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B: Applications

Mobile RTK: Using Low-Cost GPS and Internet-Enabled Wireless Phones

Government regulation such as E911 and the promise of location-based services (LBS) are the biggest drivers for integrating positioning capability into mobile phones. The increasing sophistication of applications and refinement of map databases are continually tightening the accuracy requirements for GNSS positioning. In particular, location-based games and features such as “friend finder” sometimes require better accuracy than what is achievable with state-of-the-art network-assisted GPS (A-GPS) platforms.

Government regulation such as E911 and the promise of location-based services (LBS) are the biggest drivers for integrating positioning capability into mobile phones. The increasing sophistication of applications and refinement of map databases are continually tightening the accuracy requirements for GNSS positioning. In particular, location-based games and features such as “friend finder” sometimes require better accuracy than what is achievable with state-of-the-art network-assisted GPS (A-GPS) platforms.

Cellular standards for GPS assistance data exist for both control plane and user plane protocols. These protocols carry information that help the integrated GPS receiver to improve its sensitivity, speed up signal acquisition, and especially reduce the time to first fix. However, these approved standards do not contain sufficient information for the receiver to do carrier phase positioning.

Until now, no compelling reason existed for adding carrier phase positioning related features into cellular standards so that they could employ real-time kinematic (RTK) techniques. Generally, RTK-enabled devices on the market are expensive and intended primarily for geodetic and survey applications. Also, there has been no real need in the cellular world for the accuracy RTK provides. With evolving LBS applications, however, this situation is changing.

This article describes a solution called mobile RTK (mRTK), a system specifically designed and implemented for the cellular terminal use. Its design incorporates low-cost single-frequency A-GPS receivers, Bluetooth (BT) communications, and inertial sensors.

Basically, the technique involves exchanging measurements in real-time between two units — one designated as the reference and the other as the user terminal — and producing the best possible estimate of the baseline between the terminals using RTK techniques. We are developing the solution so that in the future it will be possible to add any other Global Navigation Satellite System (GNSS) measurements in addition to GPS measurements — or even instead of GPS measurements.

Using a simulator, we shall provide data that show it is possible to enable high-precision, carrier phase-based positioning in handsets with minimal additional hardware costs. Further, we shall describe some of the protocol aspects and especially the aspects of adding support for mRTK messaging to already existing cellular standards — GSM and UMTS. We believe that the mRTK solution will bring high performance to the mass market.

Moreover, additional GPS signals, such as L2C and L5, and other GNSSes such as Galileo will become operational in the near future. Consequently, it would be very beneficial to begin incorporating mRTK into the pertinent wireless standards now so that the infrastructure and the service providers will be ready when business opportunities present themselves.

. . .

mRTK Solution Overview
A plethora of RTK surveying solutions is available on the market today. Generally, they are characterized by the use of both GPS frequencies, L1 and L2, enabling ambiguity resolution in seconds over baselines of up to 20 kilometers, or even 100 kilometers with more time and under good conditions.  We must emphasize that this article does not claim to demonstrate similar performance and reliability as high-performance dual-frequency receivers.

We are designing the mRTK solution to work with low-cost, off-the-shelf GPS receivers with certain requirements (for example, the ability to report carrier phase measurements and data polarity). Therefore, performance degradations are expected in terms of time to ambiguity resolution, accuracy, and achievable baseline length.

. . .

Testing the System
The mRTK performance testing was accomplished using two identical hardware platforms containing 12-channel off-the-shelf high-sensitivity OEM GPS receiver modules and a 3-axis accelerometer. We constructed this test system to determine the physical limitations and requirements for the protocol and messaging aspects.

. . .

We conducted several experiments using the testing system and a GPS simulator. The simulator was configured to output data from the same eight satellites for both receivers with using several different baseline lengths varying from 0 meters to approximately 5 kilometers , and using scenarios for different GPS weeks.

. . .

Testing Protocol
The testing protocol used in the mRTK solution was designed specifically for use in research and development and as a reference design for proposed changes to the pertinent cellular standards. The protocol was designed to be as efficient as possible and especially to take advantage of the properties of TCP/IP. As TCP/IP already guarantees that transmitted data are error-free and also preserves the order of the data, our protocol did not need to include extensive error corrections and packet order counts.

. . .

Cellular Protocol Aspects
During the testing protocol design and implementation, several issues emerged concerning the addition of the mRTK feature into cellular protocols . . . User-to-user relative positioning is not recommended for control plane systems because it would require a lot of protocol and implementation work to get the binding of two terminals and relaying measurements between two terminals to actually work.

. . .

Future Work
This article has introduced a new concept called mobile Real-Time Kinematics and shows that RTK-like features are possible using low-cost components and existing cellular communication carriers. Even though a lot of development work remains on the mRTK algorithm side, the biggest challenge still involves cellular carriers and their standardization. Of course, even after standardization, the development of the infrastructure would require a huge effort.

Future work with the existing testing protocol includes more testing, especially field testing, and testing with different signal conditions and satellite constellations. The testing protocol itself should be modified with new features such as the VRS service. Using VRS, the baseline can always be kept very short, and accurate absolute positioning is available everywhere using mRTK.

One of the ideas that also need to be further developed is peer-to-peer protocols. In those protocols the mRTK measurements would be transmitted directly from one terminal to another without the use of a server in between.

As an example, this kind of protocol could be embedded into voice-over-IP (VoIP), in which the data channel for the voice encoding is already open and could easily accommodate other data transmissions that do not have strict real-time requirements, such as mRTK. Other peer-to-peer protocol means would exist, for instance, in WLAN, where the terminals are connected to the same subnet and would be able to open direct connections to each other.

The solution we have presented holds a lot of potential. Especially with the forthcoming satellite systems (e.g., Galileo and modernized GPS), the solution will significantly improve the accuracy of positioning in the mobile terminal. Nonetheless, the standardization of the mRTK features will require a lot of joint effort among terminal and network manufacturers and cellular operators.

For the complete story, including figures, graphs, and images, please download the PDF of the article, above.

This article is based in part on two papers, “Bringing RTK to Cellular Terminals Using a Low-Cost Single-Frequency AGPS Receiver and Inertial Sensors,” by L. Wirola, K. Alanen, J. Käppi, and J. Syrjärinne, and “Inertial Sensor Enhanced Mobile RTK Solution Using Low-Cost Assisted GPS Receivers and Internet-Enabled Cellular Phones,” by K. Alanen, L. Wirola, J. Käppi, J. Syrjärinne, presented at the IEEE/ION PLANS 2006 conference, © 2006 IEEE.


GPS III, Block IIF Programs Hit New Delays

The GPS program appears to be struggling on several fronts recently.

GPS III, the next-generation modernization project for the space and ground segments, is facing renewed uncertainty and possible schedule delays. At the same time, anticipated first launch of the follow-on block of satellites (Block IIF) with the new civil L5 signal has been postponed.

Read More >

By Inside GNSS

Civil L1 Signals: Galileo ICD, GPS L1C, New MBOC

Within weeks of a bilateral working group’s recommendation for a common civil GNSS signal design, the European Galileo and U.S. GPS programs have filed draft interface specifications (IS) or interface control documents (ICDs) for the new signals planned for the L1 frequency (around 1575 MHZ).

Read More >

By Inside GNSS
April 1, 2006

Using Maps as Automotive Sensors

Accurate real-time positioning is a necessary condition for many land transportation applications. But positioning alone cannot ensure successful and safer navigation, let alone higher-order driver assistance and awareness applications. The most common accessory to positioning is a map database — of more or less sophisticated design with greater or lesser data content and granularity.

Accurate real-time positioning is a necessary condition for many land transportation applications. But positioning alone cannot ensure successful and safer navigation, let alone higher-order driver assistance and awareness applications. The most common accessory to positioning is a map database — of more or less sophisticated design with greater or lesser data content and granularity.

Another resource and tool for navigation, route guidance, and advanced assistive systems is the application of geometrical principles to the positioning and mapbase data to anticipate or project upcoming conditions and events along a route.

This article introduces the map database as a sensor in driver assistance and awareness applications, which begin with a map-matched position and then look ahead from that position to determine the most likely driving path (MLP). From this calculation, we can support assistance and awareness applications such as curve speed warning, predictive adaptive front lighting systems, adaptive cruise control, and forward collision warning.

We will explore the role of MLP in these applications as well as its use in modifying route guidance instructions and map-matched positions. Finally, this article will also take up the question of map requirements and the navigation system interface needed for such applications.

Path Prediction
Adaptive cruise control (ACC) and forward collision warning (FCW) require systems that can determine the primary target in the host vehicle lane and then accurately estimate the geometry of the road between the host and the target vehicle. Curve speed warning (CSW) also requires knowing the geometry of the intended driving path to warn the driver of going too fast for the upcoming curve. Predictive adaptive front lighting can use the predicted road geometry to swivel the headlamps in the road curvature direction.

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Driver Assistance, Awareness
Visteon has used GPS and map databases as sensors. In a road departure crash warning (RDCW) field operational test funded by the U.S. Department of Transportation (DoT) and completed last year, Visteon developed a CSW functionality using a commercial navigation system and map database. The CSW system warns the driver when the vehicle is traveling too fast for an upcoming curve by processing the map database geometric and attribute information.

. . .

