Author: GPS World Staff

The System: NTIA, FCC Waiver No More on LS
“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.
March 1, 2012
Galileo’s Surveying Potential: E5 Pseudorange Precision

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^s_r or δI^s_r 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 P₁^s_r (E1 CBOC) and P₅^s_r (E5 AltBOC) can be modeled as

(1)

for i = 1,5, where ρ^s_r is the true geometric distance between satellite s and receiver r, c is the speed of light in a vacuum, δt^s is the given s satellite clock correction, R ^s is the relativistic “correction” for satellite s, T ^s_r is the modelled or given tropospheric delay, f₁, f₅ are the frequencies of E1 CBOC and E5 AltBOC respectively, I^s_r / f ²_i are the modelled or given ionospheric delays, and b_i^s are the given biases for satellite s.

In the above pseudorange observation equation, we will estimate the receiver position X_r (included in ρ ^s_r ), the receiver clock correction δ^t_r, the correction δT ^s_r to the modelled or given tropospheric delay T ^s_r , the term δI^s_r related to the correction δI ^s_r / f²_i to the modelled or given ionospheric delays I ^s_r / f²_i, and the receiver frequency dependent biases b_ir. In equation 1, ρ^s_r 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: δ^t_r is a random walk with rather large driving white noise variance [rw (∞)]; δT ^s_r as rw (0.0152 m2), PSD level; b_ir as rw (0.00172 m2), PSD level (b_1r is set to 0); and (I ^s_r + δI ^s_r ) / f²_i as rw (σ² m² ) 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 ^s_r the actual parameter to be estimated δI ^s_r and, specifically δI ^s_r , / f²_i 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 ^s_r . For δI ^s_r , / f²_i , 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/N_o 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=√ μ²_E + μ²_N where μ_E , μ_N are the position RMSE in the North and East components respectively; μ_V 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 (μ_H = 7 centimeters) does not differ much from that of half-an-hour positioning (μ_H = 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 ( μ_H = 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 μ_V = 19 centimeters for kinematic positioning and μ_V = 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 μ_H = 14 cm (kinematic case) to μ_H = 7 cm (half-an-hour static case). In all cases, they would meet the C2 INCRA category (μ_H = 20 cm). Vertical accuracy ranges from μ_V = 35 cm (kinematic case) to μ_V = 18 cm (static case, S-10) to μ_V = 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.

March 1, 2012
The Business — March 2012

Download the PDF.

March 1, 2012
Sensing Location: Software Receiver Estimates Signal States During Outages

By Hans-Georg Büsing, Ulrich Haak, and Peter Hecker

Future safety-relevant driver assistant systems demand vehicle state estimations accurate enough to match the position within a road lane, which cannot be provided by standalone GPS. A promising approach to meet the requirements is the fusion of standalone or differential GNSS measurements with vehicle sensor data like odometers or accelerometers. To achieve deeper sensor integration, a software GNSS receiver was developed at the Institute of Flight Guidance (IFF) that is able to use dead reckoning sensors to support its signal acquisition. This article presents an approach to estimate the signal states during outages based on the tightly coupled vehicle state, which reduces the reacquisition time and significantly increases the signal availability.

GNSS-based navigation is a key enabler for future advanced driver assistance systems (ADAS). Car manufacturers have identified automotive assistance systems as core devices to propose their uniqueness mainly in the luxury and upper-class market segments. While the precision and availability of loosely coupled single-frequency GPS navigation satisfies the requirements of typical route guidance systems, future automotive systems — especially those that enhance driving safety — are more demanding on positioning system performance.

The Institute of Flight Guidance (IFF) of the Technische Universität, Braunschweig, Germany, is involved in two research projects evaluating the performance of unaided traditional GNSS receivers coupled with vehicle sensor measurements such as odometers in a tightly coupled architecture. Besides these involvements, the IFF has developed a general-purpose software-based GNSS receiver allowing full access to signal processing routines.

The benefits of the tight sensor fusion are reliable state estimations even during total signal outages that are common in the automotive sector due to tunnels, parking decks, or urban canyons. In this architecture, the GNSS receiver works autonomously to deliver raw GNSS-measurements only. Additional knowledge provided by the vehicle sensors cannot be used to support the receiver in any way. Besides other beneficial aspects in the tracking channels, additional external knowledge about the vehicle state has the potential to reduce acquisition times and improve the measurement availability significantly.

The Institute of Flight Guidance uses a software environment called “Automotive Data and Time-Triggered Framework” (ADTF) for research in the field of ADAS and automotive navigation. In this software framework, the overall system architecture is assembled with independent modules. These modules are implemented as libraries and loaded into ADTF. Data is exchanged via pins that are defined as public variables. The framework also attaches timestamps to the individual measurements and adds a data recording and playback functionality.

From a general-purpose software GNSS receiver, presented at the ION GNSS 2010, we have derived an automotive-specific ADTF software receiver module. The software framework adds the flexibility to synchronously process measurements from vehicle sensors additionally to the IF data from the front end. This gives us the opportunity to aid signal processing in the software GNSS receiver with additional external sensors.

For positioning, a tightly coupled positioning filter based on GPS raw data measurements and the rear-wheel odometers is implemented. The vehicle’s motion is modeled using a kinematic relationship between the vehicle sensors and the GNSS measurements.

Based on the tightly coupled vehicle state estimation, an acquisition state is processed during signal outages that enables the software GNSS receiver to reacquire the satellite signal instantaneously with high precision.

In this article, the constituent parts of the system are presented and the estimation of the acquisition state derived. The system was tested in an urban scenario, and the state estimations validated with the recorded measurements.

System Architecture

The software-defined GNSS receiver developed by the IFF was designed to process the computationally expensive signal correlation on an Nvidia graphics board using the vast parallel processing capability of graphics processing units (GPUs). With the use of common graphics boards, an entire receiver can be implemented on an ordinary PC, needing only a front-end to receive digital GNSS signals in an intermediate frequency (IF) band.

