The Lockheed Martin team developing the U.S. Air Force’s next generation Global Position System III satellites has completed a key flight software milestone validating the software’s ability to provide reliable and effective command and control for the GPS III satellites planned for launch into orbit.
The GPS III program will affordably replace aging GPS satellites, while improving capability to meet the evolving demands of military, commercial and civilian users. GPS III satellites will deliver better accuracy and improved anti-jamming power while enhancing the spacecraft’s design life and adding a new civil signal designed to be interoperable with international global navigation satellite systems.
The milestone, known as Software Item Qualification Testing (SIQT), was completed for the satellite’s spacecraft bus flight software, which is critical to controlling the spacecraft on orbit and monitoring the health and safety of the satellite’s subsystems. SIQT included 131 individual test events and represented the culmination of a rigorous software engineering risk reduction and development phase. The software will next be integrated and tested on the first GPS III satellite, which is on schedule for launch availability in 2014.
“Completion of this flight software milestone demonstrates our continued positive program momentum and is another step forward in reducing risk up front to facilitate long term affordability,” said Lt. Col. William ‘Todd’ Caldwell, the U.S. Air Force’s GPS III program manager. “In this challenging budget environment, the entire government and industry team is focused on delivering the critical GPS III satellites affordably and efficiently for users worldwide.”
To further reduce risk, the flight software has already been integrated and tested on the program’s satellite prototype, known as the GPS III Non-Flight Satellite Testbed (GNST).
“Delivering fully qualified flight software this early in program development demonstrates the rigor of our GPS III software development processes,” said Keoki Jackson, vice president of Lockheed Martin’s Navigation Systems mission area. “Through up-front investments in high-fidelity, flight equivalent hardware and software testbeds, our team successfully executed on schedule to develop and qualify the flight software critical to the success of the GPS III program.”
Lockheed Martin is on contract to deliver the first four GPS III satellites for launch. The Air Force plans to purchase up to 32 GPS III satellites.
The GPS III team is led by the Global Positioning Systems Directorate at the U.S. Air Force Space and Missile Systems Center. Lockheed Martin is the GPS III prime contractor with teammates ITT Exelis, General Dynamics, Infinity Systems Engineering, Honeywell, ATK and other subcontractors. Air Force Space Command’s 2nd Space Operations Squadron (2SOPS), based at Schriever Air Force Base, Colorado, manages and operates the GPS constellation for both civil and military users.
Topcon has introduced the HiPer V receiver, which features Topcon’s Vanguard technology. The HiPer V provides users with the choice of GPS and GLONASS signals (as well as Galileo when operationally available), and also includes a variety of choices of internal radio, cellular and Bluetooth communication options and what Topcon calls a state-of-the-art power supply.
The core of the HiPer V is the new Vanguard GNSS technology, according to Ewout Korpershoek, Topcon senior vice president and chief marketing officer. With its 226 channels and Universal Tracking, the Vanguard chipset is future proof, as it will track signals from all available and currently planned GPS, GLONASS and Galileo satellites.
“Topcon’s Universal Tracking provides a whole new definition of ‘channel technology.’ There is nothing available like it. Universal Tracking allows a single receiver channel to ‘automatically’ select and track any satellite signal,” Korpershoek said. “Because our channels are not pre-programmed to receive only one specific signal or a type of signal, Topcon users will always receive the maximum number of signals at any given time. In addition, Topcon’s Universal Tracking will automatically weigh the best combination of available signals based on health, geometry and application, providing unmatched accuracy, speed of initialization and fixing. HiPer V will work at places where other receivers will not, at highest accuracy, and with greatest ease of use.”
Other features include the rugged, durable magnesium alloy housing, the choice of communication options, “and longest life rechargeable battery while maintaining the lightest weight in its class,” Korpershoek said.
The Institute of Navigation (ION) Satellite Division held its third annual ION Autonomous Snowplow Competition January 24-27 at Rice Park in downtown Saint Paul, Minnesota, as part of the 127th Saint Paul Winter Carnival.
Sponsored by The ION Satellite Division and held in cooperation with the ION North Star Section, the ION Annual Autonomous Snowplow Competition is a national event open to college and university students, as well as the general public, that challenges teams to design, build, and operate a fully autonomous snowplow using navigation and control technologies to rapidly, accurately and safely clear a designated path of snow.
Eight teams participated in the four-day competition, each using state-of-the-art navigation systems to plow two different snowfields. Teams included students, partners from private industry and faculty advisors from Case Western Reserve University; Dunwoody College of Technology; Miami University (Ohio); Ohio University; The University of Michigan – Dearborn, and The University of Minnesota.
Teams were judged based on their cumulative scores earned throughout the competition phases: 75 percent of the total score was based upon the plowing competition; and 25 percent of the total score was based on the presentations and pre-event report.
