s subcomitÉ de navegaciÓn, ncsr 7/5 comunicaciones y ... · 2 resultados: 2.9 medidas que han de...

I:\NCSR\7\NCSR 7-5.docx

S

SUBCOMITÉ DE NAVEGACIÓN, COMUNICACIONES Y BÚSQUEDA Y SALVAMENTO 7º periodo de sesiones Punto 5 del orden del día

NCSR 7/5

15 octubre 2019 Original: INGLÉS

Difusión al público antes del periodo de sesiones: ☒

APLICACIÓN DEL "SISTEMA REGIONAL INDIO DE NAVEGACIÓN POR SATÉLITE (IRNSS)" EN EL ÁMBITO MARÍTIMO Y ELABORACIÓN

DE NORMAS DE FUNCIONAMIENTO PARA EL EQUIPO RECEPTOR DEL IRNSS DE A BORDO

Reconocimiento del Sistema regional indio de navegación por satélite (IRNSS)

Nota presentada por India

RESUMEN

Sinopsis: En el presente documento se facilita información adicional y datos pormenorizados sobre el Sistema regional indio de navegación por satélite (IRNSS), sobre aspectos que incluyen, entre otros, el funcionamiento, la capacidad, las pruebas y la aplicación del sistema, para que los examine el Subcomité.

Principios estratégicos, si son aplicables:

2

Resultados: 2.9

Medidas que han de adoptarse: Véase el párrafo 22.

Documentos conexos: Resolución A.915(22), MSC 96/25, NCSR 4/29, NCSR 5/5, NCSR 5/5/1, NCSR 5/WP.1, NCSR 6/23 y MSC 101/24.

Antecedentes

1 En su 96º periodo de sesiones, el Comité de seguridad marítima examinó el documento MSC 96/23/8 (India), en el que se propone reconocer al IRNSS como un componente futuro del Sistema mundial de radionavegación (WWRNS) y elaborar normas de funcionamiento para el equipo receptor del IRNSS de a bordo, y acordó incluir en el orden del día bienal correspondiente a 2018-2019 del Subcomité NCSR y el orden del día provisional del NCSR 5, un resultado titulado "Aplicación del "Sistema regional indio de navegación por satélite (IRNSS)" en el ámbito marítimo", con 2019 como año de ultimación previsto.

NCSR 7/5 Página 2


2 El NCSR 5 examinó la propuesta de India para que la OMI reconozca al IRNSS como un componente del WWRNS. El Subcomité examinó el documento NCSR 5/5, en el que se describe el IRNSS, junto con el proyecto de normas de funcionamiento para el equipo receptor del IRNSS de a bordo (NCSR 5/5/1). El Subcomité, tras tomar nota del apoyo general manifestado, invitó a India a que proporcionara más información y datos pormenorizados al NCSR 6. El NCSR 5 examinó la propuesta de India (NCSR 5/5/1) sobre el proyecto de normas de funcionamiento para el equipo receptor del IRNSS de a bordo y, tras un examen, las aprobó. Al hacerlo, el Subcomité invitó a la CEI a que examinara la conveniencia de elaborar normas de prueba conexas. 3 Durante las deliberaciones que tuvieron lugar en el NCSR 6, la delegación de India informó de que no había estado en condiciones de cumplir el plazo para la presentación de documentos al NCSR 6, y de que, siguiendo las prescripciones, se presentaría la información adecuada al MSC 101 y al NCSR 7. Tras deliberar, y habida cuenta de la información facilitada por India, el Subcomité invitó al Comité a que ampliara el plazo de ultimación previsto para este resultado hasta el año 2020. 4 Por consiguiente, India presentó información pormenorizada al MSC 101, en forma de un documento informativo, que abarca la descripción del sistema IRNSS, la capacidad del servicio del sistema, las pruebas del sistema y su aplicación, junto con referencias y enlaces pertinentes a sitios web. Se presenta un documento idéntico al NCSR 7 para que lo examine. Introducción 5 El IRNSS es un sistema regional de navegación por satélite independiente desarrollado y operado por India. Es compatible e interoperable con otros sistemas de radionavegación mundiales existentes. Cabe señalar que también se conoce al IRNSS como NavIC (Navegación con constelación de India). 6 El segmento espacial y el segmento de control en tierra están en estado de funcionamiento estable y su rendimiento de servicio cumple las prescripciones de proyecto estipuladas en varias pruebas y evaluaciones de las terminales de los usuarios. 7 A fin de promover la aplicación amplia del IRNSS y para fomentar que las compañías trabajen en la investigación y desarrollo de las terminales del IRNSS, en 2014 se divulgaron oficialmente para el dominio público sus documentos de control de interfaz de señal de espacio (ICD) (https://www.isro.gov.in/sites/default/files/irnss_sps_icd_version1.1-2017.pdf). Utilizando la información ICD, las compañías han producido receptores IRNSS y los han desplegado para aplicaciones de determinación de la situación, navegación y cronometría en India. Descripción del sistema 8 El IRNSS consta de tres componentes: el segmento espacial, el segmento de control en tierra y el segmento de control del usuario. 9 La constelación espacial consiste en tres satélites geoestacionarios, en las posiciones 32,5º Este, 83º Este y 129,5º Este. Los cuatro satélites IGSO están desplegados en bandas orbitales, dos de ellos en 55º Este y dos en 111,75º Este, con una inclinación de 29º. Con esta geometría se garantiza que, en la zona de cobertura primaria, los usuarios siempre tienen un mínimo de cinco satélites visibles.

