MEMSIC has launched its latest inertial system, the INS380 — a complete inertial navigation system with a built-in 48-channel GPS receiver. The INS380 is part of a portfolio of inertial systems enabled with MEMSIC’s SmartSensingtechnology for a broad range of precision-motion sensing applications.
The MEMSIC portfolio consists of inertial measurement units (IMU), vertical gyros (VG), attitude and heading reference systems (AHRS), inertial navigation systems (INS) and tilt measurement systems in a variety of packages for system designers and end-equipment manufacturers.
The SmartSensing technology enables a turnkey system with better than 0.01 m/s velocity measurement accuracy. The integrated 3-axis magnetometer allows for accurate operation when the GPS signal is lost or when the vehicle comes to a stop. SmartSensing provides users with sensor fusion and performance in critical motion sensing applications.
SmartSensing combines enhanced and patented Kalman-based algorithm with proprietary temperature, motion and alignment calibration for consistent and high-accuracy performance over a wide range of extreme operating conditions. Applications include unmanned ground and aerial vehicles, platform stabilization, avionics, precision agriculture, construction and more.
INS380SA-400 EVALKIT is available for evaluation and ships completer with an INS380 unit along with necessary accessories for quick installation. Designers can evaluate and configure the system using MEMSIC’s NavView Software, available for download.
When Beijing UniStrong Science & Technology Co. Ltd. in Beijing, China, acquired the Hemisphere GPS OEM business back in January 2013, and the significant Hemisphere GPS agriculture business went off on its own under the new AgJunction name, it’s possible that people may have gotten the impression that the OEM business might have been weakened by the break-up. (Read my column about the changes here.)
There was word of a long-term supply agreement where the newly created Hemisphere GNSS was to still supply AgJunction with OEM receivers, but the OEM business now had to stand alone and fully support itself — perhaps a challenge for the teams in Scottsdale, Arizona, and Calgary, Alberta, that became part of the new company.
After the first transition year in 2013, Jon Ladd, chairman of the new Hemisphere GNSS board of directors and former CEO of Novatel, along with the other Hemisphere board members, decided to hire Chuck Joseph in January 2014. Prior to joining Hemisphere GNSS, Chuck Joseph was president and CEO of an energy technology company, and he was also senior VP and general manager of a tactile feedback technology company focused on GPS centric mobile and industrial applications. But the key experience that may have brought Chuck to Hemisphere GNSS was probably when he was corporate VP of marketing and sales at Magellan Corporation and executive VP and general manager of Trimble.
I talked at length with Chuck Joseph and his team recently about how things have gone since he joined Hemisphere and the changes that have brought them to some new product launches now being announced.
Chuck reviewed some of his experiences from Trimble — a time when even Trimble was struggling in the early days and he helped with a reorganization that pulled them back from some big losses around the time of the first Gulf War — and how that has helped him at Hemisphere GNSS. Focusing on the consolidation of products and markets that work, and moving away from things that don’t work as well — this is always a key element for any recovery.
As a part of Hemisphere GPS, the OEM business may have been at a major disadvantage when it was tied so tightly to the success of its own agriculture business — all of its receiver-development efforts were focused on agriculture applications and on whatever worked best for agricultural customers. So the rest of the company’s efforts to create a self-sustaining OEM business all came in second. But with some of the brightest innovators and developers in the GNSS OEM business, Hemisphere had a wealth of experience and a store of existing Intellectual Property (IP) ready to open up when the opportunity came around as a part of the new organization.
Chuck likes to talk about Hemisphere GNSS being a “start-up inside a reinvention” — a phrase that describes how life may have been re-energized and changed for the people in the new company. With UniStrong support, there was no need to seek other outside external investment for company expansion and sustainment, so all management effort could be initially focused on the re-engineering effort. Staff working groups were formed that were able to brainstorm and come up with new concepts, explore how they fit with their market and existing customers, and over time create viable approaches, turn them into strong business cases and then go find the support they deserved. “Disruptive” market ideas were at the forefront — ideas/products/services that would allow Hemisphere to make advances in the OEM market that would offset the strengths of the competition and allow them to succeed. Closer partnering with new and existing customers to provide improved value was a major leading concept.
The first product to hit the market from the new Hemisphere GNSS process came out of a 10-person team who set out to re-engineer and improve Hemisphere RTK — the release of Athena was announced at the beginning of May. As the announcement goes, this new RTK “excels in virtually every environment where high-accuracy GNSS receivers can be used.”
Customers have already validated Athena’s performance in long baseline, in open-sky environments, under heavy canopy, and in geographic locations with significant scintillation. Key features include:
Initialization in less than 15 seconds at better than 99.9% reliability
Robustness under the most aggressive of geographic and landscape environments
Industry-leading position stability for long baseline applications, with position quality often exceeding the performance of the best-of-breed RTK systems on the market
Sustained accuracy within GNSS scintillation-affected areas
Testimonials in the Athena release support Hemisphere’s claims — from independent testing (Andy Carbognin, Vecto Geomatics), marine construction and hydrographic survey (Cable Arm), land survey and machine control (Carlson Software) and agriculture precision steering (Novariant).
And Hemisphere GNSS has more new products coming — the company just announced its Atlas GNSS global correction service on June 15. Hemisphere is marketing Atlas using a “disruptive” approach, intended to not only provide end customers with the best value and best performance global correction service available today, but also to support the sales channel that the customers buy through. The sales angle chosen is to allow the sales channel to actually sell and bundle the Atlas service directly to the customer and make money from the sale of the service. This approach is not currently used by other correction service distributors, who tend to have manufacturers and customers deal with them directly for service, sales and support.
Hemisphere GNSS put together a team of seasoned developers to build Atlas that between them have already generated a huge amount of IP around corrections technology. Together, they have now developed the Atlas GNSS correction service, available via L-Band satellite broadcast and over the Internet, which uses the very latest technologies to deliver a correction service that matches or exceeds existing competitive system performance:
Positioning accuracy: Atlas provides competitive positioning accuracies down to 2 cm RMS in certain applications, often exceeding competitive systems’ capabilities
Positioning sustainability: Position quality maintenance in the absence of correction signals, using Hemisphere’s Tracer technology.