Land Vehicle Navigation
Route guidance is an essential feature in current land navigation systems. In this navigation feature, a driver feeds the navigation system with the desired trip destination. The route guidance algorithm calculates the route for the driver to follow. The driver may make mistakes in following the intended (calculated) route, and the route guidance system will have to adjust its instruction to correct this mistake.

. . .

Map Database as a Sensor
Current commercial map databases are designed for navigation purposes. The accuracy of these maps is sufficient for navigation in a large variety of road scenarios. However, they sometime fail in such situations as service drive/highway, highway/exit ramp, fork, complex overpasses, and mountain area/single road. All of these scenarios could lead to placing the vehicle on the wrong road or off the road.

. . .

Map database can provide detailed information of the road segment at the vehicle position and the road segments ahead of the vehicle. This information when processed can be used for advanced driver assistance and awareness applications Moreover, these systems should incorporate a map corrective/updating capability due to the changing nature of the roads and associated driving restrictions.

Map database errors can arise in such road scenarios as merging, road connections (overpasses), divided/undivided roads, and mountains areas In order to optimally use the map database, such error sources should be defined and modeled. Furthermore, inclusion of additional information such as height or elevation could extend the usage of the map for other automotive applications.  From a commercialization perspective, it is recommended to standardize the navigation system interface.

For the complete story, including figures, graphs, and images, please download the PDF of the article, above.


Builders Notes: Russian GLONASS at the Stage of Active Implementation

Modernized GLONASS-M satellite (left), A GLONASS-M satellite design (right)

On December 25, 2005, from the Baikonur Launch Site, there were three launched three navigation satellites belonging to the GLONASS system: one GLONASS satellite (the last of the first generation) and two new GLONASS-M satellites (see photo, above left).

This launch ensured the possibility of completing the flight tests for the modernized GLONASS system and performing the direct navigation determination using four GLONASS-M satellites simultaneously (two of these GLONASS-M satellites were launched earlier in 2003 and 2004).

On December 25, 2005, from the Baikonur Launch Site, there were three launched three navigation satellites belonging to the GLONASS system: one GLONASS satellite (the last of the first generation) and two new GLONASS-M satellites (see photo, above left).

This launch ensured the possibility of completing the flight tests for the modernized GLONASS system and performing the direct navigation determination using four GLONASS-M satellites simultaneously (two of these GLONASS-M satellites were launched earlier in 2003 and 2004).

Today, the orbital GLONASS constellation includes 16 satellites (12 GLONASS satellites and 4 GLONASS-M satellites). This article discusses the planned modernization of the GLONASS satellite navigation system with particular emphasis on the improved design of GLONASS-M satellites.

A New Commitment
The first satellite of the Russian navigation system GLONASS was launched on October 12, 1982, and the system was introduced into operation in 1993, being deployed to the complete constellation of 24 satellites in 1995. With 24 satellites in orbit, the GLONASS system can ensure the continuous global navigation for military and civil users by employing two types of signal: a signal of standard accuracy for civil users and a high-accuracy signal for military users.

When Russia faced new economical conditions in the 1990s, the financing for the space industry was reduced leading to the orbital GLONASS constellation reduction and decrease of its effectiveness.

Bearing in mind that the Space Navigation System GLONASS is a part of the national patrimony of Russia, in 2001 the president of Russian and the government of the Russian Federation ratified the policy directives setting out the intent to conclusively preserve and develop this navigation system. The Federal Target Program “Global navigation system” is one of these documents.

This program has been developed to be completed for the decade (from 2002 to 2011). During this period certain research and development activities shall be performed, including the ground experimental development for the prospective navigation spacecraft as well as flight and design tests; the ground control segment for the navigation system shall be modernized; the orbital constellation with the nominal number of satellites (24) shall be replenished.

GLONASS Modernization
The 10-year program of creation and operation of the modernized Russian Navigation System GLONASS space segment covers two stages: the current GLONASS-M satellites – at the first stage, and the proposed GLONASS-K satellites – at the second stage.

The GLONASS system is being modernized based on the following main conditions:

•     qualitative improvement of radio-navigation signal (introduction of the third frequency, increase in message rate, addition of new information into a navigation signal, etc), shift in the frequency bands keeping the possibility to work for the current existing users of the GLONASS system
•     improvement of the reliability and accuracy of the navigation support provided
•     increase of the satellite operation autonomy period and decrease of the level of the Ground Control Segment support needed to control the satellites
•     reduction of maintenance costs for satellite constellation as a result of increased satellite lifetime, reduced mass and resulted decrease of cost per satellite in-orbit
•     extension of the range of mission tasks to be performed.

With the preceding conditions implemented, there is kept the orbital configuration established earlier (three planes, with eight satellites in each plane), the orbital parameters (Н=19,400 km, i=64.8°, е=0) and the quantity of satellites in the nominal constellation (24 satellites). This enables the GLONASS operators to maintain the principles and methods of ballistic support of the satellite constellation and to provide the high-accuracy ephemeris.

New Generation Satellites
A GLONASS-М satellite, which is being developed at the first stage of the GLONASS Space navigation system modernization, has the following specific features as compared to a GLONASS satellite which is in use now:

1)     upgraded navigation radio signal
2)     implementation of intersatellite radiolinks to provide ranging measurements and data exchange between satellites located in the same plane and in different planes
3)     the stability of navigation signals increased up to 1·10-13 as a result of providing precision thermal stabilization of on board cesium frequency standards
4)     an improved dynamic model will decrease the level of unaccounted active forces impacting the satellite, mainly as result of increased accuracy of solar arrays pointing towards the Sun
5)     increased operational life of a satellite — up to seven years.

A GLONASS-М satellite can be injected into orbit by a cluster launch (three satellites by a single launch vehicle — see photo at the top of this article) from the Baikour Launch Site (using Proton LV and Breeze-M Booster) or by a single satellite launch from Plesetsk Launch Site using Soyuz-2 LV and Fregat Booster.

Spacecraft Design
A GLONASS-М satellite design (see Figure 1, above right) is based on a pressurized container inside which comfortable temperature conditions are maintained, ensuring the temperature range from 0 to 40°С, and local areas of temperature stabilization (near atom frequency standards) with ±1°С accuracy level. The temperature range is maintained by an active gas loop, shutter subsystem with electrical drivers and a set of controlled heaters. All dissipating mission equipment units are located outside the pressurized container on the antenna module in the areas not illuminated by the Sun.

Due to the fact that on board a GLONASS-M satellite there is a great amount of mission equipment units operating in the open space environment, the satellite design represents the intermediate stage between pressurized and non-pressurized design. In the nominal mode, the satellite longitudinal axis is continuously maintained pointed to the Earth, with accuracy of 0.5°, the satellite lateral axis is kept in the Sun-satellite-Earth plane with accuracy of ~0.5°, solar array axes are oriented towards the Sun with the accuracy of 2°. The orientation is provided by electrical wheels, periodically unloaded by electromagnets.

The propulsion subsystem being a single component thruster subsystem based on the catalytic thermal hydrazine separation method provides the possibility to form control torques within the initial orientation modes of the satellite, and to generate pulses for orbit correction. The orbit correction is performed after the satellite has been injected into orbit, while drifting to the designated orbital slot. High accuracy of the initial correction of orbital parameters allows keeping the satellite within the specified station limits (±5° latitude argument) without need for further corrections during the remaining lifetime.

An electric power subsystem based on nickel-hydrogen batteries and silicon solar arrays (30m2 area) provides electric power supply for onboard equipment of continuous stable voltage of 27+1-2 V and the power of up to 1400W, continuously in eclipse and illuminated orbit arcs. The onboard control subsystem based on an onboard digital computer provides data exchange between the equipment via MIL-STD-1553-B buses and performs the functions of control, diagnostic, intersatellite ranging data processing, calculation and generation of ephemeris time data.

For figures, graphs, and images, please download the PDF of the article, above.


Geodesy and Satellite Navigation

There has always been a love-hate relationship between geodesy and satellite navigation. Indeed, satellite positioning started life as an extension of terrestrial geodesy. When the first satellite, Sputnik 1, started orbiting the Earth in 1957, geodesists in several countries realised that satellites offered substantial potential as a geodetic positioning and navigation tool.

There has always been a love-hate relationship between geodesy and satellite navigation. Indeed, satellite positioning started life as an extension of terrestrial geodesy. When the first satellite, Sputnik 1, started orbiting the Earth in 1957, geodesists in several countries realised that satellites offered substantial potential as a geodetic positioning and navigation tool.

The basic technologies of terrestrial geodesy of the day, notably triangulation, traversing, and precise leveling, were slow and cumbersome, mainly because of the effect of the curvature of the surface of the Earth, which limited the range of measurements to theodolite observations between points situated on hilltops, observation towers, and triangulation masts.

The advent of EDM (electronic distance measurement) in the 1960s helped terrestrial geodesy, but it, too, was affected by the same limitation, namely the shortness of observable EDM ranges due to the Earth’s curvature.

Earth orbiting satellites did not suffer from this drawback. They could be viewed simultaneously from several points on Earth, and therefore direction and range measurements made, provided that the space vehicles were not obscured by high natural features or tall man-made structures. This led to several new satellite geodesy positioning methodologies.

