Join GPS World’s Survey and GIS Editor Eric Gakstatter March 15 for the webinar, “Everything Else but GPS: How GLONASS, Galileo, and Compass Will Affect High-Precision Users.” The webinar will be held at 10 a.m. Pacific (1 p.m. ET/6 pm. GMT); registration is free.
“In a rapidly changing world — which is the world of GPS and GNSS — those who invest significant amounts of their operating capital in hardware must plan carefully for the future,” said Gakstatter, who serves as moderator of the webinar. “Will your survey receiver remain relevant and up to date long enough for you to recoup your investment? How could taking advantage of newly operational constellations improve your efficiency and competitiveness? GLONASS is operational now. Compass has put forward a very aggressive schedule for regional and then global operations. Galileo is moving steadily forward.”
Gakstatter closely follows all these systems, and can relate their capabilities — current and future — directly to surveyors’ needs. His guest speakers will add to the insight. This webinar is required listening for anyone planning to stay on survey’s leading edge.
“We conclude that LightSquared’s proposed mobile broadband network will impact GPS services and that there is no practical way to mitigate the potential interference at this time.” These words from Lawrence Strickling, U.S. assistant secretary for communications and information and head of the National Telecommunications and Information Administration (NTIA), appear to signal the end of LightSquared’s run.
Strickling’s letter to Federal Communications Commission (FCC) chairman Julius Genachowski appeared in public on February 14. Later that same day, FCC spokesperson Tammy Sun released a statement from that agency that “the Commission will not lift the prohibition on LightSquared,” and that it plans to “vacate the Conditional Waiver Order, and suspend indefinitely LightSquared’s Ancillary Terrestrial Component authority.”
The NTIA and the FCC share responsibility for controlling U.S. radio spectrum use. The FCC supposedly has final authority in these matters, although the NTIA, representing government interests, may swing the bigger cat in the room. LightSquared’s inability to satisfy the requirements of the Federal Aviation Administration (FAA), coupled with unremitting frowning and glowering from the Department of Defense, may have been the deciding factors — more so than the uproar among most GPS manufacturers. The FAA and the U.S. military, two key government entities with widely fielded GPS equipment and applications, constituted the backbone that the NTIA finally showed, although the military has been, with one notable exception, silent on the issue, and indeed is not mentioned in the NTIA letter.
Strickling’s eight-page letter recaps the history, with a July 6, 2011, early climax: “Test results demonstrated that LightSquared’s then-planned deployment of terrestrial operations posed a significant potential for harmful interference to GPS services.” He relates further NTIA testing of cellular GPS receivers, joint continued analysis by FAA and LightSquared of impact on aviation receivers, and testing of general/personal navigation GPS receivers by the Executive Steering Group of the Interagency National Executive Committee for Space-Based Positioning, Navigation, and Timing (EXCOM).
Strickling quotes a January 13 letter from Ashton Carter, deputy secretary for defense, and John Porcari, deputy secretary for transportation: “It is the unanimous conclusion of the test findings by the EXCOM agencies that both LightSquared’s original and modified plans for its proposed mobile network would cause harmful interference to many GPS receivers. Additionally, an analysis by the FAA has concluded that the LightSquared proposals are not compatible with several GPS-dependent aircraft safety-of-flight systems. . . There appear to be no practical solutions or mitigations that would permit the LightSquared broadband service, as prosposed, to operate in the next few months or years without significantly interfering with GPS. As a result, no additional testing is warranted at this time.”
But Wait. We’re not done yet. Strickling calls for GPS receiver standards to be developed, citing the EXCOM’s decision that “federal agencies will move forward this year to develop and establish new GPS spectrum interference standards that will help inform future proposals for non-space commercial uses in the bands adjacent to the GPS signals.”
NTIA and PNT EXCOM will devise “standards for the development and procurement of GPS receivers to support their various mission requirements.” NTIA recognized “the importance that receiver standards could play as part of a forward-looking model for spectrum management even beyond the immediate issue of GPS.”
The FCC, in its concurrence statement to the NTIA letter, begins by reciting the mantras of “economic growth, job creation, and to promote competition . . . freeing up spectrum for mobile broadband,” and gradually works its way around to its decision on the waiver. This signals an ongoing commitment to make further efforts towards broadband implementation.
In-Car Nav Under Safety Scrutiny
The U.S. National Highway Traffic Safety Administration (NHTSA) proposed voluntary guidelines for car manufacturers on February 16, including a recommendation to design dashboards so that distracting devices are automatically disabled unless the vehicle is stopped and the transmission is in park. The agency is concerned about proliferation of text messages, GPS images, phone calls, and web surfing, and wants carmakers to curb those distractions when vehicles are moving.
Technological advances, among them GPS-enabled navigation, have raised concerns that drivers’ attention is being diverted too much from the road.
“We recognize that vehicle manufacturers want to build vehicles that include the tools and conveniences expected by today’s American drivers,” said NHTSA Administrator David Strickland. “The guidelines would offer real-world guidance to automakers to help them develop electronic devices that provide features consumers want without disrupting a driver’s attention or sacrificing safety.”
Under the guidelines, GPS and other navigation devices that provide directions would be permitted while driving, but NHTSA asks that they be designed so that drivers can’t manually enter a destination unless the car is in park. A spokesperson for the Alliance of Automobile Manufacturers cautioned against this. “There are often passengers in the car who can enter addresses, so we need to consider that when looking at requiring these technologies to only be used in park,” she said. “And if the GPS is disabled when moving, consumers can always bring their own Garmin into the vehicle. It’s complicated.”
Other dashboard technologies recommended for automatic disabling include text-messaging, Internet browsing, social media browsing, phone dialing and computer screen messages of 30 characters or more that are unrelated to driving.
Manufacturers are also urged to revise in-car designs to reduce to two seconds or less the amount of time drivers must divert their eyes from the road to use a device. Devices should also be designed so that drivers don’t have to use more than one hand or glance through extraneous information.
A spokesperson for state highway safety offices said that “the safest thing is for drivers not to use these systems at all — both hands on the wheel and the mind focused solely on driving.”
The process for writing actual federal rules often takes years to complete. The guidelines represent a way “ to continue the drumbeat” that distracted driving is a serious safety issue that costs lives.
NHTSA is also considering guidelines to address portable electronic devices drivers carry with them into cars, including GPS navigation systems.
SSTL-OHB to Build Eight More Galileo Satellites
European Commission Vice President Antonio Tajani announced in London that the consortium led by OHB System AG and Surrey Satellite Technology Ltd. (SSTL) will build a further eight satellites for the European Union’s Galileo satellite navigation program under the supervision of the European Space Agency.
The new contract will see SSTL, builder of the GIOVE-A satellite, continuing its role as payload prime, assembling, integrating, and testing the navigation payloads in the UK, while OHB System, as the prime contractor, builds the eight satellite platforms and executes final integration of all the satellites in Germany. The SSTL-OHB partnership is already building 14 satellites for the Galileo program and will draw on its heritage and experience to produce the additional satellites to demanding schedules.
SSTL is assembling the Galileo program payloads at its recently opened purpose-built Kepler technical facility in Guildford, UK. SSTL will manufacture the electrical harnesses and the electronics to interface the navigation payload with the satellite platform.
The remaining payload equipment will be externally procured by SSTL from European and other suppliers. SSTL’s payload solution is based on European-sourced atomic clocks, navigation signal generators, high-power traveling-wave tube amplifiers, and antennas, and will provide all of Galileo’s services.
Compass Poised
As this magazine goes to press, a new GNSS satellite may simultaneously be rising. The Chinese government issued a Notice to Airmen (NOTAM) for a satellite launch on, February 24, at about 16:20 UTC. According to web reports, the launch from the Xichang Satellite Launch Center will orbit the fifth geostationary satellite in the BeiDou-2/Compass constellation.