Convergence time: Industry-leading convergence times of 10-40 minutes.
Receiver-agnostic capability: Atlas is the most receiver-agnostic positioning system available. SmartLink technology allows an AtlasLink antenna to be used as an Atlas signal extension for any GNSS system which uses open communication standards.
Network RTK augmentation: BaseLink technology allows Atlas-capable receivers to self-calibrate, self-survey, and automatically manage the transmission of RTK corrections to augment or extend established or new GNSS reference networks in areas of poor Internet connectivity.
Atlas subscriptions: Subscriptions are now available for a range of Hemisphere GNSS’s multi-frequency, RTK-capable products — AtlasLink, R330u, V320, and VS330u — and will soon be available via the Atlas web portal and from a number of channel partners and OEMs such as Carlson Software.
Available Hemisphere GNSS Atlas service levels:
Service Level
Position Accuracy
H100
100 cm 95% (50 cm RMS)
H30
30 cm 95% (15 cm RMS)
H10
8 cm 95% (4 cm RMS)
The provision of “agnostic” corrections via the SmartLink service is a new twist that allows customers to buy the best correction service they choose, rather than being tied to a particular receiver manufacturer and/or their corrections services supplier. Using the Hemisphere GNSS AtlasLink smart antenna, corrections can be supplied over a standard interface to any make of GNSS receiver, provided it has an interface that is compatible with “open-standard” correction data, such as RTCM data format. It remains to be seen if this “receiver-agnostic” approach to corrections supply changes the way that PPP and other correction services are supplied across the industry.
The service can also be used to set up base stations to transmit corrections to an existing network using the BaseLink service option, which Hemisphere is also making available.
Meanwhile, back at UniStrong in China, Xinping Guo, president and CEO of UniStrong — or ‘XP’ as he is known to the Hemisphere GNSS team — has been actively seeking further funding through potential additional stock offerings, not only to maintain support for Hemisphere, but also to buy additional companies in China. While Hemisphere GNSS has ramped up revenue since being purchased by UniStrong and is on its way to a record year in 2015, it is clearly doing more things and announcing more new products and initiatives than its normal revenue ramp would solely support. So, just as in the case of a start up, UniStrong is supplying supplemental resources to support this very fast track growth.
Coordination of activities across the UniStrong and Hemisphere GNSS companies continues as the Hemisphere GNSS company/brand relaunch rolls out during the second half of this year. Product designs will flow back and forth across the group, too, with Hemisphere GNSS software used in UniStrong products, and BeiDou capability going into Hemisphere GNSS fourth-generation chips. The collaboration of the UniStrong and Hemisphere product development teams is producing products unique to each market place, to be sold and supported by the respective sales, support and marketing teams, helping both companies. While UniStrong may be able to claim to be leading in China in the single-frequency product (GIS, etc.) market, it’s also easy to see that bringing Hemisphere GNSS multi-frequency capability into China could also improve its domestic market share.
So, it’s been a good start to the reshaping of Hemisphere GNSS as a company, its capabilities and its approach to its chosen markets. Let’s see how this roll-out and the anticipated growth continue through the rest of the year, and we’ll check in again in detail with them in the fall. Many thanks to Chuck Joseph and his team for this inside look into what’s going on in the remaking of Hemisphere GNSS.
A free app for both iOS and Android features the results of European GNSS Agency (GSA) supported research and development initiatives. The new EGNSS Research and Development (R&D) application highlights the tangible results coming out of the 7th Framework Programme (FP7) and is designed to serve as inspiration for those participating in the Horizon 2020 (H2020) period.
The FP7 and H2020 programs, supported by the GSA, aim to support the development of EGNSS applications in key market segments. Both are geared towards accelerating the development of a European market for satellite navigation applications and creating new opportunities for European industry.
“The app is an excellent opportunity for the GNSS community to take stock in the lessons learned during the FP7 funding period and set our sights on future R&D initiatives,” said GSA Executive Director Carlo des Dorides. “The application’s segment-specific search feature responds to the varied needs of our users, providing them with easily accessible and relevant information at their fingertips.”
In addition to the search function, des Dorides notes that the demographics included with each project can help users identify opportunities for partnerships across segments and regions, and create virtual R&D networks.
The FP7 programmes had a considerably positive impact on the GNSS market, GSA said (download the brochure). Within the frame of the projects, 45 products were developed, and 80 prototypes were tested and validated during the 115 demonstrations that took place.
Today, Horizon 2020 is bringing new opportunities for GNSS applications development. Information on the 25 projects granted in the first H2020 Galileo call is already included in the application, and early next year it will be updated to include the 2nd call portfolio of projects.
The app is available for free download from the iTunes and Google Play stores.
The Multi Micro Hornet by OriginGPS was designed small with wearables in mind.
OriginGPS has launched the Multi Micro Hornet, a tiny fully integrated multiple constellation antenna module. The innovative architecture packs functionality and high-quality components in a small space to improve wearables’ fashion and function, the company said.
“A recent study by the European Global Navigation Satellite Systems Agency (GSA) showed that multi-constellation is becoming a standard feature in today’s user equipment,” said Gal Jacobi, CEO of OriginGPS. “Developers of wearables need modules with these features in the smallest size possible to be competitive in a market the GSA predicts will reach 14 million by 2023.”
The Multi Micro Hornet is designed for devices that require a small form factor, low power consumption, and high sensitivity. In keeping with the company’s “Mini + Mighty” corporate mantra, OriginGPS has reduced the total volume in size by over 68 percent of other GNSS antenna modules without sacrificing performance, the company claims.
The Multi Micro Hornet by OriginGPS.
The Multi Micro Hornet has features that will improve the navigation experience of wearables and other Internet of Things devices, including:
Small size, high performance: Despite its miniature outline of 10 x 10 mm and height of 5.9 mm, the Multi Micro Hornet module offers superior sensitivity and outstanding performance, achieving rapid Time To First Fix (TTFF) of less than one second, accuracy within as little as one meter, and sensitivity at -165 dBm by tracking both GPS and GLONASS constellations simultaneously.