First place was awarded to Ohio University’s Avionics Engineering Center with students Samantha Craig, Ryan Kollar, Adam Naab-Levy, Pengfei Duan and Kuangmin Li with support from faculty advisors Dr. Frank van Graas, Dr. Wouter Pelgrum and Dr. Maarten Uijt de Haag who submitted their four-wheeled Monocular Autonomously Controlled Snowplow (M.A.C.S.). The first place prize included $5,000 and a golden snow globe trophy. Ohio University also captured the Best Student Presentation Award that included $500 and the “Golden Shovel” Award and the Best Written Report that included $500 and the “Golden Pen” Award.
Second place was awarded to the Miami University team “RedBlade” that included students Mark Carroll, Chad Sobota, Robert Cole, Richard Marcus, Harrison Bourne, Jamie Morton and Michael Harris with support from advisors Dr. Yu (Jade) Morton, Dr. Peter Jamieson, Steve Taylor. The second place prize included $4,000 and a silver snow globe trophy.
Third place was awarded to the University of Michigan (Dearborn) team “Yeti 3.0” that included students Angelo Bertani, Zachary DeGeorge, Ahmed Alkirsh, Abdelqwee Yaffai, Mark Bajor, Craig Cowling, Cody Schmitt, Jacob Mack and Mengxing (Simon) Chen with support from faculty advisor Narasimhamurthi (Nattu) Natarajan. The third place prize included $3,000 and a bronze snow globe trophy.
In addition, the first place team, Ohio University, has been invited to display its winning snowplow during ION GNSS+ 2013 conference September 16-20 in Nashville, Tennessee.
Sponsors of the second annual ION Autonomous Snowplow Competition included Honeywell, Inc., Alliant Techsystems Inc., Lockheed Martin Corporation, ASTER Labs, Inc., Space Exploration Technologies Corp., The Toro Company, Proto Labs, Inc. and U.S. Bank.
The Fourth Annual ION Autonomous Snowplow Competition will be held in January 2014 at the Saint Paul Winter Carnival, St. Paul, Minnesota.
NovAtel Inc., supplier of OEM GNSS components and subsystems, has announced the addition of a new commercially exportable MEMS IMU to its line of SPAN GNSS/INS products. Available for immediate shipping, this custom Analogue Devices MEMS inertial sensor is exclusive to NovAtel, and can be paired with an OEM6 receiver card to provide continuously available position, velocity and attitude (roll, pitch, yaw) in a small, single-unit form factor.
SPAN tightly couples NovAtel’s precise GNSS technology with highly accurate inertial measurement technology to provide a robust, stable and continuous 3D navigation. The new OEM-ADIS-16488 sensor is designed to be coupled with NovAtel’s OEM6 receivers via the MEMS Interface Card (MIC), providing integrators with a compact, powerful GNSS/INS engine, NovAtel said.
The OEM-ADIS-16488 features low noise gyros and accelerometers in a small, lightweight form factor. This IMU enables precision measurements for applications that require low cost, high performance and rugged durability. Tight-coupling of the two technologies enables continuous robust positioning in difficult environments where satellite signals are unreliable or unavailable for short periods of time.
The OEM-ADIS-16488 is now available for order and immediate shipment.
Symmetricom, Inc. today announced two new capabilities for its SSU 2000 Synchronization Supply Unit: a GLONASS timing reference that uses signals from the satellite navigation system operated by the Russian Aerospace Defense Forces, and Synchronous Ethernet (SyncE), an ITU-T synchronization standard that delivers frequency synchronization over the Ethernet physical layer.
This enhanced version of the SSU 2000 will be the first in a series of forthcoming Symmetricom products that include GLONASS capabilities.
Available as an integrated card for the Symmetricom SSU 2000, the GLONASS referencing feature will allow customers to support both GPS and GLONASS simultaneously, providing added protection should signals from one navigation system become unavailable. GPS has long served as the primary reference signal for timing and synchronization in telecommunications and other networks. Operators in some regions prefer to use the GLONASS system, either as the primary time reference or in conjunction with GPS signals. Symmetricom has enhanced the SSU 2000 satellite receiver functionality to meet this demand.
“GLONASS signals have become an important primary reference for timing and synchronization systems,” said Laura Finkelstein, vice president of product management for Symmetricom. “The SSU 2000 is well-established as the synchronization platform for communication service providers globally. The integrated capability to simultaneously support both GPS and GLONASS provides our customers another way to improve the reliability of their network.”
Timing and synchronization are a focal point technology in Ethernet and mobile carrier networks today. Synchronous Ethernet allows frequency signals to transfer at the physical layer over Ethernet, helping improve network reliability by offering synchronization services to Carrier Ethernet networks. Using SyncE to complement IEEE 1588 Precision Time Protocol (PTP) can enhance PTP services being delivered to mobile base stations deployed in radio access networks. The new SSU 2000 capability puts SyncE and PTP on the same output port, thus providing an ideal synchronization solution for the evolution of mobile networks as they extend coverage and increase capacity.
Designed in a NEBS-compliant package, the SSU 2000 integrates intelligent functional modules into a flexible, fully redundant system. This enables telecom network operators to seamlessly satisfy current and future requirements for generating and distributing superior synchronization signals for advanced network services.
The SSU 2000 has been deployed in more than 125 countries as a timing and synchronization distribution system for communications service providers.
