GPS World

Category: GNSS

  • Second Galileo IOV Satellite Transmitting Signals

    News courtesy of CANSPACE Listserv.

     

    On Monday, 16 January, at about 02:18 UTC, the second of the two Galileo In-Orbit Validation (IOV) satellites, FM2 (Flight Model 2) also known as GSAT0102, started transmitting navigation signals on the L1/E1 frequency using the E12 ranging code, according to tracking reports from the COoperative Network for GIOVE Observation (CONGO).

    FM2 was launched together with PFM, the ProtoFlight Model (GSAT0101), on October 21, 2011. PFM started transmitting E1 signals on December  10, 2011, and E5 signals on December 14, according to CONGO network tracking reports. Subsequently, ESA confirmed that the E6 transmitter was powered up the weekend before Christmas.

    CONGO is a global network of 19 tracking stations established by the German Space Operations Center (DLR/GSOC) and the German Federal Agency for Cartography and Geodesy (BKG) in cooperation with several agencies including Technische Universitaet Muenchen.

  • U.S. Air Force Awards Contract to Lockheed Martin for GPS III Launch, Checkout

    The U.S. Air Force has awarded Lockheed Martin a $21.5 million contract to provide a Launch and Checkout Capability (LCC) to command and control all GPS III satellites from launch through early on-orbit testing.

    The LCC, which will be integrated into the Raytheon-developed Next Generation Operational Control System (OCX), will ensure launch availability for the first GPS III satellite in 2014. The LCC includes trained satellite operators and engineering solutions in partnership with OCX to support launch, early orbit operations and checkout of all GPS III satellites before the spacecraft are turned over to Air Force Space Command for operations.

    “Achieving initial launch capability in 2014 is critical to introducing new GPS capabilities on time and will  enable the GPS III program to continue its production pace, maximize efficiencies and reduce long term costs for the GPS enterprise as a whole,” said Colonel Bernard Gruber, director of the U.S. Air Force’s Global Positioning Systems Directorate. “The Launch and Checkout Capability will ensure we can launch in 2014, effectively closing the time gap between GPS III and the Next Generation Operational Control System.”

    The GPS III program will replace aging GPS satellites while improving capability to meet the evolving needs of military, commercial and civilian users worldwide. The satellites will deliver better accuracy and improved anti-jamming power while enhancing the spacecraft’s design life and adding a new civil signal designed to be interoperable with international global navigation satellite systems, according to Lockheed Martin.

    The GPS III team is led by the Global Positioning Systems Directorate at the U.S. Air Force Space and Missile Systems Center. Lockheed Martin is the GPS III prime contractor with teammates ITT Exelis, General Dynamics, Infinity Systems Engineering, Honeywell, ATK and other subcontractors. Air Force Space Command’s 2nd Space Operations Squadron (2SOPS), based at Schriever Air Force Base, Colo., manages and operates the GPS constellation for both civil and military users.

  • GLONASS Modernization: Maybe Six Planes, Probably More Satellites

    According to the GLONASS Information-Analytical Centre, proposals made at a December 27, 2011 meeting on the status and future of the satellite constellation included one to expand the GLONASS constellation to 30 satellites using six orbital planes. Five other options for upgrading the constellation were also aired, a draft of the tactical and technical requirements for GLONASS in 2025 was reviewed, and a report was given on the status the Glonass-K2 satellite under construction and the timing of the start of flight tests.

    Present at the meeting of the Presidium of the TsNIImash Council, held in the Moscow suburb of Korolyov, were Yuri Urlichich, general director and general designer of the Joint Stock Company (JSC) Russian Space Systems, and Sergey Revnivykh, TsNIImash deputy director general, among others. TsNIImash (the Central Research Institute of Machine Building) is the arm of Roscosmos, the Russian Federal Space Agency, with responsibility for civil aspects of GLONASS.

    A press conference following the meeting discussed the six options for upgrading the constellation, foremost among them the six-plane, 30-satellite concept. The other options include adding one more satellite to each of the existing three planes, but that would involve rephasing almost all of the operating satellites, which could cause many problems, according to Urlichich. Another option would add a reserve satellite to each operating satellite, but that option had already been rejected. Adding three new planes to the constellation, each with two satellites, is the leading option; Urlichich said this would be considered in detail over the next few months.

    It is not clear how the present frequency division multiple access (FDMA) channel spectrum used by GLONASS could handle 30 satellites. As indicated in the current publicly available version of the GLONASS Interface Control Document (version 5.1, dated 2008), there are 14 available channels (channel numbers from -7 to +6), with antipodal satellites sharing the same channel. It appears that this arrangement can only handle a maximum of 28 satellites. However, at least one recent GLONASS spectrum plot shows GLONASS channels going from -7 to +8, rather than to +6 as in the ICD. Such an expansion to 16 channels could support 32 satellites and is a partial return to the pre-2005 use of higher frequency channels, although the Russians had previously agreed to abandon their earlier use of the higher channels to avoid interfering with radio astronomers’ use of the 1610.6-1613.8 MHz observation band to observe the spectral line of the hydroxyl molecule.

