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1 INTRODUCTION

The subject of research presented in this paper was

"Adaptation of DGPS-PL station devices of the IALA

standard”, organization of measurements and

participation during sea trials of transmission and

reception of R-Mode signals and tested in the course

of the R-Mode Baltic project in the year 2020. Similar

modifications were made at 7 Baltic DGPS stations.

They included 3 Swedish stations, 3 German stations,

one Polish station and one Danish station on key

position Bornholm Island - see the description on the

project website: https://projects.interreg-

baltic.eu/projects/r-mode-baltic-90.html.

Having finalized technical and adaptation works,

the team took part in the system tests on land

(Rozewie 03-06th August 2020), and then assisted the

R-Mode marine tests on Baltic Sea. The route of the

Swedish research vessel m/s Fyrbyggaren is shown in

Fig. 1.

Figure 1. The route of the Swedish vessel M / S

Fyrbyggaren

Signal Research for Alternative Baltic Navigation

System

M. Dziewicki & J. Młotkowski

Maritime Office in Gdynia, Gdynia, Poland

T. Stupak

Gdynia Maritime University, Gdynia, Poland

ABSTRACT: In the project R-Mode a navigation system for Baltic Sea is designed. In the range of these actions

in summer of 2020 the signal for DGPS base station Rozewie were adopted and measurements on the sea were

performer. This experiment is shown in the article.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 14

Number 4

December 2020

DOI: 10.12716/1001.14.04.02

800

2 GENERAL ASSUMPTIONS OF THE PROJECT

Based on the analysis and research tests of the project

in 2018-2020, the requirements of the new R-Mode

signal were determined, in particular the linearity of

transmitters and the required stability of the

frequency and time source needed to meet the

assumptions of geographic position error in the new

radio navigation system on Baltic Sea. On their basis,

requirements were formulated for the parameters of a

new type of signal modulator delivered by German

partner WSV, and atomic, rubidium type frequency

generators - implemented by the Swedish partners.

The propagation analysis performed for the Baltic

Sea in 2019 by GRAD (Trinity House - UK) indicated

which Baltic stations should be used for testing. The

optimization of their geometry (HDOP), i.e. the R-

Mode signal emission points, was aimed at

minimizing errors in determining the geographical

position of the vessel. As a result of this analysis,

Polish DGPS Rozewie and Dziwnów stations were

also selected. The project leader (DLR) determined

the order of the tests and Rozewie station was

selected as a first one. At the same time, it was agreed

that the new modulator and time/ frequency

generator blocks will be loaned to UMG by project

members for carry out land and sea tests, until March

31, 2021.

The R-Mode operation at the Rozewie included

the measurement of the new frequency spectrum

(band), transmitted power, phase stability of the

signals, as shown in Fig. 3. Common procedure of

station calibration and coverage range verification

were performed prior to marine tests.

During the sea tests, measurements of the signal to

noise ratio, the static and dynamic position based

on R-Mode emissions were logged and compared to

the reference position of the ship.

2.1 Preparatory works

Due to the COVID19 pandemic, system readiness was

postponed twice, but at that time preparatory works

were agreed by teleconference with staff of the

project. Measurement of the spectrum of the pure

DGPS signal in the air was performed to prepare the

reference data after adjustments and R-Mode

installation. To minimize possible signal phase

changes, a fine tuning of the ATU matching

characteristic of the transmitting MF antenna was

performed thereafter. The geographic coordinates of

the transmitting MF antenna were measured using

the RTK technique based on the corrections via radio

signal from the Jastarnia reference base station.

Preparatory works covered also:

− Final selection of stations for R-Mode calibration

near the Rozewie station,

− Preparation of the assembly station for new R-

Mode modules in the existing DGPS rack.

− Installation of the IT equipment to organize

independent remote access via GSM 4G/LTE,

− Installation and adjustment power transmitters

with the required linearity and power (Amplidan

15770 2x100W type) at the DGPS Rozewie station,

see Fig. 2 – rack of R-Mode located at Rozewie

− Measurement of the reference coordinates of MF

R-DGPS antenna using RTK technology,

Figure 2. Rack of R-Mode equipment at the top

Figure 2. Spectrum of the new R-Mode / DGPS signal in the

air, called 2CW or R-DGPS

Figure 3. Block diagram of R-Mode modules installed at R-

DGPS Rozewie.