Trimble is launching a high-accuracy correction service for the agriculture market. The Trimble RangePoint RTX correction service is expected to be available in March.
According to Trimble, the RangePoint RTX service is an introductory, cost-effective correction service available to farmers across the contiguous U.S. as well as most of Canada, South America, Russia, and the Commonwealth of Independent States, Africa, Asia and Australasia. It’s designed for broadacre agriculture applications. For 2013, all compatible devices — the Trimble CFX-750 display, FmX integrated display, and the AG-372 GNSS receiver — are eligible for an introductory, free 12-month subscription to the RangePoint RTX correction service.
The new service uses satellite broadcast capabilities to deliver real-time accuracies of better than 50-centimeter (20-inch) repeatable, or a superior 15-centimeter (6-inch) pass-to-pass, and does not require the use of traditional reference station infrastructure. Trimble RTX technology supports both GPS and GLONASS satellite constellations, increasing accuracy and reliability for users by leveraging the availability of multiple satellite systems. As a result, the RangePoint RTX service can provide a more accurate, reliable correction solution than some of the traditional Satellite Based Augmentation Systems (SBAS), and is also available in certain geographic areas where SBAS is not currently accessible.
“Trimble is committed to expanding the services and software applications that we provide to the global farming community,” said Mike Martinez, market manager for Trimble’s Agriculture Division. “We recently expanded the availability of real-time, satellite-delivered corrections to most of the world through Trimble’s CenterPoint RTX correction service. Now, we are enhancing the Trimble correction services portfolio by providing an introductory RTX-based option for farmers looking for more accuracy at an affordable price point. Our customers want a broad range of solutions, and we’re delivering those options.”
Trimble RangePoint RTX real-time satellite delivered corrections can be received directly by compatible GNSS receivers, so there are no additional costs for mobile data plans or requirements for additional hardware such as radios and antennas. The RangePoint RTX service is compatible with the Trimble CFX-750 display, FmX integrated display and the AG-372 GNSS receiver.
On January 31, Hemisphere GNSS Inc., a subsidiary of Beijing UniStrong Science & Technology Co. Ltd., purchased the Precision Products business and related GNSS technology and intellectual property from Hemisphere GPS Inc. for $15 million US. In a related press release, Hemisphere GPS Inc. has announced the intention to change its company name to AgJunction.
As part of the transaction, Hemisphere GNSS acquired all of the high-precision GNSS product lines, all related intellectual property rights and the Hemisphere GPS trademarks and brands. The Precision Products segment generated revenues of approximately $13.3 million in 2012 serving marine, land survey, construction, mapping, and OEM segments.
Hemisphere GNSS will operate its business headquarters out of Scottsdale, Arizona, and will maintain its operations in Calgary, Alberta, Canada.
Phil Gabriel has been appointed president of Hemisphere GNSS Inc. and will also serve as a board member. Gabriel has more than 15 years of experience with Hemisphere GPS, serving for the past six years as the vice president and general manager of the Precision Products business. “We are truly excited about our future growth prospects as a fully focused GNSS products and technology provider,” Gabriel said. “I would like to assure all our global distribution partners, suppliers and customers that it remains business as usual as we take our first steps forward with the strong backing of UniStrong.”
With this acquisition, UniStrong is expanding its capabilities in the high-precision GNSS business and also expects to promote commercial applications of China’s BeiDou Navigation System. UniStrong is listed on the Shenzhen Stock Exchange under ticker 002383.
Business analysts have reported in China that this is the first acquisition of an internationally renowned enterprise initiated by a domestic enterprise in China’s satellite navigation industry and represents an important milestone in the development of the industry. “The acquisition will create an international route enabling UniStrong to expand its global business outlook, enhance our ability to attract international talent, and lay the foundation for international growth and profitability,” stated Xingping Guo, president and CEO of UniStrong.
As part of the agreement, Hemisphere GNSS and AgJunction have formed a strategic alliance and a collaborative business relationship covering supply chain management, customer support, technology development and cross-licensing. “Having already established a relationship with UniStrong as one of our resellers made our new alliance a win-win for both parties,” said Rick Heiniger, president and CEO of AgJunction. “I am very pleased to be working together in this close technology-sharing relationship.”
Hemisphere GNSS’s newly appointed board of directors brings additional GNSS industry experience to the company. The board is chaired by Jonathan W. Ladd, former president and CEO of NovAtel Inc. Also joining the board is Werner Gartner, former executive vice president and CFO of NovAtel Inc.
“Hemisphere’s talented team will leverage its core GNSS capabilities and product marketing knowledge with UniStrong’s high quality, low cost GNSS product design and development resources,” said Ladd. “Hemisphere’s existing and future customers and partners will most certainly benefit from the resulting rapid, cost-effective product innovation across multiple product lines.”
Beijing UniStrong is focused on GNSS industry, with R&D, production, engineering, sales and service facilities. Its technical solutions and products cover GPS/GLONASS/COMPASS receivers, multi-system navigation and positioning, high-accuracy surveying, GNSS data post-processing, and system integration.
