Global Positioning System Signal Reception Research Articles

A framework for preventing unauthorized drone intrusions through radar detection and GPS spoofing

The increasing use of Global Positioning System (GPS)-based autonomous drones in various civilian and military applications has raised concerns about malicious or unintentionally harmful activities that can be carried through them. It is necessary to detect these intruding drones within protected areas and prevent their unauthorized access by denying them entry. We propose a framework that combines the detection of intruding drones using an L-band radar and then counters by transmitting fake GPS coordinates toward the drones, effectively redirecting them. This article explains the setup required to add to an existing monostatic radar that provides two-dimensional information, i.e., range and azimuth information, to enable the proposed setup to get the elevation angle of the drone. We propose a linear array design using digital receive-only beamforming techniques in the elevation domain to compute the elevation angle in addition to the range, velocity, and azimuth information being provided by the monostatic radar to get complete information about the intruding drone. The simulation of drone detection is followed by an examination of the impact of transmitting fabricated GPS coordinates to the drone. Experimental verification has been conducted to validate both the digital beamforming algorithm and the spoofing technique. This approach blocks the reception of actual GPS signals in the drone and replaces the drone's GPS coordinates with alternative, desired coordinates. The proposed framework can be used to prevent unauthorized drone intrusions in the protected area.

A Jamming Aware Artificial Potential Field Method to Counter GPS Jamming for Unmanned Surface Ship Path Planning

Global positioning system (GPS) plays an important role in the path planning of unmanned surface ships. As we know, the civil GPS signal is not encrypted, and its structure is open. Meanwhile, the power strength of GPS signals arriving at receivers is weak. All of these make GPS vulnerable to jamming. GPS jamming attacks adversely affect the accuracy of the received GPS signals, thus affecting the path planning results of unmanned surface ships and even causing collisions. This article presents a jamming aware artificial potential field (JA-APF) method. The JA-APF method first determines whether GPS jamming exists in unmanned surface ships' surrounding environment by detecting the receivers' received signal strength and calculating the packet error rate. Then, the JA-APF method calculates the position range of the jamming source. Finally, the JA-APF method replans the path according to the resultant force of the attraction around the goal, the repulsion around obstacles, and the repulsion around multiple GPS jammers. Through the simulation, we determine the value of the repulsive potential factor of the jammer to optimize the path planning results of the JA-APF method and analyze the influence of the jamming power on the path planning results. The simulation results show that the JA-APF method can effectively solve the impact of GPS jamming on the results in the path planning process and recover as soon as possible.

Blind Estimation of GPS M-Code Signals under Noncooperative Conditions

In the process of Global Positioning System (GPS) modernization, M-code signals with better immunity to interference have been proposed and used in place of P(Y) signals as new authorization signals. A typical positioning, navigation, and timing (PNT) service is based on the local interrelation operation between the reference signal and the received signal. To obtain a PNT, the receiver should generate replicas of the pseudorandom code for acquisition and tracking. However, due to the use of an encryption algorithm, the receiver cannot use the M-code signal under noncooperative conditions. This paper presents an algorithm for estimating M-code sequences without prior knowledge. This algorithm adopts a waveform matching technique and a time domain filtering method to extract M-code from the in-phase channel and quadrature channel of the GPS L1 band. A high-gain antenna is used to receive GPS signals to keep the signal from being drowned out by noise. The experimental results show the feasibility of the method. Therefore, it is helpful for studying and evaluating the performance achieved without prior knowledge of the GPS signals.