801

The initial commissioning of the new R-Mode

2CW modulator using the output signal from

standard RS1 reference station was unsuccessful,

despite contact with the manufacturer and attempts

to modify remotely his firmware. Finally, another

modern RTK / DGPS receiver was reinstalled and

tested. Having done that remote test (via the

Internet), new set worked properly with the 2CW

modulator and the rest of the blocks. Final

configuration of R-Mode blocks was shown in Fig. 3

2.2 Field tests

Several measurements of the signal strength and its

characteristics (structure) in the air were carried out.

The proper operation was confirmed by testing the

spectrum of the DGPS signal and the R-Mode / DGPS

signal at the transmitter output, then in the air - Fig.

2. Carriers: L1 = 301.00kHz, L2 = 300.775kHz, L3 =

301.025kHz.

Field measurements included:

− Determination of the 3D geographic coordinates of

the broadcasting antenna (as the R-Mode emission

reference point),

− Geographic coordinates of the calibration point, to

check the new emission stability and phase

measurements.

Both positions were made using the RTK

technique and the correction signal from the UMG

RTK Jastarnia reference base station at the frequency

of 449.025MHz.

The compliance of the new R-Mode signal with

the mandatory ITU-R standard was checked as well.

The coverage of the signal was checked by data

analysis from remote DGPS signal monitors installed

in Gdańsk, Northern Port (distance 45 km) and in

Jarosławiec (distance 120 km). The parameters of the

signal and the accuracy of the static position did not

change, although there was a decrease in signal

strength by about 2-3 dB, however a significant

increase in the average age of DGPS corrections was

noted.

2.3 Calibration procedure

Calibration of the station was performed jointly with

the German team. A static operation was checked for

signal phase stability by setting the R-Mode receiver

with a reference antenna having known phase

characteristics at the calibration point. Next, using a

two-channel oscilloscope, the phase adjustment of the

transmitted carriers was made. The comparison of the

measured distance (range) from the emission source

corresponded to the calculated phase shift of the

three carriers of the R-Mode signal (L1 = 301.00kHz,

L2 = 300.775kHz, L3 = 301.025kHz).

3 MARINE TEST

The partners from Sweden (SMA) and Germany

(DLR, WSV) organized the test cruise around the

Southern Baltic. The task of that marine test in the MF

band was verification of coverage and accuracy of the

dynamic positions. The test of the R-Mode system

from the board of the Swedish vessel m/s

Fyrbyggaren (Gross tonnage: 551) began with

installation works in Stockholm and lasted from 28/08

to 01/09/2020.

3.1 Organization of technical assistance

The task of the Polish team was to ensure the

continuous operation of the R-Mode transmitting

devices installed at Rozewie, data collection related to

the ship's route and distance from the Polish

transmitting station. Communication with the team

onboard was via satellite telephone and GSM when

the ship was in the coastal area. In order to monitor

the operation of the Rozewie station devices, the

following technical measures were organized:

− a spectrum analyzer with an audible alarm was

used for continuous, 24/7, especially at night,

analysis of the R-M signal in the air with the alarm

option of exceeding the limit parameters

(spectrum, amplitude, band). At night, the

receiving antenna was mounted on the hotel

balcony from the Rozewie side (distance from the

transmitter approx. 4 km).

− to verify the correctness of DGPS transmission, the

Beacon.net software was used, enabling 24-hour

online observation of operating screens (SS, SNR,

position errors) of R-DGPS remote receivers in the

Port Północny and in Jarosławiec.

− the survey vessel's route was recorded by tracking

the AIS of the m / s Fyrbyggaren, MMSI =

265289000. At intervals of 2-3 hours, screenshots

of the ship's route were taken for documentation

of its maneuvers.

− the operation of the Rozewie station transmitter

was checked by the readings of the output power

(nominal 100W), UPS power status, AC240V local

generator readiness, RM modulator status (via

GSM network), rubidium clock status of time and

frequency.

− communication with the ship took place via the

satellite communication system and GSM in the

coastal zone (email, telephone, SMS).In particular,

Master of the vessel, entering the Polish waters,

notified both VTS Świnoujście Traffic and VTS

Zatoka Gdańska.

3.2 Voyage events

M/s Fyrbyggaren entered the signal range of the R-

DGPS Rozewie station on August 28th at 12h00 LT,

100 nautical miles (195 km) from Rozewie at the SOG

speed 10.7 knots. The ship was tracked using AIS

HELCOM network; her navigational parameters have

been logged. Then she sailed along the Swedish coast

north of Bornholm, and then around 21h15 turned

south. On 28/08 at approx. 23h50, on the west side of

Bornholm, she made a 360-degree loop, and then

headed towards Świnoujście. The captain notified

VTS by e-mail about his plans to enter Polish waters.

