Let’s all remember, brevity is the soul of wit.

GPS III Flexible Signal Generator. With completion of the Delta Preliminary Design Review for the GPS III satellites, Lockheed Martin and the U.S. Air Force announced that “an innovative new waveform generator permits the addition of new navigation signals after launch to upgrade the constellation without the need to launch new satellites.”

IGS Real-Time Service. The International GNSS Service, a worldwide federation of agencies involved in high-­precision GNSS applications, announced the launch of its Real-­Time Service (RTS). The RTS is a global-scale GNSS orbit and clock correction service that enables real-time precise point positioning and related applications requiring access to IGS low-latency products. The RTS is offered in beta as a GPS-­only service for the development and testing of applications.

QZSS Will Grow to Four. The Japanese government has ordered three navigation satellites from Mitsubishi Electric Corp. to expand the Quasi-Zenith Satellite System, currently orbiting the sole Michibiki. QZSS augments GPS navigation signals for users in the Asia-Pacific region. NEC Corporation has been awarded a contract for the QZSS ground control segment.

Real-Time PPP with Galileo. Fugro Seastar AS achieved this task within a week of all four Galileo satellites being activated. Fugro is now generating Galileo orbit and clock corrections, which can be used in conjunction with the Fugro G2 decimeter-level corrections associated with its GPS/GLONASS PPP service.

BeiDou Ground System Approved. The BeiDou Ground-Based Enhancement System (BGBES), a network of 30 ground stations, an operating system, and a precision positioning system, was approved by a Chinese government evaluation committee. The system is expected to improve BDS positioning accuracy to 2 centimeters horizontal and 5 centimeters vertical via tri-band real-time precision positioning technology, and to 1.5 meters with single-frequency differential navigation technology.

CNAV Test on GPS L2C and L5. The U.S. Air Force Space Command announced that CNAV capabilities on the GPS L2C and L5 signals will be tested in June. The civilian navigation message to be carried by modernized GPS will have similar data to the existing NAV message, but its structure will be different, with increased message bandwidth for greater information density. L2C and L5 users and receiver manufacturers are encouraged to review the test plan, provide comments, and participate in the evaluation process.

GPS at the Smithsonian. Brad Parkinson’s presentation, “GPS for Humanity — The Stealth Utility,” is now available as video on UStream.The talk helped introduce the new Smithsonian National Air and Space Museum exhibit, “Time and Navigation: The Untold Story of Getting from Here to There,” which is now open and free to the public in Washington, D.C.

Measurements of individual Galileo horizontal position fixes performed for the first time using the four Galileo satellites in orbit plus the worldwide ground system between 1000 and 11:00 CET on Tuesday 12 March 2013, showing an overall horizontal accuracy over ESTEC in Noordwijk, the Netherlands, of 6.3 m.

Galileo Logs First Autonomous Fix; Galileo over Canada (By James T. Curran, Mark Petovello, and Gérard Lachapelle); and Indoor Nav: Early Steps towards FCC Standards

Galileo Logs First Autonomous Fix

Entitling its release “From Orbit with Love,” the European Space Agency (ESA) announced March 12 that the four current satellites of the Galileo constellation achieved their first autonomous position fix. The feat was replicated by the NavSAS group of Politecnico di Torino, by GNSS manufacturer Septentrio, and by a University of Calgrary team as the four satellites appeared over North America.

The obtained accuracy lies in the 10-meter range, according to ESA, adding that this fulfills expectations, considering the infrastructure is only partly deployed. The fix was obtained by ESA’s Netherlands navigation lab, using the four satellites, launched in October 2011 and 2012, and the Galileo programme’s ground infrastructure: control centers in Italy and Germany and a global network of ground stations.

With only four satellites for the time being, the full Galileo constellation is visible at the same time for a maximum two to three hours daily. This frequency will increase as more satellites join the constellation in orbit, along with extra ground stations coming online, for Galileo’s early services to start at the end of 2014.

With the validation testing activities under way, users might experience breaks in the content of the navigation messages being broadcast, said ESA. In the coming months the messages will be further elaborated to define the offset between Galileo System Time and Coordinated Universal Time (UTC), enabling Galileo to be relied on for precision timing applications, as well as the Galileo to GPS Time Offset, ensuring interoperability with GPS.

NavSAS Confirmation. Almost simultaneously with the ESA announcement, the NavSAS group of Politecnico di Torino and Istituto Superiore Mario Boella in Turin, Italy, also achieved a position fix using the signals of the four In-Orbit Validation satellites (PFM, FM2, FM3, FM4). NavSAS researchers computed the positions using full software receivers developed by the team.

