Category: BeiDou

The System: EGNOS Toolkits Enhance GPS Accuracy

EGNOS Toolkits Enhance GPS Accuracy

Free downloadable software Toolkits at www.egnos-portal.eu can help cell-phone and handheld receiver developers enhance location and timing applications with GPS corrrection data from the European Geostationary Navigation Overlay Service (EGNOS) satellite-based augmentation system.

The Toolkits include software packages, demo applications, and supporting materials, enabling application developers, researchers, university students, and others to create, use, and maintain EGNOS-capable positioning applications.

For handheld receiver manufacturers and mobile-phone developers, the Toolkit contains free source code for easy integration of EGNOS capabilities into a smartphone, and all the necessary files for the demonstration application, for use as a basis for a new application, as well as core libraries, to integrate enhanced EGNOS positioning capability into an existing application.

For the simply curious, an EGNOS Toolkit provides a means of exploring and understanding the entire chain from the raw GNSS satellite signal to enhanced EGNOS positioning data.

The development kit provides an easy way incorporate all EGNOS corrections and integrity capabilities, allowing developers to perform real EGNOS integration directly into a smartphone. It works with different operating systems, including Android, Apple, and RIM.

Static and kinematic tests show that EGNOS performs well in both cases: “The EGNOS SDK provides an average increase of 30 percent in position accuracy over GPS alone,“ according to developer DKE Aerospace.

EGNOS Software Development Kit provides a software receiver to enhance GPS positions, displaying position accuracy increases on average of 30 percent.

DOT Blank Stare on LightSquared

The U.S. Department of Transportation (DoT) responded to a Freedom of Information Act (FOIA) request by GPS World for its recommendations to the National Telecommunications and Information Administration (NTIA) regarding LightSquared interference with GPS. The DoT wrote, “We are withholding two pages [of thirteen relevant pages] in part and eleven pages in their entirety,” and enclosed two completely blacked-out pages.
Kathy Ray, DoT FOIA officer, added, “We have determined that the release of the redacted and withheld portions would foreseeably cause harm to the government’s deliberative process.”

The blacked-out DOT letter is dated August 25, 2011. How it differs from the agency’s July 21 “LightSquared Impact Assessment,” publicly available courtesy of the U.S. House of Representatives Committee on Science, Space, and Technology, cannot, of course, be known.

The Department of Homeland Security wrote in response to GPS World’s FOIA request, “We conducted a comprehensive search of files with the Science and Technology Directorate’s Homeland Security Enterprise and First Responders Group, and Cyber Security Division for records that would be responsive to your request. Unfortunately, we were unable to locate or identify any responsive records.”

The National Institute of Standards and Technology of the Department of Commerce replied, “NIST has no documents that are responsive to your request.”

The Department of the Interior provided the same documents that were previously made public by the House committee.

The National Aeronautics and Space Administration made a similar determination, but did not send a document, referring instead directly to the committee’s public website.

PNT Board Hears Proposal for LightSquared Solution

The November 9 meeting of the National Space-Based Position Navigation and Timing (PNT) Advisory Board in Alexandria, Virginia got several earfulls regarding the LightSquared/GPS controversy. One of seven speakers on a two-hour panel, Javad Ashjaee, president and CEO of JAVAD GNSS, demonstrated his company’s newly developed filter technology that he said could protect GPS receivers from LightSquared broadband network interference.

As Ashjaee stated, the proposed solution does not protect against interference from the so-called high-10 signals, one of two bands (the other is known as the low-10) for which LightSquared has received a conditional waiver. Unless and until a solution for the terrestrial high-10 signals is found, LightSquared transmissions in that band will still interfere with the GPS signal. The technical solution proposed by JAVAD GNSS addressed only the low-10 band.

Proposed filter to “harden” high-precision GPS receivers against Lightsquared Lower 10 (click to enlarge.)
The JAVAD GNSS proposed fix consists, in simplified form, of a ceramic filter followed by a series of surface acoustic wave (SAW) filters.
A PDF of Ashjaee’s 76-slide Powerpoint demonstration, without his verbal explanations and commentary, along with other presentations from the board meeting, are available at www.pnt.gov/advisory/2011/11/. A December 8 GPS World webinar reprised the same presentation, and the download at env-gpsworld-integration.kinsta.cloud/webinar includes audio of Ashjaee’s remarks.

Ashjaee said that his company’s testing of its own filter methodology found no GPS signal loss due to a low-10 (10L) signal power of –10 dBm. An “Ultimate Test: Special Zero Baseline” put receivers on a Moscow skyscraper with multipath from both above and below. One antenna fed two receivers (zero baseline). One receiver used standard filtering and the other the new filters. He said that over 15 hours of testing the average carrier-phase error between the two receivers was 0.2 millimeters, and the average code difference was about 5 centimeters.

JAVAD GNSS has started production of what Ashjaee calls “LightSquared-compatible” Triumph GNSS receivers. He brought 40 units to the PNT Board meeting. The company will begin manufacturing “LightSquared-integrated” receivers in May 2012, for RTK positioning using the proposed LightSquared broadband network for high-speed communication, if and when it is deployed.

Fellow presenter Jim Kirkland, vice president and general counsel for Trimble Navigation, pointed out that such filters represented a potential solution only for one class of high-precision receivers. Whether it would work for other classes of high-precision receivers had yet to be verified. Kirkland said that even if further independent testing shows that the filter solution is viable at the lower 10 MHz of the spectrum, retrofits would be costly and time consuming.

Questions regarding cost and responsibility of retrofit, should the solution prove practical, were not discussed at length at the meeting, nor was any solution proposed.

LightSquared executive vice president Martin Harriman did not directly answer a question as to whether his company intends to develop the upper 10 MHz for which it has been given a conditional waiver.

Scott Burgett, software engineering manager for Garmin International, said, “It is almost impossible to design new products compatible with LightSquared’s proposed system without knowing its technology’s end state.” He estimated 10–15 years to properly retrofit Garmin devices, which are widely distributed in general aviation, personal navigation, car navigation, and other sectors, so that they could coexist with LightSquared.

The panel was moderated by Tom Stansell of Stansell Consulting, who concluded, “I think we learned, thanks to Javad, about a very clever solution to a particular problem for a particular range of products — the products he is most familiar with. It may or may not fit in some of the other applications.

“What we have not addressed is the elephant in the living room,” Stansell continued. “That is the cost, and time delay, and changeover process if LightSquared is allowed to go forward. Will it be the lower 10, upper 10? That has to be resolved. There are very large questions remaining to be discussed, and [they] may or may not be fully solved in a short period of time.”

Constellation Updates

Where Is Compass ICD?

The long-awaited signal interface control document (ICD) for China’s Beidou/Compass GNSS has not yet appeared, despite an announcement at the ION-GNSS conference by Chinese delegates that ICD document v1.0 will be published in 2011, “probably” in the month of October. When it does appear, it should be available for download on the Compass website, www.beidou.gov.cn (as yet without an English version), also at www.compass.gov.cn.

The delay in publishing a document may reflect a system very much in formulation, with ongoing discussions among the principal parties to its design, with different views on system architecture and possibly even final signal structure. This was one possible conclusion that could be inferred — a dynamic system in formation and growing rapidly — from varying reports given by different Chinese representatives, governent and academic, at the ION Compass session.

There was some disagreement among panelists at that time as to, for example, the final targeted number of satellites in the system: either 30, or 35.

The ICD has been rumored to be available previously to receiver manufacturers within China, creating some disgruntlement among companies outside the country. One of the ION panelists affirmed that GPS/Compass chips and receivers are being actively developed by many Chinese manufacturers and research institutes.

The next BeiDou/Compass launch, which will be for the system’s fifth inclined geosynchronous orbit satellite, is expected during the first few days of December, according to web discussions. As of press time for this magazine, there had been no official announcement on the Chinese official government BeiDou website, www.compass.gov.cn.

The site has posted Chinese and English versions of a document titled “Report on the Development of BeiDou (COMPASS) Navigation Satellite System (V1.0)” by the China Satellite Navigation Office. The pages are viewable as separate images.

Galileo Under Control

Europe’s first two in-orbit validation satellites reached their final operating slotss 23,222 kilometers above Earth, have been activated, and are now undergoing tests of their navigation payloads, reports the European Space Agency (ESA).

Marking the formal end of their Launch and Early Operations Phase, control of the satellites passed on November 3 from the French space agency (CNES) center in Toulouse to the Galileo Control Centre in Oberpfaffenhofen, Germany.

Oberfaffenhofen, operated by the German Aerospace Center (DLR), will be in charge of the satellites’ command and control for the whole of their 12-year operating lives. The navigation signals are being checked out by ESA’s ground station in Redu, Belgium, where a 20-meter antenna measures the shape of the signals to a high degree of accuracy. Once the navigation payload is fully checked out and activated, a second Galileo Control Centre in Fucino, Italy, will oversee all navigation services. All activities are performed under contract to SpaceOpal, a joint subsidiary of DLR and the Italian company Telespazio.

GLONASS as Expected

The Satellite System Mission Control Center of the Russian Ministry of Defence, with the ISS-Reshetnev Information Computation Center, established communication with the three GLONASS satellites launched November 4. The satellites are earth- and sun-oriented, and their subsystems are functioning properly.

According to NORAD tracking, the three satellites were inserted into Plane 1. This was expected as there are only seven active satellites in this plane, whereas the other two planes have a full complement of eight satellites. Orbit slot 3 in Plane 1 is currently vacant. According to Nikolay Testoyedov, ISS-Reshetnev general designer and director general, the new satellites will ensure the operation of a complete 24-satellite GLONASS constellation, and allow creating the necessary orbital reserve.

GPS GEO-MEO Floated

In a presentation titled “Analysis of Alternatives for Future GPS Architecture; Considerations for Constellation Sustainment,” made to the U.S. PNT Advisory Board on November 9, Kirk Lewis, senior advisor from the Institute for Defense Analyses (IDA), put forth the concept of “boosting” GPS III payloads onto commercial geostationary Earth-orbit (GEO) satellites.

After concluding that the current program of launches and orbit costs extending into the Block III-C generation is not sustainable, Lewis presented several alternatives, but quickly eliminated two that involved low-Earth-orbit satellites and non-space options, due to technical, scheduling, and performance issues. Remaining in play are “potential and realistic” GEO and mid-Earth orbit (MEO, the configuration of the present GPS constellation) options, used individually or in combination.

IDA analysis found that two GEO satellites, separated by 15 degrees or more longitude, supplied almost the same signal performance as adding six MEO satellites. The presentation is available at www.pnt.gov/advisory/2011/11/.