https://www.isro.gov.in/sites/default/files/irnss_sps_icd_version1.1-2017.pdf

https://www.isro.gov.in/sites/default/files/irnss_sps_icd_version1.1-2017.pdf

NCSR 7/5 Página 3


10 El segmento de control en tierra consta de los centros de navegación (NC), las estaciones de enlace ascendente (US), una red de estaciones de telemetría y control de integridad (RIMS) distribuidas geográficamente y estaciones de telemetría CDMA (CDR) con suficientes duplicaciones. Las principales funciones de los centros de navegación son obtener datos de observaciones de cada RIMS y CDR, procesar los datos de telemetría y los datos diferenciales y de integridad para poder generar mensajes de navegación por satélite, efectuar la planificación y programación de las misiones, y operar y controlar el sistema. Los mensajes de navegación por satélite y las operaciones de comando para el control de la carga útil y la gestión del bus del satélite se envían desde las estaciones de enlace ascendente. Las funciones de las RIMS y las CDR son recibir la información continua de seguimiento y control de los satélites de navegación, incluidas las señales de navegación, y enviar los datos de observación a los centros de navegación para determinar la órbita de los satélites y la sincronización cronométrica. 11 El segmento del usuario incluye varios tipos de terminales de los usuarios del IRNSS que cumplen los requerimientos de las distintas aplicaciones de varios campos y sectores. 12 El IRNSS opera en tiempo universal coordinado (UTC). La diferencia entre el UTC y la hora del IRNSS es siempre inferior a 100 ns. 13 El marco de coordenadas del IRNSS es el dátum WGS-84. Capacidad de servicio del sistema 14 El IRNSS presta servicios de determinación de la situación, navegación y cronometría para un número ilimitado de usuarios en su zona de servicio.

Funciones principales: determinación de la situación, determinación de la velocidad y cronometría.

Zona de servicio: Regional (55º longitud E, 50º latitud N, 110º longitud E y 5º latitud S).

Precisión de la situación: 20 m

Precisión cronométrica: 100 ns.

15 En la actualidad, las normas de funcionamiento del servicio abierto del IRNSS son las siguientes:

Precisión de la situación: 10 m

Precisión cronométrica: 50 ns, unidireccional.

Pruebas del sistema 16 India ha efectuado las pruebas de aplicaciones de los usuarios utilizando plataformas de aplicación en vehículos, en buques y en aeronaves a fin de medir y evaluar el rendimiento del servicio del IRNSS. Los resultados revelaron que el funcionamiento del sistema es mejor que el previsto en las especificaciones de proyecto. 17 Se facilitan pormenores del funcionamiento del sistema IRNSS como referencia para el Subcomité. En el anexo 1 se muestra el funcionamiento del IRNSS en la región de India y en el anexo 2 el funcionamiento del sistema en la región oceánica.

