for the generation of

the DGPS corrections to be broadcast by the

transmitter could be the SBAS Signal in Space or

the SBAS messages received from EDAS.

 AIS Service Manager (ASM): The RTCM

corrections generated by the central facility are

transmitted to the AIS Service Manager which

converts them in an IEC 61162 VDM sentence

(discarding the preamble and parity fields) to be

then distributed to the final users by the AIS base

stations using the VDL channel. Considering that

the corrections are generated and integrity

checked in the central server, the communication

links and the protocol for the data transmission

between the central server and the ASM shall be

designed to ensure the integrity of the corrections

provided. In case of using the NTRIP protocol for

the data transmission, the TLS option could be

selected to ensure communication privacy and

data integrity.

Internally to the AIS service each correction set

will be routed to the target AIS Base Station (AIS-

PCU) by the AIS-LSS.

 Monitoring Network: For the integrity

monitoring check, the Central Facility needs to

have access to GPS measurements collected from a

receiver located within the validity area of each

set of DGNSS corrections. How this data is fed in

the central facility would depend on each

particular implementation. For instance, the

NTRIP protocol designed to disseminate GNSS

raw data and differential corrections over internet

could be used to transmit the raw data from the

receiver location to the central facility. In the case

of the Koblenz and Budapest pilot projects, since a

single monitoring receiver is used, standard

TCP/IP connections are used.

4.4 Performance assessment: definitions and assumptions

 Availability: percentage of time EGNOS-based

corrections are available to the user. This means

that the following failures have not been included

in this computation:

 HW and SW failures related to pilot project

setup and not representative of an

operational set-up.

 Malfunctions detected in the rover receiver.

 Continuity: Probability that a signal failure

incident will start during the Continuity Time

Interval (CTI).

𝐶𝑜𝑛𝑡𝑖𝑛𝑢𝑖𝑡𝑦 = 1 − 𝐶𝑇𝐼/𝑀𝑇𝐵𝐹

where CTI is 15 minutes as stated in [4] and

MTBF is the Mean Time Between Failures

measured over two years.

For the present analysis, a failure is considered an

event when the EGNOS-based DGPS corrections

are not available for the user (after being integrity-

checked) and therefore, it is not possible to

compute a differential solution.

 Accuracy: it is based only on the DGPS epochs

using EGNOS-VRS corrections marked healthy

(standalone epochs, “not-monitored” and “not-

working” epochs are excluded from the accuracy

statistics).

 Integrity analysis: integrity approach is based on

the Pre-Broadcast Monitoring concept. Corrections

are checked both in the pseudorange and position

domains as already explained for the preliminary

tests.

This means that:

 EGNOS SiS/EDAS data gaps are taken into

account for the availability and continuity results.

 Monitoring station data gaps are taken into

account for the availability and continuity results.

 Transmission failures are taken into account for

the availability and continuity results.

 User receiver data gaps are NOT taken into

account for the availability and continuity results.

4.5 Minimum user requirements

In order to assess the compliance with the minimum

maritime user requirements for coastal and inland

waterways navigation defined by IMO [4], a detailed

analysis of the accuracy, availability, continuity and

integrity performance has been performed for each

pilot project. According to [3], the following table

summarises the requirements specified in [4],

augmented by those described in [5]:

Figure 5. Maritime requirements based on IMO

Recommendations

Based on the above maritime requirements

specified by IMO and IALA, European inland

waterway navigation experts defined the following

set of requirements in the framework of the IRIS

Europe II project [6]:

 Horizontal Accuracy (95%): 3 m

 Availability (per 30 days): 99.8 %

 Continuity (over 15 minutes): 99.97 %

 Integrity Time to Alarm: 10 s

Although more stringent in terms of accuracy,

these requirements are deemed to be suitable for

inland waterways by the experts and therefore have

been taken into account in the current report.

Furthermore, according to [7]1, the continuity of

each individual reference station shall be >99.95% in

case the DGNSS service consist of areas of

overlapping coverage. Due to the relatively flat

terrain of Hungary and the dense network of AIS

Base Stations deployed along the Hungarian stretch

of the river Danube, the VHF signal of multiple AIS

Base Stations can be received at any location on the

river, including the capital Budapest. Therefore the

continuity minimum requirement of >99.95% has

been applied in this pilot project.