December 1, 2011
Doing GNSS Business in China
China represents a huge potential market for Western GNSS companies, even though the country has a strong and growing GNSS capability of its own. Before booking a flight to Shanghai or Beijing, however, some careful preliminary research will likely pay off: looking for potential Chinese industry partners with whom you would jointly work to open a market niche. The key ingredient — a huge investment in developing personal relationships, two-way trust, and understanding — is the only way to really penetrate the Chinese market. This month’s columns recaps some of the highlights of our recent webinar on this topic, and explores further with questions from our audience and the answers from our panel of experience China businesspeople.

Back on July 21, we held a GPS World webinar on “Doing GNSS Business in China.” The presenters were Vic Hsiao, CEO of Knowledge Access in California; Francis Yuen, CEO of Baseband Technology in Calgary, Canada; Jianhui Lee, president of BDStar in Beijing, China; and myself. The presentations were not only informative, but also generated a host of questions from a very well-informed group of GNSS-ers who logged on for the webinar. It’s therefore useful that we review what was discussed and that we try to summarize some of the key issues raised by the web audience.

Vic Hsiao has clearly spent significant time in China in his current consulting capacity, and previously with NavCom, Qualcomm, and Magellan, so he knows the dos and don’ts of trying to market in China. China represents a huge potential market for Western GNSS companies, even though there is a strong and growing GNSS capability, as Jianhui Lee explained the wide range of activities in which BDStar has become involved. Francis Yuen added a number of well illustrated commentaries around culture, communications, and negotiation which are particular to doing business in China.

In the slew of questions we received, there were a couple of common themes which I’ll try to address first. There is a really wide-felt concern about protection of intellectual property (IP) when doing business in China. While China is becoming aware of the need for IP protection, especially as its own GNSS industries create their own Beidou/COMPASS IP, and the filing of indigenous patents has grown by a whopping 57% (!), it’s still difficult to say that Chinese industry has fully grasped the concept of IP ownership and value.

So what could you do to protect your key “crown jewels” when, as a Western company, you venture into China? That question actually leads us into what would be the best way to enter the Chinese market. Showing up in Beijing with a catalogue and samples and knocking on doors is probably not the preferred approach. Before booking a flight, careful research would likely pay off looking for potential Chinese industry partners with whom you would jointly work to open a market niche. Then that leads to the key ingredient — huge investments in developing personal relationships, two-way trust, and understanding. This is the only way to really penetrate the Chinese market, through an extremely well-known and trusted partner.

And with a trusted partner, IP protection should be easier because personal relationships usually help understanding and acceptance of each other’s needs. Nevertheless, both sides need to protect their stuff as you would in a working relationship between two Western companies where trade secrets are retained and discussed only at the top level. I’ve known of instances where only object code has changed hands, and yes, object code and chips can also be cracked, which is why you need a trusted partner, as well as well established, long-term personal relationships and a business relationship which is mutually beneficial.

But don’t be fooled, China does understand IP protection very well — just ask anyone who’s still trying to get hold of the Beidou/COMPASS signal in space ICD. The Chinese government has restricted access to this key to tracking the full Beidou/COMPASS signal, and we’ve only seen Chinese companies making direct use of this ICD. Again, just another reason why you need a great Chinese industrial partner — they may be able get access to the ICD. Not that that will help you directly — you still have to work through your partner to implement Beidou signal tracking — maybe in an application embedded in the end product/receiver.

And is this all worthwhile? It’s not the easiest market to access. It’s a long way from home and the effort involved in servicing this market from the West (even with a great in-country partner) is significant. The estimated market for GNSS in China is probably around $18 Billion in 2011 and growing at a whopping 50% annual rate, so even though it takes a lot of work, the potential for a healthy return is still huge. This market will likely continue to exist for some time for Western companies, provided you’ve got the right products and have established your Chinese market baseline as we’ve outlined. But don’t wait too long — China has announced its intention to join the GNSS market on an equal footing with all the other GNSS constellation-capable nations, and that intention is not only for sovereign control of its navigation assets, it’s also to gain market share for its own industries. Import duties for GNSS products are, however, still low (around 1.5 to 5% of selling price), so it’s still possible to sell Western GNSS equipment into China. And it’s generally accepted that dual-frequency GNSS chipsets are all still imported from outside China.

Some other questions we may have not yet addressed include:
- How receptive are the Chinese to women entrepreneurs? There are a lot of women in leading positions in this industry, and Vic Hsiao believes there are a large number of Chinese women entrepreneurs — so being a Western woman trying to do business in China should be a positive thing.
- What is the requirement to offer integrated receivers with Beidou/Compass capability? As China is investing heavily in Beidou/Compass, it wouldn’t be unreasonable to expect something in the future like when Russia mandated GLONASS capability in Russia. The safe way forward is to find a Chinese partner and implement Beidou/Compass capability.
- Negotiation strategies? This is perhaps the hardest thing for Western companies to get their heads around. Chinese want the best deal possible and they will likely try to wring the last cent out of any negotiated sale. This is particularly true in the commercial market where pricing is the only edge Chinese companies can get in an increasingly competitive internal market. The best strategy is to look at the longer term and work hard to stay connected to the business over many years. If you drift away from your partner, expect things to come off the rails, so remain as closely connected partners. Make a deal that is good for both sides, even though you might feel you could have done better. It’s a huge market and a few points of margin might be worth it for a long-term business presence in one of the largest, fastest growing markets in the world.
So, lots of information for people looking to make their first foray into GNSS in China — maybe not so much new news for those who are old hands, but hopefully there was the odd bit which was useful. Certainly there were a lot of questions we stirred up with our webinar. Thanks for everyone who participated; if I missed your concern, please drop me an e-mail ([email protected]) and I’ll do my best to get you some help.

Tony Murfin
GNSS Aerospace
August 25, 2011
What’s Going on in China?

When I first visited Beijing a few years ago, I came there from a stop in India. This was just before the Olympics in 2008, but there were signs then of big-scale preparations in terms of highway infrastructure and building. As the two most populous countries in the world, India (1.13 billion people) and China (1.3 billion people) both are making huge strides forward. China does appear for the moment, however, to be more focused on the commercialization of GNSS.

True, both countries are working towards their own GNSS constellations using their own launchers — China with Beidou/COMPASS and India with IRNSS — but China does appear to be ahead in this particular “space race.” While India plots a path towards IRNSS and GAGAN is up and running, Beidou Geostationary satellites are already in orbit, and western users have already reported tracking signals. With seven satellites already on orbit, Beidou/COMPASS is well on its way towards becoming first a regional and then a global satellite navigation system.

A whole heap of Chinese companies are working on GNSS in China — those who have developed low-end single-frequency, mass-market receivers and applications, and many who have imported receivers from the West and built applications around them, with lots of software applications, ancillary items such as antennas, handheld enclosures, and more. With this level of capability, it’s not surprising that indigenous multiple-frequency Beidou/GPS/GLONASS professional receivers may already be available.

I talked recently with some old friends in Beijing to catch up on Chinese GNSS and to learn more about the activities of their company — known as BDStar. Originally established in 2000, significant growth led in 2007 to an Initial Public Offering — this IPO in itself is a sign of significant economic change and growth in China. From an initial start-up staff of a few key individuals in 2000, this company has now grown to employ more than 650 people at several locations around China, working through the BDStar parent and in five subsidiary companies.

BDStar started off by importing Western survey-quality receivers and building them into survey-related applications, including high-precision vehicle tracking, geographic information systems, control, and telemetry. While port automation projects are not new, BDStar also undertook several of these as far back as 2003. It’s easy to see how Chinese companies are becoming world class when we look at the extensive skills and technical capabilities needed for these large-scale, complex projects.

BDStar took on a key project which propelled its growth when it successfully provided its first container inventory systems for a Chinese port. These containers are the large shipping boxes we see in the holds and on the decks of huge cargo ships, and sometimes flying by us on the backs of 18 wheelers. It takes enormous cranes and transporters to move them around when they leave or arrive at ports around the world. Huge dockside cranes unload containers from ships, then rubber-wheeled gantries move them from the dock to massive storage areas. These gantries acquire data when they hook up — such as where the container is coming from, where it’s going to, and when it will get its next ride — then location information is added to the container data file. When the gantry deposits the container at its temporary storage location, an RTK measurement tags the exact position at which it is stored within the vast maze of container stacks so workers can find it again later and move it onwards to its destination.

The system extends to the unloading quayside cranes, various forms of fork-lift trucks, and trailers used to transport containers about the yard. This all adds up to hundreds of radio links and radio management issues, difficult RTK receiver installations on vibrating, all-weather moving platforms — all of which need visibility of the sky and access to RTK correction signals — plus huge amounts of data acquisition and handling and display systems: a highly complex system solution that BDStar has now replicated at several ports.

Locating, tracking, and moving containers to and from their ships, in some of the largest shipping yards in the world, is no small problem. The BDStar system appears to have automated and simplified container movement for ports that include Ninbo Port Second Container Terminal, Shanghai Yangshan Container Terminals, Shenzhen Chiwan Container Terminals, Tianjin Container Terminals, and other container terminals in Shenzhen and Hong Kong. BDStar claims that the production efficiency of ports equipped with its system is improved by between 5 and 10 percent. Sure are a lot of containers at these “super-ports” in China and around the world, so improving the tracking and transit of containers through these ports can significantly improve profitability for the shipping companies.

Then, in a completely different direction, BDStar designed and implemented the ground control and monitoring command center for the early Beidou satellites. The system provides positioning, time-transfer, and short-message information for onwards distribution to Beidou users. The Beidou system not only provides positioning and timing data, but also has a “short-message” capability. BDStar has adapted this ground system so that China’s long-distance fishing fleet can be tracked and supported from mainland China. China has the largest marine fishing fleet in the world — about 280,000 vessels and a fishing industry with nearly 10 million people with the most dangerous jobs in China. It is estimated that 8,774 fishermen died and 22,345 vessels were lost while fishing between 1993 and 2004.

Vessel position data is transmitted over the Beidou short-message system, frequently from ships which are thousands of miles away from port. The BDStar system gathers this information and redistributes it to vessel operator companies on shore. The system also cross-connects the Beidou short message system with land-based cell-phone systems. Customers can respond over the Beidou short-message system; for instance, in the event that a ship is in distress, other ships in the vicinity can be routed to assist. This is currently the primary application for Beidou civilian usage, and through it BDStar has become the number one Beidou operator and terminal provider in China.

With an estimated 20m positioning accuracy, Beidou is well on its way to being a regional GNSS in 2012. By 2020 the system is planned to be global. Beidou capable receivers are clearly already being sold within China — mostly in applications using the short-message function. Unicore, a BDStar subsidiary, advertises Beidou/GPS/GLONASS receivers and chipsets developed in China.

A 2009 report estimated the GNSS market in China to be worth close to $9 billion U.S., mostly in consumer applications, and growing at around 50 percent annually! BDStar therefore has lots of local competition, and increasing competition from western GNSS suppliers aligned with other local GNSS companies. But as in most markets it’s likely that healthy, successful companies like BDStar will continue to thrive and prosper. Growth like this is good for the GNSS industry, as opportunities seem to abound for everyone in such an expanding Chinese marketplace.

