According to Quectel, this paper details the challenges eMobility providers face in enabling vehicles such as eScooters and eBikes to be located in deep urban canyons. The white paper also examines why accurate location data will be vital in enabling the ride-sharing industry to comply with regulation to restrict eMobility usage on sidewalks and other areas, Quectel said.
The report also details drive test data conducted on an eScooter in San Francisco. The data demonstrates the enhanced accuracy offered by L1 and L5 plus dead reckoning capability.
Finally, the white paper discusses how the Quectel LC79D is enabling the eMobility industry to harness the fusion of different sensors in a very small footprint at low incremental cost with unparalleled accuracy, the company added.
“eMobility providers face substantial challenges when dealing with location in deep urban environments,” said Mark Murray, vice president of sales for GNSS and automotive at Quectel. “First and foremost, customers need to be able to find the vehicle and cities need to have the assurances that these eBikes and eScooters are operated in mutually agreed locations.”
OriginGPS has collaborated with Broadcom to create a new miniature module with L1 + L5 support provided by the BCM47758 chip, enabling ultra-accurate GNSS positioning. The module was developed for solutions requiring super-precision GNSS and a dual-frequency combination.
Photo: OriginGPS
The ORG4600-B01 is OriginGPS’ first dual-frequency GNSS module. The module enables customers to build solutions with sub-1-meter accuracy without implementing external components.
Measuring 10 x 10 mm, the ORG4600-B01 module supports L1 + L5 GNSS reception with one RF port, enabling the use of a low-cost, dual-band antenna delivering sub-1-meter accuracy performance in real-world operating conditions.
Alternate Build. An alternate build option allows for separate L1/L5 RF outputs when dual antennas are required. The ORG4600-B01 is suitable for solutions requiring ultra-accurate positioning, such as telematics, the Internet of Things (IoT) and auto OBD applications.
“This year has seen several satellites launched into orbit every month, most of them fitted with L5/E5 capabilities, and the Chinese and European Union governments plan to have their satellite constellations fully operational by 2020.” said Haim Goldberger, CEO of OriginGPS.
Developing the ORG4600-B01 module with the BCM47758 GNSS receiver chip by Broadcom Inc. was the fastest and surest way to add a high-quality dual-frequency module to our portfolio and meet our customers’ increasing requirements for ultra-accurate GNSS modules,” Goldberger said.
“Size is a crucial parameter in GNSS dual-frequency solutions,” said Prasan Pai, product marketing director for the Wireless Communications and Connectivity Division at Broadcom. “The collaboration with OriginGPS has created the industry’s smallest dual-frequency module with ‘no compromise’ quality. For our customers seeking an ultra-accurate GNSS solution in a compact form factor, the ORG4600-B01 fits the bill. The collaboration enables Broadcom to reach new markets, such as precision agriculture, security, children tracking and fleet management.”
“OriginGPS is interested in additional partnerships to enable bringing advanced solutions to market quickly,” said Haim Goldberger, CEO of OriginGPS.
OriginGPS is presenting its products with real-life demonstrations at MWC 2019, Los Angeles, Oct 22-24, Booth S2938.
Allystar Technology Co. Ltd., headquartered in Shenzhen, China, is offering new patch antennas: the AGR6302 and AGR6303. Both GNSS antenna models are designed for precision dual-frequency positioning.
AGR6302 is capable of receiving L1/L2 bands, and AGR6303 is capable of receiving L1/L5 bands. They are designed for UAVs, precision agriculture, autonomous vehicles and other applications where precision matters.
The AGR6302/AGR6303 active antenna is designed by unique technology to cover GPS, BDS, Galileo, GLONASS, IRNSS and the QZSS system (see table).
Table: Allystar
The antenna features stable signal quality at low cost. It employs a stack four-feeds antenna architecture with hybrid to achieve the multi-band operation, lower axial ratio, wider half-power beamwidth and excellent right-hand circular polarization, the company said.
Antenna size. (Image: Allystar)
With its new architecture, the active part has two stages. It has two level low noise amplifiers (LNAs) —one for the lower bands, the other for the higher bands. Then, the combiner and the third-level LNA output the RF gain to receiver. With this architecture, the antenna provides an excellent noise figure/RF linear and LNA gain, and out-band rejection, resulting in good signal-to-noise ratio and anti-interference.
It is housed in a compact, industrial-grade waterproof and magnet mount enclosure. Using internal magnets, the antenna can be installed almost anywhere, allowing for greater flexibility.
Detection of anomalous harmonics in the L1 spectrum
Interfering signals are one of the most well-known nuisance for GNSS receivers. A number of terrestrial systems and devices can generate various types of interference, either intentionally or not, but one would not expect interfering signals to arrive from space. On May 17, researchers of the Navigation Signal Analysis and Simulation (NavSAS) Group at the Politecnico di Torino detected the presence of anomalous spikes in the L1 signal spectrum. The origin of the spikes was identified to be the transmission of non-standard codes from a non-operational GPS satellite (GPS IIF-9, SVN49). In this article, we report on some of the most significant signal observations we performed in an effort to identify and localize the source of the interference and we address the possible impact it could have on GNSS signal processing.
By Fabio Dovis, Nicola Linty, Mattia Berardo, Calogero Cristodaro, Alex Minetto, Lam Nguyen Hong, Marco Pini, Gianluca Falco, Emanuela Falletti, Davide Margaria, Gianluca Marucco, Beatrice Motella, Mario Nicola and Micaela Troglia Gamba
On the afternoon of May 17, 2017, during an outdoor data collection experiment, researchers of the NavSAS Group detected the presence of two spikes in the L1 spectrum, with sufficient power to be clearly visible on a display of the spectrum obtained by processing the raw digital samples at the receiver’s intermediate frequency. The initial check looked for a possible interfering source in the experimental set-up, since it was quite complex and included multiple GNSS receivers, PCs, a video camera and a couple of car batteries. But the likelihood of this source was soon dispelled as the same kind of spectrum was visible on a spectrum analyzer (SA) connected to an active, survey-grade GNSS antenna mounted on the lab roof, as displayed in FIGURE 1. The spectrum is centered at 1575.42 MHz, with the SA set to a frequency span of 5 MHz. Connecting the SA to a different survey-grade antennas on the lab roof, we saw no remarkable differences.
The spikes also appeared on subsequent days, becoming clearly visible at about 13:00 UTC and disappearing at about 19:00 UTC, as illustrated in FIGURE 2. The main lobe of the GPS signal spectrum is visible, along with two spikes, at approximately ±0.5 MHz above and below the L1 carrier frequency. Weaker harmonics are also visible at ±1.5 MHz from the central frequency.
Figure 1. L1 Spectrum of the received signal at 16:51 (Central European Summer Time; 14:51 UTC) on May 19, 2017, at the NavSAS Lab, Torino (located at 45°03’54.98767″ N, 7°39’32.28920″ E, 311.9667 meters).Figure 2. Spectrogram of the received signal. Power spectral density (PSD) is color coded.
Response from the U.S. Air Force about the anomaly
The 2nd Space Operations Squadron is performing maintenance on a presently non-operational satellite. SVN49 is broadcasting non-standard C/A and non-standard Y codes as described in IS-GPS-200. Space professionals continue to conduct safe and responsible command and control of the constellation to continue to provide accuracy that exceeds established system requirements.
As always, GPS users who experience issues should address them through the appropriate channels: military users should contact DSN 560-2541, commercial 719-567-2541 while civilian users should contact the U.S. Coast Guard Navigation Center at 703-313-5900.
Very Respectfully,
NICHOLAS J. MERCURIO, Capt, USAF Director, 14th Air Force (Air Forces Strategic)/JFCC SPACE Public Affairs
Exclusion of terrestrial sources
The 24-hour repetition period of the phenomenon, along with the shape of the spectrum, could indicate the presence of a signal anomaly from a GNSS satellite. However, we could not exclude the hypothesis of unintentional interference generated by a nearby terrestrial communication system, since the area is crowded with research labs belonging to the Instituto Superiore Mario Boella and the Department of Electronics and Telecommunications of Politecnico di Torino. Nevertheless, we probed the L1 spectrum in a wider area using a simple setup, consisting of a patch antenna and a narrow-band front end. We analyzed the spectrum at the output of the front-end’s analog-to-digital converter, plotting the results on a smartphone running our software receiver in real time.