4.6 Performance results

The following table summarizes the results obtained

during the test campaign:

Table 2. Pilot projects performance results

__________________________________________________________________________________________________

Pilot Project Availability Continuity Accuracy Integrity

(95%, m)

__________________________________________________________________________________________________

HU (RSOE, 99.98 % 99.95 % 2.05 m Pseudorange domain: several high PRC residual error events

Budapest) affecting individual low-elevation satellites only

Position domain: 2 major events (both not-monitored) taking

several minutes each and 7 short events (most of them not-

monitored and a few no data) ranging from a few seconds to a few

minutes

DE (WSV, 99.99 % 98.95 % 1.11 m Pseudorange domain: several high PRC residual error events

Koblenz) affecting individual low-elevation satellites only.

Position domain: Lots of short events (unmonitored).

LV (MRCC, 99.83 % 98.98 % 3.60 m Pseudorange domain: No events.

Riga) Position domain: Some short events (unmonitored).

ES (PdE, 99.97% 99.38% 0.65 m No integrity events detected.

Rota)

__________________________________________________________________________________________________

4.7 Budapest pilot project results

This pilot project has run smoothly and results have

met all the requirements set for inland navigation.

The availability and continuity performance were

impacted by two regional EGNOS performance

degradation events occurred on the 20

of October

(which lasted for about 27 minutes) and the 11

November (which lasted for approximately 11

minutes). These performance degradation events

only affected the south-east part of Europe. Accuracy

results could have been improved if a higher quality

FFM receiver with a geodetic antenna had been used

in the test.

On the other hand, during the pilot project RSOE

started transmitting differential corrections from

other AIS Base Stations that follow the classical

approach. This caused the transponder to swap from

non-EGNOS based corrections to EGNOS-based

corrections back and forth. Unfortunately, the

transponder had problems when receiving the two

sets of corrections and kept going to standalone mode

even though corrections are being transmitted from

at least one of the two locations. A firmware upgrade

recommended by the manufacturer could not be

fulfilled.

4.8 Koblenz pilot project results

Various installation/setup issues not related with

EGNOS were solved at the beginning of the pilot

project and from there onwards the pilot has run

smoothly. The service continuity does not meet the

requirement due to frequent continuity events caused

by monitoring station data gaps and therefore not

related with the EGNOS-based corrections

themselves, but to the fact that the connection

between the monitoring station and the central server

is a simple DSL line.

It is noted that both the service level availability

and the system level accuracy results obtained during

the reporting period met the corresponding

requirements for inland navigation.

4.9 Riga pilot project results

Due to some disturbances in the area, there were

occasions when the rover transponder did not receive

corrections in time. The reason for these

transmission failures is not fully clear, but it affects

the VHF signal availability.

It is noted that both the service level availability

and the system level accuracy results obtained during

the reporting period met the corresponding

requirements for maritime navigation. Accuracy

values are slightly worse than in other pilot projects,

probably due to local interferences. It is suspected

that rover in Dzirnezers (used as Far Field Monitor) is

affected by multipath since it is installed in a metal

tower. In any case, these values could have been

improved if a higher quality FFM receiver with a

geodetic antenna had been used in the test.

The continuity requirement could not be met.

Continuity events were caused by monitoring station

data gaps (LAN communication issues) or

configuration changes (SW restarts), and therefore,

not related with the EGNOS-based corrections

themselves.

4.10 Rota pilot project results

Several issues with the installation, failures on the

transmitter (allegedly due to drops in the line

voltage) and problems with the rover receiver led to

the situation where no clean statistics could be

derived for the first period of analysis (from June to

beginning of October). In October 2018, the former

receiver and the antenna were replaced by a Trimble

SPS351 DGPS/Beacon receiver and the GA530

antenna. Also, the communication line in Rota was

updated to optical fibre technology.

The new performance analysis is remarkable for

the excellent accuracy results obtained with the

newly installed Trimble receiver (horizontal error at

the 95 percentile clear below 1 meter) and also for the

high availability of the EGNOS-based corrections

computed at the central server. The continuity

computed at the Rota DGPS (service continuity) was

99.38%.

