LEO PNT panel
1.           Dr. Alexander Mitelman (USDOT) (in-person)
2.           Mr. Patrick Shannon (TrustPoint) (remote)
3.           Mr. Bryan Chan (Xona Space) (remote)
4.           Mr. Pietro Giordano (ESA) (remote)
5.           Dr. Daehee Won (KARI) (remote)
6.           Dr. Yoji Takayama (Furuno Electric) (in-person)
7.           Dr. Masaya Murata (JAXA) (in-person)

Lunar PNT panel
1.           Mr. Joel Parker (NASA) (remote)
2.           Dr. Javier Ventura-Traveset (ESA) (remote)
3.           Ms. Cheryl Gramling (NASA) (remote)
4.           Mr. Ricardo Verdeguer Moreno (Spirent) (in-person)
5.           Dr. Jung Min Joo (KARI) (in-person)
6.           Dr. Ashish K Shukla (ISRO) (remote)
7.           Ms. Siliang Yang (DSEL) (remote)
8.           Dr. Masaya Murata (JAXA) (in-person)

These panelists are all representing lunar PNT and LEO PNT fields. For details on in-person and online participation, visit the MGA2025 conference homepage and view the program agenda here.

The post The 15th Multi-GNSS Asia Annual Conference to Feature Lunar PNT and LEO PNT Panels appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

THIERRY AUTHIÉ, GUILLAUME COMELLI, SÉBASTIEN TRILLES, THALES ALENIA SPACE, TOULOUSE, FRANCE BYUNGSEOK LEE, MINHYUK SON, KOREA AEROSPACE RESEARCH INSTITUTE, REPUBLIC OF KOREA CHEON SIG SIN, ELECTRONICS AND TELECOMMUNICATION RESEARCH INSTITUTE, REPUBLIC OF KOREA

The Korean Augmentation Satellite System (KASS) is a satellite-based augmentation system (SBAS) developed by the Republic of Korea (South Korea) to augment the functionality of the Global Positioning System (GPS) in the Korean Peninsula and the surrounding regions. KASS was designed to enhance the accuracy and reliability of GPS signals within the country. In aviation, it enables more precise and reliable navigation for aircraft, supporting instrument approach procedures and improving operational efficiency.

A SBAS is a Global Navigation Satellite System (GNSS) augmentation system standardized in the International Convention on Civil Aviation SARPS Annex 10 [1], Volume 1, published and maintained by the International Civil Aviation Organization (ICAO). KASS provides safety-critical services for civil aviation, up to Approach with Vertical Guidance 1 (APV I ) service level, as well as an open service usable by other forms of transportation and possibly other position, navigation and timing (PNT) applications.

The KASS system provides improved GNSS navigation services for suitably equipped users in the agreed service areas of the Republic of Korea by broadcasting an augmentation signal of the GPS Standard Positioning Service (SPS).

To ensure the smooth operation of the system, KASS includes a network of ground receiver stations dedicated to collecting GPS measurements, a set of ground processing stations responsible for monitoring and controlling the satellites, and a set of ground uplink stations managing the transmitted signals toward two Geostationary Earth Orbiting (GEO) satellites. These ground control stations accurately calculate the orbit and clock information of the satellites, as well as the mono frequency L1 ionosphere delay, and continuously update the transmitted signals accordingly.

One of the system’s key features is its ability to enhance the integrity and reliability of positioning information. KASS incorporates integrity monitoring functions to detect and alert users of any potential errors or anomalies in the GPS signals. This is crucial for safety-critical applications that require precise positioning data, such as aviation and maritime navigation.

The augmentation signal provides corrections of GPS satellites orbits and clocks and integrity bounds of orbit/clock residual errors, as well as corrections and integrity bounds for ionosphere delays. The KASS satellites transmit signals that are compatible with GPS, allowing KASS-capable receivers to seamlessly switch between GPS and KASS signals and to compute a navigation solution with greater accuracy.

The KASS system qualification was achieved by December 15, 2023, and safety of life aeronautical services have been fully operational since December 28, 2023. 

The current network of KASS Reference Stations (KRS) is composed of seven KRS sites all deployed on the Republic of South Korea land masses. Each KRS includes two independent channels based on NovAtel WAAS GIII receivers that provide GPS signal tracking and measurements. This concentrated network allows users to reach APV I service level but not more stringent service levels like the Category 1 (CAT 1) approach.

This article presents an analysis of a system upgrade to reach the CAT I service level based on representative synthetic data scenario. This analysis involves an extension of the KRS network and minor changes in the navigation algorithms.

KASS Services and Architecture

KASS is designed to provide performance-based navigation (PBN) aeronautical procedures, such as RNAV or RNP approaches, enable aircraft to fly along precise paths during departure, enroute and approach phases. PBN is a modern concept in aviation that uses satellite-based navigation technology and proposes a set of procedures that enhance operating efficiency, reduce flight distances, improve airspace capacity and enhance safety.

The KASS system is designed to ensure four safety critical service levels:

• Enroute continental over the Incheon FIR area. Flight segments after arrival at initial cruise altitude until the start of descent to the destination.

• Enroute terminal over the Incheon FIR area for descent from cruise to Initial Approach Fix. 

• NPA over the Incheon FIR area. For non-precision approaches in aviation, this instrument approach and landing uses lateral guidance but not vertical guidance.

• APV I over South Korea landmasses (including Jeju Island) for precision approaches with vertical guidance.

KASS will provide open service over Incheon FIR area. 

Figure 1 shows the KASS service areas.

The KASS system is designed to be a system-of-systems ensuring the following main functions [2-3]:

• Collect GPS data at various locations in the Republic of Korea (and possibly other states in the future) through Korea Receiver Stations (KRS).

• Compute corrections and associated integrity bounds from ranging measurements of GPS satellites in view of KASS, and format messages compliant with the SBAS user interface standardized in ICAO SARPS Annex 10 [1] and the RTCA MOPS 229-D Change 1 [4]. This function is ensured by the Korean Processing Stations (KPS).

• Uplink a signal carrying these messages to navigation payloads on the KASS GEOs with Korean Uplink Stations (KUS).