For research in the field of vehicle state estimation, a derivate of the software receiver of the Institute of Flight Guidance has been implemented in the “Automotive Data and Time-Triggered Framework” (ADTF). The software is commonly used in the automotive industry for the development of ADAS. Figure 1 shows a typical system layout in ADTF. A central component of the framework is the ability to record and play back measurement data, which is indicated by the buttons on the left of the screenshot.

Figure 1. System Architecture in ADTF. (Click to enlarge.)

Within ADTF, the systems are assembled from modules that are shown as blocks within the graphical configuration editor. Standard modules such as the connection of common hardware are provided with the framework. Custom modules can be implemented in C++ by the user. Every module is implemented as a dynamic library (DLL) and interpreted by the framework. Modules can be featured with input and output pins.

These pins are implemented by using specific data types from the framework. The communication and data exchange between the modules is handled via these pins. They can be connected by graphically drawing connector lines in the configuration editor.

ADTF provides the user with classes for timing and threading. Processes can thereby be linked to the ADTF system time, which is especially important as the data replay can be slowed down or sped up for debugging.

The instantaneous reacquisition algorithm is based on a traditional approach of tightly coupling GNSS raw data with vehicle sensor measurements. The fusion is based on a kinematic model following the Ackermann geometry establishing the relationship between the vehicle’s motion and the respective measurements.

At each time step of an arriving measurement, the vehicle’s motion is predicted based on the last estimated state with an extended Kalman filter. The prediction is then corrected using either measurements from the vehicle sensors or GNSS raw measurements. The range and Doppler measurements are calculated in the tracking channels of the ADTF software GNSS receiver. The corrected vehicle state is then fed back into the kinematic model for the next update cycle.

In case the GNSS signal is lost in a tracking channel, a virtual tracking channel is initialized with the last calculated channel states. The change in the channel output is then predicted utilizing the change in the vehicle state and the current evaluation of the ephemeris. The schematic implementation of the channel state prediction is shown in Figure 2.

Figure 2. Schematic of Channel State Prediction. (Click to enlarge.)

Signal State Estimation

Using the tightly coupled architecture presented above, an estimated position and velocity can even be provided during total signal outages. Assuming that the last valid observation of a satellite signal is stored together with its respective time t_o and position, an estimation of the signal state (that is, Doppler frequency, code- and carrier-phase) based on the estimation of the vehicle state during the signal outage at time t₁ can be used for an instantaneous signal reacquisition. Using the ephemeris data provided by the respective GPS satellite the range between a user position x_u and the satellite x_sv can be calculated using the following terms
    (1)
and
(2)
with |…| indicating the Euclidian distance.

Therefore the change of the range can be obtained with equations (1) and (2):
(3)
Assuming an unbiased Gaussian error distribution of the measurements, the tightly coupled system provides an estimation of the covariance matrix of the vehicle state. Using only the submatrix
(4)
related to the vehicle position, the covariance of the user position along the line-of-sight to the satellite can be obtained with the Euclidean norm of the line-of-sight vector
(5)
and the law of error propagation:
(6)

Furthermore, using the law of error propagation, it can be shown that the variance of the change of range estimation in equation (3) is obtained by:
   (7)

With the last valid range measurement related to time t_o, the signal state at time t₁ can be obtained for the pseudo-range PSR
   (8)
and the carrier phase Φ:
    (9)

The resulting variance of these estimations can by expressed by
   (10)
and
   (11)
respectively. The estimate of the Doppler and the related variance can be obtained analogous.
Considering the variances of the estimation, it can be decided if the signal can be reacquired instantaneously or if the receiver has to find the signal using standard acquisition routines in a limited search space.

Experimental Validation

The Volkswagen Passat station wagon operated by the Institute of Flight Guidance was used to evaluate the performance of the proposed algorithm (see PHOTO.) The test vehicle is customized from the standard by adding an additional generator to meet the power requirements of the measurement and processing hardware. In addition, the Controller Area Network (CAN) is mirrored and open to access the data collected by the sensors of the vehicle. The relevant sensors include a longitudinal accelerometer, a gyro for measuring the yaw rate as well as the odometers of all four wheels. The test vehicle is equipped with a GNSS front-end developed by the Fraunhofer Institute for Integrated Circuits. It is capable of streaming L1, L2, and L5 RF samples via two USB ports. The sampling rate of L1 is 40.96 MHz at an intermediate frequency of 12.82 MHz.

Test Vehicle. A customized Volkswagen Passat was used to evaluate performance of the algorithm.

The vehicle sensor data is streamed via CAN to an automotive PC from Spectra. It is equipped with an Intel quadcore CPU, 8 GB RAM, a Vector PCI CAN device and 256 GB SATA solid state disk allowing up to 195 MB/s writing speed. Additionally, it has been equipped with an Nvidia GeForce GT 440 graphics board that is used for processing the GNSS RF data. This specific graphics board was chosen because it offers a comparably high performance of the GPU at relatively low power consumption.

Both GNSS RF data and data from the vehicle sensor network are streamed to an ADTF hard disk recorder. Due to the setup of the data acquisition, several challenges have to be solved. The first challenge is that the front-end needs to be used as hardware-in-the-loop. It is by itself not equipped with an automated gain control. Therefore, it is not possible to just stream the RF data but it has to be decoded, processed for adjusting the gain, and then stored to the hard drive.

Secondly, the recording setup needs to cover high data rates. The GNSS front-end streams approximately 20 MB/s. As the data needs to be decoded and processed for gain control, the expanded data rate for recording is ~40 MB/s. In total including vehicle sensor measurements, >2000 data packets per second are streamed to the recorder. Because this could not be done using mechanical hard drives, we used solid state disks that also allow data storage during times of high vibration.