Tony Murfin
GNSS Aerospace

March 23, 2011
Expert Advice: The Strategic Significance of Compass
Scott Pace

By Scott Pace

On November 1, 2010, China’s state news agency reported that the sixth Compass satellite was launched from the Xichang Satellite Launch Center. This was the fourth Compass satellite put into orbit this year, following launches in January, June, and August. Joining the United States, Russia, and the European Union, China is deploying is own global navigation satellite system of five geosynchronous satellites, 27 in medium Earth orbit (MEO) and three in highly inclined geosynchronous orbits (IGSO).

Sometimes referred to as Beidou-2, Compass is a global RNSS (radio-navigation satellite system) that broadcasts one-way precision time signals to enable receivers to calculate their position. An earlier Chinese satellite navigation system, Beidou-1, was an RDSS (radio-determination satellite system) that provided regional coverage and required two satellites to get a position fix using two-way communications with a centralized ground station.

Like the U.S. GPS and the European Galileo system, signals from Compass use the CDMA (code-division multiple access) channel access method as distinct from the FDMA (frequency-division multiple access) method used by GLONASS. CDMA enables more precise positioning as compared to FDMA, and GLONASS is planning to shift to CDMA for its future satellites.

Compass is designed to operate on three primary L-band frequencies:
- 1559.052–1591.788 MHz,
- 1166.22–1217.37 MHz,
- 1250.618-1286.423 MHz
while offering both an open service and an authorized service. The latter is expected to require cryptographic keys for access and will be reserved for military and public safety-related uses. Compass is intended to provide service to the Asia-Pacific region sometime in 2012 and to attain global-service levels around 2020.

Reasons for Compass

The Russian GLONASS was developed to support the Soviet Navy, and the U.S. GPS arose from the merger of previously separate Air Force and Navy satellite navigation efforts. China began researching satellite navigation and positioning technologies in the 1960s, but it was not until 1983 that a plan for satellite navigation and positioning system was developed. The “Double Star Rapid Positioning System” was the basis for the Beidou-1 two-satellite RDSS system that was formally approved for development in 1994. The impetus for the Compass systems is not fully known, but press reports attribute it to military requirements for more accurate missile targeting.

The Chinese were close observers of the role of GPS in the first Gulf War. Chinese writings on military doctrine began to talk of “war under informationalized conditions” and how information from space-based systems such as GPS was changing the nature of modern warfare. Exploiting these new information sources required not just space capabilities but changes in how military forces were organized, trained, and equipped.

Chinese security interests encompass not only China itself and nearby areas, but also the sea lanes that enable the import of raw materials and export of finished goods. In recent years, China has shown an increasing interest in “maritime domain awareness,” in which satellite navigation is used for monitoring the transit of ships in the Indian Ocean (for example, oil from the Middle East) and the South China Sea (minerals from Australia, fishing zones). Satellite navigation is a dual-use, commercial and military, interest for China, and this may have prompted support for the more advanced, independent GNSS that would become Beidou-2 or Compass.

Regardless of the cause, People’s Liberation Army officials have said that China needs it own satellite positioning system to ensure its ability to conduct independent military actions. The later 1990s saw continued Beidou-1 satellite deployments while design of the newer Beidou-2/Compass satellites began. China joined the Galileo consortium in 2003 but abandoned it in 2006 in dissatisfaction over access to technology and work share arrangements. Efforts on Compass accelerated, and the first experimental satellite of the new system was launched in 2007.

In a September 2010 interview with Chinese press, Duan Zhaoyu, vice president of BDStar Navigation, said that there are currently more than 20,000 civilian users of the Beidou-1 navigation system, 60 percent of whom use products from his company. More than 10,000 of these users are fishermen in the South China Sea. Not surprisingly, the Chinese government and military constituted the majority of users as it was also reported that as of August 2009, there were only 60,000 Beidou users in total. The number of registered terminal users amounted to only 1 percent of the system’s capacity, leaving the satellite resource seriously under-used.

The underutilization of Beidou-1 is both a challenge and an opportunity for the Compass system in both domestic and international applications. The designer of the first Chinese satellites and current Beidou chief designer, Sun Jiadong has stressed the importance of actual utilization in arguing that “satellites in the sky should be coordinated with ground applications” and “pushing China’s Beidou satellite navigation system to bring as much economic and social benefit as early and as quickly as possible.” In order to do this, “…the state should promulgate corresponding policies, regulations, and systems as soon as possible to support development of the new satellite navigation application industry. It should guide, encourage, and attract even more Chinese enterprises and public institutions to actively participate in the construction of an industrial chain for ground applications.”

Internationally, China has stressed cooperation with other GNSS systems. At the June 2010 meeting of the Asia-Pacific Economic Cooperation (APEC) organization, the Chinese presentation said that Beidou-2 (Compass) would “provide high-quality open services free of charge from direct users, and worldwide use of Beidou is encouraged,” and that Beidou-2 will “pursue solutions to realize compatibility and interoperability with other satellite navigation systems.”

While satellite deployments have been accelerating, there continue to be delays in the public release of interface control documents (ICD) for incorporating Compass signals into GNSS receivers. The technical preparation of Beidou-2 Signal-in-Space ICD (version 1.0) has reportedly been finished but has not yet been posted on the Chinese government website for the program at www.beidou.gov.cn. In October 2009, Cao Chong, the director of the consulting center at the China Technical Application Association for Global Positioning System, gave a speech at Stanford University where he said that English and Chinese versions of the ICD have already been completed. But their release had been postponed due to pressure from domestic companies in China.

The point of an open ICD, as done with GPS, is that as soon as it is released, anyone can use it on an equal basis. Reported opposition from Chinese companies seeking to gain a head start on foreign competitors would seem to indicate a domestic misperception of RNSS systems and an internal contradiction in Chinese policy toward Compass. Like other RNSS systems, Compass does not use a two-way signal for which direct users fees can be easily assessed; thus the idea of “head start” is illusionary. The necessary technologies for RNSS receivers are all found in consumer electronics and software — areas in which C
hina is already capable.

In addition, efforts to discourage or delay foreign adoption of Compass signals poses the risk of the system being of limited relevance to global markets, as is the situation of Beidou-1 today. This is contrary to the stated intent of the Chinese government that Compass be a world-class GNSS system.

ITU System Coordination

A primary concern of all GNSS users and operators is compatibility, that is, the ability of multiple satellite navigation systems to co-exist in the same international spectrum allocations without causing harmful interference to any individual service or signal. The signals may or may not be interoperable but they should not harm each other. In the case of Compass, its signals do overlap some Galileo frequencies, particularly with respect to the Galileo Publicly Regulated Service (PRS) and to a lesser extent the edges of the GPS M-Code that is used exclusively for defense purposes. In general, however, Compass signals do not overlap the GPS or GLONASS frequencies. Informal Chinese comments suggest that they consider GPS and GLONASS to be well-established “legacy” systems that new arrivals should seek to avoid overlapping. On the other hand, Galileo and Compass are seen as having equal standing as new RNSS systems within the terms of the International Telecommunications Union (ITU).

Chinese presentations have identified several Compass signals that would overlap those of other GNSS providers. These include the Compass B1 at 1575.42 MHz with the GPS L1 signal, B2a at 1176.45 MHz with the GPS L5 signal, and B2b at 1207.14 MHz with the Galileo E5b signal. The Chinese believe that “the frequency spectrum overlap of open signals is beneficial for the realization of interoperability for many applications” and makes it easier to develop and manufacture interoperable receivers. While these claims are true to a point, GNSS providers experiencing the overlap may not agree.

Even if signals do not experience harmful interference from an overlap, the signal provider may suffer constraints on its ability to control the service it provides to specific users, as in public safety or military applications. The long negotiations between the United States and the European Union over Galileo proposals to overlay major portions of the GPS M-Code eventually resulted in the 2004 US-EU Agreement on GPS-Galileo Cooperation. More recently, the European Union has raised its concerns with China’s plans to overlay Compass signals on the Galileo signals used for the PRS service.

Within the ITU, RNSS operators (which includes the GNSS system providers) engage in direct coordination under what is known as a Resolution 609 process. This process was adopted at the 2003 World Radiocommunication Conference in Geneva, Switzerland and calls for “Consultation Meetings between administrations operating or planning to operate systems in the aeronautical radionavigation service (ARNS) and systems in the radionavigation satellite service (RNSS) in the 1164–1215 MHz frequency band.” It should be noted that the resolution does not encompass all GNSS signals, but does focuses on those at the GPS L5, Galileo E5, and Compass B2. The most recent meeting was the 7th Consultation Meeting of Resolution 609, June 23–25, 2010 in Toulouse, France.

EPFD Levels. As the Resolution 609 process has continued, calculations of aggregate, equivalent power flux density levels (epfd) show that levels from filed RNSS systems (some operational, some planned) are nearing the allowable maximum aggregate epfd level. This level is specified in Resolution 609 itself, as revised at the last World Radiocommunications Conference (WRC-07). The United States position is that it is important to discuss methods to ensure that this limit is not in fact exceeded.

The Toulouse Consultation Meeting discussed three potential methods to achieve this important objective:
- use of actual operational characteristics (for example, maximum operational power levels, instead of filed parameters);
- use of the actual number of satellites in orbit, instead of the filed number; and
- technical revisions to the epfd calculation methodology (per ITU-R Recommendation M.1642-2).
The meeting also considered proposals in the case where calculations show the aggregate epfd level would be exceeded, to perform a second aggregate epfd calculation including only satellites that are in actual operation, or are planned to be in operation before the next Resolution 609 Consultation Meeting is scheduled to occur (that is, within the next 12 to 16 months). The point of the second calculation would determine that epfd actually being produced from RNSS satellites in the 1164–1215 MHz band will not in fact exceed the allowable epfd limit.

In addition to the Resolution 609 multilateral meetings, the United States and China have also engaged in five operator-to-operator coordination meetings under ITU auspices from 2007–2010. The United States has also offered the possibility of direct bilateral talks with China on GNSS services and applications — as was done with Japan, Russia, and the European Union.

Europe similarly has sought to have direct talks with China to coordinate their concerns over Compass-Galileo. There have been at least six meetings on frequency compatibility and interoperability during 2007–2010, alternating between Beijing and Brussels. While both sides continue to express support for compatibility and even interoperability, the European side continues to oppose Compass overlays of the Galileo PRS while China shows no indication of being willing to change its frequency plans.

Finally, with respect to Russia, a Beidou-GLONASS frequency compatibility meeting was held in Moscow in January 2007, but there seems to have been little follow-up. Given the lack of overlap between the frequencies used by the two systems, this is not surprising.

