Services of the Quasi-Zenith Satellite System (QZSS) officially started on Nov. 1, according to a statement from Japan’s National Space Policy Secretariat, Cabinet Office.
Government and industry hope the turn-on will generate new services worth nearly 5 trillion yen ($44.4 billion) by 2025 as players like SoftBank Group, Mitsubishi Electric and Hitachi plan applications in automated driving, farming and more.
“Our lifestyles would be impossible without GPS,” Prime Minister Shinzo Abe said at initialization ceremony marking the start of the service. The Michibiki satellite constellation, known officially as QZSS, would let Japan turn “a new page in history,” he continued.
The system keeps at least one of the current four Michibiki satellites over Japan at all times, offering an advantage over GPS-only services with a precise bird’s-eye view uninterrupted by mountains or tall buildings. With special receivers, the satellites can narrow margins of error to 10 centimeters.
The signal is free for anyone with a device capable of receiving the signal.
Prime Minister Shinzo Abe delivers a congratulatory address as QZSS is officially launched. (Photo: Japan Cabinet Public Relations Office)
Japan’s cabinet and other government bodies have invested 120 billion yen in QZSS. Expectations are particularly strong for applications in the rapidly advancing field of automated driving, with some businesses estimating the market for positioning services in that field alone at roughly 500 billion yen.
QZSS offers lane-level positioning capability, is a key step towards auto autonomy.
Michibiki means guidance in Japanese. In his remarks, Abe said the satellite-based augmentation system (SBAS) “will guide us to Society 5.0, the society of the future. There are high hopes for the ever greater use of this satellite system in a wide range of fields. The government aims to expand the system to a seven-satellite constellation by FY2023, with the goal of achieving an even more stable positioning service.
“More than 10 years have passed since its conception. I am sure that taking on this challenge, the first of its kind in the world, must have required much hard work. I would like to express my utmost respect for the efforts of the engineers responsible for the development and all those involved with this project.
“To what degree will the ‘Michibiki’ change our lives? I hope to follow its progress with great excitement, together with you all.”
Galileo, BeiDou, QZSS, IRNSS, and more join GPS and GLONASS to bring you wider, broader, greater, more accessible and above all more accurate PNT. How to get all that’s coming at you?
Multi-GNSS paves the way for complete exploitation of new signals and constellations in navigation, surveying, geodesy and remote sensing.
The free 1-hour webinar, which will take place at 1 p.m. Eastern [10 a.m. Pacific, 7 p.m. (1900h) Central European Time] on Thursday, Sept. 20, will review advantages of using multi-GNSS for the end-user and challenges in obtaining maximum efficiency when combining multiple constellations and signals. It will also discuss different approaches of testing GNSS receivers against jamming and spoofing attacks.
You will learn:
Advantages of using multi-GNSS
Challenges when combining multiple constellations
Robustness of multi-GNSS receivers to jamming and spoofing
Test solutions for GNSS receivers.
The webinar presents sponsored content by Skydel and Talen-X. Register for it here.
According to the company, the module supports hybrid positioning technologies including GNSS, Cell ID and Wi-Fi aided positioning, and enables position tracking in both indoor and outdoor environments.
Quectel’s MC90 integrates the multi-GNSS system, including GPS, GLONASS, Galileo and QZSS, which makes it suitable for urban areas with high-rise buildings and complex environments, the company added.
The MC90 also adopts Wi-Fi hotspot positioning technology for blind spots and satellite coverage. It integrates multi-aiding positioning technologies to offer customers with optimized GNSS performance. It also supports EPO technology, which provides predicted Extended Prediction Orbit to speed up TTFF without the need of any extra server.
The MC90 features a compact design, low power consumption and supports dual SIM single standby function. According to Quectel, it can be used for a wide range of internet of things applications, including bicycle sharing, student ID card, vehicle tracker, wearable device, pet tracker, asset tracker, driving recorder and more.
Curtin University researchers found the launch of new Japanese satellites has boosted satellite positioning capabilities in Western Australia (WA), offering huge potential benefits across numerous industries including mining, surveying and navigation.
New research, published in the journal GPS Solutions, found signals from the recently launched Japanese QZSS satellites provide centimeter-level positioning accuracy, and thus significantly enhanced positioning capabilities in WA, thereby improving accuracy, reliability and availability.
Lead researcher Professor Peter Teunissen, of Curtin’s School of Earth and Planetary Sciences, said these results will improve further when the QZSS signals are combined with those from other satellite systems such as the Indian NavIC system.
Teunissen said the analyses done by Curtin’s GNSS Research Centre demonstrated the highly accurate centimeter-level positioning capabilities that can now be achieved.
“Such improved positioning, accuracy and reliability would offer great benefits when applied in fields such as open-pit mining, surveying, hydrography, automated navigation, structural health monitoring, and subsidence and tectonic deformation monitoring used in the geospatial industry,” Teunissen said. “The benefits are not only restricted to positioning, but cover the whole range of satellite signal applications, including atmospheric sensing (ionosphere and troposphere) as used for climate change and space weather studies, and numerical weather prediction.”
Teunissen said WA was in the fortunate and unique geographical position of being located beneath the flight paths of both the Japanese QZSS and the Indian NavIC regional satellite systems.
“Using both satellite systems, QZSS and NavIC, offers huge benefits to users in Australia – and this is an opportunity to work on future developments with such technologies,” Professor Teunissen said.
“The United States of America, for example, can’t use these signals the way we can in Australia, so this places us in a position of great advantage when it comes to the understanding, modelling and analyses of these satellite signals and their many practical applications.
“The tracking and analyses were done using Javad GNSS receivers and Curtin’s theory of integer ambiguity resolution, which enables millimeter-level satellite ranging, and was achieved with the use of only the four currently available QZSS satellites.”