FIGURE 3 shows the L1 spectrum observed several kilometers from the NavSAS Lab. The shape of the spectrum is different than that in Figure 1 because of the narrow-band filter of the front end, but again, the presence of the two spikes is clearly visible at ±0.5 MHz from the central frequency, approximately with the same power strength. In addition, during a dynamic data collection experiment, we recognized that the interfering signals disappeared when the western part of the sky was obscured by buildings, as demonstrated in Figure 3. This was further investigated (and confirmed) when we processed the collected set of data in the lab. At that time (May 19), the hypothesis of an interfering signal from space became more plausible.
Figure 3. L1 Spectrum of the received signal observed on the afternoon of May 19 in Torino, 6.7 kilometers away from the NavSAS Lab: (left) in open sky conditions, (right) with the western portion of the sky obscured by a nearby building.
Meanwhile, the presence of suspicious spikes was confirmed by colleagues at the European Commission Joint Research Centre located in Ispra, Italy, and also from researchers of the Finnish Geodetic Institute in Helsinki, Finland, and by the South African National Space Agency at the station of the South African National Antarctic Expedition IV. These multiple observations definitely excluded the possibility that the interference it could be coming from terrestrial sources or from within the receiving equipment.
Checking the satellites in view during the presence of the spikes in the spectrum (that is, from about 13:00 to about 19:00 UTC) and bearing in mind the periodicity of the event over consecutive days, we excluded the possibility that a Galileo satellite could be the source of interference. It is indeed known that, due to an orbital period of approximately 14 hours for observers on the ground, the constellation geometry repeats only every 10 days.
Figure 4. Visible operational GPS, Galileo and BeiDou satellites over Turin for the full time window between 13:00 and 19:00 UTC on May 20, 2017.
FIGURE 4 shows the visibility of operational satellites over the full time window of interest for the GPS, Galileo and BeiDou constellations.
Considering the duration of the satellites’ visibility, the search for the source of interference was restricted to SVN71 (PRN26), SVN45 (PRN21) and the C11 BeiDou satellite. However, considering the previous tests, the satellite should have been in the western portion of the sky with respect to our location, and the only operational satellite of this set is SVN71, which we initially identified as the possible source of the interfering signal.
GPS SVN71 (PRN 26) or SVN 49?
The frequency of the harmonics could be measured over time. The first peak at approximately 0.5 MHz above the central frequency was analyzed by post-processing a set of digital samples collected with an Universal Software Radio Peripheral, which was slaved to a 10-MHz rubidium standard and which converted the RF signal to baseband, sampling it at 5 MHz. The frequency was measured exploiting a Welch periodogram, based on a 102,400-point discrete Fourier transform, with rectangular windowing and no window overlaps.
FIGURE 5 (a) shows the trend of the measured frequency versus time, from 12:43 to 18:38 UTC, on May 21. The frequency profile reveals that it is not constant and has a trend similar to the typical Doppler frequency shift of a GPS satellite. FIGURE 5 (b) shows the derivative of the frequency, with a minimum around 16:22 UTC. At that time, we expected to have a null Doppler shift from GPS PRN26, whereas the frequency of the peak was equal to 510.449 kHz. This is the inverse of 1.959056 microseconds, which is close to the inverse of twice the chip length, 2/Rc = 1.955034 microseconds. This indicates that the interfering signal could be a square wave with the same rate as the C/A spreading code.
Figure 5(a). Measured frequency of the first upper harmonic versus time.Figure 5(b). Measured frequency of the first upper harmonic versus corresponding frequency rate.
FIGURE 6 shows the Doppler frequency of PRN26 (blue line), as estimated by the tracking loop of a GNSS software receiver, and compares the Doppler shift to the frequency of the first upper peak (orange line), measured on the spectrum. It is possible to note that the two curves almost overlap, with a significant difference at the beginning and at the end of the observation. Thus, although the frequency of the peak follows the Doppler trend of a GPS satellite, it does not exactly match the Doppler curve of PRN26. This result weakened the hypothesis indicating that PRN26 was the source of the interference.
Furthermore, since it was still possible to acquire and track the L1 C/A-code signal from PRN26, this satellite was unlikely to be the source of the interfering components. Thus, also motivated by the mismatch in the Doppler shift of PRN26 (as previously highlighted in Figure 6), we started to think that the source of the interference could be another satellite broadcasting a GPS-like signal.
The search then focused on potential sources of interference coming from a non-operational satellite. The non-operational GPS satellite SVN49, launched on March 24, 2009 (also known as NAVSTAR 63 with NORAD ID 34661), has an orbit similar to that of SVN71 (see FIGURE 7). The previous remarks, let us guess that the transmission of a non-standard code (NSC) from such a satellite was the origin of the problem in the L1 spectrum. Such a case, could be similar to what has been previously reported in by Zhu et al. [1,2] when discussing the effects of the transmission of an NSC on Nov. 28, 2006.
Figure 6. Doppler shift of GPS PRN26 estimated by a tracking loop (blue line) and comparison with the measured frequency of the first upper harmonic versus time (orange line).Figure 7. Skyplot illustrating the path of SVN71 (PRN26) and SVN49 over the time window of interest.
Transmission of NSCs for testing purposes is foreseen in the GPS Interface Specification, IS-GPS-200 [3]. GPS satellites can switch off regular broadcasts of the C/A code and the P/Y code and transmit a non-standard C/A code and non-standard Y code. Such operation is intended to protect users from receiving and utilizing erroneous satellite signals in case of unhealthy conditions on the spacecraft. Strictly speaking, this case cannot be formally considered as an “anomaly,” because the transmission of non-standard codes is documented in the IS-GPS-200. Therefore, the transmission of an NSC can be considered a normal operation in itself, even though it may reflect a problem with the transmitting satellite.
However, in this case the choice of the spreading sequence, which is likely a square wave, allowed the total power of the signal to be concentrated in just a few spectral components, thus originating continuous-wave-like in-band signals.
The distribution of the harmonics, the main components of which are at ±500 kHz, and the presence of the odd harmonics only, matches the case recalled by Zhu et al. [1,2], of a transmission of an NSC modulated as a binary-phase-shift-keying (BPSK) sequence with alternating logical 0s and 1s, transmitted at the C/A code chipping rate (Rc=1.023 megachips per second). The spectrum of this “square wave” with period used as a spreading signal is in fact know to be (1)
where δ is the Dirac-δ function. Zhu et al. [1,2] considered this specific case of a “non-standard code” to be especially remarkable, because it can affect the L1 spectrum, introducing multiple harmonic components similar to those previously illustrated in Figure 1 and Figure 3 (a).
Figure 8. Spectrum of the simulated NSC for different C/N0 values.
The hypothesis of the BPSK with Rc=1.023 megachips per second spreading signal has been verified by simulation. Figure 8. shows how the tested case of a received signal from SVN49 with a C/N0=55 dB-Hz best matches the measured spectrum when SVN49 is at its maximum elevation angle and the power of the received signal is the strongest.
However, it has to be remarked that according to Zhu et al. [1,2], the NSC is designed to have negligible effect on tracking other healthy GPS satellite signals. Nonetheless, their analyses showed that an NSC transmission (as occurred on Nov. 28, 2006) can have a non-negligible impact in the performance on user equipment. In detail, when a GPS satellite is switched to NSC mode, a receiver immediately loses its capability to track that satellite signal. This is not the case with SVN49 as it is currently declared non-operational. However, due to the modified code sequence, an even worse effect is possible. In fact, the NSC introduces irregular components at a sustained level in the GPS signal spectrum.
As a final confirmation of the transmission of the NSC from SVN49, we have used the technique of averaging and summing over the code period as described by Mitelman [6]. Considering a time window during which the Doppler shift of the signal is negligible, we have extracted the spreading code, confirming the square wave hypothesis (see FIGURE 9).
Figure 9. Square wave code obtained by averaging and summing.
According to the Notice Advisory to Navstar Users (NANU) 2001701, SVN49 was broadcasting standard signals as PRN04 (although set unhealthy) since the beginning of the year, but NANU 2017042 announced that PRN04 was to be re-allocated to SVN38 starting from May 18. This switch actually matches the dates when we started to see the spikes in the spectrum, since, probably, the SVN49 started that day to use the “square wave” for the spreading.
Implementing the square wave local code, it has been possible to successfully acquire and track the NSC, as shown in FIGURE 10.