The first of these was satellite triangulation, which was used initially to supplement and strengthen terrestrial triangulation networks. Satellite triangulation consisted of geodetic direction measurements derived from high power photographs of satellite orbits made against a stellar background of stars, with known right ascension and declination.

A few years later, this was followed by range measurements to satellites, made from Earth-bound EDM equipment to corner cube reflectors placed on the early satellites. The methodology used thus far was an extension of geodetic astronomy, with little reference to physical geodesy.

This situation changed significantly when geodesists realized that they could use the Doppler shift on the signal broadcast from a satellite to obtain differential range measurements that, together with the known Keplerian orbit of the satellite, could lead to a relatively fast positioning, or navigation, method. The Keplerian orbital motion of satellites is primarily based on the Earth’s gravity field, a subject of expertise by practitioners of physical geodesy.

This technical advance gave birth to Transit-Doppler, the first satellite navigation technology. Transit-Doppler was used in the late 1970s and early 1980s not only for the positioning of naval ships and of submarines surfacing in the polar regions, but also for the strengthening and scaling of national and continental terrestrial triangulation networks.

However, practitioners soon realized that positioning by Transit-Doppler to a reasonable degree of accuracy took several minutes, and, therefore, precluding its use as a full navigation methodology, which requires quasi-instantaneous positioning.

Enter GPS
These were the early days of a new global satellite positioning, navigation, and timing system, first called the NAVSTAR Global Positioning System, a name later shortened to just GPS. The rest is history. The early decision to base GPS on a constellation of 24 medium-Earth orbit satellites was taken on the advice, as you would expect, of geodesists at the U.S. Naval Surface Weapons Center in Dalgren, Virginia.

The close relationship between the early GPS and geodesy was further demonstrated by the adoption of WGS84, the World Geodetic System 1984, as the basis of the 3-D coordinate system of GPS. As GPS was born during the Cold War, it was declared a US military navigation system, with full access to NATO but only restricted access and down-graded positioning accuracies for civilian users.

This so-called Selective Availability (SA) gave the green light to the civilian geodetic community to come up with new methodologies that could counter the effects of SA. As always, human ingenuity did not disappoint, and two new differential techniques were developed. The first was the differential GPS (DGPS) technique, which improved relative positioning accuracies of GPS by at one order of magnitude, down to a few meters. As a result, DGPS soon became the standard methodology for the offshore positioning of oil platforms, pipelines, etc.

The next advance in improving the accuracy of satellite positioning was made on the advice of radio-astronomers, who proposed replacing the standard GPS pseudorange measurements, which are based on timing the modulated signal from satellite to receiver.

Instead, they suggested making measurements on the basic carrier frequencies of these signals, just as they did with extra-galactic signals arriving at, say, two widely spaced radio telescopes in so-called very long baseline interferometry (VLBI), leading as a by-product to the Cartesian coordinate differences between the two telescopes. This was the beginning of centimetric positioning by the carrier phase GPS method, which was later developed further by geodesists into kinematic GPS and centimetric navigation.

GPS had now become the universal high precision quasi-instantaneous positioning and navigation tool, creating the basis for hundreds of new applications. Again, geodesists led the way, concentrating on high precision scientific and engineering applications. These included surveying and mapping, positioning in offshore engineering, the monitoring of local crustal dynamics and plate tectonics, the relative vertical movements of tide gauges, and the continuous 3-D movements of critical engineering structures, such as tall buildings, dams, reservoirs, and long suspension bridges.

All of these applications required very high relative positioning accuracies, but not quasi-instantaneously as in the safety-critical navigation and landing of civilian aircraft. This came much later.

Geodesy and Navigation
Initially, GPS was considered as a standard navigation tool for military vehicles on land, sea, and air, but not for safety-critical civilian transportation. This was because, unlike military positioning and navigation, safety-critical civilian transportation not only requires quasi-instantaneous and accurate positioning, but also so-called “high integrity and good coverage.”

Geodesists will immediately realize that “integrity” stands for the geodetic concept of “reliability,” whereas “coverage” refers to the availability of a sufficient number of satellites that can be sighted by a receiver continuously and are not obscured by natural or man-made obstructions, such as high mountains, tall buildings, and the wings of an aircraft.

On its own, GPS cannot meet these requirements to the level required in safety-critical civilian transportation. Military transportation, on the other hand, has relatively modest requirements, which can be met by GPS. Indeed, you do not become a NATO Air Force pilot if you want a safe life. Flying as a passenger in a commercial airline is something else all together.

The penetration of satellite navigation, and primarily GPS, into civil aviation involved yet again, as you would expect, geodesists. They had to develop jointly with the civil aviation community the necessary theoretical and practical tools, which could be used to establish and quantify their requirements of accuracy, integrity, and coverage.

This involved the use of existing geodetic tools, such as the covariance matrix, the analysis of least squares residuals, and the well-established geodetic reliability measures. New tools were also introduced, such as the concept of RAIM or receiver autonomous integrity monitoring, based on the analysis of the least squares residuals.

Persuading Non-Geodesists
These geodetic tools, which were highly beneficial to the civil aviation community, initiated a fruitful, long-term collaboration between the two communities. However, this has not always been a straightforward and smooth relationship, and it involved — especially at the beginning — a deep suspicion of these “academic” geo-scientists. Here are a few notable examples of this love-hate relationship.

As a general rule, the existing civil aviation horizontal coordinates were based on latitudes and longitudes, with no particular reference to a reference datum. Heights in civil aviation were and still are based on barometric altimetry, on the assumption that all that matters is “the relative heighting between airplanes,” which is not affected significantly by a change in barometric pressure.

This assumption disregards, of course, the fact that the heights of natural features on the ground, such as mountains, do not change with changing barometric pressure. The first challenge was to convince the international civil aviation community that their horizontal coordinates, that is, latitudes and longitudes, required a proper geodetic datum and, as GPS was being contemplated as a future navigation tool, it made sense to adopt the same reference datum, namely WGS84. It took a while to convince the community to accept that.

The adoption of WGS84 led to the resurveying of most airports, runways, and various en route and landing navigation aids in order to bring them into WGS84, in preparation for the introduction of GPS. This led to the discovery of some large discrepancies, at airports and among navaids in many countries, between the existing horizontal coordinate values and their new WGS84 equivalents. Geodesists will be familiar with such occurrences, whenever they start dealing with a new community, whether they are civil or offshore engineers, oceanographers or meteorologists.

The first GPS receivers did not lend themselves to mass market adoption. Geodesists of a certain age will also remember some of the earliest commercial GPS receivers, such as the TI 4100 receivers, made by Texas Instruments. These early receivers operated by measuring sequentially four pseudoranges to four different satellites. Consequently, the receivers were programmed to first check the geometry of the satellites in view and decide on the best four in terms of geometrical configuration.

However, later on, with the emergence of new receivers that could measure all the available pseudoranges quasi-simultaneously, there was no need to carry on with measurements only to the “best four” satellites. One could track all available satellite signals and process these measurements by least squares, rejecting those with relatively large residuals, if any. This standard processing of observations is bread-and-butter stuff to surveyors and geodesists.

However, this was not the case with a number of navigation experts, who persisted on recommending the use of only the “best four” satellites for quite sometime, before they finally abandoned the practice.

A New Era of GNSS
Satellite navigation and positioning has changed substantially and significantly over the last 5 to 10 years. With Galileo in its development and in-orbit validation phase, the future developments in GPS IIF and GPS III, renewed interest in GLONASS, and satellite navigation initiatives in Japan, China, India, Australia, and several other countries, GNSS or the Global Navigation Satellite System is moving from being a concept, largely based on GPS alone, to a full global reality. A comprehensive program of GPS modernization currently under way aims to deliver significant improvements to both military and civil users.

The earliest mass-market applications of GPS involved road vehicles and mobile phones. In both cases, the twin aims are navigation (where am I, and how do I go to my destination?) and tracking (where is he, she, or it?). In the case of road vehicle tracking, successful applications include fleet monitoring (taxis or road transport companies), theft recovery of private cars, “black box” incident recorders, and the transport of hazardous or valuable cargoes.

Typically, most of these applications share three common features, namely prior knowledge of the proposed route, the continuous tracking of position and velocity by GPS, and the trigger of an alarm by a significant deviation.

Similarly, a number of GPS tracking applications use mobile phone technology (GSM or GPRS), but these are not as developed and widespread as vehicle tracking. Typically, these involve vulnerable people, such as young children, the elderly, key workers in some risky environments (for instance, railways), individuals with a chronic or contagious disease, and even VIPs.

Person tracking with GPS+telematics could also involve judicial cases (ordered by a court of law), of suspected criminals or anti-social elements. Other proposed applications include environmental information, location-based security, and location-sensitive marketing.

On its own, a GPS-enabled phone offers location and communication. This may answer the questions “Where is she or he?” and “Where am I?” but nothing more. However, when position and communication are combined with an appropriate geographic information system (GIS) database and a direction sensor, the combined system could answer two other very important questions, namely “What’s around me?” and “What’s that building over there?”

This could be achieved by a GPS+compass device, providing positional and directional data, which the mobile phone or the PDA transmits to a remote server. The server calculates the user’s position and identifies the building along the measured azimuth, gets the relevant information from the database, and sends it back to the client.

This is clearly valuable for the public utilities (water, gas, electricity, TV), shopping and leisure (restaurant menus, theater tickets), house hunting (details of the property advertised for sale), and of course, for visitors and tourists (museums, notable buildings, archaeological sites).