The results bode well for the future, with the Japanese system being further developed from the current four-satellite system into a mature seven-satellite system that is expected to be operational by 2020.
The report, “Australia-First High-Precision Positioning Results with New Japanese QZSS Regional Satellite System,“ is available online.
The Hibiki processors can take input from up to four frequency GNSS signals simultaneously.
The Hibiki front-end can process up to four GNSS signals for software receivers. (Image: Lighthouse)
The Japanese Quasi-Zenith Satellite System (QZSS) broadcasts GNSS signals in four frequency bands: L1, L2, L5 and L6. Similarly, GPS and GLONASS broadcast in three bands, and the European Galileo and Chinese BeiDou systems broadcast in four bands.
However, many conventional front-ends process only two bands at the same time, and cannot be used for highly specialized applications such as processing multiple signals with different frequencies at the same time.
The Hibiki front-end processor was designed to answer to this GNSS technology demand and is able to process up to four frequency bands simultaneously, the company said.
Hibiki has a high data transfer rate performance using USB 3.0, stably transmitting signal data to the host computer up to 50 million samples per second. This high sampling frequency is much greater than conventional front-end processors, improving L5 signal-receiving performance and reducing multipath.
By Peter Steigenberger, Steffen Thoelert, André Hauschild, Oliver Montenbruck and Richard B. Langley
INNOVATION INSIGHTS with Richard Langley
POP QUIZ: What is the most populous metropolitan area in the world? According to Wikipedia, it is Tokyo. In fact, Japan has three cities in the list of the 50 largest cities in the world. Not only are there a lot of people in these cities, they also have many tall and densely packed buildings. And that’s a problem for GPS and the other global navigation satellite systems.
Radio signals travel in straight lines. Well, mostly so. At very low frequencies, radio waves propagate as ground waves and can achieve long-distance propagation in the waveguide formed by the surface of the Earth and the ionosphere. At slightly higher frequencies, such as those used by AM radio, signals still travel as ground waves. However, additionally, the signals propagate upwards as skywaves. During daylight hours, the D layer of the ionosphere absorbs the skywaves, but when the D layer dissipates at night, the higher ionospheric levels can reflect skywaves back to Earth allowing long-distance reception. And communication by shortwave is virtually all by ionosphere-bounce skywaves. Above 30 MHz or so, signals normally travel along line-of-sight raypaths. The atmosphere can slightly bend the raypath, but the signals essentially travel in straight lines. Of course, that’s what makes GPS possible.
GPS works exceedingly well as long as a receiver’s antenna has a line-of-sight “view” of the satellites. Obstacles such as mountains and buildings block the relatively weak GPS signals. In concrete canyons, for example, that may leave a receiver with fewer than four satellites in view, meaning that 3D positioning is impossible. Even if four or more satellites are visible, they may be bunched together in the sky, resulting in high dilution of precision values and potentially large position errors.
In an effort to alleviate the GPS positioning problem in both urban and mountainous areas of Japan, the Japanese government has developed the Quasi-Zenith Satellite System (QZSS). A constellation of three inclined geosynchronous orbit (IGSO) satellites and one geostationary satellite transmits GPS-compatible signals to enhance positioning availability and accuracy. The IGSO satellites have repeating figure-eight ground tracks with the satellites spending most of their one-sidereal-day orbit, centered around apogee, over the Japanese archipelago. The satellites sequentially hover in the sky near the zenith for long periods of time. The satellites also provide both standard and advanced augmentation signals.
The first, or prototype, Block I QZSS satellite was launched in 2010 and, based on the positive test results from this satellite, an additional three satellites were launched in 2017, completing a four-satellite constellation. In this month’s column, we examine the recent developments of this unique and innovative navigation system.
With the launch of two additional spacecraft in August and October 2017, the Japanese Quasi-Zenith Satellite System (QZSS) reached the goal of a four-satellite constellation with the first fully-operational services expected to start in 2018. Aug. 19, 2017, marked the launch of QZS-3, the first geostationary Earth orbit (GEO) QZSS satellite, while the third spacecraft in inclined geosynchronous orbit (IGSO), QZS-4, was subsequently launched on Oct. 10, 2017. An artist’s view of the constellation is shown in FIGURE 1.
FIGURE 1. An artist’s view of the QZSS satellites. The upper-most satellite is the geostationary QZS-3 spacecraft with the additional S-band dish antenna whereas the other satellites pictured are the inclined geosynchronous satellites. (Image: Mitsubishi Electric)
Table 1 lists the four satellites of the current QZSS constellation. Whereas the first generation Block I satellite QZS-1 was launched in 2010, the three Block II satellites joined the constellation in 2017.
Table 1. QZSS constellation as of December 2017. SVN: space vehicle number, PRN: pseudorandom noise (code number), IGSO: inclined geosynchronous orbit, GEO: geostationary Earth orbit.
The most obvious visual difference between the QZSS Block I and II satellites is the different number of subpanels for the solar arrays: three for the Block I satellite and two for the Block II satellites with spanned widths of 25.3 meters and 19.0 meters, respectively. The reduced size of the Block II array has been achieved through the use of new, high-efficiency solar cells. The GEO satellite in addition carries S- and Ku-band antennas with diameters of 3.2 meters and 1.0 meter, respectively. While the IGSO satellites are equipped with a helix antenna array for transmission of the main L-band navigation signals, the GEO satellite uses a patch antenna array similar to that of the Galileo satellites.