Figure 10. Acquisition and tracking of the NSC. Source: GPS World
Source: GPS World
The real-time software receiver N-Gene, documented by Molino et al. [5],has been forced to acquire and track in real time the signal coming from SVN49. FIGURE 11 shows a screenshot of the N-Gene graphical interface while processing this signal.
Figure 11. N-Gene software receiver processing the SVN49 signal.
The receiver was able to perform the decoding of the navigation message transmitted by SVN49, which exhibits a regular format, even if marked with an unhealthy flag (see FIGURE 12).
Figure 12. Decoded navigation message.
Impact on receiver signal processing
It is well known that the spectrum of GNSS signals is basically a line spectrum in the frequency domain, which is susceptible to interference (see, for example, the book edited by Davis [4]).
Interference with harmonic components such as those generated by the use of a square wave could strongly impact a GNSS receiver in the acquisition and tracking blocks because the interference power is dispersed over the whole search space by the correlation with the local code, compromising the acquisition accuracy and impacting other functional blocks. The impact of interference spectral lines strongly depends on their location within the frequency band. This is due to the almost periodic nature of the GNSS signals. In fact, the spectrum of a GNSS signal has components spaced at multiples of the inverse of the code period (for example, 1 kHz for GPS C/A code) with different power allocated to each component depending on the shape of the code spectrum. The effect is larger in case of matching of the interference spectral components with the ones of the GNSS signal. Furthermore, in the present case, the strongest harmonics are close to the L1 carrier frequency and are not mitigated by the front-end filter since they fall within its narrow bandwidth.
As opposed to the case discussed by Zhu et al. [1,2] when GPS was virtually the only code-division-multiple-access system occupying the bandwidth around L1, the overall GNSS scenario has changed a lot recently. Galileo and BeiDou are also present, and the signals of the Galileo system, due to the different structure and code periods, have spectral lines spaced at 0.25 kHz. The frequency modulation of the interfering signal due to the variable Doppler shift is then even more likely to hit some of the spectral components of these signals.
We are performing further investigations are being performed to assess the impact of the interfering signal from SVN49 on Galileo-based high accuracy applications.
Acknowledgments
The NavSAS Group thanks Dr. Matteo Paonni (EC Joint Research Centre) for the support given in the analysis of the L1 signal spectrum and Dr. Laura Ruotsalainen (Finnish Geospatial Institute) and Danielle Taljaard (South African National Space Agency), who performed the data collection in Antarctica.
Bios
Fabio Dovis, Nicola Linty, Mattia Berardo, Calogero Cristodaro, Alex Minetto and Lam Nguyen Hong are with the Navigation Signal Analysis and Simulation (NavSAS) Group, Politecnico di Torino, Torino, Italy.
Marco Pini, Gianluca Falco, Emanuela Falletti, Davide Margaria, Gianluca Marucco, Beatrice Motella, Mario Nicola and Micaela Troglia Gamba are with the Navigation Technologies Research Area of Istituto Superiore Mario Boella, Torino.
[2] “Satellite Anomaly and Interference Detection Using the GPS Anomalous Event Monitor” by Z. Zhu, S. Gunawardena, M. Uijt de Haag and F. van Graas in Proceedings of the 63rd Annual Meeting of The Institute of Navigation, Cambridge, Massachusetts, April 23–25, 2007, pp. 389–396.
[4] GNSS Interference Threats and Countermeasures by F. Dovis (ed.) published by Artech House, Norwood, Massachusetts, 2015.
[5] “N-Gene GNSS Software Receiver for Acquisition and Tracking Algorithms Validation” by A. Molino, M. Nicola, M. Pini and M. Fantino in Proceedings of EUSIPCO 2009, the 17th European Signal Processing Conference, Glasgow, Scotland, Aug. 24–28, 2009, pp. 2171-2175.
Beginning Wednesday, Jan. 25, Air Force Space Command (AFSPC) will conduct a limited-duration test implementing an increase of the Ll C/A power level on the GPS Block IIR-M and llF satellites — a total of 19 satellites.
The C/A power will remain within IS-GPS-200-H specifications, and the power increase is not expected to increase the noise floor by more than 0.3 signal-to-noise ratio in the worst case.
“We assess that there will be no adverse impacts to civil, commercial or military GPS users, but anyone who experiences issues during this test should address them through established reporting channels,” said Gen. John W. Raymond, U. S. Air Force (USAF) commander, in a “Memorandum for Distribution.”
Military users can contact the GPS Operations Center at DSN 560-2541, while civilian users can contact the U.S. Coast Guard Navigation Center at 703-313-5900. In the event of unexpected critical impacts, a process to cease testing operations has been put in place.
The AFSPC point of contact for this test is Maj. Jeffrey Koch, DSN 692-0233, commercial 719-554-0233.
After extensive ground and space testing, the SES-5 GEO satellite has entered into the European Geostationary Navigation Overlay Service (EGNOS) operational platform, broadcasting EGNOS Signal-In-Space (SIS), according to the European GNSS Agency (GSA).
SES-5 — which replaces Inmarsat-4F2 — will ensure reliable EGNOS services until 2026. It has been introduced through EGNOS System Release V241M, which will enable a range of performance improvements. In particular, EGNOS will offer even greater stability during periods of high ionospheric activity.
“SES-5 is the first step of the complete renewal of the EGNOS Space Segment, securing the EGNOS services for the next decade and the future transition to the dual-frequency multi-constellation services,” said Carlo des Dorides, GSA Executive Director. “It will be completed by the introduction of the ASTRA-5B signals and the procurement of a new EGNOS payload which are both planned for 2016.”
SES-5, carrying EGNOS L1 and L5 band payloads, was launched in July 2012. The integration of a second EGNOS SBAS L1/L5 band payload on SES ASTRA-5B GEO satellite is currently ongoing. The introduction of this second SES GEO satellite for EGNOS is planned at the end of 2016. SES won the contract following an open-tender procedure.
“SES is looking forward to many years of successful operation in delivering EGNOS services to the European citizens and beyond,” said Ferdinand Kayser, chief commercial officer at SES.
EGNOS is operated by the European Satellite Services Provider (ESSP), under contract by the GSA on behalf of the European Commission.
The TET-1 satellite has Septentrio on board. (Image: DLR)
Septentrio announced today that a PolaRx2 receiver has reached more than 330 hours of successful operation on board “Technologie-Erprobungs-Träger 1” (TET-1), the first satellite of the German On-Orbit-Verification program. The Septentrio receiver is the backbone of the Navigation and Occultation Experiment (NOX) developed by German Aerospace Center (DLR). The purpose of the experiment is to prove the suitability of commercial-off-the-shelf (COTS) technology for use in space missions.
The receiver provides GPS observations on the L1 and L2 frequencies, which are used for precise orbit determination and atmospheric sounding. The dual-frequency observations allow reconstructing the orbit of TET-1 with decimeter or better 3D accuracy. A dedicated antenna pointed into the anti-flight direction of the satellite is used to collect measurements during GPS radio occultations, where the signals are tracked through the Earth’s atmosphere.
After the first activation on July 26, 2012, the receiver has operated flawlessly in the harsh environment 500 km above the Earth’s surface and has been unaffected so far by space radiation. The receiver demonstrates quick acquisition of GPS signals and tracks a sufficient number of satellites even under challenging visibility conditions. The short time-to-first-fix together with the high availability of position and timing information from the navigation solution make the PolaRx2 a very suitable receiver for space-borne applications.
“We are proud to see a new illustration that our standard commercial receivers perform flawlessly even in the harshest circumstances,” said Peter Grognard, Septentrio’s founder and CEO. “Our customers benefit every day from the same high quality and robustness for their demanding industrial applications on earth ”
In the more than 100+ articles I’ve written for GPS World magazine over the past seven years, I don’t think I’ve ever written about a new product introduction like you will see below. I tend to focus on GNSS and geospatial technologies rather than a brand-specific products and services. In fact, last week I had an outline prepared for my article that included some really cool free and useful GPS/GNSS apps. I decided to set that outline aside until later, in favor of writing about this product.
Although certainly different than mainstream GPS/GNSS receivers, I wouldn’t refer to this new product as a disruptive one (a marketing term used to describe something that is industry-changing) and it doesn’t incorporate leading-edge GPS/GNSS technology. In fact, it’s relatively low-tech in comparison to the other GPS/GNSS surveying receivers available in the marketplace.
