APPLICATION OF THE INDIAN REGIONAL NAVIGATION … · System description 8 IRNSS is composed of...

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SUB-COMMITTEE ON NAVIGATION, COMMUNICATIONS AND SEARCH AND RESCUE 7th session Agenda item 5

NCSR 7/5

15 October 2019 Original: ENGLISH

Pre-session public release: ☒

APPLICATION OF THE "INDIAN REGIONAL NAVIGATION SATELLITE SYSTEM (IRNSS)" IN THE MARITIME FIELD AND DEVELOPMENT OF PERFORMANCE STANDARDS

FOR SHIPBORNE IRNSS RECEIVER EQUIPMENT

Recognition of the Indian Regional Navigation Satellite System (IRNSS)

Submitted by India

SUMMARY

Executive summary: This document provides further information and detailed data on the Indian Regional Navigation Satellite System (IRNSS) including system performance, capability, testing and application for consideration by the Sub-Committee

Strategic direction,

if applicable:

2

Output: 2.9

Action to be taken: Paragraph 22

Related documents: Resolution A.915(22); MSC 96/25; NCSR 4/29; NCSR 5/5, NCSR 5/5/1, NCSR 5/WP.1; NCSR 6/23 and MSC 101/24

Background

1 The Maritime Safety Committee, at its ninety-sixth session, considered document MSC 96/23/8 (India), proposing to recognize IRNSS as a future component of the World-Wide Radio Navigation System (WWRNS) and develop performance standards for shipborne IRNSS receiver equipment, and agreed to include, in the 2018-2019 biennial agenda of the NCSR Sub-Committee and provisional agenda for NCSR 5, an output on "Application of the Indian Regional Navigation Satellite System (IRNSS) in the maritime field" with a target completion year of 2019.

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2 NCSR 5 reviewed India's proposal for IMO to recognize IRNSS as a component of WWRNS. The Sub-Committee considered document (NCSR 5/5) providing the description of IRNSS along with the draft performance standards for shipborne IRNSS receiver equipment (NCSR 5/5/1). The Sub-Committee, having noted the general support expressed, invited India to provide further information and detailed data to NCSR 6. NCSR 5 considered the proposal by India (NCSR 5/5/1) on draft performance standards for shipborne IRNSS receiver equipment and, after some consideration, approved them. In doing so, the Sub-Committee invited IEC to consider the development of related test standards.

3 During the deliberations at NCSR 6, the delegation of India advised that they had not

been in a position to meet the deadline for submission of documents to NCSR 6, and that

appropriate information, in accordance with the requirements, would be submitted to MSC 101

and NCSR 7. After consideration and in view of the information provided by India, the

Sub-Committee invited the Committee to extend the target completion year for this output

to 2020.

4 Accordingly, detailed information was provided by India to MSC 101, as an

information document, encompassing the IRNSS system description, system service

capability, system testing and system application along with relevant references/website links.

An identical document is now submitted to NCSR 7 for its consideration.

Introduction

5 IRNSS is an independent regional navigation satellite system developed and operated by India. It is compatible and inter-operable with other existing global radionavigation systems. It may be noted that IRNSS is also termed as NavIC (Navigation with Indian Constellation). 6 The space segment and the ground control segment are in stable working condition and their service performance meets the design requirements as indicated by various user terminal tests and assessment.

7 For the purpose of promoting wide application of IRNSS and to encourage the research and development of IRNSS terminal by enterprises, its space signal Interface Control Documents (ICDs) were officially released in 2014 into the public domain https://www.isro.gov.in/sites/default/files/irnss_sps_icd_version1.1-2017.pdf. Using the ICD information, IRNSS receivers have been produced by enterprises and deployed for positioning, navigation and timing applications in India. System description 8 IRNSS is composed of three components: space segment, ground control segment and user segment. 9 The space constellation consists of three GEO satellites, positioned at 32.5° E, 83° E and 129.5° E, respectively and four IGSO satellites deployed two each at 55° E and 111.75°E orbital slots with an inclination of 29°. This geometry ensures a minimum of five satellites visible to the users in the primary coverage area. 10 The ground control segment consists of Navigation Centres (NC), Uplink Stations (US), a network of geographically distributed Ranging & Integrity Monitoring Stations (RIMS) and CDMA Ranging Stations (CDR) with sufficient redundancies. The main tasks of NC are to collect observation data from each RIMSs and CDRs, to process range data, differential and

