The Effect of Intermittent Signal on the Performance of Code Tracking Loop in GNSS Receivers

This paper analyzes the code tracking performance in the presence of signal blanking in Global Navigation Satellite System (GNSS). The blanking effect is usually caused by buildings that obscure the signal in either a periodic or random manner. In some cases, ideal blanking is used to remove random or periodic interference. Nevertheless, the effect of temporary discontinuity of signal often leads to the tracking and position error. To analyze this problem, three types of blanking model are considered: no blanking, periodic blanking, and random blanking of the signals input into the code tracking loop. The mean time to lose lock (MTLL) is to assess the performance of code tracking system under signal blanking. Finally, the effect of steady-state tracking errors on the performance of tracking loop resulting from blanking environment is also discussed

Detection of GNSS multipath with time-differenced code-minus-carrier for land-based applications

Ground transportation systems demand accurate and robust localizationfunctions. Satellite navigation is considered a key element in those systems, but its position determination can be highly corrupted in urban environments because of the presence of reflected signals (i.e. multipath). This paper deals with the detection of multipath in the code measurements of GNSS receivers for mobile users in urban scenarios. First, we discuss the different alternatives and limitations to properly isolate multipath autonomously at the receiver based on Code-Minus-Carrier (CMC) techniques in challenging GNSS applications.We then propose a practical methodology to design a suitable multipath detector based on the time difference of CMC. All the analysis and evaluations are supported with real measurements collected in Railway scenarios.This work has been funded by the European GSA H2020 project ERSAT-GGC. The authors would like to thank all the partners of the ERSAT-GGC consortium.Peer ReviewedPostprint (published version

Pseudolite Architecture and Performance Analysis for the FAA\u27s NextGen Airspace

By 2025 the FAA plans to have fully implemented its NextGen Airspace design. NextGen takes advantage of modern positioning technologies as well as automation, data sharing, and display technologies that will allow more efficient use of our ever busier National Airspace (NAS). A key element of NextGen is the transition from surveillance RADAR providing aircraft separation and navigation to the use of the GPS and Automatic Dependent Surveillance Broadcast (ADS-B). ADS-B couples the precision of the GPS with networked ground and airborne receivers to provide precise situational awareness to pilots and controllers. The result is increased safety, capacity, and access with reduced reliance on an outdated and costly existing infrastructure. Reliance on the vulnerable GPS requires a backup system with higher positioning accuracy than those that are in place today. The USAF 746th Test Squadron at Holloman AFB, in partnership with Locata Corp., has demonstrated an Ultra High Accuracy Reference System (UHARS) over the Holloman Range composed of pseudolites (ground based satellites) transmitting GPS like signals. This study evaluates the suitability of the UHARS when applied on a national scale to meet Alternate Precision Navigation and Timing (APNT) requirements. From a systems architecture perspective UHARS is evaluated against APNT CONOPs stated Operational Improvements and Scenarios. From a signal architecture perspective the UHARS is evaluated against frequency and bandwidth constraints, service volume requirements and positioning accuracy determined by NextGen Airspace aircraft separation criteria

A Survey on Low-Power GNSS

With the miniaturization of electronics, Global Navigation Satellite Systems (GNSS) receivers are getting more and more embedded into devices with harsh energy constraints. This process has led to new signal processing challenges due to the limited processing power on battery-operated devices and to challenging wireless environments, such as deep urban canyons, tunnels and bridges, forest canopies, increased jamming and spoofing. The latter is typically tackled via new GNSS constellations and modernization of the GNSS signals. However, the increase in signal complexity leads to higher computation requirements to recover the signals; thus, the trade-off between precision and energy should be evaluated for each application. This paper dives into low-power GNSS, focusing on the energy consumption of satellite-based positioning receivers used in battery-operated consumer devices and Internet of Things (IoT) sensors. We briefly overview the GNSS basics and the differences between legacy and modernized signals. Factors dominating the energy consumption of GNSS receivers are then reviewed, with special attention given to the complexity of the processing algorithms. Onboard and offloaded (Cloud/Edge) processing strategies are explored and compared. Finally, we highlight the current challenges of today’s research in low-power GNSS.Peer reviewe

