Probabilistic Snapshot GNSS

Lead Research Organisation: University of Oxford

Abstract

Brief description of the context of the research including potential impact: Conventional global nav-igation satellite system (GNSS) receivers operate in multiple consecutive steps to estimate their position. Instead, direct position estimation (DPE) is based on a probabilistic model of the received GNSS signal and performs position estimation in one step using maximum-likelihood estimation (MLE). This approach has the potential to be robust in scenarios where conventional GNSS fails, such as low-quality signals recorded with an energy-saving low-cost device, weak signals, e.g., in a multi-path environment, or signals as short as one millisecond. Furthermore, Bayesian DPE allows to directly integrate prior knowledge into the probabilistic model. Advancements of DPE such that it can be employed in practice would allow to build GNSS receivers with significantly lower costs and lower energy consumption. Such devices would, e.g., enable conservationists to perform more affordable wildlife tracking on a broader scale.
Aims and objectives: One of the main goals is to develop open-source hardware and software for low-cost low-energy wildlife tracking. This requires improving DPE such that it can work with real data, especially, short signals (snapshots) with low amplitude and frequency resolution. A first im-portant step is to revisit the underlying probabilistic model to make it more robust and allow faster likelihood optimisation. Second, the development of new tailored optimisation methods for MLE in DPE is required to speed up the processing of large amounts of signal captures. Other questions are how to efficiently use multiple GNSS in DPE and how to address uncertain time and frequency measurements resulting from an imprecise receiver clock. Finally, domain specific prior knowledge shall be integrated to improve positioning accuracy and robustness.
Novelty of the research methodology: While DPE has already been proposed in theory, it has not been transferred to real-world applications yet. This is due to different hurdles, some of which are described above, some of which might yet have to be discovered. For this reason, this project aims at developing hardware and software for a snapshot GNSS receiver, which can be employed by end-users for a real-world application. In this way, the project will identify challenges that prevent snapshot GNSS with DPE from being applied in practice and will develop probabilistic approaches to address them.
Alignment to EPSRC's strategies and research areas: Digital signal processing, sensors and instru-mentation, artificial intelligence technologies, (robotics)

Planned Impact

AIMS's impact will be felt across domains of acute need within the UK. We expect AIMS to benefit: UK economic performance, through start-up creation; existing UK firms, both through research and addressing skills needs; UK health, by contributing to cancer research, and quality of life, through the delivery of autonomous vehicles; UK public understanding of and policy related to the transformational societal change engendered by autonomous systems.

Autonomous systems are acknowledged by essentially all stakeholders as important to the future UK economy. PwC claim that there is a £232 billion opportunity offered by AI to the UK economy by 2030 (10% of GDP). AIMS has an excellent track record of leadership in spinout creation, and will continue to foster the commercial projects of its students, through the provision of training in IP, licensing and entrepreneurship. With the help of Oxford Science Innovation (investment fund) and Oxford University Innovation (technology transfer office), student projects will be evaluated for commercial potential.

AIMS will also concretely contribute to UK economic competitiveness by meeting the UK's needs for experts in autonomous systems. To meet this need, AIMS will train cohorts with advanced skills that span the breadth of AI, machine learning, robotics, verification and sensor systems. The relevance of the training to the needs of industry will be ensured by the industrial partnerships at the heart of AIMS. These partnerships will also ensure that AIMS will produce research that directly targets UK industrial needs. Our partners span a wide range of UK sectors, including energy, transport, infrastructure, factory automation, finance, health, space and other extreme environments.

The autonomous systems that AIMS will enable also offer the prospect of epochal change in the UK's quality of life and health. As put by former Digital Secretary Matt Hancock, "whether it's improving travel, making banking easier or helping people live longer, AI is already revolutionising our economy and our society." AIMS will help to realise this potential through its delivery of trained experts and targeted research. In particular, two of the four Grand Challenge missions in the UK Industrial Strategy highlight the positive societal impact underpinned by autonomous systems. The "Artificial Intelligence and data" challenge has as its mission to "Use data, Artificial Intelligence and innovation to transform the prevention, early diagnosis and treatment of chronic diseases by 2030". To this mission, AIMS will contribute the outputs of its research pillar on cancer research. The "Future of mobility" challenge highlights the importance the autonomous vehicles will have in making transport "safer, cleaner and better connected." To this challenge, AIMS offers the world-leading research of its robotic systems research pillar.

AIMS will further promote the positive realisation of autonomous technologies through direct influence on policy. The world-leading academics amongst AIMS's supervisory pool are well-connected to policy formation e.g. Prof Osborne serving as a Commissioner on the Independent Commission on the Future of Work. Further, Dr Dan Mawson, Head of the Economy Unit; Economy and Strategic Analysis Team at BEIS will serve as an advisor to AIMS, ensuring bidirectional influence between policy objectives and AIMS research and training.

