Concept of Multi Regional Satellite for Increasing Accuracy in GNSS

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Preliminary Design-Concept of Multi Regional Satellite for Increasing Accuracy in GNSS (Precise Point Positioning) Conference Paper · September 2017 CITATIONS

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IAC-17-F1.2.3 Preliminary Design-Concept of Multi Regional Satellite for Increasing Accuracy in GNSS (Precise Point Positioning) Pratiwi Kusumawardani*a, Oniosun Temidayo Isaiahb, Yasith Ramawickrama c, Leila Ghasemzadehd, Stephanie Wane, Prabin Gyawalif, Siddesh Naikg, Vincenzo Capuanoh a

YGNSS (Space Generation Advisory Council), c/o European Space Policy Institute, Schwarzenbergplatz 6, 1030 Vienna, Austria, pratiwi.k10@gmail.com, b YGNSS (Space Generation Advisory Council), c/o European Space Policy Institute, Schwarzenbergplatz 6, 1030 Vienna, Austria, temidayo.isaiah@spacegeneration.org, c YGNSS (Space Generation Advisory Council), c/o European Space Policy Institute, Schwarzenbergplatz 6, 1030 Vienna, Austria, yasith.lakmal@spacegeneration.org, d YGNSS (Space Generation Advisory Council), c/o European Space Policy Institute, Schwarzenbergplatz 6, 1030 Vienna, Austria, Leila_qasemzade@yahoo.com, e YGNSS (Space Generation Advisory Council), c/o European Space Policy Institute, Schwarzenbergplatz 6, 1030 Vienna, Austria, Stephanie.Wan@spacegeneration.org, f YGNSS (Space Generation Advisory Council), c/o European Space Policy Institute, Schwarzenbergplatz 6, 1030 Vienna, Austria, prabngyawali@gmail.com, g YGNSS (Space Generation Advisory Council), c/o European Space Policy Institute, Schwarzenbergplatz 6, 1030 Vienna, Austria, siddhesh.naik@spacegeneration.org

Abstract The use of GNSS is ever increasing for such various applications as science, weather monitoring, precise military and civil position or mass market applications. Its impact in the economic and technological development is evident in its numerous applications. The use of GNSS for safety of life applications or as a means of navigations for drones or automatic vehicles calls for higher performances, especially in accuracy and integrity.

As the non-GPS navigation systems develop, the international cooperation between providers becomes more relevant as a way to increase the accuracy, continuity, availability and integrity of the overall GNSS service. The interaction between GNSS systems to improve the performances at user level could be classified in two main categories: augmentation systems (as in WAAS or EGNOS) which interacts at a system level and Interoperability (as in the combined use of GPS and Galileo), which interacts at user level.

Increasing the number of systems through interoperability reduces the impact of perturbations such as ionospheric effects, signal scattering, tropospheric delay, etc. Augmentation systems can reduce satellite orbit and clock error as well as most of the errors mentioned before. Certain regional systems are certified to be used in SoL applications, enhanced capabilities like this one can only be achieved by GNSS with the assistance of a regional system.

This paper aims at analysing the existing regional GNSS and estimate the impact they have over their coverage regions. Such an analysis will help set some guideline for trade-offs in future potential regional systems.

Keywords: GNSS, Navigation, Satellite, Precise Point Positioning Acronyms/Abbreviations GNSS – Global Navigation Satellite System; GPS – Global Positioning System; WAAS - Wide Area Augmentation System; EGNOS – GBAS – Ground Based Augmentation System; SBAS – Space Based Augmentation; ECEF – Earth-Cantered Earth-Fixed; RTK – Real Time Kinematics; WARTK – Wide Area RTK; FAS – Final Approach Segment;

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VHF - Very High Frequency; VDB - Data Broadcast; FAA - Federal Aviation Agency; WRS - Wide-area Reference Stations; WMS - WAAS Master Stations; GUS - Ground Uplink Stations; GEO Geosynchronous Communication Satellites; IOC - Initial Operating Capability;

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1. Introduction Navigational Satellite System work based on positional data, and its need accuracy. All data that given to the receiver can be an inaccurate data with several meters or more. This inaccurate can caused a bad effect for many situation.