• Broadcast the signal to users after frequency-conversion to the L1 band.

The KPS is the core component of the KASS system responsible for computing orbit, clock, ionosphere corrections, and alert information below the Navigation Overlay Frame (NOF). It uses data from a set of reference stations, the KRS, to perform these calculations. The KPS consists of two independent elements known as the processing set (PS) and the check set (CS).

The PS is responsible for computing the complete navigation context for the GNSS constellation, including orbits, clocks and the ionosphere model. It then prepares and sends the NOF, which is broadcasted to users. The CS acts as a supervisory entity by applying the NOF to GPS messages, ensuring consistency with an independent set of measurements to maintain integrity and control.

The KPS-PS component plays a critical role in achieving high-performance levels, specifically for the APV I service level. APV I is a type of PBN approach that provides lateral and vertical guidance to aircraft during the approach and landing phase. APV I approaches typically use satellite-based augmentation systems like the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS) and now the Korean Augmentation Satellite System (KASS). These approaches provide accurate lateral and vertical guidance, allowing pilots to perform precision approaches with reduced reliance on ground-based navigational aids.

From APV I to CAT I Aviation Service for KASS

CAT I (localizer performance with vertical guidance 200) is another type of PBN approach that offers even higher precision and accuracy than APV I. CAT I approaches also use satellite-based augmentation systems like WAAS or EGNOS. With CAT I, the lateral and vertical guidance is provided by the aircraft’s flight management system, enabling pilots to fly approach paths that closely resemble traditional instrument landing system (ILS) approaches. CAT I approaches can provide the same level of guidance and minimums as Category I ILS approaches, with decision heights as low as 200 feet above the runway.

Both APV I and CAT I approaches provide increased flexibility, safety and efficiency compared to traditional ground-based navigation systems. They allow for greater access to airports in various weather conditions, reduce reliance on infrastructure, and enable more precise and efficient aircraft operations. These approaches have become increasingly popular and are being implemented worldwide to enhance flight safety and optimize airspace use.

Performance of a satellite navigation system can be expressed through Five Criteria: accuracy, integrity, continuity, availability and time-to-alert (TTA). The overall detailed performance specifications are depicted in Table 1.

Accuracy is the difference between the computed value and the actual value of the user position and time. Usually, accuracy is defined as the 95th percentile of the positioning error distribution.

The system TTA is defined as the time starting when an alarm condition occurs to the time the alarm is displayed in the cockpit. Time to detect the alarm condition is included as a component of integrity.

The alert limits are the maximum allowable error in the user position solution before an alarm is to be raised within the specific time to alert. This alert limit is dependent on the flight phase, and each user is responsible for determining its own integrity in regard to this limit for a given operation phase following the information provided by the SBAS SIS.

The integrity risk is the probability during the period of operation that an error, whatever the source, might result in a computed position error exceeding a maximum allowed value, called alert limit, and the user not be informed within the specific time to alert.

To display the integrity of the satellite corrections for each GPS satellite, the UDRE Safety Index is used to assess the integrity margin. The UDRE Safety Index is defined as the ratio . The Satellite Residual Error for the worst user location (SREW) was computed as the pseudorange error projection due to the remaining satellite ephemeris and clock errors, after KASS corrections were applied for the worst user location of the relevant service area. The relevant service area corresponds to the intersection of the service area and of the monitored satellite footprint.

Also, to display the integrity of the ionosphere corrections for each IGP, the notion of Grid Ionosphere Vertical Error (GIVE) Safety Index is used. The GIVE Safety Index is defined as the ratio , with the GIVE Error defined as the vertical pseudorange error at the considered IGP location due to the remaining ionospheric delay after applying the GIVE corrections.

Continuity defines the ability of a system to perform its function without interruption during the operation planned by the user (for example landing phase of an aircraft). It is evaluated as the probability that from the moment when the criteria of precision and integrity are completed at the beginning of an operation, they remain so for the duration of the operation.

Availability is the percentage of time when, over a certain geographical area, the criteria of accuracy, integrity and continuity are met.

Finally, the service area is the geographic zone where the SBAS shall provide service availability.

As depicted in Table 1, the major difference between CAT I and APV I is more demanding requirements in terms of vertical alarm limit and TTA, resulting in a reduction from 50m to 35m for the vertical protection level and from 10s to 6s for TTA.

The KASS system is designed according to the same architectural principles as the European EGNOS system, which complies with the CAT I service requirements concerning TTA. Therefore, all the elements justifying the TTA performance developed for the EGNOS system apply to the KASS system without any restrictions. This aspect is thus not considered a difficulty.

The main challenge in achieving the CAT I service level concerns the domain of vertical protection volume. Currently, KASS is compliant to APV I precision approach procedure but is limited for the achievement of CAT I service level due to the impact of ionosphere error estimation. With the low number of available measurements from only seven collocated stations, it results in very high integrity bounds (GIVE), which directly affects protection volumes in the vertical direction.

To overcome the limitation of the available measurement volume using only the contributions from the GNSS system, two steps are being considered.

The first step is to include new observables by incorporating measurements from the Galileo constellation into the ionosphere estimation algorithms. It should be noted that Galileo measurements are not incorporated into other navigation algorithms, meaning the system does not monitor the Galileo constellation or calculate any orbit or clock corrections for it.

The second step is to add stations outside of Korea, which would provide better observability in both the dynamics of ionosphere activity and orbit estimation. This addition of external stations would enhance the overall measurement coverage and improve the accuracy of the estimation process.

For all these assessments, fault-free synthetic data are used (analyzed September 3-5, 2002), allowing a first level of performance the KASS system may reach for the provision of CAT I approach service. The results are produced with the same set of KPS navigation algorithms.

CAT I Performances Reached with Introduction of Galileo 

The first extended configuration considers the introduction of Galileo measurements and the current KASS reference station network.

The simulations is realized with:

• Seven reference stations (Yangju, Gwangju, Jeju AP, Jeju TS, Yeongdo, Dodong and Yangyang).

• 27 GPS: for satellites and ionosphere monitoring.

• 24 Galileo: for ionosphere monitoring only.

The different cases presented indicate the availability of CAT I by monitoring the satellites from a minimum elevation angle of 5° with at least one station in the network, then at 10° and 15°.