GPS spoofing detection via crowd-sourced information for connected vehicles

Modern vehicular systems rely on the Global Positioning System (GPS) technology to provide accurate and timely services. However, the GPS has been proved to be characterized by an intrinsic insecure design, thus being subject to several security attacks. Current solutions can reliably detect GPS spoofing attacks leveraging the physical features of the received GPS signals or resorting to multiple antennas. However, these techniques cannot be deployed when the physical properties of the received signals cannot be accessed, which is the most general case for commercial GPS receivers. Alternative solutions in the literature rely on the cross-check of the received signal with information coming from additional sources. However, such proposals are typically limited to a single source, are rarely supported by experimental results, and do not provide insights on the impact of several parameters, such as detection accuracy, time, false-positives, and robustness to malicious information. To overcome the cited limitations, in this paper, we propose an innovative approach, resorting to combined crowd-sourced information from the mobile cellular infrastructure and the WiFi networks to detect GPS spoofing attacks. Our analysis leverages an extensive experimental dataset, available online for the research community, gathered by driving around a car in urban, suburban, and rural scenarios, for around 5 h and covering more than 196 km. Our solution allows for a tunable tradeoff between detection delay and false positive; for instance, we can detect an attack in approximately 6 s, when leveraging the information coming from only the WiFi, while the delay increases to 30 s when using the information from the mobile cellular network, still achieving a false positive probability strictly less than 0.01. We also show the limitations and trade-offs of our approach, in terms of minimum detection accuracy, time, and robustness to malicious information. The data adopted in this work are publicly released to allow results replicability and foster further research in the highlighted directions.

Dynamic Calibration of GPS Effective Isotropic Radiated Power for GNSS-Reflectometry Earth Remote Sensing

Global Navigation Satellite System (GNSS) Reflectometry uses reflected GNSS signals for Earth remote sensing applications. Absolute calibration of a Delay Doppler Map (DDM) requires an accurate estimate of the effective isotropic radiated power (EIRP) of the GNSS transmitter, e.g., Global Positioning System (GPS). However, variable transmit power by numerous Block II Follow-on (IIF) and II Replenishment-Modernized (IIR-M) GPS space vehicles has been observed due to their flex power mode. Nonuniformity in the GPS antenna gain patterns further complicates EIRP estimation. A dynamic calibration approach is developed to address GPS EIRP variability. It uses measurements by the direct received GPS signal to estimate GPS EIRP in the specular reflected direction and then incorporates it into the calibration of normalized bistatic radar cross section (NBRCS). Error analyses using Monte Carlo simulations and a root sum of squares (RSS) approach show that the resulting error in NBRCS is about 0.32 dB. Dynamic EIRP calibration instantaneously detects and corrects for power fluctuations in the GPS transmitters and significantly reduces errors due to GPS antenna gain azimuthal asymmetry. It allows observations with the most variable Block IIF transmitters (approximately 37% of the GPS constellation) to be included in the standard data products and further improves the calibration quality of NBRCS and geophysical data products.

An improved two-step time-parallel semi-bit method for GPS weak signal acquisition

The Global Positioning System (GPS) receivers often encounter problems of code Doppler and navigation bit sign transitions which decrease output SNR of acquisition stage. The traditional methods of code phase search acquisition with post-correlation detections for weak signal acquisition fail to enhance the number of integrations between the received GPS signal and local Coarse/Acquisition (C/A) code; especially, when the code Doppler and navigation bit sign transitions occur. We propose an improved two-step time-parallel semi-bit acquisition method to overcome the navigation bit sign transition and the code Doppler limitations. This proposed method compensates the navigation bit sign transitions and code Doppler in the first and second step, respectively. Also, Fast Fourier Transform (FFT) is applied to increase the speed of code delay search. Experimental results demonstrate that the proposed method outperforms compared to the conventional methods such as coherent, non-coherent, differential coherent detection, coherent time parallel, non-coherent time parallel, differential time parallel, and improved semi-bit compensation. In contrary to the other conventional methods, the presented method can detect at least four satellites with 40.8% less SNR.

