Civilian GPS Signal Research Articles

Experimental Analysis of GPS L2C Signal Quality under Various Observational Conditions

To appropriately handle the GPS L2C signal for the future development of positioning algorithms, this contribution has endeavoured to figure out its features by computing some quality measures of all the modernised satellites (i.e., twenty-three as of January 2022) and comparing them with those of the C/A and P2(Y) code. A series of quality analyses have been carried out to GPS measurements at twenty-four continuously operating reference stations (CORS) equipped with eight receiver models. In addition, experimental data acquired by a combination of high-end and cost-effective receivers have been intensively assessed to characterise the relative signal quality of the L2C to the legacy codes. The observational conditions considered in this study include different multipath environments and receiver dynamics. The results of the analyses, in general, indicate that the quality of the L2C-derived measurements is equivalent to the legacy civilian code (i.e., C/A) but superior to the encrypted military signal (P2(Y)). Hence, it is expected that the new civilian GPS signal enhances the positioning performance of dual-frequency measurements with both high-end and cost-effective receivers.

Synchrophasor Data Under GPS Spoofing: Attack Detection and Mitigation Using Residuals

The installation of Phasor Measurement Units (PMUs) is a step towards achieving wide-area situational awareness for the power grid. PMUs utilize GPS signals for time synchronization and are vulnerable to GPS Spoofing Attacks (GSAs) as civilian GPS signals are unencrypted and have low signal power. We propose a novel Residual-based Spoofing Detection and Measurement Correction (RSDMC) algorithm for the power grid that detects GSAs and corrects spoofed PMU measurements. During one or multiple GSAs, RSDMC iteratively minimizes the residual norm to correct spoofed PMU measurements. We derive a necessary condition for our proposed algorithm to show that the residual norm increases during GSAs. We perform Monte Carlo simulations to verify our derived necessary condition. We further simulate the IEEE 14, IEEE 118, and Illinois 200 bus test cases to validate RSDMC against multiple GSAs.

Spoofing Resilient State Estimation for the Power Grid Using an Extended Kalman Filter

Real-time monitoring of a wide-area power grid network has become feasible with time-synchronized Phasor Measurement Units (PMUs). PMUs use GPS signals for time synchronization and are susceptible to GPS Spoofing Attacks (GSAs) since civilian GPS signals are unencrypted and have low signal power of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> Watts. We propose a novel Spoofing-Resilient State Estimator (SR-SE) that fuses time-varying GPS and PMU measurements using an Extended Kalman Filter (EKF). We design our measurement model that relates the coupling between GPS and PMU measurements to improve the performance of SR-SE. We perform software as well as Hardware-In-the-Loop (HIL) simulations to validate SR-SE against GSAs. We conduct 100 Monte Carlo (MC) simulations with IEEE 14, IEEE 39, and Illinois 200-bus test systems in software simulations. In HIL simulation, we simulate and generate GPS-PMU integrated datasets for the IEEE 14-bus test system using Real-Time Digital Simulator, PMUs, and GPS clock.

Design of a low noise amplifier for L-band GPS applications

The low noise amplifier (LNA) is a key part of any receiving system to prevent signal degradation due to different types of noise and the need for long transmission. This paper describes the procedures to design an LNA using a commercial SiGe hetero-junction bipolar transistor (HBT), BFP640, from Infineon Technologies. The amplifier, which satisfies certain specifications, may then be used to strengthen the L2C second civilian GPS signal. The design process was carried out using a powerful microwave CAD package, Advanced Design System (ADS), by Keysight Technologies, which provides a complete RF circuit design facility. The LNA was designed to meet the desired specifications of a low noise figure less than 1 dB, power gain of grater than 20 dB, and output voltage standing ratio (VSWR) of less than 2. The centre frequency used was 1.227 GHz, with an operating bandwidth of 40 MHz. This work thus presents a prototype model that can be readily implemented based on the calculated components of matching networks, as the simulation results demonstrate that the amplifier circuit satisfies the desired requirements.