The ground tracks of the four QZSS satellites are plotted in FIGURE 2. The ground tracks of all of the IGSO satellites have the characteristic figure-eight shape due to the large orbit eccentricity of 0.075 and results in a longer visibility period for users in the northern hemisphere. The ground tracks do not precisely match, however. QZS-1 and QZS-4 have similar orbit inclinations (with respect to the equator) of 40.9° and 40.5°. QZS-2, on the other hand, has a larger inclination of 44.5°, which leads to a wider extension of the ground track in the north-south direction.
FIGURE 2. Ground tracks of the four-satellite QZSS constellation as of Dec. 4, 2017. The blue square indicates the sub-satellite point of the geostationary QZS-3 satellite. (Image: Authors)
Also, the central longitude of the ground tracks, which marks the center of the figure-eight shape, varies between 130° and 140° E. These differences are still within the tolerances defined in the QZSS Interface Specification, version 1.8 of Oct. 3, 2016, which specifies the inclination to be 43° ± 4° and the central longitude of the ground track to be 135° ± 5° E. The GEO satellite QZS-3 is located at 127° E and has been controlled to stay within a 0.1° inclination window since achieving its initial orbit.
All QZSS satellites transmit navigation signals in the L1, L2 and L5 bands compatible with GPS, namely L1 C/A, L1C, L2C and L5 (the Positioning, Navigation and Timing or PNT service). QZSS-specific signals are transmitted in the L1, L5 and L6 bands: the Sub-meter Level Augmentation Service or SLAS (formerly, Submeter-class Augmentation with Integrity Function or SAIF) signals for all satellites on L1 and, in addition, on L5 for Block II satellites (see TABLE 2).
Table 2. QZSS signals. The L2C and CLAS signals use interleaved bit streams for concurrent transmission of two independent ranging sequences. The L1S signal consists of SLAS, a message service, and L1Sb, an SBAS signal. (Based on Table 11.2 in the Springer Handbook of Global Navigation Satellite Systems).
Starting in 2020, the GEO satellite will also provide a satellite-based augmentation system (SBAS) signal called L1Sb with range corrections and integrity information for aviation applications in particular. The SLAS and SBAS signals are transmitted via dedicated antennas but they are phase coherent with the GPS-compatible navigation signals transmitted via the main L-band antenna. The L6 signal provides the Centimeter Level Augmentation Service or CLAS (formerly, the L-band Experiment or LEX) on all QZSS satellites, but employs a different signal structure for Block I (L61) and Block II (L62). An overview of the various L-band signals and corresponding PRN assignments is given in TABLE 3. QZS-3 also provides the QZSS Safety Confirmation Service (Q-ANPI) to support rescue operations with S-band communication in case of a disaster. The total transmit power is 500 watts for the Block II IGSO satellites and 550 watts for the GEO satellite.
Table 3. PRN code assignment of QZSS satellites according to the interface specifications (see Further Reading). RINEX: PRN code in RINEX observation files; NAV: PRN code for L1 C/A, L1C, L2C and L5 navigation signals; NSTD: non-standard codes of IGSO/GEO satellites.
QZS-3/4 SIGNAL TRANSMISSION
Tracking of the QZS-3 L1 C/A and L5 signals by receivers in the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt or DLR) and International GNSS Service networks started on Sept. 10, 2017, at 09:04 UTC followed by the L1C and L2C signals at 09:27 UTC. L5 tracking started with a very low carrier-to-noise-density ratio (C/N0) of 10 – 20 dB-Hz that increased to 50 – 55 dB-Hz shortly after the activation of the L1C and L2C signals. QZS-3 broadcast ephemerides were first transmitted on Oct. 4, 2017, at 16:00 UTC. However, tracking of the L1, L2 and L5 navigation signals with common geodetic receivers is currently limited to receivers with experimental firmware versions developed by three different manufacturers.
Signal transmissions from QZS-4 started on Nov. 1, 2017. The first L1 C/A signals of PRN J03 were received at 02:50 UTC. At the same time, L5 signal transmission started but this signal was only tracked by a very limited number of receivers due to its low signal strength resulting in a C/N0 of only about 15 dB-Hz. At 03:14 UTC, an increase of the C/N0 by about 40 dB occurred and many additional receivers started tracking the L5 signal. At the same time, the L1C and L2C signals were also activated followed by the L1 SLAS signal at 03:20 UTC.
It is interesting to note that QZS-4 also transmitted the non-standard code J06 on different frequencies during its first weeks of operation. This code cannot be used for positioning and is used for test purposes or in case of system errors. Until Nov. 27, 2017, QZS-4 regularly switched between transmission of standard and non-standard codes. An example of such a switch for the station UNX200AUS located in Sydney, Australia, is shown in FIGURE 3. During this test period, several outages of individual or all navigation signals also occurred. Since Nov. 24, 2017, 5:00 UTC, broadcast ephemerides of QZS-4 have been available and transmission of the L5 SLAS signal started at 09:31 UTC.
FIGURE 3. QZS-4 signals tracked by DLR’s JAVAD Delta-3TH receiver in Sydney, Australia. The top plot shows the standard code PRN J03 and the bottom plot the non-standard code J06. The measured C/N0 is shown for L1 C/A (black), L1C (blue), L2C (red) and L5 (green). (Image: Authors)
FIGURE 4 shows the L-band normalized power spectra of QZS-2 and QZS-4. The spectra were obtained from in-phase (I) and quadrature (Q) data recorded with DLR’s 30-meter high-gain antenna in Weilheim, Germany. Almost identical characteristics can be seen for the signals of both satellites in the L1, L2 and L6 bands. However, in the L5 band, QZS-4 shows a slightly lower power than that of QZS-2 due to the lack of the L5 SLAS transmission during the data recording. Unfortunately, QZS-3 is not visible from Weilheim due to a longitude difference of more than 115°.