Design an Adjustable Narrow Correlator to Track GPS Signals

Multipath signals problem is still the main challenge for the global positioning system (GPS) receiver to obtain an accurate localization measurement. However, many techniques have been developed to mitigate the impact of these undesired signals at the expense of adding a burden to the GPS receiver design. Even though, none of the techniques in the works of literature was able to solve the loose signal lock issue efficiently. In this piece of work, we used a new approach to maintain the tracking synchronization when the receiver moves from outdoors to indoors /harsh environment. We design a dynamic narrow correlator in the delay lock loop, which made the space between the early and late correlators adjusted according to the receiver’s location. Consequently, this will enable the receiver to keep tracking the received GPS signal in a challenging environment and reduce the thrashing the available resources (power/processing) to acquire the GPS signal again. The results show that the ranging error has been reduced in comparison with a traditional narrow correlator, as well as the bit transition in the in-phase arm has been also maintained.

An Indoor Position-Estimation Algorithm Using Smartphone IMU Sensor Data

Position-estimation systems for indoor localization play an important role in everyday life. The global positioning system (GPS) is a popular positioning system, which is mainly efficient for outdoor environments. In indoor scenarios, GPS signal reception is weak. Therefore, achieving good position estimation accuracy is a challenge. To overcome this challenge, it is necessary to utilize other position-estimation systems for indoor localization. However, other existing indoor localization systems, especially based on inertial measurement unit (IMU) sensor data, still face challenges such as accumulated errors from sensors and external magnetic field effects. This paper proposes a position-estimation algorithm that uses the combined features of the accelerometer, magnetometer, and gyroscope data from an IMU sensor for position estimation. In this paper, we first estimate the pitch and roll values based on a fusion of accelerometer and gyroscope sensor values. The estimated pitch values are used for step detection. The step lengths are estimated by using the pitching amplitude. The heading of the pedestrian is estimated by the fusion of magnetometer and gyroscope sensor values. Finally, the position is estimated based on the step length and heading information. The proposed pitch-based step detection algorithm achieves 2.5% error as compared with acceleration-based step detection approaches. The heading estimation proposed in this paper achieves a mean heading error of 4.72° as compared with the azimuth- and magnetometer-based approaches. The experimental results show that the proposed position-estimation algorithm achieves a high position accuracy that significantly outperforms that of conventional estimation methods used for validation in this paper.

Temperature Trends and Anomalies in Modern Satellite Data: Infrared Sounding and GPS Radio Occultation

AbstractTrends in monthly average, zonal average temperature in the stratosphere as retrieved from highly accurate modern satellite data are intercompared and compared with climate reanalyses from 2003 through 2014. The data sets used are those of Atmospheric Infrared Sounder and Global Positioning System (GPS) radio occultation, and the reanalyses are those of MERRA and ERA‐Interim. Trends produced by all data sets agree to within 0.02 K/year in the lower stratosphere and 0.05 K/year in the middle stratosphere. A number of retrieval errors are found that introduce incorrect trends and seasonal anomalies. Adding microwave data to the infrared retrieval changes trends by approximately 0.01 K/year, thus improving agreement with the other data sets. The signature of the quasi‐biennial oscillation in temperature and the annual cycle of temperature over Antarctica as retrieved from infrared data contain null‐space errors of more than 3 K due to erroneous priors used in retrieval. Nonuniformity in GPS radio occultation gives rise to errors because changes in received GPS signal strength alter the upper boundary initialization in radio occultation retrieval. Finally, an incorrect specification of atmospheric water vapor introduces an erroneous seasonal cycle of temperature as retrieved from GPS radio occultation data in the upper troposphere. All of these time‐dependent retrieval errors can be corrected with future research and improvements to spectral infrared and GPS radio occultation retrieval systems.