This experimentation shows CAT I service level can be reached by introducing more observables for the ionosphere monitoring. Indeed, the availability at 99% is reached with the constraint of satellites monitored from 5° elevation by one station. 

First, these new measurements enrich the internal ionosphere model and then contribute to reduce the ionosphere correction errors.

However, because of the direct impact of the integrity bounds on the calculation of protection volumes, the most visible impact of these new measurements on achieving availability is their contribution to reducing GIVE at each Ionosphere Grid Point. 

Second, we observe a clear and direct dependence between the availability of CAT I service level and the minimum angle of satellite monitoring. This phenomenon is the result of waveform deformation (EWF for Evil Wave Form) processing in navigation algorithms, which requires at least one multi-correlator station to lock onto a satellite.

In all maps the integrity target is held with a good margin:

• The maximum satellite Safety Index is 0.77.

• The maximum Ionospheric Grid Point Safety Index is 0.76.

• Integrity is ensured as long as the Safety Index is below 5.33.

Focusing on the Incheon Airport location [127° E;37° N], Figure 3 shows performance in terms of position error and protection levels achieved for Sept. 4, 2022.

The VPL evolves mainly between 15m and 30m, except for a few minutes where it goes above the alarm limit of 35m. The HPL always remain below 30m. 

CAT I Performances Reached with Reference Station Extension (Large Network)

The second extended configuration considers the introduction of Galileo measurements and additional reference stations located outside South Korea landmass to build a large station network.

The added KASS reference stations are depicted in Figure 4.
Five new references stations are considered: Ulaanbaatar (Mongolia), New Delhi (India), Perth (Australia), Wellington (New Zealand) and Hawaii.

The simulation is performed with:

• 12 reference stations.

• 27 GPS: for satellites and ionosphere monitoring.

• 24 Galileo: for ionosphere monitoring only.

Figure 5 shows the availability performance results with satellite monitoring performed using measurements at a minimum of 15° elevation. 

• Again, in all maps, the integrity target is held with a good margin.

• The maximum satellite Safety Index is 0.92.

• The maximum Ionospheric Grid Point Safety Index is 1.33.

In this case, CAT I availability performance is improved with 12 stations. The effect is not on the reduction of integrity value (GIVE) regarding the ionosphere, as the additional five stations are too far away to have an impact. However, having remote stations allows for much better satellite monitoring. This is clearly visible in Figure 6. 

Because satellites are monitored much earlier with 12 stations, the effect of EWF monitoring becomes negligible by removing satellites if they are not seen by at least one station at more than 10° or 15°. As soon as a satellite becomes visible in the service area, there is always a remote station that can see the satellite with a good elevation.

However, EWF monitoring has a noticeable effect in the case with seven KRS, where the availability decreases as the minimum angle increases.

Focusing on Incheon Airport location [127° E;37° N], Figure 7 shows performance in position error and protection levels achieved on September 4, 2002.

This approach has also high interest in the frame of geographical extension of KASS service, for instance the APV I coverage is extended. Table 2 shows the comparison between the APV I availability with the seven KRS and 12 KRS networks.

Again, in all maps the integrity target is held with a good margin:

• The maximum satellite Safety Index is 0.92.

• The maximum Ionospheric Grid Point Safety Index is 1.33.

CAT I Performances Reached with Reference Station Extension (Narrow Network)

The third extended configuration considers the introduction of Galileo measurements and additional reference stations located outside the South Korea landmass to build a narrow station network.

Added KASS reference stations are depicted in Figure 8. Five new reference stations are considered: Shangai, Dalian, Mudanjiang (China), Izumo and Goto Tsubaki (Japan).

Figure 9 shows the availability performance results with a satellite monitoring performed using measurements with a minimum of 15° elevation. 

Here again, in all maps the integrity target is held with a good margin:

• The maximum satellite Safety Index is 0.87.

• The maximum Ionospheric Grid Point Safety Index is 0.85.

Focusing on the Incheon Airport location [127° E;37° N], Figure 10 shows the performances achieved on Sept. 4, 2002.

Much like the previous cases, the VPL remains around 15 to 25m, except for a spike around 5 p.m. The HPL remains around 10m the entire day. The narrow network extension has a benefit aspect on the navigation error NSE, mainly because of better ionosphere corrections accuracy.

Conclusion

The experimentation shows the KASS system evolution makes it possible to achieve the CAT I operational approach. The system’s adherence to architectural principles warrant its ability to meet the TTA requirements. Leveraging the Galileo system, the introduction of new GNSS measurements with the unchanged KRS network results reduces ionosphere integrity bounds, further enhancing the legacy system’s overall availability below the vertical alert limit compatible to CAT I. The study has also envisaged the addition of new external reference stations whose results have established a significant impact on satellite monitoring. With these new adjunctions, the KASS system would improve its capabilities to provide effective and accurate positioning services, proposing for safer and more efficient navigation in the CAT I operational approach.

References 

(1) “Standards and Recommended Practices (SARPS) Annex 10 to the Convention on International Civil Aviation,” Volume I, up to Amendment 86, July 2006, ICAO (International Civil Aviation Organization). 

(2) Houllier, Carolle, Authié, Thierry, Comelli, Guillaume, Lee, ByungSeok, Lee, Eunsung, Yun, Youngsun, SIN, Cheon Sig, “KASS: The Future of SBAS in Korea.” Inside GNSS, Junary–February 2023, pp 50-57

(3) Thierry Authié, Mickael Dall’Orso, Sébastien Trilles, Heonho Choi, Heesung Kim, Jae-Eun Lee, Eunsung Lee, Gi-Wook Nam, “Performances Monitoring and Analysis for KASS,” In Proc. of ION GNSS+, pp 958–978, 2017

(4) “Minimum Operational Performance Standards (MOPS) for Global Positioning System/Wide Area Augmentation System Airborne Equipment,” RTCA/DO-229D with Change 1, February 1, 2013.

Authors

Thierry Authié is a specialized engineer in space flight dynamics, precise orbit determination and navigation. He received his MS degree in Applied Mathematics from the INSA, Toulouse (France) in 2004. He currently works on SBAS and navigation algorithm at Thales Alenia Space.