    Nevertheless, the six-plane concept is still only just that — a concept — and the Russian Defense Ministry among others would have to get on board for it to go ahead.

    SBAS. Information on the Russian satellite-based augmentation system, the System for Differential Correction and Monitoring or SDCM, was also revealed during the press conference. SDCM will use a global ground network of monitoring stations and transponders on the Luch Multifunctional Space Relay System geostationary communication satellites to transmit correction and integrity data using the GPS L1 frequency. The first of these satellites, Luch-5A, was launched on 11 December.

    Luch-5A is temporally located in a stable geostationary orbit at about 58.5 degrees east longitude according to U.S. tracking data. Testing of the satellite is being carried out at this location but it will eventually be deployed to 16 degrees west longitude for operational use. It was announced during the press conference that SDCM testing is to start after the Russian Christmas holidays.

    Negotiations for additional SDCM ground stations in Australia, Indonesia, Brazil, and Nicaragua are ongoing to provide adequate coverage in the southern hemisphere. If one or more of the proposed ground stations cannot be realized, then additional stations at Russia’s Antarctic research bases could be deployed, Urlichich said. SDCM already has stations at the Bellingshausen and Novolazarevskaya research bases. Presentations by TsNIImash staff at international meetings have indicated that additional stations could be installed at the Progress and Russkaya Antarctic bases. According to Urlichich, the SDCM stations on Russian territory could be sufficient for northern hemisphere coverage.

  • First Galileo IOV Satellite Producing Full Spectrum of Signals

    Galileo team at Redu receiving signals.

    Europe’s first Galileo satellite appears to be functioning as expected, transmitting test signals received by the European Space Agency’s ground station in Redu, Belgium, across the whole of its assigned radio spectrum, ESA reports.
     
    The first two Galileo satellites were launched by Soyuz from Europe’s Spaceport in French Guiana on October 21. They are currently in the midst of a rigorous campaign to check that their highly sophisticated navigation payloads are operating as planned, unaffected by the strains of launch.

    Testing is centered on the first Galileo satellite for now, and expected to progress to the second satellite early in the new year.

    The Galileo system offers various groups of users a total of 10 different modulated signals across three spectral bands, known as E1, E5 and E6. The weekend before Christmas, all Galileo signals were activated simultaneously across these bands for the first time, following the switch-on and outgassing — warming up to vent potentially harmful vapours — of power amplifiers in the remaining E6 band.

    The signals were received by Galileo Test User Receivers deployed at the Redu ground station, within Belgium’s Ardennes forest, as well as by identical receivers at ESA’s Navigation Laboratory, in ESA’s ESTEC technical centre in Noordwijk, the Netherlands.

    These test receivers work in the same way as operational receivers will once Galileo begins its initial services in 2014. They are capable of processing the Open Service, Commercial Service and Safety-of-Life Service signals from the Galileo constellation.
     

    Galileo combines multi-frequency signals with the most accurate atomic clock ever flown in space for navigation, accurate to one second in three million years, ESA said. Its signals should open up a large number of commercial applications by combining this accuracy with the increased reliability of dual- or triple-frequency measurements. Receiver developers can choose among the variety of Galileo signals on offer to meet the needs of their customers in the most efficient way. They can also combine the processing of Galileo signals with GPS or Russian GLONASS signals to offer more robust positioning information in challenging environments such as city center urban canyons.

    First Galileo triple band signals. (Click to enlarge.)
     

  • The System: Galileo in Its Glory

     


    GALILEO PROTOFLIGHTMODEL satellite began transmitting E1 and E5 signals in early December. ESA reports them well within power and shape specifications, and suited for interoperability with GPS.

    The Galileo ProtoFlightModel (PFM) in-orbit validation (IOV) satellite GSAT0101 began transmitting E1 signals on December 10 using the E11 ranging code, and E5 signals early on December 14. Launched at the same time, Flight Model 2 (FM2), GSAT0102, has not yet started transmitting navigation signals. Several companies and laboratories around the world immediately began processing the PFM signals. This story briefly aggregates their reports.

    The European Space Agency (ESA) proudly released a statement: “Europe’s Galileo system has passed its latest milestone, transmitting its very first test navigation signal back to Earth. [. . . . ] The turn of Galileo’s main L-band (1200-1600 MHz) antenna came on the early morning of Saturday 10 December. A test signal was transmitted by the first Galileo satellite in the E1 band, which will be used for Galileo’s Open Service once the system begins operating in 2014.  [. . . . ]

    “The signal power and shape was well within specifications. The shape is especially important because its modulation is carefully designed to enable interoperability with the L1 band of U.S. GPS navigation satellites: Galileo and GPS can indeed work together as planned.