GPS spoofing detection for the power grid network using a multireceiver hierarchical framework architecture

In the future, the modernized power grid, or smart grid, will utilize devices called phasor measurement units (PMUs) to continuously monitor the power grid state in real time. These devices utilize GPS to synchronize the voltage and current phasor measurements across the continental network; however, because the civilian GPS signals are unencrypted, PMUs are susceptible to GPS spoofing attacks. We propose a spoofing detection algorithm using a wide-area, hierarchical architecture. In the network, each PMU transmits conditioned signal fragments containing the military P(Y) signal, which serves as an encrypted signature in the background of all authentic GPS signals. This signature is then verified among a subnetwork consisting of a select number of well-dispersed receivers. We subsequently compare representative signals generated for each subnetwork in order to detect coordinated attacks against the subnetwork receiver collection. Using real-world data recorded during a government-sponsored, live-sky spoofing event, we demonstrate that our algorithm successfully evaluates the authenticity of a widely dispersed receiver network.

A Stealthy GPS Spoofing Strategy for Manipulating the Trajectory of an Unmanned Aerial Vehicle

GPS is of great importance for autopilot of an Unmanned Aerial Vehilce (UAV). Recently, GPS spoofing attack on UAV has attracted widespread research interests due to the vulnerability of civilian GPS signal. This paper specifies a scenario in which the GPS spoofing attacker intends to drive the UAV equipped with a fault detector to any arbitrary destination without triggering the detector. We formulate the problem as a constrained optimization problem, and provide an effective solution to compute the falsified GPS measurement of each time instant. In addition, we analyze and compute the largest attainable location set of the UAV under GPS spoofing attack, which quantifies the capability of GPS Spoofing attack under the constraint of the fault detector. Numerical simulations under various parameter settings are conducted to verify the results.

Real-Time GPS Spoofing Detection via Correlation of Encrypted Signals

A method for detecting the spoofing of civilian GPS signals has been implemented and successfully tested in a real-time system. GPS signal spoofing is an attack method whereby a third party transmits a signal that appears authentic but induces the receiver under attack to compute an erroneous navigation solution, time, or both. The detection system described herein provides a defense against such attacks. It makes use of correlations between the unknown encrypted GPS L1 P(Y) code signals from two narrow-band civilian receivers to verify the presence or absence of spoofing. One of these receivers is assumed to be at a secure location that is not subject to spoofing. The other receiver is the potential spoofing victim for which the present developments constitute a defense. Successful detection results are presented using a reference receiver in Ithaca, New York, a victim receiver in Austin, Texas, and a spoofer in Austin, Texas. Copyright © 2013 Institute of Navigation.

FFT based Acquisition Techniques of GPS L2C Signals

The modernization of the GPS lead to the launch of additional GPS signal, L2C second civilian GPS signal to become available in full constellation. L2C signals have longer ranging codes which leads to larger search space and increase in computational complexity. L2C signals makes use of two PRN sequences CM (Civil Moderate) and CL (Civil Long) of 20ms and 1.5sec long. In this paper a code generator is designed for generating the CM and CL sequences, and two local replica codes NRZ (Non Return Zero) and RZ (Return Zero) Codes are designed. The code phase and carrier Doppler are estimated based on the various FFT (Fast Fourier Transform) based acquisition techniques.

RF Replay System for Narrowband GNSS IF Signals

Although global navigation satellite systems (GNSS) radio frequency (RF) signal simulators have long possessed the capability to generate scenarios, they are, for example, not yet able to model a specific realistic scenario with complex multipath. Software-defined receivers bridge the gap between simulated and real data to the extent that they may offer a replay capability, where a data set is first recorded to disk and later can be processed several times. Unfortunately the recorded data generally cannot be used by hardware-based GNSS receivers, making receiver-to-receiver comparisons difficult and time consuming. A system capable of replaying recorded IF data into any narrow bandwidth L1 (the frequency band of the traditional civilian GPS signal) GNSS receiver is described here, including an evaluation of the difference (position, timing, and signal-to-noise ratio (SNR)) between live and replayed data using a high sensitivity, consumer-grade receiver. The performance of the replayed data set was, with regards to the position and timing, found to match that of the live data.