Impact and mitigation of space weather effects on GNSS receiver performance

It is well known that Global Navigation Satellite System (GNSS) signals suffer from a number of vulnerabilities, out of which a potential severe vulnerability is the effect of space weather. Space weather effects on the signals transmitted by GNSS include the effect of ionospheric perturbations and solar radio bursts. Intense solar radio bursts occurring in the L-band can impact the tracking performance of GNSS receivers located in the sunlit hemisphere of the Earth and are therefore a potential threat to safety-critical systems based on GNSS. Consequently monitoring these events is important for suitable warnings to be issued in support to related services and applications. On the other hand, the space weather effects leading to ionospheric perturbations on the GNSS signals are either due to dispersion or scintillation caused by plasma density irregularities. Scintillation can cause cycle slips and degrade the positioning accuracy in GNSS receivers. The high-latitude scintillation occurrence is known to correlate with changes in the solar andinterplanetary conditions along with a consequential impact on GNSS receiver tracking performance. An assessmentof the GNSS receiver tracking performance under scintillation can be analysed through the construction of receiver phase-locked loop (PLL) tracking jitter maps. These maps can offer a potentially useful tool to provide users with the prevailing tracking conditions under scintillation over a certain area and also be used to help mitigate the effects of scintillation on GNSS positioning. This paper reviews some of recent research results related to the impact and mitigation of space weather effects on GNSS receiver performance

New on-board multipurpose architecture integrating modern estimation techniques for generalized GNSS based autonomous orbit navigation

This dissertation investigates a novel Multipurpose Earth Orbit Navigation System (MEONS) architecture aiming at providing a generalized GNSS based spacecraft orbit estimation kernel matching the modern navigation instance of enhanced flexibility with respect to multiple Space Service Volume (SSV) applications (Precise Orbit Determination for Earth Observation satellite, Low Thrust Low to High Autonomous Orbit Rising, formation flying relative navigation, Small Satellite Autonomous Orbit Acquisition). The possibility to address theoretical and operational solutions within a unified framework is a foundamental step for the implementation of a reusable and configurable high performance navigation capability on next generation platforms

PNT cyber resilience : a Lab2Live observer based approach, Report 1 : GNSS resilience and identified vulnerabilities. Technical Report 1

The use of global navigation satellite systems (GNSS) such as GPS and Galileo are vital sources of positioning, navigation and timing (PNT) information for vehicles. This information is of critical importance for connected autonomous vehicles (CAVs) due to their dependence on this information for localisation, route planning and situational awareness. A downside to solely relying on GNSS for PNT is that the signal strength arriving from navigation satellites in space is weak and currently there is no authentication included in the civilian GNSS adopted in the automotive industry. This means that cyber-attacks against the GNSS signal via jamming or spoofing are attractive to adversaries due to the potentially high impact they can achieve. This report reviews the vulnerabilities of GNSS services for CAVs (a summary is shown in Figure 1), as well as detection and mitigating techniques, summarises the opinions on PNT cyber testing sourced from a select group of experts, and finishes with a description of the associated lab-based and real-world feasibility study and proposed research methodology

Detection solution analysis for simplistic spoofing attacks in commercial mini and micro UAVs