The re-branding of Hemisphere GPS as AgJunction is an integral part of the strategic re-focusing of the company’s resources on precision agriculture, and part of the restructuring initiated in September 2012. The company maintains ownership of its key patents and leading agricultural brands including AgJunction, Outback Guidance, and Satloc.
LabSat 2 now has the ability to record and replay satellite signals from the rapidly expanding Chinese navigation system, BeiDou. LabSat 2 users can now record and replay any combination of two channels from the three available constellations, GPS, GLONASS, and Beidou.
Existing LabSat 2 users can download the latest firmware (v2.0.0) and PC software (v2.6.14) to add this functionality with no cost.
There is a growing trend to include multi-constellation capability into new satellite navigation receivers, giving the end user better coverage in urban canyons, and overall improved positional accuracy, LabSat said.
There are now 14 operational Beidou satellites, and we have recorded a number of different files from Europe and China containing between 6 and 8 satellites. These scenarios are now included on the hard disk which is shipped with a LabSat 2, which can also be shipped out to existing customers on request.
The new firmware and software is now available from the Support section of the LabSat website. Follow the upgrade firmware instructions in the manual to upgrade your LabSat 2. For more information contact our LabSat Product Manager, Mark Sampson, [email protected].
Conception, Realization, Evaluation of a Seven-Element GNSS CRPA
By Frederic Leveau, Solene Boucher, Erwan Goron, and Herve Lattard
A controlled radiated pattern antenna can be an effective way to protect GPS receivers against jamming. A new CRPA, composed of seven elements, works on the E5a, E5b, E6, L2, and L1 bandwidths. This article reports on radiation pattern measurements of the array in a test facility.
Controlled radiation pattern antenna (CRPA) technique is considered to be the best GPS pre-correlation protection technique against interference. It consists of an antenna array and a processing unit that performs a phase-destructive sum of the incoming interference signals, this process being equivalent to making nulls towards interferers in the array radiation pattern.
Considering the growing Galileo system and the possible interest of the French Ministry of Defense in the Public Regulated Service (PRS) , a prospective study was undertaken to develop an array compatible with GPS M-code, Galileo PRS, and aeronautical radionavigation signals in the E5 bandwidth. The French Expertise & Procurement Defence Agency (DGA) awarded the French company SATIMO a feasibility contract to design, conceive, realize, and evaluate a circular array composed of seven elementary patch antennas (see Figure 1).
Figure 1. CRPA unit receiving satellite and jammer signals.
Product Features
SATIMO, a company specializing in R&D for antennas and in innovative antenna test ranges, has since developed this GPS-Galileo CRPA antenna, shown below.
New CRPA developed by SATIMO.
The CRPA consists of seven elementary patches covering E5a, E5b, L2, E6, L2, and L1 frequency bandwidths, using microstrip multilayer technology. Each element is housed in a 9-centimeter (diameter) by 2-centimeter (height) radome, connector excluded. In that volume, a space provision has been reserved to include a low-noise amplifier (LNA) and two filters for a sharp out-of-band rejection. As a consequence, it is possible to configure three types of arrays: passive without filters, passive with two passband filters, and finally active (including a LNA, with a gain > 26dB, NF<0.9dB) with two passband filters. The maximum gain levels in these configurations are from 3.6 dBi to 29.8 dBi. For radiation patterns, see Figure 2.
The design of the single element has been optimized to control the deviations of each patch antenna when included in a seven-element array.
To limit mutual coupling with respect to the array dimensions, the distance between the elements’ phase centers has been chosen close to 0.7 λ at L1 frequency. This value results in a 36.5-centimeter (diameter) array. The standalone antenna and the CRPA antenna have been validated through an environmental testing campaign.
Product Development
The usual iterative tuning and the optimization process for prototyping have been performed on SATIMO’s arch test range. This test facility indeed significantly reduces the time required to characterize the antenna-under-test (AUT) radiation pattern, in comparison with classical anechoic chamber test facilities.
More precisely, the arch test range instantaneously scans the field in one whole site angle cross-section plane, whereas the legacy systems mechanically scan the same cross-section plane by rotating the AUT for each incremental angle value. The spatial sampling of the near-field radiated by the AUT, thanks to a large number of probes along the arch surrounding it, enables a significant savings in time. The near-field results in the current plane can be displayed in real-time on a computer screen. Then, the rotation of AUT around its axis is automatically controlled by the measurement system, and a new acquisition is performed for each new cross-section plane. A Fourier transform computation is eventually applied to the 3D near-field to get the far-field radiation pattern.
The radiating characterization of the CRPA has been performed with a SATIMO SG24 system. With such a system, we have measured the complete 3D radiation patterns of each single element in less than 40 minutes per antenna.
Evaluation
The evaluation of the CRPA array was performed with this test bed in SATIMO’s facility (see photos below). The process begain with measuring an element alone on a ground plane, in order to extract the gain, the axial ratio, the aperture angle, the matching values, and every feature that defines a fixed-radiation pattern antenna. The evaluation secondly consisted of characterizing the array, that is, extracting the gain and the phase of each element in the array, with respect to a reference element. To implement such a reference anytime during the near-field acquisition process, the arch test range (Figure 3) is very powerful, because all the probes constantly point at the center of the array, despite AUT’s motions. On the contrary, the need for such a reference makes measurements difficult in anechoic chambers, which often require canceling out misalignments, thanks to specific motions that must be taken into account in the computations.