Related to the before-mentioned challenges, an efficient thread management needed to be implemented. The software framework’s threading classes are utilized to parallelize the receiver processes. Additionally, it has arisen that a significant part of the processing time is taken by the data transfer to the memory of the GPU.

In order to prove the advantages of an odometer-aided reacquisition, an applicable testing scenario was chosen. To distinguish an odometer-based aquisition approach from a model-based approach, a trajectory was chosen that features a right turn of 90 degrees immediately after cutting off the GNSS signal. A model-based kinematic prediction would project the trajectory in the direction of the latest known heading derived by the GNSS solution. Only a sensor-based state estimation is able to resolve the right turn. The driven trajectory is shown in Figure 3.

The GNSS signal has been cut off for approximately 10 seconds, which is equivalent of a 75-meter drive on dead reckoning sensors only after the right turn.

Figure 3. Trajectory of test drive includes a 90-degree turn. (Click to enlarge.)

Results

The following plots in Figure 4 show the performance of the virtual tracking channels. The plots in the upper row show the pseudorange output over time. For vividness they have been corrected for the motion of the respective satellite that is dominant due to their high speeds. Over a short period of time the satellites’ motion relative to the receiver can be linearly approximated. The pseudorange measurements over time were fit using a linear regression. The respective value of the linear regression was then subtracted from the pseudorange and plot over time as shown in the figures in the second row, leaving only the approximated influence of the vehicle’s motion.

Figure 4. Modified pseudorange and Doppler results of the virtual tracking channels. (Click to enlarge.)

The Doppler measurements have been similarly compensated by just subtracting the minimum measurement. These modifications of the pseudorange and Doppler measurements allow a direct comparison of each other as the Doppler can be understood as the first derivate of the pseudorange over time.

The results of PRN 6 show that the Doppler estimate during the GPS outage smoothly fits into the surrounding measurements without any major outliers. The plot of the pseudorange shows a similar behavior. The pseudorange could have potentially been modeled using a dynamic prediction that is not based on vehicle sensors due to the limited dynamics on the pseudorange measurements.

The Doppler plot of PRN 16 shows a strong change in the relative velocity between satellite and receiver. If a further projection of the Doppler using a linear dynamic model would have been used instead of predicting with vehicle sensors, it would likely have misled the reacquisition by ~ 50 Hz. The trend in the pseudorange measurements is comparable to PRN 6 at a higher rate of change.

The plots of PRN 21 probably show the advantages of using vehicle sensors for reacquisition best as the dynamics on pseudorange and Doppler are the most significant in the group. Both pseudorange and Doppler show a turning point during the GNSS outage. Especially, the pseudorange would have been mismodeled using a kinematic predicion that is not relying on additional sensors.

Conclusion

In this article, a tightly coupled positioning system implemented in the automotive-specific framework ADTF was presented that is based on the fusion of standard automotive sensor data and software receiver measurements. We showed that, using the tightly coupled solution, an acquisition state during signal outages can be estimated that allows the tracking channels to reacquire the signal instantaneously without the need of computationally expensive acquisition routines.

Under the assumption of a tightly coupled RTK position and small outage times, a reacquisition of the carrier phase without loosing the information about the phase ambiguity seems possible.

In the next version of the automotive GNSS receiver, the authors are planning to integrate the vehicle sensors to aid the tracking loops, which is likely to further improve tracking continuity especially in scenarios with high vegetation. Additionally, we plan to show that the implementation is capable of working in real time. Improvements of the initialization of the virtual tracking loops are also intended.

Acknowledgments

This article is based on a paper presented at ION-GNSS 2011, held September 19–23 in Portland, Oregon.

This work was funded by the Federal State of Lower Saxony, Germany. Project: Galileo – Laboratory for the research airport Braunschweig.
The authors would like to thank their colleagues working in the automotive navigation group for continuous support with the ADTF framework.

Hans-Georg Büsing holds a Dipl.-Ing. in aerospace engineering from the Technische Universität Braunschweig and has been a research engineer at IFF since 2008. He works in the area of applied satellite navigation, especially in the field of vehicle positioning.

Ulrich Haak holds a Dipl.-Ing. in mechanical engineering from the Technische Universität Braunschweig and joined IFF in 2008 as a research engineer. He works in the areas of receiver design and positioning algorithms.

Peter Hecker joined IFF in 1989 as research scientist. Initial focus of his scientific work was in the field of automated situation assessment for flight guidance. From 2000 until 2005, he was head of the DLR Pilot Assistance department. Since April 2005, he has been director of IFF. He is managing research activities in the areas of air/ground cooperative air traffic management, airborne measurement technologies and services, satellite navigation, human factors in aviation, and safety in air transport systems.

March 1, 2012
Letters to the Editor: Antennas and the Human Body

Antennas and the Human Body

We have been reading with much interest the Innovation column, “GNSS Antennas and Humans” (Innovation, February issue). As the interaction with the human body is something many companies designing GPS into their products do not consider, it is great to see this topic being given some recent attention. We do feel, however, that we should comment on some issues we see in the article, especially as one of our antennas has been used as part of the testing.

As rightly mentioned in the article, many of the products using GPS where performance close to the body is potentially an issue are consumer products. These typically are of small size or at very least have major space constraints placed on those designing them. As such it is very unlikely that they would use either a large active patch antenna or in fact an active antenna from Sarantel. In the vast majority of consumer applications, either smaller patch antennas (12 × 12 millimeters, maximum) will be used with smaller ground planes or even small chip or planar inverted-F antenna (PIFA) style antennas.