Enamus droone kasutab lennundusest pärit GPS navigatsiooniseadmeid, millel puuduvad turvaprotokollid ning nende riskioht pahatahtlike rünnakute sihtmärgina on kasvanud hüppeliselt lähimineviku arengute ja progressi tõttu SDR ja GNSS simulatsioonitarkvara valdkonnas. See on loonud ligipääsu tehnikale amatöörkasutajatele, millel on saatja aadressi võltsimise jõudlus. Need potensiaalsed rünnakud kuuluvad lihtsakoeliste kategooriasse, kuid selle uurimustöö tulemusena selgus, et nendes rünnakute edukuses on olulised erinevused teatud GPS vastuvõtjate ja konfiguratsioonide vahel. \n\rSee uurimustöö analüüsis erinevaid saatja aadressi võltsimise avastamise meetodeid, mis olid avatud kasutajatele ning valis välja need, mis on sobilikud mini- ja mikrodroonide tehnonõuetele ja operatsioonistsenaariumitele, eesmärgiga pakkuda välja GPS aadresside rünnakute avastamiseks rakenduste tasandil avatud allikakoodiga Ground Control Station tarkvara SDK. Avastuslahenduse eesmärk on jälgida ja kinnitada äkilisi, abnormaalseid või ebaloogilisi tulemväärtusi erinevates drooni sensiorites lisaallkatest pärit lisainfoga. \n\rLäbiviidud testid kinnitavad, et olenevalt olukorrast ja tingimustest saavad saatja aadressi võltsimise rünnakud õnnestuda. Rünnakud piiravad GPS mehanismide ligipääsu, mida saab kasutada rünnakute avastuseks. Neid rünnakuid puudutav info asetseb infovoos või GPSi signaalprotsessi tasandis, kuid seda infot ei saa haarata tasandile kus SDK tarkvara haldab kõigi teiste sensorite infot.Most of UAVs are GPS navigation based aircrafts that rely on a system with lack of security, their latent risk against malicious attacks has been raised with the recent progress and development in SDRs and GNSS simulation software, facilitating to amateurs the accessibility of equipment with spoofing capabilities. The attacks which can be done with this setup belong to the category simplistic, however, during this thesis work there are validated different cases of successful results under certain GPS receivers’ state or configuration.\n\rThis work analysis several spoofing detection methods found in the open literature, and selects the ones which can be suitable for mini and micro UAV technical specifications and operational scenario, for proposing a GPS spoofing detection solution developed in the application layer of an open source code Ground Control Station software SDK. The detection solution is intended to monitor and correlate abrupt, abnormal or unreasonable values of different sensors of the UAV with data obtained from available additional sources.\n\rThe conducted tests validate the cases and circumstances where the spoofing attacks were successful. Limitations include the lack of mechanisms to access GPS values which can be useful for detection spoofing attacks, but reside in the data bit or signal processing layer of the GPS and can not be retrieve to the layer where the SDK in computing all data of other sensors

Contributions to the foundations of a safety case for the use of GNSS in railway environments

The use of GNSS in the railways for passenger information services and selective door opening is already commonplace but the advancement of this increasingly popular navigation technique into safety of life rail applications has been hindered by the unknown level of measurement error caused by the local rail environment, especially that due to multipath. Current state of the art receiver technologies are discussed along with the additional advantages of signal differencing using local base stations. Limiting factors for hardware in a kinematic environment are also discussed and specific examples to the rail environment highlighted. Safety critical analysis techniques such as FMEA, HAZOP and FTA are reviewed to illustrate the evaluation of safety integrity values and the possibility of system risk, leading to the formation of a structured safety case. Three main data sets from electrified, rural and urban rail environments have been collected using dual frequency geodetic receivers in order to enable analysis of multipath effects in normal railway operations. The code and phase data have been combined to compute fluctuations in multipath errors and these have been used to characterise this effect in both space and time. Where phase positioning is possible comparisons with standard code-based positions have been made to assess the overall quality of the type of GNSS positioning expected to be operationally-viable on the railways. Experiments have also been undertaken to evaluate the possible effects of electromagnetic radiation from overhead cables used to power the trains. Finally, the ways in which the results of these experiments can be used to help build a safety case for the use of GNSS on the railways are discussed. Overall it is concluded that it is unlikely that multipath errors or electromagnetic interference will be the limiting factors in utilising GNSS for safety-critical railway applications