터널 내 소화기 표시등 검출을 이용한 3D LIDAR 기반 차량정밀측위

Vehicle localization is essential for autonomous driving. Basically, the position information of the autonomous vehicle is obtained from the Global Positioning System (GPS). More accurate localization can be performed by using maps and various sensors that are mounted on the autonomous vehicle. GPS receivers cannot receive GPS signals in tunnels, so dead reckoning (DR) is used for vehicle localization. However, the error from DR continuously accumulates. Therefore, this error must be corrected by using vehicle-mounted sensors, such as Light Detection and Ranging (LIDAR) and cameras. Tunnels have very specific shape information, which is usually an ellipse, and several emergency facilities exist in tunnels. Some facilities are separated from the tunnel wall, which can be detected by using 3D LIDAR. In particular, fire extinguisher lamps are periodically installed at intervals of 50 m, which can serve as good landmarks. First, the point cloud for the tunnel wall must be removed to effectively detect fire extinguisher lamps. This process can be easily conducted by using shape information. After this removal, we detect the fire extinguisher lamps. In this paper, we propose a 3D LIDAR-based vehicle-localization method that uses ellipse parameters and fire extinguisher lamps in road tunnels. These experiments are conducted at the Maseong tunnel in South Korea. The experimental results show that the root mean square (RMS) position errors in the lateral and longitudinal directions were 0.06 m and 0.23 m, respectively, exhibiting precise localization accuracy.

Frequency-Locked Detector Threshold Setting Criteria Based on Mean-Time-To-Lose-Lock (MTLL) for GPS Receivers.

Frequency-locked detector (FLD) has been widely utilized in tracking loops of Global Positioning System (GPS) receivers to indicate their locking status. The relation between FLD and lock status has been seldom discussed. The traditional PLL experience is not suitable for FLL. In this paper, the threshold setting criteria for frequency-locked detector in the GPS receiver has been proposed by analyzing statistical characteristic of FLD output. The approximate probability distribution of frequency-locked detector is theoretically derived by using a statistical approach, which reveals the relationship between probabilities of frequency-locked detector and the carrier-to-noise ratio (C/N0) of the received GPS signal. The relationship among mean-time-to-lose-lock (MTLL), detection threshold and lock probability related to C/N0 can be further discovered by utilizing this probability. Therefore, a theoretical basis for threshold setting criteria in frequency locked loops for GPS receivers is provided based on mean-time-to-lose-lock analysis.

EFFECT OF THE X5.4 CLASS SOLAR FLARE EVENT OF SOLAR CYCLE 24 ON THE GPS SIGNAL RECEPTION IN PENINSULAR MALAYSIA

Abstract. In this paper, we examine the effect of solar flare event on the Global Positioning System (GPS) signal reception in Peninsular Malaysia during the X5.4 class solar flare on 7th March 2012, 00:24 UT at active region AR1429. GPS data from six MyRTKnet stations that cover the northern, southern, western and eastern regions of Peninsular Malaysia were used, namely Langkawi (Kedah), Bandar Baharu (Pulau Pinang), Pekan (Pahang), Mersing (Johor), Tanjung Pengelih (Johor) and Malacca (Malacca). The total electron content (TEC) was estimated based on the single layer ionospheric model. Next, the ionospheric delay for each GPS frequency of L1 (1575.42 MHz), L2 (1227.60 MHz) and L5 (1176.45 MHz) was then calculated. The results show that solar flare event can influence the GPS signal reception in Peninsular Malaysia where the X5.4 class solar flare shows significant effect of the ionospheric delay within the range of 9 m – 20 m. These research findings will significantly contribute to space weather study and its effects on space-based positioning system such as the GPS.

Open-Loop Tracking of Rising and Setting GPS Radio-Occultation Signals From an Airborne Platform: Signal Model and Error Analysis

