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In this second installment of our review of innovations in GNSS receivers, we present the responses from ComNav Technology, Raytheon, TeleOrbit and Unicore to the same questions that we posed to CHC Navigation, Eos Positioning Systems, Hemisphere GNSS, Hexagon | Novatel, Javad GNSS, Septentrio and Trimble in the January issue:

• utilizing Galileo and BeiDou
• dealing with jamming and spoofing
• integration with inertial measurement units (IMUs) and other sensors
• positioning using cell phones and other consumer devices
• any other areas or challenges they find particularly significant.

All four respondents in this issue, like to those in the January issue, report that they are making full use of the new GNSS signals available, taking hardware and software measures to counter jamming and spoofing, and integrating IMUs and other sensors with their GNSS receivers to help achieve continuous navigation and positioning in obstructed environments. In addition, they are continuing to develop mass-market applications, because high-precision positioning is becoming increasingly important for cellphones and wearable devices. For a fuller review of these trends, see my introduction to the first installment.

Notably, two of the companies featured in this issue, ComNav Technology and Unicore, are Chinese.

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Raytheon

With Chad Pillsbury, Senior Director, Raytheon Intelligence & Space’s Resilient Navigation and Reconnaissance Solutions

Utilizing Galileo and BeiDou
Integration and fusion of multiple space position services is a key element in achieving assured positioning, navigation and timing (PNT). A combination of commercial and military-code navigation signals, when coupled with evolving sensors, provide more resilient methods of navigation and enable new concepts of operations related to PNT. Over the next two years, RI&S will customize these concepts of operation (CONOPS) for our United States and international allies to harness the power of fusion in resilience.

Dealing with jamming and spoofing
As threats to GPS continue to evolve and mature, RI&S continues to develop alternative navigation solutions, as well as GPS-capable receivers and antennas, aimed at defending against a variety of spoofing and jamming technologies. Our latest anti-jam, anti-spoof and high-precision solutions leverage a recent technology breakthrough that lowers size, weight, power and cost while boosting performance in the new M-code and alternative navigation applications.

Integration with IMUs and other sensors
IMUs are the cornerstone of high-performance navigation systems and will continue to be in the future. Recent innovations allow some systems to become more IMU agnostic, or even to consider microelectromechanical systems (MEMS) IMUs depending on performance, which can allow the customer greater flexibility and a more open architecture.

Positioning with consumer devices
RI&S sees 5G as a game-changing technology, with a lot of possibilities in the assured navigation market. We also look to cellphones as a great area of interest — especially for exploring unforeseen signals, considering human international models, and learning how the next generation of GPS users expect to see PNT information displayed.

Other significant challenges and opportunities
The future of GPS lies in a system-of-systems approach. Using time as a backbone, navigation systems can securely share time, data, position and intent across the network. Broadly, this approach can be used in civil, commercial and military environments. RI&S is fully focused on developing capabilities to achieve this ideal state.

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Unicore Communications

With Gao Jingbo, Marketing Director

Utilizing Galileo and BeiDou
Most of Unicore’s high-precision products support all constellations and multiple frequencies. The new BeiDou 3 provides precise point positioning (PPP) service from three geostationary satellites via the B2b frequency, while Galileo offers up to five frequencies — E1, E5a, E5b, E5 AltBOC and E6. End users will benefit from improved PNT availability, reliability and continuity as access to those signals greatly reduces multipath effects and allows faster PPP convergence times.

Dealing with jamming and spoofing
To effectively deal with signal jamming and spoofing, it is important to know their sources. GNSS receivers also are susceptible to electronic interference and vulnerable to complex electromagnetic environments. Unicore integrates GNSS RF, baseband and algorithms into a single GNSS system-on-chip (SoC) that mitigates external interference. Joint time-frequency domain interference mitigation technology also is adopted in chip design.

Integration with IMUs and other sensors
Demand for seamless, accurate indoor-outdoor location is increasing. The integration of GNSS with IMUs, lidar, cameras and other sensors helps achieve continuous navigation and positioning in obstructed environments such as urban canyons and tunnels. Unicore offers receivers integrated with both high-end IMUs and affordable MEMS-based devices. Dual-frequency GNSS plus MEMS provides an ideal positioning solution for automotive applications.

Positioning with consumer devices
High-precision positioning is becoming increasingly important for cellphones and wearable devices, and multi-scenario adaptation is necessary. Instead of integrating standalone GNSS chips with smartphone processors, cellphone manufacturers prefer to cooperate with GNSS manufacturers through GNSS intellectual property (IP) licensing. To ensure high-precision service, better cellphone antennas are also important.

Other significant challenges and opportunities
We strive to deliver reliable, timely and smart positioning for anything, anywhere, anytime. Next-generation GNSS location products and services should be more end-user-friendly. The hardware interface will be more universal, flexible, configurable and adaptable with different algorithms for a diverse range of applications.

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Teleorbit

With Daniel Seybold, CEO

Utilizing Galileo and BeiDou
Our GOOSE receiver has been able to use Galileo since its beginning and BeiDou since the forth quarter of 2020. Signals from both can be used individually or with other signals (GPS, Galileo, GLONASS and BeiDou, plus SBAS).

Dealing with jamming and spoofing
Open Service Navigation Message Authentication (OSNMA) is now implemented on the GOOSE, which helps mitigate spoofing attacks. GOOSE’s recording function enables users to record simulated jamming/spoofing attacks, and then analyze the behavior of the GOOSE and the received signals. We are developing various GNSS antenna arrays for nulling and beamforming, as well as a left- and right-hand circular polarized (LHCP/RHCP) antenna with GOOSE adaption for signal processing.

Signal conditioning on the GOOSE platform is based on a high-rate discrete Fourier transform (DFT)-based data manipulator algorithm, known as an HDDM algorithm, that fulfills multiple roles. The HDDM algorithm removes a wide range of interference signals, equalizes the spectrum, or restructures the spectrum.

Integration with IMUs and other sensors
We offer a GNSS antenna with an integrated IMU. Thanks to its open software interface, fusing IMU or other sensor data with GNSS data is easily done with GOOSE. Vector tracking, deep coupling and other sensor fusions (for example, 5G) are on the GOOSE roadmap.

Positioning with consumer devices
Our ongoing AMELIE project will study advanced techniques for the miniaturization and radiation enhancement of GNSS mass-market antennas to be applied in the design, manufacturing and testing of a multi-frequency, low-cost, high-gain dual circularly polarized antenna for the next generation of consumer devices. In 2021, we will build the following antenna demonstrators: single-frequency (L1/E1), dual-frequency (L1/G1/E1, L5/E5a/E5b) and multi-frequency (L1/G1/E1, L5/E5a/E5b, L2, E6).

Other significant challenges and opportunities
GOOSE can track the Galileo E5AltBOC (wideband) signal, which provides code-range variances below a few decimeters. This offers a significant increase in the accuracy of code measurements in terms of reduced noise and mitigation of multipath effects, compared to conventional signals. GOOSE will provide two different approaches for robust tracking: vector tracking for dealing with challenging environments where multipath occurs or buildings block signals, and adaptive tracking to allow the receiver to acclimate to its surroundings by adapting the bandwidth in the loop depending on movement, such as high dynamics.