Leaving mobile phones aside, satellite navigation can also be used for location-based- security. For example, a briefcase or a portable PC can be programmed to unlock safely only in a specified location and nowhere else. This would minimize the risk of sensitive military or commercial material falling into the wrong hands.

Some working prototype systems already exist. Other location-and-context-based applications under consideration include the marketing and selling of goods, the reception of pay-TV, credit card security, spectator sports, road user charging and many others.

Indeed, the qualification of “critical application” is no longer restricted to safety-critical transportation, but it also applies now to financial-critical, legal-critical, security-critical, and business-critical applications as well. This creates a problem with standard off-the-shelf autonomous GPS receivers, which cannot operate indoors, because of signal attenuation and multipath.

Over the last few years, GPS chip and receiver manufacturers have tried, with some success, to develop high sensitivity GPS (or HS-GPS). The latest HS-GPS receivers, which incorporate up to 200,000 correlators operating in parallel, make it relatively easy to identify true pseudoranges from among the many signal and multipath reflections. Several manufacturers in the United States, Japan, Korea, and Europe, already advertise HS-GPS chips, and many other companies use such chipsets in their receivers.

GNSS Evolution
Like nearly all the technologies that preceded it, satellite navigation and positioning is going through the standard stages of development from birth to maturity. Older surveyors and geodesists may well remember the advent of EDM, using microwaves or lightwaves in the late 1960s and the 1970s. When the first EDM instruments were introduced, the distances measured were also measured with tapes, just in case.

Then came the second phase, when surveyors became fully confident about EDM and used it routinely for fast and precise range measurements. It took a few years and several critical mistakes in local mapping and national triangulation, to realize that EDM instruments could go wrong and that they had to be calibrated regularly in order to determine their accuracy and systematic biases.

The development of satellite navigation and positioning is following practically the same stages as EDM did 40 years ago. Only now we can formalize these successive stages of development of a technology and give them names by using Gartner’s famous “Hype Cycle Curve,” which was invented about 10 years ago in conjunction with new information technology products.

Using a simplified version, these successive stages of technology development are now formally called “Technology Trigger,” followed by “Peak of Inflated Expectation,” leading to “Trough of Disillusionment”, happily followed by the “Slope of Enlightenment,” and hopefully leading to the “Plateau of Productivity.”

As I write this, the first Galileo satellite, GIOVE-A, has been launched and tested successfully, opening a new era in satellite navigation. Hopefully, this will lead to the development of a large number of new critical applications — and involve close collaboration with geodesy and several other related disciplines — for the benefit of business, government and society.

Here is one last example about the strange relationship between geodesy and GPS. The U.S. delegation to the International Telecommunications Union (ITU) recently proposed to abolish leap seconds, and thus cut the link between Solar Time and Coordinated Universal Time (UTC) and ipso facto GPS Time.

At present, whenever the difference between UTC and Solar Time approaches 0.7 second, a leap second correction is made in order to keep the difference between them under 0.9 second. This is done every few years on the recommendation of the International Earth Rotation and Reference Systems Service, which monitors continuously the difference between Solar Time and UTC.

This leap second correction, which has to be applied every few years to GPS Time, apparently causes software problems because it has to programmed in manually. However, considering the difficulties that this change would cause to other scientific communities, such as astronomers, and even to users of GPS time itself for some critical applications, the U.S. proposal has now been postponed for the time being.

In conclusion, I must declare a conflict of interest. Although all the work I do at present involves GNSS, my academic background is clearly in geodesy. However, a change is in the air now, as safety-critical transportation is no longer the only critical application that has to be catered to. It has now been joined by several other emerging critical applications, notably financial-critical, legal-critical, security-critical and business-critical applications, which will also require nearly the same level of accuracy, integrity and coverage as safety-critical transportation.

This is where geodesy could step in again and create some new statistical tools, which will differentiate between the navigation and positioning systems on offer, and assess their suitability for the specific critical application.

For figures, graphs, and images, please download the PDF of the article, above.

March 2, 2006

White House Defense Budget Proposes GPS Funds

The Bush Administration’s Fiscal Year 2007 (FY07) budget proposal for the Department of Defense (DoD), announced in February, allocates $315,314,000 in advanced technology development for GPS, including work on the GPS III program. If approved by Congress, that would represent a sizable increase from the FY06 expenditures of more than $85 million and $33 million in FY05.

Read More >

By Inside GNSS
March 1, 2006

Carrier Phase Ambiguity Resolution, GNSS Use In Cellular Telephone Systems, and New Antennas?

Q: Will I need a new antenna for the new GPS and Galileo signals? Will one antenna work for both systems?

A: To answer these questions, information will be presented on the GPS and Galileo signal formats, some antenna basic fundamentals with various user applications in mind, followed by some predicted performance assessment.

Q: Will I need a new antenna for the new GPS and Galileo signals? Will one antenna work for both systems?

A: To answer these questions, information will be presented on the GPS and Galileo signal formats, some antenna basic fundamentals with various user applications in mind, followed by some predicted performance assessment.

The well known “Basic GPS” signals are centered at L1 (1575.42 MHz) and L2 (1227.60 MHz), with the GPS Coarse/Acquisition (C/A) code, at a chipping rate of 1.023 Mcps (million chips per second) on L1. The Precise (P) code is transmitted with a chipping rate of 10.23 Mcps on L1 and L2; if encrypted, it is then called the P(Y) or Y-code when broadcast at the 10.23 Mcps rate.

For these binary phase shift key (BPSK) modulated signals we often use the null-to-null bandwidth (twice the chipping rate) to characterize the signal bandwidth, which is 2.046 MHz and 20.046 MHz for the C/A and P(Y) codes that are transmitted in phase quadrature, respectively. Note that for many high performance applications we often require additional signal bandwidth to include the power in the sidebands of the signal spectrum. This is a very important factor in considering antenna bandwidth for a particular application.

(For the rest of Dr. Chris Bartone’s answer to this question, please download the complete article using the PDF link above.)

Q: How will the new frequencies in GPS and Galileo affect carrier phase ambiguity resolution?

A: In the years to come, GNSS users will benefit from the availability of more satellites and signals with the coming of Galileo and the modernization of GPS. Galileo will consist of a brand new constellation of 30 satellites transmitting their signals on four frequencies. Four different navigation services will be offered, meaning that some of the signals and information is available for free to every user, but other services are either to be paid for or are only available to certain authorities.

The first milestone for GPS modernization is the availability of the L2C code for civil users. In the next phase, the L5 signal will also be available.

GNSS positioning will thus be possible with improved precision, reliability, availability and integrity. Still, for rapid and high precision positioning, carrier phase ambiguity resolution remains indispensable. Only with the ambiguities fixed to their correct integer values do the carrier phase observations start to act as very precise pseudorange observations. This implies that the probability of correct integer estimation, generally referred to as the success rate, should be very close to unity.

(For the rest of Sandra Verhagen’s answer to this question, please download the complete article using the PDF link above.)

Q: Aside from E-911 and E-112, how is GNSS used in cellular telephone systems?

A: While mobile positioning for E-911 and E-112 emergency services are becoming more pervasive, other important applications of GNSS exist that are less obvious. These fall into two main categories: namely, those associated with direct mobile user applications based on the mobile’s location and those associated with enhancing the performance of the overall cellular network.

A plethora of user applications based on mobile location are rapidly emerging including street map and direction finding, fleet position data logging and targeted advertising. No dominant “killer application” has emerged at this stage, but the steady accumulation of these minor location-sensitive services is rapidly making GNSS an indispensable component of cellular functionality and markets.

The other main application category of GNSS in cellular telephony is associated with the enhancement of the overall performance of the wireless network infrastructure from the perspective of network capacity and quality of service. First-generation cellular wireless systems were based on time division or frequency division multiplexing.

(For the rest of Dr. John Nielsen’s answer to this question, please download the complete article using the PDF link above.)


Building Monitors

Severe loading conditions such as strong winds and earthquakes acting on modern tall buildings and structures can cause significant loads and vibrations. Recent trends toward slender, flexible, and light-weight buildings have left a large number of buildings susceptible to wind-induced motion. Furthermore, human perception of building motion has become a critical consideration in modern building design.

Severe loading conditions such as strong winds and earthquakes acting on modern tall buildings and structures can cause significant loads and vibrations. Recent trends toward slender, flexible, and light-weight buildings have left a large number of buildings susceptible to wind-induced motion. Furthermore, human perception of building motion has become a critical consideration in modern building design.

More complex building shapes and structural systems further accentuate eccentricities between the mass center, the elastic center, and the instantaneous point of application of aerodynamic loads, and consequently will generate significant torsional effects.

Verifying dynamic structural analysis requires the development of direct dynamic measurement tools and techniques in order to determine the natural frequencies, damping characteristics, and mode shapes. Among these tools accelerometers have played the most important part in analyzing structural response due to severe loading conditions. However, they provide only a relative acceleration measurement. The displacement from acceleration measurement cannot be obtained directly by double integration.