Even more fascinating is the fact that the product was developed not by any of the mainstream GPS/GNSS receiver manufacturers you hear about today, but rather an electrical engineer from Utah who leveraged the design/manufacturing expertise of one of China’s largest manufacturers of GPS/GNSS surveying receivers.
The final nail in the coffin is the fact that I’ve expended thousands of words in GPS World denouncing the future of post-processing and celebrating the virtues of high-precision, real-time GNSS (RTK, SBAS, PPP) receivers.
I tried to talk myself out of writing this article more than once, telling myself that I’ve never written specifically about a new product and I wasn’t going to start now. But, as much as I didn’t want to, I always came back because it is so darned compelling.
While the product is not aligned with my vision of real-time being the future of high-precision GNSS receivers, it is perfectly aligned with my vision that the cost of high-precision GNSS receivers are dropping and will continue to decline considerably over the next few years.
However…it is incredibly inexpensive, and it is designed to be perfectly simple to operate.
iGage X90-OPUS Photo: iGage
In one sentence, the X90-OPUS is a one-button, dual-frequency GPS receiver that is specifically designed to use the National Geodetic Survey’s free online OPUS post-processing service to achieve centimeter-level GPS positioning anywhere in the United States and surrounding countries.
You might say to yourself, “So what? There are plenty of GPS receivers on the market that are capable of providing this functionality.” I would make the same comment, except it has one product feature that I’ve never seen before.
The Price
What makes the X90-OPUS so compelling is its low cost. The X90-OPUS GPS receiver sells for US$2,450, including all software and accessories (except for tripod/tribrach) that allow you to submit GPS data files to OPUS in a very automated fashion.
At US$2,450, the X90-OPUS may open a new world for surveyors, engineers, and scientists who have previously shunned high-precision GPS receivers due to their high cost and complexity.
Simplicity
For those of you who yearn for the yesteryear of the one-button Ashtech’s legacy Locus GPS receiver, the X90-OPUS reminds me of that sort of simplicity, but on steroids. The X90-OPUS is a dual-frequency (L1/L2) receiver, while the Locus was a single-frequency receiver. The difference is that one can use OPUS and the other cannot. OPUS post-processing doesn’t support single-frequency GPS receivers. However, Mark Silver, the electrical engineer from Utah, has taken it a step further by developing software that automates the OPUS data submission process. Although I’ve made it clear in the past that I’m not a fan of post-processing, it doesn’t get any easier than this. You don’t need to buy a base station, and you don’t need to own post-processing software. It’s a two-button push operation: once to turn it on, and once to turn it off.
X90-OPUS Software Photo: iGage
The X90-OPUS receiver was characterized by the National Geodetic Survey back in March 2013 and is listed on the NGS’s Individual Antenna Calibration website.
Photo: iGagePhoto: iGage
Pertinent Background
You might think that with the US$2,450 price point and not being offered by a major GPS receiver manufacturer, this is some home-brew GPS receiver. If you thought that, you would be incorrect. The GPS engine in the X90-OPUS is a Pacific Crest BD950, the same engine found in many receivers from other GNSS system manufacturers. CHCNav integrated the GPS engine into its casing to produce the X90 receiver. However, Mark added his own special sauce to the X90 to turn it into the X90-OPUS so this isn’t just a CHCNav receiver being marketed by iGage (Mark’s company).
In all fairness, I’ve not touched the X90-OPUS yet. I likely will in the next few days. However, unless the hardware is unreliable, I don’t see how this product is not going to be a winner, and it will introduce high-precision GPS receivers to an entirely new group of surveyors, engineers and scientists who have been holding out on using GPS.
Summary: A look at the challenge of dealing with horizontal datums in your GIS. We are moving into a new era in dealing with datum transformations. Geodata 2.0 is coming, and it can create big headaches when attempting to combine disparate geospatial databases. Sensors such as GPS receivers, remote sensing imagery, and 3D scanning provide much more accurate data, setting up a collision with outdated and mismatched legacy horizontal datums.
Speakers:
Kevin Kelly, Geodesist, ESRI, Inc.
Kevin Kelly is a Geodesist with ESRI in Redlands, California where he researches and implements geodetic algorithms and applications for the ArcGIS software. His experience spans over 35 years in hydrography, geodesy, surveying and most recently, geographic information systems. He has held the posts of Manager of Geodetic Services for the Province of Ontario, Chief Geodesist for the Kingdom of Saudi Arabia’s Military Survey Department and Senior Project Surveyor for The Keith Companies (now Stantec, Inc.). Mr. Kelly received a Master of Applied Science in Geodesy at the University of Toronto, Canada and holds an Honors Diploma in Hydrographic Surveying Technology from Humber College in Toronto. He is also a licensed Geodetic Surveyor in the Province of Ontario, Canada.
Craig Greenwald, Technical Director, GeoMobile Innovations
Craig Greenwald is the Technical Director and a principal at GeoMobile Innovations Inc. He has worked in the GPS and Mobile GIS industry for over 13 years, including seven years for GIS software leader, ESRI and is well known for his work on the ESRI ArcPad team. Craig leads the GeoMobile software development and consulting team specializing in Mobile GIS and field data collection applications and technology providing Mobile GIS software, consulting, and training services to GeoMobile Innovations? clients. Craig has real world experience designing, implementing, and consulting on all sizes of projects, ranging from local campground trash mapping to the U.S. national census, and has been a key developer in GeoMobile?s commercial applications such as LaserGIS for ArcPad and Geo-Photo Inventory Tool for Garmin GPS solutions.
Michael L. Dennis, RLS, PE, Geodesist, NOAA
Michael L. Dennis, RLS, PE, is a geodesist at NOAA’s National Geodetic Survey (NGS) where his duties include analysis of geometric (“horizontal”) and vertical datums; evaluation of data processing and survey network adjustment procedures; development and promotion of standards and guidelines; integration of NGS products and services with GIS; and public outreach. Mr. Dennis is also a registered professional engineer and surveyor with private sector experience, including ownership of a consulting and surveying firm. Mr. Dennis is an officer of the American Association for Geodetic Surveying (AAGS), an American Congress on Surveying and Mapping (ACSM) Fellow, and a member of the Arizona Professional Land Surveyors Association and the Geomatics Division of the American Society of Civil Engineers.
Moderator:
Eric Gakstatter, Editor of Geospatial Solutions Monthly and Survey Scene
Eric Gakstatter has been involved in the GPS/GNSS industry for more than 20 years. For 10 years, he held several product management positions in the GPS/GNSS industry, managing the development of several medium- and high-precision GNSS products along with associated data-collection and post-processing software.
Generating Distorted GNSS Signals Using a Signal Simulator
By Mathieu Raimondi, Eric Sénant, Charles Fernet, Raphaël Pons, Hanaa Al Bitar, Francisco Amarillo Fernández, and Marc Weyer
INNOVATION INSIGHTS by Richard Langley
INTEGRITY. It is one of the most desirable personality traits. It is the characteristic of truth and fair dealing, of honesty and sincerity. The word also can be applied to systems and actions with a meaning of soundness or being whole or undivided. This latter definition is clear when we consider that the word integrity comes from the Latin word integer, meaning untouched, intact, entire — the same origin as that for the integers in mathematics: whole numbers without a fractional or decimal component.
Integrity is perhaps the most important requirement of any navigation system (along with accuracy, availability, and continuity). It characterizes a system’s ability to provide a timely warning when it fails to meet its stated accuracy. If it does not, we have an integrity failure and the possibility of conveying hazardously misleading information. GPS has built into it various checks and balances to ensure a fairly high level of integrity. However, GPS integrity failures have occasionally occurred.
One of these was in 1990 when SVN19, a GPS Block II satellite operating as PRN19, suffered a hardware chain failure, which caused it to transmit an anomalous waveform. There was carrier leakage on the L1 signal spectrum. Receivers continued to acquire and process the SVN19 signals, oblivious to the fact that the signal distortion resulted in position errors of three to eight meters. Errors of this magnitude would normally go unnoticed by most users, and the significance of the failure wasn’t clear until March 1993 during some field tests of differential navigation for aided landings being conducted by the Federal Aviation Administration. The anomaly became known as the “evil waveform.”