FIGURE 4. Normalized power spectra of QZS-2 and QZS-4 measured with DLR’s 30-meter high-gain antenna on July 18, 2017, and Nov. 7, 2017, respectively. (Image: Authors)
ATTITUDE
Usually, QZS-2 and QZS-4 follow a nominal yaw steering attitude with the spacecraft z-axis pointing towards the Earth and the y-axis (solar panel axis) oriented perpendicular to the plane defined by the locations of the satellite, the Sun, and the Earth. The maximum yaw rate of these satellites is limited to 0.055° per second and can be exceeded by the nominal yaw rate when the angle of the Sun with respect to the orbital plane (the beta angle, β) is between -5° and +5°. During orbit control maneuvers, the QZSS Block II IGSO satellites are operated in orbit normal mode with the z-axis pointing to the Earth and the y-axis perpendicular to the orbital plane. The geostationary QZS-3 satellite is continuously operated in orbit normal model while QZS-1 enters orbit normal mode for |β| < 20°.
Detailed information about the different attitude rules as well as spacecraft reference frame, mass, center of mass, phase center offsets and variations of the navigation antenna, laser retroreflector offsets, satellite group delays as well as the total transmit power of all four satellites is provided by the Cabinet Office, Government of Japan, in the QZSS satellite information documents.
Since all QZSS satellites are equipped with a separate L1 SLAS transmit antenna, which is mounted with an offset to the main L-band antenna, each satellite’s attitude can be directly estimated from single-difference carrier-phase observations between the two spacecraft antennas.
FIGURE 5 illustrates the attitude of QZS-4 estimated from L1 C/A and L1 SLAS observations from 10 tracking stations as well as the nominal yaw steering attitude. QZS-4 had a beta angle of about 11° on Dec. 9, 2017, confirming that this satellite does not enter orbit normal mode for |β| < 20° as does QZS-1. Differences between nominal yaw steering attitude and estimated attitude are usually within ±1.5° reflecting estimation errors as well as differences between nominal and true attitude.
FIGURE 5. Nominal yaw steering attitude (blue) and estimated attitude (red) of QZS-4 for Dec. 9, 2017 (β ≈ 11°). (Image: Authors)
CLOCK PERFORMANCE
The clock stability represented by the modified Allan deviation is given in the upper panel of FIGURE 6 for the QZSS IGSO satellites. The QZSS Block II IGSO satellites show an almost identical stability for integration periods up to 100 seconds. For longer periods, the QZS-2 clock seems to perform slightly better.
However, this effect is probably related to the number of stations contributing to the clock solutions of the individual satellites which differs by a factor of more than two. For comparison purposes, the Allan deviation of two Galileo rubidium clocks (GAL-101 and GAL-204) and a Galileo passive hydrogen maser (PHM, GAL-207) are plotted in the bottom panel of Figure 6.
Whereas the performance of the QZSS and Galileo rubidium clocks is very similar, the Galileo PHM is more stable by a factor of two to five over all integration periods.
FIGURE 6. Modified Allan deviations of the QZSS IGSO rubidium clocks, Galileo rubidium clocks (GAL-101 and GAL-204) and a Galileo passive hydrogen maser (GAL-207). (Image: Authors)
CONCLUSIONS
With the launch of the third IGSO spacecraft and the first GEO spacecraft, the QZSS constellation has reached a four-satellite configuration, which is required for the provision of operational augmentation services. QZS-3 and QZS-4 were declared useable for PNT, SLAS, and CLAS trial services on Dec. 18, 2017, and Jan. 12, 2018, respectively. Inclusion in the operational QZSS constellation is expected for 2018 and this will provide continuous visibility of three satellites in the service area. An expansion to a constellation of seven satellites is planned for 2023 including a Public Regulated Service for authorized users.
MANUFACTURERS
Data used in this article was collected using Javad GNSS Delta-G3TH, Trimble NetR9 and Septentrio PolaRx4 and PolaRx5 receivers.
Authors Peter Steigenberger, Steffen Thoelert, André Hauschild and Oliver Montenbruck are from the German Aerospace Center (DLR).
Richard B. Langley is from the University of New Brunswick and authors the monthly “Innovation” column for GPS World magazine.
FURTHER READING
• Quasi-Zenith Satellite System
“Quasi-Zenith Satellite System” part of “Regional Systems” by S. Kogure, A.S. Ganeshan and O. Montenbruck, Chapter 11 in Springer Handbook of Global Navigation Satellite Systems, edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017.
“QZS-2 Signal Analysis, QZS-3 Launched” by S. Thoelert, A. Hauschild, P. Steigenberger, O. Montenbruck and R.B. Langley in GPS World, Vol. 28, No. 9, September 2017, pp. 10–14.
A U.K. government report issued on Jan. 30 looks at the vulnerability of all satellite-based positioning systems: GPS, Galileo, GLONASS, BeiDou, QZSS and more. Issued by the Office of the Government Chief Scientific Adviser, Sir Mark Walport, and informally called the Blackett Report, designating the highest level of government scientific studies, named after a UK physicist who won the 1948 Nobel Prize, the review aims to “lay out the breadth, scale and implications of our reliance on ‘the invisible utility’ mainly in terms of existing critical national infrastructure (CNI).”
“Satellite-derived Time and Position: A Study of Critical Dependencies” states in the forward that it “represents a vital step in understanding the UK’s dependency on GNSS and recommends measures to improve our resilience. Importantly, it also recognises that innovation will be key to realising, fully and safely, the economic and societal benefits offered by GNSS.”
The report points to the fragility of satellite positioning signals which can be affected by cheap jammers, spoofers, weather and interference from other radio signals — among other vulnerabilities. The 86-page PDF document is downloadable here.