From a Sarantel perspective, we would recommend our smallest antenna, the passive SL1300, for these types of applications. In terms of how this would then affect the results of the test described in the article, our extensive testing of various antennas would suggest that with smaller patch antennas and linear antennas like chip and PIFA types, the impact of the body on antenna performance is greater than you would typically see with a large patch with a large ground plane. In addition, one of the reasons we would recommend our smaller antenna for this kind of application is because the ceramic material used has a much higher dielectric value than our larger products and as such is affected much less by the body or other interfering aspects of a product design.

As I mentioned, we have done extensive testing of various antennas, much of which is available through the Application Centre section of our website. Further information can be shared if it would be of interest to your readers.

— Chris Muir
Director of Sales, Sarantel Limited

Spectrum Swap

I read with interest your article today (Latest News, February 1) concerning LightSquared looking at a possible spectrum swap in the current Aeronautical Mobile Telemetry band, used heavily by both the DOD and commercial side, primarily for aircraft and missile testing. I found it more interesting that the DOD MIDLANT Area Frequency Coordinator had been contacted concerning the same.

First let me say that both the DOD and civil aviation and defense industries guard these bands quite strongly as individual users and via the Aerospace Flight Test Radio Coordinating Council (AFTRCC). AFTRCC is also the recognized non-government coordinator for these bands and resists any encroachment in these bands, while additionally allowing some temporary sharing when feasible.

Secondly, I would add the the DOD has seven total Area Frequency Coordinators geographically spread across the United States, so contacting one would serve little purpose. Additionally, the coordinators are members of the DOD Frequency Management Group who one would say is the DOD equivalent of AFTRCC and believe me, both organizations are on the same sheet of music when it comes to defending AMT for flight-test purposes and even meet jointly twice a year to do just that. Combined with the DOD and if one looks at the member companies of AFTRCC any attempt to wrest any portion ATM spectrum away from the aerospace industry and DOD would be an expensive and lengthy process.

This email does not constitute a response from either DOD or AFTRCC but that of a private citizen.

— Wayne Morris
Greenville, Texas

Privacy Matters

Good editorial (“When the Gavel Comes Down,” February issue). The three or four bases for the unanimous ruling in the instant case show a diversion of philosophy on this matter that is dangerous for resolution only through case and constitutional law.

You are dead right, legislation is needed at the federal level before a hodgepodge of states and other jurisdictions make up their own policies for a global utility with manifold applications affecting privacy and personal and intellectual property, for good and for evil; morally neutral technology, as always….not just GNSS but as in most instances, GNSS enhanced.

It would not be popular with the federal legislature, but I think some European Union deliberations on these subjects would be instructive for the U.S. Congress to heed in writing legislation. I wish that the White House and an interagency group like EXCOM could first take a non-political look at the trades and lead Congress, but that is unlikely to happen. Look at what nearly happened with the Software Owners Protection Act (SOPA) because of the lobbying power of media interests.

Truly we live in interesting times, also from the stress on our constitutional concepts which often use tortured analogies to keep the law inside the four corners of the constitution.

— James D. Litton
President/CEO, Litton Consulting Group, Inc.

March 1, 2012
Unmanned Air Systems: Precision Navigation for Critical Operations
Figure 1. Autonomous air refuleing operational view.

By Alison K. Brown, Dien Nguyen, and Paige Felker, NAVSYS Corporation, Glenn Colby and Frank Allen, PMA-268 NAVAIR

An alternative precision GPS architecture, Precision RELNAV, enables an airborne tanker plane and a Navy unmanned combat aircraft to navigate independently to a high degree of precision without requiring carrier-cycle ambiguity resolution using precision GPS ephemeris updates to a tightly coupled GPS/inertial solution onboard each aircraft. The solution rivals that of conventional relative kinematic techniques while providing more robust positioning that reduces message traffic between aircraft and does not require a long filtering time.

Naval Unmanned Combat Air System (N-UCAS) is the U.S. Navy’s program to demonstrate technologies and reduce risk for unmanned, carrier based strike and surveillance aircraft. The Unmanned Combat Air System Carrier Demonstration (UCAS-D) program is specifically maturing technologies for unmanned carrier operations and Autonomous Aerial Refueling (AAR). Successful demonstration of UCAS-D technologies provides for transition and risk reduction to future unmanned and manned programs.

A key enabler for N-UCAS is the ability to perform AAR so that the N-UCAS can support long duration missions. As shown in Figure 1, the intent is for AAR operations to mirror current manned Aerial Refueling operations as much as possible and to operate using existing Navy probe and drogue and US Air Force boom receptacle refueling methods.

The planned refueling architecture for probe and drogue and boom-receptacle refueling developed by PMA-268 is shown in Figure 2 and Figure 3. For both of these architectures, the GPS/inertial navigation system on the UAS and tanker are used to calculate a precise relative position to be used by the UAS to approach the tanker from astern. For drogue systems, the final connection to the basket is performed using aiding from a laser-based drogue positioning system. In addition, an optional machine vision system is used to aid both methods of refueling from the receiver. Under the UCAS-D demonstration program testing is being conducted with surrogate aircraft to verify the CONOPS procedures and performance of the precision GPS/inertial navigation solution alternatives being evaluated. NAVSYS is supporting this program through a Small Business Innovation Research (SBIR) contract and is demonstrating a Precision-RELNAV (P-RELNAV) tightly coupled GPS/inertial solution that improves the robustness of the relative navigation solution as described in the following sections.

Figure 2. Probe and drogue refueling architecture.

Figure 3. Boom receptacle refuleing architecture

Precision RELNAV Algorithm

The first method that PMA-268 implemented for computing a relative GPS solution used the GPS/inertial integration approach illustrated in Figure 4. The inertial navigation solution from both aircraft was used to calculate the relative inertial vector e that is used for the real-time AAR guidance. The tanker’s raw GPS observations are also passed over the data link to the UAS where a relative kinematic solution is calculated to derive the carrier-phase based relative position between the aircraft, a. This approach relies on solving for the integer carrier cycle ambiguities on the observations from the two aircraft using the same algorithms that were previously developed for use in performing GPS precision approach and landings on the carrier. The precise GPS relative position is then applied to calibrate the inertial derived relative position and the resulting GPS/inertial solution is used to calculate an offset to the center of the refueling envelope (u) for guidance of the UAS to connect to the receptacle.