    “The test campaign is concentrating on the first satellite for the reminder of the year, with the focus moving to the second Galileo satellite from the start of 2012. The plan is to complete In-Orbit Testing by next spring.

    “The next pair of Galileo In-Orbit Validation satellites will also be launched next year, to form the operational nucleus of the full Galileo constellation. Meanwhile the next batch of Galileo satellites are currently being manufactured for launch in 2014.”

    Thales Avionics. Thales Avionics has developed a Galileo receiver capable of processing the Open Service, Commercial Service, and Safety of Life service of the Galileo constellation.

    Figure 1 shows a screenshot of the Thales Avionics receiver interface program, highlighting the L1 signal energy (top right) and the pilot secondary code (bottom). The satellite Doppler and C/N0 values have been recorded and are provided in Figure 2.


    Figure 1. Screen of Thales Avionics receiver interface highlighting L1 signal energy (top right) and the pilot secondary code (bottom). (Click to enlarge).


    Figure 2. Satellite doppler and C/N0 values from the Thales Avionics receiver.

    Thales has developed a coherent processing of the Galileo E5 AltBOC(15,10) signal compatible with hardware architecture designed for independent processing of both E5a and E5b. This processing is fully compatible with the mismatch between the two RF channels on E5a and E5b, thanks to real-time calibration based on satellite signals. This processing only requires software implementation, without additional recurrent costs. The technique is relevant for future receivers operating in the E5 band, in order to significantly enhance the accuracy, with respect to thermal noise and multi-path, and to improve the cycle slip probability.

    CONGO. Several COoperative Network for GIOVE Observation (CONGO) stations, including one at the University of New Brunswick, are tracking both the E1 and E5 signals. Figure 3 shows C/N0 values collected at UNB.


    Figure 3. C/N0 values in dB-Hz of PFM 1-Hz data collected at the University of New Brunswick, on December 10. Time axis runs for 24 hours starting at 01:00 UTC. Receiver is a Javad Delta-G2T.
    JAVAD GNSS. On December 12, JAVAD GNSS announced that it has tracked the Galileo in-orbit validation satellite, temporarily designated PRN-11.

    “An important point is that we tracked it with our units that are already in the market,” said Javad Ashjaee, CEO. “This is not a lab tests. Our customers can track it too.”

    Figure 4 shows the company’s tracking results of PRN-11: plots of pseudorange (in chips), doppler (in Hz), and SNR (relative number).


    Figure 4. JAVAD GNSS tracking results of Galileo PRN-11 for now, plots of pseudorange (in chips), doppler (in Hz), and SNR (relative number).

    Calgary PLAN Group. The University of Calgary sent a detailed report. (See Figure 5 and next item.)

    Figure 5. Raw correlator values for the E1 B/C, E5aI/Q and E5bI/Q signals. The bit periods can be clearly seen on E1B, E5aI and E5bI. The secondary code can be observed on E1C while the pilot signal can be seen on singals E5aQ and E5bQ. (From the Calgary Report.)

    Galileo E1 and E5: the Calgary Report

    By James T. Curran and Aiden Morrison

    Researchers in the Position, Location and Navigation (PLAN) Group at the University of Calgary recorded E1 and E5 data using a single dual-channel front-end and subsequently acquired and tracked E1 B/C, E5a and E5b signals in the early morning of December 15.

    Using a dual channel front-end designed in-house, a Novatel GPS-703-GGG antenna and a laptop computer, IF data was collected to examine these new signals. This data was processed by GSNRx, a reconfigurable a multi-system, multi-frequency software receiver developed by the PLAN Group.

    At approximately 03:20 MST (UTC – 7:00) more than 20 GNSS satellites were visible from a rooftop mounted antenna. Having reconfigured the front-end to accommodate the E5 band, IF data was collected which included Galileo E1 B/C and E5 A/B, GIOVE-B E1 B/C and E5a, GPS L1 C/A and L5, and GLONASS L1 C/A. Following some last-minute modifications to GSNRx to include the Galileo E5b signals, the samples were processed, simultaneously tracking GPS and Galileo on both the L1/E1 and L5/E5 frequencies and GLONASS on L1.

    A subset of the raw correlator values for the E1 B, E1 C, E5a I and E5a Q signals are shown in Figure 5 above. Note that the E1 C values have been offset by -2.0×105 for clarity. A data-rate of 250 symbol/s is clearly visible on the E1 B and E5b signals while a 50 symbol/s stream can be observed on the E5a I signal. The 25 chip secondary code is also evident on E1 C at a rate of 250 chip/s.