The review incorporates the results of a separate but related study, issued in April 2017, looking at the fiscal consequences of a GNSS disruption in. “Economic Impact to the U.K. of a Disruption in GNSS” was briefly summarized in a June 2017 column from this magazine (scroll down to “At What Cost Ignorance?”). The report attempted to quantify the cost of a GNSS disruption, should one occur. The authors came up a figure of 5.2 billion pounds ($6 billion) for a 5-day disruption.
David Last, a UK consultant engineer specializing in radio navigation and communications systems, professor emeritus at the University of Bangor, Wales and past president of the Royal Institute of Navigation, consulted on the June 2017 economic impact report, and was a member of the expert panel and co-author of the January 2018 Blackett Report. He was to have given a presentation on them at the ION International Technical Meeting in Reston, Virginia on January, but could not make the trip. The following materials are drawn from his prepared presentation.
Some of the conclusions from the June 2017 economic impact study are:
There are alternatives to GNSS, specific to each application
However, there is no universally-applicable single alternative for positioning and navigation
Among the most salient needs: higher quality (more expensive) oscillators for timing
“The most applicable mitigation strategies for the largest number of applications are eLoran and Satelles.”
“Omnisense and Locata may be preferred for localised applications that require high levels of accuracy.”
From the just-issued Blackett Report, the first figure displayed above presents recommended mitigations to impacts on GNSS applications in road, rail, maritime and aviation. Alternative options include composite or hybrid navigation, terrestrial radio systems, space weather forecasting, eLoran, various methods of interference detection, multi-frequency receivers and differential GNSS.
A second figure from Last’s presentation, shown above, covers the mitigations recommended for telecoms, finance, energy, and emergency services sectors. Mitigations for these applications include a resilient architecture with diverse network routing to high-stability atomic clocks, terrestrial radio systems, time-by-fiberoptics, multiconstellation receivers, holdover devices, GNSS integrity monitoring, and inertial navigation.
Concluding recommendations of the Blackett Report:
CNI operators to review and report on their reliance on GNSS. Cabinet Office to assess overall dependence of CNI on GNSS.
Add loss or compromise of GNSS-derived PNT to National Risk Assessment, not just as a dimension of space weather.
In allocating radio spectrum to new services and applications, address the risk of interference to GNSS-dependent users, including CNI.
Review the legality of the sale, ownership and use of devices and software to cause deliberate interference to GNSS receivers or signals.
Assess the need to monitor interference of GNSS at key sites such as ports and share the data with government
Employ GNSS-independent back-up systems.
Cross-government PNT Working Group to report to Cabinet Office on ways to improve national resilience.
Government to facilitate as those procuring GNSS equipment for CNI specify performance standards.
Map PNT testing facilities and explore how industry and critical services can better access them.
Leverage UK academic and industrial expertise in time and geo-location, increasing coordination among existing centres of excellence.
The Japan-Australia QZSS Industrial Utilisation Workshop will be held Feb. 6 at the University of New South Wales (Kensington Campus), Room Chemical Sc M18, Sydney, Australia.
The workshop will share information about QZSS and GPS related technologies and the latest developments in the applications of this technology in a range of sectors including in agriculture, autonomous driving, advanced route guidance and the maritime sector.
The workshop will explore avenues for future cooperation with Australian organisations, both in the private and public sectors and report on trials undertaken in Australia using QZSS applications.
The QZSS Workshop will feature a range of keynote speakers from key Japanese Ministries including: the Ministry of the Economy and Industry (METI), the National Space Policy Secretariat (Cabinet Office), the Ministry of Internal Affairs and Communications (MIC) , Ministry of Agriculture, Forestry and Fisheries (MAFF) and Japanese industry, including Toyota Tsusho, Mitsubishi Electric (MELCO), Global Positioning Augmentation Service Corporation (GPAS), Hitachi Zosen Corporation (HITZ), as well as keynote speakers from the Australian public and private sectors.
The second satellite of Japan’s Quasi-Zenith Satellite System (QZSS) has started transmitting navigation signals. QZS-2, or Michibiki-2, was launched on June 1, 2017, and joins its predecessor QZS-1 (Michibiki-1), which has been in orbit since September 2010.
Both satellites have been placed into inclined geosynchronous, elliptical orbits, which enable extended satellite visibility periods over Japan and are characteristic features for this regional navigation system.
The third satellite QZS-3 was launched on Aug. 19, 2017, into a geostationary orbit. If all goes according to plan, a fourth satellite in an eccentric orbit will follow by the end of this year and complete the constellation.
Three of six new Lockheed Martin-developed receivers are now deployed at U.S. Air Force monitoring stations to maintain the accuracy of GPS satellite signals.
In June, the first Monitor Station Technology Improvement Capability (MSTIC) receiver became operational at Cape Canaveral Air Force Station, Florida. Upgrades continued at USAF monitoring stations at Kwajalein Atoll and Hawaii. These upgrades from early 1990s technology are part of an overall effort to modernize the current GPS ground control system, known as the Architecture Evolution Plan Operational Control Segment.
MSTIC software-defined radio technology replaces legacy receivers’ hardware-based application-specific integrated circuit platform. MSTIC leverages commercial off-the-shelf hardware without the need for custom firmware. Standard interfaces and architecture configurability simplify sustainment and enable MSTIC software to migrate to new hardware platforms as commercial vendors increase processing power, improve reliability and enhance cybersecurity. MSTIC enables remote application of mission-specific software updates to improve performance and enable reception of modernized GPS signals, according to the company.
The three remaining GPS Monitoring Stations will be upgraded with MSTIC receivers by the end of 2017.