Septentrio, Too. Septentrio became the first receiver manufacturer to report an autonomous real-time position calculation using Galileo IOV satellites with its own standard commercial receiver. The company based in Leuven, Belgium announced on March 12 that it performed  standalone position calculated from in-orbit navigation messages using a standard PolaRx4 GNSS receiver equipped with commercially released firmware.

This achievement was followed by a further Septentrio release stating performance of what it believes to be the first 4-constellation PVT by a standard commercial receiver, on March 12 at approximately 10:35 UTC.

The milestone in all three accounts is that it is Galileo-only real-time positioning. Galileo positioning in post-processing mode was described by authors from the Technische Universität München and the German Space Operations Center, in a GPS World account, February 2012 issue.

Galileo over Canada

By James T. Curran, Mark Petovello, and Gérard Lachapelle

Within a day of activation over Europe, Galileo satellites were visible over North America. The PLAN Group of the University of Calgary captured and processed signals from Galileo PRN 11, 12, and 19 on E1B/C. The PLAN software GSNRx  simultaneously tracked GPS L1 and GLONASS L1 for combined solutions in real time.

The Galileo navigation message on E1B stated that the satellite health status is flagged as E1BHS=3 meaning “Signal Component currently in Test” and the data validity status is flagged as E1BDVS=1 meaning “Working without guarantee.” Current Galileo-ready commercial receivers may automatically discard measurements from a satellites broadcasting such messages. Parsing the received words in the I/NAV message, more than 50 percent were of type 0, although all words (types 0 to 10) were decoded at some point during the test.

Figure 1. 2D position errors.

Data was collected using a roof-mounted NovAtel 702GG antenna and an in-house two-channel digitizing front-end clocked by a high quality OCXO, in addition to a three-channel National Instruments front-end for post-processing. The two-channel intermediate frequency data was streamed live to a laptop computer for real-time processing with GSNRx. The GPS and GLONASS signals were tracked using a Kalman-filter-based tracking strategy while the Galileo signals were tracked using a specialized data-pilot algorithm.

Pseudorange and Doppler observations were extracted from the tracking strategies at a rate of 2 Hz. Single-frequency single-point position solutions were then computed for each of the three systems, each of the three pairs of systems and for the full combined Galileo-GLONASS-GPS. In the case of the three-satellite Galileo solution, the height was held fixed. Figure 1 shows 2D position errors with respect to antenna ITRF coordinates. Departures of the solutions involving GLONASS are likely due to orbital biases, given location of Calgary with respect to GLONASS ground stations.

Figure 2. Pseudorange residuals.

Next, by fixing the known position in the solution and solving only for the three clock biases, accurate pseudorange residuals were computed and are shown Figure 2. Galileo PRN 19, launched a year later than PRN 11 and 12, exhibits larger residuals, perhaps attributable to ephemeris or orbital errors. The overall results show very good consistency of the Galileo results and the PLAN Group equipment and GSNRx receiver.

Indoor Nav: Early Steps towards FCC Standards

The Federal Communications Commission (FCC) on March 14 released two reports from its Communications Security, Reliability, and Interoperability Council (CSRIC): the “Indoor Location Test Bed Report,” and “Leveraging LBS and Emerging Location Technologies for Indoor Wireless E9-1-1.”
They report on Bay Area tests of technology from NextNav, Polaris Wireless, and Qualcomm, in four representative morphologies (dense urban, urban, suburban, rural) and various building types. They are available online, via www.gpsworld.com/csric, are the subject of an Expert Advice column (see page 10), and will be more fully discussed in May issue.  For now, this summary from the first-named report:

“Seven location vendors/technologies began the process to demonstrate their performance indoors through the common test bed, but only three completed the process. Of these three, two technologies (AGPS/AFLT and RF Fingerprinting) are already in common use for emergency services, while the third (metropolitan beacons) is not yet commercially available. However all technologies tested demonstrated relativity high yield and various levels of accuracy in indoor environments.

“Significant standards work is required for practical implementation of many emerging location technologies for emergency services use.

“Many positioning methods require handset modifications. Integration of these modified handsets into the subscriber base, once the location technology is commercially available, will take years to complete.

“Progress has been made in the ability to achieve significantly improved search rings in both a horizontal and vertical dimension. However, even the best location technologies tested have not proven the ability to consistently identify the specific building and floor, which represents the required performance to meet Public Safety’s expressed needs. This is not likely to change over the next 12–24 months. Various technologies have projected improved performance in the future, but none of those claims have yet been proven through the test bed process. It is hoped that such technologies would be tested and validated in future test bed campaigns.”