High sensitivity and noise immunity: The Multi Micro Hornet continues to leverage OriginGPS’ patented and proprietary Noise Free Zone NFZ technology to ensure high sensitivity and noise immunity even under marginal signal conditions.
Reduced power consumption without compromising connectivity: It detects changes in context, temperature, and satellite signals to achieve a state of near continuous availability. By opportunistically updating its internal fine time, frequency and satellite ephemeris data, the Multi Micro Hornet is able to stay connected while consuming mere microwatts of battery power.
An intelligent design that shortens time to market: The Hornet family of GPS / GNSS antenna modules integrates a GNSS receiver and patch antenna in a single module. As a cornerstone of the OriginGPS portfolio, the Multi Micro Hornet’s pin-to-pin compatibility with the Micro and Nano Hornet modules ensures a seamless migration from GPS to GNSS and gives developers the ability to create new product offerings in the shortest time to market while minimizing costly design risks. Developers can connect it to a power source on a single layer PCB and be off and running.
Additionally, the Multi Micro Hornet module combines OriginGPS’ proprietary low-profile GPS+GLONASS antenna with a dual-stage LNA, RF LDO, SAW filter, TCXO, RTC crystal and RF shield with SiRFstarV GNSS system on chip.
Researchers experimentally demonstrate the first wireless network synchronized with accuracy of a billionth of a second.
A new timing protocol, dubbed “Blink,” would allow for timing greater than that provided by GPS satellites. According to researchers, the protocol would allow for wireless transmission over longer distances with less energy — while improve the overall efficiency of wireless networks.
Such an enhanced timing technology could result in applications like coordinated signal jamming of enemy military receivers; extremely precise localization; coordinated navigation, tracking, and operation of UAVs; convoys of autonomous vehicles; and distributed beam forming.
At the 2015 IEEE International Conference on Communications, being held June 8-12 in London, Andreas Molisch, professor of Electrical Engineering at the University of Southern California’s Viterbi School of Engineering, presented the paper, “Experimental Demonstration of Nanosecond-Accuracy Wireless Network Synchronization.”
Molisch co-authored the paper with Marcelo Segura and S. Niranjayan, former post-doctoral students at USC, and Hossein Hashemi, also professor of Electrical Engineering at USC Viterbi.
In the paper, the researchers experimentally demonstrate the first wireless network synchronized with nanosecond accuracy.
Segura, Niranjayan, Hashemi and Molisch have developed a prototype, consisting of four nodes that synchronize to each other with an accuracy of approximately three nanoseconds. They also introduced a scalable protocol, which they call the “Blink” algorithm, that extends the same accuracy of the current small-size prototype (in this case, four wireless devices) to hundreds or even thousands of wireless devices.
“Previous research has addressed precision synchronization, but, in the publically available literature, nanosecond accuracy was achieved only by connecting devices via cables, and only between few wireless devices. Even though GPS is widely used and is considered very precise, it does not easily provide this level of accuracy, and cannot be used in many indoor settings,” Hashemi said.
Instead of requiring a precision of minutes, wireless devices have to make their clocks match within very small fractions of a second. This “clock synchronization” is needed for a large range of purposes — from increasing cellphone coverage, to increasing data speed rates, to enabling precision localization in places where GPS is not available. Some of these activities require synchronization within “only” a millionth of a second, a requirement that has been achieved by a variety of methods.
One nanosecond, a billionth of a second, is how long it takes light to travel over one foot through the air. It is at this focused level that researchers have competed to develop solutions to push synchronization to a billionth of a second, or what is known as “nanosecond accuracy.”
Synchronizing a whole network of wireless devices to such accuracy would enable a host of new possible applications, from precise localization to energy-efficient transmission for “Internet of things” sensor networks. However, it is remarkably hard to achieve such a level of synchronization, especially when the clocks in the devices are low-cost and not very precise.
While this work has considerable applications for the military, it also has indications for other instances in which increased precision is necessary such as communication among a group of driverless cars to share location information. Other possible applications include helping a person with limited sight navigate an indoor physical space, or providing a map for robots employed in the home or in industrial settings.
The research was supported primarily by the Office of Naval Research and the Ming Hsieh Institute at USC.
Precise, Accurate and Multipath-Resistant Distance and Speed Measurements
In this month’s column, we take a look at a short-distance two-way ranging system using a 5.8-GHz carrier to supply not only precise and accurate distance measurements but also complementary measurements of speed.
By Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor
INNOVATION INSIGHTS by Richard Langley
THERE IS A LONG HISTORY of determining distances using radio waves with a large number of techniques being developed over the years for positioning, navigation, situational awareness and other purposes.
Of course, we are all familiar with the latest and greatest distance-measuring technology: GPS and its GNSS brethren. The distance to each observable satellite is determined by measuring the time it takes for the radio signal to travel from the transmitting antenna of the satellite to the receiver’s antenna and then, using the speed of light in a vacuum (which is also the speed of radio waves), converting the signal travel time into a distance. Distances can be determined from either the signal’s modulation (the pseudorandom noise codes) or the carrier phase. Both approaches require modeling and estimation to account for various errors or biases.
GPS is an example of one-way ranging. Other systems, notably radar, are two-way systems relying on reflections (passive ranging) or transponders (active ranging) to return a signal to the point of transmission.
Radar was developed during Word War II although radio-ranging technologies and techniques existed before the war started (to measure the height of the ionosphere, for example) and allowed radar’s rapid development and use during the war.
Besides ranging to terrestrial objects, radar has been used extraterrestrially. Independent experiments in the United States and Hungary in 1946 resulted in the first detections of radar reflections from the moon. Radar has been used subsequently to range to other solar system bodies as well.
Also developed during World War II were several radio-based systems for aircraft navigation. An outgrowth of these were the Loran-C and Omega hyperbolic positioning systems. They operated with networks of coordinated transmitters using frequencies at the low end of the radio spectrum. With widespread GPS availability, Omega was shut down in September 1997 followed by the North American Loran-C chains in 2010. Other chains are threatened with closure. However, there is an ongoing debate about bringing Loran-C back to North America in the form of Enhanced Loran (eLoran) as an autonomous backup for GPS. The United Kingdom has already implemented an eLoran network. Among other improvements, eLoran uses range measurements from multiple transmitters to determine position fixes.