International GNSS Coordination

Compass is represented in broader GNSS coordination activities, not just those involving the ITU. The most important of these is the International Committee on GNSS (ICG) that was established in 2005 as an outgrowth of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). The most recent, and fifth, meeting of the ICG was held in October 2010 in Turin, Italy.

The purpose of the ICG is to “promote the use of GNSS infrastructure on a global basis and to facilitate exchange of information.” Through meetings of the ICG, GNSS providers have adopted various principles such as transparency for open services, that is, every provider should publish documentation that describes signal and system information, policies of provision, and minimum levels of performance for its open services.

On a regional basis, China participates in the APEC GNSS Implementation Team. This team was established by the APEC Transportation Working Group in 2000 with a mission of promoting regional GNSS augmentation systems to enhance inter-modal transportation. The United States hosted the 14th APEC GIT meeting this past June in Seattle, Washinmgton; the next meeting is tentatively scheduled for Brisbane, Australia, in May 2011. The significance of the APEC meetings on GNSS is their recognition of the value of such systems to states at greatly varying levels of development, not just the providers of GNSS or major GNSS augmentations. Although the group has a transportation focus, the productivity, safety, and environmental benefits of GNSS uses provide an incentive for common efforts across the Asia-Pacific region.

In addition, the group calls for cooperating with non-APEC organizations (such as the ITU) as necessary to provide for seamless implementation.

Strategic Significance of Compass

Unlike Galileo, Compass is not a multinational cooperative program nor did it ever consider being a public-private partnership. Like GPS and GLONASS, Compass was created as an independent strategic effort by
a national government for military and economic benefits.

Unlike the history of GPS and GLONASS, however, the Chinese government from the beginning recognized the dual-use nature of Compass signals. Like GPS today, Compass plans to deploy CDMA signals at multiple frequencies to support a full range of application, from transportation to precision positioning and timing.

Like Galileo, Compass still has to demonstrate that its signals are stable, operationally reliable, and accurately represented by published interface control documents to attract manufacturers to build the capability into their products. Galileo, Compass, and GLONASS all have the challenge of meeting the expectation of the existing installed base of billions of GPS users — whether or not they know they are reliant on GPS.

The technical management of Compass is clearer than its policy management. Compass and Beidou-1 are the responsibility of the China Aerospace Science and Technology Corporation (CASC), the administrative holding company for the China Academy of Spaceflight Technology (CAST), the primary state-owned contractor for the Chinese space program. The military plays a large role in all Chinese space activities, and in recent years there has been uncertainty as to who is the government policy leader for space. In particular, the role of the China National Space Agency (CNSA) appears to have diminished in recent years. CNSA leaders scheduled to speak at major international conferences, such as the International Astronautical Federation, have cancelled at the last minute, while PLA speakers have presented instead.

When U.S. President Barack Obama and China’s President Hu Jintao met in Beijing in 2009, their joint summit statement included a call for the NASA administrator to meet with an unspecified Chinese counterpart. Some of this may be coincidence due to other time demands such as launch schedules, but the Chinese decision-making hierarchy for space remains as opaque as it does in so many other areas.

The opaqueness of Chinese political decision-making prompts speculation as to what China’s long-term strategic intent is with respect to Compass. The advent of open Compass signals would be potentially positive for the current installed base of GPS users — providing interoperable signals that improved the availability of positioning solutions. Internationally, the Chinese presence helps secure the international use of the RNSS spectrum and could be a potential ally in suppressing commercial sales of GNSS jamming devices — some of which are manufactured in China today. The view from Russia with respect to GLONASS is likely to be similar to that of GPS; Compass is largely a complementary system.

From a European perspective, however, Compass is more problematic, both technically and commercially. The signal overlay on the Galileo PRS is a potential complication for Europe being able to deny PRS access in times of emergency.

Perhaps more importantly, the rapid pace of Compass satellite deployments means that Compass may reach an initially operational capability sooner than Galileo. This is highly probable for coverage in Asia and increasingly likely on a global basis as Galileo faces criticism over cost increases and schedule delays. While Galileo has published an open service ICD and China has not, it would be a simple matter for China to time the release of an official Compass ICD one product cycle (that is, 18 months) before the 2012 completion of Asia-Pacific coverage. This would make Compass potentially very attractive to manufacturers looking to decide what would be of most benefit to the existing installed base.

In general, China pursues its space activities as part of broad approach to what might be termed “comprehensive national power” to include military power, economic power, diplomatic influence, scientific and technological capabilities, and even political and cultural unity. This need not necessarily mean that such power will be used for aggressive purposes.

If China’s strategic intent is to ensure its own independence and a place at the global table, then it is possible that Compass will not be harmful to U.S. interests. This outcome will depend on whether China continues to work with the international community in forums such as the ITU, the ICG, APEC, and so on, maintains open markets, and does not use Compass in military efforts to force changes in the status quo regarding Taiwan, the South China Sea, or the Indian Ocean.

Since China’s strategic intentions are unclear, it makes sense for the United States to seek bilateral discussions with China on Compass and to maintain a close strategic dialog with other countries in the region, notably Japan, Australia, Korea, Russia, and India. These countries are not only militarily and economically important, but also have their own GNSS-related systems and equities to consider.

The choices for China are whether Compass will be part of its “peaceful rise” and will serve truly national interests. Those interests could be seen as harnessing the kinds of dramatic IT productivity benefits other economies have seen in GNSS applications — enhanced by open, market-driven innovation and competition.

Alternatively, it is possible to imagine China closing off its domestic market, protecting domestic state-owned enterprises, and focusing on the space and military aspects of Compass rather than market-driven civil and commercial applications.

The question for Chinese leaders is whether they should measure the success of Compass just by the success of Chinese firms at home or by the global acceptance of Compass as a reliable brand name for GNSS services and signals.

Compass is like China itself, where there are both great promise and some concerns. The signs to date for Compass are positive and will hopefully continue on the path of engagement and cooperation. The United States and the global GPS community should continue to encourage those positive signs in working with China, commercially, diplomatically, scientifically, and (perhaps especially) with more direct military-to-military contacts. All of these efforts can increase the chances that China will join the United States as another good steward of GNSS.

SCOTT PACE is the director of the Space Policy Institute and a professor at George Washington University’s Elliott School of International Affairs. His research interests include civil, commercial, and national security space policy. From 2005–2008, he served as the associate administrator for program analysis and evaluation at NASA. Previously, he was the assistant director for space and aeronautics in the White House Office of Science and Technology Policy.
December 1, 2010
The System: QZSS Puts L1C on the Air

QZSS Puts L1C on the Air

JAVAD Receivers Track the First Truly Interoperable Signal

JAVAD GNSS engineers in Moscow have released plots of the C/A, L2C, L5, SAIF, and the new L1C signals broadcast by Japan’s QZSS Michibiki, the first satellite to transmit L1C.

The company stated that all of its current GNSS receivers can track QZSS signals with a software update that is available as an option to purchase.

A new civil signal, L1C is designed to be interoperable among GNSSs. Currently, agreements are in place between the U.S. GPS, Europe’s Galileo, and Japan’s QZSS systems regarding broadcast and use of L1C. The U.S. system is not destined to add the L1C signal until the GPS III block of satellites, still more than three years out.

The SAIF (Submeter-class Augmentation with Integrity Function) signal is a GPS augmentation with information on positioning correction and system health. The QZSS L1-C/A, L2C, L5, and L1C signals are GPS augmentation signals that can be operated reciprocally with positioning signals provided by GPS. The figures supplied by JAVAD GNSS show SNR (top) and code-minus-phase (bottom) plots for L1C.

Plot of QZSS L1C signal, SNR.

Plot of QZSS L1C signal, code minus phase (above).

EC’s Galileo Manager Discusses Progress, Interoperability

Paul Verhoef, the European Commission’s program manager for European Union (EU) satellite navigation programs, discussed current issues at length with GPS World, in a conversation on November 10. He addressed aspects of interoperability with GPS and prospects for further development in that area, the need for an ongoing political commitment by the EU to Galileo, the challenges of financing, the prospects for an 18-satellite constellation (which he dismisses as unrealistic), military considerations for both Galileo and GPS, and the recent uncertainty around Galileo’s Public Regulated Service.

The full conversation is available here. Here are a few extracted quotes:

Interoperability. “We have seen in the process with the U.S. that first of all there has been a quite clear political commitment on both sides, at the highest levels, that interoperability was wanted. Secondly, in the implementation we’ve had a very good working relation with our U.S. colleagues in order to establish that. The advantage that I see is that we have been able at a very early stage to deliver on such an interoperability agreement, that this is clear to industry, it provides for predictability. It allows industry to monitor clearly how the two systems are evolving, and when this interoperability is actually going to be available in the marketplace, and it allows them to time their investments, their R&D, their production, and all the rest.” [ . . . . ]

Challenges. “It is time that Galileo delivers something concrete. We’ve had many years of discussion behind us on whether the system will come, and if it will come, and how it will come, and what it will look like, and all the rest. For my part, I’m very happy to see that in 2011, we plan to launch.

The first four satellites are on the way; they are almost ready. About half the ground infrastructure is currently under implementation, we have every couple of months the opening of another ground station around the world. With this, the system becomes a reality, and I think once the satellite launches will go across television screens in the whole world, people will see that the system is becoming a reality. And I think that is desperately needed in order to give it a sense that things are moving forward. I’m really looking forward to that. That is a piece of good progress we have achieved over the last couple of years.

Constellation. “There is a bit of a discussion for some reason in Europe, for some reason some people seem to think that we could do away with 18 satellites. Well, from me you will hear a solid ‘No.’

“The availability figures for an 18-satellite constellation are around 90 percent on average, which means that for an aggregate total of some six weeks a year you would not receive sufficient views, not have sufficient satellites in sight to actually determine a position. There are going to be sectors like aviation where this is completely unacceptable, and they would never invest in anything if that is what we’re going to do. So my sense is that we will always have a lot of upward pressure in terms of constellation size. Of course it needs to be offset against costs and other considerations, but I think the pressure is always going to be there. It is very premature for people to be trying to take a shortcut, to think, well, maybe we could do with less. Because in the end you would have a constellation with a technical performance which the marketplace is not interested in, and then you would have a real problem.”

Click here for the full discussion, spanning many topics.

GPS Control Upgrade

The U.S. Air Force 2nd Space Operations Squadron is scheduled to release the next software upgrade for the GPS ground system in early December, as part of an ongoing effort to improve and maintain the GPS Operational Control Segment before the next-generation GPS Control Segment is deployed in 2015. The upgrade is expected to be completed in early January 2011. The upgrade does not change the navigation message and should be transparent to GPS users. Tests have shown that the navigation message produced by the new software is identical to that produced by the current ground software. While no anomalies are expected, civilians experiencing any anomalies should contact the Coast Guard Navigation Center at (703) 313-5900.