Few country start to make their own navigational system, such as India and Japan, and this might be one of the solutions to minimize inaccurate data. This paper aim to analyse if the regional system can be the solution to minimize the inaccurate data by seeing the effect of existence of the regional navigational satellite system to global navigation satellite system. This is just the preliminary design concept how to do research further.

With the lower cost than global navigational system, each country has higher chance to make a collaboration to accuracy of the navigational system. That is the how we need to start Preliminary Design-Concept of Multi Regional Satellite for Increasing Accuracy in GNSS. 2. Material and methods Relative static positioning used several stationary receivers simultaniously and collecting data during observation. It should be minimum four satellites visible, and the sky has no obstructions. The geometry and number of staellite also important in this method.

Data of Navigation Satellite System can improve receiver performance and reduce the processing process on the receiver. Management of the load processing is also important. Besides, a netwrok assisted system, such a period validity is useful in this method, especially if the receiver has difficult obrstruction that make tracking gaps and make an incomplete navigation data from the satellites.

3. Theory and calculation 3.1 Global Positioning System (GPS) Global Positioning System (GPS) is a global navigation satellite systems with 24 satellite in the constellation. This system provide 24 hours and 7 days services with the coverage worldwide. Its also provide Standard Positioning Service and Precise Positioning Servuce for military use.

A GNSS augmentation system aims at “augmenting” the navigation system’s performance by using external information to the standalone GNSS into the user position solution [1]. Indeed, the achievable positioning accuracy is limited by different kind of errors affecting

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the GNSS observations. Among several sources of error, an augmentation system, also known as “Differential GNSS”, compensates for errors in the transmitters ‘clock and ephemeris and for the signal delays caused by the atmosphere.

A GNSS augmentation system uses earth reference stations, the location of which is known with very high precision.

The precisely known location is compared with a GNSS-based positioning solution and the resulting difference is used to compute corrections, which are transmitted to the user (a GNSS receiver) via geostationary satellites or terrestrial radio.

A ground based augmentation system (GBAS) makes use of terrestrial radio towers for the transmission, while a space based augmentation (SBAS) system uses orbiting satellites.

In a SBAS, Geostationary satellites are used to provide local coverage: since they are fixed in the Earth-Centered Earth-Fixed (ECEF) and then rotate with the Earth, they transmit the corrections always to the receivers located in their coverage area. SBAS system provide services also for improving GNSS integrity and availability. The integrity is enhanced by sending alerts to the receivers about satellite signals errors and satellites the receiver should not track. Also the availability can be improved if the satellites of the SBAS transmit ranging signals. A SBAS system include reference stations, uplink stations and satellites [2]. The reference stations are distributed in a precisely known location in the SBAS service area to receive the GNSS signals and forwarding them to the master stations, where the wide-area corrections are accurately calculated and uplinked to the SBAS satellites. The SBAS satellites then, broadcast the corrections to the GNSS receivers in their coverage area. The user GNSS receiver located in the SBAS coverage area and in the SBAS service area (where the reference stations are distributed), applies the correction to the range calculations [2]. Different methods can be adopted, whether for the computation of the augmentation information, the accuracy improvements use a dense network of reference stations (Differential GNSS, Real Time Kinematics (RTK) or Wide Area RTK (WARTK)) or just a few stations (Precise Point Positioning (PPP)) [1].

Ground-Based Augmentation System (GBAS) aim essentially at enhancing GNSS service levels for aviation, during approach, landing and departure phases, and to support surface operations. They provide a limited local service coverage (e.g. the surroundings of

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an airport). Their primary goal of GBAS is to provide integrity assurance for safety, although it also increases the accuracy to the sub-meter level (1 sigma) [1].

GBAS infrastructure includes two or more GNSS receivers that collect GNSS observations for the GNSS satellites in view. By means of observations collected on the surveyed position by two or more receivers, differential corrections and integrity-related information (pseudo range corrections, integrity parameters and various locally relevant data such as Final Approach Segment (FAS) data) are computed and broadcasted transmitted from the ground system via a Very High Frequency (VHF) Data Broadcast (VDB).