CRPA in measurements.CRPA in measurements.Figure 3. Arch test range working principle.
Uses
Functional tests are another important part of the CRPA unit evaluation. Usually, two kind of tests can be conducted: outdoors or in anechoic chamber.
Classical Tests. DGA plans to perform outdoor test campaigns by utilizing an array placed on the roof of an all-terrain vehicle (see photo). The array will be connected to a CRPA GPS processing unit and to a receiver in the vehicle. Some interferers will be located along the trajectory of the vehicle, according to various scenarios defining their waveforms and their power levels. The CRPA capability to reject those interferers can then be assessed. These kinds of outdoor tests naturally suit CRPA’s processing unit and array characterization, as they involve radiated GPS and interfering signals. However, these kinds of tests are not reproducible and are quite complicated to set up.
Outdoor jamming test campaign.
Some tests in anechoic chambers could be an alternative in order to obtain reproducible test results, but in that case, transmitting GPS constellation signals indoor becomes a challenge. An option could be the use of a GPS signal simulator, but this means a unique direction of arrival of GPS signals. Moreover, no dynamic trajectory could be done.
New Test Bed. DGA recently acquired a test bed, developed by INEO Defense, that enables evaluating CRPA units in conducted mode, for example. There is no longer a need to radiate either GPS signals or interfering signals. The purpose of this test bed, called BAnc de Caractérisation des Antennes Réseaux Antibrouillage (BACARA), or test bed to characterize anti-jamming antenna arrays (Figure 4 and Figure 5), is to replace the array and simulate its GPS and jamming environment. This means that it is able to create elementary antenna phase delays and gains resulting from the array geometry, by using finite impulse response (FIR) filters (Figure 6). This is the reason why this test bed must be fed with the array phase and gain measurement results obtained with the arch test range.
Figure 4. BACARA test bed.Figure 5. BACARA working principle.Figure 6. BACARA working principle.
Alternatively, these results can be obtained with traditional anechoic chamber measurements. 10 channels of a multi-channel GPS simulator, each one matched with a satellite, are used by the test bed. Thus, BACARA coherently sums GPS constellation simulator output channels and interfering signals, so as to accurately simulate the array’s behavior in the laboratory. As a result, for any CRPA processing unit, it is possible to compare the array’s impact on a processing unit with an ideal array being composed of perfect elementary antennas.
Unfortunately, BACARA currently operates on L1 or L2, but not on the E6 and E5 bandwidths. On the other hand, this test bed is able to simulate dynamic trajectories, with the mobile positions and attitudes. Up to 10 internal jammers with various waveforms can be set up, and their power levels over time are computed by software like Warfare or Matlab. A numerical calibration allows some transparency of the test bed for CRPA units under test.
Figure 7. BACARA graphical user interface.Figure 8. Examples of available simulated array geometry.
Conclusion
SATIMO, a company specializing in electromagnetic field measurements in the microwave frequency range and part of the Microwave Vision Group, has developed an array for the reception of M-code, PRS, and aeronautical radionavigation signals. This antenna array has been fully evaluated and qualified through electrical and environmental tests. The measurement methods have enabled the company to demonstrate the feasibility of the performances expected. Functional evaluations restricted to GPS are still under way. To do so, DGA will utilize its complementary outdoor and indoor test means, especially its laboratory test bed BACARA, as a tool to precisely evaluate GPS CRPA units.
Frederic Leveau works at the French MoD (DGA Information Superiority) as a radionavigation expert. His main interests are Galileo PRS prospective studies and developments and the integration of CRPA systems within French platforms.
Solene Boucher works at the French MoD (DGA Information Superiority) as a radionavigation expert. Her main interests are Galileo PRS prospective studies and developments. She is also responsible for the test bed BACARA.
Erwan Goron is an engineer at SATIMO Industries (Microwave Vision Group). His main activity is antenna conception.
Herve Lattard is an engineer at SATIMO Industries (Microwave Vision Group). His main activity is antenna conception.
BeiDou ICD: Signal Specs Are Free At Last; First Demonstration of Galileo-Only Positioning (By Peter Steigenberger, Urs Hugentobler, and Oliver Montenbruck)
BeiDou ICD: Signal Specs Are Free At Last
The interface control document (ICD) describing the details of the BeiDou B1I open service signal on 1561.098 MHz was released December 27 at a news conference held in Beijing by the Chinese State Council Information Office. The ICD includes details of the navigation message, parameters of the satellite almanacs, and ephemerides that did not appear an earlier, incomplete version of the ICD released at the end of 2011.
Beidou
An English version is available for download courtesy of the University of New Brunswick. The ICD specifies the relations of the signal in space interface between BeiDou Navigation Satellite System and users’ terminal receivers. It is the essential technical document to develop and make receivers and chips.
Anyone who has questions about the ICD is invited to submit them to [email protected].