    All six components of the Galileo-PFM signals shown above (transmitted on PRN 11) were tracked independently and their signal modulations were found to agree with the Galileo Open Service ICD. A trace of the measured carrier-to-noise floor ratios for the Galileo signals is shown in Figure 6. As indicated by the ICD, the E5b signals were observed at 2 dB lower power than the E1 B and C signals. The E5a signals, however, were expected to be received at the same power as E5b and yet were observed at approximately 4 dB lower power. This is believed to be a combination of the antenna and IF filtering within the front-end as the E5a center frequency is located relatively near the pass-band edge of both.  This front-end was initially designed for 40 MHz bandwidth, but used in this experiment at 50 MHz, as will be discussed later.

    Figure 6. C/N0 for Galileo-PFM signals.

    The software receiver was once again reconfigured, this time to produce signal correlator values spaced along a delay of approximately 700 m and 70 m for the E1 A/B and E5 A/B signals, respectively, such that the cross-correlation of the received and local-replica PRN sequences could be examined. The signals were tracked for 10 seconds and the 1 ms correlator values averaged, to produce estimates of the code cross-correlation function. The characteristic ripple of the CBOC modulation on E1 B/C can be seen in Figure 7 (left), particularly on the right-most ascending feature of the envelope. Likewise, the alt-BOC cross-correlation of E5a Q in Figure 7 (right) is as expected. It is noted that the E5a I signal has suffered some distortion due to the filtering effects mentioned above.

    Figure 7. Measured cross-correlation functions for the Galileo PFM E1 B and C signals (left) and E5a I and E5b I signals (right).

    For details of the PLAN group’s front-end, a flexible GNSS signal capture tool, and other specifics on the process employed, see the full-length article.

    GPS III Testbed Sat Delivered

    Lockheed Martin delivered the the GPS III Non-Flight Satellite Testbed (GNST), the program’s pathfinder spacecraft, to its Denver-area facility. The pathfinder will now undergo final assembly, integration, and test activities.

    The GNST is a full-sized, flight equivalent prototype of a GPS III satellite used to identify and solve development issues prior to integration and test of the first space vehicle. According to the company, the approach reduces risk, improves production predictability, increases mission assurance and lowers overall program costs. In Denver, the GNST will be mated with its core structure, navigation payload, and antenna elements before completing pathfinding activities and checkout of environmental test facilities. The GNST will then be shipped to Cape Canaveral Air Force Station, Fla., for pathfinding activities at the launch site.

    GPS III satellites, when launched as scheduled to being in 2014, will replace aging on-orbit GPS satellites to deliver better accuracy and improved anti-jamming power, while enhancing spacecraft design life and adding a new civil signal designed to be interoperable with international global navigation satellite systems.

    In parallel with the GNST, progress on the first space vehicle is progressing on schedule. Lockheed Martin received the core structure for the first GPS III satellite in Stennis, Mississippi, on August 4, and is now integrating the space vehicle’s flight propulsion subsystem. The integrated core propulsion module will be shipped to the GPF in the summer of 2012 and will then undergo final assembly, integration and test in order to meet its planned 2014 launch.

    The GPS III team is led by the GPS Directorate at the U.S. Air Force Space and Missile Systems Center. Lockheed Martin is the GPS III prime contractor with teammates ITT, General Dynamics, Infinity Systems Engineering, Honeywell, ATK and other subcontractors.

    Drone Downed

    Press reports speculate that GPS spoofing was used to get the RQ-170 Sentinel Drone to land in Iran. According to an Iranian engineer quoted in a Christian Science Monitor story, “By putting noise [jamming] on the communications, you force the bird into autopilot. This is where the bird loses its brain.” At that point, the drone relies on GPS signals to get home. By spoofing GPS, Iranian engineers were able to get the drone to “land on its own where we wanted it to, without having to crack the remote-control signals and communications.”

    “The GPS navigation is the weakest point,” the Iranian engineer told the Monitor, giving a detailed description of Iran’s electronic ambush of the highly classified pilotless aircraft.

    In 2011, the U.S. Air Force awarded two $47 million contracts to BAE Systems and Northrop Grumman for development of a navigation warfare sensor to replace military GPS receivers on aircraft and missiles, and designed to maintain freedom of action under extreme GPS countermeasures.

    GLONASS Fully Operational

    For the first time in more than 15 years, GLONASS is fully operational, with 24 satellites in their designated orbital slots, set healthy, and providing world coverage.

    GLONASS 744, an M-class satellite and one of three launched from Baikonur on 4 November, was set healthy December 8, bringing the number of healthy operating satellites to the full complement of 24.

    GLONASS briefly achieved a 24-satellite constellation in early 1996 but it degraded rapidly due to Russia’s economic difficulties following the break-up of the Soviet Union coupled with the short lifetime of the GLONASS satellites. Since 2002, the GLONASS constellation has slowly but surely been rebuilt with the Russian government’s commitment to provide a global positioning and navigation system comparable to that of GPS.

    Luch SBAS. Roscosmos also launched the Luch-5A geostationary relay satellite on December 11.