Both GBAS and SBAS are used to increase safety for civil aviation; the main difference is that GBAS provides local corrections to the GNSS observations (pseudo ranges) adopting only ground infrastructure in the vicinity of the served airport, while SBAS broadcasts corrections valid for an area as big as a continent. The much larger service area of the SBAS, is possible thanks to a much larger number of earth stations in the augmented area and two or more geostationary satellites [1].

Inertial sensors can be considered another form of augmentation system useful for an autonomous vehicle that does not have access to differential corrections, mostly for adding robustness in presence of interference. Inertial sensors in combination with wheel sensors and magnetic compass (usually integrated by using a Kalman filter) are used to provide navigation when the satellite signals are blocked in urban canyons (i.e., city streets surrounded by tall buildings) [3].

SBAS in US The Wide Area Augmentation System (WAAS) is the United States SBAS. Its development, started in 1992, carried out by the Federal Aviation Agency (FAA), specifically conceived for the civil aviation community. Today WAAS, officially operational since 2003 [4], supports thousands of aircraft approaches phases in more than one thousand airports in USA and Canada [5]. As well as US, WAAS service area also includes CONUS, Alaska, Canada and Mexico [6].

WAAS is used to provide improved integrity, accuracy, availability, and continuity of service, specifically to the GPS Standard Positioning Service (SPS) for the Civil Aviation community, by providing a signal-in-space to WAAS users (all aircraft with approved WAAS avionics) for all phases of flight, in particular, for the precision approach. The WAAS is a safety-critical system.

In addition, the WAAS GEO satellites have ranging capabilities, and therefore can provide an extra GPS observation to enhance the navigation performance.

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WAAS signals broadcast augmentation information that corrects GPS ephemeris and ensures the integrity.

Currently, WAAS supports the following flight procedures [7]: LNAV (Lateral Navigation).

LNAV/VNAV (Lateral Navigation/Vertical Navigation).

LP (Localizer Performance).

LPV (Localizer Performance with Vertical guidance).

The main parts of WAAS architecture are: WAAS Ground Segment. It includes: reference stations (Wide-area Reference Stations, WRS) positioned with high precision to collect the signals transmitted by the GPS satellites, master stations (WAAS Master Stations, WMS) that receive and process the observations collected by the WRS to build the augmentation message containing the corrections to the GPS data, uplink stations (Ground Uplink Stations, GUS) to transmit the augmentation message to the Space segment, and operational centers.

WAAS Space Segment. It is composed of multiple geosynchronous communication satellites (GEO) that broadcast the WAAS augmentation messages (provided by the WMS) to the User segment.

WAAS User Segment. Typically any aircraft with approved WAAS avionics.

According to the official document “GLOBAL POSITIONING SYSTEM WIDE AREA AUGMENTATION SYSTEM (WAAS) PERFORMANCE STANDARD” [8], the WAAS service area is divided in five coverage zones: Zone 1: CONUS. Zone 2: Alaska.

Zone 3: Hawaii.

Zone 4: Puerto Rico and some other Caribbean islands.

Zone 5: US territory excluding zones 1 to 4.

The coverage includes volume covered up to 100.000 feet above the surface.

The WAAS Development Phases are [9]: Phase I: Initial Operating Capability (IOC).

Completed in 2003.

Phase II: Full LPV Performance. Completed in 2008.

Phase III: Full LPV-200 Performance. Planned for 2009-2013.

Phase IV: Dual Frequency Operations. Planned for 2014-2028.

The WAAS programme then, is still evolving towards a dual-frequency augmentation service [7].