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ComNav Technology

With Min Xu, Director of GNSS Technology R&D Department

Utilizing Galileo and BeiDou
We keep up with the development of GNSS. Our new K8 series of high-precision GNSS modules support the recently completed BDS-3 and Galileo constellations concurrently, significantly improving positioning accuracy especially when signals are partially obstructed. Despite their complex design, the size of K8 modules decreased by almost 36% from their precursors and power consumption dropped to 1.0W, making them easier to integrate.

Dealing with jamming and spoofing
We have developed algorithms to eliminate specific forms of jamming and spoofing, with a focus on narrowband interference. The newly released Quantum III SoC chip — integrated with wideband signal-receiving technology, wideband and narrowband anti-interference technology, and anti-continuous wave interference technology — can provide high-quality observation information in a complex electromagnetic environment.

Integration with IMUs and other sensors
There is an increasing need to add IMUs to supplement obstructed GNSS signals. Empowered by a high-precision IMU, our N5 receiver supports tilt survey with accuracy of less than 2.5 cm. Users can survey without a centering bubble as its calibration-free tilt compensation protects it from magnetic disturbances. We are also focusing on image sensors, such as cameras and radars, to make data collection more flexible and reliable.

Positioning with consumer devices
Our high-precision products are mainly used in professional fields such as land surveying, deformation monitoring, and UAVs. We are continuing to explore GNSS products for consumer markets, which are sensitive to power consumption and cost. The upcoming M10 GNSS is a compact and portable receiver for mass-market applications, such as person or vehicle tracking and fleet management.

Other significant challenges and opportunities
GNSS technology can be widely applied in agriculture, transportation and infrastructure construction. We developed the AG360/AG360 Pro Agricultural Automatic Driving system, which drives autonomously without damaging crops. We collaborated with China Mobile to build more than 2,000 CORS stations to provide high-precision positioning services in support of smart-city construction, IoT and location-based services.

Alliance membership has tripled in past 13 months as the organization grows advocacy for ever-increasing importance of GPS technologies to the global economy.

The GPS Innovation Alliance (GPSIA) has announced L3Harris Technologies as the newest member of the organization.

L3Harris Technologies, a global aerospace and defense technology innovator, joins a core of companies committed to furthering GPS innovation, creativity and entrepreneurship.

As the newest member, L3Harris Technologies will work with GPSIA to promote the modernization of GPS and its impact on military operations, economic growth and technological innovation.

“With the addition of L3Harris, the alliance welcomes a company recognized globally for developing and advancing innovative uses of GPS to protect our nation’s national security,” said GPSIA Executive Director J. David Grossman. “Having now tripled membership over the last 13 months, GPSIA is in a position of strength to continue leading advocacy for the promotion, protection and enhancement of GPS, both in the U.S. and around the globe. L3Harris Technologies is an integral part of the deployment of next-generation GPS III satellites and we look forward to working with them to ensure this technology remains the gold standard for delivering positioning, navigation and timing functions to our military as well as a wide range of other sectors, including transportation, agriculture, electricity and finance.”

L3Harris Technologies has played an integral part in the story of GPS, as it has provided navigation technology for every U.S. GPS satellite ever launched. L3Harris Technologies is developing 10 GPS III satellite navigation payloads for the U.S. Air Force’s GPS III satellite program, four of which are already operational.

The company will also provide navigation payloads with fully digital Mission Data Units (MDU) for the U.S. Air Force’s GPS III Follow-On, known as GPS IIIF, satellites. The MDU will provide even more powerful signals and ensure flawless atomic clock operations.

“GPS technology is an important part of the modern world and critical for the warfighter,” said Joseph Rolli, L3Harris Technologies Positioning, Navigation and Timing.

“With more than 40 years of experience developing GPS technologies, L3Harris aims to continue to improve the system with a more powerful, reliable, and flexible signal. We look forward to joining GPSIA and its other industry leading members as we advocate for continued support of this incredible system,” Rolli said.

The National Institute of Standards and Technology (NIST) has drafted guidelines for applying its Cybersecurity Framework to critical technologies such as GPS that use positioning, navigation and timing (PNT) data. Part of a larger NIST effort to safeguard systems that rely on PNT data, these cybersecurity guidelines accompany NIST efforts to provide and test a resilient timekeeping signal that is independent of GPS.

Formally titled the “Cybersecurity Profile for the Responsible Use of Positioning, Navigation and Timing (PNT) Services (NISTIR 8323),” the new guidelines are designed to help mitigate cybersecurity risks that endanger systems important to national and economic security, including those that underpin modern finance, transportation, energy and additional economic sectors.

The draft profile is part of NIST’s response to the Feb. 12, 2020, Executive Order on PNT. In early 2020, NIST sought public input regarding the general use of PNT data. The PNT profile will join the growing list of profiles created to help apply the NIST Cybersecurity Framework to particular economic sectors, such as manufacturing, the power grid and the maritime industry. The scope of the profile includes any system, network or other asset that uses PNT services, including systems that receive and rebroadcast PNT data.

While its scope does not include ground- or space-based source PNT signal generators and providers (such as satellites), the profile still covers a wide swath of technologies. Partly for this reason, NIST’s Jim McCarthy said that it is intended to be a foundational set of guidelines that PNT users can customize.

“The profile is meant to help a broad set of users address their cybersecurity needs,” said McCarthy, one of the draft’s authors. “Rather than focus on a single economic sector, we designed it to apply to all users of PNT. Agencies and companies can tailor it to their needs based on their particular cybersecurity risk and other sector-specific factors.”

As directed by the Executive Order, the profile can help organizations accomplish four tasks:

• identify systems that use PNT data, and/or that propagate this data based on a source signal
• identify PNT data sources, such as a GPS signal
• detect disturbance to and manipulation of systems that use PNT services
• manage the risks that come with responsible use of these PNT services

“Our premise is that there are organizations that may not realize they are using PNT data, or know how they are using it,” McCarthy said. “Part of our goal is to help them make these connections so they can protect their operations more effectively.”

The Executive Order also delegates to the Department of Commerce the critical task of providing a source of Coordinated Universal Time (UTC) that is independent of GPS. To this end, NIST also recently conducted initial tests of a special calibration service for companies, utilities or other organizations that wish to receive NIST’s version of the global time standard, UTC(NIST), through commercial fiber-optic cable.

The service aims to provide a time reference directly traceable to UTC(NIST) with an accuracy of 1 microsecond — good enough for telecom networks, the power grid and financial markets, and thereby boosting the resilience of accurate time distribution and the infrastructure sectors and subsectors that use timing services.

The initial link is a collaboration between NIST and OPNT, a commercial time-service provider based in Amsterdam, the Netherlands. While the work was led by researchers at NIST’s Boulder, Colorado, campus, the dedicated optical fiber connects the reference time scale at NIST headquarters in Gaithersburg, Maryland, to a facility in McLean, Virginia, that will ultimately serve as the hub for East Coast distribution of timing data.

OPNT has extended the initial fiber link to Atlanta, Georgia, about 800 kilometers from McLean. Preliminary data suggest that this link will be able to support the requirements of the Executive Order.

My last column highlighted an ArcGIS web application that incorporates various datasets and data layers to assist surveyors planning vertical control surveys. On Jan, 29, the National Geodetic Survey (NGS) released the latest experimental geoid model, xGeoid20, and a new gravity interpolation tool (see box below, “NGS Releases Annual e& Gravity Interpolation Tools”).