(I’m not sure who first came up with this moniker for the anomaly. Perhaps it was the folks at Stanford University who have worked closely with the FAA in its aircraft navigation research. The term has even made it into popular culture. The Japanese drone-metal rock band, Boris, released an album in 2005 titled Dronevil. One of the cuts on the album is “Evil Wave Form.” And if drone metal is not your cup of tea, you will find the title quite appropriate.) Other types of GPS evil waveforms are possible, and there is the potential for such waveforms to also occur in the signals of other global navigation satellite systems. It is important to fully understand the implications of these potential signal anomalies. In this month’s column, our authors discuss a set of GPS and Galileo evil-waveform experiments they have carried out with an advanced GNSS RF signal simulator. Their results will help to benchmark the effects of distorted signals and perhaps lead to improvements in GNSS signal integrity.
“Innovation” is a regular feature that discusses advances in GPS technology andits applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering, University of New Brunswick. He welcomes comments and topic ideas.
GNSS signal integrity is a high priority for safety applications. Being able to position oneself is useful only if this position is delivered with a maximum level of confidence. In 1993, a distortion on the signals of GPS satellite SVN19/PRN19, referred to as an “evil waveform,” was observed. This signal distortion induced positioning errors of several meters, hence questioning GPS signal integrity. Such events, when they occur, should be accounted for or, at least, detected.
Since then, the observed distortions have been modeled for GPS signals, and their theoretical effects on positioning performance have been studied through simulations. More recently, the models have been extended to modernized GNSS signals, and their impact on the correlation functions and the range measurements have been studied using numerical simulations. This article shows, for the first time, the impact of such distortions on modernized GNSS signals, and more particularly on those of Galileo, through the use of RF simulations. Our multi-constellation simulator, Navys, was used for all of the simulations.
These simulations are mainly based on two types of scenarios: a first scenario, referred to as a static scenario, where Navys is configured to generate two signals (GPS L1C/A or Galileo E1) using two separate RF channels. One of these signals is fault free and used as the reference signal, and the other is affected by either an A- or B-type evil waveform (EW) distortion (these two types are described in a latter section).
The second type of scenario, referred to as a dynamic scenario, uses only one RF channel. The generated signal is fault free in the first part of the simulation, and affected by either an A- or B-type EW distortion in the second part of the scenario. Each part of the scenario lasts approximately one minute.
All of the studied scenarios consider a stationary satellite position over time, hence a constant signal amplitude and propagation delay for the duration of the complete scenario.
Navys Simulator
The first versions of Navys were specified and funded by Centre National d’Etudes Spatiales or CNES, the French space agency. The latest evolutions were funded by the European Space Agency and Thales Alenia Space France (TAS-F). Today, Navys is a product whose specifications and ownership are controled by TAS-F. It is made up of two components: the hardware part, developed by ELTA, Toulouse, driven by a software part, developed by TAS-F.
The Navys simulator can be configured to simulate GNSS constellations, but also propagation channel effects. The latter include relative emitter-receiver dynamics, the Sagnac effect, multipath, and troposphere and ionosphere effects. Both ground- and space-based receivers may be considered.
GNSS Signal Generation Capabilities. Navys is a multi-constellation simulator capable of generating all existing and upcoming GNSS signals. Up to now, its GPS and Galileo signal-generation capabilities and performances have been experienced and demonstrated. The simulator, which has a generation capacity of 16 different signals at the same time over the entire L band, has already been successfully tested with GPS L1 C/A, L1C, L5, and Galileo E1 and E5 receivers.
Evil Waveform Emulation Capabilities. In the frame of the ESA Integrity Determination Unit project, Navys has been upgraded to be capable of generating the signal distortions that were observed in 1993 on the signals from GPS satellite SVN19/PRN19. Two models have been developed from the observations of the distorted signals.
The first one, referred to as Evil Waveform type A (EWFA), is associated with a digital distortion, which modifies the duration of the GPS C/A code chips, as shown in FIGURE 1. A lead/lag of the pseudorandom noise code chips is introduced. The +1 and –1 state durations are no longer equal, and the result is a distortion of the correlation function, inducing a bias in the pseudorange measurement equal to half the difference in the durations. This model, based on GPS L1 C/A-code observations, has been extended to modernized GNSS signals, such as those of Galileo (see Further Reading). In Navys, type A EWF generation is applied by introducing an asymmetry in the code chip durations, whether the signal is modulated by binary phase shift keying (BPSK), binary offset carrier (BOC), or composite BOC (CBOC).
FIGURE 1. Theoretical L1 C/A code-chip waveforms in the presence of an EWFA (top) and EWFB (bottom).
The second model, referred to as Evil Waveform type B (EWFB) is associated with an analog distortion equivalent to a second-order filter, described by a resonance frequency (fd) and a damping factor (σ), as depicted in Figure 1. This failure results in correlation function distortions different from those induced by EWFA, but which also induces a bias in the pseudorange measurement. This bias depends upon the characteristics (resonance frequency, damping factor) of the filter. In Navys, an infinite impulse response (IIR) filter is implemented to simulate the EWFB threat. The filter has six coefficients (three in the numerator and three in the denominator of its transfer function). Hence, it appears that Navys can generate third order EWF type B threats, which is one order higher that the second order threats considered by the civil aviation community. Navys is specified to generate type B EWF with less than 5 percent root-mean-square (RMS) error between the EWF module output and the theoretical model. During validation activities, a typical value of 2 percent RMS error was measured. This EWF simulation function is totally independent of the generated GNSS signals, and can be applied to any of them, whatever its carrier frequency or modulation.
It is important to note that such signal distortions may be generated on the fly — that is, while a scenario is running. FIGURE 2 gives an example of the application of such threat models on the Galileo E1 BOC signal using a Matlab theoretical model.
FIGURE 2. Theoretical E1 C code-chip waveforms in the presence of an EWFA (top) and EWFB (bottom).
GEMS Description
GEMS stands for GNSS Environment Monitoring Station. It is a software-based solution developed by Thales Alenia Space aiming at assessing the quality of GNSS measurements. GEMS is composed of a signal processing module featuring error identification and characterization functions, called GEA, as well as a complete graphical user interface (see online version of this article for an example screenshot) and database management.
The GEA module embeds the entire signal processing function suite required to build all the GNSS observables often used for signal quality monitoring (SQM). The GEA module is a set of C/C++ software routines based on innovative-graphics-processing-unit (GPU) parallel computing, allowing the processing of a large quantity of data very quickly. It can operate seamlessly on a desktop or a laptop computer while adjusting its processing capabilities to the processing power made available by the platform on which it is installed. The GEA signal-processing module is multi-channel, multi-constellation, and supports both real-time- and post-processing of GNSS samples produced by an RF front end.
GEMS, which is compatible with many RF front ends, was used with a commercial GNSS data-acquisition system. The equipment was configured to acquire GNSS signals at the L1 frequency, with a sampling rate of 25 MHz. The digitized signals were provided in real time to GEMS using a USB link.
From the acquired samples, GEMS performed signal acquisition and tracking, autocorrelation function (ACF) calculation and display, and C/N0 measurements. All these figures of merit were then logged in text files.
EWF Observation
Several experiments were carried out using both static and kinematic scenarios with GPS and Galileo signals.
GPS L1 C/A. The first experiment was intended to validate Navys’ capability of generating state-of-the-art EWFs on GPS L1 C/A signals. It aimed at verifying that the distortion models largely characterized in the literature for the GPS L1 C/A are correctly emulated by Navys.
EWFA, static scenario. In this scenario, Navys is configured to generate two GPS L1 C/A signals using two separate RF channels. The same PRN code was used on both channels, and a numerical frequency transposition was carried out to translate the signals to baseband. One signal was affected by a type A EWF, with a lag of 171 nanoseconds, and the other one was EWF free. Next, its amplified output was plugged into an oscilloscope. The EWFA effect is easily seen as the faulty signal falling edge occurs later than the EWF-free signal, while their rising edges are still synchronous. However, the PRN code chips are distorted from their theoretical versions as the Navys integrates a second-order high pass filter at its output, meant to avoid unwanted DC emissions. The faulty signal falling edge should occur approximately 0.17 microseconds later than the EWF-free signal falling edge.