Guillaume Comelli
is a system engineer and system architect at Thales Alenia Space. He received his MS degree in electrical engineering from the INSA, Lyon (France) in 1994. He has been the Technical Manager for the KASS program since 2019.

Sébastien Trilles is an expert in orbitography and integrity algorithms at Thales Alenia Space in Toulouse, France. He holds a PhD in Pure Mathematics from the Paul Sabatier University and an advanced MS in Space Technology from ISAE-Supaero. He heads the Performance and Processing Department where high precise algorithms are designed as orbit determination, clock synchronization, time transfer, reference time generation, integrity and ionosphere modelling algorithms for GNSS systems and augmentation.

ByungSeok Lee received a BS degree in electric and electrical engineering, a MS degree and a PhD in electrical and computer engineering from University of Seoul, Seoul, Korea, in 2002, 2009, 2015, respectively. He has conducted research related to a Global Navigation Satellite System (GNSS) including the Satellite Based Augmentation System (SBAS) in Korea Aerospace Research Institute. He was in charge of the KASS program from November 2020 to February 2024. He is currently responsible for the entire KASS operation and maintenance.

Minhyuk Son received his BS and MS degrees in electrical engineering from Daegu University, South Korea, in 2009, and 2011, respectively. He joined the Korea Aerospace Research Institute in 2011 and is currently in charge of operation safety technology development for KASS.

Cheon Sig SIN received a BS degree in electric and electrical engineering from Hanyang University, and a MS degree from Chungnam University, Korea in 1990, 2000 respectively. He conducts research related to a GNSS Signal Interference Detection and Mitigation Technology and Global Navigation Satellite System (GNSS) including the Satellite Based Augmentation System (SBAS) in Electronics and Telecommunication Research Institute. He has been in charge of the GK-3 SBAS Payload Development program since April 2021.

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Wide-area safety systems and services are becoming the norm as the world moves towards greater levels of automation and autonomy. Developed economies, including the United States and Canada, Europe, Japan, India and others, have now or will soon have access to high-integrity safety services via SBAS, such as WAAS, EGNOS, MSAS and GAGAN. The UK, on the other hand, since 2021, has not had access to such services, its EGNOS working agreements having been suspended after the UK left the European Union. That means, among other things, safety-critical LPV (localizer performance with vertical guidance) landing approaches have not been available at key commercial airports in the UK.

The objective of the UKSBAS testbed project, led by Viasat, which acquired Inmarsat Navigation Ventures in 2023, was to rapidly establish a UK capability utilizing Inmarsat satellites already in orbit, and a navigation signal generator with associated SBAS data processing and monitoring software from GMV NSL. A UK ground station was used for signal in space (SiS) uplink from Goonhilly Earth Station to the GEO navigation transponder.

In a second phase, the project defined future system architecture options for UKSBAS and conducted live trials in maritime navigation, and in static and dynamic aviation and road and rail transport scenarios.

Delivering the goods

At a final project presentation event hosted by ESA, Paul Ocen of Viasat, in the company of representatives from GMV NSL and consulting firm CGI, said the project has been providing testbed services over the past two years, starting with UKSBAS L1-frequency SiS, since May 2022, delivered by Viasat/Inmarsat 3F5 satellite and through SiSNET (SiS through the internet), and including UKSBAS DFMC (dual-frequency multi-constellation – GPS L1/L5 and Galileo E1/E5a), since June 2023, also through SiSNET. Further, a UKSBAS PPP service has been active since October 2023, delivered over NTRIP (networked transport of RTCM [real time correction message] via internet protocol).

Ocen said results computed over 18 months show that UKSBAS, despite remaining a testbed using non-dedicated reference stations, has achieved impressive performance levels, in terms of accuracy and availability, comparable to current operational legacy SBAS such as EGNOS, and compatible with LPV-200 service level.

The next-generation L5 DFMC SBAS service has shown remarkably superior performance over legacy SBAS L1 augmentation at system and user level. The PPP service has also shown outstanding results in terms of accuracy and convergence time. Viasat now intends to deploy a further three SBAS payloads on satellites of the I-8 class, due in orbit in 2028, to provide global coverage at 178E, 64E and 54W GEO slots.

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The agreement is signed under the Telecom Technology Development Fund (TTDF) scheme of the Department of Telecommunications, Government of India. This scheme, designed to fund Indian startups, academia, and R&D institutions, is an enabler for designing, developing, and commercializing telecommunication products and solutions. It aims to enable affordable broadband and mobile services, playing a significant role in bridging the digital divide across India. 

Silizium Circuits, with support from the Telecom Technology Development Fund (TTDF), is set to develop advanced semiconductor solutions for LEO satellite components. This initiative aims to drive innovation in India’s satellite communication ecosystem by addressing key challenges such as power efficiency, high-speed data transmission, and robust signal integrity. Leveraging its expertise in analog, RF, and mixed-signal technologies, Silizium Circuits will contribute to the creation of high-performance, reliable communication systems. The goal is to support a wide range of LEO satellite infrastructure projects, catering to both the global market and India’s vision for a self-reliant, future-ready satellite communication network that enhances connectivity both in urban and rural circles, and advances next-generation broadband services.

The agreement was signed during a ceremony attended by the CEO, C-DOT – Dr. Rajkumar Upadhyay, Mr. Rijin John the Co-Founder & CEO of Silizium Circuits, Dr. Pankaj Kumar Dalela, Ms. Shikha Srivastava, Directors of C-DOT along with senior officials from DOT Dr. Parag Agarwal, DDG (TTDF) and Shri. Vinod Kumar, DDG(SRI).

Dr. Rajkumar Upadhyay underlined the importance of developing chips for communication needs and emphasized the support of C-DOT including its infrastructure during the project implementation.

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The primary goal of the project is to develop next-generation collaborative PNT systems. The project will demonstrate the feasibility of large-scale constellations in LEO, address the vulnerability of existing Global Navigation Satellite Systems (GNSS) in denied environments, explore additional applications for PNT signals that can be exploited from LEO, and provide a roadmap for enabling collaborative LEO-PNT through the demonstration of the resilience of large-scale constellations that can be easily updated and reconstituted.