An April 16 GPS World Webinar covers this topic with test participants. Registration is free.

New Organization Advocates for GPS Industry; Galileo Lives to Fly Another Day, Budget Passed; Safer Skies for EGNOS; and GLONASS in Brazil

New Organization Advocates for GPS Industry

A new group, the GPS Innovation Alliance, has formed and announced itself as the voice of the U.S. GPS industry and community of users, to “support the ever-increasing importance of GPS” in the U.S. capital, Washington, D.C.  The organization subsumes and replaces both the U.S. GPS Industry Council, an entity of longstanding, and the Coalition to Save Our GPS, which arose in March 2011 in response to a Federal Communications Commission (FCC) conditional waiver granted to LightSquared.

The alliance appears to reflect a desire on the part of some industry members to take a more aggressive approach inside the Washington Beltway, a sign, it would seem, of the political times. Some of those involved spoke informally of a desire to take advantage of contacts made on Capitol Hill and in the media during the highly visible LightSquared combat, fought in the glare of media attention heretofore unknown in industry circles.

Members of the Alliance are drawn from a variety of fields and businesses reliant on GPS, as well as leading manufacturers of GPS equipment. The former group includes, aviation, agriculture, construction, transportation, first responders, and surveying and mapping, and consumer organizations representing users of GPS for boating and other outdoor activities, and in automobiles, smartphones, and tablets.

Joining John Deere, Garmin, and Trimble — three lead drivers of the Coalition effort at the FCC — are NovAtel Inc. and Topcon Positioning Systems. All five were previously long-time members of the USGIC, and they appear as founding members of the alliance at www.gpsalliance.org.

Affiliate members listed on the website include the Association of Equipment Manufacturers, General Aviation Manufacturers Association, National Association of Manufacturers, Association for Unmanned Aerial Vehicles International, and Boat Owners Association of the United States.

The alliance plans to build on “the proud heritage and extensive expertise of the United States GPS Industry Council (USGIC), which was formed in 1991 to promote broader commercial applications of GPS and to expand global markets while assisting in safeguarding the technology’s military advantages. The council has a long history of highly effective advocacy on behalf of the GPS industry, as well as serving as a trusted source of objective information for policy makers, the media and the public both in the U.S. and around the world.” The alliance website gives a longer statement about the history and record of the USGIC, highlighting its role in international negotiations.

Michael Swiek, executive director of the USGIC, has transitioned to become the executive director, executive branch and international, of the Innovation Alliance. In addition to working closely with leading offices of executive branch departments of the U.S. government, he will continue well-established dialogs with governmental, private sector and academic entities in areas critical to GPS and satellite navigation among key players in Europe, Japan, Russia, Korea, China, and elsewhere.

Heather Hennessey, a principal of Innovative Federal Strategies LLC, a “comprehensive government relations firm,” has taken the position of executive director, legislative, at the alliance. Hennessey has seven years of service in the House of Representatives, including two years as chief of staff for Congressman Jack Kingston of Georgia.

An active voice in alliance representations on Capitol Hill will presumably be that of Jim Kirkland, vice president and general counsel for Trimble. Kirkland was the most prominent spokesperson for the coalition during the LightSquared battle, which appears to be either over or nearly so. “The alliance is committed to ensuring constructive, robust dialog between GPS users, manufacturers and policy makers on critical policy issues affecting GPS,” Kirkland said, “a commitment Trimble is pleased to be a part of as the industry continues to innovate and modernize.”

The alliance mission statement cites the importance of GPS to global economy and infrastructure; vows to aid further GPS innovation, creativity and entrepreneurship; and to protect, promote and enhance the use of GPS.

The GPS Innovation Alliance officially launched on February 13 with a reception on Capitol Hill, a traditional lobbying tactic that previous efforts had perhaps not envisioned.  The organization has also hired a public relations firm, Prism Public Affairs, and commissioned a logo.

Galileo Lives to Fly Another Day, Budget Passed

BeiDou ICD: Signal Specs Are Free At Last

The interface control document (ICD) describing the details of the BeiDou B1I open service signal on 1561.098 MHz was released December 27 at a news conference held in Beijing by the Chinese State Council Information Office. The ICD includes details of the navigation message, parameters of the satellite almanacs, and ephemerides that did not appear an earlier, incomplete version of the ICD released at the end of 2011.

An English version is available for download courtesy of the University of New Brunswick. The ICD specifies the relations of the signal in space interface between BeiDou Navigation Satellite System and users’ terminal receivers. It is the essential technical document to develop and make receivers and chips.

Anyone who has questions about the ICD is invited to submit them to BeiDouICD@beidou.gov.cn.