A spectrum analyzer was used to verify, from a spectral point of view, that the EWFA generation feature of Navys was correct. For this experiment, Navys was configured to generate a GPS L1 C/A signal at the L1 frequency, and Navys output was plugged into the spectrum analyzer input. Three different GPS L1 C/A signals are included: the spectrum of an EWF-free signal, the spectrum of a signal affected by an EWF type A, where the lag is set to 41.1 nanoseconds, and the spectrum of a signal affected by an EWF type A, where the lag is set to 171 nanoseconds. As expected, the initial BPSK(1) signal is distorted and spikes appear every 1 MHz. The spike amplitude increases with the lag.
EWFA, dynamic scenario. In a second experiment, Navys was configured to generate only one fault-free GPS L1 C/A signal at RF. The RF output was plugged into the GEMS RF front end, and acquisition was launched. One minute later, an EWFA distortion, with a lag of 21 samples (about 171 nanoseconds at 120 times f0, where f0 equals 1.023 MHz), was activated from the Navys interface.
FIGURE 3 shows the code-phase measurement made by GEMS. Although the scenario was static in terms of propagation delay, the code-phase measurement linearly decreases over time. This is because the Navys and GEMS clocks are independent and are drifting with respect to each other.
The second observation is that the introduction of the EWFA induced, as expected, a bias in the measurement. If one removes the clock drifts, the bias is estimated to be 0.085 chips (approximately 25 meters). According to theory, an EWFA induces a bias equal to half the lead or lag value. A value of 171 nanoseconds is equivalent to about 50 meters.
FIGURE 4 represents the ACFs computed by GEMS during the scenario. It appears that when the EWFA is enabled, the autocorrelation function is flattened at its top, which is typical of EWFA distortions. Eventually, FIGURE 5 showed that the EWFA also results in a decrease of the measured C/N0, which is completely coherent with the flattened correlation function obtained when EWFA is on.
Additional analysis has been conducted with Matlab to confirm Navys’ capacity. A GPS signal acquisition and tracking routine was modified to perform coherent accumulation of GPS signals. This operation is meant to extract the signal out of the noise, and to enable observation of the code chips. After Doppler and code-phase estimation, the signal is post-processed and 1,000 signal periods are accumulated. The result, shown in FIGURE 6, confronts fault-free (blue) and EWFA-affected (red) code chips. Again, the lag of 171 nanoseconds is clearly observed. The analysis concludes with FIGURE 7, which shows the fault-free (blue) and the faulty (red) signal spectra. Again, the presence of spikes in the faulty spectrum is characteristic of EWFA.
FIGURE 6. Fault-free vs. EWFA GPS L1 C/A signal.FIGURE 7. Fault-free vs. EWFA GPS L1 C/A signal power spectrum density.
EWFB, static scenario. The same experiments as for EWFA were conducted for EWFB. Fault-free and faulty (EWFB with a resonance frequency of 8 MHz and a damping factor of 7 MHz) signals were simultaneously generated and observed using an oscilloscope and a spectrum analyzer. The baseband temporal signal undergoes the same default as that of the EWFA because of the Navys high-pass filter. However, the oscillations induced by the EWFB are clearly observed.
The spectrum distortion induced by the EWFB at the L1 frequency is amplified around 8 MHz, which is consistent with the applied failure.
EWFB, dynamic scenario. Navys was then configured to generate one fault-free GPS L1 C/A signal at RF. The RF output was plugged into the GEMS RF front end, and acquisition was launched. One minute later, an EWFB distortion with a resonance frequency of 4 MHz and a damping factor of 2 MHz was applied. As for the EWFA experiments, the GEMS measurements were analyzed to verify the correct application of the failure. The code-phase measurements, illustrated in FIGURE 8, show again that the Navys and GEMS clocks are drifting with respect to each other. Moreover, it is clear that the application of the EWFB induced a bias of about 5.2 meters on the code-phase measurement. One should notice that this bias depends upon the chip spacing used for tracking. Matlab simulations were run considering the same chip spacing as for GEMS, and similar tracking biases were observed.
FIGURE 9 shows the ACF produced by GEMS. During the first minute, the ACF looks like a filtered L1 C/A correlation function. Afterward, undulations distort the correlation peak.
Again, additional analysis has been conducted with Matlab, using a GPS signal acquisition and tracking routine. A 40-second accumulation enabled comparison of the faulty and fault-free code chips. FIGURE 10 shows that the faulty code chips are affected by undulations with a period of 244 nanoseconds, which is consistent with the 4 MHz resonance frequency. This temporal signal was then used to compute the spectrum, as shown in FIGURE 11. The figure shows well that the faulty L1 C/A spectrum (red) secondary lobes are raised up around the EWFB resonance frequency, compared to the fault-free L1 C/A spectrum (blue).
FIGURE 10. Fault-free vs EWFB GPS L1 C/A signal.
FIGURE 11. Fault-free vs EWFB GPS L1 C/A signal power spectrum density.
Galileo E1 CBOC(6, 1, 1/11). In the second part of the experiments, Navys was configured to generate the Galileo E1 Open Service (OS) signal instead of the GPS L1 C/A signal. The goal was to assess the impact of EWs on such a modernized signal.
EWFA, static scenario. First, the same Galileo E1 BC signal was generated using two different Navys channels. One was affected by EWFA, and the other was not. The spectra of the obtained signals were observed using a spectrum analyzer. The spectrum of the signal produced by the fault-free channel shows the BOC(1,1) main lobes, around 1 MHz, and the weaker BOC(6,1) main lobes, around 6 MHz. The power spectrum of the signal produced by the EWFA channel has a lag of 5 samples at 120 times f0 (40 nanoseconds). Again, spikes appear at intervals of f0, which is consistent with theory. The signal produced by the same channel, but with a lag set to 21 samples (171.07 nanoseconds) was also seen. Such a lag should not be experienced on CBOC(6,1,1/11) signals as this lag is longer than the BOC(6,1) subcarrier half period (81 nanoseconds). This explains the fact that the BOC(6,1) lobes do not appear anymore in the spectrum.
EWFB, static scenario. The same experiments as for EWFA were conducted for EWFB. Fault-free and faulty (EWFB with a resonance frequency of 8 MHz and a damping factor of 7 MHz) signals were simultaneously generated and observed using the spectrum analyzer. The spectrum distortion induced by the EWFB at the E1 frequency was evident. The spectrum is amplified around 8 MHz, which is consistent with the applied failure.
EWFA, dynamic scenario. The same scenario as for the GPS L1 C/A signal was run with the Galileo E1 signal: first, for a period of one minute, a fault-free signal was generated, followed by a period of one minute with the faulty signal. GEMS was switched on and acquired and tracked the two-minute-long signal. Its code-phase measurements, shown in FIGURE 12, reveal a tracking bias of 6.2 meters. This is consistent with theory, where the set lag is equal to 40 nanoseconds (12.0 meters). GEMS-produced ACFs show the distortion of the correlation function in FIGURE 13. The distortion is hard to observe because the applied lag is small.
FIGURE 12. GEMS code-phase measurements on Galileo E1 pilot signal, EWFA dynamic scenario.FIGURE 13. GEMS ACF computation on Galileo E1 pilot signal, EWFA dynamic scenario.
A modified version of the GPS signal acquisition and tracking Matlab routine was used to acquire and track the Galileo signal. It was configured to accumulate 50 seconds of fault-free signal and 50 seconds of a faulty signal. This operation enables seeing the signal in the time domain, as in FIGURE 14. Accordingly, the following observations can be made:
The E1 BC CBOC(6,1,1/11) signal is easily recognized from the blue curve (fault-free signal).
The EWFA effect is also seen on the BOC(1,1) and BOC(6,1) parts. The observed lag is consistent with the scenario (five samples at 120 times f0 ≈ 0.04 chips).
The lower part of the BOC(6,1) seems absent from the red signal. Indeed, the application of the distortion divided the duration of these lower parts by a factor of two, and so multiplied their Fourier representation by two. Therefore, the corresponding main lobes should be located around 12 MHz. At the receiver level, the digitization is being performed at 25 MHz; this signal is close to the Shannon frequency and is therefore filtered by the anti-aliasing filter.
FIGURE 14. Fault-free vs EWFA Galileo E1 signal.
The power spectrum densities of the obtained signals were then computed. FIGURE 15 shows the CBOC(6,1,1/11) fault-free signal in blue and the faulty CBOC(6,1,1/11) signal, with the expected spikes separated by 1.023 MHz.
FIGURE 15. Fault-free vs. EWFA Galileo E1 signal power spectrum density.