Funding Affirms NextGen; Unmanned Flight Advances Also
For the last five years, the Federal Aviation Adminstration (FAA) has made do with 23 short-term funding appropriations from Congress, but on January 30, congressional leaders agreed on a four-year, $63 billion funding bill. The funding will accelerate the creation of the NextGen (Next Generation Air Transportation System) air traffic control system. A new post will be created — the Chief NextGen Officer — to oversee the effort, and a schedule for progress will be set.
A key piece of NextGen includes GPS-enabled Required Navigation Performance (RNP), which allows an aircraft to fly a specific path between two 3-dimensionally defined points in space.
The bill also assures funding subsidies for rural airports at $190 million a year. New labor rules will make it harder for airline employees to unionize, requiring half the workers in a bargaining unit to petition for a vote to certify a union, an increase from the current 35 percent.
“All of us at this table made compromises,” Sen. Jay Rockefeller, D-W.Va., chair of the Senate’s transportation committee, told USA Today. “The outcome is that we have a bill that will take steps to modernize our air traffic control system, make the air transportation system safer than ever, and make certain small communities have access to critical air service.”
Unmanned Aircraft. Congress also passed legislation starting the clock on a number of deadlines the FAA must meet to safely integrate unmanned aircraft systems (UAS) into the national airspace system. Chief among them is a deadline for full integration by September 2015.
Using GPS to underlie the whole concept, the UAS industry has made significant technological advancements during the last decade, and the legislation recognizes the important role UAS will play in the future air transportation system.
Michael Toscano, president of the Association for Unmanned Vehicle Systems International (AUVSI) said, “UAS are truly a revolutionary-type technology, and I’m confident that once people can fly UAS in the national airspace for civil and commercial purposes, such as oil and pipeline monitoring, crop dusting, and search and rescue, a whole new industry will emerge, inventing products and accomplishing tasks we haven’t even thought of yet.”
Other major provisions of the bill include:
Requiring six UAS test sites within six months (similar to the language in the already-passed Defense Authorization bill);
Requiring small UAS (under 55 pounds) be allowed to fly in the U.S. Arctic, 24-hours-a-day, beyond line-of-sight, at an altitude of at least 2,000 feet, within one year;
Requiring expedited access for public users, such as law enforcement, firefighters, emergency responders;
Allowing first responders to fly very small UAS (4.4 pounds or less) within 90 days if they meet certain requirements.
The goal is to grant law enforcement and firefighters immediate access to start flying small systems to save lives and increase public safety.
Spectrum Swamp
On January 30, the same day that a LightSquared VP told an Institute of Navigation audience that moving to a different spectrum posed formidable difficulties, a company working on behalf of LightSquared contacted a Department of Defense official to discuss just such a spectrum swap.
The McChrystal Group, led by retired four-star general Stanley McChrystal, contacted the Department of Defense’s Mid-Atlantic Area Frequency Coordinator at Pawtuxet River, Maryland, to discuss “a spectrum swap.” The McChrystal representatives indicated interest in the upper 10 MHz (1515–1525 MHz) of the Aeronautical Mobile Telemetry band (1435–1525 MHz). This spectrum is vital to the development and test of aircraft and weapon systems, for both government agencies and industry, is heavily scheduled and utilized, and is also used for safety of life services (see “Letters to the Editor” in this issue, page 8).
Moving LightSquared’s license to a different radio frequency spectrum has been suggested by some as a possible exit strategy from the LightSquared/GPS interference conflict. At least one wireless industry analyst has surmised that this constituted a part of LightSquared’s strategic plan all along.
A source familiar with the situation contacted GPS World after this story appeared online to say that “a swap would be complicated but never ‘insurmountable.’ The bottom line is that [LightSquared’s VP] did not talk about swaps of any specific spectrum. He talked about the difficulty to get a wireless company up and running, and if you’ve got something that has spectrum, technology, and a successful business model, then that’s very rare, and you can’t necessarily duplicate it. But he said nothing about whether a swap of some specific kind of spectrum could be done. If the parties are willing, it’s actually not that hard.”
Nevada OKs Unmanned Driving
Nevada became the first state in the nation to authorize the use of autonomous vehicles on its roadways.
Manufacturers are developing vehicles that could allow a motorist to plug in a destination and let the vehicle drive there automatically. Google has several prototypes, logging more than 160,000 test miles.
The Nevada Department of Motor Vehicles will formalize licensing procedures for companies that want to test their vehicles in the state.
General Motors has run several tests, some in conjunction with Carnegie-Mellon University on a self-driving Chevrolet Tahoe, The Boss. BMW has several test vehicles in operation, as does Audi in collaboration with Stanford University. Many of these cars, or their predecessors, have participated in DARPA Grand Challenges, reported in this magazine.
SVN-49 Broadcasting on L-Band
GPS satellite SVN-49 began transmitting an L-band signal on or about February 2. SVN-49 is currently being used as a vehicle of opportunity for satellite subsystem testing. However, SVN-49 is declared unusable until further notice, and will not be included in the broadcast almanac.
By Ismael Colomina, Christian Miranda, M. Eulàlia Parés, Marcus Andreotti, Chris Hill, Pedro F. da Silva, João S. Silva, Tiago Peres, João F. Galera Monico, Paulo O. Camargo, Antonio Fernández, José Maria Palomo, João Moreira, Gustavo Streiff, Emerson Z. Granemann, and Carmen Aguilera
New Galileo signals have great potential for pseudorange-based surveying and mapping in both optimal open-sky conditions and suboptimal under-canopy environments. This article reviews the main features of Galileo’s E5 AltBOC and E1 CBOC signals, describes generation of realistic E5 and E1 pseudoranges with and without multipath sources, and presents anticipated horizontal positioning accuracy results, ranging from 4 centimeters (open-sky) to 14 centimeters (under-canopy) for E5/E1.
The history of GNSS surveying has been written in the carrier phase language — until now. The well known reason for this is the high precision, at the millimeter level, of the carrier phase observables and the low precision, at half a meter or worse, of the pseudorange observables. The progress and results of carrier-phase positioning are also well known and, today, surveyors can count on many effective ways for relative and absolute, static and kinematic, accurate positioning procedures like RTK, PPP and others. On the other hand, pseudorange observables have been used for various cadastral, GIS and mapping applications with meter and lower level accuracy requirements. The main advantages of pseudorange positioning are the simplicity and robustness of data processing. Moreover, the typical user of GNSS (pseudorange) mapping gear needs less GNSS education and training than the typical GNSS geodetic surveyor.
However, there are cadastral and mapping applications that require better accuracies than current pseudoranges provide and there are surveying applications that do not require the cm to dm level accuracies that carrier phases provide. There is a gap where no choice is optimal: either the choice is unnecessarily expensive (receivers, processing software, trained personnel) or it is unacceptably inaccurate. This gap can be reduced or eliminated with the new GPS and Galileo signals. It is therefore convenient that the size of the new smaller gap, if any, be analyzed as soon as possible even if the analysis has to rely on simulated signals.
According to the simulations performed, it is expected that pseudoranges can be extracted from the Galileo E5 AltBOC signals with tracking errors (1-σ level) ranging from 0.02 m (“open sky” scenarios) to 0.08 m (“tree covered” scenarios with 15% through-foliage visibility) whereas for the Galileo E1 CBOC signals the tracking errors range between 0.25 m and 2.00 m respectively. With these tracking errors and with the explicit estimation of the ionosphere parameters, the available simulations indicate “open sky” horizontal/vertical accuracies of 0.04/0.17 m for static positioning and 0.04/0.20 m ones for (low dynamics) kinematic positioning; and “tree covered” accuracies of 0.05-0.13/0.07-0.30 m for static positioning and 0.15/0.35 m for (low dynamics) kinematic positioning.