In addition to advancing PNT systems, the project aims to improve environmental sensing through GNSS-Reflectometry (GNSS-R) and Radio Occultation (GNSS-RO) technology, providing a better understanding of the Earth’s oceans, droughts, and floods. These technologies will also enhance real-time space weather and terrestrial weather forecasting, as well as emerging applications like tsunami monitoring and warning, demonstrating the technical expertise of both Australian and Indian organizations.

Michael Frater, CEO of Skykraft, expressed his pride in leading this joint Australia/India project, which will establish a strong foundation for both countries to develop and launch a next-generation PNT system. He looks forward to working with partners from both nations to successfully deliver the project and encourage the development of an operational independent PNT system.

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ArkEdge Space will utilize its expertise in the planning and design to mass production and operation of micro-satellite constellations to lead the development of a next-generation Lunar Navigation Satellite System (LNSS), a vital component to the International “LunaNet” initiative, driven by NASA (National Aeronautics and Space Administration), ESA (European Space Agency) and JAXA. LunaNet seeks to establish essential infrastructure to support sustainable lunar exploration and foster growth of the lunar economy. See recent LunaNet coverage in Inside GNSS here and access the Inside GNSS webinar on LunaNet.

This program, supported by up to 5 billion yen (US$32.5 million) over four years, tasks ArkEdge Space with developing a 100 kg class micro-satellite, developing crucial technology including the:

1.  Lunar navigation payload
2.  Demonstration satellite platform, along with a system operations plan
3. Establishment of an approach to mission evaluationy

These efforts will help reduce development costs and timeframes while advancing core LNSS technologies and enabling the development of future lunar navigation system demonstration satellite.

ArkEdge Space’s work on LNSS leverages its expertise in satellite technology and builds on its ongoing collaboration with JAXA. A key innovation of the project involves the use of faint GNSS (Global Navigation Satellite Systems) signals, originally designed for Earth, to determine satellite position and time in lunar orbit—approximately 380,000 kilometers from Earth. Additionally, LNSS complements advancements in Low Earth Orbit Positioning Navigation and Timing (LEO-PNT) systems, which utilize small satellite constellations at Low Earth Orbit altitudes. These systems provide high-precision, robust navigation services globally, enhancing existing GNSS infrastructure.

As lunar exploration accelerates—driven by initiatives including Artemis and other international efforts—high-precision infrastructure has become indispensable for activities such as rover navigation, base construction, and in-situ resource utilisation. LNSS not only supports lunar operations, but also serves as a stepping stone for future exploration of Mars and deep space.

The LNSS initiative comes at a pivotal time as nations worldwide consider developing regular lunar positioning services to support diverse lunar activities. To safely and efficiently enable these operations, the Moon requires real-time, high-accuracy positioning services like those of Earth-based GNSS.

ArkEdge Space has been developing essential communications and navigation infrastructure for lunar missions since 2021 under the Stardust Program (Strategic Program for Accelerating Research, Development, and Utilization of Space Technology). They also intend to support Initial Operational Capability (IOC) for globally coordinated, high-precision navigation services.

In October 2024, ArkEdge Space initiated a joint study with JAXA to explore the development of a Low Earth Orbit Positioning Navigation and Timing (LEO-PNT) system. LEO-PNT is envisioned as a revolutionary satellite constellation of low-Earth orbit satellites designed to provide higher-intensity, and higher-precision positioning data globally, surpassing the capabilities of traditional GNSS. The system works by receiving GNSS signals, processing the observational data on-board the satellite, and generating precise positioning signals for distribution. This innovative approach builds on the advanced technologies and expertise developed during the development of key LNSS subsystems. By leveraging these technological advances, ArkEdge Space aims to continually improve its satellite navigation capabilities and apply the results to broader Earth orbit-based business ventures.

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Synch Industries is working to build a national time distribution network free from GNSS-dependency. They will offer Time as a Service (TaaS) to a wide range of industries, such as telecom, media companies, fintech, data centers and power utilities. The implementation of GNSS-independent time distribution will strengthen national resilience and eliminate reliance on foreign influence in this vital national service. The network will go live in Q1, 2025 and the plan is to expand it further during the year.

“We are thrilled to achieve this technologically advanced network through the collaboration with Net Insight and GDS Technologies and we are excited to see that the project is in its final stages of going commercial,” says Neeren Ramharakh, Founder and CEO of Synch Industries. “In an increasingly interconnected world, the demand for precise, accurate, and secure time has never been more critical. Our commitment to providing a trustworthy source of time lays the foundation for businesses to thrive, enhance their operational efficiency, and forge ahead in the digital age.”

“We are very proud to welcome a new customer in time synchronization, which serves as a strong testament to the relevance and the growing demand for our solution. This milestone opens a new market and creates opportunities in this region,” says Per Lindgren, Group CTO and Head of Synchronization at Net Insight. “We look forward to teaming up with GDS Technologies and Synch Industries to create a network for distribution of national time in South Africa.”

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CAROLLE HOULLIER, CÉLINE BENASSY FOCH, GUILLAUME COMELLI THALES ALENIA SPACE, FRANCE; BYUNGSEOK LEE, MINHYUK SON, DAEHEE WON KOREA AEROSPACE RESEARCH INSTITUTE, REPUBLIC OF KOREA; CHEON SIG SIN ELECTRONICS AND TELECOMMUNICATION RESEARCH INSTITUTE, REPUBLIC OF KOREA

The Korea Augmentation Satellite System (KASS) is the satellite-based augmentation system (SBAS) of the Republic of Korea, currently developed by the Korea Aerospace Research Institute (KARI). Its mission is to provide SBAS services compliant with the International Civil Aviation Organization (ICAO) SARPS Annex 10 [1] over the South Korea area with service level up to APV I.