The first terrestrial electromagnetic-distance-measurement or EDM device using microwave signals was the Tellurometer. Developed for surveying in 1954, it initially used a 3-GHz carrier modulated by frequencies near 10 MHz and was capable of accurately measuring distances up to at least 50 kilometers (line of sight).
Ranging can be performed with virtually any radio signal, and viable positioning techniques have been developed to use so-called signals of opportunity such as AM, FM and TV signals. And purpose-designed systems have been developed using ultra-wideband and other short-distance radio technologies.
An issue with any radio-based ranging system is multipath where, in addition to a direct line-of-sight signal, interfering signals are received after being reflected off nearby structures. Multipath degrades the system’s achievable precision and accuracy. Better performance can be obtained by using measurements on the signal’s carrier rather than on its modulation, and the higher the carrier frequency, generally the smaller will be the multipath error in the distance measurement. In this month’s column, we take a look at a short-distance two-way ranging system using a 5.8-GHz carrier to supply not only precise and accurate distance measurements but also complementary measurements of speed.
“Innovation” is a regular feature that discusses advances in GPS technology and its applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering, University of New Brunswick. He welcomes comments and topic ideas. Email him at lang @ unb.ca.
Reliable measurements of distance and speed are a critical aid to integrated positioning and navigation systems. Several different sensor technologies can provide such measurements including a variety of radio frequency (RF) ranging techniques. Previous work by the authors based on round-trip time-of-flight RF ranging using the baseband code phase of direct sequence spread spectrum (DSSS)-modulated signals achieves centimeter-level distance estimation performance. This DSSS ranging implementation approaches the Cramér-Rao lower bound in a benign RF channel (the theoretical lower bound on the variance or corresponding standard deviation of any unbiased estimator of a deterministic parameter — the best we can ever expect to achieve). A distance measuring radio (DMR) produced by our company is shown in FIGURE 1.
FIGURE 1. Distance measuring radio. The dimensions of the radio are 160 × 69 × 13.3 millimeters with a mass of 180 grams. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
Our baseband ranging capability has been demonstrated on a direct conversion radio operating in the unlicensed 5.8-GHz industrial, scientific and medical (ISM) band with approximately 20 MHz RF signal bandwidth, and has been previously implemented in the 2.4 GHz and 915 MHz ISM bands. The system uses an 11-megachip-per-second chipping rate and a symbol rate of about 687 kHz per channel (16 chips per symbol). This method has been implemented with both binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulation. The same signal that is used for ranging is also used for data communications. A decentralized asynchronous carrier-sense multiple access with collision avoidance (CSMA/CA) networking layer supports networked operation.
The DMR performs real-time digital signal processing on a Kintex-7 field-programmable gate array (FPGA) baseband processor to compute ranging observables on the received baseband packet structure. A round-trip measurement duration under three milliseconds allows for approximately 350 measurements per second for a single pair of DMRs. Measurements do not require a priori synchronization of the remote radios nor high-performance reference oscillators, as remote oscillator behavior is observed in the ranging operation. The measurement is highly compatible with frequency agility techniques. A system of ranging radios provides networked operation for measurements between multiple platforms.
The primary limitation of DSSS code-phase ranging is degraded accuracy and reliability in challenging multipath environments. This is somewhat mitigated by a “quality factor” observation on the characteristics of the received DSSS baseband signal, which can be used to de-weight or exclude corrupted baseband ranging measurements from an integrated navigation or positioning filter. However, it is desirable to provide a ranging measurement that has improved robustness against multipath corruption in all environments.
Multipath Effects on Carrier Phase
The carrier phase of the DSSS ranging signal in space can be used as an additional ranging measurement. Each 5.8-GHz RF carrier-wave cycle has a length of about 52 millimeters. Phase measurements on the received carrier phase in a round-trip ranging exchange are proportional to the propagation distance of the RF signal over the air. These measurements of the carrier phase can be made precisely, and they are inherently more tolerant to multipath than baseband phase measurements.
Consider a simplified two-ray RF channel model, where there is a direct RF line-of-sight (LOS) path and a multipath (MP) reflection. The two signals will have a phase difference between MP and LOS of θm and an amplitude ratio of MP to LOS of α, which lumps together the attenuation due to the additional path length of the MP signal, the reflection coefficient of the reflecting surface, the difference in antenna gain at the incidence angles and other factors. The received signal will be a superposition of the two signals with a phase difference between this composite and the original LOS of θc. This phase difference is the multipath-induced error on the received carrier phase. The worst-case error will occur when there is a small difference in total path length. In this case, the LOS and MP are inseparable by the DSSS receiver, and the error is bounded by Equation 1. The error is reduced for MP with much longer path length due to both a reduced amplitude coefficient α of the MP signal, as well as separation by the DSSS receiver due to the baseband spreading codes.
(1)
The multipath carrier-phase error bounds are ±90 degrees for α ≤ 1, which is satisfied when there is an RF LOS signal present. In practice, α is typically much less than 1. For a more practical case of α = 0.1, the maximum carrier-phase error is less than ±6 degrees. At 5.8 GHz RF, ±6 degrees corresponds to about 0.1 millimeters. A plot of this response for various values of α is shown in FIGURE 2.
FIGURE 2. Carrier-phase error due to multipath interference for various values of relative multipath amplitude. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
As a physical interpretation, the carrier-phase error goes to zero when there is zero phase difference between LOS and MP signals as the signals happen to be in phase already, and at ±180 degrees where the MP signal is in phase with the LOS signal but with inverted polarity, and serves to reduce the magnitude of the received signal, which is the case in a deep multipath fade. MP signals arrive at a dynamic receiver with an unpredictable distribution of relative phase to the LOS signal due to platform motion. This resistance to multipath is highly desirable for use in an RF ranging system. The following sections will present a ranging method that leverages this useful behavior.