The document, BeiDou Navigation Satellite System Signal In Space Interface Control Document — Open Service Signal B1I (Version 1.0), includes a system introduction, signal standards and navigation message, which defines the related contents of the open-service signal B1I between the BeiDou Navigation Satellite System and users’ terminals.
In a previous presentation given at the Seventh Meeting of the International Committee on Global Navigation Satellite Systems (ICG) in November, 2012, BeiDou officials stated that by 2020 there will be five GEO and 30 non-GEO satellites. The number of IGSO and MEO satellites was not specified, but previous presentations have said three IGSOs and 27 MEOs. These numbers are also stated in the official ICD.
“The GEO satellites are operating in orbit at an altitude of 35,786 kilometers and positioned at 58.75°E, 80°E, 110.5°E, 140°E and 160°E respectively. The MEO satellites are operating in orbit at an altitude of 21,528 kilometers and an inclination of 55° to the equatorial plane. The IGSO satellites are operating in orbit at an altitude of 35,786 kilometers and an inclination of 55° to the equatorial plane.”
The China Satellite Navigation Office presented a new official logo for the BeiDou system, with a yin/yang symbol representing Chinese culture, dark and light blue for space and Earth, and the Big Dipper constellation, symbolizing a long tradition of Chinese navigation since ancient times.
A spokesperson said the English name for China’s GNSS will be BeiDou Navigation Satellite System, abbreviated as BDS. The name Compass, which first designated the prototype regional system and has been employed in conjunction with the name BeiDou, will apparently now be discontinued.
Other salient details from the ICD include:
Signal Structure. “The B1 signal is the sum of channel I and Q which are in phase quadrature of each other. The ranging code and NAV message are modulated on carrier. The signal is composed of the carrier frequency, ranging code and NAV message.
“The B1 signal is expressed as follows:
S j (t) = A I C I j (t) D I j (t) cos (2 π f0 t φ j) + A Q C Q j (t) D Q j (t) sin (2 π f0 t + φ j)
where superscript j is the satellite number; subscript I equals channel I; subscript Q is channel Q; A is the signal amplitude; C the ranging code; D the data modulated on ranging code; f0 represents the carrier frequency; and φ the carrier initial phase.”
The nominal frequency of the B1I signal is 1561.098 MHz.
As is the norm with most other GNSSs, BeiDou’s transmitted signal is modulated by quadrature phase shift keying (QPSK). The transmitted signal will be right-handed circularly polarized (RHCP), and its multiplexing mode is code-division multiple-access (CDMA).
User-Received Signal Power Level. “The minimum user-received signal power level is specified to be -163 dBW for B1I, which is measured at the output of a 0 dB RHCP receiving antenna (located near ground), when the satellite’s elevation angle is higher than 5 degree.”
Bandwidth and Suppression. “Bandwidth (1 dB): 4.092 MHz (centered at carrier frequency of B1I); Bandwidth (3 dB): 16 MHz (centered at carrier frequency of B1I). Out-band suppression: no less than 15 dB on f0±30 MHz, where f0 is the carrier frequency of B1I signal.”
Ranging Code on B1I. “The chip rate of the B1I ranging code is 2.046 Mcps, and the length is 2,046 chips. The B1I ranging code (hereinafter referred to as CB1I) is a balanced Gold code truncated with the last one chip. The Gold code is generated by means of Modulo-2 addition of G1 and G2 sequences which are respectively derived from two 11-bit linear shift registers.”
NAV Message. “NAV messages are formatted in D1 and D2 based on their rate and structure. The rate of D1 NAV message which is modulated with 1 kbps secondary code is 50 bps. D1 NAV message contains basic NAV information (fundamental NAV information of the broadcasting satellites, almanac information for all satellites as well as the time offsets from other systems); while D2 NAV message contains basic NAV and augmentation service information (the BDS integrity, differential and ionospheric grid information) and its rate is 500 bps.
“The NAV message broadcast by MEO/IGSO and GEO satellites is D1 and D2 respectively.” The adjacent table from the BeiDou ICD gives information on nav message contents.
First Demonstration of Galileo-Only Positioning
By Peter Steigenberger, Urs Hugentobler, and Oliver Montenbruck
The European satellite navigation system, Galileo, is currently in its in-orbit validation (IOV) phase with a constellation of four satellites. The satellites, launched in pairs on October 21, 2011, and October 12, 2012, are representative of the full 30-satellite constellation. The IOV satellites will demonstrate that the satellites and the ground segment meet the system’s requirements and will validate the system’s design before completion of the rest of the constellation.
The IOV satellites have already started transmitting signals, and short periods of four-satellite visibility have allowed us to demonstrate, for the first time, absolute and relative positioning using measurements from Galileo operational satellites only. This follows the positioning demonstration last year with the signals from the Galileo IOV Element (GIOVE) test satellites and the first two IOV satellites. As in that earlier work, external orbit and clock information is necessary, since the IOV satellites were not transmitting valid navigation messages at the time of our study.