    Luch-5A is the first in a series of new data relay satellites designed to rebuild the Luch Multifunctional Space Relay System, which had ceased operating by 1998. Among other functions, 5A hosts a wideband satellite-based augmentation system (SBAS) transponder.

    The SBAS transponder will transmit correction and integrity data for GLONASS and GPS on the GPS L1 frequency with a C/A pseudorandom noise code to be assigned by the GPS Directorate. The data will be provided by the System for Differential Correction and Monitoring or SDCM, which uses a ground network of monitoring stations on Russian territory as well as some overseas stations.

    As the SDCM primary service area is Russian territory, the main lobe of the SBAS antenna beam will be directed to the north with an angle of 7 degrees relative to the direction to the equator. Transmitted power of 60 watts will give a signal power level at Earth’s surface roughly equal to that of GLONASS and GPS signals, about –158 dBW.

    The current international SBAS data format has a limited capability for broadcasting corrections for both GLONASS and GPS satellites combined. There is space for only 51 satellites, insufficient for the current number of satellites on orbit. As a result, studies are being carried out in an attempt to resolve this problem. One option is to use a dynamic satellite mask, where an SDCM satellite would only broadcast corrections and integrity data for those GLONASS and GPS satellites in view of users in the territory of the Russian Federation.

    Luch-5A is the first of three MSRS/SDCM satellites. Luch-5B will be launched in 2012 into a slot at 95 degrees east longitude and Luch-4, in 2014, into a slot at 167 degrees east longitude.

    Beidou Launch Fills Regional Nav System

    The Beidou-2/Compass IGSO-5 (fifth inclined geosynchonous orbit) satellite was launched on December. According to a Chinese government announcement, this launch completes the construction of the basic regional navigation system for service to China and will be operational by the end of the year. However, completion of the Phase II development, to provide service to the Asia/Pacific region, will require further satellite launches in 2012. Phase III global coverage, with a 30-satellite system, will be achieved by 2020 according to the Beidou website.

    The GNSS community outside China still awaits a Compass interface control document (ICD), which has been promised by the end of 2012.

    LightSquared Incompatibility Declared

    U.S. government tests conducted in November showed that 75 percent of GPS receivers examined were interfered with at a distance of 100 meters from a LightSquared (LS)base station.  The report states that “No additional testing is required to confirm harmful interference exists,” and “Immediate use of satellite service spectrum for terrestrial service not viable because of system engineering and integration challenges.”

    The tests showed interference by the LS Low 10 terrestrial signal with an overwhelming majority of general-purpose GPS receivers. Data from LS handsets was collected, analysis is underway, but no results were given. Wideband and military receivers were tested, but neither specifications nor results were presented; a classified session was convened for that purpose.

    Of the 92 receivers for which full data sets were compiled, 75 percent of them failed a 1db test, showing harmful interference at 100 meters from a LS base station. These 69 receivers failed at a broadcast level of around -15dBm from the LS transmitter.

    In a December 7 filing with the FCC, LightSquared further revised its public plans to say that it would “limit its power on the ground when transmitting in the lower 10 MHz from 1526-1536 MHz to no more than –30 dBm until January 1, 2015, –27 dBm until January 1, 2017, and –24 dBm thereafter.” According to test data, at –30 dBm, approximately 17 percent of GPS receivers would be disrupted; at –27 dBm, 25 percent; at –24 dBm, 36 percent. Proceeding with this scenario would require the assumption that the FCC, or indeed anyone, believes anything that LightSquared says at any given instant, for any given duration.

  • GMV Tracks the First Galileo IOV Satellite

    GMV, one of the world’s leading companies in satellite navigation systems, announced the tracking of both data and pilot channels of Galileo first satellite signal with its own line of GNSS receiver products.
     
    The first two Galileo satellites were launched from Kouru Spaceport in French Guiana on October 21st and are now in in-orbit test campaign. The Galileo PRN 11 started transmitting the first navigation signal last Saturday.
     
    GMV has been involved in GNSS for the last 25 years and today GMV’s GNSS team includes more than 120 highly specialized engineers, some having more than 15 years experience in the GNSS field. GMV plays a critical role in the ongoing development of Europe’s GNSS strategy, being a key partner in the EGNOS and Galileo programmes.
     
    GMV has developed its own GNSS software receiver products: SRX-10 on GPS, which has been optimized for the urban environment, NUSAR for GPS L1 and Galileo E1 and its own L1 front end. This experience has been applied, even previously to the development of the receivers, to many studies on receiver performances under very diverse signal conditions and designs, namely by processing the GIOVE satellites signal.
     
    Supported by its line of GNSS receiver products, GMV now presents its results on the first Galileo signals on both data (E1-B) and pilot (E1-C) channels of the Galileo PRN 11 satellite.