GBAS in US The current GBAS approved by FAA only augment the GPS L1 C/A broadcast. The US version of GBAS

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was initially corresponding to what is known Local Area Augmentation System (LAAS). GBAS supports navigation and more particularly precision approach operations within 23 nautical miles from the reference point (typically located within three nautical miles of all supported airport runways). An accuracy better than 1meter has been demonstrated using GBAS in both vertical and horizontal directions. GBAS is the only satellite-based navigation system for Category II/III precision approach operations that allows low visibility operations to touchdown and rollout [10]. Honeywell, is the first and currently only GBAS manufacturer to certify CAT I operations by the FAA in the U.S., as well as in Germany’s national authority (BAF), Spain’s national authority (AENA) and Civil Aviation Safety Authority (CASA) in Australia [11]. GBAS is available for most new commercial aircrafts, including as Boeing 737-NG, 747-8 and 787 and Airbus A320, A330/340, A350, and A380 [10].

3.2 European Geostationary Navigation Overlay Service (EGNOS) Europe ventured into satellite navigation to improve on the America’s Global Positioning System (GPS) by developing the European Geostationary Navigation Overlay Service (EGNOS). EGNOS makes GPS suitable for safety critical applications such as flying aircraft or navigating ships through narrow channels.

Known as a satellite-based augmentation system (SBAS), EGNOS provides both correction and integrity information about the GPS system, delivering opportunities for Europeans to use the more accurate positioning data for improving existing services or developing a wide range of new services. It improves the accuracy of GPS by providing a positioning accuracy to within three metres (GPS receivers without EGNOS can only have an accuracy within 17 metres) and provides warning when its data or system should not be used for navigation.

Band congestion could be a problem for accuracy, for example, most of the existing and planned GNSS are using the L band (1 - 2 GHz), which thus becomes more and more congested. With the increase of global satellite navigation systems (GNSS) in a limited number of frequency bands, the current spectrum dedicated to satellite navigation encounters congestion. A possible path to keep modernizing the different GNSS is to find new frequency bands where a satellite radio navigation service (RNSS) could be provide. The European Union and the United States had negotiated an agreement for a new modulation of the modernised GPD and Galileo signals to ensure compatibility and interoperability between the two systems and few bands like S-band (2 4 GHz) and C-band (4 - 8 GHz have previously been considered.

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The European Geostationary Navigation Overlay Service (EGNOS) provides an augmentation signal to the GPS standard positioning service. The EGNOS signal is transmitted on the same signal frequency band and modulation as the GPS L1 (1575.42 MHz) C/A civilian signal function. While the GPS consists of positioning and timing signals generated from spacecraft orbiting the Earth, thus providing a global service, EGNOS provides correction and integrity information intended to improve positioning navigation services over Europe. The main objective of the EGNOS safety-of-life service is to support civil aviation applications up to localizer-performance-with-verticalguidance operations; alongside this, it delivers an open service, a safety-of-life service and a commercial service.

On October 2009, EU declared the EGNOS open service ready, demonstrating the maturity of the development and qualification of EGNOS. For several years now, the EGNOS signal, of excellent quality, has been transmitted over Europe, allowing accuracies of between 1m and 2m, with an availability greater than 99 per (after augmentation of GPS by EGNOS). EU has since then been advertising the availability of their wellperforming service at no cost; the open service is accessible by any user equipped with a receiver that is compatible with GPS satellite-based augmentation systems within the EGNOS open service area in Europe.

No authorization or receiver specific certification is required to access and use the EGNOS open service, which opens the doors for GNSS receiver manufacturers and GNSS application developers to fully tailor the use of the EGNOS signal according to their needs and to benefit from the performance improvements provided

by EGNOS at no additional cost. Safety-of-life service.

Since 2010, EGNOS safety-of-life service has been available for use in civil aviation applications, in particular for “en route to non-precision approach” and “vertical guidance approach” operations.

The EU has been improving EGNOS real time (including satellite clocks and ephemeris corrections, propagation corrections and integrity information in the format of satellite-based augmentation systems); and raw data from the network of ranging integrity monitoring stations in real time (including highprecision satellite pseudorange measurements). Those products are accessible via the EGNOS Data Access Service.8 The EGNOS Commercial Data Distribution Service makes it possible to generate EGNOS postprocessed products (to be provided through specific service providers connected to the EGNOS data server) in real time (including high-rate propagation corrections, EGNOS availability warnings, internal monitoring data, performance information, etc.)