Figure 4. Precision-GPS relative GPS positioning.

With the P-RELNAV approach shown in Figure 5, Precision GPS Ephemeris data is provided to both aircraft across the tactical data links using the NAMATH system. As shown in Figure 6, NAMATH provides global services across military tactical data links through the Joint Range Extension (JRE) to provide real-time corrections to the GPS system errors using Zero-Age Precision GPS Ephemeris data, which is refreshed by the GPS Control Segment every 15 minutes. The NAMATH system is currently being used operationally by the U.S. military to improve navigation accuracy and also precision weapons delivery.

Figure 5. Tightly-coupled P-RELNAV Solution.

Figure 6. NAMATH Precision Ephemeris Delivery.

Using the PGE corrections significantly reduces the errors on the GPS observations allowing the GPS/inertial solution to rapidly converge and not exhibit step changes during satellite transitions from the GPS system bias errors. The GPS/inertial Kalman Filter on the tanker is used to observe the residual errors from the GPS satellites being tracked, and these residuals (δf) are sent from the tanker to the UAS which applies these as an update to its internal GPS/inertial Kalman Filter. As shown below, this final correction sets both the tanker and the UAS on a precise common reference frame resulting in a high accuracy relative position being derived from the vector difference of the two tightly-coupled GPS/inertial solutions (e*).

Figure 7 shows the difference in the GPS position that is calculated using the Precision GPS Ephemeris as opposed to the Broadcast Ephemeris. This shows that over a month, there can be peak position excursions as high as 5 meters in the horizontal and 10 meters in the vertical based on the GPS broadcast ephemeris. With a GPS/inertial solution, these bias offsets will cause the solution to “trend” between different position bias offsets whenever the satellite selected set changes. This trending introduces significant errors into the relative inertial vector between two aircraft (e).

Figure 7. GPS Peak Position Errors from Broadcast Ephemeris Offsets (March 2010).

P-RELNAV Flight Test Set-Up

The P-RELNAV performance was tested using data collected on a UH-1 helicopter at Eglin AFB. Two independent GPS/inertial systems were mounted on the equipment plate below the aircraft (Figure 8) and a GPS reference receiver on the ground was used to calculate a kinematic position post-test using a Magellan ZXW receiver on the aircraft as a truth system. The PGE corrections were uplinked to the aircraft through EPLRS for use in calculating a PGE-corrected navigation solution. NAVSYS used recorded GPS and inertial data from a Kearfott KN4073 and a NovAtel/LN-200 inertial system provided by Dahlgren NSWC. The raw GPS (Pseudo-range and carrier phase) and IMU (high rate acceleration and angular rate) data was processed using our InterNav solution and also recorded for post-processing. This data was then played back through InterNav to calculate independent GPS/inertial tightly coupled solutions from the two inertial systems with and without the PGE corrections and to compare the performance of the absolute and relative solutions against the kinematic positioning truth data.

Figure 8. Flight test equipment.

P-RELNAV Flight Test Results

The P-RELNAV algorithms were implemented in our InterNav software package. This has been previously used to generate very high accuracy relative kinematic solutions for providing high-rate Time Space Position Information (TSPI) for instrumenting F-16 aircraft. The InterNav software was upgraded to apply the tightly-coupled GPS updates to the inertial solution using the PGE Zero-Age Differential GPS (ZDGPS) corrections, and also to apply the GPS residual updates (δf) in the UAS Kalman Filter to compute the P-RELNAV relative position solution.

Dual-frequency observations from the GPS receivers were used to correct for the ionospheric group delays in the solution.

The performance of the P-RELNAV solution was evaluated by comparing the results from the two independent inertial solutions for the same location on the UH-1 aircraft. Tests were conducted over multiple flights with the GPS antennas at different locations on the UH-1.

The results from the first flight test are shown in Figure 9 through Figure 13. Figure 9 shows the GPS/inertial results during the flight with a tightly-coupled solution but without PGE corrections. Figure 10 shows the GPS/inertial results during the flight with a tightly-coupled solution but with PGE enabled. Figure 11 shows the satellite visibility during the flight test. These plots show that the satellite geometry changes, dramatically affecting the inertial position covariance, whenever the satellites used in the solution change. The inertial filters these errors, but the relative solution is biased and drifts resulting in over 2 meter errors. In Figure 12 the same plot is shown when the PGE corrections are applied. This shows that the relative position error has been reduced to better than 1 m per axis and 35 cm 1-sigma. For flight critical operations, such as AAR, minimizing position excursions is essential. Figure 13 and Figure 14 show a statistical measure of the percentage of time that the data exceeds a horizontal or vertical threshold. This shows the benefit of the PGE corrections in removing GPS excursions caused by satellite ephemeris errors from the navigation solution. (See the Appendix for a definition of the Inverse Circular Error Probable (ICEP) metric and its comparison with other statistical measures).

Figure 9. Flight 1: Relative position of KN and NovAtel/LN200 GPS/INS solutions.

Figure 10. Flight 1: Relative position of KN and NovAtel/LN200 PGE enabled GPS/INS solutions.

Figure 11. Flight 1: Valid PRNs used in KN GPS/INS solution.

Figure 12. Flight 1: Relative Position of KN and NovAtel/LN200 PGE enabled GPS/INS solutions.

Figure 13. Flight 1: Horizontal ICEP comparison for PGE enabled GPS/INS and GPS/INS solutions.

Figure 14. Flight 1: Vertical ICEP comparison for PGE enabled GPS/INS and GPS/INS solutions.