This newsletter will highlight some attributes of these two new products. First, why am I writing about another experimental geoid model. I discussed xGeoid18 in my December 2018 column and xGeoid16 in my June 2017 column. What’s important here is that this will be the last experimental geoid model until 2022, and the dynamic geoid model has also been updated this year in the form of xDGEOID20.

xDGEOID20 is produced by NGS within the Geoid Monitoring Service (GeMS) and is part of the new NAPGD2022. Therefore, users only have a few more years to understand the differences between the hybrid geoid model that is being used today to estimate GNSS-derived orthometric heights and the gravimetric geoid model which will be used to estimate North American-Pacific Geopotential Datum of 2022 (NAPGD2022) GNSS-derived orthometric heights.

NGS also announced a new gravity tool, denoted as “The Experimental Gravity Model 2020 (xGRAV20).” xGRAV20 is designed to provide a full-field gravity value and a digital elevation model height at a-specified location. The xGRAV20 model will be important to users that are computing leveling-derived orthometric heights consistent with NAPGD2022.

It is important to note that the xGEOIDs provide a preliminary but increasingly-accurate view of the changes expected from the upcoming NAPGD2022. Also, the xGEOID20 geoid model is the first combination of the geoid models computed by scientists at NGS and Canadian Geodetic Survey (CGS). One unique element to xGEOID20 is that the differences between the A and the B model are due to the contribution of the GRAV-D airborne gravity and differences in methodology.

The National Geodetic Survey (NGS) has published annual experimental geoid (xGEOID) models since 2014. Each of these experimental geoids demonstrate the improvements provided by the addition of airborne gravity data (GRAV-D data) and by the refinement of geoid computation methods.

First, users can access the xGeoid20 model here. See the box titled Experimental Geoid Models 2020 (xGEOID20).

As the image above indicates, the xGEOID20 is available over a very large area. The box below lists the latitude and longitude boundaries of the areas where xGeoid20 is available.

To use the xGeoid20 Interactive Computation Page, the user can click on the “ACCESS TOOL” button below the map or the Interactive Computation button on the left side of the webpage (see the image above, “Experimental Geoid Models 2020 (xGEOID20)”). I’d like to highlight a statement that NGS added as a mote on the computation page:

1. Coordinates will be processed as IGS14.
2. The epoch should be in decimal year format and reflect the user-specified output epoch. If no epoch is entered, the tool will use a default epoch equal to the epoch of the static geoid model, which is currently 2020.00.

The user needs to know that the epoch is used to compute the xDGEOID20 value. I will demonstrate how this works later in this column.

As in past xGeoid interactive computations web applications, the user can submit data in various formats. The box titled “Input Formats Permitted for xGeoid20 Webtool” provides a list of the permitted formats. It should be noted that inputting an ellipsoidal height, epoch and name are optional. However, the default epoch is 2020.00, so if you want a different epoch, you need to enter the date. Also. the program will only compute an orthometric height if the user provides an ellipsoidal height.

Users have the option of getting the output from the xGeoid20 tool on their computer screen or in the CSV format. The box below is an example of inputting data using the screen option. Once you enter your data, the user clicks on the submit button.

The next image shows an example of the output using the screen option. I have highlighted a few numbers that I’d like to address.

• Your input in NAD83 (2011) epoch 2010.00 (red). I entered my coordinates as NAD 83 (2011), and it assumed that these coordinates are epoch 2010.0.
• Your Result in IGS14 epoch 2020.00 (blue). The routine provides your output coordinates in IGS14, epoch 2020.00. This is the epoch of the static geoid model.
• The geoid height of GEOID18 (with respect to NAD83) and The orthometric height in NAVD88 (based on GEOID18) (green). This NAVD 88 value is for comparison purposes only. It is using GEOID18 and provides an estimate of the differences between the future NAPGD2022 and the current NAVD 88. The orthometric height is computed using the following formula: NAD 83 (2011) ellipsoid height (epoch 2010.0} minus GEOID18.
• Ortho Height (brown). This is the estimation of the orthometric height using the following formula: IGS14 ellipsoid height (epoch 2020.0} minus xGEOID20A (or B).
• Ortho(model)-NAVD88(GEOID18) (purple). These differences are the estimates of the differences between the future NAPGD2022 and the current NAVD 88. It provides the differences for both the xGeoid20A and xGeoid20B model. I look at the B model because it used the GRAV-D data in the development of the model.
• Accuracy (yellow). This is the estimated 95% confidence interval for geoid height.
  Example of Output Format from Screen Option.
  

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xGEOID20 Interactive Computation Output

Note: The GRS80 ellipsoid is used for both NAD83 and IGS14.

N: The geoid height at epoch t0 = 2020.0, which is geocentric and relative to the GRS80 reference ellipsoid.

Accuracy: Estimated 95% confidence interval for geoid height.

DN: The time-dependent geoid change computed between user inputted epoch (t) and t0. To obtain the dynamic geoid height at user inputted epoch (t), add N + DN.
Either Model A or Model B N values may be used for this depending on user preference.

The box below shows an example of inputting data using the CSV option.

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Example of Output Format from CSV Option

Note: The GRS80 ellipsoid is used for both NAD83 and IGS14.

N: the geoid height at epoch t0 = 2020.0, which is geocentric and relative to the GRS80 reference ellipsoid.

Accuracy: Estimated 95% confidence interval for geoid height.

DN: the time-dependent geoid change computed between user inputted epoch (t) and t0. To obtain the dynamic geoid height at user inputted epoch (t), add N + DN. Either Model A or Model B N values may be used for this depending on user preference.

Cnt,Station,NAD83_Lat,NAD83_Lon,NAD83_Eht,Input_Epoch,IGS14_Lat,IGS14_Lon,IGS14_Eht,Output_Epoch,GEOID18_Ht,Oht_NAVD88,xGEOID20A_Ht,xGEOID20B_Ht,xGEOID20A_Accuracy,Oht_xGEOID20B,Oht_NAVD88,Oht_Diff(xGEOID20A-NAVD88),Oht_Diff(xGEOID20B-NAVD88),DN,Epoch

0,PA,40.616935533762,77.4066810996784,222.425581993569,2010.00,40.6169445389,77.4066880139,221.191,2020.00,-33.685,256.111,-34.475,-34.477,0.039,255.666,255.668,-0.445,-0.443,0.000,2020.000
1,PR,18.2570177272727,66.5508117355371,6.65385123966942,2010.00,18.2570227778,66.5508102806,4.776,2020.00,-39.379,46.033,-41.690,-41.679,0.040,46.466,46.455,0.433,0.422,0.000,2020.000

The printed output from the CSV option looks very confusing, but it can be imported into an excel spreadsheet. The headings and values are all separated by a comma so everything falls into the appropriate columns after importing the data (see image below.)

I stated in the xGeoid20 write up that the dynamic geoid model has also been updated this year in the form of xDGEOID20. This model is produced by NGS within the Geoid Monitoring Service (GeMS) and is part of the new NAPGD2022. For a thorough discussion on GeMS and the time-dependent geoid, view the webinar from NGS’ presentation library. See the box titled “GeMS Webinar by Kevin Ahlgren.”

Also, one of my previous columns described NGS’ GeMS program. The images titled “Examples of the Time-Dependent Geoid Change in Alaska EPOCH 2020.0” and “Examples of the Time-Dependent Geoid Change in Alaska EPOCH 2025.0” show the change in geoid value from Epoch 2020 to Epoch 2025 for two stations in Alaska.

