Global Navigation Satellite Systems Engineering, Policy, and Design
With a Low-cost Single-frequency Multi-GNSS Receiver
Although precise point positioning (PPP) has been largely limited to applications in open environments using high-end GNSS receivers, recent test results demonstrate that a new PPP system with a mass-market receiver can significantly improve positioning accuracy in urban environments.
By Inside GNSS
Cryptographic techniques can optimize the trade-off between authentication integrity (minimizing the probability of authenticating a modified message), ease of modification of existing signals (for operator and user acceptance), and minimal impact on existing users who will form the vast majority of the GNSS user population for some time to come.
By Sam Pullen
Future miniaturized sensors, to be used for example in bee-sized drones, mini-satellites, or wearable devices, are likely to include GNSS chipsets supporting accurate outdoor localization and also offering reduced computational costs and power consumption compared to traditional GNSS receivers. The survey various energy-efficient methods for GNSS acquisition and present a discontinuous-reception acquisition algorithm, analyzed with both simulated and measurement-based data.
We are witnessing a space renaissance. Tens of thousands of broadband low Earth orbit (LEO) satellites are expected to be launched by the end of this decade. These planned megaconstellations of LEO satellites along with existing constellations will shower the Earth with a plethora of signals of opportunity, diverse in frequency and direction. These signals could be exploited for navigation in the inevitable event that GNSS signals become unavailable (e.g., in deep urban canyons, under dense foliage, during unintentional interference, and intentional jamming) or untrustworthy (e.g., undermalicious spoofing attacks).
This article reviews some of the recent results analyzing the feasibility of carrier-phase based positioning with smartphone data and highlights limitations largely arising due to the poor antenna quality. It shows how they might be overcome by antenna calibration or coupling to the phone’s inertial sensors. The goal is to perform a successful RTK positioning with the smartphone-quality data.
Discussions about spectrum allocation, familiar to GNSS designers and manufacturers on Earth, are now taking place regarding the lunar environment. ITU Radio Regulations constitute an international treaty governing all radio frequency activities. This article shows that GNSS operators in this region must transmit signals in the GNSS S-band rather than in GNSS L-bands.
A new method for multipath rejection employs a multicorrelator-based GNSS receiver with an extended Kalman Filter (EKF) as an iterative solver, replacing the conventional delay locked loop (DLL) code tracking. The technique significantly reduces the positioning error and has low complexity. It can therefore be implemented in a real-time processing environment.
Ionospheric delay is the largest source of range error for GPS Standard Positioning Service (SPS) users, at least during local daytime when solar emissions enhance these delays.
By Inside GNSS
Ligado Networks had an early-year win in the form of a Federal Communications Commission denial of the National Telecommunications and Information Administration Stay Petition involving Ligado’s license for a terrestrial service in the mobile satellite services L-band. The company continues to roll toward deployment of a nationwide 5G network. While filings trickle in from the private sector, the feds work quietly behind the scenes on Congressional due-outs. In short, wheels big and small keep churning down the river to 5G.
By Dawn M.K. Zoldi (Colonel, USAF, Ret.)
Galileo satellites 5 and 6 (E18, E14) were declared unusable in February 2021 after reports indicating repeatable daily problems with RTK. This article explores the possible impact of deviant elliptical orbits on the performance of RTK and finds that there is no reason to expect any anomalies caused by high orbit eccentricity per se. Thus there is no reason to declare the satellites unhealthy.
The addition of alternative sensors such as cameras, magnetometers, and small ranging radios increases the likelihood of a mismodeled and/or faulty sensor, affecting the accuracy and performance of the overall navigation solution. Unlike two-sensor systems such as GPS-inertial integration, systems of three or more sensors present the problem of ambiguity as to which sensor is adversely affecting the solution. This presents the need for a robust framework that can maintain navigation integrity despite the additional sensor modalities.
In a GNSS spoofing attack, a terrestrial radio transmitter mimics GNSS signals at a greater signal strength than the actual system can transmit. In order to detect and mitigate a spoofing attack, it is important to know where a spoofing signal comes from and what it tries to accomplish for its ultimate neutralization.
Interference mitigation techniques should protect GNSS receivers from interference and jamming without biasing their final position, velocity and timing solution. This column analyses five popular interference mitigation techniques, including the Adaptive Notch Filter (ANF) and Pulse Blanking (PB), evaluating their impact on pseudoranges and on the final position and timing solution. Several GNSS modulations are considered, showing the advantage of using GNSS signals with similar spectral characteristics.