The high precision of the Galileo E5 AltBOC range measurements suggests that their modeling can benefit from available research results of the precise point positioning (PPP) carrier phase-based techniques. Since, in contrast to carrier phase measurements, pseudoranges are not ambiguous, it is expected that the convergence challenges of PPP will disappear or largely be mitigated when using cm-level precise pseudoranges. As a result, in addition to standard relative positioning surveying, absolute positioning surveying is likely to emerge as a standard procedure, both in real-time (using Galileo ultra-rapid orbits hopefully available in future from the IGS) or in post-processing (similarly, using IGS final precise Galileo orbits). Clearly, the question is how fast and how well the unknown parameters in the pseudorange model will converge to the correct values. However, even low convergence might be a minor problem as, with pseudoranges, loss-of-lock situations do not require the re-initialization of some parameters in the estimation algorithms.
Absolute pseudorange positioning is of particular interest because simple GNSS surveying with pseudoranges can become a practical tool in regions with sparse GNSS permanent station distributions and for communities with limited surveying expertise. As the results and behavior of E5 AltBOC pseudorange positioning consolidate and become well understood, appropriate surveying procedures will be identified and adopted. The starting point for this is the investigation of static (absolute) and kinematic (with known initial/end points) positioning with E5 AltBOC and E1 CBOC.
The full deployment of the Galileo constellation — Full Operational capability (FOC) — is currently scheduled for 2020. As of now, two satellites of the In-Orbit Validation (IOV) have been launched and two more will follow that will complement the two experimental satellites (GIOVE-A and GIOVE-B) already in orbit. The Initial Operational Capability (IOC) is scheduled for 2014 and will include fourteen satellites that were ordered in January 2010. In addition to this, eight additional satellites have been ordered in February 2012.
Although not covered in this paper, we note that there are a number of potential ways to benefit from the E5 AltBOC signal and modulation before Galileo FOC. One of them is to combine the E1/E5 Galileo signals with the L1/L5 GPS signals and “replace” the missing Galileo signals with GPS ones. Another one that will depend on the IOV satellite configuration is to keep on working with full GPS L1/L2 satellite constellations and “assist” GPS with Galileo to speed up convergence periods in PPP or to extend the ranges of Differential GPS (DGPS).
In the paper we concentrate on the combination of E1 CBOC and E5 AltBOC signals and modulations by explicitly estimating the ionospheric bias — or a correction with respect to a model — instead of forming ionospheric-free combinations. The reason for this is that, since the E1 CBOC and E5 AltBOC pseudoranges have disparate noise levels, in the resulting ionospheric-free pseudoranges the low noise properties of E5 AltBOC will be lost. (We note the alternative method, in the presence of precise pseudoranges, of taking advantage of the ionospheric divergence of carrier phase and pseudoranges. In this approach I sr or δI sr are estimated with the use of just the E5 frequency.)
The research reported in this paper has been conducted in the frame of the international –EU and Brazil – ENCORE project. ENCORE –Enhanced Code Galileo Receiver for Land Management in Brazil – is funded by the European Commission (grant 247939) with the aim to implement the 7th European Framework Program for Research and Development (FP7). The project runs from 2010 to 2012 and is realized by a European-Brazilian consortium lead by DEIMOS Engenharia (Portugal). The goals of ENCORE are the introduction of Galileo terminals in the Brazilian market for land management applications, the stimulation of the participation of Brazilian entities in Galileo and the development of a high-precision and low-cost land management application based on Galileo signals.
The Galileo Signals
The development of new GNSS systems, as the Galileo system (as well as the modernization of currently available ones, as the GPS) will provide additional signals with increasingly complex modulations and multiplexing schemes, enabling performance enhancements in terms of availability, accuracy, and robustness.
Tracking accuracy and multipath robustness are closely related to the slope of the (main) peak of the Auto-Correlation Function (ACF) of the signals. Figure 1 shows the ACFs for the most relevant GPS and Galileo modulations. Figure 2 shows the multipath error envelopes for the corresponding GPS and Galileo signals when using an Early-Late Power discriminator and a correlator spacing of 0.1 chip (assuming one reflected ray and a carrier over multipath ratio of 2).
Figure 1. Normalized auto-correlation functions for different modulations: BPSK (n) of GPS L1, BOC (n,n) of Galileo E1 with simplified demodulation, CBOC (6n,n,1/11) of Galileo E1, and AltBOC (1.5n,n) of Galileo E5 signals.
Multiplexed BOC (MBOC) is a new modulation introduced in 2006, and included recently in the Galileo SIS ICD. The E1 Open Service modulation receives the name of Composite Binary Offset Carrier (CBOC) and is a particular implementation of MBOC. The CBOC (6,1,1/11) modulation is the result of a linear combination of a wideband BOC (6,1) sub-carrier with a narrow-band BOC (1,1) sub-carrier, in such a way that 1/11 of the power is allocated (in average) to the high frequency component.
The Galileo CBOC (6,1,1/11) signal’s demodulation can be simplified by using a BOC (1,1) modulated local replica, at the expense of tracking and multipath robustness performance (making it comparable to that of a BOC (1,1) signal) but enabling an interesting trade-off between performance and receiver complexity. In the current work the CBOC modulation is assumed.
Nevertheless, the potential of the future Galileo E5 signal is expected to outshine even these modernized signals. The Galileo E5 signal, with its Alternative Binary Offset Carrier (AltBOC) modulation, is one of the most advanced and promising signals of the Galileo system. Receivers capable of tracking this signal will benefit from unequalled performance in terms of measurement accuracy, precision, and multipath suppression. However, the signal processing techniques to implement a matched-filter AltBOC demodulation are much more challenging than those for the traditional BPSK or even for the BOC modulations (as the current GPS L1 C/A or future L1 C signals). This stems from the large bandwidth (chip rate), complex sub-carrier, elaborate multiplexing scheme (which enables the simultaneous broadcast of 4 channels on a single carrier) and complex interaction of the 4 multiplexed channels.
The AltBOC (15,10) correlation peak is similar to the one of BOC(15,10) near the main peak and, as suggested in Figures 1 and 2, it outperforms all other modulations of the current and future GPS and Galileo civil and open service signals (note that the x axis of Figure 1 is also normalized by the chip period, which is 10 times shorter for the AltBOC (15,10) modulation than for the remaining ones).
Figure 2. Multipath error envelopes for GPS L1 (BPSK(1)), Galileo E1 (demodulated as BOC (1,1) and CBOC (6,1,1/11)), and Galileo E5 AltBOC (15,10) signals (Early-Late Power discriminator, correlator spacing of 0.1 chip, carrier over multipath ratio of 2 and infinite bandwidth).
The E5 signal can be separated into two sub-bands (E5a and E5b) which can be treated separately by a Galileo E5 receiver (as BPSK (10) modulated signals), called Single Side-Band (SSB) processing. However, this would result in the loss of the promising AltBOC signal properties (resulting in a classical triangular ACF). Hence, a matched filter demodulation of the full Galileo E5 signal is desired to implement the best possible receiver in terms of accuracy and multipath robustness, at the expense of an increase in the receiver complexity and required bandwidth.
The existence of secondary peaks (as shown in Figure 1) in the ACFs of Binary Offset Carrier (BOC) modulations (as the AltBOC and CBOC) require specific techniques (i.e., bump-jumping) to ensure that the main peak is the one being tracked.
According to the simulations performed, in the absence of multipath or signal fading sources the performances achievable with E5 AltBOC and E1 CBOC in terms of accuracy of the code tracking errors is 0.02 m and 0.25 m respectively at 45 degree (about 40 dB-Hz for E1 and 44 dB-Hz for E5) with a correlator spacing of 0.1 chip and integration times of 4 ms.
If multipath and signal fading sources are present, the expected errors increase to 0.08 m and 2 m respectively (for about 36 dB-Hz for E1 and 40 dB-Hz for E5). Longer integration times will lead to better performances.