The two main issues affecting system availability

and system continuity (at the FFM receiver) are the

following:

 Monitoring data delay: On certain epochs, the

GNSS measurements collected by the Rota

receiver and used for the integrity check are

received in the central server with a delay greater

than 5 seconds. This makes the Alberding SW

discard these measurements and therefore,

consider the PRC corrections as not-monitored,

with the corresponding impact on the availability

and continuity performance.

 Obsolete corrections broadcasting: In case of

communications data gap, the corrections

generated at the central server are received all at

once at the beacon site. This information goes

from the Euronet SW in the embedded PC to the

MSK modulator for its final transmission to the

users via radio. During this whole chain, the

timestamp of the corrections is not checked, and

therefore, the obsolete corrections that were

buffered during the network failure are

transmitted to the users. Considering the low

throughput of the radio transmission, it takes

several hours till the whole buffered data is

transmitted and the current corrections are

actually broadcasted.

4.11 Pilot projects results summary

Green cells indicate that the performance is compliant

with IMO requirements, whereas red cells indicate

the opposite. Based on these results shown above, it

is concluded that the availability of the EGNOS-

based corrections is enough to meet the 99.8%

availability requirement defined by IMO in the A.915

[5] and A.1046 [4] resolutions.

As it can be derived from the table, the most

demanding performance parameter is the service

continuity. The reason why there are red cells in the

table above is due to missing monitoring raw data to

perform the Pre-Broadcast Monitoring (PBM) check.

The missing raw data causes short continuity events

that have an impact on the parameter calculation.

These raw data gaps/delays are due to the fact that

pilot projects use conventional communication lines

(i.e. not dedicated) to transmit data from the

monitoring receiver to the central facility.

Regarding the accuracy results, it is to be noted

that the position accuracy highly depends on the

quality of the antenna and the GNSS receiver. In this

sense, the results obtained for the Rota pilot project,

where a high quality antenna and GPS receiver was

used, illustrates the performance levels that could be

obtained with an EGNOS-based solution (horizontal

position error below 1 meters at the 95 percentile).

Finally, the results yield by the integrity

monitoring module show that no single satellite

correction has been discarded due to high PRC, RRC

and only a few due to high corresponding residual

values (affecting satellites at low elevations). This

provides a quantitative measurement of the

corrections quality. If the corrections are accurate, the

differences between the geometric and the corrected

pseudorange will be low and therefore good position

accuracies will be obtained. At the position domain,

only a few events with errors exceeding the

horizontal position threshold have been detected in

the Riga pilot project.

In summary, for all cases where adequate data

was available and statistics could be computed,

EGNOS-based corrections have proved to achieve

performance levels above or closely below the

requirements set by the IMO. This is mainly due to:

 the high availability of the EGNOS SiS (100% in

the period of analysis when using combined SiS),

and EDAS (only minor outages detected), and

 the high quality of the corrections generated.

5 COST BENEFIT ANALYSIS

The goal of the CBA is to translate the proposed

technical architecture (DGNSS and EGNOS-based) of

all the considered scenarios into an effective

evaluation of costs and benefits. With this aim in

mind, a five-step methodology has been developed:

Initial scenarios

assessment

Cost-benefit

mechanisms

Full Scenarios

representation

Cos t-Benefit model

implementation

Conclusions and

recommendations

Questionnaire

to Authorities

And Alberding

3 4

Figure 6. CBA methodology

The CBA builds upon a comparison (or Delta) of

costs and benefits between a reference scenario, using

traditional DGNSS infrastructure, and an EGNOS-

based scenario. These costs and benefits are mainly

originated by the difference in CAPEX and OPEX

between reference and EGNOS scenario, deriving

from different infrastructure deployment and

maintenance requirements.

In close cooperation with the participating

authorities, the consortium has developed a complete

cost-benefit model that allows to quantify potential

savings brought by EGNOS introduction in all the

scenarios and to assess the optimal deployment

strategy for maximising benefits of this transition.