GLONASS Launch Fails

The Russian Federal Space Agency announced that the December 5 launch of three GLONASS-M satellites ended in failure when the Proton-M rocket’s Block DM upper stage and its three payloads crashed into the Pacific Ocean about 1,500 kilometers (932 miles) northwest of Honolulu. Although an investigation will look into the exact cause of the failure, early unconfirmed reports indicate a software error. According to the Russian News Agency RIA Novosti, incorrect calculations were loaded into the rocket’s onboard computers.

Compass Settles, Moves

The Beidou/Compass G4 satellite launched on October 31 achieved geostationary orbit by November 6. The satellite is positioned at about 160 degrees east longitude. G4 is the furthest east of the operational Beidou geostationary satellites. Meanwhile, the orbital location of the Beidou 1A satellite has been changed.

On or about October 27, as indicated by NORAD tracking data, the satellite underwent a significant delta-V, raising its orbit by about 200 kilometers. Its orbit had been slightly drifting for a few weeks before the maneuver, and there was speculation that the satellite had been placed in a disposal or graveyard orbit. However, on November 24 a second delta-V was observed that returned the satellite to the geostationary belt.

The two maneuvers placed the satellite at a new location at about 60 degrees east longitude — the furthest west of any of the Beidou satellites. The satellite may eventually end up at 58.75 degrees east, one of the Beidou orbital slots registered with the International Telecommunication Union.

The geostationary satellite, the first for the demonstration regional Beidou system or Beidou-1, was launched on October 30, 2000, and positioned at 140 degrees east longitude. Following several years of use, there were unofficial reports that the satellite was no longer functional. However, station-keeping was maintained, implying some usefulness of the satellite. It remains unclear how functional the satellite is and whether it is still useful for the Beidou-1 demonstration system.

December 1, 2010
GNSS RF Compatibility Assessment: Interference among GPS, Galileo, and Compass

By Wei Liu, Xingqun Zhan, Li Liu, and Mancang Niu

A comprehensive methodology combines spectral-separation and code-tracking spectral-sensitivity coefficients to analyze interference among GPS, Galileo, and Compass. The authors propose determining the minimum acceptable degradation of effective carrier-to-noise-density ratio, considering all receiver processing phases, and conclude that each GNSS can provide a sound basis for compatibility with other GNSSs with respect to the special receiver configuration.

Power spectral densities of GPS, Galileo, and Compass signals in the L1 band.

As GNSSs and user communities rapidly expand, there is increasing interest in new signals for military and civilian uses. Meanwhile, multiple constellations broadcasting more signals in the same frequency bands will cause interference effects among the GNSSs. Since the moment Galileo was planned, interoperability and compatibility have been hot topics. More recently, China has launched six satellites for Compass, which the nation plans to turn into a full-fledged GNSS within a few years. Since Compass uses similar signal structures and shares frequencies close to other GNSSs, the radio frequency (RF) compatibility among GPS, Galileo, and Compass has become a matter of great concern for both system providers and user communities.

Some methodologies for GNSS RF compatibility analyses have been developed to assess intrasystem (from the same system) and intersystem (from other systems) interference. These methodologies present an extension of the effective carrier power to noise density theory introduced by John Betz to assess the effects of interfering signals in a GNSS receiver. These methodologies are appropriate for assessing the impact of interfering signals on the processing phases of the receiver prompt correlator channel (signal acquisition, carrier-tracking loop, and data demodulation), but they are not appropriate for the effects on code-tracking loop (DLL) phase. They do not take into account signal processing losses in the digital receiver due to bandlimiting, sampling, and quantizing. Therefore, the interference calculations would be underestimated compared to the real scenarios if these factors are not taken into account properly. Based on the traditional methodologies of RF compatibility assessment, we present here a comprehensive methodology combining the spectral separation coefficient (SSC) and code tracking spectral sensitivity coefficient (CT_SSC), including detailed derivations and equations.

RF compatibility is defined to mean the “assurance that one system will not cause interference that unacceptably degrades the stand-alone service that the other system provides.” The thresholds of acceptability must be set up during the RF compatibility assessment. There is no common standard for the required acceptability threshold in RF compatibility assessment. For determination of the required acceptability thresholds for RF compatibility assessment, the important characteristics of various GNSS signals are first analyzed, including the navigation-frame error rate, probability of bit error, and the mean time to cycle slip. Performance requirements of these characteristics are related to the minimum acceptable carrier power to effective noise power spectral density at the GNSS receiver input. Based on the performance requirements of these characteristics, the methods for assessing the required acceptability thresholds that a GNSS receiver needs to correctly process a given GNSS signal are presented.

Finally, as signal spectrum overlaps at L1 band among the GPS, Galileo, and Compass systems have received a lot of attention, interference will be computed mainly on the L1 band where GPS, Galileo, and Compass signals share the same band. All satellite signals, including GPS C/A, L1C, P(Y), and M-code; Galileo E1, PRS, and E1OS; and Compass B1C and B1A, will be taken into account in the simulation and analysis.

Methodology

To provide a general quantity to reflect the effect of interference on characteristics at the input of a generic receiver, a traditional quantity called effective carrier-power-to-noise-density (C/N₀), is noted as (C/N₀)_{eff_SSC}. This can be interpreted as the carrier-power-to-noise-density ratio caused by an equivalent white noise that would yield the same correlation output variance obtained in presence of an interference signal. When intrasystem and intersystem interference coexist, (C/N₀)_{eff_SSC} can be expressed as

Ĝ_s(f) is the normalized power spectral density of the desired signal defined over a two-sided transmit bandwith ß_T, C is the received power of the useful signal. N₀ is the power spectral density of the thermal noise. In this article, we assume N₀ to be –204 dBW/Hz for a high-end user receiver. Ĝ_i,j(f) is the normalized spectral density of the j-th interfering signal on the i-th satellite defined over a two-sided transmit bandwith ß_T, C_i,j the received power of the j-th interfering signal on the i-th satellite, ß_r the receiver front-end bandwidth, M the visible number of satellites, and K_i the number of signals transmitted by satellite i. I_ext is the sum of the maximum effective white noise power spectral density of the pulsed and continuous external interference.

It is clear that the impact of the interference on (C/N₀)_{eff_SSC} is directly related to the SSC of an interfering signal from the j-th interfering signal on the i-th satellite to a desired signal s, the SSC is defined as

From the above equations it is clear that the SSC parameter is appropriate for assessing the impact of interfering signals on the receiver prompt correlator channel processing phases (acquisition, carrier phase tracking, and data demodulation), but not appropriate to evaluate the effects on the DLL phase. Therefore, a similar parameter to assess the impact of interfering signals on the code tracking loop phase, called code tracking spectral sensitivity coefficient (CT_SSC) can be obtained. The CT_SSC is defined as

where Δ is the two-sided early-to-late spacing of the receiver correlator.

To provide a metric of similarity to reflect the effect of interfering signals on the code tracking loop phase, a quantity called CT_SSC effective carrier power to noise density (C/N₀), denoted (C/N₀)_{eff_CT_SSC}, can be derived. When intrasystem and intersystem interference coexist, this quantity can be expressed as

where I_GN_{SS_CT_SSC} is the aggregate equivalent noise power density of the combination of intrasystem and intersystem interference.

Equivalent Noise Power Density. When more than two systems operate together, the aggregate equivalent noise power density I_GN_SS ( I_GN_{SS_SSC} or I_GN_{SS_CT_SSC} ) is the sum of two components

I_Intrais the equivalent noise power density of interfering signals from satellites belonging to the same system as the desired signal, and I_Inter is the aggregate equivalent noise power density of interfering signals from satellites belonging to the other systems.

In fact, recalling the SSC and CT_SSC definitions, hereafter, denoted or as , the equivalent noise power density (I_Intra or I_Inter) can be simplified as

where C_i,j is the user received power of the j-th signal belonging to the i-th satellite, as determined by the link budget.

For the aggregate equivalent noise power density calculation, the constellation configuration, satellite and user receiver antenna gain patterns, and the space loss are included in the link budget. User receiver location must be taken into account when measuring the interference effects.

Degradation of Effective C/N₀. A general way to calculate (C/N₀)_eff, (C/N₀)_{eff_SSC} , or (C/N₀)_{eff_CT_SSC} introduced by interfering signals from satellites belonging to the same system or other systems is based on equation (1) or (4). In addition to the calculation of (C/N₀)_eff , calculating degradation of effective C/N₀ is more interesting when more than two systems are operating together. The degradation of effective C/N₀ in the case of the intrasystem interference in dB can be derived as

Similarly, the degradation of effective C/N₀ in the case of the intersystem interference is

Bandlimiting, Sampling, and Quantization. Traditionally, the effect of sampling and quantization on the assessment of GNSS RF compatibility has been ignored. Previous research shows that GNSS digital receivers suffer signal-to-noise-plus interference ration (SNIR) losses due to bandlimiting, sampling, and quantization (BSQ). Earlier studies also indicate a 1.96 dB receiver SNR loss for a 1-bit uniform quantizer. Therefore, the specific model for assessing the combination of intrasystem and intersystem interference and BSQ on correlator output SNIR needs to be employed in GNSS RF compatibility assessment.

Influences of Spreading Code and Navigation Data. In many cases, the line spectrum of a short-code signal is often approximated by a continuous power spectral density (PSD) without fine structure. This approximation is valid for signals corresponding to long spreading codes, but is not appropriate for short-code signals, for example, C/A-code interfering with other C/A-code signals. As one can imagine, when we compute the SSC, the real PSDs for all satellite signals must be generated. It will take a significant amount of computer time and disk storage. This fact may constitute a real obstacle in the frame of RF compatibility studies. Here, the criterion for the influences of spreading code and navigation data is presented and an application example is demonstrated. For the GPS C/A code signal, a binary phase shift keying (BPSK) pulse shape is used with a chip rate f_c = 1.023 megachips per seconds (Mcps). The spreading codes are Gold codes with code length N = 1023. A data rate f_d = 50 Hz is applied. As shown in Figure 1, the PSD of the navigation data (G_d(f) = 1/f_d sin c² (f/f_d) ) replace each of the periodic code spectral lines. The period of code spectral lines is T = 1/LT_C. The mainlobe width of the navigation data is B_d =2f_d.

Figure 1. Fine structure of the PSD of GPS C/A code signal (fd = 50 Hz ,without
logarithm operation).

For enough larger data rates or long spreading codes, the different navigation data PSDs will overlap with each other. The criterion can be written as:

Finally,

When criterion L ≥ f_c/f_d is satisfied, navigation signals within the bandwidth are close to each other and overlap in frequency domain. The spreading code can be treated as a long spreading code, or the line spectrum can be approximated by a continuous PSD.