First, looking at the box titled “Examples of the Time-Dependent Geoid Change in Alaska EPOCH 2020.0,” the change between NAPGD2022 and NAVD 88 is approximately 1 meter. Users should note that the GEOID12B is used to establish the NAVD 88 height. Alaska was not included in GEOID18. Comparing the two Alaska labeled boxes, the xDGEOID2022 change between 2020.0 and 2025.0 is –4 mm. I will address this topic in more detail in future newsletters.

As stated by NGS news announcement, “The xGEOID models provide a preliminary but increasingly-accurate view of the changes expected from the upcoming North American-Pacific Geopotential Datum of 2022 (NAPGD2022).” NGS has produced many figures that describe the bias and trend between the future NADGP2022 and NAVD 88. In my June 2017 column I provided a plot that depicted the difference between NAPGD2022 and NAVD 88 based on the GPS on Bench Mark dataset. See the image below.

These figures provide a broad picture of the change but to better understand the changes across the Nation, I used the GPS on Bench Mark dataset, that was involved in the creation of Geoid18 model, to compute an average latitude, longitude, and ellipsoid height for every State. Obviously, this is a fictitious mark but it provides an idea of the average change based on marks that have both a GNSS-derived ellipsoid and a leveling-derived orthometric height. The plot titled “Difference Between the Future NAPGD2022 and NAVD 88” depicts the average difference for each state based on the GPS on Bench Mark data file. These differences were generated using the xGeoid20B values from the output of the xGeoid20 website.

I would encourage everyone to select a couple of marks and compute the differences to understand the change in their particular region. I was the NAVD 88 Project Manager and I informed users of the potential changes between the NGVD 29 and NAVD 88 for about a decade, and I still had surveyors tell me that they didn’t know it was coming. Please take a few minutes to read NGS’ write up on xGEOID20, estimate the differences in your area of interest, and spread the word to your colleagues, friends, and clients.

The last item that I’d like to highlight is that NGS has released a beta version of s surface gravity model consistent with xGEOID20. See the box titled “Experimental Surface Gravity Model 2020 (xGRAV20).” Users can access the beta webtool here.

The access and input to the tool is similar to the xGEOID20 web tool. Saying that, I’d like highlight a few items:

• The input height should be an orthometric type of height not an ellipsoid height.
• If a height is entered, the tool will assume that is correct and use it for the gravity prediction.
• If you do not know the elevation, leave the entry blank. The tool will use the DEM interpolated height if it is blank.

The box below provides the output using the tools sample data.

This gravity tool will be important when users want to incorporate leveling-derived orthometric heights into NAPGD2022. We will address this tool in more detail in future newsletters. I want to emphasis that these two web tools are beta sites. As a beta site, users should verify all information from the site. I encourage everyone to access the tool and check out a few of their favorite marks, and then send an email to NGS informing them of what you like, what you would like to change, and what you would like to see added to the tool.

NGS is releasing this tool as a beta product to get feedback from users. They are interested in your feedback concerning its function and usability as well as how users would like to interact with NGS web tools in the future. Email NGS at ngs.feedback@noaa.gov.

In conclusion, I want to leave you with a thought about change. When I give presentations and seminars, I usually include a slide that probably expresses the thoughts of many individuals.

My brother once told me:

“If you geodesists did it correctly the first time you wouldn’t have to keep performing adjustments and changing the values. Just do it right the first time.”

He’s a doctor and said he must do it right the first time.

My response to my brother and to everyone else is the following:

If you want to improve you have to be willing to change, and if you want to continue to meet future positioning requirements you need to continually change.

Winston Churchill said it better “To improve is to change; to be perfect is to change often.”

The Institute of Navigation (ION) has announced the new members of its Executive Committee, Council and Standing Committee Chairs following its Annual Awards during the ION International Technical Meeting and Precise Time and Time Interval Systems and Applications Meeting, both held virtually Jan. 25-28.

The ION Executive Committee, Council and Standing Committee Chairs will serve a two-year term.

“ION has a distinguished and passionate group of positioning, navigation and timing professionals in key positions to advance the goals of the organization.” said Lisa Beaty, executive director at ION.

The new members include:

ION Executive Committee
• President: Frank van Diggelen, Google
• Executive Vice President: Sherman Lo, Stanford University
• Treasurer: Frank van Graas, Ohio University
• Eastern Region Vice President: Jason Rife, Tufts University
• Western Region Vice President: Tim Murphy, The Boeing Company
• Satellite Division Chair: Patricia Doherty, Boston College
• Military Division Chair: John Langer, The Aerospace Corporation
• Immediate Past President: Y. Jade Morton, University of Colorado at Boulder

Council members
• Eastern Council Member-at-Large: Seebany Datta-Barua, Illinois Institute of Technology
• Eastern Council Member-at Large, Sanjeev Gunawardena, Air Force Institute of Technology
• Western Council Member-at-Large: Paul McBurney, OneNav
• Western Council Member-at-Large: Jihye Park, Oregon State University

Technical representatives
• Fabio Dovis, Politecnico Di Torino, Italy
• Christoph Gunther, German Aerospace Center, Germany
• Allison Kealy, RMIT University, Australia
• Nobuaki Kubo, Tokyo University of Marine Science & Technology, Japan
• Alexander Mitelman, AMM Technical Consulting
• Madeleine Naudeau, Air Force Research Laboratory
• Laura Norman, NovAtel, Canada

Standing Committee Chairs
• Awards Chair: Michael Meurer, German Aerospace Center, Germany
• Bylaws Committee: Deborah Lawrence, Federal Aviation Administration
• Ethics Chair: Heidi Kuusniemi, University of Vaasa & Finnish Geospatial Research Institute, Finland
• Fellow Selection Chair: Terry Moore, United Kingdom
• Finance Chair: Gary McGraw, Collins Aerospace
• Meetings Chair: Jeff Martin, Spirent Federal Systems
• Membership Chair: Okuary Osechas, German Aerospace Center, Germany
• Nominating Chair: Y. Jade Morton, University of Colorado at Boulder
• Publications Chair: Richard B. Langley, University of New Brunswick, Canada
• Technical Committee Chair: Sherman Lo, Stanford University

Military receivers key to Orolia’s PNT Solutions

Orolia, through its Orolia Defense & Security business, announced in November 2020 the launch of M-code military GPS receivers in its line of positioning, navigation and timing (PNT) solutions.

The line includes M-code-enabled mobile mission timing and synchronization platforms, such as the SecureSync IDM resilient time and frequency reference solution, the first time server approved by the Defense Information Systems Agency (DISA), and the Versa mobile PNT platform to meet rugged size, weight, power and cost (SWaP-C) requirements.

M-code is a military signal used in the L1 and L2 GPS bands. It is required by congressional mandate for U.S. Department of Defense (DOD) military operations.
M-code is designed to enhance PNT capabilities and improved resistance to existing and emerging threats to GPS, such as jamming and spoofing. Operational benefits of M-code include:

• a higher power signal that offers improved resistance to jamming and interference
• advanced security features to prevent unauthorized access or exploitation
• improved message formats and signal modulation techniques for faster and more accurate performance.