Carrier-Phase Ranging Measurement
Each DMR round-trip ranging exchange consists of transmission and reception of a packet between two cooperating DMR devices, typically termed “originator” and “transponder” with roles determined by software configuration. For baseband ranging, the code phase is computed on the oversampled shape of the DSSS correlator output and exchanged in the round-trip measurement. The number of elapsed baseband clock periods between receive and transmit on the transponder and between transmit and receive on the originator are also observed to compute a round-trip coarse time. These measurements, plus a calibration offset due to cabling and other systematic delays, are used to perform baseband ranging.
Two additional observations are required for carrier-phase ranging: the carrier phase of the received DSSS signal in space and the carrier-frequency offset of the received carrier with respect to the local oscillator on the receiving radio. These observables are exchanged in a round-trip transaction, generating carrier-phase range (CPR), the magnitude of carrier-phase velocity (CPV) and clock-offset measurements. This section will describe the background of the CPR and CPV measurements.
Assuming the communicating DMRs operate with identical carrier frequencies, the round-trip carrier-phase ranging measurement is a function of the RF carrier wavelength λC = c/fC and the received phase on each DMR (φO and φT) in units of radians. The measurement is ambiguous by Namb half-wavelengths, as shown in Equation 2.
(2)
The frequency offsets measured at each receiver (SO and ST) in units of hertz will reflect the Doppler-based velocity offset between the two receivers, as shown in Equation 3.
(3)
While the velocity measurement is absolute, the carrier-phase ranging measurement is ambiguous within a half-wavelength in a round-trip measurement. There are several ways to overcome this limitation including using the velocity measurement to “unwrap” sequential carrier-phase observations, using baseband phase measurements to establish absolute offsets, by aiding the measurement with a strapdown inertial measurement unit (IMU) and by other means. The primary error source for carrier-phase ranging in practice is the solution of integer ambiguity, not the actual phase measurements. The quality of the phase measurements becomes the limiting factor when the integer ambiguity is resolved perfectly. An analysis of the Cramér-Rao lower bound (CRLB) for carrier-phase ranging and carrier-frequency velocity measurements along with measured performance is presented in the following section.
Measurement Performance Bounds
The CRLB for estimation of phase and frequency of a sinusoid based on a number of data samples in additive white Gaussian noise has been previously treated in the literature and can be interpreted to provide a best case, lower bound on how well the measurements could perform. The CRLBs for carrier-frequency and phase estimation are computed in terms of the sinusoid’s signal-to-noise ratio, SNR, the number of observed samples of the phase of the signal NS and the sample rate of the measurement system fS.
The CRLB for the standard deviation of carrier-phase ranging measurements is presented in Equation 4 in units of radians. In general, the standard deviation of carrier-phase measurements improves with the square root of NS and the square root of SNR.
(4)
The CRLB for carrier-phase estimation can be used to compute the CRLB for carrier-phase ranging by scaling each measurement by λC
(5)
This CRLB can be interpreted for the carrier-phase ranging observable generation process used in this DMR system. NS can be expanded to Equation 6, with NC = 12 chips out of a 16-chip pseudorandom noise code, α = 400 symbols typically tracked (assuming 100 symbrols are consumed in automatic gain control out of a 512-symbol preamble), and fSample/fChip = 44 MHz/11 MHz = 4. [Note different use of the character α here than in the section on multipath.] This gives NS = 400 · 12 · 4 = 19,200 in a typical usable DMR preamble as currently implemented.
(6) FIGURE 3 shows the CRLB for carrier-phase ranging measurement evaluated over a range of SNR and with a varying number of symbols used in the ranging preamble, with typical α = 400 in the current implementation. Evaluating the phase CRLB at a conservatively low SNR = 10 dB and typical NS = 19,200 on a 5.8-GHz RF carrier yields a lower bound of about 27 micrometers standard deviation for a round-trip carrier-phase ranging measurement.
FIGURE 3. Cramér-Rao lower bound for carrier-phase ranging with different numbers of symbols used in the ranging preamble. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
The CRLB for the standard deviation of carrier-frequency-offset measurements is presented in Equation 7 in units of hertz. In general, the standard deviation of carrier-frequency observation improves with NS3/2 and the square root of SNR.
(7)
The CRLB for carrier-frequency estimation can be used to compute the CRLB for carrier-phase velocity by scaling each measurement by λC to convert to meters per second, and reducing the standard deviation by the square root of 2 due to the two independent phase measurements being conducted in the round-trip experiment as shown in Equation 8.
(8)
Evaluating the round-trip carrier-phase velocity CRLB at a conservatively low SNR = 10 dB and typical NS = 19,200 on a 5.8-GHz RF carrier yields a lower bound of about 10 centimeters per second velocity standard deviation. FIGURE 4 shows the CRLB for velocity measurement evaluated over a range of SNR and with varying number of symbols used in the ranging preamble.
FIGURE 4. Cramér-Rao lower bound for carrier-phase velocity with different numbers of symbols used in the ranging preamble. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
These CRLB levels predict that excellent CPR with precision much better than millimeter level and CPV precision much better than a meter per second should be achievable with the designed system assuming a perfect carrier-frequency generation circuit operating in additive white Gaussian noise. The practical limiting factor for these measurements at high SNR is typically the phase-noise performance of the reference oscillators themselves.
Measurement Results
CPR measurements have been implemented in our DMRs and tested in a variety of environments. In a static data collection, CPR demonstrates a stationary precision of approximately 0.1 millimeters at one sigma as shown in the histogram in FIGURE 5. The red line indicates the best-fit to a Gaussian curve of the measurement data, showing very well behaved data.
FIGURE 5. Histogram showing carrier-phase range precision. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
A static collection of CPV measurements demonstrates a precision of approximately 15 centimeters per second at one sigma as shown in the histogram of CPV data in FIGURE 6, which also has the best fit Gaussian distribution overlaid. The performance of these measurements approaches the CRLB.