During the project, the above simulation results will be compared against those obtained with Galileo live signals. Figure 3 shows the ENCORE hardware receiver prototype, which is composed by the FPGA board, the RF FE board, the LNA and the antenna. The mezzanine board and the two voltage converters, which can also be seen in figure, enable the receiver testing using recorded IF signals or synthetic IF data.
Figure 3. ENCORE hardware receiver prototype.
Positioning Models and Algorithms
The observation equations for pseudorange measurements follow the modelling principles of PPP. Thus, the observed pseudoranges P1sr (E1 CBOC) and P5sr (E5 AltBOC) can be modeled as
(1)
for i = 1,5, where ρsr is the true geometric distance between satellite s and receiver r, c is the speed of light in a vacuum, δts is the given s satellite clock correction, R s is the relativistic “correction” for satellite s, T sr is the modelled or given tropospheric delay, f1, f5 are the frequencies of E1 CBOC and E5 AltBOC respectively, I sr / f 2i are the modelled or given ionospheric delays, and bis are the given biases for satellite s.
In the above pseudorange observation equation, we will estimate the receiver position Xr (included in ρsr ), the receiver clock correction δtr , the correction δT sr to the modelled or given tropospheric delay T sr , the term δI sr related to the correction δI sr / f 2i to the modelled or given ionospheric delays I sr / f 2i , and the receiver frequency dependent biases bir. In equation 1, ρsr is a well-known function of the satellite ephemeris, the receiver position, the satellite and receiver antenna phase centre offsets, and of all the effects, like solid Earth tides, usually included in PPP models.
The time dependent unknown parameters in equation 1 are further modelled as random walk stochastic processes for the stochastic differential equation of the prediction step (Kalman filter estimation approach) or of the dynamic model (dynamic network estimation approach) as follows: δtr is a random walk with rather large driving white noise variance [rw (∞)]; δT sr as rw (0.0152 m2), PSD level; bir as rw (0.00172 m2), PSD level (b1r is set to 0); and (I sr + δI sr ) / f 2i as rw (σ2 m 2 ) with
(2)
where , T = 64 × 60 s, and τ is the time interval (in seconds) between two successive measurements. Clearly, the stochastic model for the total ionospheric delay depends on assumptions for and T that also depend on the solar activity. Furthermore, depending on the model or data used for I sr the actual parameter to be estimated δI sr and, specifically δI sr , / f 2i will obey to different “amplitude” and “time correlation” T values. For the results reported in the paper, the three-dimensional, time dependent ionospheric electron density NeQuick model was used for I sr . For δI sr , / f 2i , the values , T = 5 × 60 s, were adopted.
In the ENCORE project, the above models are being used to investigate the performance of the various positioning modes (absolute and relative, static and kinematic) and procedures (with and without a “ground presurveyed” or “ground control” point in the absolute positioning mode).
Simulation Scenarios
Due to the unavailability of sufficient Galileo space vehicles at the moment, the validation of the algorithms described before was done using the Navigation Sensor Simulation (NSS) tool, developed by University of Nottingham. The NSS data simulation tool was originally designed to simulate the types of measurements that can be made using a GNSS receiver. Specifically the simulator has the capability of producing code, carrier and Doppler measurements on L1, E1, E5a, E5b, E5 (combined), L2c, L5, and E6 frequencies, covering GPS and Galileo systems. The simulation is achieved by using the true locations of both the receiver and the satellites to calculate the true, error-free measurements. Error models are then applied to account for the various inaccuracies seen in real-world measurements. The simulation results are returned to the user in a file in the standard Receiver Independent Exchange (RINEX) observations format.
The user of the NSS tool is required to define a simulation scenario. The main inputs from a scenario definition are the satellite ephemeris data and the true location of the receiver as well as the parameters for the various error models and the time period for which data should be simulated. It is possible to simulate data using the true locations of the satellites for any day in the past.
For the purpose of this work, the precise orbits used for the Galileo system were obtained from the GalileoSat System Simulation Facility (GSSF) simulator. The expected error on the estimated values for BGD (E1 E5a) and BGD (E1 E5b) was also applied,
NSS provides models for the two types of discriminator widely used in GPS receivers: the Early-Minus-Late Power (EMLP) and the Dot-Product (DP) discriminators. For this, NSS accepts parameters for front-end filter bandwidth, correlator spacing, DLL loop bandwidth and integration time for each of the signal modulations it is capable to work with: GPS BPSK (1), GPS BPSK (10), Galileo CBOC (6, 1, 1/11), and Galileo AltBOC (15, 10).
Table 1. Galileo orbit error factors applied.Table 2. Parameters for the generation of the simulated pseudoranges.
C/No values for GPS and Galileo for various satellite elevation angles are tabled inside NSS in accordance with measurements available from various sources. The values in those tables are interpolated via respective spline equations for intermediate elevation angles.
For the scope of the ENCORE project and its application for land management in rural areas, it is assumed that the influence of the vegetation on the satellite signals will be of creating diffuse, non-coherent signal scattering, resulting in signal loss but not significantly in signal delay. Therefore the ITU-R model is of greater interest as this model gives empirical values of cumulative signal fade due to tree shadowing, based in multiple measurement campaigns. The ITU-R signal fading model takes as input the signal frequency, the satellite elevation angle and the “estimated signal visibility percentage” of the signal. This last parameter accounts for the foliage effect on the signal, and will have a low value when the tree is in full foliage and a high value when the trees are without leaves.
For the tropospheric delay, NSS makes use of the EGNOS Troposphere Model, although in NSS this model is used to simulate the delay experienced due to the troposphere rather than correct for it. For the ionospheric delay, NSS has been developed to read Total Electron Content (TEC) maps in the standard IONEX file format. These files may contain 2 or 3 dimensional maps of the TEC at a number of equally spaced epochs, usually covering a 24 hour period. The TEC for each sub-ionospheric pierce point at a given epoch is calculated by interpolating between two TEC maps at consecutive epochs. The maps are firstly rotated around the z-axis to compensate for the strong correlation between the ionosphere and the sun’s position. A standard 4 point interpolation scheme is then used to interpolate each TEC map to the required latitude and longitude.
The scenario definition is completed by selecting the number and type of measurements to be simulated along with the data interval for the measurements and the elevation masking angle of the receiver.
The preliminary results presented in this paper are based on simulation scenarios created from the base settings presented in tables 1 and 2, for the “open sky” (OS) and “tree covered” (TC) cases, using 8 Galileo satellites (of a 27-satellite constellation) for a fixed point in Brazil that has been processed in the absolute and static/kinematic modes. Thus 10 cases have been investigated that result from combining the OS and TC ones with the kinematic (K) and static (S) cases. The static cases have been computed for observation periods of 1, 5, 10 and 30 minutes respectively (cases S-1, S-5, S-10 and S-30). For all test cases a 45 minute data set measured at 1 Hz has been processed together with start/end initialization periods –i.e., observations processed in the static mode– of 5/10 minutes respectively. Thus, the test OS S-5 (confer table 3) corresponds to the “open sky” scenario for static point determination with observation periods of 5 minutes and the test TC-K corresponds to the “tree covered” scenario for kinematic point determination at 1 Hz.
Results from Simulated Measurements
Table 3 summarizes the results of the tests described in the previous section. Each table cell contains the Root Mean Square Error (RMSE) of the horizontal (μH) and vertical (μV) positioning results when compared to the known true value of the fixed point established for the simulations. Figures 4 to 7 represent the receiver’s position and clock errors for the OS and TC cases. Note again, that positioning is performed in the absolute and post-processing mode.
Figure 4. Position accuracy for the Open Sky scenario, case K.Figure 5. Receiver’s clock accuracy for the Open Sky scenario, case K.Figure 6. Position accuracy for the Tree Covered scenario, case K.Figure 7. Receiver’s clock accuracy for the Tree Covered scenario, case K.