Telephone connections were made with VTS

operators in Gdynia and Świnoujście, officer on duty

informed that the vessel had the appropriate

permission to maneuver in the Polish waters. The

ship's research team sent an SMS informing that the

802

Polish R–Mode station is being received and the

signal is at the appropriate SS and SNR levels. Then

m /s Frybyggaren entered the waters of EEZ RP on

August 29 at approx. 06h in the morning. Then the

ship continued its route along the Polish coast at a

lower speed towards the Rozewie traversing it at the

distance approx. 10 NM. When the ship entered Bay

of Gdańsk on August 30th, in addition to MF R-Mode

measurements, also VHF signals were recorded from

the VDES broadcasting station in Gdynia port. That

VDES base station created by the partner NIT

(National Institute of Telecommunication) is

collocated to the MOG Monitoring Center tower (RL

Gdynia). Here the ship performed a series of

maneuvers at different courses along a rectangular

route,. She also stopped drifting at a speed close to 0

kn, see AIS track examples in Fig. 4 and Fig.5.

During the final phase of these tests, the Polish

team was notified by the call phone from the ship

about suspected drift of the R-Mode modulator clock.

Inspection activities were undertaken at Rozewie

station on 31/8 early morning. All the indicators of

the atomic clock, and in particular the signal from the

GPS antenna, were correct. The transmitter power

stability and set-up of the reference receiver have

been tested. Finally, the UMG was informed that the

source of the error was found in the set-up of

onboard post-processing unit.

4 MARINE TEST RESULTS

Timing of the ground installations and the voyage

itself were threatened and modified by the COVID19

pandemic. The technical assistance was provided to

ensure that the cruise prepared with a great expense

of effort and resources of the project will take place

without technical disturbances. During the tests, R-

Mode devices of the modified DGPS Rozewie station

were operating properly, what was confirmed by

messages from the vessel as well as conversations

carried out during and after the cruise. Some doubts

that arose during the course of the process were

clarified on an ongoing basis. In view of the very

limited number of stations (7) adapted to broadcast a

new signal, it was not possible to risk "falling out" of

even one, because it would disturb the required

geometry of signal distribution in the South Baltic.

Although all data from the dynamic test has not

been processed yet, the forecasted signal range

parameters (SS, SNR), the geometry parameters of

selected stations (HDOP) have been confirmed and

the possibility of determining the ship's position

based on the MF band signals with the predicted

accuracy has been demonstrated in practice.

5 CONCLUSIONS BY THE END OF 2020

On September 14th, a project partner’s teleconference

initiated by the DLR was held, during which the

initial test results of the marine MF systems with the

participation of the DGPS Rozewie station were

presented. This was the first marine test performed

within EU waters, and one of the first on the globe.

The obtained results showed that the system

operation can be initially assessed as positive. The

principle of operation of R-Mode and the predicted

accuracy of positioning were verified and confirmed.

The operation of MF transmission was stable. Thanks

to practical tests some refinement was proposed, but

it does not require supervision greater than standard

DGPS. Due to the fact that only preliminary results of

measurements lasting 5 days were announced, it is

too early to provide detailed results of collective

studies of both individual parameters and their

behavior over time.

Due to conclusions of IALA workshop (Edinburgh

2020) on the future of DGNSS systems, the R-Mode

system can be the successor of ground based

differential systems (DGPS, DGlonass etc.) and may

became the real backup to GNSS itself.

Figure 4. Track of m/s Fyrbyggaren passing R-DGPS

Rozewie

Figure 5. Maneuvers during the VDES test on Gdansk Bay

REFERENCES

1. Adaptation of DGPS-PL station devices of the IALA

standard, organization of measurements and

participation in sea trials of transmission and reception

of R-Mode signals. Gdynia Maritime Office, 2020

2. Dziewicki M, Ledóchowski M, Stupak T.: Badanie

zasięgu i dokładności Krajowego Systemu

Radionawigacyjnego DGPS, Transcomp Zakopane,

Technika Transportu Szynowego 9/2012 nr 437 str.

4165-4173 (na CD).

3. Dziewicki M, Ledóchowski M, Stupak T.: Koncepcja

monitorowania Krajowego Radionawigacyjnego

Systemu DGPS/RTK z funkcją generowania poprawek

przez stacje monitorujące. Przegląd Telekomunikacyjny

Rocznik LXXXV nr 11/2013 str. 1652 -1655