The document, BeiDou Navigation Satellite System Signal In Space Interface Control Document — Open Service Signal B1I (Version 1.0), includes a system introduction, signal standards and navigation message, which defines the related contents of the open-service signal B1I between the BeiDou Navigation Satellite System and users’ terminals.

In a previous presentation given at the Seventh Meeting of the International Committee on Global Navigation Satellite Systems (ICG)  in November, 2012, BeiDou officials stated that by 2020 there will be five GEO and 30 non-GEO satellites. The number of IGSO and MEO satellites was not specified, but previous presentations have said three IGSOs and 27 MEOs. These numbers are also stated in the official ICD.

“The GEO satellites are operating in orbit at an altitude of 35,786 kilometers and positioned at 58.75°E, 80°E, 110.5°E, 140°E and 160°E respectively. The MEO satellites are operating in orbit at an altitude of 21,528 kilometers and an inclination of 55° to the equatorial plane. The IGSO satellites are operating in orbit at an altitude of 35,786 kilometers and an inclination of 55° to the equatorial plane.”

The China Satellite Navigation Office presented a new official logo for the BeiDou system, with a yin/yang symbol representing Chinese culture, dark and light blue for space and Earth, and the Big Dipper constellation, symbolizing a long tradition of Chinese navigation since ancient times.

A spokesperson said the English name for China’s GNSS will be BeiDou Navigation Satellite System, abbreviated as BDS. The name Compass, which first designated the prototype regional system and has been employed in conjunction with the name BeiDou, will apparently now be discontinued.

Other salient details from the ICD include:

Signal Structure. “The B1 signal is the sum of channel I and Q which are in phase quadrature of each other. The ranging code and NAV message are modulated on carrier. The signal is composed of the carrier frequency, ranging code and NAV message.

“The B1 signal is expressed as follows:

S ^j (t) = A _I C _I ^j (t) D _I ^j (t) cos (2 π f₀ t φ ^j) + A _Q C _Q  ^j (t) D _Q ^j (t) sin (2 π f₀ t + φ ^j)

where superscript j is the satellite number; subscript I equals channel I; subscript Q is channel Q; A is the signal amplitude; C the ranging code; D the data modulated on ranging code; f₀ represents the carrier frequency; and φ the carrier initial phase.”

The nominal frequency of the B1I signal is 1561.098 MHz.

As is the norm with most other GNSSs, BeiDou’s transmitted signal is modulated by quadrature phase shift keying (QPSK). The transmitted signal will be right-handed circularly polarized (RHCP), and its multiplexing mode is code-division multiple-access (CDMA).

User-Received Signal Power Level. “The minimum user-received signal power level is specified to be -163 dBW for B1I, which is measured at the output of a 0 dB RHCP receiving antenna (located near ground), when the satellite’s elevation angle is higher than 5 degree.”

Bandwidth and Suppression. “Bandwidth (1 dB): 4.092 MHz (centered at carrier frequency of B1I); Bandwidth (3 dB): 16 MHz (centered at carrier frequency of B1I). Out-band suppression: no less than 15 dB on f₀±30 MHz, where f₀ is the carrier frequency of B1I signal.”

Ranging Code on B1I. “The chip rate of the B1I ranging code is 2.046 Mcps, and the length is 2,046 chips. The B1I ranging code (hereinafter referred to as CB1I) is a balanced Gold code truncated with the last one chip. The Gold code is generated by means of Modulo-2 addition of G1 and G2 sequences which are respectively derived from two 11-bit linear shift registers.”

NAV Message. “NAV messages are formatted in D1 and D2 based on their rate and structure. The rate of D1 NAV message which is modulated with 1 kbps secondary code is 50 bps. D1 NAV message contains basic NAV information (fundamental NAV information of the broadcasting satellites, almanac information for all satellites as well as the time offsets from other systems); while D2 NAV message contains basic NAV and augmentation service information (the BDS integrity, differential and ionospheric grid information) and its rate is 500 bps.

“The NAV message broadcast by MEO/IGSO and GEO satellites is D1 and D2 respectively.”  The adjacent table from the BeiDou ICD gives information on nav message contents.

First Demonstration of Galileo-Only Positioning

By Peter Steigenberger, Urs Hugentobler, and Oliver Montenbruck

The European satellite navigation system, Galileo, is currently in its in-orbit validation (IOV) phase with a constellation of four satellites. The satellites, launched in pairs on October 21, 2011, and October 12, 2012, are representative of the full 30-satellite constellation. The IOV satellites will demonstrate that the satellites and the ground segment meet the system’s requirements and will validate the system’s design before completion of the rest of the constellation.