Performance and extending the geographic coverage of EGNOS services for all modes of transport, including

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maritime and land based vehicles that might require more stringent augmentation requirements. Commercial service 3.3 Globalnaya Navigazionnaya Sputnikovaya Sistema (GLONASS) GLONASS is Russian Navigation Satellite System with the coverage worldwlide or global. It launched in 1982 for the first time. GLONASS provides standard precision (SP) navigation signal and a high precision (HP) navigation signal sevices.

The accuracy of GLONASS horizontal positioning accuracy within 5–10 meters, vertical positioning within 15 meters. GLONASS ground segment consisting sytem control centre, fie telemetry tracking and command centers, two laser ranging stations, and monitoring and measuring stations.

3.4 Indian Regional Navigation System (IRNSS) IRNSS (Indian Regional Navigation System) is one of the successful regional navigation system. It has many purpose and application from the satellite constellation system. For example, Terrestrial, Aerial and Marine Navigation Disaster Management, Vehicle tracking and fleet management, Integration with mobile phones, Precise Timing, Mapping and Geodetic data capture.

This constellation had 7 satellites (IRNSS-1A, IRNSS-1B, IRNSS-1C, IRNSS-1D, IRNSS-1E, IRNSS1F, IRNSS-1G). Three satellites in Geo Stationary orbit at 32.5°, 83° and 131.5°East 4 Satellites in GEO Synchronous orbit at inclination of 29° with Longitude crossing at 55° and 111.75°Eastmwith accuracy of 20 meter in India areas.

IRNSS has been operated for civilian and military purpose. Its architecture including User Segment, Space Segment anad also Ground Segment. The User Segment also known as ground segment has a function to controlling and monitoring the performance of its satellites. And The Space segment is the detail of how many satellite on the constellation. The exact position of the satellite on orbit, its including the orbital parameter, and signal of the satellite.

The signal system using 1176.45 MHz in L5 band

(1164.45 to 1188.45 MHz) and another with 2492.08 MHz in S band (2483.5 to 2500 MHz). The signal transmitted by Helix array antennas 3.5 QZSS The QZSS covers Asia and Pacific region. Signals by the first QZSS Satellite (QZS-1) contain L1C/A, L1C, L2C and L5, L1S (L1-SAIF) on 1575.42 MHz L6 (LEX) on 1278.75MHz (L1Sb is expected to be added as SBAS from 2020’s). The first QZSS satellite is Michibiki, and the total number of the satellite is four, with 3 QZ orbit and 1 geostationary orbit.

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According to relative positioning simulation, the navigation by QZSS could obtain a horizontal accuracy of 10 m or better and vertical 14 m or better with moderate user range (Yamad et. al. 2012) The path loss of QZSS varied by 1.5dB because of eccentricity of orbit compared to GPS (Hanschild et.al 2012). Regional Orbits and clocks for real-time PPP solutions using would be generated and delivered through the QZSS LEX signal (Harima et.al 014) The achievable performance of GPS augmentation using QZNSS were obtained using software simulation in 2004. The simulation analysis indicated that QZNSS does not only effectively increase the availability accuracy of GPS but also improve the reliability of GPS positioning in Japan and neighbouring area (Wu et.al 2004).

3.6 REGIONAL NAVIGATION SYSTEM REGULATIONS 3.6.1 GPS According to Obama's 2010 National Space Policy; the key elements of this policy are to maintain free global civil access to the GPS, encourage compatibility and interoperability with foreign GNSS systems and invest in resiliency measures for GPS as well as relevant backup systems. it is the belief of the US GPS provider that as long as it continues to provide signals to users free of charge than it will not bear any international liability for issues relating to faulty service. It is possible that liability may attach for claims that arise in the use and are brought in the US court under the US Federal Tort Claims Act (FTCA).