More specifically, for all the scenarios analysed the

results have been the following:

Table 3. Phase 2 CBA results

__________________________________________________________________________________________________

Port Authority/ Domain Reference Scenario EGNOS Option Total Savings percentage

State Architecture Architecture Savings (EGNOS Option vs

Reference Scenario)

__________________________________________________________________________________________________

MRCC/Latvia Maritime AIS decentralised AIS centralised 0,19 Mln Eur 52%

Puertos del Estado/ Maritime IALA decentralised IALA centralised 1,8 Mln Eur 28%

Spain (Hybrid Centralised)

RSOE/Hungary IWW AIS centralised AIS centralised 0,80 Mln Eur 19%

WSV/Germany IWW AIS centralised AIS centralised 0,36 Mln Eur 5%

__________________________________________________________________________________________________

In Latvia, EGNOS could bring considerable added

value in the transmission of corrections over the AIS

Network; through centralisation, the EGNOS-based

centralised option allows a notable amount of savings

in comparison to the Reference Scenario. This

happens since the CAPEX and OPEX for the central

server and IM Stations in the EGNOS option are

lower than the purchase costs of the required beacon

stations to generate corrections in the reference

scenario (no IALA beacons are available in Latvia).

EGNOS could also provide benefits to the

rationalisation and modernisation of the IALA

Network in Spain. The adoption of EGNOS allows

benefits both in CAPEX and in OPEX. This happens

since the setup costs for the central server and the

purchase costs of IM stations in the EGNOS option

are lower than the purchase costs of redundant

traditional IALA beacons in the reference scenario,

even taking into account that the proposed EGNOS

based options are not fully centralised and maintain

some decentralised components (especially for

remote broadcast sites where reliable

communications may not be available).

In Hungary, EGNOS could provide considerable

benefits in the transmission of corrections over the

AIS Network. Specifically, the CAPEX and OPEX for

the central server and the additional IM Stations

needed in the EGNOS option are lower than the

purchase costs of DRS and IMS in the reference

scenario. Besides cost advantages, the EGNOS

solution foresees the generation of more localized sets

of corrections for the AIS Base Stations (one set for a

group of 3 stations with EGNOS versus one set for a

group of 5 stations with DGNSS), providing

additional operational benefits (performance

improvement).

Finally, in Germany, the introduction of EGNOS

could provide some benefits as well, since the

purchase costs of IM Stations in the EGNOS option

are lower than the purchase costs of RS in the

reference scenario. It should be noted that in this case

economic benefits are more limited. This is mainly

due to the fact that the primary German system is

already based on centralised approach (not EGNOS

based), being already quite optimized from a

cost/infrastructure point of view. In this case, the

inclusion of EGNOS is expected to bring significant

benefits in terms of robustness/redundancy.

6 OPERATIONAL BENEFITS

The project has also identified some operational

benefits obtained when a centralized EGNOS-based

solution is implemented, namely:

 Reduction of spares and maintenance effort: The

rationalization of the infrastructure permits to rely

on a more agile and lighter architecture, consisting

on a smaller number of devices and tools, also for

maintenance purposes. In return, this derives on a

reduced number of man-days effort required to

perform the maintenance activities.

 Increased infrastructure robustness against RF

interferences (jamming/spoofing): In an EGNOS-

based centralized architecture Reference Stations

(RS) do not exist and hence, they cannot be

jammed or spoofed. Only Integrity Monitoring

Stations (IMS) can suffer this attack, which can be

minimized by adding redundant IMS. In

traditional DGNSS systems, however, since

normally both RS and IMS are co-located, they can

be equally jammed/spoofed.

 Increased infrastructure robustness against

failures: When EGNOS is used in combination

with traditional DGNSS (hybrid solution), EGNOS

introduces redundancy on the source of the

corrections. Furthermore, EGNOS corrections can

be obtained via a double source: SiS or EDAS. This

implies that, when a source of corrections fails, the

system can automatically switch to a different

source to avoid service interruption. Thus, the

system is more robust to potential malfunctions

coming either from: HW failures, SW failures and

communication lines failures.