KASS will offer safety-critical services for civil aviation as well as an open service, usable by other forms of transportation and possibly other position, navigation and timing (PNT) applications. To provide improved GNSS navigation services for suitably equipped users in the agreed service areas, KASS will broadcast an augmentation signal of the U.S. Global Positioning System (GPS) Standard Positioning Service (SPS). The augmentation signal will provide corrections of GPS satellites, orbits and clocks and integrity bounds of orbit/clock residual errors, as well as corrections and integrity bounds for ionosphere delays. The augmentation signal will be broadcast by two Geostationary Earth Orbiting (GEO) satellites and leveraged by GPS/SBAS user equipment to compute a navigation solution.

Thales Alenia Space is the industry prime contractor of this development.

A Closer Look at KASS

The KASS system implements the following segments obtained from different manufacturers or service providers:

• A ground segment including a network of KASS Reference Stations (KRSs), redundant KASS Processing Stations (KPSs), KASS Control Stations (KCSs), KASS Uplink Stations (KUSs) and an external data interface.

• A network segment ensuring the communication network between all subsystems distributed across Korea (WAN) and the WAN Network Monitoring (WNM).

• A space segment including the GEOs and the navigation payloads on-board the GEOs.

The KASS system deployment started at the end of 2020 and was completed at the end of 2022 with the integration of the ground segment with the GEO satellite (MEASAT-3D). The KASS navigation signal has been broadcast since December 2022 with open service configuration (Message Type 0/2 broadcast). The final system qualification was in December 2023, allowing for the start of safety life services.

This article presents the overall KASS architecture and the performance results achieved during the site qualification phase with KASS operational configuration fully deployed.

The KASS system is designed to ensure four safety-critical service levels:

• En-Route over Incheon FIR area, flight segments after arrival at initial cruise altitude until the start of descent to the destination

• Terminal over Incheon FIR area for descent from cruise to Initial Approach Fix

• NPA over Incheon FIR area, for non-precision approaches (NPA) in aviation, an instrument approach and landing that uses lateral guidance but not vertical guidance

• APV I over South Korea land masses (including Jeju Island) for precision approaches with vertical guidance.

KASS will provide open service over the Incheon FIR area. Figure 1 shows the KASS service areas.

KASS is designed to be a system-of-systems ensuring these main functions:

• Collect GPS data at various locations in the Republic of Korea (and possibly in other states in the future).

• Compute corrections and associated integrity bounds from ranging measurements of GPS satellites in view of KASS.

• Format messages compliant with the SBAS user interface standardized in ICAO SARPS Annex 10 [1] and the RTCA MOPS 229-D Change 1 [2].

• Uplink a signal carrying these messages to navigation payloads on the KASS GEOs.

Broadcast the signal to the users after frequency-conversion to the L1 band.

Additional support functions are implemented:

• Wide area network between the KASS sites

• Monitoring and control of the KASS elements

• Support to KASS operations

Main elements of the KASS architecture are:

• 14 KRS (reference stations) channels on the seven KRS sites.

• Two KPS (processing units) and two KCS (monitoring and control units) deployed on the two main control center sites.

• Three KUS (uplink stations) deployed on three KUS satellite broadcast sites.

• A wide area network ensuring inter-sites data exchanges.

Figure 2 shows the overall KASS architecture.

Key Performance Parameters

In the frame of the analysis, KASS performances are evaluated to verify the main SBAS requirements.

Performance of a satellite navigation system can be expressed through five criteria: accuracy, integrity, continuity, availability and time-to-alert (TTA).

The accuracy feature is the difference between the computed value and the actual value of the user position.

The integrity risk is the probability during the period of operation that an error, whatever the source, might result in a computed position error exceeding a maximum allowed value, called alert limit, and the user not be informed within the specific TTA.

The alert limits are the maximum allowable error in the user position solution before an alarm is to be raised within the specific TTA. This alert limit is dependent on the flight phase, and each user is responsible for determining its own integrity in regard of this limit for a given operation phase following the information provided by the SBAS SIS.

The system TTA is defined as the time starting when an alarm condition occurs to the time the alarm is displayed in the cockpit. Time to detect the alarm condition is included as a component of integrity.

The continuity feature defines a system’s ability to perform its function without interruption during the operation planned by the user (for example landing phase of an aircraft). It is evaluated as the probability that from the moment the criteria of precision and integrity are completed at the beginning of an operation, they remain so for the duration of the operation.

Finally, the availability feature is the percentage of time when, over a certain geographical area, the criteria of accuracy, integrity and continuity are met.

Performance requirements include:

• The system performance in Fault Free conditions.

• The system performance in front of Feared Events (GPS FE, KRS FE, Hardware FE).

Additional system performance assessed at system qualification is the KASS system time synchronization with GPS system time that shall be maintained in the range of 50 ns.

Overall Performance Qualification Campaign Results

The performance qualification phase was run from December 2022 to June 2023. Four different periods have been deeply analyzed.

The consolidated performance results (average values over all observation periods) are listed in Table 3.

Moreover, no integrity issue has been raised during the overall qualification test campaign.

Focus on Global Performance for May to June Final Test Phase

The final performance results presented are computed over 15 days from May 24, 2023, to June 6, 2023.

Integrity From Satellite Corrections

To display the integrity of the satellite corrections for each GPS satellite, the notion of UDRE Safety Index is used to assess the integrity margin. The UDRE Safety Index is defined as the ratio

The satellite residual error for the worst user location (SREW) is computed as the pseudorange error projection due to the remaining satellite ephemeris and clock errors after KASS corrections have been applied for the worst user location of the relevant service area. The relevant service area corresponds to the intersection of the service area and of the monitored satellite footprint. The “true” SREW has been computed with the help of the precise GPS ephemerides provided by the International GNSS Service in sp3 format.

The user differential range error (UDRE) is defined in the section A.4 of MOPS [2] and provided by the KPS subsystem. For a given satellite, user integrity is ensured as long as the UDRE SFI remains lower than 5.33.

Figure 3 shows the UDRE Safety Index computation for May 30, 2023.

The satellite SFI remains under the value of 1 for all GPS satellites on this day, which demonstrates the large integrity margin of the UDRE corrections broadcast by KASS.

Integrity of Ionosphere Corrections

To display the integrity of the ionosphere corrections for each IGP, the notion of GIVE Safety Index is used. The GIVE Safety Index is defined as the ratio

With ∆GIVE the contribution the 1-sigma value that accounts for the pseudo-range error induced by the effect of the ionospheric divergence on the user smoothing filter defined in [2].