  • E1 and E5 Galileo IOV Signals: Report from U. Calgary

    This article gives a brief overview of the acquisition and tracking of Galileo IOV signals received from the GSAT0101 satellite on the morning of December 15. Researchers in the PLAN Group successfully recorded E1 and E5 data using a single dual-channel front-end and subsequently acquired and tracked E1 B/C, E5a and E5b signals using the PLAN Group GSNRx software GNSS receiver.  

    A little over seven weeks after launch, one of the two Galileo IOV satellites began to transmit on the E1 band. To the delight of eagerly waiting researchers worldwide, Galileo-PFM (GSAT0101) broke radio silence on December 10, 2011. Within hours the community was alive with reports of successful acquisition and tracking of the E1 B/C signals. Four days later the E5 signal was also activated. In the early hours of the morning of the 15th of December researchers gathered in the PLAN Group at the University of Calgary and observed the sky filled with broadcasting satellites from three GNSS. Using a dual channel front-end designed in-house, a Novatel GPS-703-GGG antenna and a laptop computer, IF data was collected to examine these new signals. This data was processed by GSNRx, a reconfigurable a multi-system, multi-frequency software receiver developed by the PLAN Group [1]. The equipment used to acquire and process the data is shown in Figure 1.

    Figure 1 The equipment used to acquire and process the Galileo-PFM signals included an in-house dual frequency front-end, a 10 MHz OCXO, a Novatel GPS-703-GGG antenna and a standard laptop computer running the GSNRx software receiver.

    At approximately 03:20 MST (UTC – 7:00) more than 20 GNSS satellites were visible from a rooftop mounted antenna. Having reconfigured the front-end to accommodate the E5 band, IF data was collected which included Galileo E1 B/C and E5 A/B, GIOVE-B E1 B/C and E5a, GPS L1 C/A and L5, and GLONASS L1 C/A. Following some last minute modifications to GSNRx to include the Galileo E5b signals, the samples were processed, simultaneously tracking GPS and Galileo on both the L1/E1 and L5/E5 frequencies and GLONASS on L1. A screenshot of the receiver in operation is shown in Figure 2.

    Figure 2 Screenshot of GSNRx while processing the Galileo PFM signals

    The versatility of GSNRx had been exploited in the past when new signals were brought online. In particular, the modular design adapted for PLAN’s software receiver had been utilized to quickly add new signals and new signal processing techniques. Once again this flexibility was drawn upon to facilitate the last-minute addition of the E5b I/Q signals (that very night) and to enable the stand-alone tracking of each signal component. By the same means, of course, this structure could be easily manipulated to enable composite tracking of data/pilot signal pairs or even facilitate vector tracking of all signals in view.

    A subset of the raw correlator values for the E1 B, E1 C, E5a I and E5a Q signals are shown in Figure 3, (note that the E1 C values have been offset by -2.0×105 for clarity). A data-rate of 250 symbol/s is clearly visible on the E1 B and E5b signals while a 50 symbol/s stream can be observed on the E5a I signal. The 25 chip secondary code is also evident on E1 C at a rate of 250 chip/s.

     

     

    Figure 3 Raw Correlator Values for the E1 B/C, E5aI/Q and E5bI/Q signals. The bit periods can be clearly seen on E1B, E5aI and E5bI. The secondary code can be observed on E1C while the pilot signal can be seen on singals E5aQ and E5bQ.

    All six components of the Galileo-PFM signals shown above (transmitted on PRN 11) were tracked independently and their signal modulations were found to agree with the Galileo Open Service ICD [2]. A trace of the measured carrier-to-noise floor ratios for the Galileo signals is shown in Figure 4. As indicated by the ICD, the E5b signals were observed at 2 dB lower power than the E1 B and C signals. The E5a signals, however, were expected to be received at the same power as E5b and yet were observed at approximately 4 dB lower power. This is believed to be a combination of the antenna and IF filtering within the front-end as the E5a center frequency is located relatively near the pass-band edge of both.  This front-end was initially designed for 40 MHz bandwidth, but used in this experiment at 50 MHz, as will be discussed later.

    Figure 4 Measured C/N0 for Galileo-PFM Signals

    The software receiver was once again reconfigured, this time to produce signal correlator values spaced along a delay of approximately 700 m and 70 m for the E1 A/B and E5 A/B signals, respectively, such that the cross-correlation of the received and local-replica PRN sequences could be examined. The signals were tracked for 10 seconds and the 1 ms correlator values averaged, to produce estimates of the code cross-correlation function. The characteristic ripple of the CBOC modulation on E1 B/C can be seen in Figure 5 (left), particularly on the right-most ascending feature of the envelope. Likewise, the alt-BOC cross-correlation of E5a Q in Figure 5 (right) is as expected. It is noted that the E5a I signal has suffered some distortion due to the filtering effects mentioned above.

    Figure 5 Measured cross-correlation functions for the Galileo PFM E1 B and C signals (left) and E5a I and E5b I signals (right).