The IOV satellites have already started transmitting signals, and short periods of four-satellite visibility have allowed us to demonstrate, for the first time, absolute and relative positioning using measurements from Galileo operational satellites only. This follows the positioning demonstration last year with the signals from the Galileo IOV Element (GIOVE) test satellites and the first two IOV satellites. As in that earlier work, external orbit and clock information is necessary, since the IOV satellites were not transmitting valid navigation messages at the time of our study.

Three Javad GNSS Triumph-VS receivers with external antennas were set up at Technische Universität München (TUM) in Munich, Germany. The reference station TUME is equipped with a Javad GNSS RingAntG3T choke-ring antenna whereas the stations TUMW and TUMO are equipped with Javad GNSS GrAntG3T antennas. Unfortunately, all antennas are mounted near metal surfaces introducing pronounced multipath effects. The resulting baseline lengths are approximately 19.4 meters for TUME-TUMW and 101.7 meters for TUME-TUMO. Galileo satellite orbit and clock information was determined from stations of the Cooperative Network for GNSS Observation (CONGO) and the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS). For GPS satellites, the rapid products of the Center for Orbit Determination in Europe (CODE) were used. All computations were performed with a modified version of the Bernese GPS Software 5.0.

Figure 1. Single-point positioning results for the TUME reference station based on E1/E5a dual-frequency pseudorange measurements of the four Galileo IOV satellites. The standard deviations in the north, east, and up directions are given. Note the different scale of the north component.

At a cutoff angle of 10 degrees, the four IOV satellites were jointly visible from TUM on January 6, 2013, for about two hours – from 04:16 to 06:09 UTC. Using an ionosphere-free dual-frequency linear combination of pseudorange measurements on the Galileo E1 and E5a frequencies, the position of the TUME reference station could be determined with a 3D position error of less than 1.5 meters (see Figure 1).

In addition to absolute positioning, relative positions between pairs of receivers were computed from Galileo E1, E5a, E5b, and E5 AltBOC single-frequency carrier-phase observations. Two GPS solutions covering the same time interval serve for comparison purposes. The first solution utilizes all visible GPS satellites (9 to 12 per epoch) whereas the second solution is intentionally limited to four satellites (G06, G16, G27, G29) for best comparison with the Galileo case. So-called kinematic-style processing was used where the baseline is not constrained to be unchanging and a relative-position solution is computed for each epoch of measurements. 3D standard deviations of the different solutions are listed in Table 1. The overall accuracies are at the level of a few centimeters.

Tabe 1. 3D position errors (standard deviation) of carrier-phase-based kinematic-style Galileo and GPS baseline solutions.

A slightly degraded performance is achieved for the TUMO-TUME baseline, which can be attributed to both the larger separation and the inferior multipath environment compared to the TUMW-TUME baseline.

Comparing the individual Galileo signals, the best relative positioning results were obtained for the E1 carrier-phase measurements. Interestingly, the use of carrier-phase measurements from the E5 AltBOC tracking yielded a lower performance in our test than use of either the E5a or E5b observations.  Apparently, the carrier-phase tracking benefits less from the ultra-wideband signal than the code tracking, where AltBOC usually offers notably reduced noise and multipath.  Besides their good performance for Galileo-only positioning, the E1 and E5a carrier-phase measurements will be particularly relevant for future relative positioning applications due to the possibility of mixed-constellation ambiguity resolution with GPS L1 and L5 signals.

For illustration, Figure 2 shows the Galileo E1 solution as well as the GPS L1 solution computed from four satellites. For the north component, the scatter of the Galileo solution is larger by a factor of two compared to GPS whereas it is on almost the same level for the east and up components as a result of the specific geometry of the satellites employed.

Figure 2. Kinematic positioning results for the TUMW-TUME baseline based on Galileo E1 (left) and GPS L1 (right) carrier-phase observations of four satellites. The standard deviations in the north, east, and up directions are given. Note the different scale of the north component.

With the recent testing of navigation messages on the first pair of IOV satellites, Galileo-based positioning as described in this article will not be limited to post-processing, but will be available to real-time users as well.

Peter Steigenberger is a staff member in the Institut für Astronomische und Physikalische Geodäsie of the Technische Universität München (TUM) in Munich, Germany.

Urs Hugentobler is the head of the Fachgebiet Satellitengeodäsie (Department of Satellite Geodesy) and the Forschungseinrichtung Satellitengeodäsie (Research Facility for Satellite Geodesy) at TUM.

Oliver Montenbruck is the head of the GNSS Technology and Navigation Group in the German Space Operations Center in Oberpfaffenhofen, Germany, and a TUM associate faculty member.