Orolia has long supported the DOD’s need for selective availability anti-spoofing module (SAASM)-enabled PNT equipment, explained Hironori Sasaki, president of Orolia Defense & Security. “This announcement emphasizes our move toward M-code and the availability of M-code in our products,” Sasaki said. “Our focus has always been on staying in sync with the DOD and providing the latest and greatest technologies.”
Orolia now supports M-code in all its user products and offers two capabilities: simulation and M-code-enabled end-user devices. “They will each have a different approval process for export,” Sasaki said. “We follow DOD guidance on getting that capability out there.”

SecureSync, which is SAASM-enabled, has been deployed with DOD for many years, so Orolia has “a very good install base” of these devices, according to Sasaki. “We are providing a very easy and seamless upgrade path to go from SAASM to M-code in that platform.” The company’s Versa platform consists of the VersaSync and the VersaPNT, both small form-factor PNT devices designed for rugged application in military vehicles or military aircraft.

DOD has given Orolia approval to advertise the fact that it has these capabilities in its products. “We are expecting shipments to start in early 2021,” said Sasaki. “So, we are well on our way in development, implementation and productization.”

“We have been focusing on providing products that have a modular architecture, both in software and hardware,” Sasaki added. “We are embracing this approach of open architecture and continue to support the DOD in providing different layers of sensing and PNT protection in a way that can be incorporated into future DOD systems.

“We have already demonstrated our ability to deliver PNT solutions in various form factors, so I think we are in a good position to continue pushing forward with that open architecture approach,” Sasaki said.

What should the new administration’s priorities be to make PNT more resilient?

We asked Brad Parkinson, the “Father of GPS” and a GPS World Editorial Advisory Board member, what the new U.S. administration’s priorities should be to make positioning, navigation and timing (PNT) more resilient. For more answers from board members, see below.

Protect the Spectrum. Reverse FCC authorization for relatively high-powered Ligado transmitters that have been proven to degrade GPS and other GNSS operation for thousands of PNT users. All U.S. government departments and major user groups affected have pleaded with the FCC to reverse this terrible decision. There is little benefit from it to the American public.

Protect the rapidly evaporating and self-proclaimed Gold Standard of GPS. The GPS satellite designs are showing their age. They need to go to multiple launch (three at a time) and revert to simpler designs without the spot-beams and other weighty add-ons that greatly increase complexity and cost. The Chinese have added to BeiDou (a) inter-satellite precision ranging and wide-band communications, (b) geosynchronous satellites, probably with good spot-beam acquisition aids, and (c) a WAAS-like correction directly on the satellites, which may have accuracies down to real-time kinematic (RTK, perhaps a few centimeters). Also, they claim their basic accuracies to be better than GPS (it might be true!) — I think they already have operational retro-reflectors.

Allow and encourage export of the basic and quickest fix to jamming and spoofing for high-value PNT users. More than 40 years ago, we demonstrated, in hardware, a high anti-jamming receiver that could fly directly over a 10 kW GPS jammer and not be affected. We know that high-gain, digital beam-steering antennas will create close to immunity, but our manufacturers will not move this way because we cannot sell or use them on the international market.  These devices, combined with inexpensive inertial components and the newer signals, would make PNT virtually immune to current threats of interference — both jamming and spoofing.

Move the military focus from alternative PNT techniques to seriously upgrading their receivers and useful signals. No current or reasonably anticipated alternative can provide the accuracy (3D), availability or integrity of GPS. The new M-code and L1C signals have been in the queue for about 20 years. (Loran for ground operations probably is very vulnerable to direct attack in a fluid battlefield operation. Loran’s main value is to distribute time and for maritime users.) In those 20 years, we now have cellphone chips costing less than $5 that can listen to about 200 ranging signals and process RTK, as well as use all the corrections available (WAAS, EGNOS, etc.). Such capability cannot be found in military receivers. The Defense Department must improve its acquisition strategy in terms of both speed and competition, and ncorporate existing civil capability into military user equipment.

Take government actions to rapidly identify, shut down, and prosecute GPS jammers. Some believe this problem is much larger than recognized already. All cellphones should be required to report extraordinary spectrum noise levels or apparent attempts at spoofing. This should be fed to a dynamic national database, perhaps maintained by the Coast Guard. GPS users should have an automated way to find out whether there are substantial threats in their operating area.

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Brad Parkinson is the Edward Wells Professor, Emeritus, Aeronautics and Astronautics (recalled) and co-director of the Stanford Center for Position, Navigation and Time at Stanford University.

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Editorial Advisory Board PNT Q&A

Here are additional responses to the question from more GPS World Editorial Advisory Board members.

“We hope the new administration continues on the path established with the Executive Order last year for resilient PNT, supporting progress made by DHS and NIST in establishing resilient and cybersecure frameworks. It will be important for them to maintain an open market concept toward future innovative solutions and not mandate a particular PNT approach. Awareness of the criticality for trusted PNT in our mobile connected society is established and we must not lose this.”
John Fischer
Orolia

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“Resilient PNT should be a national security priority. Its continuity is vital to both military and economic/social activities of all kinds. Its qualities of spatial awareness and synchronization enable the efficient functioning of the most sophisticated modern technologies in the physical and cyber worlds while also simply getting people and things from point A to point B on schedule. In that context, the elements which comprise resilient PNT should be protected from natural or hostile disruption.”
Jules McNeff
Overlook Systems Technologies

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“Truly resilient PNT requires combining multiple positioning technologies to maximize resiliency. However, the government’s influence in many of the augmentation technologies (sensors, vision, etc.) is limited. What the administration can do is make GPS itself more resilient by speeding up the launch and acquisition schedule of GPS Block III. The new signals, particularly at L5, are invaluable for improved resiliency to jamming and spoofing as well as providing a significant improvement in accuracy.”
Greg Turetzky
Consultant

“Seen & Heard” is a monthly feature of GPS World magazine, traveling the world to capture interesting and unusual news stories involving the GNSS/PNT industry.

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Lost and found

Taking video from an airplane window 300 feet up carries its share of risks, discovered Brazilian documentary filmmaker Ernesto Galiotto. The bad news: A strong wind snatched his iPhone 6 from his hand. The good news: GPS enabled him to recover the phone, which suffered only a minor crack in its protective cover. The best news: The phone captured the entire 15-second drop on video. The incident happened over Peró beach 75 miles east of Rio de Janeiro, reported Brazilian news outlet G1.

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Finding particular trees in the forest

Locating and documenting a single tree in a forest planting can be difficult. Technicians at Land Life, an Amsterdam-based land restoration company, have switched from using QR codes and readers for tree identification to GNSS. By replacing the QR codes with accurate GNSS positioning, Land Life produced a four-fold increase in monitoring productivity. The company measures sapling height and health and combines that data with tree species, location, soils and environmental conditions to support planning and care. Field teams now use a Trimble R1 GNSS receiver to stream positioning data via Bluetooth to their smartphones.

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Answering an SOS

Yacht skipper Kevin Escoffier faced disaster during the Vendée Globe solo round-the-world sailing race. His yacht was pounded apart in raging seas 840 nautical miles southwest of Cape Town, South Africa. Once his raft hit the water, its rescue beacon activated. Through the Cospas-Sarsat service, the signal moved from Galileo satellites to ground stations in Toulouse, France, to Canberra, Australia, then to race directors, who sent the closest competitor to assist.

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No stopping required

India will be free of toll booths in two years, said Nitin Gadkar, the country’s transportation minister. According to the Times of India, the government will roll out GPS-based tolling across its national highway sytem. Tolls will be deducted directly from drivers’ bank accounts based on distance traveled. While commercial vehicles registered after January 2019 have tracking systems, the government has yet to outline plans to install GPS receivers in older private vehicles.