NCSR 7/5 Página 4


Aplicación del sistema 18 Se han desarrollado diversas plataformas de aplicaciones de usuarios que promueven la capacidad de transmisión de mensajes y navegación del IRNSS. Como resultado de las pruebas que se han efectuado con éxito, varios sectores y servicios públicos están adoptando gradualmente el IRNSS, entre ellos, el transporte, los levantamientos geográficos y cartográficos, pronósticos meteorológicos, pesquerías marinas, supervisión de deformaciones, búsqueda y salvamento, navegación de vehículos y teléfonos inteligentes, lo que genera beneficios sociales y económicos tangibles. 19 Ya están disponibles o en fase de desarrollo conjuntos de chips compatibles con varias aplicaciones derivadas del IRNSS. Entre estos conjuntos, hay módulos de chips múltiples (MCM), chips individuales y variantes de sistema en chip. Varias empresas están desarrollándolos y comercializándolos en versiones del IRNSS exclusivamente y versiones híbridas multi-GNSS, incluidas versiones de IRNSS. Se están utilizando en dispositivos tales como dispositivos de seguimiento de vehículos, sistemas de información sobre transporte por ferrocarril, gestión de flota/vigilancia del transporte a bordo de buques, etc. Se ha demostrado con éxito que los conjuntos de chips reciben señales del IRNSS a partir de dos teléfonos móviles y se están desarrollando más conjuntos de chips para seguir expandiendo este segmento de aplicación. 20 El IRNSS ha sido aceptado por el Proyecto Asociación de Tercera Generación (3GPP) como un punto de trabajo (release 16) como parte de la especificación asistida del GNSS. El Proyecto 3GPP reúne a las organizaciones internacionales que elaboran normas sobre telecomunicaciones y elabora protocolos para las tecnologías de las telecomunicaciones celulares. 21 A fin de incluir al IRNSS dentro de la norma del Comité especial 104 (SC-104) de la Comisión Técnica de los Servicios de Radiocomunicaciones Marítimas (RTCM) para las aplicaciones del sistema diferencial mundial de navegación por satélite (D-GNSS), la RTCM constituyó un grupo de trabajo integrado por 15 miembros sobre el Sistema regional indio de navegación por satélite (IRNSS) durante la reunión de la SC-104 de la RTCM celebrada en mayo de 2018 en Harbin (China). Los resultados de las pruebas de compatibilidad de la señal del IRNSS han sido aprobados por la reunión plenaria del SC-104 celebrada en Trondheim (Noruega) los días 23 y 24 de septiembre de 2019. Está previsto que se someta a votación la propuesta en la próxima reunión plenaria del SC-104 en enero de 2020, con miras a incluir los mensajes del IRNSS en la norma RTCM 3.X. Medidas cuya adopción se pide al Subcomité 22 Se invita al Subcomité a que:

.1 examine la información facilitada en el presente documento; y .2 recomiende al Comité que reconozca el IRNSS como componente del

Sistema mundial de radionavegación (WWRNS).

***

NCSR 7/5 Annex 1, page 1


ANNEX 1

(English only)

PERFORMANCE OF THE INDIAN REGIONAL NAVIGATION SATELLITE SYSTEM

(IRNSS) ACROSS THE INDIAN LANDMASS

1. Introduction

1.1 IRNSS is a regional navigation satellite system compatible with other navigation satellite systems worldwide. The IRNSS is an independent regional system developed and operated by India which comprises of three major components: space segment, ground control segment and user terminals. The space segment is a constellation of seven satellites, of which four are geosynchronous earth orbit (GSO) satellites inclined at 29° to the equatorial plane with longitude crossings at 55° E and 111.75° E (two satellites in each slot) and three in geostationary satellite orbit (GEO) satellites positioned at 32.5° E, 83° E, 129.5° E orbital slots respectively. This geometry ensures that a minimum of five satellites are visible to users within service area with a position dilution of precision (PDOP) ≤ 6. Each satellite transmits standard positioning service signal on "L5" and "S" bands with carrier frequencies as 1176.45 MHz and 2492.028 MHz respectively. Standard positioning signals include ranging code which could provide the open service. A navigation data message is superimposed on this code. IRNSS satellites are identified by PRN codes.

1.2 The IRNSS Standard Positioning Service (SPS) provides positioning, navigation and timing services, free of direct user charges. The IRNSS receiver equipment should be capable of receiving and processing the standard service signal.