In contrast to accelerometers, GPS can directly measure position coordinates, thereby providing an opportunity to monitor, in real-time and full scale, the dynamic characteristics of a structure. GPS used in the real-time kinematic mode (GPSRTK) offers direct displacement measurements for dynamic monitoring. Earlier studies by the authors and other researchers, referenced in the Additional Resources section at the end of this article, have shown the efficiency and feasibility of structural deformation monitoring by combining accelerometer and GPS-RTK.

However, GPS-RTK has its own limitations. For example, the measurement accuracy can be affected by multipath and depends strongly on satellite geometry. Moreover, the typical GPS-RTK 20Hz sampling rate will limit its capability in detecting certain high mode signals of some structures. The new 100Hz GPS-RTK systems need to be further tested in order to ensure the independence of the measurements.

In order to exploit the advantages of both GPS-RTK and accelerometers, two data processing strategies have typically been used, namely to convert GPS measured displacement to acceleration through double differentiation and compare it with the accelerometer measurements (what we refer to as forward transformation), or to convert the accelerometer measurements into displacement through double integration and compare it with GPS measured displacement (the reverse transformation).

The latter approach is much more challenging because we have to determine two integration constants in order to recover all the components of displacement (static, quasi-static and dynamic). If the structure to be monitored is subject to a quasi-static force, as in the case of a typhoon, this further complicates the analysis.

Although earlier research has proposed a lab-based threshold setting for accelerometers to deal with the quasi-static issue, we believe that avoiding this procedure and developing new ways to recover the false and missing measurements from GPS by acceleration transformation would provide a preferred approach.

This article discusses recent efforts to design such a system based on a new integration approach that employs the correlation signals directly detected from a GPS-RTK system and an accelerometer to transform one form of measurement to the other. The methodology consists of a Fast Fourier Transform (FFT) for correlated signal identification, a filtering technique, delay compensation, and velocity linear trend estimation from both GPS and accelerometer measurements. We also present results derived from its installation on structures in Japan that subsequently experienced the effects of an earthquake and typhoon.

(For the rest of this story, please download the complete article using the PDF link above.)

January 1, 2006

GLONASS: The Once and Future GNSS

Once widely written off as another victim of the economic and political disarray following the collapse of the USSR, Russia’s GLObal NAvigation Satellite System (GLONASS) has arguably demonstrated the most stability of the world’s three GNSS programs in recent years.

Once widely written off as another victim of the economic and political disarray following the collapse of the USSR, Russia’s GLObal NAvigation Satellite System (GLONASS) has arguably demonstrated the most stability of the world’s three GNSS programs in recent years.

GLONASS followed the Global Positioning System into space with its first satellite launch on October 12, 1982, 4½ years behind the first GPS satellite went up. After reaching a high point in 1996 with more than two dozen operating satellites in orbit, GLONASS dwindled over the next five years to a nadir of seven operational satellites.

Strapped for cash and expecting a greater role in Europe’s Galileo project, Russia allowed paying commercial payloads from foreign customers to get in line ahead of GLONASS at its launch facilities. A dispute with newly independent Kazakhstan over maintenance, operation, and funding of the Baikonur launch facility further complicated the picture. Meanwhile, the relatively short design life of the spacecraft (three years compared to 7½ years for GPS) contributed to a rapid decline in operational satellites.

In 2001, a new Russian government under President Vladimir Putin reassessed its commitment to space-based positioning, navigation, and timing (PNT), and refashioned its development timeline to more sustainable dimensions. An August 21, 2001, decision committed the government to a 2002-2011 program to rebuild and modernize GLONASS.

A schedule of annual launches since then has doubled the constellation to 13 operational satellites. As a result, since 2001 the gap in worldwide navigation with GLONASS declined from 14 to 2 hours as of November with coverage 98 percent of the time over Russia, according to Sergey Revnivykh, an official with Roscosmos’ Satellite Navigation Department at the Mission Control Center of the Central Research Institute of Machine Building.

Picking Up the Pace

On December 25, Russia placed three more spacecraft into orbit and brought the system within striking distance of an 18-satellite constellation, which should be in place late next year with all satellites in service by early 2008. Under the current plan, the frequency of launches would increase over the next two years to provide a 24-satellite constellation by 2010–11.

The day after the December 25 launch, however, Putin expressed support for accelerating the GLONASS effort. According to the Russian Information Agency Novosti, Putin told government members, “The GLONASS system should be created before 2008, as it was originally planned. We have the possibility. Let us see what can be done in 2006-2007.”

RIA Novosti subsequently quoted Anatoly Perminov, head the Russian Federal Space Agency, as saying a proposal for earlier completion of the system would go to Putin before January 15, 2006.

Modernized GLONASS spacecraft (GLONASS-M) with a 7-year design life have flown on the launches since 2003. Two more went up with the most recent launch. Not well known is the fact that these include a second open civil signal at L2.

The availability of a second full open signal provides little practical benefit, however, because of the lack of user equipment outside the GLONASS control segment that can process the GLONASS L2 civil signal. New 72-channel chips recently announced by Javad Navigation Systems (the GeNiuSS) and Topcon Positioning Systems (Paradigm – G3) employ a common technical design that can process the GLONASS L2 signals, both C/A-code and P-code, as well as the new Galileo signals. Topcon has launched a new line of surveying equipment based on the technology, with the first product to be released as the NET-G3 receiver for reference station installations.

Technology, Policy, and Budgets

Unlike the Global Positioning System and Galileo, in which each satellite broadcasts a distinct code on the same frequency, GLONASS broadcasts the same code on different frequencies. At the L1 frequency, for example, the GLONASS open signal is spread between 1598.0625 MHz to 1607.0625, in sub-bands with signal peaks separated by 0.5625 MHz. This RF strategy requires broader swaths of increasingly rare radio spectrum and, at one point, brought the Russian system under pressure from radioastronomers and satellite communication systems that wanted to operate at the upper end of its RF allocation.

An agreement in the late 1990s committed Russia to an “antipodal” signal strategy that halved the number of bands on which satellites transmit their signals by assigning the same frequency to spacecraft orbiting on opposite sides of the Earth. This ensured that GLONASS receivers would not see conflicting signals on the same frequency, while allowing the bandwidth that it required to be compressed toward the lower portion of its allocation.

A 1999 presidential decree formally established GLONASS as a dual-use (civil and military) system, as is GPS. An Interagency Coordination Board comprised of civil and military agencies provides inputs from user communities, similar to the U.S. Interagency GPS Executive Board and its successor, the Space-Based PNT Executive Committee. The Russian Ministry of Defense (MoD) maintains and controls the system’s ground and space assets, although Roscosmos – the Russian Space Agency – acts as the program coordinator.

GLONASS receives funding directly from the Russian federal budget through line items in the MoD and Roscosmos agency allocations. Until recently, however, getting the funds through the civil agency remained problematical, according to Russian sources. The run-up in oil prices over the past couple of years has benefited Russia substantially. The nation produces and sells on the world market large quantities from its central Asian petroleum fields. President Putin has primarily used the funds to pay down indebtedness to the International Monetary Fund. Military programs, however, have received higher levels of support, which has translated into more stable funding for GLONASS, too.

Closing the Performance Gap

Shorter satellite survival on orbit has exacerbated the difficulty of sustaining the GLONASS constellation. All of the current operational spacecraft have been launched since 2000, and the mean mission duration (actual operational lifespan) is 4.5 years – about half that of GPS satellites.

Moreover, GLONASS performance has lagged behind GPS. A March 2005 study by the Swiss Institute of Science Research and Engineering, cited in a Tokyo symposium in November, reported that the accuracy of GPS ephemerides (the orbital locations of satellites broadcast as part of the navigation message) averaged about one meter compared to postprocessed tracking data from monitoring stations. In contrast, GLONASS ephemerides averaged about seven to eight meters.

In part, that reflects the more difficult challenge of tuning multiple signal/frequency combinations and accounting for the different propagation effects of carrier waves with slightly varying lengths. But the quality of on-board atomic clocks and system timekeeping, as well as weaknesses in the satellite navigation payload software and ground monitoring network, also contributed to the problem.

Now Russia is implementing an accuracy improvement program with modernization of satellites and ground infrastructure. Beginning with the GLONASS-M, manufactured by Reshetnev Applied Mechanics Research and Production Association (NPO-PM) in Krasnoyarsk, on-board clock stability over 24 hours has improved from 5×10-13 to 1×10-13. An improved dynamic model in the satellite navigation software will produce a lower level of unpredicted accelerations.

GLONASS-M spacecraft use previously reserved bytes in the navigation message to provide additional information, including the divergence of GPS and GLONASS time scales, navigation frame authenticity (validity) flags, and age of data information. Moreover, improved filters have been installed to reduce out-of-band emissions.

On the ground, GLONASS will also gain 3 stations from military tracking facilities and 9 to 12 from the Roscosmos network, much as the United States has done by incorporating National Geospatial-Intelligence Agency monitoring sites into the GPS tracking network. Both the United States and Russia are evaluating the utility and security of adding facilities from the International GNSS Service, an extensive network coordinated by NASA’s Jet Propulsion Laboratory in California.

New system clocks with high stability and improved systemwide synchronization will further improve GLONASS timing. Definition of the GLONASS coordinate system will tie it to the International Terrestrial Reference System, an international standard. As a result of these modernization efforts, Russian officials predict that GLONASS performance will equal that of GPS by 2008.