3.6.2 GALILEO AND EGNOS Galileo was initially structured to be managed and operated as a Public-Private Partnership (PPP), to allow financing by both private and public funds. However, after the PPP efforts failed, it was decided in 2008 to finance the system entirely by public funds. Within the European Union, each member State is responsible for its own spectrum activities, although European bodies such as the European Conference of Postal and Telecommunications Administrations (CEPT), the European Telecommunications Standards Institute and the European Union ensure a good degree of spectrum harmonization, standardization and cooperation. The RNSS spectrum is managed by the relevant national authority of each country and there is coordinated, but no common, management of the RNSS spectrum at the European level. In the cases of Galileo and EGNOS, the European Union, as programme manager, has been given the authority to negotiate frequency matters, as well as compatibility and interoperability agreements with relevant international partners. The European Union is supported in this by the national administrations in Europe.

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3.6.3 GLONASS According to the concept of international cooperation in the area of GNSS and augmentation system, GLONASS implies special importance and responsibility of Russia, thus underscoring its increasing role in solving issues of the global sustainable development. International cooperation of Russia is targeted at promoting competitiveness of GLONASS in the world market, expanding its use all over the world and providing for its compatibility and complimentarily with other GNSS. The international legal base of international cooperation of Russia on GNSS consists of cooperation agreements (with Brazil, India, Ukraine etc.) memoranda of understanding with the People Republic of China, joint use and development of GLONASS with USA and deployment of DCMS reference stations on a mutual basis. Special attention is given to the prospective implementation of the ERAGLONASS system (Belarus and Kazakhstan), joint ventures (Venezuela, South Africa, turkey and others), reduction of user navigation equipment and other GLONASS-based competitive products in Russia and abroad.

3.6.5 IRNSS Regulation Even though IRNSS is strategically important to India, no dedicated legal framework exists governing use of the system. Although India has ratified all major international space treaties, including the 1967 Outer Space Treaty, 1968 Rescue Agreement, 1972 Liability Convention, and 1975 Registration Convention, no specific laws regulate the country’s space activities.

However, India’s Constitution, Article 51, provides the foundation for implementing obligations arising from the international space treaties. Currently, India’s space policy framework mainly consists of two documents, the 2000 SATCOM policy and the 2011 Remote Sensing Data Policy (RSDP). However, neither are applicable to satellite navigation.

3.6.6 BeiDou The BeiDou system is able to provide four types of services; open, authorized, wide area differential and short-message services. The positioning accuracy more accurate than 10 meters (the positioning accuracy is better than 5 meters in regions with low geographic latitude), the timing accuracy surpass 20 nanoseconds and the velocity accuracy is faster than 0.2 meters per second. The BeiDou system has been the subject of several international agreements relating to bilateral and multilateral cooperation, cooperation on applications, international standardization and technical exchanges.

The project committee on China-Russia GNSS cooperation has been founded and the first bilateral round table meeting on GNSS cooperation has been

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held. The MOU on China-Russia cooperation in the field of satellite navigation has been signed. The onsite survey has been completed including GLONASS ground station in China and BeiDou ground stations in Russia, and the Joint Statement on Compatibility and Interoperability has also been released. The first bilateral meeting of the China-US, civil GNSS cooperation has been held. The cooperation mechanism between BeiDou and GPS has been established, and the Joint statement between these two systems have been signed. The frequency coordination towards navigation frequency channel between BeiDou and GALILEO has been completed.

3.7. PPP Precise point positioning (PPP) is a global navigation satellite system (GNSS) positioning method to calculate precise positions at centimetre- or even millimetre-level accuracy with a single GNSS receiver using precise satellite orbit and clock products. Over the past decades, PPP using Global Positioning System (GPS) has been proved as an effective approach for the measurement of arbitrarily large ground motions and seismic displacements induced by earthquakes.

BeiDou Navigation Satellite System (BDS) began to offer positioning, navigation, and timing services in the Asia-Pacific region at the end of 2012. It is aimed at serving global users upon its completion by 2020. Many studies have been conducted to investigate the performance of BDS precise positioning. With three geostationary Earth orbit (GEO) and three inclined geosynchronous orbit (IGSO) satellites, Shi et al. demonstrated that precise relative positioning at an accuracy of 1–2 cm in horizontal and 4 cm in vertical components can be obtained in short baseline mode (~436 m). Montenbruck et al. presented an initial assessment of the positioning performance of BDS. Using BDS observations, they showed that the accuracy of BDS kinematic relative positioning was comparable to that of GPS kinematic positioning, exhibiting a root mean square (RMS) of 3, 3, and 6 mm in the east, north, and vertical components, respectively.