Broad understanding of autonomous systems is crucial in making a society robust to the transformations they will engender. AIMS will foster such understanding through its provision of opportunities for AIMS students to directly engage with the public. Given the broad societal importance of getting autonomous systems right, AIMS will deliver core training on the ethical, governance, economic and societal implications of autonomous systems.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S024050/1 01/10/2019 31/03/2028
2242651 Studentship EP/S024050/1 01/10/2019 31/12/2023 Jonas Beuchert
 
Description Snapshot GNSS is a more energy-efficient approach to location estimation than traditional GNSS positioning methods. This is beneficial for applications with long deployments on battery such as wildlife tracking. However, only a few snapshot GNSS implementations have been presented so far and all have disadvantages. Most significantly, they typically require the GNSS signals to be captured with a certain minimum resolution, which demands complex receiver hardware capable of capturing multi-bit data at sampling rates of 16 MHz and more. By contrast, we developed fast algorithms that reliably estimate locations from twelve-millisecond signals that are sampled at just 4 MHz and quantised with only a single bit per sample. This allowed us to build a snapshot receiver at an unmatched low cost of $14, which can acquire one position per hour for a year. On a challenging public dataset with thousands of snapshots from real-world scenarios, our system achieves 97% reliability and 11 m median accuracy, comparable to existing solutions with more complex and expensive hardware and higher energy consumption. We provide an open implementation of the algorithms as well as a public web service for cloud-based location estimation from low-quality GNSS signal snapshots.

In summer 2021, we deployed SnapperGPS on nesting loggerhead sea turtles (Caretta caretta) on the island of Maio, Cape Verde. We tagged 20 nesting females on the beach and recovered nine of the tags two weeks later when the individuals returned. The successful tracks demonstrate that the snapshot positioning worked reliably, providing a position fix whenever the receiver collected data at the surface. SnapperGPS was able to compute positions from significantly shorter signal captures than assisted GPS (milliseconds instead of seconds), whilst being more affordable to manufacture and more energy-efficient.
Exploitation Route The developed software has been made open under a permissive license and the same will be done with the developed hardware. This allows others to easily build on our work.
Furthermore, the developed system can be used by zoologists, conservationists etc. for their own research. The system is especially suitable for this because it has low costs, comes with an accessible user interface, and is open-source.
Sectors Digital/Communication/Information Technologies (including Software),Electronics,Environment