Since both GPS receivers used in the test had a reasonably clear view of the sky, they were both tracking the same satellites. In the AAR CONOPS, the UAS approaches the tanker from below and so will have some satellites obscured from view by the tanker (see Figure 4). In this case, the use of different satellites can significantly increase the relative position error when PGE corrections are not available. In the case shown where one satellite was forced as a drop-out, the non PGE corrected vertical error grew to 4 meters for the relative solution.

Further improvements in the P-RELNAV performance will be achieved using the residual (δf) update mode in the InterNav Kalman Filter to set the estimated observation residuals for the common satellites to the same values for the UAS and Tanker GPS/inertial filters. This mode is currently being tested and the results will be presented in a follow-on paper.

Figure 15. Flight 1: Horizontal ICEP plot for PGE enabled GPS/INS and GPS/INS solutions. Different satellites tracked by the receivers.

Figure 16. Flight 1: Vertical ICEP comparison for PGE enabled GPS/INS and GPS/INS solutions. Different satellites tracked by the receivers.

Conclusion

The P-RELNAV solution has the following advantages over using a conventional relative kinematic positioning solution in meeting the Automated Aerial Refueling precision positioning requirements.
- Fast initialization — does not require time for carrier ambiguity cycles to be resolved.
- Robust operation during satellite obscuration by the tanker — is not dependent on common satellites being maintained in view between platforms.
- Insensitive to loss of carrier lock — does not require cycle ambiguity reinitialization if carrier lock is lost during the UAS approach to the tanker.
Work is proceeding on testing the P-RELNAV solution. Additional test data is being collected for performance evaluation under the UCAS-D demonstration program using dual aircraft as surrogates to demonstrate the P-RELNAV performance and compare the benefits of the P-RELNAV tightly coupled approach with the PGPS kinematic solution.

This work was sponsored under NAVAIR contract N68335-10-C-0094. The authors gratefully acknowledge the support of PMA-268 and the assistance of NSWC Dahlgren in collecting the flight test data and providing the truth reference for the P-RELNAV analysis.

Appendix: Inverse Circular Error Probable (ICEP)

For safety-of-life applications, the statistic of the excursion events, for example when a horizontal error is outside the safe error bound, is often more important than the knowledge of the percentage of points that are within a smaller error bound, such as CEP or DRMS. These excursion, or low probability, statistics can be examined with the Inverse Circular Error Probability (ICEP) function. The ICEP provides the horizontal position error (HPE) with a specified probability that a result could be outside this value. An optional input to the function is a filtering time constant, with the filter applied to the time-series horizontal error data before calculating the ICEP. This separates the effect of bias errors from short term noise errors that could be filtered (for example with an inertial unit) from the HPE.

HPE = ICEP (P%, τ)

Where
HPE= Horizontal Position Error value [m]
P% = Percent of total horizontal errors (x) that are larger than HPE
τ = filter time constant to reduce short term white noise

Note that the Circular Error Probable (CEP) which is the radial value that encloses 50% of the positioning results is closely related to ICEP, with
CEP = ICEP(50%, 0)

Also the R95 which is the radial value that encloses 95% of the positioning results is related to ICEP, with
R95=ICEP(5%,0)

Other common statistics used are the DRMS and 2DRMS values which are defined below, are also related to ICEP through the following equations.

For a Gaussian, uncorrelated error distributions with sigma of one meter in the range and azimuth axes, the ICEP is shown in Figure A-1 in blue. For each horizontal position error value, the ICEP gives the percentage of the distribution that has larger errors. Also shown on this plot are the CEP, DRMS, 2DRMS and R95 values which match the 1-sigma scale factors shown in the table above. Figure A-2 is the same data with a log₁₀ plot. In this plot the y-axis is probability rather than percent. This plot is useful for examination of outlier behavior, as it shows low probability events more clearly.

Figure A-1. ICEP(P,0) for a Gaussian Distribution with 1 m 1-sigma.

Figure A-2. Log Scale ICEP(P,0) for a Gaussian Distribution with 1 m 1-sigma.

Alison Brown is president and chief executive officer of NAVSYS Corporation, which she founded in 1986. NAVSYS Corporation specializes in developing next generation Global Positioning System (GPS) technology. She has a Ph.D. in mechanics, aerospace, and nuclear engineering from UCLA.

Dien Nguyen works for NAVSYS Corporation as a research engineer specializing in Kalman filtering estimations, kinematic positioning, and related navigational optimization techniques. He holds an M.S. in electrical engineering from Clemson University.

Paige Felker is a research engineer in the Algorithms and Analysis group at NAVSYS Corporation. She holds an M.S. in aerospace engineering from the University of Texas at Austin.

Glenn Colby is the chief architect for the Navy Unmanned Combat Air System at the Naval Air Systems Command in Patuxent River, Maryland. He has led the research, development, and testing of advanced aircraft, navigation and communications systems for more than 26 years. He received his B.S. in aerospace engineering with honors at the University of Virginia in 1984.

Frank Allen is the technology manager for the Navy Unmanned Combat Air System at the Naval Air Systems Command. In the last 16 years he has worked in management of research and development of advanced aircraft navigation and communications systems. Frank received his M.S. in physics from Northeastern University.
March 1, 2012
FCC Begins GPS Receiver Design Discussions with Workshop

The Federal Communications Commission (FCC) Office of Engineering and Technology will host a workshop on spectrum efficiency and receivers on Monday, March 12, and Tuesday, March 13, in the Commission Meeting Room at FCC Headquarters in Washington, D.C. The meeting is part of the FCC’s efforts to enhance the use of spectrum for mobile broadband — including LightSquared — and is being held in conjunction with the Wireless Telecommunications Bureau and the Office of Strategic Planning.