FIGURE 6. Histogram showing carrier-phase velocity precision. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
To further quantify the accuracy of CPR, a test was conducted comparing CPR to the distance measured by a survey-grade total station laser rangefinder. The transponding radio was mounted on a tripod and moved to varying distances away from the originating radio, which was located near the total station. FIGURE 7 shows the distance-measurement results. The blue dots are the baseband distance measurements and the red dots are the unwrapped carrier-phase range distance measurements. The mean distance and scatter within each stationary period were used to evaluate the precision and accuracy of CPR versus the total station rangefinder values.
FIGURE 7. Distance determined from baseband ranging (blue) and carrier-phase ranging (red) data collected during a test with varying distances between originating and transponding radios and using a total station to provide ground-truth. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
FIGURE 8 shows the outcome of the laser-based total station ground-truth validation of the carrier-phase distance measuring performance in an outdoor LOS environment. The red lines indicate the ±8 millimeter experimental accuracy of the laser ground-truth test setup. The error from each surveyed point is within the uncertainty of the test, with an experimental precision of 0.6 millimeters at one sigma indicated by the vertical error bars on each data point.
FIGURE 8. Range comparison between CPR and a total station. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
System Integration
CPR and CPV measurements have been successfully integrated into a pedestrian tracking dual boot-mounted inertial system. In this configuration, one industrial-grade microelectromechanical systems IMU operating at 400 Hz (three-axis accelerometer, three-axis gyro and three-axis magnetic compass) is mounted on the heel of each boot, and a DMR with CPR/CPV capability is attached to the medial side of each boot. The DMRs perform inter-boot ranging and velocity measurements at 360 Hz throughout system operation. The walking motion generates a very high-dynamic, high-multipath environment that is challenging for RF systems.
FIGURE 9 shows four strides of walking data collected in this configuration. Periodic walking motion is clearly visible on CPR and CPV as the range between boots increases up to 0.6 meters at the extents of strides and passes near zero during foot crossings. CPV measurements are internally consistent with CPR. The first difference of CPR is equivalent to the independent Doppler-based CPV measurement. A significant benefit of the CPV measurement as opposed to the first difference of CPR is that CPV is an absolute measurement with no integer ambiguity.
FIGURE 9. CPR and CPV data for four strides from boot-mounted distance measuring radios. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
For this system, IMU data is integrated using both interpreted zero-velocity updates (ZUPTs) and ranging measurements to determine dead-reckoning motion of each individual boot. The high-precision, multipath-tolerant CPR and CPV measurements are used to constrain inter-boot position and velocity in a centralized extended Kalman filter (CEKF). CPR and CPV residuals from the CEKF are shown in FIGURE 10 and FIGURE 11, representing measurement accuracy in a challenging, high-dynamic environment. All system errors including antenna phase response, integrated IMU errors, and others are included in these histograms, so the true CPR and CPV measurement errors are likely significantly lower, even for this high-multipath environment. This is why we believe our results are a good estimate of the system’s accuracy capability.
FIGURE 10. Histogram showing carrier-phase range accuracy. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)FIGURE 11. Histogram showing carrier-phase velocity accuracy. (Image: Bradley D. Farnsworth, E.J. Kreinar and David W.A. Taylor)
While the overall CPR measurement accuracy of about 11 millimeters is two orders of magnitude worse than the stationary measurement precision of 0.1 millimeters, it should be noted that this includes all measurement biases in the system and various error sources.
CPV achieves an in-system measurement accuracy of 0.31 meters per second, which is approximately a factor of two degraded from the stationary, LOS collection (0.15 meters per second). In this sense, CPV is shown to be an extremely robust measurement in the presence of multipath and non-ideal antenna patterns throughout actual walking motion.
Conclusions
This article presents a new method to perform highly precise, accurate and multipath-resistant measurements of distance and velocity using a small portable radio. Measurements that are as accurate as a laser require only milliseconds to complete and are insensitive to multipath interference. This opens up a wide range of applicability as an aiding sensor to integrated navigation systems. Performance has been demonstrated in the high-dynamic and high-multipath environment between the boots of a walking pedestrian, and similar performance is expected in industrial and military applications. By employing a conventional communications link, measurements of CPR and CPV should be scalable to longer distances with the availability of the measurements roughly comparable to the availability of the communications link.
CPR and CPV achieve stand-alone measurement precision of much better than 1 millimeter standard deviation, and about 15 centimeters per second velocity respectively at a rate of hundreds of measurements per second. In-system performance of CPR and CPV measurement residuals demonstrates 1-centimeter CPR accuracy and 30 centimeters per second CPV accuracy. The measurements presented in this article are typically 100 times more precise than typical baseband round-trip RF measurements in a similarly challenging RF environment.
Acknowledgments
The work described in this article was sponsored by ENSCO Inc.
Manufacturers
The distance measuring radio is manufactured by ENSCO Inc. The inertial measurement unit used in the boot test was a Memsense LLC model H3, while the total station used for calibration was a Leica Geosystems AG model TS30.
BRADLEY D. FARNSWORTH is the chief engineer for positioning, navigation and timing (PNT) at ENSCO Inc., Springfield, Va. He holds several U.S. patents and has expertise in real-time signal processing, autonomous systems and mixed-signal design. He received his B.S. summa cum laude and M.S. degrees in electrical engineering from Case Western Reserve University, Cleveland, Ohio.
E.J. KREINAR is with ENSCO Inc. and holds B.S. and M.S. degrees in electrical engineering from Case Western Reserve University. He has expertise in optimal estimation using Kalman filters, real-time signal processing and autonomous systems.
DAVID W.A. TAYLOR is the director of technology development and business area lead for PNT at ENSCO Inc., where he leads R&D programs developing sensors and systems for national security applications. He holds several U.S. patents and is an expert in GPS-denied navigation technologies. Taylor holds a B.S. in physics from Rhodes College, Memphis, Tenn. and a Ph.D. in geophysics from Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, Va.
FURTHER READING
Authors’ Conference Paper on which the Article is Based
“Precise, Accurate, and Multipath-Resistant Networked Round-Trip Carrier Phase RF Ranging” by B.D. Farnsworth, E.J. Kreiner and D.W.A. Taylor in Proceedings of ITM 2015, the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, Calif. January 26–28, 2015, pp. 651–656.