    The PLAN group’s front-end is a highly flexible GNSS signal capture tool ideally suited for use with the GSNRx software receiver. The front-end, photographed in Figure 6, allows software reconfiguration of oscillator source (onboard, or external), antenna bias voltage, sampling rate, and IF bandwidth in addition to other low level control options making it highly adaptable.   Furthermore, the center frequency, and filter bandwidth of each of the two hardware channels is independently configurable between 1150 – 2000 MHz, and between 4—40 MHz bandwidth (single sided) respectively.

    Figure 6: PLAN group two-channel reconfigurable front-end with main system blocks labeled.  The external clock and GNSS antenna SMA connectors are along the right edge, while the data interface is via mini-USB on the opposite side of the front-end.

    Typically the front-end is configured to collect dual bands of 40 MHz two-sided bandwidth in order to cover the L1 and L2 transmission bands of both GPS and GLONASS as is shown in the right and central blocks within Figure 7.  To allow the capture of E5a/E5b, the front-end configuration software was used to move the center frequency of channel B from 1237 MHz to 1192 MHz, the bandwidth of channel B from 33 MHz to 50 MHz, and to increase the sampling rate of both channels from 40 to 50 Ms/s.

    Figure 7: Front-end channel A and channel B typically configured to capture GPS and GLONASS L1+L2, but reconfigured here to allow capture of Galileo IOV E5a+E5b signal in lieu of L2 band.

    While each of the E5a and E5b signals have main lobe widths of 20.46 MHz (two sided), the composite E5 signal covers 50 MHz of spectrum, overlaying both the current GPS L5 signal at 1176, and the future GLONASS L3 signal near 1207 MHz.  In order to demonstrate the capabilities of the GSNRx software receiver as an L5/E5 + L1/E1 system, it was desirable to capture the new IOV signals in their entirety.

    The Galileo PFM satellite was observed from the Calgary Laboratory on the E1 link since the 12th of December at approximately 08:00 hrs and on the E5 link since the 14th of December at approximately 18:00 hrs. The last successful acquisition of the satellite on either E1 or E5 was at 03:20 hrs on the 15th of December and indicated a Doppler of approximately +2.3 kHz at E1. This figure is compatible with a reported elevation of approximately 40 degrees and rising, as reported by a number of software packages operating on a TLE [3]. Researchers recorded IF data once again at 03:55 on the 15th of December but failed to acquire any of the Galileo-PFM signals, suggesting the satellite may temporarily have ceased transmission.

    References
    Petovello, M. G., and C. O’Driscoll, G. Lachapelle, D. Borio and H. Murtaza (2008), “Architecture and Benefits of an Advanced GNSS Software Receiver,” Journal of Global Positioning Systems, vol. 7, no. 2, pp. 156-168.
    Galileo Project Office. Galileo OS SIS ICD. http://ec.europa.eu/…/galileo/files/galileo-os-sis-icd-issue1-revision1_en [Accessed: 15 December 2011].
    NORAD Two-Line Element Sets.  http://celestrak.com/NORAD/elements/, [Accessed: 15 December 2011].
     

  • E5 Aloft, Second Galileo Signal Transmitted

    The Galileo PFM IOV satellite (GSAT0101) began transmitting E5 signals early on December 14. It had already started airing E1 signals on December 10. Several COoperative Network for GIOVE Observation (CONGO) stations, including one at the University of New Brunswick, are now tracking both the E1 and E5 signals.

    Meanwhile, the European Space Agency (ESA) has released a statement on the start of IOV satellite transmissions, titled "Galileo in tune: first navigation signal transmitted to Earth":
     
    "Europe’s Galileo system has passed its latest milestone, transmitting its very first test navigation signal back to Earth.
     
    "The first two Galileo satellites were launched into orbit on 21 October. Since then their systems have been activated and the satellites placed into their final orbits, positioned so that their navigation antennas are aligned with the world they are designed to serve.

    "Last weekend marked the first orbital transmission from one of these navigation antennas. The stage was set, the singer in place and an audience – in the shape of engineers on the ground – was waiting eagerly.

    "The question was would the singer make music, and if so, would it be in tune?  
     
    "The turn of Galileo’s main ‘L-band’ (1200-1600 MHz) antenna came on the early morning of Saturday 10 December. A test signal was transmitted by the first Galileo satellite in the ‘E1’ band, which will be used for Galileo’s Open Service once the system begins operating in 2014.

    "To prepare for the test, the payload power amplifiers were switched on and ‘outgassed’ – warmed up to release vapours that might otherwise interfere with operations – before transmission began.
        
    "The signal power and shape was well within specifications. The shape is especially important because its modulation is carefully designed to enable interoperability with the ‘L1’ band of US GPS navigation satellites: Galileo and GPS can indeed work together as planned.