The role of receivers in enabling access to spectrum for new services implicates federal stakeholders, as well as the private sector, the FCC said in its announcement of the meeting. “Receiver performance issues have often arisen as a conflict between legacy stakeholders and new entrants where deployment of new technologies and services threatens to adversely impact an incumbent or place restrictions on the new entrant. Past examples include interference issues between new cellular radio systems and public safety radio systems, satellite digital radio systems and proposed terrestrial data services, unlicensed Wi-Fi systems and FAA weather radar systems, and ancillary terrestrial service on mobile satellite spectrum and GPS.

“The resolution of such matters has historically required a public process involving regulators, stakeholders and other parties. Because such discussions sometime begin upon the introduction of a new service or technology, full deployment of such new services could be hindered. New approaches to spectrum management focusing on spectrum efficiency and receiver performance may enable more assured deployment of new services and reduce the necessity for the involvement of regulators.”

The two-day workshop will discuss the characteristics of receivers and how their performance can affect the efficient use of spectrum and opportunities for the creation of new services, the FCC said. Key topics will include current practices for receiver design, case studies involving interference due to receiver characteristics, and approaches for promoting interference avoidance and efficient use of spectrum, given the current receiver base and potential future deployments. The workshop will include perspectives from licensees, equipment manufacturers, component providers, and other interested parties.

For more information, contact Michael Ha, Office of Engineering and Technology at (202) 418-2099 or by email: [email protected].

Accessibility Information. To request information in accessible formats (computer diskettes, large print, audio recording, and Braille), send an email to [email protected] or call the FCC’s Consumer and Governmental Affairs Bureau at (202) 418-0530 (voice), (202) 418-0432 (TTY). The public notice can also be downloaded in Word and Portable Document Format (PDF) a FCC.gov.

February 28, 2012
Gakstatter to Discuss LightSquared on America’s Web Radio February 27

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.

February 24, 2012
LightSquared Snuffed by NITA, FCC
The more than year-long battle between wireless start-up LightSquared and the GPS industry peaked earlier this week when the National Telecommunications and Information Administration (NTIA), tasked by the Federal Communications Commission (FCC) to study the potential interference problem between LightSquared’s mobile wireless proposal and GPS receivers, issued a statement and report with the following conclusion:

“The federal agencies and LightSquared have invested significant time and resources to identify and analyze proposed solutions to address the impact of LightSquared’s planned network implementations. Based on the testing and analyses conducted to date, as well as numerous discussions with LightSquared, it is clear that LightSquared’s proposed implementation plans, including operations in the lower 10MHz would impact both general/personal navigation and certified aviation GPS receivers. We conclude at this time that there are no mitigation strategies that both solve the interference issues and provide LightSquared with an adequate commercial network deployment.”

Read the entire letter from the NTIA to the FCC here (pdf).

Read the NTIA technical report here (pdf).

The FCC subsequently issued a statement including the following paragraph:

“NTIA, the federal agency that coordinates spectrum uses for the military and other federal government entities, has now concluded that there is no practical way to mitigate potential interference at this time. Consequently, the Commission will not lift the prohibition on LightSquared. The International Bureau of the Commission is proposing to (1) vacate the Conditional Waiver Order, and (2) suspend indefinitely LightSquared’s Ancillary Terrestrial Component authority to an extent consistent with the NTIA letter. A Public Notice seeking comment on NTIA’s conclusions and on these proposals will be released tomorrow.”

As promised, the FCC subsequently opened a Public Notice seeking comments based on NTIA’s report and conclusions. View the Public Notice here. Public comments close on March 1, 2012. If you have invested in GPS technology, you should enter your comments to protect your investment.

Submitting your comments to the FCC only takes five minutes. You don’t need to write an essay. Just state that you support the NTIA’s conclusion.

You can compose your comments in a text editor like Notepad, then save the file and attach it. Once you go to the FCC comment submission website, it will make sense. If you have any problems, email me.
1. Go to the FCC comment submission website by clicking here.
2. Type in the following information:
- Proceeding Number: 11-109
- Name of Filer: Enter your name
- Address Line 1: Enter your address
- City: Enter your city
- State: Enter your state
- Zip: Enter your zipe code
- Attach your comments
That’s it. Five minutes and you’re done.

You might have heard about another Public Notice that the FCC issued regarding LightSquared. It is in response to LightSquared’s petition to rule that GPS receivers are not entitled to interference protection. I wrote about it last week. You can read my article here. At that time, I was planning to submit my comments, but that was before the NTIA released its report and conclusions this week. I wouldn’t suggest you not enter a comment to the earlier Public Notice, but certainly I’d focus on entering comments on the latest Public Notice in support of NTIA’s report and recommendations.

For those of you who heard that LightSquared might have been a good idea in order to make wireless mobile Internet access more affordable, I have serious doubts about that statement. Here’s why…

Borrowing from my article last week, LightSquared is relying on Sprint’s infrastructure (~31,000 towers) for its terrestrial operations, and supplementing them with ~3,400 LightSquared towers at some point. I’ve used Sprint’s mobile phone service for about 12 years, and I used Sprint’s data card service for several years (not any longer). I pretty much know that Sprint is good for metro areas and poor for rural areas. Like other wireless providers (AT&T, Verizon, T-Mobile, etc.), Sprint is strong in some geographic areas, and weak in others. Since LightSquared is focused on serving people (densely populated areas) rather than geographic areas (e.g., farmlands), their terrestrial service is not going to be even close to being nationwide. LightSquared’s solution for areas not covered by their terrestrial service is to use satellite communications for internet connectivity. If you want to know more about this, read Tim Farrar’s blog on the subject, which includes a map of LightSquared’s terrestrial coverage. I’ve asked LightSquared for the most current deployment map, but received no response. I’ve been unable to find it even in their FCC filings (maybe you can), but I have to believe that if it was something to be proud of, they would be showing it to everyone.