RF Ranging for Location Awareness by S.M. Lanzisera and K. Pister, Technical Report No. UCB/EECS-2009-69, Dept. of Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, Calif., May 19, 2009.
Direct Sequence Spread Spectrum Radio Frequency Ranging
“High-Precision 2.4 GHz DSSS RF Ranging” by B.D. Farnsworth and D.W.A. Taylor in Proceedings of ITM 2011, the 2011 International Technical Meeting of The Institute of Navigation, San Diego, Calif., January 24–26, 2011, pp. 178–183.
“High Precision Narrow-Band RF Ranging” by B.D. Farnsworth and D.W.A. Taylor in Proceedings of ITM 2010, the 2010 International Technical Meeting of The Institute of Navigation, San Diego, Calif., January 25–27, 2010, pp. 161–166.
Forsberg Germany has begun a strategic partnership with Septentrio Satellite Navigation. Forsberg Germany is an OEM component supplier and system integrator, and Septentrio is a designer and manufacturer of GPS/GNSS receivers.
Under the partnership, Forsberg Germany will become a distributor of Septentrio’s OEM boards. Forsberg Germany will sell and support Septentrio OEM receivers in Germany, Austria and Switzerland. This partnership combines Septentrio’s cm-accurate GNSS positioning technology and products with Forsberg Germany’s extensive market experience and engineering expertise, the companies said in a statement.
“We are excited about this new partnership with Forsberg Germany,” said Koen Gutscoven, vice president of sales at Septentrio. “Forsberg Germany is a pioneer in European professional navigation systems and has in-depth knowledge of our technology and markets. They are an excellent partner in guiding and supporting our customers towards winning implementations in which reliability and accuracy matter.”
“We believe that our partnership with Septentrio to supply their products and services will bring enormous benefits to our customers and Forsberg Germany,” said Charles Forsberg, managing director of Forsberg Services Limited. “Septentrio are renowned throughout the industry for first-class positioning technology and customer support. We highly value the opportunity to work with Septentrio.”
PlanetiQ has started testing its first Pyxis weather instrument with successful processing of GPS signals. The Pyxis represents a new paradigm in satellite weather sensor technology that can penetrate through clouds and storms to produce the highly calibrated data required to dramatically improve weather forecasting, climate monitoring and space weather prediction, all at a much lower cost than traditional satellite weather instruments, PlanetiQ said.
Pyxis will track GPS signals traveling through Earth’s atmosphere and convert them into dense, precise measurements of global temperature, pressure and water vapor — similar to data collected by weather balloons but on a global scale — using a technique called GPS radio occultation (GPS-RO).
Pyxis is the only GPS-RO sensor in such a small package that is powerful enough to routinely probe down into the lowest layers of the atmosphere where severe weather occurs. In addition, Pyxis is able to track signals from all four major satellite navigation systems (GPS, Galileo, Beidou and GLONASS).
PlanetiQ’s planned microsatellite constellation, with an initial set of 12 satellites launching in 2016 and 2017, will deliver more than 8 million observations per day of temperature, pressure and water vapor, or more than 10 times the amount of data available from GPS-RO sensors currently on orbit.
GPS-RO has shown the highest impact per observation on forecast accuracy among the satellite data sources ingested into computer weather models, and is particularly effective at improving predictions of high-impact weather such as hurricanes, severe weather outbreaks and winter storms. However, the amount of GPS-RO data available to date has been sparse.
The Pyxis sensor development team is based in Boulder, Colo., and led by PlanetiQ Founder Chris McCormick, who was instrumental in designing the sensors on the U.S.-Taiwan Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC), the world’s first and only satellite constellation of proven GPS-RO sensors.
“Weather has an immense human and societal impact and affects businesses on a daily if not hourly basis, with a $9.7 trillion economic influence globally,” said Anne Hale Miglarese, president and CEO of PlanetiQ. “Improving the weather forecast and developing innovative risk analytics tools are critical to mitigate these growing costs, and the key is more high-quality weather data.”
“The Earth’s atmosphere is radically under-sampled at present especially over the oceans, which cover 70 percent of the Earth’s surface. With the speed of innovation in sensor technology, space hardware and launch, the weather forecast will dramatically change for the better in the near future,” McCormick said. “The Pyxis represents a major step forward in improving forecast accuracy for both routine weather and big storms, while leveraging the latest advances in science, technology and miniaturization to drive down costs.”
Explore further:
PlanetiQ President and CEO Anne Hale Miglarese discussed the project on The Weather Channel in August 2014.
Attila Komjathy, a NASA Jet Propulsion Laboratory principal investigator and adjunct professor in the University of New Brunswick’s Department of Geodesy and Geomatics Engineering, was named a Fellow of the Institute of Navigation in January for his work on remote sensing of the Earth’s ionosphere using signals from GNSS.
The OriginGPS Multi Spider module provides high sensitivity and noise immunity by incorporating its proprietary Noise Free Zone technology for faster position fix and navigation stability even under challenging satellite signal conditions.
SiRFstarV — CSR’s GNSS receiver that tracks both GPS and GLONASS satellites — has the CSR mbed Shield, which comes fitted with the OriginGPS Multi Spider module (ORG4572) requiring 1V8 supply, ground, UART interface and connection to GNSS capable antenna. Additional IOs are available for interrupts, turning the receiver on and off, reset, fix status and power mode information.
The OriginGPS Multi Spider is a tiny GPS + GLONASS module designed to support ultra-compact applications in which size is at a premium, such as smartwatches, wearable devices, trackers and digital cameras. It is a fully integrated, highly sensitive GPS + GLONASS receiver module measuring 7 x 7 x 2.1 millimeters.
The Multi Spider continuously tracks all GPS and GLONASS satellites in view and provides real-time positioning data in the standard industry format, defined by the U.S. National Marine Electronics Association (NMEA).
For more information about GPS/GNSS modules, visit OriginGPS.
The GN-87 multi-GNSS receiver by Furuno Electric Co.
Furuno Electric Co.’s latest multi-GNSS receiver module, the GN-87, has been adopted for use in the new My Driving Pal (MDP) device.