 Synergies between IALA and AIS systems: A

centralised EGNOS solution could increase

synergies between IALA and AIS systems, since

the central server could generate corrections for

both systems in an efficient way thanks to the VRS

concept. These synergies could in return decrease

the costs of generating corrections to be

broadcasted by both systems.

 Enhanced integrity at system level: EGNOS

corrections contain integrity alerts either in the

Integrity Information Message (MT6) or the Fast

Corrections Messages (MT2 to MT5 and MT24).

The application SW will map these integrity alerts

into DGNSS RTCM format for transmission by

either setting the DGNSS MT1/9 PRC field to

binary 1000 0000 0000 0000 (which means this

satellite cannot be used for the navigation

solution) or even, when the alert condition affects

all satellites, by setting the Station Health field to

“not working”. On top of the EGNOS integrity

check, the DGNSS system will continue providing

alerts also at integrity monitoring level, as they

currently do.

7 PROJECT RECOMMENDATIONS

A set of recommendations have been derived from

the project, both for the National Competent

Authorities (NCA) interested in implementing a

similar solution as well as for the GSA. Some of these

recommendations are as follows:

1 On the grounds of the outcomes of this project,

NCAs are invited to carry out custom-built

technical and Cost Benefit Analysis to evaluate the

feasibility and benefits of using an EGNOS-based

solution. The analysis should be particularized to

their existing infrastructure, the typography of

their country as well as the EGNOS coverage area.

2 GSA should try to push investigation of some

outstanding issues at IALA level related to AIS,

such as cross-borders coordination between

countries and the fact that there is no body at

European/International level to control the time

slots used by AIS.

3 GSA should contribute to the generation of a full-

European model to provide AtoN services based

on EGNOS, perhaps through the development of

more pilot projects to gain further understanding

of the benefits of EGNOS at country level.

4 GSA should also continue supporting the

investigation on the transmission of EGNOS-

based corrections through VDES.

8 CONCLUSIONS

The project has demonstrated that EGNOS

corrections, when retransmitted by existing IALA

beacons and/or AIS Base Stations, perform in a very

similar way as traditional DGNSS solutions and can

yield important savings to authorities due to a

rationalization of the infrastructure required at the

transmitter sites.

This kind of solution also presents benefits, such

as increased infrastructure robustness (against

jamming and spoofing events and infrastructure

failures), reduction of maintenance costs and an

enhanced user integrity at system level.

In order to avoid gaps in the monitoring raw data

due to communication problems, it is recommended

to increase redundancy in the communication means

by either (a) relying on a network of monitoring

stations in the service area, and/or (b) diversifying the

data links. This is the reason why it is highly

advisable to make use of already available public

GNSS data networks to minimise costs when adding

this redundancy.

The results of the project have increased the

EGNOS awareness among the maritime and the IWW

communities, and are expected to act as a catalyst for

the adoption of EGNOS in other sites and countries.

ACKNOWLEDGMENTS

The authors would like to acknowledge the European

GNSS Agency (GSA) for their initiatives and efforts to

analyze the potential of EDAS/EGNOS SiS to support the

maritime community as a promising alternative for

maritime navigation infrastructure modernization and

rationalization.

The authors would also like to thank the seven European

authorities involved in the project for their contributions

and for giving us the possibility of using part of their

infrastructure to deploy a pilot project.

REFERENCES

[1] IALA Guideline G1129 “The retransmission of SBAS

corrections using MF RB and AIS” – Edition 1 -

December 2017

[2] RTCM 10401.2 Recommended Standards for Differential

Navstar GPS Reference Stations and Integrity Monitors

(RSIM), December 18, 2006

[3] Performance and Monitoring of DGNSS Services in the

Frequency Band 283.5 – 325 kHz, IALA Guideline 1112

[4] IMO Resolution A.1046, Worldwide Radionavigation

system

[5] IMO Resolution A.915 (22) “Revised maritime policy

and requirements for a future global navigation satellite

system (GNSS)”.

[6] Determination and verification of accuracy

requirements, IRIS EUROPE II (Implementation of

River Information Services in Europe) sub-activity 2.2

report, v1p0 final, 18 October 2010

[7] Performance and Monitoring of DGNSS Services in the

Frequency Band 283.5 – 325 kHz, IALA Guideline 1112