It is noteworthy that the EWFA has been applied to the entire E1 OS signal, which is B (data component) minus C (pilot component). EWFA could also affect exclusively the data or the pilot channel. Although such an experiment was not conducted during our research, Navys is capable of generating EWFA on the data component, the pilot component, or both.
EWFB, dynamic scenario. In this scenario, after one minute of a fault-free signal, an EWFB, with a resonance frequency of 4 MHz and a damping factor of 2 MHz, was activated. The GEMS code-phase measurements presented in FIGURE 16 show that the EWFB induces a tracking bias of 2.8 meters. As for GPS L1 C/A signals, it is to be noticed that the bias induced by EWFB depends upon the receiver characteristics and more particularly the chip spacing used for tracking.
FIGURE 16. GEMS code-phase measurements on Galileo E1 pilot signal, EWFB dynamic scenario.
The GEMS produced ACFs are represented in FIGURE 17. After one minute, the characteristic EWFB undulations appear on the ACF.
FIGURE 17. GEMS ACF computation on Galileo E1 pilot signal, EWFB dynamic scenario.
In this case, signal accumulation was also performed to observe the impact of EWFB on Galileo E1 BC signals. The corresponding representation in the time domain is provided in FIGURE 18, while the Fourier domain representation is provided in FIGURE 19. From both points of view, the application of EWFB is compliant with theoretical models. The undulations observed on the signal are coherent with the resonance frequency (0.25 MHz ≈ 0.25 chips), and the spectrum also shows the undulations (the red spectrum is raised up around 4 MHz).
FIGURE 18. Fault-free vs EWFB Galileo E1 signal.FIGURE 19. Fault-free vs. EWFB Galileo E1 signal power spectrum density.
Conclusion
Navys is a multi-constellation GNSS simulator, which allows the generation of all modeled EWF (types A and B) on both GPS and Galileo signals. Indeed, the Navys design makes the EWF application independent of the signal modulation and carrier frequency.
The International Civil Aviation Organization model has been adapted to Galileo signals, and the correct application of the failure modes has been verified through RF simulations. The theoretical effects of EWF types A and B on waveforms, spectra, autocorrelation functions and code-phase measurements have been confirmed through these simulations.
For a given lag value, the tracking biases induced by type A EWF distortions are equal on GPS and Galileo signals, which is consistent with theory.
Eventually, for a given resonance frequency-damping factor combination, the type B EWF distortions induce a tracking bias of about 5.2 meters on GPS L1 C/A measurements and only 2.8 meters on Galileo E1 C measurements. This is mainly due to the fact that the correlator tracking spacing was reduced for Galileo signal tracking (± 0.15 chips instead of ± 0.5 chips). (Additional figures showing oscilloscope and spectrum analyzer screenshots of experimental results are available in the online version of this article.)
Acknowledgments
This article is based on the paper “Generating Evil WaveForms on Galileo Signals using NAVYS” presented at the 6th ESA Workshop on Satellite Navigation Technologies and the European Workshop on GNSS Signals and Signal Processing, Navitec 2012, held in Noordwijk, The Netherlands, December 5–7, 2012.
Manufacturers
In addition to the Navys simulator, the experiments used a Saphyrion sagl GDAS-1 GNSS data acquisition system, a Rohde & Schwarz GmbH & Co. KG RTO1004 digital oscilloscope, and a Rohde & Schwarz FSW26 signal and spectrum analyzer.
MATHIEU RAIMONDI is currently a GNSS systems engineer at Thales Alenia Space France (TAS-F). He received a Ph.D. in signal processing from the University of Toulouse (France) in 2008.
ERIC SENANT is a senior navigation engineer at TAS-F. He graduated from the Ecole Nationale d’Aviation Civile (ENAC), Toulouse, in 1997.
CHARLES FERNET is the technical manager of GNSS system studies in the transmission, payload and receiver group of the navigation engineering department of the TAS-F navigation business unit. He graduated from ENAC in 2000.
RAPHAEL PONS is currently a GNSS systems engineering consultant at Thales Services in France. He graduated as an electronics engineer in 2012 from ENAC.
HANAA AL BITAR is currently a GNSS systems engineer at TAS-F. She graduated as a telecommunications and networks engineer from the Lebanese Engineering School of Beirut in 2002 and received her Ph.D. in radionavigation in 2007 from ENAC, in the field of GNSS receivers.
FRANCISCO AMARILLO FERNANDEZ received his Master’s degree in telecommunication engineering from the Polytechnic University of Madrid. In 2001, he joined the European Space Agency’s technical directorate, and since then he has worked for the Galileo program and leads numerous research activities in the field of GNSS evolution.
MARC WEYER is currently working as the product manager in ELTA, Toulouse, for the GNSS simulator and recorder.
Additional Images
GEMS graphical interface.Observation of EWF type A on GPS L1 C/A signal with an oscilloscope.Impact of EWF A on GPS L1 C/A signal spectrum for 0 (green), 41 (black), and 171 (blue) nanosecond lag.Observation of EWF type A on GPS L1 C/A signal with an oscilloscope.Impact of EWF B on GPS L1 C/A signal spectrum for fd = 8 MHz and σ = 7 MHz.Impact of EWF A on Galileo E1 BC signal spectrum for 0 (green), 40 (black), and 171 (blue) nanosecond lag.Navys hardware equipment – Blackline edition.
Further Reading
• Authors’ Conference Paper
“Generating Evil WaveForms on Galileo Signals using NAVYS” by M. Raimondi, E. Sénant, C. Fernet, R. Pons, and H. AlBitar in Proceedings of Navitec 2012, the 6th ESA Workshop on Satellite Navigation Technologies and the European Workshop on GNSS Signals and Signal Processing, Noordwijk, The Netherlands, December 5–7, 2012, 8 pp., doi: 10.1109/NAVITEC.2012.6423071.
• Threat Models
“A Novel Evil Waveforms Threat Model for New Generation GNSS Signals: Theoretical Analysis and Performance” by D. Fontanella, M. Paonni, and B. Eissfeller in Proceedings of Navitec 2010, the 5th ESA Workshop on Satellite Navigation Technologies, Noordwijk, The Netherlands, December 8–10, 2010, 8 pp., doi: 10.1109/NAVITEC.2010.5708037.
“Estimation of ICAO Threat Model Parameters For Operational GPS Satellites” by A.M. Mitelman, D.M. Akos, S.P. Pullen, and P.K. Enge in Proceedings of ION GPS 2002, the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, September 24–27, 2002, pp. 12–19.
• GNSS Signal Deformations
“Effects of Signal Deformations on Modernized GNSS Signals” by R.E. Phelts and D.M. Akos in Journal of Global Positioning Systems, Vol. 5, No. 1–2, 2006, 9 pp.
“Robust Signal Quality Monitoring and Detection of Evil Waveforms” by R.E. Phelts, D.M. Akos, and P. Enge in Proceedings of ION GPS-2000, the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation, Salt Lake City, Utah, September 19–22, 2000, pp. 1180–1190.
“A Co-operative Anomaly Resolution on PRN-19” by C. Edgar, F. Czopek, and B. Barker in Proceedings of ION GPS-99, the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, September 14–17, 1999, pp. 2269–2271.
• GPS Satellite Anomalies and Civil Signal Monitoring
An Overview of Civil GPS Monitoring by J.W. Lavrakas, a presentation to the Southern California Section of The Institute of Navigation at The Aerospace Corporation, El Segundo, California, March 31, 2005.
• Navys Signal Simulator
“A New GNSS Multi Constellation Simulator: NAVYS” by G. Artaud, A. de Latour, J. Dantepal, L. Ries, N. Maury, J.-C. Denis, E. Senant, and T. Bany in Proceedings of ION GPS 2010, the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, September 21–24, 2010, pp. 845–857.
“Design, Architecture and Validation of a New GNSS Multi Constellation Simulator : NAVYS” by G. Artaud, A. de Latour, J. Dantepal, L. Ries, J.-L. Issler, J. Tournay, O. Fudulea, J.-M. Aymes, N. Maury, J.-P. Julien , V. Dominguez, E. Senant, and M. Raimondi in Proceedings of ION GPS 2009, the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation, Savannah, Georgia, September 22–25, 2009, pp. 2934–2941.