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Table 1: Details about the satellite systems Meanwhile, intensive attention is also paid to PPP with BDS-only observations. Li et al. and Xu et al. realized static and kinematic PPP at centimetre-level accuracy by using BDS observations at a sampling interval of 30 s. Zhao et al. assessed the contributions of BDS GEO, IGSO, and medium Earth orbit (MEO) satellites to PPP in Asia-Pacific region. By using various combinations of different satellite constellations, they showed that BDS IGSO has the largest contribution to the acceleration of convergence and improvement of positioning accuracy to PPP, particularly in the east component. Recently, Li et al. presented that the real-time BDS PPP mode with an accuracy of 5 cm in horizontal and 10 cm in vertical components could be obtained after 3 h convergence.

Moreover, BDS has played an important role in high-precision applications, such as the derivation of the zenith tropospheric delay and the capture of seismic waves. Geng et al. first used 1 Hz BDS observations to measure ground motions induced by the 2015 Mw 7.8 Gorkha, Nepal earthquake. They employed the variometric approach to estimate the velocity time series and to reconstruct displacements by integrating the velocity time series. A novel approach of a linear trend removal was performed to minimize long-period drifts due to mismodeling of different intervening effects during integration to displacements. However, none of the previous studies has been conducted on the monitoring of seismic displacements/waveforms using the BDS PPP approach. With the BDS PPP approach, the seismic displacements are able to be derived directly. As a consequence, the procedure of integration, a requirement of the variometric approach, is successfully circumvented.

The availability of precise satellite orbit and clock products is of great importance to the realization of PPP. For the GPS constellation, the International GNSS Service (IGS) is able to routinely provide final products containing satellite orbits and clocks with an accuracy of ~2.5 cm and ~75 ps, respectively. With the advent of new GNSS constellations such as BeiDou, Galileo, Quasi-Zenith Satellite System (QZSS), and Indian Regional Navigation Satellite System (IRNSS), the IGS has initiated the Multi-GNSS Experiment (MGEX) project to pave the way for the provision of high-quality data and products for all GNSS constellations. At present, there are three MGEX Analysis Centers (ACs) providing the final satellite orbit and clock products of BDS (i.e., Center for Orbit Determination in Europe (CODE), Geo Forschungs Zentrum Potsdam (GFZ), and Wuhan University (WHU)). It is worth noting that CODE only provides the final products of IGSO and

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MEO. GFZ has been providing 5 min orbit and 30 s clock products instead of 15 min orbit and 5 min clock products since 3 May 2015.

System GPS

EGNOS

Accuracy (meters) 17

GLONASS IRNSS

16 horizontal 20 vertical 3 20

BeiDou

5

QZSS

10 horizontal 15 vertical

Integrity

Coverage

1x10-5 Probability Over Any Hour 2e-7/150s

Global

Global

Global India region China region Asia and Pacific region

4. Results Regional Navigation Satellite System can increase the accuracy of global navigation. Its also cheaper than make global navigation system, so many country have posibilities to make it.

Specific regulation of the Satellite Navigation System still not exist in many countries, while communication regulation alreadly exist.

5. Discussion All the research in this paper only by study literatur method, it will be better if there is further research that include the simulation. The simulation can start by combine few satellite constellation and see the acuracy and any other performance factor.

6. Conclusions Regional Navigation Satellite System is important, and the research on this should be increasing because it will effect the performance of global regional navigation system.

Acknowledgements This work was supported by the Space Generation Advisory Council (SGAC) the project group of YGNSS. References [1] GMV, GNSS Augmentation, 3 Sepetember 2017, http://www.navipedia.net/index.php/GNSS_Augmen tation. [Accessed 3 September 2017].

[2]

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[11] Honeywell.,https://aerospace.honeywell.com/en/pro ducts/navigation-and-sensors/smartpath-groundbased-augmentation-system. [Accessed 3 September 2017].

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