1.3 IRNSS receiver equipment intended for navigation purposes on ships with a speed not exceeding 70 knots, in addition to the general requirements specified in resolution A.694(17), should comply with the following minimum performance requirements.

1.4 The standards cover the basic requirements of position fixing, determination of course over ground (COG), speed over ground (SOG) and timing, either for navigation purposes or as input to other functions. The standards do not cover other computational facilities which may be in the equipment nor cover the requirements for other systems that may take input from the IRNSS receiver.

1.5 It should be noted that this is the regional navigation satellite system being recognized as a future component of the World-Wide Radio Navigation System (WWRNS) and the service is limited to the coverage area, which is:

"Area enclosed by the 55° E Longitude, 50° N Latitude and 110° E Longitude, 5° S Latitude"

2. Current Status, System Performance and Analysis

2.1 Space Segment: Seven satellites are available and beaming signals in L5 and S band

for Navigation service. One additional satellite is available for "Messaging Service".

2.2 Ground Segment: Navigation Software, Navigation Control Centres, Reference

Stations, IRNSS System Timing Centres and Satellite Control Centres have been established

and operational.

2.3 IRNSS Performance plot over the Indian region: The IRNSS system has been

evaluated for performance over specific station points across the coverage. Performance plots

for both single-frequency (L5) and dual-frequency (L5 & S) are presented hereunder.



IRNSS Performance Plots for Single Frequency (L5)

The following plots show the position errors in the extreme end areas across the Indian region

covering four stations i.e. Bangalore, Jodhpur, Shillong and Gaggal. For 98% of the time, the

position error is within 7 m. The maximum worst-case position error observed is 10 m in the

Shillong region.



IRNSS performance plots dual frequency (L5&S)

The following plots indicate the position errors in the extreme end areas across the Indian

regions covering the stations of Bangalore, Jodhpur, Shillong and Gaggal. For 98% of the time

of observation, the position error is less than 5 m. Further, it is always less than 7 m when dual

frequency L5 and S are used for computing the position.



C/No Received from all IRNSS Satellites

Plots showing the C/No received from all the on-board IRNSS satellites around the Indian

region areas shown below. C/No received in the entire region is between 40 to 50dB-Hz, which

is well within the sensitivity of the Receiver.

Received signal strength at S-Band frequency

Received Signal Strength at L5-Band frequency



Documents published/ready for publishing

Information on the IRNSS signal structure and algorithms for user receiver development have

been published as follows:

Signal-in-Space (SIS) Interface Control Document (ICD) for Standard Positioning Service SPS

(Online)

Available: https://www.isro.gov.in/sites/default/files /irnss_sps_icd_version1.1-2017.pdf (Date

last accessed 22 January 2018).

SIS ICD for the IRNSS messaging service (Online)

Available: https://www.isro.gov.in/sites/default/files/sis_icd_irnss1a_messaging.pdf (Date last

accessed 22 January 2018).

The NMEA 0183 standard for IRNSS/NavIC (Online)

Available: https://www.tronico.fi/OH6NT/docs/NMEA0183.pdf (Date last

accessed 22 January 2018).

NavIC programme and status (Online)

Available: https://www.isro.gov.in/irnss-programme (Date last accessed 22 January 2018).

A Comparative Study and Performance Analysis Using IRNSS and Hybrid Satellites (2017),

Kiran, B & N, Raghu & K N, Manjunatha

10.1007/978-981-10-2471-9_7 (Online)

Available:

https://www.researchgate.net/publication/311216047_A_Comparative_Study_and_Performa

nce_Analysis_Using_IRNSS_and_Hybrid_Satellites

Comparative evaluation of IRNSS performance with special reference to positional accuracy,

Vasudha, M.P. &Raju, G. GyroscopyNavig. (2017)

8: 136. (Online).

Available: https://doi.org/10.1134/S2075108717020109.

