The System: Galileo in Its Glory

January 1, 2012  - By


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.

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