A new generation of satellites — GLONASS-K — is planned for launch beginning in 2008. These satellites will have a 10-year design life and carry a third civil signal at L3 frequency band, with a couple of frequency schemes under consideration in the 1198 to 1208 MHz band. Current plans for GLONASS-K include providing GNSS integrity information in the third civil signal and global differential ephemeris and time corrections to enable sub-meter real-time accuracy for mobile users.

Renewed Initiative

The recent progress in rebuilding and modernizing GLONASS appears to have bolstered the confidence of Russian officials in promoting the system internally and internationally. Russian state policy enacted last June mandates that, beginning in 2006, federal GNSS users employ only GLONASS or combined GLONASS/GPS receivers on Russian territory for aerospace and transport vehicles as well as for geodesy and cadastral surveying. And even before Putin’s recent remarks, Russia had re-engaged in several initiatives

The most recent round of talks with the United States led to a joint statement in December 2004 confirming that direct user fees would be imposed on civil GLONASS or GPS services and committed the two nations to ensuring the compatibility and interoperability of the two systems, implementing search and rescue functions using GNSS positioning, and cooperating on GNSS issues at international organizations.

On December 6, Russia and India signed an intergovernmental pact on the protection of classified military technologies during long-term cooperation under an agreement reached a year earlier for the joint development and peaceful use of GLONASS. This includes cooperation in GNSS ground infrastructure development and launch of GLONASS-M satellites on India’s Geosynchronous Satellite Launch Vehicle (GSLV). The GSLV design incorporates Russian rocket engine technology.

Finally, consultations with the European Union continue on a prospective Galileo/GLONASS agreement, with a technical working group scheduled to submit a proposal in April on signal compatibility and interoperability at the GLONASS L3 and Galileo E5b bands. Russian rockets will help launch Galileo satellites, including a Soyuz-Fregat used in the successful first launch of GIOVE-A on December 28 (See article on page 16.), and laser retro-reflectors produced by NIIPP, the Russian Scientific-Research Institute of Precision Instrument-Making, will measure the altitude of both GIOVE spacecraft to within centimeters.


The Perils (and Pearls) of Galileo

Successful launch of the first Galileo satellite on December 28 marks the culmination of a process that began almost exactly 13 years earlier.

Successful launch of the first Galileo satellite on December 28 marks the culmination of a process that began almost exactly 13 years earlier.

On January 19 the European Space Agency and Galileo Industries GmbH, the European company steering a consortium of more than 100 subcontractors, signed a €950 million (US$1.15 billion) contract that will pave the way for the operational deployment of Galileo. The contract calls for a mini-constellation of four satellites backed by an extensive network of tracking and control stations that will validate the design of the Galileo space and ground infrastructure. Four satellites are the minimum required to generate three-dimensional positioning and precise timing over the selected showcase sites.

In December 1992, however, Galileo was just a glimmer in a few visionaries’ eyes. That was the month that two European Commission (EC) directorates-general — those for transport and science, research, and development – decided to fund a modest study of satellite navigation options for Europe. The intervening years produced a kind of programmatic version of “The Perils of Pauline,” the cliffhanger serial movie in which each installment ends with the title character – a perpetual damsel in distress – placed in a situation that threatens her imminent demise, only to be rescued at the beginning of the next episode.

Galileo’s most recent “peril” revolved around a dispute between Germany and other members of the European Union (EU) over the allocation of contracts and responsibilities that they would have during the deployment phase of the system. A December 5 agreement on sharing Galileo operational and control centers among five nations rescued Galileo from the months-long impasse.

The next (but probably not final) act of the “Perils of Galileo” remains to be played out: the signing of an agreement with a consortium of companies that will complete the development of the space and ground segments and operate the system for the next 20 years. Current estimates place that milestone in the latter half of 2006, reflecting delays that have dogged the program since its inception and finally pushed its timeline for completion to 2010 – two years beyond the date long proposed by the EC and its Galileo partner, the European Space Agency (ESA).

Nonetheless, the launch of GIOVE-A, the experimental Galileo spacecraft built by Surrey Satellite Technology Ltd., marks a major—and probably irrevocable—step forward for the European GNSS. The start of transmissions from GIOVE-A and a second testbed satellite, GIOVE-B, manufactured by Galileo Industries, will allow the system to lay claim to use of the radio frequencies allocated at World Radio Conferences in 2000 and reaffirmed in 2003.

They will also allow ESA to evaluate on-orbit performance of several new satellite components and technologies and, significantly, also enable GNSS receiver developers to work with real signals in space. For example, GIOVE-B will be launched in the first half of 2006 and will have a passive hydrogen-maser clock as an additional payload, the first such clock ever flown into space. Current spaceborne clocks are cesium and rubidium frequency standards. Galileo satellites will also have rubidium clocks on board.

Political Merry-Go-Round

Several aspects of the €3.8 billion (US$4.6 billion) Galileo program distinguish it from its U.S. and Russian counterparts, GPS and GLONASS: full civilian control, a so-called public-private partnership (PPP) in its deployment and operation, international participation, and a multitude of services, including some that will be fee-based with guaranteed delivery of service. Indeed, the political challenges have long eclipsed the technical ones.

Fusing the interests of 15 (later 25) EU member-states, three additional non-EU ESA participants, and their leading industrial factors into a single enterprise has required a sustained exercise in what’s sometimes called “concertation.” Galileo represents the first Europe-wide infrastructure project and, consequently, challenged the EU and ESA to achieve a new level of political capability — within themselves and between one another. After the original 1992 satnav study, it took nearly seven years before Galileo even got its name in a February 1999 EC document, “Involving Europe in a New Generation of Satellite Navigation Services.”

Until then the program had been known rather generically as GNSS 2, distinguishing it from GNSS 1, the European Geostationary Navigation Overlay Service (EGNOS), a satellite-based augmentation of GPS and GLONASS. In May 1999 the ESA Ministerial Council approved the GalileoSat program; in June 1999 the EU Transport Council endorsed a first resolution on Galileo.

A November 22, 2000, EC communication to the European Parliament and European Council laid out the financing, organization, R&D, and implementation plan. In November 2001 the ESA Ministerial Council approved the development of Galileo (Phase-C/D, with a budget of €550 million). In May 2002 the Council authorized a joint undertaking, an institutional entity envisioned under Article 171 of the European Community Treaty but only implemented once previously, which allows the EU to collaborate in a single enterprise with non-EU bodies.

ESA and the EC (on behalf of the EU) comprised the initial membership of the Galileo Joint Undertaking (GJU), which has as its primary task the completion of a concession contract. Subsequently, non-EU governmental organizations representing China and Israel signed on with the GJU. Other nations, including Ukraine and India, are expected to join soon. The concessionaire will complete deployment of the Galileo satellites and ground infrastructure and operate the system over the next 20 years, monitored by a Galileo Supervisory Authority.

Final action to deploy the system only came with European Council action on December 10, 2004. Along the way, however, the growing EU-ESA cooperation on Galileo led to a broader initiative on a common European space policy. Late in 2003 the two institutions issued a White Paper on Space and signed a “framework agreement” for cooperation in space activities. Under the agreement, “the EC and ESA will launch and fund joint projects, participate in each other’s schemes, create common management agencies, carry out studies and jointly organize conferences and training of scientists, exchange and share experts, equipment and materials, and access to facilities.”

The overall cost of the Galileo system was first estimated at €3.4 billion, with a public investment for the development and validation phase of €1.1 billion divided between the EC and ESA. This phase was re-evaluated in 2005 at €1.5 billion.

The Art of the Deal

Currently, a “grand coalition” of leading European aerospace, telecommunications, and banking interests is negotiating with the GJU in a formerly competitive process that saw the merger of the two leading consortia in March 2005. Last month’s agreement on Galileo’s operational and administrative direction saw Eurely — a grouping led by Alcatel, Finmeccanica, and Vinci Networks — and the iNavSat consortium headed by the European Aeronautic Defense and Space Company (EADS), Thales, and Inmarsat, joined by a new consortium of Munich, Germany–based companies. The latter group, TeleOp, includes the commercial arm of the German Space Agency (DLR), the LfA Förderbank Bayern, and subsidiaries of EADS and T-Systems.

But the agreement didn’t come easily. Multi-sided talks by representatives of eight companies and five governments (France, Germany, United Kingdom, Italy, and Spain) would reach tentative accords at one level or with one group of negotiators but then fall apart when brought to another forum. Coloring the dialog were national ambitions to be seen as leading the Galileo program and the sensitivity to geographic return — the practice of spreading contracts and revenues among program participants in a proportion close to the contributions made by the various nations.

“Finally, we realized we can’t keep on fighting over these assets without getting an agreement,” Martin Ripple, director of Galileo Program for EADS Space Services, told Inside GNSS. “So, EADS said let’s put the all industrial players in one room and get the five governmental players into the same room. And lock them in until they come out with something.”

What they came out of the room with was a plan that reallocated key components of Galileo operations among the five leading space nations in Europe. The headquarters of the Galileo concessionaire will be located in Toulouse, France, with administrative and market development responsibilities. Inmarsat will have overall management leadership of the operations company based in the United Kingdom and responsible for global network operations, including performance monitoring and operations security. The two control centers (for constellation and mission) will be located in Germany (near Munich in Bavaria) and Italy (Fucino space center in Abruzzo region) along with two performance evaluation centers supporting the concessionaire headquarters. Spain will host backup control centers as well as facilities related to Galileo safety-critical applications.