Although the results can still be considered preliminary, they illustrate what can be expected from the proposed combination of E1 and E5 Galileo pseudoranges. The horizontal accuracy estimator μH is computed as μH=√ μ2E + μ2N where μE , μN are the position RMSE in the North and East components respectively; μV is the position RMSE in the height component. In the OS scenario, the horizontal accuracy estimator is always below 10 centimeters and is rather independent of the processing mode as the horizontal accuracy of kinematic positioning (μH = 7 centimeters) does not differ much from that of half-an-hour positioning (μH = 5 centimeters). When, in the future, actual Galileo E1 and E5 measurements can be used instead of simulated ones, it is likely that remaining unmodelled systematic errors slightly worsen the reported positioning accuracy. As usual, this can be overcome with differential positioning at the expense of loosing some precision. On the other side, an easy and robust procedure for absolute positioning is of interest for land surveying and cadastral mapping of vast areas. The mentioned values, even if they may seem optimistic because of their simulated origin, still fall comfortably within the specifications of the official Brazilian National Institute for Colonization and Agrarian Reform (INCRA) for all surveying categories down to the fundamental C1 ( μH = 10 cm). In Figure 4, the results of the kinematic positioning simulation exhibit a remaining systematic, rather constant and at the few cm level, error dominating the N and E horizontal components. The vertical error is much noisier than the horizontal one and this behaviour may indicate that further research on the overall modelling of the combined E5/E1 signals is required. However, model fine tuning in the absence of actual signals has its limitations and dangers and, therefore, no big effort has been devoted to this issue. Last but not least, vertical accuracy ranges between μV = 19 centimeters for kinematic positioning and μV = 12 centimeters, for the kinematic and half-an-hour static cases respectively. The same discussion applies here as for the horizontal case, when the actual Galileo signals become available.
Table 3 also contains the corresponding RMSE results for the TC case. As expected they are worse than those of the OS case and range between μH = 14 cm (kinematic case) to μH = 7 cm (half-an-hour static case). In all cases, they would meet the C2 INCRA category (μH = 20 cm). Vertical accuracy ranges from μV = 35 cm (kinematic case) to μV = 18 cm (static case, S-10) to μV = 0.07 (static case, S-30) although the last S-30 result is thought to be a lucky coincidence rather than a representative figure.
Table 3. Empirical results (errors) of point positioning for the E1/E5 combination (click to enlarge).
Conclusions and Ongoing Work
We have discussed the potential of the combination of Galileo E1 CBOC and E5 AltBOC pseudoranges for surveying and mapping applications in the frame of the international cooperation Galileo project ENCORE. Via simulations, we have investigated the tracking precision of the E1 and E5 pseudoranges under “open sky” and strong “tree coverage” scenarios resulting in 0.25 to 2.00 m (E1) and 0.02 to 0.08 m (E5) pseudorange precisions. We have further investigated the post-processed results — therefore with final precise Galileo orbits — in the OS and TC scenarios cases for kinematic and static modes and given preliminary results.
According to them, in the OS case, the positioning accuracy of the used E1/E5 combination and parameter estimation approach is at the cm-level for the E, N horizontal components and at the dm level for the height component. In the TC case, the accuracy estimates are at the low dm-level for the horizontal components and at the dm-level for the vertical ones. In the OS case, the INCRA C1 tolerances are met and in the TC case, the C2 tolerances are met. The accuracy estimates are at the low dm-level for the horizontal components and at the dm-level for the vertical one.
In the next months, up to the completion of the ENCORE project, we plan on extending the simulation analysis to the whole scenario spectra, with and without a complete Galileo constellation, with and without GPS L1/L5 measurements, in static and kinematic modes, in real-time and post-processing modes, and with precision and broadcast orbits. In parallel, we also plan to finish the E5/E1 ENCORE prototype receiver and software, a joint effort of DEIMOS Engenharia and OrbiSat da Amazônia, a Brazilian consortium member.
Acknowledgments
The reported research has been conducted within the “Enhanced Code Galileo Receiver for Land Management in Brazil” (ENCORE) project funded by the European Commission (grant 247939) with the aim to implement the 7th European Framework Program for Research and Development (FP7). The project runs from 2010 to 2012 and is realized by a European-Brazilian consortium lead by DEIMOS Engenharia (Portugal) and with participation of DEIMOS Space (Spain), the Institute of Geomatics (Spain), the Institute of Engineering Surveying and Space Geodesy of the University of Nottingham (UK), the São Paulo State University (UNESP, Brazil), OrbiSat da Amazônia (Brazil), Santiago e Cintra (Brazil) and MundoGeo (Brazil).
Ismael Colomina is director of the Institute of Geomatics (IG) of Spain, holds a Ph.D. in mathematics from the University of Barcelona (UB), and is a member of GPS World’s Editorial Advisory Board.
Christian Miranda received his MSc in telecommunication engineering and management from Universitat Politècnica de Catalunya. He is a research assistant at the IG.
M. Eulàlia Parés holds an MSc in meteorology and vlimatology (UB) and an MSc in airborne photogrammetry and remote sensing (IG). She is a research assistant and PhD candidate at the IG.
Marcus Andreotti received a Ph.D. in engineering surveying from the University of Nottingham (UN), where he was a research associate at the Institute of Engineering Surveying and Space Geodesy (IESSG). He is currently with NovAtel, Canada.
Chris Hill is a principal research fficer at the IESSG, holding a Ph.D. in satellite laser ranging.
Pedro F. Silva received his aerospace engineering degree from Instituto Superior Técnico (IST), Portugal. He works at DEIMOS Engenharia as head of the GNSS Division.
João S. Silva received his aerospace engineering degree from IST. He is currently a project manager in DEIMOS Engenharia’s GNSS Technologies Division.
Tiago Peres received his MSc degree in Aerospace Engineering from Instituto Superior Técnico, Portugal. He is a Project Engineer in the GNSS Technologies Division of DEIMOS Engenharia
João F. Galera Monico is an associate professor at the Universidade Estadual Paulista (UNESP), Brazil. He is a researcher and consultant of the Brazilian Research Council (CNPq), FAPESP and CAPES.
Paulo O. Camargo is an assistant doctor at UNESP, developing his post-doctoral activities at the National University of La Plata, Argentina.
Antonio Fernandez received an MSc degree in aeronautical engineering from the Polytechnical University of Madrid (UPM) and an MSc in physics from the UNED University of Spain. He is head of GNSS Division in the Aerospace Engineering Business Unit at DEIMOS Space, Spain.
José M. Palomo received a telecommunication engineering degree from the UPM. He works in GNSS receiver technologies and OFDM (WiMax) communication systems at DEIMOS Space.
João Moreira is technical director of Orbisat da Amazônia Indústria e Aerolevantamento SA. He received his Ph.D. in microwave technology at at theTechnical University of Munich.
Emerson Z. Granemann graduated in cartographic engineering from the Universidade Federal do Paraná, Brazil. He is founder and chief executive of MundoGEO Publishing.
Carmen Aguilera is market development officer at the European GNSS Agency. She holds an MSc in telecommunications engineering.
Eric Gakstatter, Survey Scene and GIS editor, along with Gavin Schrock (Administrator, Washington State Reference Network) and Laurence Socci (ACSM/NSPS Government Affairs Consultant) will be guests on America’s Web Radio on Monday, February 27, at 11 a.m. Eastern Time to discuss the latest developments in the LightSquared/GPS interference debate as well as other GPS/GNSS issues.
The one-hour program is hosted and moderated by American Congress on Surveying and Mapping’s (ACSM) executive director Curt Sumner.
You can listen to the radio broadcast by visiting America’s Web Radio website. The show will also be recorded and available on the ACSM and GPS World websites for download.