A roundup of recent products in the GNSS and inertial positioning industry from the January 2021 issue of GPS World magazine.

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Receiver board

Enhanced with corrections

The AsteRx-m3 Sx OEM board dual-antenna receiver combines Septentrio’s latest core GNSS technology with the SECORX-S sub-decimeter correction service to enable plug-and-play positioning. High-accuracy positioning is available directly out of the box, GNSS corrections automatically streamed to the receiver. This significantly simplifies the set-up process and eliminates the need for corrections service subscription and maintenance. Corrections are delivered via internet or L-band satellites, ensuring sub-decimeter service even in remote locations where there is no easy internet access.

Septentrio, septentrio.com

GNSS antenna

Smart antenna for 5G timing

The new TW5382 smart GNSS antenna is designed for high-accuracy 5G timing. The TW5382 is a multi-band, multi-constellation 5G smart GNSS antenna/receiver that provides 5 ns (1-sigma, clear sky view) timing accuracy. It consists of two components: a Tallysman GNSS Accutenna technology antenna and a professional-grade GNSS timing receiver module. Accutenna supports the full bandwidth of the TW5382 receiver, strong multipath mitigation and deep filtering in a compact IP69K enclosure. These features enable the antenna to provide a strong, pure, in-band, right-hand circular polarized signal to the receiver. The TW5382’s professional-grade multi-constellation and multi-signal timing receiver tracks GPS/QZSS (L1/L2), GLONASS (G1/G2), Galileo (E1/E5b), and BeiDou (B1/B2) signals.

Tallymatics, tallymatics.com

IoT GNSS module

For quick integration of precise positioning

The new Precision GNSS Module (PGM) is designed to offer fast evaluation and a quick path to production for those requiring a precise positioning solution. It is available in a simple-to-use, industry-standard mPCIe (mini peripheral component interconnect express) format and is designed specifically for Swift’s Starling positioning engine running on a host application processor to deliver real-time precision navigation. The PGM utilizes STMicroelectronics’ TeseoV chipset in Quectel’s multi-constellation, dual-band LG69T-AP receiver to create an affordable, easy-to-use solution for customers building industrial, last-mile and internet of things (IoT) platforms. This solution operates with the highest accuracy when used with Swift’s Skylark positioning service.

Swift Navigation, swiftnav.com

Inertial navigation system

Success in ultra-high-altitude flight simulation

CAST Navigation tested Emcore’s SDN500 inertial navigation system (INS) in an ultra-high-altitude flight simulation and achieved success. The test required simulating performance at an altitude of more than 24,000 meters and velocities over 600 m/s. Only a few aircraft in the world have such capabilities, including the SR-71 Blackbird, but it is not practical to participate in a test flight on the SR-71. Simulating the SDN500 INS test flight to specific customer profiles on a CAST system is straightforward and cost-effective. Emcore relies on GNSS/INS simulators for hardware-in-the-loop testing to verify the expected performance of algorithms. Emcore sought to validate the velocity and altitude limits of a new GNSS receiver along with the algorithm performance in a tactical-grade SDN500 system.

Emcore, emcore.com
CAST Navigation, castnav.com

5G chipset

Ready for mass-market 5G phones

The Dimensity 700 5G smartphone chipset is a system on chip (SoC) designed to bring advanced 5G capabilities and experiences to the mass market. MediaTek’s Dimensity family of 5G chips is designed to give device makers a suite of options for 5G smartphone models. The chips range from flagship and premium to mid-range and mass market devices to make 5G more accessible for consumers everywhere. GNSS signals received include GPS L1CA and L5, BeiDou B1I and B2, GLONASS L1OF, Galileo E1 and E5, QZSS L1C and L5, and NavIC.

MediaTek, mediatek.com

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UAV

Inspection software

For transmission towers

IHawk allows users to inspect sites remotely and then download and view the analysis anywhere in the world. It eliminates the need for engineers to climb towers for inspections or work in hazardous environments. The imagery and information gathered provides a detailed and highly accurate analysis of the condition of power transmission towers.

Cyberhawk, thecyberhawk.com

Heavy-lift UAV

System designed for Turkish rescue and security

The Alpin UAS is a long-range, heavy-lift unmanned helicopter capable of carrying up to 160 kg with a range of up to 840 km. The UAS includes a wideband satellite communication channel from its command-and-control station — a valuable feature, particularly for operations in remote areas. The Alpin unmanned helicopter is able to withstand severe weather conditions, carry multiple payloads, and transmit real-time information to defense forces and decision-makers in the field. Its system autopilot has features and advantages such as fully autonomous take-off and landing, remote ground-control network capability, auto-rotation landing capability and high efficiency flight control based on a total energy control system (TECS).

UAVOS, uavos.com

Metadata mapping

Secure web application enhanced for dji drones

LineVision Online now provides enhanced support for visualizing and mapping DJI drone video camera metadata and field-of-view projections. The secure web application is designed for immersive mapping, analysis, search, sharing and archive of geo-referenced videos, full-motion video, photos and other survey, inspection and surveillance datasets. With enhanced camera metadata mapping in LineVision Online, DJI drone videos can now display a dynamic, field-of-view outline representing where the gimbal camera was looking on the Earth as the video plays in the web-based map interface. Users can select any point along the UAV’s flight track on the map to immediately cue the video to play what was recorded at that location click point.

Remote GeoSystems, remotegeo.com

Agriculture drone

Comprehensive spraying system

The Agras T20 drone can conduct autonomous operations over a variety of terrains, such as broad-acre farmlands, terraces and orchards. As a comprehensive spraying system, the T20 allows users to easily set flight and operation parameters. With a built-in real-time kinematic (RTK) centimeter-level positioning system and RTK dongles, centimeter-level waypoint recording is enabled, strengthening operations and ensuring precision spraying.The T20 is equipped with eight nozzles and high-volume pumps that can spray at a rate of up to 6 liters per minute. A highly optimized wind field produces droplets of the correct size and consistency. The T20 is also equipped with a new four-channel electromagnetic flow meter, which monitors and controls four hoses individually, ensuring an efficient flow rate for each nozzle.

DJI, dji.com

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SURVEYING AND MAPPING

Virtual base station

New feature in post-processing software

A new virtual base station (VBS) feature is available in Qinertia, GNSS and inertial navigation system (INS) post-processing software. Trajectory and orientation are greatly improved by processing inertial data and raw GNSS observables in forward and backward directions. The VBS computes a virtual network around a project in which position accuracy is maximized, homogeneous and robust, such as a PPK short baseline. Once surveyors collect data, Qinertia chooses the most relevant reference stations, builds a virtual network and brings the project to centimeter-level accuracy with no convergence effects, even in urban areas.

SBG Systems, sbg-systems.com

3d data processing

Designed to decipher unstructured data

Enview Explore is a powerful web application that leverages artificial intelligence and cloud computing to automatically process 3D data at a high speed and scale. Enview performs a variety of geospatial operations, including object recognition, feature extraction, feature-based change detection, and 2D/3D measurement. Enview’s technology has been deployed on thousands of square miles worldwide to protect vital infrastructure and support mission-critical operations. Its unique method for classifying 3D data reduces time to action by focusing on finding meaningful insights.