“It’s a major step toward a concession contract,” says Ripple.

The Same, Only Different

On the technical side of the program, Galileo has entered the in-orbit validation (IOV) and development phase using the two GIOVE experimental satellites to test out ESA’s spacecraft design and ground control. The IOV phase will conclude with the deployment of four operational satellites in 2008. According to the current schedule, an additional 26 satellites will then be launched over the following two years with full operational capability (FOC) declared in 2010.

Galileo operational satellites will transmit signals in a variety of bands clustered around the 1176-1207 MHz spectrum near the GPS L2 frequency, 1775.42 MHz centered at the GPS L1 frequency, and 1278.75 MHz. The latter band lies at some distance from the GPS L2 signals at 1227.6 MHz, but would fall within one of the bands that Russia is considering for the third civil GLONASS signal that will begin broadcasting with launch of its new satellites in 2008.

Galileo signal structures include a combination of biphase shift keying (BPSK) and binary offset carrier (BOC) designs. (Current GPS signals are BPSK variations, but future signals will also be BOC-based.) Recently, the Galileo Signal Task Force has proposed the addition of a composite binary coded symbols (CBCS) design that superposes BOC and a binary coded symbol waveform with the same chipping rate.

Galileo will offer five services: a free open service; a fee-based, encrypted commercial service offering higher accuracy and service guarantees; a safety of life service the includes signal authentication and integrity alerts (targeting, for example, commercial aviation); a search and rescue service operating in near-real time with a return communications link possible; and an encrypted governmental service known as the “public regulated service” or PRS, which will be used by public safety agencies and, conceivably, military forces. Certification for safety of life services is scheduled to occur within a year after FOC.

This final point and the liability issues that it raises probably is the largest complication for the final negotiations in the concession contract. Sizing and sharing the risk associated with service guarantees introduces a problematical element to the Galileo project not faced by its GPS and GLONASS counterparts. As one participant in the deliberations has posed the dilemma: What do you do if a hiker in the Rocky Mountains gets lost and sues Galileo in front of a U.S. judge? Once signed, the concession agreement will lead to the phasing out of the GJU and the advent of the Galileo Supervisory Authority’s role. The concession contract also represents the turning point of the public-private partnership that marks Galileo as a different kind of beast from publicly funded GPS and GLONASS. The framework for negotiating the concession contract assumes a two-thirds contribution from the private sector for the €2.2 billion deployment phase and all of the €220 million annual expense of operating and maintaining Galileo.

Given the past history of the European GNSS initiative persevering and escaping perils — including self-created ones, the Galileo project will probably manage to solve the PPP riddle and get on with the (comparatively) simple task of building and operating a system.


Bold Advice: Report of the Defense Science Board Task Force on GPS

Secretary of Defense Donald H. Rumsfeld

DSB Task Force Members

Robert Hermann
, Global Technology Partners, LLC
James Schlesinger, MITRE Corporation

DSB Task Force Members

Robert Hermann
, Global Technology Partners, LLC
James Schlesinger, MITRE Corporation

Task Force Members
John Darrah, Institute for Defense Analyses
William Delaney, MIT Lincoln Laboratory
Arnold Donahue, National Academy of Public Administration
Kirk Lewis, Institute for Defense Analyses
USAF Gen. James McCarthy (Ret), U.S. Air Force Academy
Steve Moran, Raytheon Corporation
Ruth Neilan, NASA Jet Propulsion Laboratory
Robert Nesbit, MITRE Corporation
Brad Parkinson, Stanford University
James Spilker, Stanford University
John Stenbit, Private Consultant, former Assistant Secretary of Defense for Networks and Information Integration (ASD NII)
USAF Gen. Larry Welch (Ret), Institute for Defense Analyses

Executive Secretary
Ray Swider, ASD NII

Recommendations from a high-level Defense Science Board (DSB) Task Force on the Global Positioning System, if implemented, would profoundly alter the way that GPS is managed and operated: a significantly redesigned and enlarged satellite constellation, a larger contractor role in running the system, more focused responsibility and authority for GPS, and permanent elimination of Selective Availability.

A memo from U.S. Secretary of Defense Donald Rumsfeld, drawing on the task force analysis and recommendations, has been drafted to provide guidance to departmental leaders and the Air Force officials responsible for overseeing and managing the program.

The DSB presented the group’s analysis and recommendations in a 109-page report, “The Future of the Global Positioning System,” signed by Under Secretary of Defense Kenneth Krieg and released publicly in early December. In a far-ranging critique, the report identifies potential gaps in sustainment of the GPS satellite constellation, delays in upgrading the operational control segment, and diffuse lines of authority within the Department of Defense (DoD). It calls for changes in how the United States funds GPS, how DoD manages the system and acquires military user equipment, and how the U.S. Air Force contracts for modernized GPS infrastructure and operates the satellites.

The ultimate significance of the report probably depends on the willingness and perseverance of its co-chairs, former defense and energy secretary Jim Schlesinger, and former National Reconnaissance Office director Robert Hermann, to advocate vigorously for the product of the task force’s labors.

Schlesinger briefed Rumsfeld and Deputy Secretary of Defense Gordon England, who also co-chairs the National Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee (NPEC). The DSB report was on the committee agenda for its January 26 meeting.

Established by Krieg’s predecessor Michael Wynne, the task force’s objective initially had been framed to address competitive concerns in light of Europe’s move to implement its own GNSS, Galileo.

“Without significant DoD movement on GPS, the introduction of Galileo may marginalize GPS to an expensive military use only system,” Wynne wrote in an April 9, 2004, memo to DSB Chairman William Schneider, Jr.

Within a couple of months, however, the signing of a US/EU agreement on cooperation in GPS and Galileo matters broadened the focus of the task force — fortuitously, one might argue. President Bush’s policy directive on space-based positioning, navigation, and time further influenced the scope and emphasis of the group’s work.

An impressive mix of old GPS hands and former defense leaders comprised the task force — a gathering of what used to be known in less gender-sensitive days as “graybeards” or “wise men.”

“It was a unique confluence of expertise and leadership that we won’t have again for some time,” says Jules McNeff, vice president of strategy and programs for Overlook Systems Technologies, Inc., who staffed the task force and oversaw the drafting of its report. McNeff himself has more than 20 years invested in GPS, both inside and outside of DoD.

Rattling Cages
After 18 months of study, more than a dozen outside briefings, and deliberations, this “unique” task force produced a trenchant volume of solidly reasoned findings and recommendations (The full report can be download from the Internet at <http://www.acq.osd.mil/dsb/reports/2005-10-GPS_Report_Final.pdf>.)

Inevitably, such a collection of strong-willed, independent free-thinkers with a broad mandate produced some real zingers. Among those proposals:

•    Permanently eliminate Selective Availability (SA), the ability to degrade positioning accuracy in open civil signals “with the objective of deleting the hardware and software overhead for its implementation from throughout the future system.”

•    Change the constellation to a three orbital plane configuration with 30 satellites, rather than the current requirement of 24.

•    “Selectively” integrate technical personnel from private contractors into direct satellite monitoring and control operations at the Master Control Station at Schriever Air Force Base — a break from long-standing tradition of only uniformed Air Force personnel operating the satellites.

•    Prepare for discussions regarding possible use of Galileo services for military purposes by NATO member nations.

•    Require each U.S. military service to fund its own R&D program to best ensure position and timing information is integrated into equipment and operational capabilities. (The function is currently coordinated by the NAVSTAR GPS Joint Program Office.)

•    Designate a single focal point within the Office of the Secretary of Defense responsible for all GPS policy and oversight matters.

•    Limit GPS III satellite weight to permit launch of two satellites on a single mid-size launch vehicle, including the transfer, if necessary, of the Nuclear Detonation Detection System now on board GPS satellites to other host spacecraft.

Leadership and Capacity
Throughout the report’s analysis and recommendations, two concerns stand out: the task force’s strong desire to see a greater GPS system capability funded, built, and brought on-line in a timely fashion, and the perceived need to create a clear, unified line of authority and responsibility for GPS — what McNeff refers to as “a single belly button” that can be pushed to get GPS the attention it needs.

But just sustaining the GPS constellation at its current 24-satellite fully operational capability (FOC) level is at risk, according to the task force, as a result of budgetary uncertainty and delays in modernization programs. States of the task force findings:

“The current on-orbit inventory is 28 satellites; however, with expected failures, the AF Space Command December 2004 PNT Functional Availability Report reflects a nominal probability between 5–20 percent and a worst-case probability between 20–40 percent that the constellation will fall to fewer than 24 satellites in the 2007– 2012 period based on current satellite replacement schedules.”

Moreover, the capability to operationally control new GPS L2C and L5 signals will not be present in the GPS control segment until 2009 at the earliest, the report suggests.

Upgrading the Block IIR and IIF satellites to include M-code, L2C, and L5 signals, along with an annual rather than multi-year purchase strategy, nearly doubled the cost of those spacecraft. Looking ahead, the price tag for GPS III satellites will be nearly double that of the preceding generation. As a way to mitigate the expense of the GPS III program, satellites should be designed so as to allow two to be launched at the same time, even if this means eliminating unrelated functions such as NDS.