Three Javad GNSS Triumph-VS receivers with external antennas were set up at Technische Universität München (TUM) in Munich, Germany. The reference station TUME is equipped with a Javad GNSS RingAntG3T choke-ring antenna whereas the stations TUMW and TUMO are equipped with Javad GNSS GrAntG3T antennas. Unfortunately, all antennas are mounted near metal surfaces introducing pronounced multipath effects. The resulting baseline lengths are approximately 19.4 meters for TUME-TUMW and 101.7 meters for TUME-TUMO. Galileo satellite orbit and clock information was determined from stations of the Cooperative Network for GNSS Observation (CONGO) and the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS). For GPS satellites, the rapid products of the Center for Orbit Determination in Europe (CODE) were used. All computations were performed with a modified version of the Bernese GPS Software 5.0.
Figure 1. Single-point positioning results for the TUME reference station based on E1/E5a dual-frequency pseudorange measurements of the four Galileo IOV satellites. The standard deviations in the north, east, and up directions are given. Note the different scale of the north component.
At a cutoff angle of 10 degrees, the four IOV satellites were jointly visible from TUM on January 6, 2013, for about two hours – from 04:16 to 06:09 UTC. Using an ionosphere-free dual-frequency linear combination of pseudorange measurements on the Galileo E1 and E5a frequencies, the position of the TUME reference station could be determined with a 3D position error of less than 1.5 meters (see Figure 1).
In addition to absolute positioning, relative positions between pairs of receivers were computed from Galileo E1, E5a, E5b, and E5 AltBOC single-frequency carrier-phase observations. Two GPS solutions covering the same time interval serve for comparison purposes. The first solution utilizes all visible GPS satellites (9 to 12 per epoch) whereas the second solution is intentionally limited to four satellites (G06, G16, G27, G29) for best comparison with the Galileo case. So-called kinematic-style processing was used where the baseline is not constrained to be unchanging and a relative-position solution is computed for each epoch of measurements. 3D standard deviations of the different solutions are listed in Table 1. The overall accuracies are at the level of a few centimeters.
Tabe 1. 3D position errors (standard deviation) of carrier-phase-based kinematic-style Galileo and GPS baseline solutions.
A slightly degraded performance is achieved for the TUMO-TUME baseline, which can be attributed to both the larger separation and the inferior multipath environment compared to the TUMW-TUME baseline.
Comparing the individual Galileo signals, the best relative positioning results were obtained for the E1 carrier-phase measurements. Interestingly, the use of carrier-phase measurements from the E5 AltBOC tracking yielded a lower performance in our test than use of either the E5a or E5b observations. Apparently, the carrier-phase tracking benefits less from the ultra-wideband signal than the code tracking, where AltBOC usually offers notably reduced noise and multipath. Besides their good performance for Galileo-only positioning, the E1 and E5a carrier-phase measurements will be particularly relevant for future relative positioning applications due to the possibility of mixed-constellation ambiguity resolution with GPS L1 and L5 signals.
For illustration, Figure 2 shows the Galileo E1 solution as well as the GPS L1 solution computed from four satellites. For the north component, the scatter of the Galileo solution is larger by a factor of two compared to GPS whereas it is on almost the same level for the east and up components as a result of the specific geometry of the satellites employed.
Figure 2. Kinematic positioning results for the TUMW-TUME baseline based on Galileo E1 (left) and GPS L1 (right) carrier-phase observations of four satellites. The standard deviations in the north, east, and up directions are given. Note the different scale of the north component.
With the recent testing of navigation messages on the first pair of IOV satellites, Galileo-based positioning as described in this article will not be limited to post-processing, but will be available to real-time users as well.
Peter Steigenberger is a staff member in the Institut für Astronomische und Physikalische Geodäsie of the Technische Universität München (TUM) in Munich, Germany.
Urs Hugentobler is the head of the Fachgebiet Satellitengeodäsie (Department of Satellite Geodesy) and the Forschungseinrichtung Satellitengeodäsie (Research Facility for Satellite Geodesy) at TUM.
Oliver Montenbruck is the head of the GNSS Technology and Navigation Group in the German Space Operations Center in Oberpfaffenhofen, Germany, and a TUM associate faculty member.
Economically, the System Differs Significantly from Its GNSS Cousins
John W. Lavrakas
In May 2007, I authored an article in GPS World looking ten years into the future and envisioning how the GNSS field would operate at that then-distant time. Reviewing my assessments, I see that I was both accurate and wide of the mark with my predictions.
The prediction that has proved accurate was that the GNSS world would be hybrid, with no one system as the sole provider of satellite-based positioning and timing services. This was hardly a risky prediction. Most in the GNSS community would have come to the same assessment.
But what I did not see coming were the advances China would take with its BeiDou program. My original assessment was based on three GNSSs only: GPS, GLONASS, and Galileo, and did not include BeiDou.
When I did my analysis in 2006, China was pretty quiet on BeiDou: no technical descriptions, no interface control document (ICD); no presentations at conferences of the Institute of Navigation. What little we knew about BeiDou was that it was a limited system, offering at best a regional solution. The original design was an active system using geosynchronous satellites, requiring each remote unit to request position from the satellite, which was calculated and sent back to the remote station.