Enview, enview.com

Pile installation

Machine-guidance system ready for solar

PDGrade — a machine guidance and positioning system that uses GNSS for pile driving applications — is now optimized for the solar industry with an increased capability in pile installation and navigation accuracy. It removes the need for surveying piles and reviewing as-built information by centralizing all relevant information and providing necessary details to operators and site supervisors.The system features both software and hardware applications to provide operators with detailed information such as pile navigation, pile location, positioning and height information, project progression tracking, and detailed accuracy. The PD machine is fitted with Carlson sensors and a ruggedized Windows-based MC10 tablet. The entire system is then calibrated within PDGrade.

Carlson Software, carlsonsw.com

By Jade Morton,
Guest Author

After more than five years of hard work by 131 authors from 18 countries, the new book set Position, Navigation, and Timing Technologies in the 21st Century (PNT21) is finally ready to meet readers.

Published by Wiley-IEEE Press, PNT21 offers a uniquely comprehensive coverage of the latest developments in the field of PNT by world-renowned experts. The two-volume set contains 64 chapters organized into six parts.

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Position, Navigation, and Timing Technologies in the 21st Century
Integrated Satellite Navigation, Sensor Systems, and Civil Applications
Y. Jade Morton, Frank van Diggelen, James J. Spilker Jr. and Bradford W. Parkinson, editors; Sherman Lo and Grace Gao, associate editors
Publisher: Wiley-IEEE Press
Hardcover Publication Date: January 2021
Vol. 1: ISBN: 978-1-119-45841-8, 1288 Pages
Vol 2: ISBN: 978-1-119-45849-4, 912 Pages

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Volume 1 focuses on satellite navigation systems, technologies, and applications. It starts with a historical perspective on GPS and other related PNT development.

Part A consists of 12 chapters on fundamentals of and latest developments in global and regional satellite navigation systems (GNSS and RNSS), the need for their coexistence and mutual benefits, signal quality monitoring, satellite orbit and time synchronization, and satellite- and ground-based augmentation systems that provide information to improve the accuracy of navigation solutions.

Part B contains 13 chapters on recent progress in satellite navigation receiver technologies such as vector processing, assisted and high sensitivity GNSS, precise point positioning (PPP) and real time kinematic (RTK) systems, direct position estimation techniques, and GNSS antennas and array signal processing. Also included are the challenges of multipath-rich urban environments, handling spoofing and interference, and ensuring PNT integrity.

Part C finishes the volume with eight chapters on satellite navigation for engineering and scientific applications. A review of global geodesy and reference frames sets the stage for discussions on the broad field of geodetic sciences, followed by a chapter on GNSS-based time and frequency distribution. One chapter each is dedicated to severe weather, ionospheric effects and hazardous event monitoring. Finally, comprehensive treatments of GNSS radio occultation and reflectometry are provided.

Volume 2 addresses PNT using alternative signals and sensors and integrated PNT technologies for consumer and commercial applications. An overview chapter provides the motivation and organization of the volume, followed by a chapter on nonlinear estimation methods which are often employed in navigation system modeling and sensor integration.

Part D provides seven chapters devoted to using various radio signals-of-opportunity transmitted from sources on the ground, from aircraft, or from low Earth orbit (LEO) satellites for PNT purposes.

In Part E, eight chapters cover a broad range of non-radio frequency sensors operating in passive and active modes to produce navigation solutions, including MEMS inertial sensors, advances in clock technologies, magnetometers, imaging, lidar, digital photogrammetry, and signals received from celestial bodies.

A tutorial-style chapter on GNSS/INS integration methods is included in Part E. Also included are chapters on the neuroscience of navigation and animal navigation.

Finally, Part F presents a collection of contemporary PNT applications such as surveying and mobile mapping, precision agriculture, wearable systems, automated driving, train control, commercial unmanned aircraft systems, aviation, satellite orbit determination and formation flying, and navigation in the unique Arctic environment.

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Table of Contents

Volume 1: Satellite Navigation Systems, Technologies, and Applications

• Part A: Satellite Navigation Systems
• Part B: Satellite Navigation Technologies
• Part C: Satellite Navigation for Engineering and Scientific Applications

Volume 2: Integrated Navigation Systems, Technologies, and Applications

• Part D: Position, Navigation, and Timing Using Radio Signals-of-Opportunity
• Part E: Position, Navigation, and Timing Using Non-Radio Signals-of-Opportunity
• Part F: Position, Navigation, and Timing for Consumer and Commercial Applications

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Collective Goal. Because of the diverse authorship and topics covered in PNT21, the chapters were written in a variety of styles. Some offer high-level reviews of progress in specific subject areas, while others are tutorials. A few chapters include links to MatLab or Python example code as well as test data for readers who desire hands-on practice.

The collective goal is to appeal to industry professionals, researchers and academics involved with the science, engineering and application of PNT technologies. The website pnt21book.com provides downloadable code examples, data, homework problems, select high-resolution figures, errata and a way for readers to provide feedback.
Jade Morton is a professor at the University of Colorado Boulder and director of the Colorado Center for Astrodynamics Research (CCAR).

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Jade Morton is a professor at the University of Colorado Boulder and director of the Colorado Center for Astrodynamics Research (CCAR).

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Excerpt from PNT21

14.1 Anatomy of a GNSS Receiver

Irrespective of the receiver type, the functionality of all GNSS receivers can be broken down into three major blocks: RFFE, baseband processor (BBP), and system processor (SP). In the literature, the term “baseband processor” may be used to refer to the combination of both the BBP and SP defined here. The general anatomy of a GNSS receiver is shown in Figure 14.3.

The RFFE converts the signals induced at one or more antennas into digitized sample streams. Depending on the application and market segment, data rates for these streams may be as low as 0.4 Mbytes/s (e.g. L1 band sampled at 3.5 MSPS and 1-bit sampling in an asset tracking device) to greater than 3 GB/s (e.g. L1 and L2 bands sampled at 60 MSPS and 16 bits across seven elements in an anti-jam military GPS receiver).

The BBP performs digital signal processing to acquire and track GNSS signals present in the digitized sample streams to produce raw GNSS observables for each visible satellite. These observables include time of transmission (TOT), accumulated Doppler Range (ADR), signal quality metrics such as carrier-to-noise density ratio (C/N0), in-phase and quadrature prompt correlator output (I/Q), and raw symbols of a GNSS signal’s broadcast navigation message (which are subsequently decoded). In addition, modern receivers typically perform varying degrees of situational awareness processing to monitor in-band interference such that a level of confidence can be assigned to these raw observables. Some advanced receivers have the ability to identify spoofing signals. Depending on the application, situational awareness outputs may be as rudimentary as the automatic gain control (AGC) voltage used to adjust front-end amplification or as sophisticated as spectrogram, histogram, and sample statistics for all streams evaluated at full sample precision.

The BBP also contains a counter that is driven by a digital clock signal that is phase-locked to the receiver’s reference oscillator. This counter is the basis for the receiver’s clock and is used to generate time-of-reception (TOR) epochs. Raw observables for all satellites in view that lead to range measurements are computed with respect to TOR epochs. Since the receiver clock is based on its reference oscillator, it drifts with respect to GNSS system times. Although possible, the frequency bias, drift, and drift rate of the reference oscillator are typically not adjusted to align with GNSS system time because dynamic adjustment of the oscillator can lead to instabilities. Instead, these parameters are estimated and used to drive a separate adjustable-rate counter that compensates for the reference oscillator errors. This forms the basis for GNSS disciplined oscillators.