ACSM, with its largest Member Organization being the National Society of Professional Surveyors (NSPS), was founded in June 1941 and is incorporated as a non-profit educational organization whose goal is to advance the sciences of surveying and mapping and related fields, in furtherance of the welfare of those who use and make maps. ACSM also encourages the development of educational programs and supports publications that represent the professional and technical interests of surveying and mapping. The society is comprised of four independently incorporated Member Organizations which include more than 5000 surveyors, cartographers, geodesist, and other spatial data information related professionals from private industry, government, and academia throughout the world. Each member Organization serves the specific interests of their respective members, while working collectively to achieve the overall goals of ACSM.
“We conclude that LightSquared’s proposed mobile broadband network will impact GPS services and that there is no practical way to mitigate the potential interference at this time.” These words from Lawrence Strickling (right), U.S. assistant secretary for communications and information and head of the National Telecommunications and Information Administration (NTIA), appear to signal the end of LightSquared’s run.
Strickling’s letter to Federal Communications Commission (FCC) chairman Julius Genachowski appeared in public on February 14. Later that same day, FCC spokesperson Tammy Sun released a statement from that agency that “the Commission will not lift the prohibition on LightSquared,” and that it plans to “vacate the Conditional Waiver Order, and suspend indefinitely LightSquared’s Ancillary Terrestrial Component authority.”
Together, the NTIA and the FCC share responsibility for controlling U.S. radio spectrum use and making band allocations. The FCC supposedly has final authority in these matters, although the NTIA, representing government interests, may swing the bigger cat in the room. LightSquared’s inability to satisfy the requirements of the Federal Aviation Administration (FAA), coupled with unremitting frowning and glowering from the Department of Defense, may have been the deciding factors — more so than the uproar among most GPS manufacturers. The FAA and the U.S. military, two key government entities with widely fielded GPS equipment and applications, constituted the backbone that the NTIA finally showed, although the military has been, with one notable exception, silent on the issue, and indeed is not mentioned in the NTIA letter.
Strickling’s eight-page NTIA letter recaps the background of our story, with a July 6, 2011 early climax: “The test results demonstrated that LightSquared’s then-panned deployment of terrestrial operations posed a significant potential for harmful interference to GPS services.” He continues with the history of the further NTIA testing of cellular GPS receivers, joint continued analysis by FAA and LightSquared of impact on aviation receivers, and testing of general/personal navigation GPS receivers by the Executive Steering Group of the Interagency National Executive Committee for Space-Based Positioning, Navigation, and Timing (EXCOM).
Strickling quotes a January 13 letter to him from Ashton Carter, U.S. deputy secretary for defense, and John Porcari, deputy secretary for transportation:
“It is the unanimous conclusion of the test findings by the EXCOM agencies that both LighSquared’s original and modified plans for its proposed mobile network would cause harmful interference to many GPS receivers. Additionally, an analysis by the FAA has concluded that the LighSquared proposals are not compatible with severl GPS-dependent aircraft safety-of-flight systems. Based upon this testing and analysis, there appear to be no practical solutions or mitigations that would permit the LightSquared broadband service, as prosposed, to operate in the next few months or years without significantly interfering with GPS. As a result, no additional testing is warranted at this time.”
But wait, we’re not done yet. Strickling calls for GPS receiver standards to be developed, citing the EXCOM’s decision that “federal agencies will move forward this year to develop and establish new GPS spectrum interference standards that will help inform future proposals for non-space commercial uses in the bands adjacent to the GPS signals.”
The FCC, in its concurrence statement to the NTIA letter, actually begins by reciting the mantras of “economic growth, job creation, and to promote competition . . . freeing up spectrum for mobile broadband,” and only graduallyl works its way around to its decision. This signals an ongoing, solid commitment to make further sallies in this area.
Jean-Yves Le Gall, chairman and CEO of Arianespace, and Didier Faivre, director of the Galileo Program and Navigation-related Activities at the European Space Agency (ESA), signed an agreement February 2 in London to launch satellites in Europe’s Galileo satellite positioning system by Ariane 5 launchers.
This agreement provides for the possibility of using Ariane 5 launchers in 2014 and 2015 to complete the deployment of the Galileo constellation. Arianespace will have launched the 26 satellites in this constellation using a combination of Soyuz launch vehicles (two satellites per launch), and Ariane 5 launchers (four satellites per launch). The contract for adapting the Ariane 5 launcher to enable simultaneous launch of four Galileo satellites was also signed today by the European Space Agency and EADS-Astrium.
The Galileo satellite launch contract is managed by ESA on behalf of the European Commission. The contract signing ceremony was also attended by David Willets, U.K. Minister of State for Universities and Science, and Antonio Tajani, Vice President of the European Commission.
These satellites, built by the team of OHB Technology of Germany and Surrey Satellite Technology, Ltd. of the United Kingdom, will be placed in a circular orbit at an altitude of 23,000 kilometers by Soyuz and Ariane 5 launchers operating from the Guiana Space Center in French Guiana.
Arianespace and its subsidiary Starsem have already orbited the Giove-A and Giove-B in-orbit validation satellites, thus securing the frequencies allocated to the Galileo constellation. On October 21, 2011, Arianespace launched the first two satellites in the constellation — built by Astrium during the IOV (In Orbit Validation) phase — using a Soyuz launcher at the Guiana Space Center.
With both Ariane 5 and Soyuz, Arianespace offers the best solution for launching the entire Galileo constellation, thus guaranteeing independent access to space for Europe, Arianspace said.
European Commission Vice President Antonio Tajani announced in London that the consortium led by OHB System AG and Surrey Satellite Technology Ltd. (SSTL) will build a further eight satellites for the European Union’s Galileo satellite navigation program under the supervision of the European Space Agency.
The new contract will see SSTL continuing its role as payload prime, assembling, integrating and testing the navigation payloads in the UK, whilst OHB System, as the prime contractor, builds the eight satellite platforms and executes the final integration of all the satellites in Germany. The SSTL-OHB partnership is already building fourteen satellites for the Galileo program and will draw on its heritage and experience to produce the additional satellites to demanding schedules.
Matt Perkins, SSTL Group CEO commented “SSTL has played a key role in the development of the Galileo program for nine years and we have the commitment, experience and track record to deliver this substantial contract. We are delighted to have been selected with our partner, OHB, to continue to play our part in building Europe’s operational navigation system.”
SSTL is assembling the Galileo program payloads at its recently opened purpose-built Kepler technical facility in Guildford, UK. Under the contract, SSTL is fully responsible for the construction and test of the navigation payloads. SSTL will manufacture the electrical harnesses and the electronics to interface the navigation payload with the satellite platform. The remaining payload equipment will be externally procured by SSTL from European and other suppliers. SSTL's payload solution is based on European-sourced atomic clocks, navigation signal generators, high power travelling wave tube amplifiers and antennas and will provide all of Galileo’s services.
Galileo is Europe’s own Global Navigation Satellite System (GNSS), providing real-time positioning, navigation and timing services with unrivalled accuracy and integrity. It will be interoperable with the American GPS system and Russia’s GLONASS system.
The Full Operational Capability phase of the Galileo program is managed and fully funded by the European Union. The Commission and ESA have signed a delegation agreement by which ESA acts as design and procurement agent on behalf of the Commission. The views expressed in this Press Release can in no way be taken to reflect the official opinion of the European Union and/or ESA. “Galileo” is a trademark subject to OHIM application number 002742237 by EU and ESA.
European Commission Vice President Antonio Tajani announced in London that the consortium led by OHB System AG and Surrey Satellite Technology Ltd. (SSTL) will build a further eight satellites for the European Union’s Galileo satellite navigation program under the supervision of the European Space Agency.
The new contract will see SSTL continuing its role as payload prime, assembling, integrating and testing the navigation payloads in the UK, whilst OHB System, as the prime contractor, builds the eight satellite platforms and executes the final integration of all the satellites in Germany. The SSTL-OHB partnership is already building fourteen satellites for the Galileo program and will draw on its heritage and experience to produce the additional satellites to demanding schedules.