The navigation payload before integration into the second GPS III SV, which now is in environmental testing. (Photo: Harris)
GPS III Payloads Delivered
Harris Corporation has delivered the third of 10 advanced navigation payloads to Lockheed Martin. The payloads will increase accuracy, signal power and jamming resistance for GPS III satellites. They feature a Mission Data Unit (MDU) with a 70-percent digital design that links atomic clocks, radiation-hardened computers and powerful transmitters, enabling signals three times more accurate than those on current GPS satellites. The new payloads also boost satellite signal power, increase jamming resistance by eight times and help extend the satellite’s lifespan.
The payload was integrated into GPS III SV03 over the summer. The first navigation payload is integrated aboard GPS III SV01, which is in storage awaiting expected 2018 launch.
Harris announced it is in full production and on target to deliver the fourth GPS III navigation payload to Lockheed Martin in fall. Harris is also developing a fully digital MDU for the U.S. Air Force’s GPS III Space Vehicles 11+ acquisition. The new MDU will be demonstrated in fall 2017 and provides even greater flexibility, affordability and accuracy versus existing GPS satellites.
Next GLONASS-M Readied
The Russian navigation satellite GLONASS-M 52 moved from ISS-Reshetnev Company’s assembly plant to the Plesetsk Cosmodrome launch site about 800 km north of Moscow in August. One of the system’s ground spares, it was built more than two years ago and stored awaiting launch. The satellite is due to launch in September.
There are six GLONASS-M satellites in ground reserve.
This month we bring you a guest column by Steffen Thoelert, André Hauschild, Peter Steigenberger and Oliver Montenbruck of the German Aerospace Center (DLR) and Richard B. Langley of the University of New Brunswick.
UPDATE:Since Sept. 10, continuously operating DLR receivers in Sydney, Australia, and Chofu, Japan, have been reporting measurements from QZSS satellite J07, which, according to the QZSS Interface Control Document, is the geostationary satellite QZS-3.
The second satellite of Japan’s Quasi-Zenith Satellite System (QZSS) has started transmitting navigation signals. QZS-2, or Michibiki-2, was launched on June 1, 2017, and joins its predecessor QZS-1 (Michibiki-1), which has been in orbit since September 2010.
Both satellites have been placed into inclined geosynchronous, elliptical orbits, which enable extended satellite visibility periods over Japan and are characteristic features for this regional navigation system.
The third satellite, QZS-3, was launched on Aug. 19, 2017, into a geostationary orbit. If all goes according to plan, a fourth satellite in an eccentric orbit will follow by the end of this year and complete the constellation.
QZS-2 Signal Tracking
It is not straightforward to tell when QZS-2 started signal transmission exactly. About four weeks after launch, on June 27 between 10:17 and 12:37 UTC, several Septentrio PolaRx GNSS receivers in the Asia-Pacific region recorded continuous L5 observations. About one week later, on July 4 shortly after 03:02 UTC, Javad and Trimble receivers picked up L1 C/A and L5 signals from QZS-2 for a few seconds. Then again, between 23:03 UTC on July 6, and 01:36 UTC on July 7, several receivers intermittently tracked the L1 C/A, L2C and L5 signals. Finally, on July 10, starting at approximately 01:03 UTC, these three signals were continuously tracked until approximately 04:00 UTC on July 12. Up until Aug. 1, signal tracking had remained intermittent, but has been stable since. This was presumably the result of interruptions in the signal transmission due to test activities.
Figure 1. QZS-2 signals tracked by GNSS receivers in Chofu, Japan, (top plot) and Sydney, Australia, (bottom plot). The plots depict the measured C/N0 for L1 C/A (black), L2C (red) and L5 (green) together with the observed pseudorange (grey). The frequent discontinuities in the pseudorange are due to the receiver clock adjustments. Both receivers exhibited a short tracking outage at approximately 06:00 UTC. The interruption in tracking at Chofu around 08:00 UTC is due to the low elevation angle of the satellite.
The plots in FIGURE 1 show QZS-2 signals as tracked by GNSS receivers in Japan and Australia on July 10. The two first sets of broadcast messages were transmitted on July 16 at 6:00 and 7:00 UTC. Regular transmission of broadcast ephemerides started on July 27 at 22:00 UTC, but deviations from the hourly update rate still occur from time to time.
Identical or Fraternal Twins?
At first glance, QZS-2 seems like a look-alike of QZS-1, but there are many differences between the two spacecraft. Most apparent is the presence of an additional auxiliary antenna. Like QZS-1, QZS-2 transmits its navigation signals on the L1, L2, L5 and L-band Experiment (LEX) frequencies through the main antenna, while the augmentation signal L1S (formally known as Submeter-class Augmentation with Integrity Function or SAIF) is transmitted from a separate antenna. However, the new L5S signal, which is introduced with QZS-2, is transmitted with yet another antenna.
The new satellite also has a shorter “wingspan” of only 19 meters, since it is equipped with two solar panel segments on each side, compared to three segments for QZS-1 with a width of 25.3 meters. The second QZSS satellite also follows a different attitude model: Unlike QZS-1, which switches between yaw-steering mode and orbit-normal mode depending on the sun’s elevation angle with respect to the orbit plane, QZS-2 always remains yaw-steering except for short periods of time when orbit maneuvers are performed. Further differences will become apparent in the analysis of the signal spectra in the subsequent sections.
The Cabinet Office of the Government of Japan, which oversees QZSS as a national undertaking, has published QZSS satellite metadata information on its official website. At the time of writing, only one document for QZS-2 is available, which contains information about the satellite’s properties such as mass, dimension, attitude law and reference frame, but also antenna and laser retroreflector positions, antenna phase-center offsets and variations as well as signal group delays.