It is possible to partition all baseband processing into two categories: sample processor (SMP) and reduced-data processor (RDP). The SMP performs high-rate but simple and algorithmically regular operations which largely comprise multiply-accumulate operations performed at the sample rate. The SMP may also contain configurable timers and pulse/event generators that determine sample processing intervals, as well as output precise timing pulses that are synchronized down to the nanosecond level with respect to GNSS system times (timing accuracy and precision are dependent on the application and market segment). The RDP performs low-rate but algorithmically complex operations. Some representative software functions running within the RDP are illustrated in Figure 14.3.

Bidirectional communications occur between the SMP and RDP at regular timed intervals corresponding to a kilohertz rate. This rate is easily handled by all modern microprocessors. Since these SMP/RDP transactions are time critical, the RDP runs either bare-metal code (i.e. no operating system) or a real-time operating system. The operations within the BBP are inherently parallel and largely independent of each other at the signal processing level. Some coupling occurs, for example‚ in code-carrier aiding, inter-frequency aiding (see Chapter 15), inter-satellite aiding (referred to as vector tracking, described in Chapter 16), and multi-element processing. However, this coupling is typically implemented at higher levels of abstraction. Modern multi-band and multi-constellation receivers are capable of tracking hundreds of GNSS signals simultaneously. To facilitate this highly complex command and control structure – which also needs to be dynamically scalable and adaptive depending on the number of satellites in view, environmental conditions‚ and operating modes – the control architecture is typically layered (i.e. hierarchical). Control at the individual signal acquisition and tracking layers is performed using simple configurable finite state machines (FSMs) whose state transitions are based on signal condition indicators such as code lock, phase lock, C/N0, and code-carrier divergence (CCD). These FSMs operate independently but are typically managed at a high level by the SP.

The SP takes the raw signal observables produced by the BBP and transforms them to the standard GNSS receiver measurements. These measurements include pseudorange (PR), accumulated Doppler range (ADR), carrier phase (CP), carrier Doppler, and C/N0. All modern GNSS receivers also compute position, velocity, and time (PVT) at configurable rates (1 to 100 Hz depending on the receiver type). The SP encodes these in one or more industry-standard data formats for distribution. These formats include Receiver Independent Exchange Format (RINEX), the National Marine Electronics Association (NMEA) format, the Radio Technical Commission for Maritime Services (RTCM) format, and vendor-specific proprietary binary formats.

The SP also performs all high-level functions that include receiver initialization, channel management, and user interface functions. Unlike the BBP, the operations within the SP are generally not time critical. In modern GNSS receivers, the SP is often an embedded computer running an advanced non-real-time operating system. It may also support modern data interfaces (wired USB and Ethernet, or wireless/cellular connectivity) and an advanced graphical user interface with touchscreen support. While too numerous to mention, representative software processes running within the SP are illustrated in Figure 14.3.

Although not shown in Figure 14.3, modern receivers (or the navigation system to which they are interfaced) may also support aiding from external sensors such as inertial measurement units (IMUs), magnetometers, inclinometers, barometers, wheel sensors, RADAR, lidar, infrared (IR), and electro-optical (EO) sensors. This external aiding to GNSS can occur at three levels: loose coupling (position level), tight coupling (measurement level), or ultra-tight coupling (sampled signal processing level). GNSS aiding using various non-GNSS sensors is described in Chapters 43–51 in Volume II, Part E.

As shown in Figure 14.3, a stand-alone GNSS receiver contains battery-powered low-power circuitry to keep track of absolute time while it is turned off. A real-time clock (RTC) driven by a low-power crystal oscillator accomplishes this task. In some cases, this crystal may be the same as the reference oscillator. Knowledge of absolute time, along with the last known location and previously decoded almanac/ephemeris data stored in the receiver’s non-volatile memory, allows it to estimate satellites in view and their Doppler offsets, thereby significantly reducing the TTFF: the time needed to acquire satellites and produce the initial PVT solution. In the case of modern military receivers such as M-Code, or subscription-based services such as the Galileo Public Regulated Service (PRS), the receiver must acquire the cryptographically generated spreading code that may never repeat. In this case, the initial time uncertainty has a significant impact on the acquisition search space and consequently the computational resources consumed by the acquisition engine as well as power consumption. The TTFF can be dramatically reduced when absolute time, the satellites in view, their Doppler frequencies, and ephemerides are sent to the receiver from a nearby reference station via a communications link. This describes the basis of Assisted GNSS (A-GNSS) technology, covered in Chapter 17 of this book.

In some respects, the reference oscillator can be considered the single most important component that affects GNSS receiver performance. Although the PVT solution estimates the deterministic components of the reference oscillator’s frequency error (i.e. short-term bias, drift, and drift rate), the stochastic component cannot be estimated and hence represents additional dynamics that must be tracked (i.e. in addition to satellite motion, user motion, satellite clock motion, and any ionospheric scintillation and multipath). The bandwidth of the carrier tracking loops must be increased to accommodate this close-in phase noise of the reference oscillator. This in turn increases the variance of the range measurements. The reference oscillator is also the only “moving part” in the receiver since it is based on the resonance of a quartz crystal or microelectromechanical systems (MEMS) structure. In addition to microphonics, which are small phase variations that may occur within the RFFE due to external forces (particularly if the RFFE comprises large discrete components), these forces couple through the resonating element leading to shock and vibration sensitivity [6]. Similarly, thermal expansion of the crystal as well as analog components in the RFFE due to changing ambient temperature, unless appropriately compensated or isolated, causes temperature sensitivity. The frequency synthesizer in the RFFE multiplies the oscillator phase noise and dynamics by the ratio of the synthesizer output frequency to the oscillator fundamental frequency, thus placing a significant short-term stability requirement on the reference oscillator. Oscillator short-term stability limits the coherent integration time, which is proportional to the processing gain. Hence, the quality of the reference oscillator directly impacts the recever’s attainable sensitivity (i.e. the minimum observable signal levels) as well as the rate at which it can output statistically independent measurements. Oscillator effects are covered in detail in Chapter 47.

The receiver intelligence process within the SP shown in Figure 14.3 performs functions such as determining what satellites are in view, how best to mitigate any in-band interference (as observed by the situational awareness indicators), dynamically adapting to varying operating conditions, determining the best set of range measurements to use for the PVT solution based on optimum satellite geometry and estimated range error metrics indicated by C/N0 (for signal blockage) and CCD fluctuations (for multipath and ionospheric effects), and many such highly complex decisions. Typically, these high-level functions occur at a lower rate such as 1 Hz or less. To a large degree, the level of sophistication and engineering embedded within the receiver intelligence block, as well as the other low-level control functions determines the receiver’s performance in the real world, as expressed by established figures of merit. These include measurement accuracy, update rate, TTFF, sensitivity, dynamics handling capability, multipath mitigation performance, interference detection and mitigation capability, receiver autonomous integrity monitoring, and fault detection and exclusion (see Chapter 23). In other words, for a given market segment and its associated SWaP-C constraints, the receiver’s hardware and available signal processing capabilities can only do so much. The rest, and quite often the attributes that distinguish it in the marketplace, lies within the hundreds of thousands of person-hours and centuries of combined experience baked into its sophisticated software/firmware.