How things have changed.
Since 2007, China has reshaped the BeiDou concept into a full-fledged modern GNSS, offering CDMA codes, navigation messages, and data rates comparable to GPS and Galileo — and lots of satellites. The ICD states in section 3.1, “When fully deployed, the space constellation of BDS consists of five geostationary Earth-orbit (GEO) satellites, twenty-seven medium Earth-orbit (MEO) satellites, and three inclined geosynchronous satellite orbit (IGSO) satellites.” No dates are provided, however, regarding attaining these numbers. So the BeiDou system promises to be on par with the other GNSSs.
Why does this matter?
While technically the BeiDou system resembles its cousins, economically it presents quite a different animal. Unlike other nations offering GNSS, China has a huge capacity for manufacturing at low cost. Considering this situation from a business perspective, a possible scenario could be that China offers GNSS chipsets that operate with BeiDou (either solely or as a hybrid with another GNSS)at extremely low prices. In doing so, China could corner the market for general purpose LBS applications (setting aside specialty receivers, such as for surveying and aviation applications). The price point would be so attractive that LBS services would employ Chinese devices in preference to the GPS ones, much like consumers purchase television sets: most come from China, and none are made in the United States any more.
China offers something, then, in this scenario that neither Russia, Europe, nor the United States can currently match. This may not be the scenario that eventually occurs, but it is possible. Other factors such as local terrestrial PNT solutions and dual-frequency improvements will come into play, but what I have described is one possible scenario. While the signal is free, the equipment is not, and when we are talking about a billion or more installations, cost is going to be a big driver.
Am I going out on a limb and saying that BeiDou will be the system of choice in another ten years or so? No, I would not go this far.
But I do say that serious competition for GNSS users (read “market share”) is now in play. Further, it is important for each GNSS operator to recognize this as they consider the services and features they choose to offer, and the impact these have in capturing their share of the market. GNSS providers now must factor the business aspect of their services as much as the technical, scientific, or safety of life. The U.S. government, for one, has gotten a bit complacent in upgrading GPS services to meet user needs, operating from a basis that it is the only GNSS on the block. It could wake up one day and find this no longer to be the case.
John Lavrakas is president of Advanced Research Corporation, where he provides consulting services on satellite navigation and fishery information systems. He has spent 32 years in GPS, supporting development of the GPS Control Segment, GPS user equipment, GPS performance analysis capabilities, and developing and marketing location-based systems. He is past president of the Institute of Navigation and an ION Fellow.
We have reached our tipping point, say the seven U.S. military Joint Chiefs of Staff in a January 14 letter to Senator Carl Levin, chairman of the U.S. Senate Committee on Armed Services.
“We are on the brink of creating a hollow force,” they continue. By this they mean that the military of the size that they are required to maintain may be incapable of performing the duties for which it is relied upon.
This sounds a great deal like the scenario forecast in Don Jewell’s “2C or Not 2C” column in this magazine. Five GPS satellites currently on orbit have the capability of broadcasting new signals essential to security and economic growth. But that capability is hollow because of a lack of — what? money? resolve? back-up? — to turn it on and use it. Those satellites could actually die in a couple of decades without ever performing the function for which they were designed.
The hollow-force concept as applied to the GPS constellation reverberates eerily through John Lavrakas’ “BeiDou, How Things Have Changed” piece in this issue. If GNSS matters continue developing along the same paths they follow now, the hierarchy of satnav systems, by user numbers, market share, health, robustness, economic viability, yea even unto military prowess, may well shift.
The uncertain fiscal year 2013 funding caused by the combined effects of a possible year-long Continuing Resolution in the U.S. Congress and radical budget surgery known as sequestration currently has military chiefs directing severe reductions to operation and maintenance spending.
Operations and maintenance keep satellites flying.
“Our proposed near-term actions,” write the civilian Secretary of the Air Force and the U.S.A.F. General Chief of Staff, “include . . . defer[ring] non-emergency Facilities Sustainment, Restoration, and Modernization (FSRM) projects, resulting in a reduction of roughly 50 percent in FSRM spending; where practical, de-obligat[ing]/incrementally fund[ing] contracts to encompass only FY13.”
Modernization will (or would) keep GPS apace with user requirements, growing security needs, and an increasingly digital world. Incremental funding has delayed new signals and new capabilities time and again; sounds like it’s set to do more.
“For now, and to the extent possible, any actions taken must be reversible at a later date in the event that Congress acts to remove the risks I have described,” writes Ashton Carter, Deputy Secretary of Defense, to nearly every one under the sun connected with the military and money.
When is decay reversible? The notion of a tipping point is that, once passed, it cannot be re-crossed again in the opposite direction. Neither the status quo nor stability can be restored.
Many of us in the private sector have gone through successive rounds of cutbacks and lay-offs. Such measures first trim away the fat. This can be healthy, to some extent, although fat stores energy for later use. Then they start slicing into muscle. This reduces the ability to function. Finally, in many cases, they take a hacksaw to the bones. This not only cripples the organism, it effectively destroys it.