Furthermore, in a huge FOIA (Freedom of Information Act) document release last week by the FCC, documents reveal what LightSquared was planning to charge their wholesale customers (not retail) when customers were out of range of their terrestrial system and forced to use LightSquared’s satellite for wireless broadband. The wholesale cost of their satellite broadband service was to be $10 per megabyte (not gigabyte), an astonishingly high price for a company that’s been touting affordable, nationwide wireless broadband Internet service. If you want to read for yourself, click here. You can read about LightSquared’s objections to the FOIA document release here.

LightSquared bankruptcy looming?

Of course, after the NTIA issued its report and conclusions this week, there were many rumors that LightSquared would soon declare bankruptcy. In response, LightSquared financier Phil Falcone told Reuters “It is clearly not on our table” and that “There are other ways around this.”

Other rumors include a proposed spectrum swap that GPS World reported two weeks ago. Although it’s tough to rule out anything, this would be quite a stretch, especially for the spectrum mentioned in the GPS World article (1515-1525 MHz) since it’s still close enough to LightSquared’s 10L signal (1526-1536 MHz) that failed to pass the NTIA’s interference testing that it would likely require another round of GPS interference testing. Furthermore, one of the NTIA’s sticking points was the potential interference from LightSquared’s mobile devices, which operate (uplink) in the 1626.5-1660.5 Mhz range, so that would need to be addressed as well.

The beginning of a new era of GPS/GNSS technology.

Included in the NTIA report was a recommendation that, with time, GPS receivers could be redesigned in order to accomodate LightSquared’s 10L signal.

NTIA also reported that during the January 13 Excom (Position, Navigation, Timing Executive Committee) meeting, it was agreed 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 and ensure that any such proposals are implemented without affecting existing and evolving uses of space-based PNT services vital to economic, public safety, scientific, and national security needs.”

In summary, GPS/GNSS receiver designs will change in the coming years and move towards more efficient use of spectrum. To me, a critical statement in the NTIA letter to the FCC is “without affecting existing and evolving,” meaning that not only should GPS be considered but also GPS-like systems from other countries such as Russia’s GLONASS, Europe’s Galileo, and other evolving satellite navigation systems and applications.

For the latest news, join me next Monday on the ACSM Radio Hour (Monday, February 20)

The LightSquared situation is still very fluid. There seems to be a new twist almost daily.

This past Monday, I was a guest on ACSM’s (American Congress on Surveying and Mapping) Radio Hour with Gavin Schrock and Laurence Socci, hosted by ACSM’s Curt Sumner. You can listen to a recording of the show here.

Due to the significant events that occured this week, I’m returning as a guest either next Monday or the following along with Gavin Schrock to discuss the latest developments. You can join us here at 8 a.m. Pacific/11 a.m. Eastern U.S. time on either day, or the show will be recorded and available for you to listen to at a later date.

Thanks, and see you next week.

Follow me on Twitter at http://twitter.com/GPSGIS_Eric
February 16, 2012
NTIA Thumbs Down LightSquared; FCC Concurs

“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.

February 15, 2012
Ariane 5 to Launch Galileo Constellation

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.

February 7, 2012
Ohio University Team Wins Second ION Autonomous Snow Plow Competition

Photo: Ohio University

An Ohio University team won the Institute of Navigation (ION) Satellite Division’s second annual ION Autonomous Snowplow Competition. The competition was held January 26-29, at Rice Park in downtown Saint Paul, Minnesota, in conjunction with the 126^th Saint Paul Winter Carnival.

Sponsored by The Institute of Navigation Satellite Division and held in cooperation with the ION North Star Section, the ION Annual Autonomous Snowplow Competition is a national event open to college and university students, as well as the general public, that challenges teams to design, build, and operate a fully autonomous snowplow using state of the art navigation and control technologies to rapidly, accurately and safely clear a designated path of snow.

Six teams participated during the four-day competition, each using unique vehicle design approaches.

Teams included students, partners from private industry and faculty advisors from Dunwoody College of Technology; Miami University (Ohio); Ohio University; The University of Michigan, Dearborn; and The University of Minnesota.

Teams were judged based upon their cumulative scores earned throughout the competition phases: 75% of the total score was based upon the plowing competition; and 25% of the total score was based upon the presentations and pre-event report.

First place was awarded to Ohio University students Samantha Craig, Ryan Kollar, Kuangmin Li and Pengfei Duan with support from faculty advisors Frank van Graas, Woulter Pelgrum and Maarten Uijt de Haag. The first place prize included $3,000 and a golden snow globe trophy.

Second place was awarded to Miami University students Chad Sobota, Mark Carroll, Robert Cole, Mark Stratis, with support from student advisors Steve Taylor, Ryan Wolfarth and Harrison Bourne and faculty advisors Jade Morton, Peter Jamieson and Janet Burge. The second place prize included $2,000 and a silver snow globe trophy.

Third place was awarded to the University of Michigan (Dearborn) students Angelo Bertani, Zach DeGeorge, Mark Lawrence, Doris Kotori, Alf Williams, with support from student advisors Benjamin Craig, Jhonatan Ferrer, and faculty advisor Narasimhamurthi Natarajan. The third place prize included $1,000 and a bronze snow globe trophy.

In addition, the first place team, Ohio University, will be invited to display their winning snowplow during ION GNSS 2012 Conference September 17-21, 2012 in Nashville, Tennessee.

Sponsors of the second annual ION Autonomous Snowplow Competition included Lockheed Martin Corporation, ASTER Labs, Inc, Honeywell, Inc., Alliant Techsystems Inc., U.S. Bancorp, Hitching Post Motorsports, Space Exploration Technologies Corp., and The Toro Company.

The Third Annual ION Autonomous Snowplow Competition will be held in January 2013 at the Saint Paul Carnival, St. Paul, Minnesota.

The First Place team from Ohio University. Photo: Ohio University

February 7, 2012