The MDP device and app communicate with each other via Bluetooth low energy (BLE). When the MDP device and a phone running the MDP app are within range of each other (approximately 15 meters), the device keeps its internal GPS in idle mode. When the phone is out of Bluetooth range and the object that is carrying the MDP device is moving (for instance, under the seat of a stolen bicycle or in the pocket of a wandering child), the MDP device activates its built-in GNSS receiver and cellular modem, tracks the asset, and immediately notifies the user on a phone via remote push notification.
The range is unlimited, because the MDP device will track the asset anywhere in the world, with an accuracy level of meters. To protect user’s privacy, all tracking data remains locally on the phone and is not transmitted to any backend server.
In April, the GN-87 receiver was adopted for the new quadcopter Bebop Drone, made by Parrot SA. The GN-87 provides positioning accuracy and smooth ground tracking because of its multi-GNSS technology, which allows it to receive more satellite data even in harsh environments such as urban canyons.
My Driving Pal (MDP) is a technology startup based in Silicon Valley that develops advanced Internet of Things solutions. MDP’s mission is to improve road safety by enabling vehicle to vehicle and vehicle to infrastructure communications. A small percentage of new vehicles are connected, but still the vast majority have no connectivity, not including motorcycles and bicycles. The MDP product delivers a suite of security, monitoring, and tracking applications, from delivering remote notification on phone if interior temperature of car gets too high, to automatically tracking the bike, if it’s ever stolen.
For more information on the MDP device (capabilities, availability, distribution, retail or partnerships), send an email to [email protected], or follow MDP on Facebook.
Apple has acquired Coherent Navigation, according to various media reports.
Coherent Navigation is a Bay Area GPS firm founded in 2008 by engineers from Stanford and Cornell. One of its areas of focus was high-integrity GPS (iGPS), an enhanced version of GPS that uses both normal, high-altitude GPS satellites and lower-altitude voice and data satellites from Iridium to increase the accuracy of a consumer’s GPS reading from the ground.
The acquisition seems to be Apple’s latest efforts to bolster its mapping capabilities.
A new concept that involves mounting an instrument on the International Space Station and taking advantage of signals from navigation satellites could provide measurements of sea-surface height and information about features related to ocean currents, benefiting science and ocean forecasting.
We have all seen the beautiful photographs of our planet taken by astronauts, but orbiting Earth 16 times a day just 400 km above, the Space Station also offers a platform from which to measure certain variables related to climate change.
So, in 2011 the European Space Agency (ESA) called for proposals to explore how the Space Station could be used to make scientifically valid observations of Earth. After reviewing and assessing numerous proposals, the result is to further develop the GEROS-ISS mission concept.
Jason Hatton, GEROS-ISS project coordinator, said, “The concept is still going through feasibility studies, but the aim is to launch the experiment towards the end of 2019. It would be carried to the Space Station on a cargo vehicle and installed on ESA’s Columbus space laboratory using a robotic arm, after which GEROS-ISS would run for at least a year.”
GEROS-ISS stands for GNSS reflectometry, radio occultation and scatterometry on board the ISS. GPS and Galileo satellites send a continual stream of microwave signals to Earth for navigation purposes, but these signals also bounce off the surface and back into space.
The idea is to install an instrument with an antenna on the Space Station that would capture signals directly from these satellites as well as signals that are reflected or scattered from Earth. This process could be used to calculate the height of the sea surface, and to measure waves — or “roughness” — that can then be used to work out the speed of surface winds.
Variations in sea-surface height (cm) obtained by merging multiple altimeter measurements. GEROS-ISS would be able to observe this variability so that maps covering latitudes 51° N to 51° S can be produced every four days. (Photo: ESA)
GEROS-ISS is primarily an experiment to demonstrate new ways of observing Earth. However, if taken beyond the testing phase this new approach would complement measurements from satellites carrying altimeters such as CryoSat and Sentinel-3, and satellites carrying wind scatterometers such as MetOp.
Importantly, it is the first concept to assess the potential of spaceborne GNSS reflectometry to determine and map ocean height at scales of 10–100 km or longer in less than four days. Current satellite altimeters, in comparison, offer global maps at scales of around 80 km, which are produced from multiple datasets every 10 days.
A system based on GEROS-ISS would, therefore, complement existing satellite systems, helping to map ocean variability at finer spatial and temporal scales over a range of seas in tropical and temperate regions. It would also refine our understanding of how well the concept would work for measuring the roughness of the ocean surface.
In this respect, the development of GEROS-ISS benefits from experience gained with the UK’s TechDemoSat-1, which also measures ocean-surface roughness using a similar technique. It is also hoped that NASA’s upcoming CYGNSS constellation of mini satellites will help pave the way for GEROS-ISS.
In addition, GEROS-ISS uses a technique called radio occultation whereby the antenna receives signals that are refracted as they pass through the atmosphere. This can be used to generate vertical profiles of atmospheric humidity, pressure and temperature, as does the GRAS instrument on the MetOp satellites, for example.
GEROS-ISS will be installed on the upper balcony of ESA’s Columbus space laboratory, which provides mechanical interface plates as well as power, command and data links to the ISS systems. (Photo: ESA, taken by ESA astronaut Luca Parmitano during his spacewalk on July 9, 2013. )
“It is very flexible, combining different mission concepts and applications in one: GNSS-reflectometry to determine sea-surface height, scatterometry to measure sea-surface roughness and radio occultation for atmospheric studies,” said Jens Wickert who leads the science team that proposed GEROS-ISS.
ESA engineer Manuel Martin-Neira noted, “The original concept actually goes back over 20 years and has matured considerably through numerous studies and campaigns, however, it has never been duly tested from space.”
“Being able to use the International Space Station in this way means that we can quickly validate innovative observing techniques without having to build an entire satellite, and we expect this to lead to new opportunities for science,” added Michael Kern, ESA’s GEROS-ISS mission scientist.
The GEROS-ISS feasibility studies are being carried out through ESA’s General Studies Programme.
Editor’s Note:GPS World discussed the use of GPS for radio occultation in itsMarch 1994 Innovation column, “Monitoring the Earth’s Atmosphere with GPS,” by Rob Kursinski.