IRNSS stand-alone positioning: first results in Australia,

Safoora Zaminpardaz, Peter J.G. Teunissen & Nandakumaran Nadarajah (2016), Journal of

Spatial Science

61:1, 5-7, DOI: 10.1080/14498596.2016.1142398 (Online)

Available: https://www.tandfonline.com/doi/abs/10.1080/14498596.2016.1142398

Analysis of IRNSS Over Indian Subcontinent

Rao, V.G., Lachapelle, G., VijayKumar, S.B, Proceedings of the 2011 International Technical

Meeting of The Institute of Navigation, San Diego, CA, January 2011, pp. 1150-1162. (Online)

Available: https://www.ion.org/publications/abstract.cfm?articleID=9566

***

https://www.isro.gov.in/sites/default/files%20/irnss_sps_icd_version1.1-2017.pdf

https://www.isro.gov.in/sites/default/files/sis_icd_irnss1a_messaging.pdf

https://www.tronico.fi/OH6NT/docs/NMEA0183.pdf

https://www.isro.gov.in/irnss-programme

https://www.researchgate.net/publication/%20311216047_A_Comparative_Study_and_Performance_Analysis_Using_IRNSS_and_Hybrid_Satellites

https://www.researchgate.net/publication/%20311216047_A_Comparative_Study_and_Performance_Analysis_Using_IRNSS_and_Hybrid_Satellites

https://doi.org/10.1134/S2075108717020109

https://www.tandfonline.com/doi/abs/10.1080/14498596.2016.1142398

available:%20https://www.ion.org/publications/abstract.cfm?articleID=9566



ANNEX 2

(English only)

PERFORMANCE OF THE INDIAN REGIONAL NAVIGATION SATELLITE SYSTEM (IRNSS) ACROSS THE OCEANIC REGION SURROUNDING INDIA

1 Introduction

IRNSS is the Indian regional navigation system with a constellation of seven satellites and offering positioning and timing information over the Indian landmass and adjacent areas including the adjacent sea and oceanic regions. The IRNSS system is designed to provide a position accuracy < 10 metres over the specified service area. The intended service area for IRNSS has been assumed to be primarily the Indian landmass, in general specified as lying between longitudes 30° E to 130° E and between latitudes 30° S and 50° N. More specifically the coverage includes the Indian geo-political boundary and a region extending to about 1,500 km around it including the sea and oceanic region. Some more details about the IRNSS system are already addressed in the introductory paragraphs of annex 1 of this document and are omitted here for brevity. That annex has already addressed the performance of the system across the Indian landmass through sustained observations at multiple representative locations at extreme points of the service area. This annex addresses the IRNSS system performance over the remainder of the coverage area, in particular lying outside the landmass. A majority of this area being sea or oceanic, the observations are carried out in two modes: a set of ships were equipped with IRNSS receivers and logged data during their voyage across the coverage area. A separate set of measurements were made from a fixed station at Mauritius that also lies well outside the Indian mainland and embedded into the oceanic portion of the coverage. The subsequent sections present the measurements logged during these two measurement modes. 2 IRNSS performance in the oceanic region To carry out the crucial performance assessment across the sea and ocean regions comprising the IRNSS coverage region outside the Indian mainland, a total of 15 IRNSS receivers were installed in different ships and the receiver data were collected for analysis as the ships moved across the seas. The prime objective of this exercise was to assess feasibility of using IRNSS as a candidate navigation system for Indian ships and to comply WWRNS for eventual IMO Certification. The ships on which the receivers were installed and the period of their data collections are given in the following tables.



Significant and useful data is available from the following ships and the same has been considered for subsequent data analysis.

Sl. No

Ship's Name Voyage Start Date

Voyage End Date

1 Vessel Coral 08/12/15 06/03/16

2 DCI Dredging –XIV 06/12/15 07/06/16

3 DCI Dredge – XV 12/12/15 16/05/16

4 MT Guru Govind Singh 05/12/15 20/03/16

5 M T SwarnaSindhu 15/01/16 21/01/16

6 SCI Nalanda 28/02/16 11/03/16

7 M V Chowra 08/12/15 15/05/16

8 M V Nancowry 18/12/15 10/02/16

9 M V SCI Chennai 04/12/15 25/06/16

10 M V Jagroopa 29/11/15 18/01/16

11 Lakswadeep 11/12/15 13/12/15

12 M V Nicober 06/12/15 28/12/15



These ships, during the period of data collection, moved mainly over the water mass adjacent to the Indian landmass and particularly within the primary service area of the IRNSS. Nevertheless, there were a few ships which moved to distant ports as well. The traces of the movements for a few selected ships are shown in the figure 1 below.