C/N₀ Acceptability Thresholds

Receiver Processing Phase. The determination of the required acceptability thresholds consider all the receiver processing phases, including the acquisition, carrier tracking and data demodulation phases.The signal detection problem is set up as a hypothesis test, testing the hypothesis H₁ that the signal is present verus the hypothesis H₀ that the signal is not present. In our calculation, the detection probability p_d and the false alarm probability p_f are chosen to be 0.95 and 10^–4, respectively. The total dwell time of 100 ms is selected in the calculation.

A cycle slip is a sudden jump in the carrier phase observable by an integer number of cycles. It results in data-bit inversions and degrades performance of carrier-aided navigation solutions and carrier-aided code tracking loops. To calculate the minimum acceptable signal C/N₀ for a cycle-slip-free tracking, the PLL and Costas loop for different signals will be considered. A PLL of third order with a loop filter bandwidth of 10 Hz and the probability of a cycle slip of 10–5 are considered. We can find the minimum acceptable signal C/N₀ related to the carrier tracking process. For the scope of this article, the vibration induced oscillator phase noise, the Allan deviation oscillator phase noise, and the dynamic stress error are neglected.

In terms of the decoding of the navigation message, the most important user parameters are the probability of bit error and the probability of the frame error. The probability of frame error depends upon the organization of the message frame and various additional codes. The probability of the frame error is chosen to be 10^–3. For the GPS L1C signal using low-density parity check codes, there is no analytical method for the bit error rate or its upper bound. Due to Subframe 3 data is worst case, the results are obtained via simulation. In this article, the energy per bit to noise power density ratio of 2.2 dB and 6 dB reduction due to the pilot signal are taken into account, and the loss factor of the reference carrier phase error is also neglected.

Minimum Acceptable Degradation C/N₀. The methods for accessing the minimum acceptable required signal C/N₀ that a GNSS receiver needs to correct
ly process a desired signal are provided above. Therefore, the global minimum acceptable required signal carrier to noise density ratio (C/N₀)_{global_min} for each signal and receiver configuration can be obtained by taking the maximum of minima. In addition to the minimum acceptable required signal C/N₀, obtaining the minimum acceptable degradation of effective C/N₀ is more interesting in the GNSS RF compatibility coordination. For intrasystem interference, when only noise exists, the minimum acceptable degradation of effective C/N₀ in the case of the intrasystem interference can be defined as

Similarly, the minimum acceptable degradation of effective C/N₀ in the case of the intersystem interference can be expressed as

Table 1 summarizes the calculation methods for the minimum acceptable required of degradation of effective C/N₀.

Simulation and Analysis

Table 2 summarizes the space constellation parameters of GPS, Galileo, and Compass.

For GPS, a 27-satellite constellation is taken in the interference simulation. Galileo will consist of 30 satellites in three orbit planes, with 27 operational spacecraft and three in-orbit spares (1 per plane). Here we take the 27 satellites for the Galileo constellation. Compass will consist of 27 MEO satellites, 5 GEO, and 3 IGSO satellites. As Galileo and Compass are under construction, ideal constellation parameters are taken from Table 2.

Signals Parameters. The PSDs of the GPS, Galileo and Compass signals in the L1 band are shown in the opening graphic. As can be seen, a lot of attention must be paid to signal spectrum overlaps among these systems. Thus, we will concentrate only on the interference in the L1 band in this article. All the L1 signals including GPS C/A, L1C, P(Y), and M-code; Galileo E1 PRS and E1OS; and Compass B1C and B1A will be taken into account in the simulation and analysis.

Table 3 summarizes GPS, Galileo and Compass signal characteristics to be transmitted in the L1 band.

Simulation Parameters. In this article, all interference simulation results refer to the worst scenarios. The worst scenarios are assumed to be those with minimum emission power for desired signal, maximum emission power for all interfering signals, and maximum (C/N₀)_eff degradation of interference over all time steps. Table 4 summarizes the simulation parameters considered here.

SSC and CT_SSC. As shown in expression (1) or (4), (C/N₀)_eff is directly related to SSC or CT_SSC of the desired and interfering signals. Figure 2 and Figure 3 show both SSC and CT_SSC for the different interfering signals and for a GPS L1 C/A-code and GPS L1C signal as the desired signal, respectively. The figures obviously show that CT_SSC is significantly different from the SSC. The results also show that CT_SSC depends on the early-late spacing and its maximal values appear at different early-late spacing.

FIGURE 2. SSC and CT_SSC for GPS C/A-code as desired signal.

FIGURE 3. SSC and CT_SSC for GPS L1C as desired signal.

The CT_SSC for different civil signals in the L1 band is calculated using expression (3). The power spectral densities are normalized to the transmitter filter bandwidth and integrated in the bandwidth of the user receiver. As we saw in expression (3), when calculating the CT_SSC, it is necessary to consider all possible values of early-late spacing. In order to determine the maximum equivalent noise power density (I_Intra or I_Inter), the maximum CT_SSC will be calculated within the typical early-late spacing ranges (0.1–1 chip space).

Results and Analysis

In this article we only show the results of the worse scenarios where GPS, Galileo, and Compass share the same band. The four worst scenarios include:

◾ Scenario 1: GPS L1 C/A-code ← Galileo and Compass (GPS C/A-code signal is interfered with by Galileo and Compass)

◾ Scenario 2: GPS L1C ← Galileo and Compass (GPS L1C signal is interfered with by Galileo and Compass)

◾ Scenario 3: Galileo E1 OS ← GPS and Compass (Galileo E1 OS signal is interfered with by GPS and Compass)

◾ Scenario 4: Compass B1C ← GPS and Galileo (Compass B1C signal is interfered with by GPS and Galileo)

Scenario 1. The maximum C/N₀ degradation of GPS C/A-code signal due to Galileo and Compass intersystem interference is depicted in Figure 4 and Figure 5.

Scenario 2. Figure 6 and Figure 7 also show the maximum C/N₀ degradation of GPS L1C signal due to Galileo and Compass intersystem interference.

Scenario 3. The maximum C/N₀ degradation of Galileo E1OS signal due to GPS and Compass intersystem interference is depicted in Figure 8 and Figure 9.

Scenario 4. For scenario 4, Figure 10 and Figure 11 show the maximum C/N₀ degradation of Compass B1C signal due to GPS and Galileo intersystem interference.

From the results from these simulations, it is clear that the effects of interfering signals on code tracking performance may be underestimated in previous RF compatibility methodologies. The effective carrier power to noise density degradations based on SSC and CT_SSC are summarized in Table 5. All the results are expressed in dB-Hz.

C/N₀ Acceptability Thresholds. All the minimum acceptable signal C/N₀ for each GPS, Galileo, and Compass civil signal are simulated and the results are listed in Table 6. The global minimum acceptable signal C/N₀ is summarized in Table 7. All the results are expressed in dB-Hz.

Effective C/N₀ Degradation Thresholds. All the minimum effective C/N₀ for each GPS, Galileo and Compass civil signal due to intrasystem interference are simulated, and the results are listed in Table 8. Note that the high-end receiver configuration and external interference are considered in the simulations. According to the method summarized in Table 1, the effective C/N₀ degradation acceptability thresholds can be obtained. The results are listed in Table 9.

As can be seen from these results, each individual system can provide a sound basis for compatibility with other GNSSs with respect to the special receiver configuration used in the simulations. However, a common standard for a given pair of signal and receiver must be selected for all GNSS providers and com
munities.

Conclusions

At a minimum, all GNSS signals and services must be compatible. The increasing number of new GNSS signals produces the need to assess RF compatibility carefully. In this article, a comprehensive methodology combing the spectral separation coefficient (SSC) and code tracking spectral sensitivity coefficient (CT_SSC) for GNSS RF compatibility assessment were presented. This methodology can provide more realistic and exact interference calculation than the calculation using the traditional methodologies. The method for the determination of the required acceptability thresholds considering all receiver processing phases was proposed. Moreover, the criterion for the influences of spreading code and navigation data was also introduced.

Real simulations accounting for the interference effects were carried out at every time and place on the earth for L1 band where GPS, Galileo, and Compass share the same band. It was shown that the introduction of the new systems leads to intersystem interference on the already existing systems. Simulation results also show that the effects of intersystem interference are significantly different by using the different methodologies. Each system can provide a sound basis for compatibility with other GNSSs with respect to the special receiver configuration in the simulations.

At the end, we must point out that the intersystem interference results shown in this article mainly refer to worst scenario simulations. Though the values are higher than so-called normal values, it is feasible for GNSS interference assessment. Moreover, the common standard for a given signal and receiver pair must be selected for and coordinated among all GNSS providers and communities.

This article is based on the ION-GNSS 2010 paper, “Comprehensive Methodology for GNSS Radio Frequency Compatibility Assessment.”

WEI LIU is a Ph.D. candidate in navigation guidance and control at Shanghai Jiao Tong University, Shanghai, China. XINGQUN ZHAN is a professor of navigation guidance and control at the same university. LI LIU and MANCANG NIU are Ph.D. candidates in navigation guidance and control at the university.

December 1, 2010
The System: Galileo PRS Delivery in Question

Once envisioned to orbit 30 satellites, Galileo’s constellation has over time been reduced to a planned, though still not space-borne, four initial satellites plus 14 operational satellites for a total of 18. The European Space Agency (ESA), under direction of the European Commission (EC), confirmed at the October 19–21 European Navigation Conference (ENC) in Germany that it plans to declare an Initial Operating Capability (IOC), or FOC-1 (Full Operating Capability, Phase One) — the terminology varies — once a constellation of 18 is achieved, in the 2014–2015 timeframe.

Such a reduced system will not enable global delivery of the Public Regulated Service (PRS), planned as a Galileo-only (that is, not in interoperation with or dependent upon any other GNSS) application. The PRS will use encrypted signals, and access will be limited to authorized governmental agencies. Much sought by the EC, its member states and militaries, and in some views the original and most compelling motivation for Galileo in the first place — to wit, independence from GPS — PRS now appears to recede from view. Quite simply, more satellites are necessary.

The same geometry-in-space and radio-frequency factors apply to some of the high-precision services once envisioned for intelligent transport systems (ITS) within Europe: tools to relieve traffic congestion and decrease environmental pollution, to enable more and denser high-speed rail links and freight, and similarly for marine (in-harbor and along-canal) operations.

Galileo finds itself face to face with the potential absence of its own raison d’être. It may need to collaborate with GPS to achieve what were Galileo-only goals. A possible alternative would be to reconfigure the reduced constellation somehow so that it can provide continuous service over the European continent only. This option would not satisfy the needs of European peace-keeping missions around the world, however.

Doubts from the Floor. An audience member at the E1NC posed the question of the hour to Edgar Thielman, Head of Unit, EU Satellite Navigation Programmes, in charge of Applications, International Relations and Security Issues:

“We are going to have Galileo-only applications like the Public Regulated Service (PRS) for governments. This cannot work with 18 satellites, unless maybe — this has to be investigated — the 18 satellites are configured in a constellation that will give optimum coverage of Europe. Has this been thought about yet?”