The GIVD Error is defined as the vertical pseudorange error at the considered IGP location, due to the remaining ionospheric delay after applying the GIVD corrections. The “true” GIVD error is computed thanks to precise real ionosphere conditions provided by the International GNSS Service in IONEX format.

Figure 4 shows the GIVE Safety Index computation for the May 30, 2023, period.

The ionosphere SFI remains under the value of 2.6 for all IGPs on this day, which demonstrate the large integrity margin of the ionosphere corrections broadcast by KASS.

Given the integrity assessment of satellites corrections and of ionosphere corrections, the contribution of fault free conditions to the integrity risk is negligible with real data and is similar with the results obtained from synthetic scenarios used prior to the system deployment. Considering that integrity performance verification at pseudorange level covers assessment at user position domain level, the integrity risk (APV I and the other KASS Services) is ensured.

Accuracy at User Level

User location is defined on a grid of longitudes from 124° to 134° East, and of latitudes from 30° to 39° North, with steps of 1°. The presentation is limited to the APV I service level. The performances requirements for the other services are also fulfilled.

The horizontal and vertical navigation service errors (HNSE and VNSE) are presented in meters for each user position. For the APV I Service (at 95 percentile), performance are computed over the whole observation period.

The accuracy performance demonstrates very good behavior of the KPS algorithms, correcting the GPS orbits, clocks and ionosphere with efficiency and high accuracy in vertical as well as in horizontal axis.

Service Availability 

For APV I service, KASS performances are:

APV I service availability is fully ensured over the complete service area. Some availability degradation is limited to the extreme south, outside any KASS service area, and without impact on performance. 

For NPA/Terminal/En-route services, KASS performances are:

The NPA service availability is 100% ensured over the complete service area.

Service Continuity Risk

For APV I service, KASS performances are seen in Figure 9.

APV I service continuity is fully ensured over the South Korea landmasses including Jeju Island.

For NPA/Terminal/En-route services, KASS performances are seen in Figure 10.

NPA/Terminal/En-route services continuity is fully ensured over the complete service area corresponding to the Incheon FIR.

KASS Network Time Synchronization Performance

The KASS network time (KNT) synchronization with GPS system time is ensured by the KASS navigation algorithm.

The synchronization performance is computed as per Table 6. 

The KASS system time synchronization with GPS system time is maintained in the range of 5 ns compliant with the maximum specified value of 50 ns.

Performance Achievement at Local Reference Point

KASS system implements on-line performance monitoring at the main control center level function, making it possible to verify performances achieved in near real-time and to report daily performance consolidation. Figure 11 provides the daily performances reached at the KASS reference station located at the Jeju Tracking Station (JJT) over a full day on May 14, 2023. 

Figure 11 shows the user horizontal position error (HPE) achieved with GPS only and with SBAS position computation.

Figure 12 shows the daily evaluation of the HPE and the user horizontal protection level (HPL) achieved with SBAS compared with the horizontal alarm limit (HAL). It also shows the number of GPS satellites monitored by the SBAS.

Figure 13 shows the daily Horizontal Stanford Diagram. 

The horizontal performance achieved at the reference station confirms the global KASS performance, in particular the residual error distribution after application of SBAS correction, is in the range of 1.2 m at 95%. The protection limit computation also shows good margin versus the alarm limit at 40 m, ensuring full service availability.

Figure 14 shows the user vertical position error (VPE) achieved with GPS only and with SBAS position computation.

Figure 15 shows the daily evaluation of the user vertical position error (VPE) and the user vertical protection level (VPL) achieved with SBAS compared with the vertical alarm limit (VAL). It also shows the number of GPS satellites the SBAS monitors. 

Figure 16 shows the daily Vertical Stanford Diagram. 

The vertical performance achieved at the reference station also reflects global KASS performance. The residual error distribution after application of SBAS correction is less than 2.6 m. The protection limit computation also shows good margin versus the alarm limit at 50 m, ensuring full service availability.

Conclusions 

The performance test results achieved show very good levels of accuracy, continuity, integrity and availability. 

The KASS signal is currently broadcasting a safety of life service. The next program steps will be to declare safety of life services availability and integration of the second GEO satellite currently under development. 

Acknowledgements 

The authors would like to thank everyone who contributed to this paper and highlight this work has been performed thanks to close cooperation between the Korea Aerospace Research Institute (KARI) and Thales Alenia Space. The authors thank the major partners involved for the KASS navigation algorithms design and development.

This article was supported by a grant (21ATRP-A087579-08) from Aviation Safety Technology Research Program funded by Ministry of Land, Infrastructure and Transport of Korean government.

References 

(1) “Standards and Recommended Practices (SARPS) Annex 10 to the Convention on International Civil Aviation”, Volume I, up to Amendment 86, July 2006, ICAO (International Civil Aviation Organization). 

(2) “Minimum Operational Performance Standards (MOPS) for Global Positioning System/Wide Area Augmentation System Airborne Equipment”, RTCA/DO-229D with Change 1, February 1, 2013.

Authors

Carolle Houllier graduated with a M.S. degree from the Aeronautical and Space Engineering School, ISAE Toulouse (France), in 1997. She has been an expert engineer in algorithms for GNSS for Thales Alenia Space since 2013 and worked on various space programs for the French Space Agency CNES before that. She has been the performance manager for the KASS program since 2020.

Céline Benassy Foch is a project manager and a system engineer at Thales Alenia Space. She received an M.S. degree in Network and Telecommunication from the INSA, Toulouse (France) in 1999. She has been the project manager for the KASS program since 2019.

Guillaume Comelli is a system engineer and system architect at Thales Alenia Space. He received his M.S. degree in Electrical Engineering from the INSA, Lyon (France) in 1994. He has been the technical manager for the KASS program since 2019.

ByungSeok Lee received the B.S. degree in Electric and Electrical Engineering, a M.S. degree and a doctor’s degree in Electrical and Computer Engineering from the University of Seoul, Seoul, Korea, in 2002, 2009, 2015, respectively. He has conducted research related to GNSS including the Satellite Based Augmentation System (SBAS) in Korea Aerospace Research Institute. He has been in charge of the Korean-SBAS (KASS, Korea Augmentation Satellite System) program from November 2020 to the present.