Matt Perkins, SSTL Group CEO commented “SSTL has played a key role in the development of the Galileo program for nine years and we have the commitment, experience and track record to deliver this substantial contract. We are delighted to have been selected with our partner, OHB, to continue to play our part in building Europe’s operational navigation system.”
SSTL is assembling the Galileo program payloads at its recently opened purpose-built Kepler technical facility in Guildford, UK. Under the contract, SSTL is fully responsible for the construction and test of the navigation payloads. SSTL will manufacture the electrical harnesses and the electronics to interface the navigation payload with the satellite platform. The remaining payload equipment will be externally procured by SSTL from European and other suppliers. SSTL’s payload solution is based on European-sourced atomic clocks, navigation signal generators, high power travelling wave tube amplifiers and antennas and will provide all of Galileo’s services.
Galileo is Europe’s own Global Navigation Satellite System (GNSS), providing real-time positioning, navigation and timing services with unrivalled accuracy and integrity. It will be interoperable with the American GPS system and Russia’s GLONASS system.
The Full Operational Capability phase of the Galileo program is managed and fully funded by the European Union. The Commission and ESA have signed a delegation agreement by which ESA acts as design and procurement agent on behalf of the Commission. The views expressed in this Press Release can in no way be taken to reflect the official opinion of the European Union and/or ESA. “Galileo” is a trademark subject to OHIM application number 002742237 by EU and ESA.
Ashton Carter, U.S. deputy secretary for Defense, and John Porcari, deputy secretary for Transportation, have written an official letter to the assistant secretary of Commerce stating that “there appear to be no practical solutions or mitigations that would permit the LightSquared broadband service.” Carter and Porcari are co-chairs of the National Executive Committee for Space-Based Positioning, Navigation, and Timing. This represents the strongest intra-government statement to date on the issue.
Their letter further states that “both LightSquared’s original and modified plans for its proposed mobile network would cause harmul interference to many GPS receivers. Additionally, an analysis by the Federal Aviation Administration has concluded that the LightSquared proposals are not compatible with several GPS-dependent aircraft safety-of-flight systems.”
“No additional testing is warranted at this time,” the authors conclude.
They further propose to “draft new GPS spectrum interference standards that will help inform future proposals for non-space, commercial uses in the bands adjacent to the GPS signals.”
No response has emerged from either the Federal Communications Commission or the National Telecommunications and Information Administration, the two bodies charged with making a determination on the issue. But the letter appears to signal a coming end to a conflict that has occupied many, and tied up many resources and consumed many millions of dollars, for the past year.
One source commented off the record that “Our hope is this will be the end of the matter, and the FCC will withdrawal its initial approval and inform LSQ they must seek the 500 MHz in a different portion of the spectrum.”
Second Galileo IOV Satellite Transmits
On January 17, the E1 signal of the Galileo Flight Model 2 satellite (FM2, also known as GSAT0102) was successfully acquired and tracked by the researchers of the Navigation, Signal Analysis and Simulation (NavSAS) group at Politecnico di Torino / Istituto Superiore Mario Boella. The signal was received with a non-directive GNSS antenna, a commercial narrowband E1 RF front-end, and the N-GENE software receiver developed by the NavSAS lab.
Other research facilities and advanced GNSS companies around the world have also reported reception of a signal from this, the second in-orbit validation Galileo satellite, launched on October 21, 2011. The first IOV satellite, Galileo-ProtoFlight Model (PFM) began broadcasting in December.
FM2 currently transmits a Galileo Open Service signal on the E1 band using the Code Number 12 of the Galileo Interface Control Document (ICD). Acquisition and tracking results are reported in Figures 1, 2, and 3. The signal was received with a C/N0 of approximately 46.4 dBHz and a Doppler frequency shift equal to –2595 Hz.
Both Galileo craft were in view on January 17. Figure 4 shows both the estimated Doppler and C/N0 profiles obtained from multiple measurements performed on the same time interval.
As a final step, the demodulation of the E1b data channel has also been performed, checking the navigation messages for both the satellites. It has been noticed that, at the moment, the navigation messages present only two types of page: reserved (word type field with value 63) and type 0 (spare). Type 0 words have valid Week Number and Time Of Week fields. On the other hand, both the satellites broadcast a valid secondary code on their E1c pilot channels, compliant with the Galileo ICD.
— Fabio Dovis
FIGURE 1. Search space of the successful acquisition of the Galileo FM2 satellite (PRN 12).
FIGURE 2. Peak obtained acquiring the Galileo FM2 satellite.
FIGURE 3. Estimated C/N0 and correlation values obtained tracking the PRN 12.
FIGURE 4. Estimated Doppler and C/N0 profiles along multiple measurements performed on January 17.
More GPS III Birds, Launch, Checkout Awarded
The U.S. Air Force awarded Lockheed Martin a $238 million contract for production of the third and fourth satellites in the next-generation GPS III constellation.
In May 2008, the Air Force awarded Lockheed Martin an initial contract to design, develop and build the first two GPS III satellites. The contract also includes options for up to 10 additional spacecraft. With the most recent award, the GPS III team is now on contract to deliver four GPS III space vehicles, with the first launch scheduled in 2014. The Air Force has plans to build up to 32 GPS III satellites.
The Air Force also signed a $21.5 million contract with Lockheed Martin 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 will be integrated into the Raytheon-developed Next Generation Operational Control System (OCX). It 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 Col. Bernard Gruber, director of the GPS Directorate. “LCC will ensure we can launch in 2014, effectively closing the time gap between GPS III and the Next Generation Operational Control System.”
Lockheed Martin is the GPS III prime contractor with teammates ITT Exelis, General Dynamics, Infinity Systems Engineering, Honeywell, ATK, and other subcontractors.
Increase Proposed for GLONASS
A December 27 meeting in Moscow heard a proposal to expand the GLONASS constellation to 30 satellites and six orbital planes, among five other modernization options. The Presidium of the TsNIImash Council (Central Research Institute of Machine Building) is the arm of Roscosmos, the Russian federal space agency, responsibale for civil aspects of GLONASS.
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 problems. Adding three new planes to the constellation, each with two satellites, is the leading option, and will be considered in detail over the next few months.
It is not clear how the present GLONASS frequency-division multiple-access (FDMA) channel spectrum could handle 30 satellites. It appears that the current arrangement can only handle a maximum of 28 satellites. The concept would need support from the Russian Defense Ministry among others to go ahead.
Incomplete Compass ICD Released
China announced the official start of Compass operational positioning, navigation, and timing services to China and surrounding areas and released a test version of an interface control document (ICD) on December 27. The ICD is available in both Chinese and English in PDF format from the system’s website, www.beidou.gov.cn.
The nine-page test ICD is incomplete. It only describes the basics of the coordinate and time systems and the basic characteristics of the open service B1 signal transmitted as the in-phase component on the 1561.098 MHz carrier frequency, including the ranging codes assigned to different satellites. There is no discussion of the details of the navigation message or associated algorithms.
A spokesperson stated that the test version is being released to stimulate research and development work and promote applications as soon as possible, and that some aspects of the transmitted signals are not yet finalized or “cured” and that is why they are not discussed in the test ICD.
Leap Second
The International Earth Rotation and Reference Systems Service (IERS) announced that a positive leap second will be introduced into Coordinated Universal Time (UTC) at the end of June 2012. UTC will be retarded by 1.0 second so that the sequence of dates of the UTC markers will be:
2012 June 30 23h 59m 59s
2012 June 30 23h 59m 60s
2012 July 01 0h 0m 0s
UTC and all time scales based on UTC will be affected by this adjustment. However, GPS will not be adjusted physically. For GPS, the leap second correction contained within the UTC data of subframe 4, page 18 of the navigation message transmitted by satellites will change.