Thielman replied that European governing agencies are “in discussions about what to do.”

The EC’s problem is that there is no money available after 2014 — at least not until the next formal round of funding allocations is made.

A high-level representative of DLR, the German aerospace agency, spoke from the audience about simulations his agency had undertaken using a hypothetical constellation of 24 satellites. This seemed to hint that Germany might know where additional funding could be found for more satellites, but separate news developments (see following story) contra-indicated this possibility.

Proposal. Earlier in October, the EC released a proposal for better management of critical transport and emergency services, better law enforcement, improved internal security (border control), and safer peace missions — all through the PRS.

“The safety and security of each and every European citizen lies at the heart of this proposal,” said Antonio Tajani, EC vice president in charge of industry and entrepreneurship. “Given our increasing reliance on satellite navigation infrastructures, there is an urgent need to ensure that key services, such as our police forces and rescue and emergency services, continue to function in moments of crisis, terrorist threat, or disaster. Furthermore, the market for PRS applications offers an important opportunity for Europe’s entrepreneurs.”

Thielman Speaks. In a private conversation with GPS World, Edgar Thielman stressed that “PRS will be one of the first services of Galileo, as soon as it is functional. We envision that in the 2014/2015 timeframe, with 18 satellites enabling the IOC. We know that development of receivers and technical hardware is still to be done. Thus we put forward the proposal, to be on safe ground, to have a common understanding for industry and participants.

“The IOC constellation will provide in the beginning the Open Signal (OS), the Safety-of-Life (SOL), and the PRS. The interests are of these three services are different from one another. The PRS follows a completely different logic. But the Member States are interested in getting this specific service, and also the European Commission and the European Council.”

Thielman explained that these three collective entities anticipate PRS capabilities to deal with “crisis situations —  where the Open Signal is jammed. Government services must be able to function in very difficult circumstances, for instance, peace-keeping missions.”

He added, “We want to open this service to other international organizations and states, subject to agreement.” Such discussion on cooperation with third countries, as well as discussions within the EC and among Member States on optimization — that is, ways to overcome the deficiencies of a constellation limited to 18 satellites — are ongoing.

“We have a lot of talks. The starting point is to have a system that satisfies the needs of the EU and EC with the means we have.”

It was not stated, but seems implicit to many observers, that such means to enable the PRS may require more cooperation with and use of GPS than Galileo proponents may have originally wished.

Space, Ground Work Package Signed

The EC signed the fourth of six procurement contracts for Galileo, this one for €194 million for operations of the space and ground infrastructure, with Space-Opal GmbH, a joint venture created by DLR GfR (Germany) and Telespazio S.p.A (Italy). EC VP Antonio Tajani maintained that “Galileo is becoming a reality. Europe will have its own independent satellite navigation system capable of high precision and reliability. We are fully committed to the roll-out of the system. Given the increased reliance of companies and citizens on satellite navigation, Galileo will play an important role in our daily lives.”

Procurement for Galileo’s full operational capability is divided into six contracts. In January 2010, three contracts were awarded to ensure system engineering support, satellites, and launchers. The two remaining procurement contracts, for the completion of the ground mission infrastructure and the ground control infrastructure, will be awarded in early 2011.

Money Trouble

The global financial crisis has European finance ministers trying to back away from current Galileo funding, let alone any projected future increases. The German government asked the EC to propose ways to cut current Galileo cost projections, said that country’s Transport Ministry. According to reports, one suggestion to realize savings calls for a switch from the planned Ariane 5 launcher (operated by a largely French company) to the Russian Soyuz launcher to place Galileo satellites in orbit.

Financial Times Deutschland cited an EC report forecasting extra costs of €1.5–1.7 billion ($2.1–2.4 billion), beyond the current €3.4 billion budget. FTD said the report labels Galileo as unprofitable in the long term, at an annual loss of €750 million.

In 2007, the European Parliament withstood such running tides and devised an unusual financing scheme to keep the program going, by raiding a massive surplus agricultural support fund. Such a maneuver may not be repeatable, as farmers have long memories; EC officials, still feeling the heat from that move, profess that, barring an unforeseen occurrence, Galileo cannot get any more money.

Notwithstanding, Edit Herczog, member of the European Parliament’s committee on industry, research, and energy, stated that “If it is too big to fail, then it can’t. This is something we can build on.”

Antonio Tajani, an EC VP, rejected the German press figures as “exorbitant” and “unimagineable.” He maintained that Galileo’s costs remain at €3.4 billion ($4.7 billion). “I don’t know where these figures come from,” he stated at a news conference.

Space Agency Acts on Security, IP Concerns

ESA abruptly withdrew six technical presentations on new Galileo developments from the European Navigation Conference (ENC) without immediate explanation. Probing by GPS World elicited a reply that “the papers were withdrawn by ESA because they contained too detailed information that could have led to knowledge transfer.” A further hypothetical, and emphatically unofficial, possible reason was posited later by one knowledgeable attendee, having to do with security issues.

Most of the presentations were due to be given during a session on “Galileo Development and Test Results” on Tuesday afternoon, October 19. The withdrawal created some consternation among the several hundred conference attendees, as the session would have been the technical highlight of the conference and was much anticipated, and further because no official explanation for the action was offered. A somewhat dated presentation was offered in place of the first paper, and the rest of the session was simply dismissed.

Later during the conference, GPS World heard speculation from a conference participant, who did not have any official knowledge or clearance, that one or more of the papers may have contained information about the Galileo ground control system that, if made public, might have created vulnerabilities to Internet hacking attacks.

The withdrawn papers covered the Galileo Orbit and Synchronisation Processing Facility, results from the first user receiver-autonomous integrity monitoring and interference mitigation tests at the Galileo Test Range (GATE) — although the GATE manager stated to GPS World that this particular paper was not withdrawn by ESA for any official reason, but by the GATE itself, because it had received the special test receiver necessary from ESA too late to perform the tests in question — the Galileo ground mission segment operability chain, cumulative distribution function overbounding, the Galileo constellation system verification processes and methods, and, from a later session on GNSS software and algorithms, a paper on coherent E5 ALTBOC processing with the Galileo TUS receiver.

In the closing session, David Broughton, secretary-general of the International Association of Institutes of Navigation, summarized,”Content of the conference generally was excellent, with the exception of coverage of Galileo, with many papers withdrawn by ESA. Understandably, this caused much annoyance from the delegates. It was disappointing to see the conference treated with such disdain — if the European Navigation Conference cannot be given a true account of Galileo’s progress, then who can?” This drew applause from the delegates.

The authors of three of the papers are staffers from ESA itself; the authors of the other three come from companies under contract to the agency.

SatNav Briefs

China’s next BeiDou-2 Compass-G4 satellite rose into orbit on October 31 from the Xi Chang Satellite Launch Center in Sichuan Province, 10 years to the day from the launch of the first BeiDou-1A.

Japan’s new QZSS vehicle Michibiki has reached its final quasi-zenith orbit.JAXA, the Japanese aerospace agency, stated “we started transmission of one of the positioning signals, namely the L1-SAIF signal from the L1-SAIF antenna of the Michibiki on October 19, after we turned on its onboard positioning mission devices.

“We will make sure that the L1-SAIF signal has compatibility with the existing positioning services, and then begin transmitting signals from the L-band helical antenna, namely the L1-C/A, L2C, L5, L1C, and LEX signals.”

SBAS for Latin America. A new satellite-based augmentation system signal covering the Caribbean, Central and South America was broadcast by GMV and Inmarsat. The demonstration of an SBAS in test mode took place in front of representatives from the International Civil Aviation Organisation (ICAO).

November 1, 2010
The System: Michibiki Takes Up Station and Other GNSS Constellation Updates

As this issue goes to press in late August, the first Japan Aerospace Exploration Agency Quasi-Zenith Satellite System (QZSS) space
vehicle, nicknamed Michibiki, holds steady for a September 11 launch.

QZSS will use multiple satellites in inclined orbits, placed so that one satellite always appears near zenith above Japan, well known for its high-rise cities. The design provides high-accuracy satellite positioning service covering almost all of the country, including urban canyons and mountainous terrain.

QZSS Phase One will validate technological enhancement of GPS availability, performance, and application. Phase Two will demonstrate full system capability using three QZSS satellites, including Michibiki.

The satellites will generate and transmit their own signals, compatible with modernized GPS signals. QZSS also transmits GPS corrections and availability data.

Michibiki Profile. Dual-box shape with wing-type solar-array paddles; overall dimensions, 2.9 x 3.1 x 6.2 meters, paddles extending 25.3 meters; weight approximately 4,000 kilograms; altitude approximately 32,000–40,000 kilometers; inclination approximately 40 degrees;
period, 23 hours 56 minutes.

Compass. In early August, the first Beidou/Compass inclined geosynchronous orbit (IGSO) satellite achieved near-geosynchronous orbit. The mean east longitude of the sub-satellite ground point is currently 117 degrees, 19 minutes (see figure 1). This is one of the first, if not the first, satellite to use such a highly inclined circular geosynchronous orbit.

Figure 1. Left, the orbit path of three QZSS satellites will eventually keep at least one of them directly over Japan at all times. Right, the inclined geosynchronous orbit of the fifth Compass satellite, launched in July, has a similar ground track and mission goal.

Multi-GNSS Campaign. An international collaboration is poised to take advantage of a coming proliferation of satellites, led by Compass and QZSS but also including GPS, GLONASS, and Galileo, over the Asia/Pacific region. The website www.multignss.asia/campaign.html states, “The Asia and Oceania region is a unique place where the number of usable modernized navigation satellites will increase much faster than other areas in the world. We will see great improvement of PNT capability and hence there is a great opportunity to try, test, and validate new receiver hardware, algorithms, and applications in order to address user requirements.”

The web page also carries an animation of the availability of more than 100 GNSS space vehicles that will operate over the region in the next decade. An initial campaign workshop in Bangkok, Thailand, in January drew 195 participants from 18 countries. A second workshop is scheduled for November 21–22 in Melbourne, Australia.

GLONASS September. Three GLONASS-M satellites to be launched on September 2 completed pre-launch testing and mating to the upper stage of the booster rocket at Baikonur Cosmodrome. Numbered 36, 37, and 38, the satellites will constitute the Block 42 triad.

GPS III Design: Done. The Lockheed Martin team developing GPS III has successfully completed the program’s Critical Design Review (CDR) phase, two months ahead of baseline schedule. CDR completion validates the detailed GPS III design to ensure it meets warfighter and civil requirements. It culminates many rigorous assembly, subsystem, element, space vehicle and system-level CDR events, validates the overall design maturity of the GPS III space vehicle, and allows Lockheed Martin to enter production phase. Col. Bernard J. Gruber, U.S. Air Force GPS Wing Commander, certified the completion. Lockheed Martin, ITT, and General Dynamics are working under a $3 billion development and production contract for up to 12 GPS IIIA satellites. The team is on track to launch the first GPS IIIA satellite in 2014.