Additional documents containing metadata for QZS-1, -3 and -4 and further information about QZS-2 are in preparation.
Rubidium Clock
FIGURE 2 illustrates the stability of the QZS-2 rubidium atomic frequency standard (RAFS) by means of the Allan deviation (ADEV). Data from a global network of 150 GNSS stations was processed to estimate GPS and QZSS satellite orbit and clock parameters.
Figure 2. Allan deviation of the rubidium atomic frequency standards of GPS Block IIF satellite G32, QZS-1 (J01) and QZS-2 (J02).
However, whereas about 60 of these stations provide QZS-1 observations, QZS-2 is only tracked by 13 stations. ADEV values for QZS-1, QZS-2 and a GPS Block IIF satellite were computed from a daily solution for Aug. 3 with 30-second clock sampling.
At an integration time of 100 seconds, the QZS RAFS reaches an ADEV of better than 3 × 10-13.
At longer integration times, the QZS-2 clock almost reaches the stability of the GPS Block IIF RAFS.
Based on this preliminary analysis for only one day, the QZS-2 clock seems to perform as expected. The larger ADEV values compared to QZS-1 for integration times up to 1,000 seconds might be attributed to the significantly smaller number of tracking stations contributing to the QZS-2 clock solution. The quality of the clock solution will improve as soon as more stations are able to track QZS-2.
Signals with High-Gain Antenna
Complementary to the receiver measurements and analysis, the German Aerospace Center (DLR) has also recorded raw spectral and in-phase and quadrature (IQ) data of QZS-2 to get further insights into the transmitted signal structure and initial signal quality. FIGURE 3 shows a spectral measurement of the complete GNSS L-band frequency range, which shows the signal transmissions of QZS-2 in the L1, L2, L5 and L6 bands. The signal was captured with DLR’s 30-meter high-gain antenna at Weilheim, southwest of Munich, operated by DLR’s German Space Operations Center.
Figure 3. QSZ-2 L-band normalized power spectra recorded at Weilheim, Germany, on July 18, 2017 at 20:43 UTC.
This first view of the signal transmission shows a good spectral shape, appropriate band filtering and no out-of-band unwanted spurious emissions of the satellite. For further analysis, we looked closer at each signal-band spectrum and performed IQ-sample recording.
Comparing the QZS-2 spectra to that of QZS-1, we see differences in the signal structure for the L1 frequency band.
Figure 4. QZS-1 and QZS-2 L1 spectral flux density.
FIGURE 4 shows the L1 spectra of both satellites. The additional signal component can be seen at an offset of 6 x 1.023 MHz and 18 x 1.023 MHz from the L1 center frequency of 1575.42 MHz. This is the result of the new L1C-pilot modulation, which is based on the time-multiplexed binary offset carrier (TMBOC) modulation technique using a mixture of BOC(1,1) and BOC(6,1). See here for detailed information.
Another difference is present in the L6 band and can be seen within the signal time domain or the IQ domain. The new satellite transmits two components (one each for the I- and Q-channels) while QZS-1 transmits only one I-component. This observation is fully in line with the QZSS Interface Specification. On QSZ-2, an additional L6 signal component (Centimeter-Level Augmentation Message for Experiments, L6E) is implemented. FIGURE 5 shows the IQ constellation plots of QZS-1 and QZS-2 for the L6 band.
Figure 5. L6 IQ constellation plots for QZS-1 (left) and QZS-1(right).
Source: GPS World
Furthermore, the L5 band IQ plot of QZS-2 exhibits significant differences compared to QZS-1. These differences, which are illustrated in the plots of FIGURE 6, are due to an additional L5S signal transmitted by QZS-2.
Figure 6. L5 IQ constellation plots for QZS-1 (left) and QS-2 (right).
Source: GPS World
The QZS-2 L5 IQ diagram is fairly easy to understand as a coherent superposition of two distinct quadrature signals from two antennas. One signal is the GPS-like L5 signal transmitted from the main L-band antenna, while the other (L5S) signal originates from a new L5S antenna. This is illustrated in FIGURE 7.
Figure 7. QZS-2 L5 IQ constellation plot including demarcation of the L5 and L5S signals.
For illustration purposes, the dashed orange square in Figure 7 relates to the 10 MHz L5 signal, while the smaller red squares are the 10 MHz L5S signal.
A code generator has been setup according the QZSS L5 and L5S interface control document (ICD). An analysis of the correlations of possible pseudorandom noise (PRN) codes resulted in the detection of PRN 194 and PRN 196. Based on the information in the ICDs, PRN 194 is used for L5 and PRN 196 is used for L5S.
The performed code correlation analysis also yields the finding that the L5 signal is approximately 3.5 dB stronger than the L5S signal. Note, however, that both signals have a specified minimum receive power of -157 dBW. Due to the limited visibility of QZSS satellites from the Weilheim ground station, it is not possible to verify this value.
Conclusion
With the launch and activation of QZS–2, the deployment of Japan’s regional navigation system is moving forward again. The launch of a geostationary satellite, QZS-3, took place on Aug. 18. A fourth Japanese navigation satellite is scheduled to launch later this year. With this rapid sequence, the target date of 2018 for the completion of an operational constellation with four satellites is quite realistic.
Steffen Thoelert, André Hauschild, Peter Steigenberger and Oliver Montenbruck are from the German Aerospace Center (DLR).
Richard B. Langley is from the University of New Brunswick and authors the monthly Innovation column for GPS World magazine.