Figure 1: Course traces of selected ships during IRNSS data logging

2.1 Distribution of data sampling:

The analysis of the data logged by the shipborne receivers was carried out mainly on the basis of the performance of the receivers and the associated signal quality. In order to do so, the performance metrics which were targeted and analysed include the position fixing ability, satellite visibility and satellite signal strength, etc. Each of these metrics was observed for every individual ship. Further, the performance of position fixing was also differentiated for the ship location inside and outside the primary service region of the IRNSS system. The following pie chart in figure 2 provides the figure of the distribution of the average position of the ships inside and outside the Primary Service Area (PSA) of IRNSS.

MV Jagroopa MV SCI Chennai

DCIDredge-XIV M V Chowra



Figure 2: Pie chart indicating position distribution of the ships inside and outside PSA 2.2 Position fixing The position fixing ability of the ships was analysed from the collected data. The position of the receiver can be fixed only if there are a minimum of four satellites visible to the receiver at a given time. Since the visibility of the satellites depends upon the number of satellites available in the constellation and the location of the receiver with respect to the satellites, these secondary factors too play a role in the process. Here, the percentage of position fixing over the total period of the data collection is estimated. Further, the position fixing ability is also compared for the time when the ship was inside and outside the primary service area of the IRNSS. Considering the complete period of data collection of all ships, the overall percentage of time the receivers were able to fix the position in a combined sense is shown in the plot given in figure 3a below. Further, the position fixing ability was distinguished for the location of the ship, both inside and outside the primary service area of the IRNSS system.

Figure 3a: Consolidated position fixing of all ships

WITHIN PSA88%

OUTSIDE PSA12%

70.00

75.00

80.00

85.00

90.00

95.00

WITHIN PSA OUTSIDE PSA OVERALL

PER

CEN

TAG

E O

F FI

X



This figure is a time-weighted average from the position fixing values estimated from each ship, which has been estimated. Very obviously, it has been observed that the position fixing percentage has dropped down from more than 90% inside to around 80% outside the PSA. This is due to the reduced visibility of the satellites as the ships went outside the PSA. The chart for the individual ship is shown in the figure 3b shown below. Only 12 ships are shown in the figure as the other ships have data insufficient to derive any meaningful statistics. Ships MV Chennai and MV Jagroopa shows lesser fixing as these ships went far outside the PSA, as evident from figure 1.

Figure 3b: Overall position fixing of individual ships 2.3 Satellite visibility: The visibility of the navigation satellites plays a prime role in determining the performance of the receivers. Although only four satellites are necessary for the fixing of the position, the more the satellites are visible, the greater is the option to the receiver to switch to better satellites in terms of the signal quality and towards a better geometry which determines the accuracy of the position fix. The receivers were installed at a time when all the seven satellites of the system were still not placed in the constellation. However, the constellation was gradually filled up during the course of this data collection term and was completed when a few ships were still collecting data. Therefore, the visibility of the satellites also improved with time. To represent the exact depiction of visibility instead of only representing the total numbers of satellites visible; the visibility numbers are segregated according to the numbers of the satellites available in the constellation. The figures were arrived by averaging the visibility figures over all receivers available under each individual constellation conditions as shown in figure 4 below.

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00



Figure 4: Average visibility of satellites to the ships for different numbers of satellites in the constellation

The percentages estimated for different numbers of satellites in the constellation is over the time when exactly that numbers of satellites were present in the sky. For example, the time period used for finding the visibility figure when five satellites were in the constellation was from the date of launching of the fifth satellite to the date of the launching of the sixth satellite, the latter exclusive. An interesting aspect illustrated by the above figure needs mentioning. When the receivers were installed, there were only four satellites in the sky. From that date to the date of the launching of the fifth satellite, for 89% of the time all four were visible. However, although the fifth satellite was launched on 20 January 2016, post this date until the launching of the next; despite five satellites being in the constellation, the percentage of visibility of five satellites is much less. This is possibly due to the very short duration between the commissioning of the satellite after the IOT and the launching of the next satellite. For 52% of the time, six satellites were visible in the period when also only six satellites were in the sky. 2.4 Satellite signal quality During the ships' voyages, the installed receivers in the ships could see the satellites with different look angles and with varying C/N0. The following plots in figure 5 shows the typical temporal variations of C/No with time for different satellites, available during the trip of the ship.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