    "The test campaign is concentrating on the first satellite for the reminder of the year, with the focus moving to the second Galileo satellite from the start of 2012. The plan is to complete In-Orbit Testing by next spring.

    "The next pair of Galileo In-Orbit Validation satellites will also be launched next year, to form the operational nucleus of the full Galileo constellation. Meanwhile the next batch of Galileo satellites are currently being manufactured for launch in 2014."

  • Galileo Broadcasting Satellite Identified

    On Saturday, December 10, at about 06:00 UTC, one of the two Galileo In-Orbit Validation (IOV) satellites launched on October 21 started transmitting navigation signals on the L1/E1 frequency using the E11 ranging code.

    According to prediction visibilities based on NORAD/JSpOC tracking information, the transmitting satellite is PFM, the ProtoFlight Model (GSAT0101). The FM2 (Flight Model 2) satellite (GSAT0102) has not yet started transmitting navigation signals.

    Stations of the COoperative Network for GIOVE Observation (CONGO) were among the first to track the satellite. Results have also been reported by Thales Avionics, JAVAD GNSS, Politecnico di Torino's NavSAS group, and Thales Alenia Space.

    The following figure shows C/N0 values in dB-Hz of PFM 1-Hz data collected at the University of New Brunswick CONGO station on December 10. Time axis runs for 24 hours starting at 01:00 UTC. Receiver is a Javad Delta-G2T.

  • JAVAD GNSS Tracks Galileo IOV Satellite

    On December 12, JAVAD GNSS announced that it has tracked the Galileo in-orbit validation satellite designated PRN-11. It is one of two Galileo satellites launched on October 21.

    "An important point is that we tracked it with our units that are already in the market," said Javad Ashjaee, CEO. "This is not a lab tests. Our customers can track it too."

    Here are the company's tracking results of PRN-11 for now, plots of pseudorange (in chips), doppler (in Hz), and SNR (relative number):

    JAVAD GNSS expects to publish additional results soon.

  • Thales Avionics Tracks L1 Signal of First Galileo Satellite

    Following the recent launch of two Galileo in-orbit validation satellites, Thales Avionics of Valence, France, has successfully acquired and tracked the new L1 Open Service signal transmitted by one of the space vehicles (PRN 11) on Monday, December 12, at 13:30 (GMT). Thales Avionics has developed a Galileo receiver capable of processing the Open Service, Commercial Service, and Safety of Life service of the Galileo constellation.

    Figure 1 shows a screenshot of the receiver interface program highlighting the L1 signal energy (top right) and the pilot secondary code (bottom).

    Figure 1: Real-time measurements.

    The satellite Doppler and C/N0 values have been recorded and are provided below.

    The raw navigation message has been decoded. It contains INAV type 0 and INAV dummy data as shown in the next figure. These messages enable Galileo system time transfer.

    The signal modulation and characteristics show no discrepancy relative to the Galileo Open Service ICD released last year.

    The fact that only L1 frequency is broadcast for the moment prevents providsion of further  results based on dual-frequency measurements.

    Thales has developed a coherent processing of the Galileo E5 AltBOC(15,10) signal compatible with hardware architecture designed for independent processing of both E5a and E5b. This processing is fully compatible with the mismatch between the two RF channels on E5a and E5b, thanks to real-time calibration based on satellite signals. This processing only requires software implementation, without additional recurrent costs. The technique is relevant for future receivers operating in the E5 band, in order to significantly enhance the accuracy, with respect to thermal noise and multi-path, and to improve the cycle slip probability.

    Thales Avionics, involved for many years in GNSS receivers design and production, has developed a Galileo receiver capable of processing the Open Service, Commercial Service, and Safety of Life service of the Galileo constellation. This high-end receiver includes patented state of the art algorithms capable of processing up to four different frequencies.

  • Beidou Launch Completes Regional Nav System

    The Beidou-2/Compass IGSO-5 (fifth inclined geosynchonous orbit) satellite was launched on December 1 from Xichang, China. Exact launch time was 21:07:04.189 UTC. The third stage of the CZ-3A rocket with the satellite attached achieved a geosynchronous transfer orbit and the satellite subsequently separated according to NORAD/JSpOC. As of December 7, the satellite is still in geosynchronous transfer orbit (GTO), orbiting the Earth about twice a day with a highly eliptic orbit. To get to geosynchronous orbit, the satellite's apogee kick motor will have to be fired. The satellite is not drifting to its intended orbit, for example, like a GLONASS satellite might.

    According to an announcement on the official government Beidou/Compass website, this launch completes the construction of the basic regional navigation system for service to China and will be operational by the end of the year. However, completion of the Phase II development, to provide service to the Asia/Pacific region, will require further satellite launches in 2012. Phase III global coverage, with a 30-satellite system, will be achieved by 2020 according to the website.

    The GNSS community outside China still awaits a Compass interface control document (ICD), which has been promised by the end of 2012.