GPS Interface Specs. New IS-GPS-200E, IS-GPS-705A, and IS-GPS-800A documents have been posted to www.gps.gov/technical.
SVN62 Rubidium Clock. The U.S. Naval Research Laboratory issued a preliminary report on the rubidium atomic clock currently in use on the SVN62 Block IIF satellite. While documenting excellent short-term performance, the report notes anomalous fluctuations in the clock signal with distinct 12-hour and 6-hour periodicities. The exact cause has not been identified although it is speculated that the fluctuations are of thermal origin like SVN-62’s L5 phase variance detected earlier. But note that the clock signal analysis relies only on L1 and L2 measurements.

GPS IIF Got Active. The 50th Space Wing’s 2nd Space Operations Squadron formally took over command and control of the first Block IIF satellite on August 26 from the GPS Wing, and the satellite was set healthy on August 27, making 31 healthy GPS satellites on orbit.

Advisory Board Update
GPS World Editorial Advisory Board member Art Gower has been elected a Lockheed Martin Fellow, an honor recognizing pre-eminent technical individual contributors in the company, delivering mission success and vision by undertaking the most difficult technical challenges facing the company and its customers. Art started his career with IBM Federal Systems Division (now part of Lockheed Martin Integrated Systems and Global Solutions) in 1983, developing displays and performing navigation upload and command and control system engineering for the GPS control segment, and becoming chief engineer for the GPS control segment in 1990. He has spent the majority of his career working on GPS, GNSS, and SBAS systems.

September 1, 2010
The System: Vistas from the Summit
“This is an event where one gets one’s goals for the next year.” Paul Verhoef, program director for satellite navigation programs of the European Commission, may have exaggerated for effect, and for the benefit of his audience and hosts at the Munich Satellite Navigation Summit in March. But not by much.

The conference, now in its eighth year, has assumed increasing importance on the international circuit of GNSS policymakers and communicators. Although with a decidedly European bent, it draws representatives from most if not all systems to mingle and present. A 16-member delegation from China’s Compass system furnished one of the liveliest topics of conversation — and speculation.

“When we started in 2003, there were many technical conferences on the one side, and we saw a niche for the institutional and political side of satellite navigation,” said Berned Eissfeller of the Institute of Geodesy and Navigation, German Federal Armed Forces University, conference director and host. You can watch video clips of Eissfeller and other speakers.

GNSS came in for a check-up, a sort of self-examination this time. The 2009 conference was titled “The GNSS Race,” but this year it was “GNSS — Quo Vadis?” The Latin phrase means “Where are you going?” Following program updates, sessions focused on safety-of-life, compatibility, legal/intellectual property, and privacy issues.

Galileo. Paul Verhoef continued his remarks that open this story. “I have been given [my goal]: Galileo must succeed.

“You know the world today is not what it was a year ago. It means obviously the financial crisis has had an impact on our economies, on public finance, and therefore I would not be surprised it may leave its mark on satellite navigation. The reason is simple: the systems that are either operating or being deployed are being publicly financed. Galileo is the only system that is financed from a purely civilian budget. All the systems need more than ever to demonstrate their public utility.

“I put it to you that this is an opportunity. As we’ve already heard, there is much to be gained in this market. After the PC, mobile communications, and Internet, satellite navigation is the next breakthrough technology. There are enormous revenues foreseen and already present in this market. There are many jobs possible for those who want to get it, and we think from the European side we have an enormous chance of capitalizing on this among other things by investing in this technology. Therefore, Galileo- and EGNOS-based innovation is certainly politically of interest.

“Obviously, it is not a path of roses. There will no doubt be many more critical questions during these days. However, from our side, we have set our goals. I think they are modest, but they are firm. We want to be the second system of choice. At least in the first instance, we will see where we will go after that. Obviously, this is going to cost a bit of time. I shall invite you, if you get impatient, if the public gets impatient, to look at the history of the other systems. Developing and deploying these other systems is costing time.

“We think that Galileo will meet its deadlines. I think one of the important messages this year, and you have seen it, we are putting things in place. There are contracts in place, there are satellites on order, there are launches on order, there are installations being built — Oberpfaffenhoffen, Fucino, there are others around the world — EGNOS is operational, we’re going to declare the safety-of-life of EGNOS later this year. So we are really moving forward at good speed at the moment.

“We need to win the hearts of the users, the application providers, and the service providers. At the downstream market is the real challenge for these systems. We need to help do that. We are addressing this among other things by providing a more and more reliable schedule for availability of Galileo and EGNOS services.”

Galileo ICD Soon. “We are about to publish in the next couple of weeks the so-called signal-in-space Open Service interface control document, which I know a number of you have waited for a long time.

“We need also to move forward at a political level. In this case, no GNSS system can be credible if it is not backed by a long-term political commitment particularly by its owner. So after the decision of the Parliament and the Council to deploy the system, these two institutions are now clearly called upon to provide us such political long-term commitment that is credible in the eyes of the users.”

GPS. Anthony Russo, director of the U.S. National Space-Based PNT Coordination Office, said “Keeping cards close to the chest in a competitive situation can well become a liability, creating a future need for a re-work or undoing if you paint yourself into a technological corner.” This appeared to refer to China and its Compass system; information has been singularly difficult to obtain on almost every aspect of this budding constellation.

Regarding the April 2009 U.S. General Accountability Office report that forecast gaps in constellation availability, Russo stated, “The GAO will revise its report somewhat. They were using a model that was a little too cautious, one used by the [GPS] Wing. But satellites on orbit have been performing past estimated life. Further, we can turn off secondary payloads to conserve energy onboard satellites [and thus extend life] if needed.”

The next morning, Lt. Col. Liz Roper, Air Force Space Command, gave a status and modernization briefing; the most eagerly awaited development is the launch of the first Block II-F satellite, scheduled for some time in May. She alluded to “a few setbacks” from the August 2009 launch of SVN49 with its well-documented signal problems, but emphasized the episode’s “positive aspects: the relationships we’ve been able to build in seeking solutions to that situation.”

GLONASS. Grigoriy Stupak, deputy general director and general designer on GLONASS systems, briefed the audience in fluent Russian. For a recent launch update, see story below.

Compass. Two of the Chinese delegates spoke in the opening session. Jiao Wenhai from China Satellite Navigation Office did elaborate the basic principles of the Beidou (Compass) system:
- openness (“China will widely and thoroughly communicate with other countries on satellite navigation issues.”)
- independence
- compatibility (“China will pursue solutions to realize compatibility and interoperability with other satellite navigation systems.”)
- gradualness.
He promised an English-language version of the governmental website www.beidou.gov.cn or www.compass.gov.cn “soon.” Wenhai recapped:
- the frequencies Compass will use: 1561.098, 1207.14, and 1268.52 Mhz in Phase II until 2012; and 1575.42, 1191.795, and 1268.52 in Phase III by 2020.
- the general development plan: five geosynchronous, five inclined geosynchronous, and four mid-Earth orbit satellites providing a Chinese regional service using mainly Compass Phase II signals; then development of a global service broadcasting mainly Compass Phase III signals from five GEO, three IGSO, and 27 MEO satellites.
The Chinese speakers displayed a certain disingenuousness in giving verbally and in their slides the location of the January launch, Beidou G1 geostationary satellite, as 160 degrees East, somewhere over the open Pacific. When GPS World pointed out that NORAD satellite tracking shows G1 has been repositioned to a slot at 144.5 degrees East longitude, they huddled for several minutes before stating that yes, it had moved to that position and was undergoing in-orbit testing. That spot was previously occupied by Beidou 1D, apparently decommisioned about a year ago due to power problems. 1D currently orbits in graveyard above geostationary altitude.

A personage civilly associated with the U.S. Air Force confirmed the actual G1 location to the magazine, and could only speculate that it was more advantageous to Chinese ground control for monitoring and testing. As to why spokespersons misstated the location, that remains inscrutable.

GLONASS Back in Black

Three GLONASS-M satellites launched on March 1 are expected to enter service on March 22 and March 30, according to deputy general director Grigoriy Stupak’s statement in Munich. This would bring the constellation, according to his calculations, to 23 operational satellites, though two of those are held in reserve.

With 21 satellites broadcasting signals, the system claim 98.5 percent global availability. Block 42 (three more satellites) has an August 2010 launch date, and Block 43 one for November 2010. By December, Stupak predicted 24 active satellites on orbit, for 99.5 percent global availability.

The GLONASS-M satellites have a stated seven-year lifetime. CDMA signals will begin with next-generation GLONASS-K satellites, while FDMA signals continue in parallel. The Russians plan to “reach 5-meter accuracy by 2017, almost equal to accuracy of other GNSS,” and are “paying more attention to differential corrections for integrity monitoring.”

ICG Questions

The International Committee on GNSS (ICG) Working Group on Compatibility and Interoperability invites GPS industry members to fill out a questionnaire, provided online in two formats: as a downloadable MS Word document or a PDF.

The Industry and User Community Questionnaire is designed to obtain worldwide input from industry, academic institutions, and other representatives of the GNSS user community with technical expertise regarding GNSS signals and other system characteristics that aid or hinder the combined use of the signals in applications, equipment, or services. For instance, respondents are asked to grade certain signal characteristics as to their importance in overall interoperability considerations for a particular type of application.

Respondents are asked to e-mail completed questionnaires to the ICG by May 28.

To download instructions and the form, go to env-gpsworld-integration.kinsta.cloud/icg.
April 1, 2010
New Beidou Satellite Launched
China launched its fifth Beidou/Compass navigation satellite on Friday, April 13. The initial orbital elements (inclination = 55.0°, eccentricity = 0.62, mean motion = 3.84 orbits per day) may indicate that this is not another GEO satellite but rather the first of the MEO satellites.

Meanwhile, it seems that NORAD had “lost” the 4th Beidou satellite for awhile. Launched on February 2, the satellite reportedly had a problem with a stuck solar panel which needed to be fixed before the satellite could be transitioned from its geostationary transfer orbit to its intended geostationary location. The last publicly released element set for this satellite had been dated 8 March 2007. Perhaps this was the day the Chinese started to move the satellite to its geostationary position.

NORAD released an element set for the satellite in its near geostationary orbit. NORAD is currently reporting the satellite to be in an inclined orbit (6.3°) with a sub-satellite longitude of about 144°E. The latest Beidou/Compass might not be heading for GEO but either to an inclined geosynchronous orbit or MEO, similar to that of GPS and GLONASS satellites.

The Chinese have talked about various Beidou/Compass options:
1. 4 GEO + 9 inclined (50°) geosynchronous
2. 4 GEO + 12 MEO (55° x 20,200 km)
3. 30 MEO (56° x 21,363 km)
In one of their ITU filings, the Chinese referred to some of the satellites as Compass-M.
April 27, 2007