4 5 6 7DIS

TRIB

UTI

ON

OF

VIS

IBIL

ITIE

S

SATELLITES IN SPACE

<4 Sats Visible

4 Sat Visible

5 Sats Visible

6 Sats Visible

7 Sats Visible



Figure 5: Typical C/No variation of the received signal for different satellites



The C/No values are, however, dependent upon the relative location of the ship and the satellite. Therefore, it will be different for different ships travelling along different routes. To obtain a broad overview of the signal variations, notwithstanding the variation between the ships due to their courses, the distribution of the C/No consolidated over all ships for each satellite is provided in the figure 6 below. The box plot shown in figure 6 provides the distribution of the C/No over the times these satellites were available. The lowest point indicates the minimum C/No registered by the receiver while the highest point indicates the maximum. The other horizontal marks indicate the four quartiles of the distribution. The "X" mark shows the mean values. This is done of each individual satellite and for L band only. The S band showed similar behaviours, with values around 3dB lower than these.

Figure 6: Box plot of consolidated distribution of C/No over all ships for different satellites in L band

From the above plots, it is obvious that for IRNSS-L5-Band, the average time profile of C/No remained just around 50 dB-Hz most of the time for IRNSS-1A and IRNSS-1B while IRNSS-1D and IRNSS-1E remained around 45 dB-Hz. These values for IRNSS-1F and IRNSS-1G remained above 40 dB-Hz. Only for IRNSS-1C, the value remained above 50 dB-Hz. Finally, the mean signal level inside and outside the Primary service region is shown in the following figure 7. The mean value inside the primary region is obviously high at around 52 dB-Hz while that outside is 43 dB-Hz as recorded by the receivers.

1A 1B 1C 1D 1E 1F 1G



Figure 7: C/No inside and outside the primary region over averaged all satellites

For IRNSS-S-Band, this average value remained around 45 dB-Hz for all except for IRNSS-1D, in which it is below 45 dB-Hz. Occasional depreciations of the values have been observed in all satellites and for both the bands. Overall, the signals remained above the necessary threshold for the period of the voyage. 2.5 Receiver clock performance The receiver clock bias variation is also an important index of its performance. The receiver clock has a bias with respect to the satellite and is expected to vary over time. However, the less the variation in the clock, the better the performance. The following plots in figure 8 show the typical time variation of the clock bias and its probability distribution.

Figure 8: Clock performance of the receiver For the receivers installed in the ships, a mean clock bias of around -10ns has been observed. However, the deviations from the mean mostly remain between -20 and +2ns with a few outliers scattered beyond this range. The standard deviation of the clock variation is around 3.0ns.

38

40

42

44

46

48

50

52

CONDITIONS

C/N

o (

dB

Hz)

INSIDE PRIMARY SERVICEREGION

OUTSIDE PRIMARY SERVICEREGION

OVERALL



2.6 Conclusions From the above measured data and analyses, it is evident that the receivers have performed as at par with the potentials with sufficiently good availability. The performance deteriorations were only observed when the ships carrying the receivers went far outside the primary service region of IRNSS, which is expected. Further, the signal conditions within the primary area are adequate for providing the necessary performance. Therefore, it can be concluded that IRNSS can be used as an alternative navigation system for ships, assuredly within the specified primary service area. 3 IRNSS performance in the Mauritius region

Apart from the receivers installed on-board ships plying the seas and the Indian Ocean region, performance of IRNSS system has also been evaluated near the Mauritius region. Mauritius lies in the extended coverage area of IRNSS, around 4,300 km from India. The receiver position performance is plotted along with GDOP w.r.t time. This parameter is an indicator of the constellation performance at that location and time separating the receiver performance. The receiver position error is plotted for around 46 hours and an average of 1-sigma RMS position error of 4.58 m is observed for this duration. Since Mauritius is at the far end of IRNSS coverage area, the GDOP observed is on the higher side, but still the position error is obtained within the assured system performance.

Figure 9: GDOP and position error observed from Mauritius (lying in IRNSS extended

coverage)

___________