UPDATE: The SVN65/PRN24 L5 transmitter has now been switched on. L5 is the civilian safety-of-life GPS signal, designed to meet demanding requirements for safety-of-life transportation and other high-performance applications.
UPDATE: The GPS Block IIF-3 satellite, SVN65, began transmitting L1 and L2 signals as PRN24 on October 8. A number of stations of the International GNSS Service are now tracking the satellite. The satellite is included in broadcast almanacs although it is set unhealthy and will continue to be so until satellite commissioning is completed. The satellite is still drifting towards its designated orbital position of Slot 1 in Plane A.
Meanwhile, SVN27/PRN27 was decommissioned from active service on October 6 and removed from the broadcast almanacs. However, the L-band
transmitters of SVN27 remain active, presumably for end-of-life testing.
UPDATE: According to Boeing, the satellite manufacturer, SVN65 is on orbit and performing as expected. A Boeing press release stated that “Controllers confirmed initial contact with the spacecraft at 11:43 a.m. Eastern time. The satellite’s GPS signals will be turned on and tested within a few days.”
Incidentally, the launch occurred exactly 55 years to the day after the launch of the world’s first satellite, Sputnik I, on October 4, 1957. It was Doppler tracking of that satellite that gave rise to the Transit navigation system and subsequently, its successor, GPS.
The launch of the GPS Block IIF-3 satellite took place as scheduled October 4 at 12:10 UTC (8:10 a.m. EDT), aboard a United Launch Alliance Delta IV rocket from Cape Canaveral, Florida. Spacecraft separation was reported at 16:27 UTC.
The Boeing-built spacecraft is designed to improve network coverage for both civilian and military networks, including a new L5 signal for improved commercial and civil aviation users.
The satellite, also known as SVN65, will be positioned in orbital slot 1, which is in plane A and will use the PRN24 ranging codes. Slot 1 was recently occupied by a Block IIA satellite, SVN39, operating as PRN09. SVN39 is one of the oldest operating satellites in the GPS fleet, having been launched on 26 June 1993. SVN39 underwent an initital Delta-V on September 27 to move it close to SVN38/PRN08 in slot 3 in plane A, making room for the new Block IIF satellite.
“Congratulations to the entire team on today’s successful launch of the GPS 2F-3 satellite,” Jim Sponnick, ULA vice president, Mission Operations, said in a post-launch press release.
“ULA and our mission partners have a rich heritage with the GPS program and we are proud to have served alongside the government and contractor teams over the last two decades to provide important Global Positioning System capabilities for our national defense and for millions of civilian and commercial users around the world.”
A Delta IV rocket lifts-off with an advanced GPS satellite from Cape Canaveral on Thursday. (Credit: ULA/Atkeison).
2. GPS SATELLITE SVN65 (PRN24) WAS LAUNCHED ON JDAY 278.
A USABINIT NANU WILL BE SENT WHEN THE SATELLITE IS SET ACTIVE TO
SERVICE.
3. POC: CIVILIAN – NAVCEN AT 703-313-5900, HTTP://WWW.NAVCEN.USCG.GOV
MILITARY – GPS OPERATIONS CENTER AT HTTPS://gps.afspc.af.mil/
GPSOC , DSN 560-2541,
COMM 719-567-2541, [email protected] , HTTP://gps.afspc.af.mil/GPSOC/GPS
MILITARY ALTERNATE – JOINT SPACE OPERATIONS CENTER, DSN 276-3514.
COMM 805-606-3514. [email protected]
Javad Ashjaee, founder and CEO of JAVAD GNSS, has filed a letter with the U.S. Federal Communications Commission (FCC) concerning his company’s development of technical possibilities in GNSS filter designs and components. He states “I hope this will be helpful in establishing realistic guidelines for the characteristics of high-precision GNSS receivers that will be used in critical applications.”
Below is the full text of the letter.
September 7, 2012
The Honorable Julius Genachowski
Chairman
Federal Communications Commission
445 12th Street, S.W.
Washington, D.C. 20554
The Honorable Lawrence E. Strickling
Assistant Secretary for Communications and Information
National Telecommunications & Information Administration
United States Department of Commerce
1401 Constitution Avenue, N.W.
Washington, D.C. 20230
Dear Chairman Genachowski and Assistant Secretary Strickling:
In this communication I want to inform you of the current status of technical possibilities in GNSS filter designs and components. I hope this will be helpful in establishing realistic guidelines for the characteristics of high precision GNSS receivers that will be used in critical applications.
We have improved our previous L1 filter and have extended the design to include all commercial GNSS bands.
Figure left above is our filter that protects GPS L1, Galileo L1 and GLONASS L1 bands. It brings in all the useful signals intact and rejects out of band signals with the slope of about 12 dB/Mhz. Similarly, Figure right above is our filter that protects GPS L2, GPS L5, GLONASS L2 and Galileo L5 and has slope of about 9 dB/Mhz.
These filters have been extensively tested with five different innovative tests and prove that the filters also improve the performance of GNSS receivers. These extensive innovative tests are embedded in the receivers that we mass-produce today and every user can test their receivers in all environments. These tests are much more extensive than those previously employed by PNT and other organizations. These embedded tests are not only much more extensive, but it takes only a few minutes to perform these by any novice user by clicking some receiver buttons. Compare that to the limited tests by PNT and others that took weeks to perform and needed experts with very expensive equipment in some laboratories to perform.
These filters not only protect GNSS signals against all LightSquared signals (10L, 10H and 10R handsets) but also from all similar signals that may appear near all commercial GNSS bands in the future. We are proud that our filters help allow better usage of these precious bands, in particular for broadband wireless communication that our country desperately needs.
These filters apply to wideband high precision GNSS receivers and the cost is even less than earlier conventional filters. The case of narrow-band low precision receivers (e.g. Garmin) is much simpler, as has been demonstrated by GPS receivers in more than 300 million cell phones and mobile devices which are not affected by LightSquared signals. The low precision receivers (L1 C/A code only) require filter slopes 10 times less steep than those presented here and do not necessitate additional costs.
In summary, the technology exists today of improved filter design and better performing GNSS receivers and can actually be done at a cost lower than current conventional GNSS receiver filter designs. I trust that the information that I have presented can be used in establishing the performance guidelines and requirements for all GNSS receivers used in critical applications.
I also would like to invite your representatives to ION-2012 GNSS conference where we present details and answer questions at 2:00 PM on September 20.
Regards,
Javad Ashjaee, Ph.D.
CEO, Javad GNSS
San Jose, California
USA
According to a spokesperson from the Space and Missile Systems Center, GPS Directorate, the Russian Space Agency (RSA) has been assigned L1 pseudorandom noise (PRN) C/A codes for its System of Differential Correction and Monitoring (SDCM) transponders on the Luch series of geostationary relay satellites.
SDCM is a satellite-based augmentation system that will be compatible with the U.S. Federal Aviation Administration’s Wide Area Augmentation System, the European Geostationary Navigation Overlay Service, and Japan’s MTSAT Satellite-based Augmentation System.
The SDCM transponders will be hosted on the satellites of the Luch Multifunctional Space Relay System (Mnogofunktsional’noi Kosmicheskoi Sistemy Retranslyatsii). In addition to seven transponders in the Ku-and S-bands to be used to relay communications and telemetry between low-Earth-orbiting spacecraft (such as the Russian segment of the International Space Station) and Russian ground facilities, the satellites will host COSPAS/SARSAT search and rescue transponders, as well as the SDCM transponders.
The first of the new Luch satellites, Luch-5A, was launched on December 11, 2011. The satellite has passed the initial inspection carried out at its temporary location at about 58.5 degrees east longitude. According to published documents, Luch-5A will eventually be relocated to its designated operational location at 16 degrees west longitude.
Two more Luch satellites are to be launched: Luch-5B, scheduled for launch around the end of August 2012 into an orbit at 95 degrees east longitude and Luch-5V (“V” is the transliteration of the third letter in the Russian alphabet) in 2014 into an orbit at 167 degrees east longitude (Luch-5V replaces the previously designed Luch-4 satellite).
The C/A codes assigned to the Luch SDCM transponders are as follows: Luch-5A, PRN 125; Luch-5B, PRN 140; and Luch-5V (Luch-4), PRN 141. Notification of the assignments was sent to the RSA on December 20, 2011.
No signals from the Luch-5A SDCM transponder have yet been detected by the monitoring stations of the International GNSS Service.