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


integrity data, to generate satellite navigation messages, to perform mission planning and scheduling, and to conduct system operation and control. Satellite navigation messages and the commanding operations for payload control and satellite bus management are uplinked from Uplink Stations. The tasks of RIMSs and CDRs are to receive the continuous tracking and monitoring information from the navigation satellites including navigation signals and send the observation data to the Navigation Centres for the satellites orbit determination and time synchronization. 11 The user segment includes various types of IRNSS user terminals to meet different application requirements in various fields and industries. 12 The IRNSS time is traced to Universal Time Coordinated (UTC). The difference between UTC and IRNSS time remains less than 100 ns. 13 The coordinate framework of IRNSS is WGS-84. System service capability

14 IRNSS provides positioning, navigation and timing services for an unlimited number of users in its service area.

Main functions: Positioning and velocity determination, timing;

Service Area: Regional (55° E Longitude, 50° N Latitude and 110° E Longitude and 5° S Latitude);

Positioning accuracy: 20 m Timing accuracy: 100 ns.

15 Currently, the IRNSS open service performance standards are as follows:

Positioning accuracy: 10 m Timing accuracy: one-way 50 ns.

System testing

16 India has carried out user application tests using vehicle-borne, shipborne and airborne application platforms to measure and assess the IRNSS service performance. Results show that the system performance is better than the design specifications. 17 Details of the IRNSS system performance are provided for the reference of the Sub-Committee. The system performance of IRNSS over the Indian region is given in annex 1 and the system performance of IRNSS over the oceanic region is given in annex 2. System application

18 Various user application platforms leveraging the IRNSS navigation and messaging capability have been developed. Subsequent to successful trials, IRNSS is being gradually adopted by industries and public services such as transportation, land survey and mapping, weather forecasting, marine fisheries, deformation monitoring, search and rescue, vehicle navigation and smart phones, yielding tangible economic and social benefits. 19 Chipsets supporting a variety of IRNSS-derived applications are now available or are under development. These include multi-chip modules (MCM's), single-chips and system-on-chip (SoC) variants. These are developed and being marketed by various industries in IRNSS-only

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and hybrid multi-GNSS including IRNSS versions. They are finding usage in devices such as vehicle trackers, railway information systems, shipborne monitoring/fleet management, etc. Chipsets have been successfully demonstrated to receive IRNSS signals from two mobile phones and more are under development to further permeate this application segment.

20 IRNSS has been accepted by 3rd Generation Partnership Project (3GPP) as a work item under release 16 as a part of the Assisted GNSS Specification. 3GPP unites international telecommunications standard development organizations and develops protocols for cellular telecommunications technologies.

21 For including IRNSS in Radio Technical Commission for Maritime Services (RTCM) Special Committee-104(SC-104) standard for Differential Global Navigation Satellite System (D-GNSS) applications, RTCM formed a 15-member Working Group on the Indian Regional Navigation Satellite System (IRNSS) during RTCM, SC-104 meeting in May 2018 in Harbin, China. The results of IRNSS Signal Interoperability testing were approved by the SC-104 Plenary Meeting held in Trondheim, Norway, on 23 and 24 September 2019. The proposal is expected to be put up for voting at the next SC-104 plenary meeting in January 2020 for the inclusion of IRNSS messages into the RTCM 3.X standard. Action requested of the Sub-Committee 22 The Sub-Committee is invited to:

.1 consider the information contained in this document; and .2 recommend the recognition of the IRNSS as a component of the World-Wide

Radionavigation System (WWRNS) to the Committee.

***

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

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46

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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)

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