Minhyuk Son received his B.S., M.S. degrees in Electrical Engineering from Daegu University, South Korea, in 2009, and 2011, respectively. He joined Korea Aerospace Research Institute in 2011 and is currently involved in the Korea Augmentation Satellite System (KASS) program. He is in charge of operation safety technology development for KASS.

Daehee Won is a senior researcher at Korea Aerospace Research Institute (KARI) and has been working on developing the KASS Control Station since 2016. He received his Ph.D. degree in Aerospace Engineering from Konkuk University (Rep. of Korea) for research on navigation sensor integration and its performance analysis. He was a postdoctoral researcher at the University of Colorado at Boulder for the development of navigation algorithms for low Earth orbit (LEO) satellites. His research interests include GNSS augmentation and multi sensor integration.

Cheon Sig SIN received the B.S. degree in Electric and Electrical Engineering from Hanyang University, M.S. degree from Chungnam University, Korea in 1990, 2000 respectively. He has conducted research related to a GNSS Signal Interference Detection and Mitigation Technology and Global Navigation Satellite System (GNSS) including the Satellite Based Augmentation System (SBAS) in Electronics and Telecommunication Research Institute. He has been in charge of the GK-3 SBAS Payload Development program from April 2021 to present.

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Project partners used EGNOS, which stands for the European Geostationary Navigation Overlay Service. It is the EU’s satellite-based augmentation system (SBAS), to ensure precise and accurate positioning during the flights. The vehicle was a a two-passenger multicopter made by EHang, production model EH216-S. Among other things, SAMVA partners developed, tested and validated new, first-flight, procedure design criteria for autonomous eVTOL passenger aircraft based on EGNOS.

The achievement highlights progress being made in integrating EGNOS satellite-based capabilities in eVTOL flight operations. It also paves the way towards incorporating these vehicles within U-Space, the set of new European services designed to support safe, efficient and secure access to airspace for large numbers of drones.

The SAMVA project (SBAS adoption in multicopter VTOL aircraft) is partly funded by the European Union Agency for the Space Program (EUSPA) and is led by engineering firm PildoLabs. In a recent communication, the company’s CEO Santiago Soley called the project a significant step forward in integrating satellite navigation into urban air mobility, enhancing safety and efficiency and placing European airspace at the forefront in the push to get eVTOL technologies up and flying. Jordi Candela, Director of Aeroports de Catalunya, called the successful SAMVA flights a milestone in advancing urban air mobility in Europe.

The key objectives of the SAMVA project include:

• Enhancing Emergency Medical Services: Implementing the first Point-in-Space and Low-Level-Route operations in Spain to improve Helicopter Emergency Medical Services.
• Deployment at Lleida-Alguaire Airport: Launching the first EGNOS services for eVTOL operations, demonstrating EGNOS’s capability in supporting airspace integration and Air Traffic Management tasks
• Advancing Safety-of-Life Services: Showcasing how current and future EGNOS services can support eVTOL integration in challenging operational environments by integrating data from onboard sensors.
• Precision Navigation Capabilities: Enabling precise guidance and supporting airspace integration for autonomous eVTOL aircraft.
• Validating Flight Procedures: Developing, testing, and validating a first flight procedure design criteria for autonomous eVTOL passenger aircraft based on EGNOS.

Using Any and All Means

Part of EUSPA’s aim in supporting SAMVA is to promote the more rapid uptake of EGNOS capabilities by rotorcraft manufacturers, operators and service providers, including providers of medical and other safety-, search- and rescue-related services. The agency is continuing to develop EGNOS products, to be used in combination with the Galileo High Accuracy Service (HAS), to provide the highest possible levels of accuracy and integrity for autonomous eVTOL operations.

The SAMVA project is now focused on further exploring how current, leading-edge navigation technologies and services, including the EGNOS Safety-of-Life Service, can be used in optimized eVTOL operations, especially in challenging urban environments, including through the fusion and hybridization of data from on-board sensors.

Certainly, the still youthful eVTOL industry is growing rapidly, gaining investment in what is now widely seen as a revolutionary technology that could radically transform air transport in the near future. Work under SAMVA brings that promise closer to fruition.

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The INS-FI is built with Tactical-grade Fiber Optic Gyroscope (FOG) technology and an IP67 rating, indicating its robustness and resistance to electromagnetic and environmental interference. This system integrates an Inertial Measurement Unit (IMU) that combines Fiber Optic Gyroscopes and MEMS Accelerometers, along with an all-constellations GNSS receiver supporting multiple bands (GPS, GLONASS, GALILEO, QZSS, BEIDOU, and NAVIC).

Key features of the INS-FI include:

• High-Performance FOG IMU: Provides GNSS-free heading (True North) with an error margin of less than 0.5 degrees.
• Accurate Positioning: Offers horizontal and vertical positioning with approximately 0.1% error of distance traveled for land applications and a drift of five nautical miles per hour for aerospace applications without GNSS signal.
• Compatibility: Fully compatible with Inertial Labs’ ADC (Air Data Computer), VINS (Visual Inertial Navigation Systems), and SAMC (Stand-Alone Magnetic Compass).

The INS-FI incorporates Inertial Labs’ latest sensor fusion filter, navigation and guidance algorithms, and calibration software to ensure optimal performance and reliability. This new system is aimed at providing precise horizontal and vertical positions, velocity, and absolute orientation (heading, pitch, and roll) for any mounted device, maintaining high accuracy for both stationary and dynamic applications.

Jamie Marraccini, CEO of Inertial Labs, highlighted the significance of this new product, stating, “The INS-FI represents a significant milestone in our mission to provide superior navigation solutions. With its advanced FOG technology and robust design, the INS-FI sets a new standard for performance and reliability in the industry.”

Inertial Labs specializes in the design, integration, and manufacturing of Inertial Measurement Units (IMUs), GPS-aided Inertial Navigation Systems (INSs), and Attitude and Heading Reference Systems (AHRSs), leveraging MEMS gyroscopes and accelerometers for high-performing inertial solutions.

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