URL https://snapper-gps.herokuapp.com/
 
Title SnapperGPS: Collection of GNSS Signal Snapshots 
Description This data collection contains digital global navigation satellite system (GNSS) signal snapshots and is accompanied by a repository with utilities to simplify working with the files, which you can find at https://github.com/JonasBchrt/snapshot-gnss-data. We recorded the data in 2020 and 2021 using three of our SnapperGPS low-cost receivers, whose core components are an Echo 27 GPS L1 antenna and an SE4150L integrated GPS receiver circuit. Like most civilian low-cost GPS receivers, SnapperGPS operates in the L1 band with a centre frequency of 1.57542 GHz. However, Galileo's E1 signal, BeiDou's B1C signal, GPS' novel L1C signal, and SBAS' L1 signal have the identical centre frequency. So, we captured those signals, too. A SnapperGPS receiver down-mixes the incoming signal to a nominal intermediate frequency of 4.092 MHz, samples the resulting near-baseband signal at 4.092 MHz and digitises it with an amplitude resolution of one bit per sample. It considers only the in-phase component and discards the quadrature component. The data collection consists of four static and seven dynamic tests under various conditions with 3700 GNSS signal snapshots in total. We captured the 225 static snapshots on a hill top, on a bridge, in a courtyard, and in a park in 5-30 s intervals and the 3475 dynamic ones while cycling in either urban or rural environments and using 10 s intervals. We obtained ground truth locations or tracks either by using an Ordnance Survey trig point, by employing satellite imagery from Google Maps or Google Earth, or with a Moto C smartphone with built-in GPS and A-GPS receiver. While the trig point provides a ground-truth position with centimetre-level accuracy, the positions obtained from satellite imagery or with the Moto C are up to 5 m wrong with outliers up to 10 m. The eleven datasets are stored in one folder per set named "A"-"K". Each snapshot is in a single binary ".bin" file with a name derived from the timestamp. One byte of the file holds the amplitude values of eight signal samples, i.e., the first byte holds the first eight samples. A zero bit represents a signal amplitude of +1 and a one bit a signal amplitude of -1. The order of the bits is 'little', i.e., reversed. For example, the byte 0b01100000 corresponds to the signal chunk [1 1 1 1 1 -1 -1 1]. In addition to the raw GNSS signal snapshots, you can find more data in a single "meta.json" file in each folder. The JSON struct in this file provides approximate latitude and longitude of the ground truth location of a static test in decimal degrees, an estimate of the true intermediate frequency in Hertz (the actual value differs from the nominal 4.092 MHz due to imprecisions of the hardware), all the file names of the binary files, the UTC timestamps of all files, and optionally temperature and pressure measurements from an on-board BMP280 sensor in degrees Celsius and pascal, respectively. Furthermore, a ".gpx" or ".kml" file holds the ground truth track for a dynamic test as nodes of a polyline. (Folder "I" contains two files that represent the first and the second part of the track, respectively.) Finally, each folder incorporates the broadcasted satellite navigation data from the respective day as RINEX 3.04 ".rnx" file downloaded from NASA's archive (https://cddis.nasa.gov/archive/gnss/data/daily/). The RINEX files allow to calculate, e.g., satellite orbits and clock corrections for all GNSS. The datasets: "A": 181 snapshots, static, hill top, ground truth from trig point, no temperatures & pressures "B": 14 snapshots, static, bridge, ground truth from Google Maps, no temperatures & pressures "C": 6 snapshots, static, courtyard, ground truth from Google Maps, no temperatures & pressures "D": 24 snapshots, static, park, ground truth from Google Maps, incl. temperatures & pressures "E": 380 snapshots, dynamic, urban, ground truth from Google Earth, incl. temperatures & pressures "F": 339 snapshots, dynamic, urban, ground truth from Google Earth, incl. temperatures & pressures "G": 693 snapshots, dynamic, urban/rural, ground truth from Google Earth, incl. temperatures & pressures "H": 628 snapshots, dynamic, urban, ground truth from Moto C, incl. temperatures & pressures "I": 1023 snapshots, dynamic, urban/rural, ground truth from Google Earth / Moto C, incl. temperatures & pressures "J": 346 snapshots, dynamic, urban/rural, ground truth from Moto C, incl. temperatures & pressures "K": 66 snapshots, dynamic, urban, ground truth from Moto C, incl. temperatures & pressures 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
Impact Unknown. 
URL https://doi.org/10.5287/bodleian:exrp1xydm
 
Title SnapperGPS 
Description The SnapperGPS receiver is a small, low-cost, and low-power GNSS receiver for non-real-time wildlife tracking. It employs the snapshot GNSS technology, which offloads the computational expensive data processing to the cloud, and: Measures just 34.5 mm x 28.0 mm and weighs 13 g, Operates for more than 10 years on a single coin cell, Has enough memory to provide almost 11,000 position fixes, Captures fixes in user-defined time intervals or externally triggered, Needs only 12 ms of signal reception for a fix, Employs multiple satellite systems for high reliability (GPS, Galileo, and BeiDou), Achieves a median real-world tracking accuracy of about 12 m, Maintains a real-time clock to accurately timestamp the fixes, Measures the temperature in addition, and Is configured via USB in your browser without the need to install a driver or an app. 
Type Of Technology Webtool/Application 
Year Produced 2021 
Open Source License? Yes  
Impact Used for turtle tracking in biology research. More researchers are interested in using the system for wildlife tracking. 
URL https://snapper-gps.herokuapp.com/
 
Title raw-gnss-fusion 
Description This repository might accompany a future publication where we present an approach to fuse raw GNSS data with other sensing modalities (IMU and lidar) using a factor graph. The goal is to localize a mobile robot in the global Earth frame without drift and discontinuity. The GNSS data is not only used to anchor the robot's trajectory in the global Earth frame and to eliminate drift, but also for highly accurate local positioning using the carrier-phase observations of a GNSS receiver. However, we do not require a base station as differential GNSS methods normally do. Jonas Beuchert, Marco Camurri, and Maurice Fallon. 2022. Factor Graph Fusion of Raw GNSS Sensing with IMU and Lidar for Precise Robot Localization without a Base Station. ArXiv, 7 pages. https://doi.org/10.48550/arXiv.2209.14649 This repository contains three pieces of work that do not depend on each other: Demo code for our carrier-phase factors Instructions how to use our public robot dataset with GNSS, IMU, an lidar data Results of our method on various datasets 
Type Of Technology Software 
Year Produced 2022 
Open Source License? Yes  
Impact Repository was forked by 14 users and stared by 69 users so far, indicating re-use of the code.