QZS-2 L-band spectra, July 18, 2017, Weilheim, Germany. (Courtesy DLR)
Second QZSS Signal on Air
The successful launch of the Michibiki No. 2 satellite of the Quasi-Zenith Satellite System (QZSS) on June 1 has been followed by broadcast initiation. Researchers at the German Aerospace Center, Deutsches Zentrum für Luft- und Raumfahrt (DLR), have been observing the satellite from their ground station in Weilheim. They will provide a written analysis in the September issue.
The Japan Aerospace Exploration Agency launched first Michibiki satellite of the anticipated four-satellite constellation in September 2010.
Air Force to Recompete GPS III Follow-on
The U.S. Air Force will launch multibillion-dollar competition between current GPS III contractor Lockheed Martin Corp. and former GPS Block I and Block II contractor Boeing Co. for as many as 22 new GPS III satellites. At press time, an industry day in was scheduled for July 20 in El Segundo, California, to solicit company input, according to a new draft Request For Proposals.
In 2015 the Air Force undertook the first phase of a now two-year process to determine whether to put the next block of satellites up for competition. An initial review “has determined that viable, low-risk, high-confidence sources exist to conduct a full and open competition” for a second phase starting in fiscal 2018, according to the draft.
Lockheed Martin is assembling the first 10 satellites of the Block III program. Formal delivery of the first satellite was scheduled earlier this year, delayed by of a series of now-resolved problems with the navigation payload, cracked capacitors and a subcontractor gaffe last year that resulted in the wrong part being tested.
The satellite, which passed all of its qualification testing and verification, has been placed in storage pending the results of an unrelated review of the propulsion systems used to boost military satellites into orbit. The plan remains to launch the first GPS III satellite by spring of 2018.
“Lockheed Martin is working closely with the Air Force on resolving any concerns about the mission readiness of SV01’s Propulsion Subsystem,” Eschenfelder said in February. “We are confident that this review will not delay the Air Force’s planned spring 2018 Initial Launch Capability (ILC).”
NAVIC Clock Failures Resemble Galileo’s
The seven orbiting satellites of the Navigation Indian Constellation (NAVIC, formerly India’s Regional Navigation Satellite System, or IRNSS) have been hit by problems with some of their rubidium atomic clocks, similar to difficulties encountered earlier by Europe’s Galileo program.
NAVIC G-1 launch April 2017.
The Indian Space Research Organization (ISRO) had announced in July 2016 that all three atomic clocks on IRNSS-1A, launched in 2013, had malfunctioned, rendering that satellite ineffective.
Now, reports indicate that four more atomic clocks on the other six satellites launched more recently are not performing as required.
ISRO plans to launch a replacement satellite called IRNSS-1H in July-August to compensate for the loss of IRNSS-1A, although it is yet to announce the failure of more atomic clocks, which has not incapacitated the clock systems on the other six satellites.
The European Space Agency reported in January that anomalies had occurred in three of 36 Rubidium Atomic Frequency Standard (RAFS) clocks in the 18-satellite Galileo system, although none of the satellites were affected. ESA had said, “These failures all seem to have a consistent signature, linked to probable short circuits, and possibly a particular test procedure performed on the ground.”
ISRO has nine satellites indented for IRNSS. While seven satellites make up the Indian regional navigation constellation, the other two were indented as backup in the event of failure. Each satellite has three atomic clocks, one the primary timekeeper and the other two acting as backup.
“Measures are being taken to correct the problems caused by the clocks in the launch of future satellites. The atomic clocks to be used in the other satellites have been modified to prevent malfunction,” a senior official in the programme said.
ISRO chairman Kumar has indicated the number of satellites could go up from the originally envisaged seven to 11 but it is not clear if this is a consequence of the failing clocks. “We are set to launch more navigational satellites. They are in the process of approvals and clearances,” he said recently, and added efforts were on to revive the IRNSS-1A clocks.”
In Europe, the European Space Agency and an industrial partner-supplier have agreed that “some refurbishment is required on the remaining RAFS clocks” to be used in new Galileo satellites.
Look to GSA Service Centre for Galileo Advisories
In July, a wide transfer of responsibilities for the Galileo constellation took place, from the European Space Agency (ESA) to the European Global Navigation Satellite System Agency (GSA) of the European Union. Key among these was a handover of communications responsibilities to manufacturers, users and markets.
All parties can now find updates in the form of Notice Advisory to Galileo Users (NAGUs) at the GSA’s Galileo Service Centre, www.gsc-europa.eu/system-status/user-notifications.
NAGUs are issued as new satellites are launched and when satellites become ready for service provision, or to give advance warning of signal unavailability owing to planned maintenance or testing activities, or to notify users of unplanned outages and then to inform them when satellites become active again.
“Keeping our users in the picture on planned activities that might lead to satellite unavailabilityhas helped them to plan their own test activities and to prepare future products,” said Rafael Lucas Rodriguez, ESA’s Galileo services engineering manager.
A total of 189 NAGUs were issued under ESA oversight in the last four years, as the constellation grew to its current 18 satellites. The user base increased from 86 to 774 registered users on the European GNSS Service Centre website as companies worked to prepare Galileo-ready products. In December 2016, Galileo’s Initial Services began operating.
One regular consumer of Galileo NAGUs, Broadcom, uses them to organize engineering activities and tests as well as input them into its orbit prediction engine for its Long Term Orbits products.
Mitsubishi Heavy Industries Ltd. and the Japan Aerospace Exploration Agency (JAXA) successfully launched a second navigation satellite on June 1.
The H-IIA Launch Vehicle No. 34 (H-IIA F34) delivered into orbit Michibiki No. 2 of the Quasi-Zenith Satellite System (QZSS) at 9:17:46 a.m. (JST) from JAXA’s Tanegashima Space Center.
The launch and flight of the rocket proceeded as planned, and the separation of the satellite was confirmed 28 minutes and 21 seconds after the launch time.