Before the leap second: GPS-UTC = +15s (that is, GPS is ahead of UTC by 15 seconds).
After the leap second: GPS-UTC = +16s (GPS will be ahead by 16 seconds).
Meanwhile, the International Telecommunication Union postponed until 2015 a vote on a proposal to do away with leap seconds completely.
The Czech government signed an agrement January 27 with the European GNSS Agency (GSA) for Prague to host the headquarters of the Galileo system. The signing took place during the Galileo Application Congress Prague 2012.
Paving the way for the Agency’s presence in the Czech Republic, the host agreement was jointly signed by Pavel Dobeš, minister of Transport, and Carlo des Dorides, executive director of the GSA, in the presence of Petr Nečas, prime minister of the Czech Republic and Antonio Tajani, vice president of the European Commission responsible for industry and entrepreneurship. The accord will see the GSA moved to Prague later this year.
The Galileo Applications Congress in Prague drew experts from around Europe and around the world to discuss Galileo and possible services. representatives of the European Union, the European Space Agency (ESA) and the GSA discussed their future roles in Europe's GNSS programmes, Galileo and EGNOS. The event also took place against a backdrop of key changes in how Europe's flagship GNSS programmes are governed.
"This is a good moment to take stock of where we are and where we are going with Galileo," said GSA Executive Director Carlo Des Dorides. "The focus is on the future, with an expanded mission for our Agency. What we can say now is that the future is bright; the market for new GNSS technologies and services, many of which you will hear about during this congress, will continue to grow, in spite of the current difficult economic conditions."
Under the current European Commission proposal for a new GNSS governance arrangement, the GSA would be charged with the commercialisation and exploitation of Galileo and EGNOS services, including the operations of the Galileo security monitoring centers to be deployed in the UK and France. The Commission itself would provide the policy framework and political support, while ESA would provide the engineering competence. And while some details still need to be clarified, including how the interfaces between these three bodies would operate, most opinions seem to be moving quickly into line with the proposal.
ESA Director General Jean-Jacques Dordain said the measure of Galileo's success will not be in the number of satellites placed in orbit but in the quality of its services. "The very existence of the GSA as the service provider is a key to this success," he said. "Working to support the GSA, therefore, will also be ESA's objective, and we are committed to seeing this happen."
“We invite comment on LightSquared’s petition, and establish a pleading cycle.” Thus spake the Federal Communications Commission (FCC), groping for a way forward in the ongoing LightSquared/GPS conflict. The FCC has opened an Internet docket for public comment on the LightSquared position that GPS users and receivers “do not merit legal protection from interference” created by LightSquared. The FCC asks for comments by February 27.
LightSquared asked the FCC in December to rule that GPS receivers and users “do not merit legal protection from interference” caused by the proposed wireless broadband service. Such interference has been amply demonstrated by comprehensive testing from May to October of last year. Opening the docket for public comment is the FCC’s way of fielding the LightSquared petition.
LightSquared claimed in its December 20 petition that GPS makers sell “unlicensed and poorly designed” receivers that improperly listen to LightSquared’s airwaves.
Jim Kirkland, general counsel of Trimble Navigation Ltd. and head of the Save Our GPS Coalition, responded that Congressional directives bar the FCC from clearing LightSquared before questions of GPS interference are settled. The company’s December requests consists of “gross mischaracterization of prior FCC decisions,” Kirkland stated. “LightSquared and its predecessors have never been allowed to interfere with GPS.”
Parties are invited to file comments in response to LightSquared’s petition for declaratory ruling in IB Docket No. 11-109 or ET Docket No. 10-142, no later than February 27. Parties may file replies in response to those comments in IB Docket No. 11-109 or ET Docket No. 10-142, as appropriate, no later than March 13.
Click here for the FCC Public Notice, “International Bureau Establishes Pleading Cycle for LightSquared Petition for Declaratory Ruling.”
On January 17, the E1 signal of the Galileo Flight Model 2 satellite (FM2, also known as GSAT0102) was successfully acquired and tracked by the researchers of the Navigation, Signal Analysis and Simulation (NavSAS) group (Politecnico di Torino / Istituto Superiore Mario Boella) for the first time at 11:54:10 CET (10:54:10 UTC).
This signal has been received at the Istituto Superiore Mario Boella (ISMB) premises (located in Torino, Italy, latitude = 45°03'54.99" N, longitude = 7°39'32.29" E, height = 311.97 meters) with a non-directive GNSS antenna, a commercial narrowband E1 RF front-end, and the N-GENE receiver, a fully software receiver developed by the NavSAS researchers.
The FM2 satellite currently broadcast a Galileo Open Service signal on E1 band using the Code Number 12 of the Galileo Interface Control Document (ICD). It is the second of the two Galileo In-Orbit Validation (IOV) satellites launched on October 21, 2011. The first IOV satellite — the Galileo-ProtoFlight Model (PFM) spacecraft — was received by NavSAS researchers for the first time on December 12.
Both the PFM and the FM2 satellites were in view January 17, and their E1 signals have been successfully received and processed.
Figure 1 and 2 show the orbits of the two Galileo satellites at the moment of the signal acquisition. These screenshots have been produced by a free software tool (Orbitron, by Sebastian Stoff). In Figure 1 the two satellites, denoted as GALILEO-PFM GALILEO-FM2, are visible. Figure 2 shows a detailed skyplot computed in Torino, Italy.
Figure 1. Galileo IOV satellite orbits at the moment of the signal acquisition.
Figure 2. Skyplot of Galileo IOV satellite orbits at the moment of the signal acquisition.
The Galileo FM2 satellite signal (PRN 12) has been successfully acquired for the first time at 11:54:10 and the first acquisition and tracking results are reported from Figures 3 to Figure 6. It can be noticed that the satellite signal was received with a C/N0 of approximately 46.4 dBHz and a Doppler frequency shift equal to -2595 Hz.
Figure 3. Search space of the successful acquisition of the Galileo FM2 satellite (PRN 12).
Figure 4. Zoom on the peak obtained acquiring the Galileo FM2 satellite (PRN 12).
Figure 5. Estimated C/N0 and correlation values obtained tracking the PRN 12.
Figure 6. Estimated Doppler values obtained tracking the PRN 12.
Also, the Galileo PFM satellite was in view on January 17, and the signals from both satellites have been measured and compared by the NavSAS researchers. Figure 7 shows the elevation patterns of PFM and FM2 satellites as obtained from prediction visibilities based on NORAD tracking information (two-line elements of Galileo satellites downloaded on January 17). Figure 8 shows both the estimated Doppler and C/N0 profiles obtained from multiple measurements performed on the same time interval: their trends agree with the satellite elevations shown in Figure 7.
Figure 7. Elevation pattern versus time of the PFM and FM2 satellites over Torino on January 17.
Figure 8. Estimated Doppler and C/N0 profiles along multiple measurements performed on January 17.
As a final step, the demodulation of the E1b data channel has also been performed, checking the navigation messages for both the satellites. It has been noticed that, at the moment, the navigation messages present only two types of page: reserved (word type field with value 63) and type 0 (spare). Type 0 words have valid Week Number and Time Of Week fields. On the other hand, both the satellites broadcast a valid secondary code on their E1c pilot channels, compliant with the Galileo ICD.
Join GPS World’s Survey and GIS Editor Eric Gakstatter March 15 for the webinar, “Everything Else but GPS: How GLONASS, Galileo, and Compass Will Affect High-Precision Users.” The webinar will be held at 10 a.m. Pacific (1 p.m. ET/6 pm. GMT); registration is free.
“We conclude that LightSquared’s proposed mobile broadband network will impact GPS services and that there is no practical way to mitigate the potential interference at this time.” These words from Lawrence Strickling (right), U.S. assistant secretary for communications and information and head of the National Telecommunications and Information Administration (NTIA), appear to signal the end of LightSquared’s run.