“The concern that the DSB has is that, if GPS III becomes another massive satellite, the department can’t afford it,” task force member Brad Parkinson told Inside GNSS. “GPS really needs 30 to 36 satellites, but the Air Force requirement is only 24.” Increasing the strength of GPS transmissions should not pre-empt the goal of populating the constellation with more spacecraft, adds Parkinson, who was the first director of the GPS Joint Program Office. “Geometry is more important than extra power.”

As for the leadership issue, one of the report’s recommendations proposes, “The Secretary of Defense should also clarify lines of authority and responsibility within the Department to eliminate ambiguity regarding GPS responsibilities that hinders decision making internally and that perpetuates the perception externally that the DoD has lost sight of its GPS stewardship responsibilities.”

Noting the President’s creation of the PNT Executive Committee, which occurred during the task force’s deliberations, the report says the new policy body “affords an opportunity for all stakeholders to correct deficiencies of the former Interagency GPS Executive Board [IGEB].” That assessment stems largely from the fact that the President’s national security directive creating the executive committee also elevated the level of its leadership to deputy secretaries of transportation and defense.

Nonetheless, reflecting the difficulty of the IGEB to gain sustained participation from its co-chairs, the task force recommends, “If Deputies do not routinely participate, then designated representatives to the . . . PNT Executive Committee . . . must be formally empowered to speak for and act on behalf of their respective Deputies for all matters coming before the [committee].”

Says Parkinson, “The [PNT] executive committee can do some good if it gets the attention of people who can make some changes.”

Mike Shaw, director of the National Space-Based PNT Coordination Office that will provide staff support for the executive committee, says he hopes the office will exercise “more insight responsibilities.” By this Shaw means looking into the agencies involved with GPS and identifying “disconnects” the prevent a common exercise of GPS policy, and then putting this information “in front of senior people” who can make the needed changes.
Glen Gibbons

NovAtel Inc.
The Defense Science Board (DSB) Task Force report focuses primarily on project strategies for correction of a number of known GPS deficiencies, with the impetus to fix things being driven by the potential future impact of Galileo. There are some good thoughts and several opportunities for improvement.

The President’s U.S. Space-Based Positioning, Navigation, and Timing (PNT) Policy announced in December 2004 already highlights areas where GPS and GPS assets are vulnerable to jamming. The DSB Task Force report once again highlights this area of vulnerability, especially for civilian users.

As the supplier of GPS reference receivers to the FAA Wide Area Augmentation System (WAAS) network and participant in the development and supply of the Galileo Reference Chain receivers for the Galileo ground control system, NovAtel has proposed an approach using a combination of antenna array and signal processing for protection of the NovAtel network reference receivers. These extensively tested and qualified national networks could substantially improve GPS signal monitoring – if only the GPS control segment could access data from the WAAS networks in US, Japan, Europe, India and even China.

NovAtel supports the initiative to permanently increase the GPS constellation to 30 satellites, and we are ready for the new L2C and L5 signals. More space vehicles means a greater probability of seeing good geometry signals, and more signals at different frequencies will improve system accuracy and signal reliability. The DSB report does not, however, appear to consider the combined use of Galileo and GPS, which together will provide up to 60 satellites. This will really improve signal reliability and usability!

Keeping pace with the coming of Galileo is a recurring theme and the threat of a competitive system runs throughout the report. However, it does not really support the need to actively monitor and use Galileo for national programs such as WAAS and Local Area Augmentation Systems (LAAS). NovAtel has already fielded a commercial dual-mode GPS/Galileo 16 channel receiver, which can provide users with the benefits of new signals and which works with both systems.

Such receivers could be readily added to the existing WAAS reference receivers. Moreover, NovAtel expects to be deeply involved in Galileo and GPS receiver development for many years to come.

As the world moves into a GPS/Galileo dual-constellation environment, where dual use will be pervasive, it seems strange that the U.S. Department of Defense may have to remain reliant on single-mode GPS while the rest of us benefit from the improved accuracy and reliability which GPS and Galileo together will provide.

Tony Murfin
Vice President, Business Development
NovAtel, Inc.

Lockheed Martin
The Defense Science Board report thoughtfully addresses many key issues as the government looks forward to and works to define future generations of the Global Positioning System. Many of the issues raised in the report have been examined by industry and the Air Force as part of the GPS III architecture and requirements studies.

The report will serve as an important resource as the Air Force finalizes its plans to acquire next-generation space and ground architectures. GPS III is a major focus area for Lockheed Martin, and we stand ready to help the Air Force create a next-generation system that will address the challenging military transformational and civil needs across the  globe, including advanced anti-jam capabilities, improved system security and  accuracy, and reliability.

Steve Tatum
Sr. Manager, Communications
Lockheed Martin Space Systems Co.

EADS Space Services
The DSB Task Force report provides a very interesting and fair overview of the Global Positioning System challenges from a performance, competitiveness and governance point of view in view of the upcoming European alternative “Galileo.” As a major actor of the future Galileo PNT system, EADS has a particular interest in the GPS evolutions and policy, especially in the field of cooperation with leading U.S. manufacturers.

The Task Force position is particularly appreciable for the navigation industry as it recommends promoting “opportunities for cooperation,” “true civil interoperability,” and considering “alternative means of funding and governance” for GPS to facilitate its international support. The underlying purpose of this collaborative approach is to improve the commercial and cost efficiency related to the PNT civil signals.

Through its recent site distribution agreement, Galileo has made a significant step forward and will provide in the near future increased satellite signal availability worldwide for navigation purposes. It is indeed a primary objective to promote the combination of the GPS and Galileo constellations for civil users in order to improve significantly the overall positioning accuracy and integrity.

Consequently, the report supports the definition of an international civil signal standardization allowing combined GPS-Galileo receivers. This common effort is necessary to facilitate a widespread usage and certification of the signals in the commercial sector. Therefore, all parties should sustain the systems interoperability with the “full disclosure of an open signal structure” and well defined geodetic and time reference transformations in receivers.

EADS also welcomes the task force proposal to “explore cooperative exchange of monitoring information” provided by the WAAS and EGNOS systems as well as a “collaborative approach” to manage and monitor both systems for better performances.

Finally, we consider that the adoption of a separate strategy and governance for the GPS military and civil activities would facilitate the system modernizations, international cooperation, and augmentations focused on the civil particular interests, while maintaining a superior military capability.

To conclude, we regret that tangible directives have still not been issued by the U.S. authorities in the direction initiated by the US-EU agreement of June 2004. It would add great benefits to the user community to initiate the creation of joint entities aimed at addressing the performance, the standardization, and the vulnerability of the GPS and Galileo signals across the Atlantic.

Martin U. Ripple
Director Galileo Program
EADS Space Services

The Boeing Company
We continue to execute on our commitment to GPS IIF production, with a goal to make the IIF the most capable and reliable navigation satellite to join the constellation. We also look forward to seeing the customer’s requirements for GPS IIIA when the request for proposal (RFP) is issued. We’re excited about the new IIIA program and await the competition.

I believe that the majority of the [DSB] comments relate to the future of GPS requirements and that is the purview of the GPS Joint Program Office (JPO).  Boeing is ready to respond to the requirements, with whatever DSB recommendations are included.  The job of the JPO is to take the opinions of all appropriate experts and meld them into a future roadmap and set of requirements which are sent to industry to propose and build. Again, Boeing stands ready to respond with a compelling proposal.

Mike Rizzo
Director, Navigation Systems
The Boeing Company

L-3/Interstate Electronics Corp.
In general, the DSB report is “right on.” Their assessments regarding current shortfalls and urgent needs bring to light the vulnerabilities that our current war fighter is faced with when depending on GPS. It is true that improved satellite coverage is needed for challenged (e.g. urban) access, modernized GPS availability to the war fighter is too far out in time, and enhanced anti-jamming (AJ) capability is not being adequately funded or fielded.

The report makes a good point about the need for sufficient, but not excessive AJ capability in user equipment. Industry has demonstrated scalable, cost-effective AJ solutions that include hardware and software-only augmentations that satisfy the DSB’s recommended minimum acceptable level of 90 dB jamming resistance. These capabilities are easily and readily incorporated into user equipment, yet there are few programs in place to incorporate and deploy it.

Agencies like the Office of Naval Research (ONR) and Air Force Research Lab (AFRL) are financing technology programs that include AJ improvements for GPS; however, these are not pointed at fielding new equipment for the war fighter. Case in point — the Modernized Receiver Card Development Program, which is in place to help establish “proof of design” for modernized GPS does not require this type of AJ enhancement.

Hopefully, with the promulgation of the DSB report more military agencies will recognize the emerging jamming threat and programs will begin requiring the deployment of more AJ capability for GPS user equipment.

L-3/IEC agrees with the report’s assessment that the new PRONAV security architecture is essential to providing the needed Information Assurance improvements to military GPS (although one might argue with the details in the DSB’s comparison of performance benefits that PRONAV provides).

However, one must be cautious with considering the permanent removal of SA or, even more importantly, with opening up DoD acquisition policies to allow non-military GPS equipment. The gamble is the price our war fighter pays by having the wrong positioning, navigation, and timing (PNT) information because he’s using vulnerable commercial GPS signals. That price can be the difference between life and death.

Carlton Richmond
Chief GPS Technologist
L3 communications, Interstate Electronics Corp