Global Positioning System (GPS) radio-occultation (RO) is an atmospheric sounding technique utilizing the received GPS signal through the stratified atmosphere to measure refractivity, which provides information on temperature and humidity. The GPS-RO technique is now operational on several Low Earth Orbiting (LEO) satellites, which cannot provide high temporal and spatial resolution soundings necessary to observe localized transient events, such as tropical storms. An airborne RO (ARO) system has thus been developed for localized GPS-RO campaigns. RO signals in the lower troposphere are adversely affected by rapid phase accelerations and severe signal power fading. These signal dynamics often cause the phase-locked loop in conventional GPS survey receivers to lose lock in the lower troposphere, and the open-loop (OL) tracking in postprocessing is used to overcome this problem. OL tracking also allows robust processing of rising GPS signals, approximately doubling the number of observed occultations. An approach for “backward” OL tracking was developed, in which the correlations are computed sequentially in reverse time so that the signal can be acquired and tracked at high elevations for rising occultations. Ultimately, the signal-to-noise ratio (SNR) limits the depth of tracking in the atmosphere. We have developed a model relating the SNR to the variance in the residual phase of the observed signal produced from OL tracking. In this paper, we demonstrate the applicability of the phase variance model to airborne data. We then apply this model to set a threshold on refractivity retrieval based upon the cumulative unwrapping error bias to determine the altitude limit for reliable signal tracking. We also show consistency between the ARO SNR and collocated COSMIC satellite observations and use these results to evaluate the antenna requirements for an improved ARO system.

Reduction of GPS Latency Using RTK GPS/GNSS Correction and Map Matching in a Car NavigationSystem

The difference between definition time of GPS (Global Positioning System) position data and actual display time of car positions on a map could reduce the accuracy of car positions displayed in PND (Portable Navigation Device)-type CNS (Car Navigation System). Due to the time difference, the position of the car displayed on the map is not its current position, so an improved method to fix these problems is required. It is expected that a method that uses predicted future positionsto compensate for the delay caused by processing and display of the received GPS signals could mitigate these problems. Therefore, in this study an analysis was conducted tocorrect late processing problems of map positions by mapmatching using a Kalman filter with only GPS position data anda RRF (Road Reduction Filter) technique in a light-weight CNS. The effects on routing services are examined by analyzing differences that are decomposed into along and across the road elements relative to the direction of advancing car. The results indicate that it is possible to improve the positional accuracy in the along-the-road direction of a light-weight CNS device that uses only GPS position data, by applying a Kalman filter and RRF.

A Robust GPS Signal Acquisition Technique Using Discrete Wavelet Transform

A novel Global Positioning System (GPS) signal acquisition scheme based on Discrete Wavelet Transform (DWT) is proposed to improve acquisition performance. Acquisition in GPS system is primary and important step to calculate the code phase in Pseudo Random Noise (PRN) code and Doppler shift in carrier frequency of received GPS signal, which is used for continuous tracking of the satellite. The performance of a GPS receiver system depends on the ability to precisely measure the code range and Doppler shift continuously in the presence of noise. Conventional GPS receivers use Fast Fourier Transform (FFT) to carry out convolution in the acquisition process. This method is unable to precisely acquire the GPS signal in the presence of noise. In this paper, a substitute algorithm using DWT is proposed to perform convolution in order to carry out robust, less complex GPS signal acquisition. The proposed algorithm is implemented on Intermediate Frequency (IF) GPS signal with different levels of noise and also compared with the conventional FFT search algorithm. The proposed algorithm allows implementation of the FFT with a reduced number of samples (2500 instead of 5000 samples), is implemented by collecting the one millisecond period data sampled at 5MHz. Performance of the algorithms are compared based on correlation ratio. Results show that the proposed algorithm using DWT outperforms the FFT search method of acquisition.

Fast Acquisition of GPS Signal Using FFT Decomposition

Acquisition in Global Positioning System (GPS) is primary and important step to measure the code phase of Pseudo Random Noise (PRN) code and Doppler shift in carrier frequency of received GPS signal. The performance of a GPS receiver system depends on the fast and accurate measure of the code phase and Doppler shift in the recived signal. A new GPS signal acquisition method based on decomposition of FFT is proposed to improve the acquisition performance. Conventional GPS receivers use Fast Fourier Transform (FFT) to carry out correlation in the acquisition process. However, this paper proposes a new method that reduces the complexity of FFT computation. The proposed algorithm is implemented, validated and compared the performance with conventional serial search and radix2 FFT search algorithms using Intermediate Frequency (IF) GPS signal. Acquisition algorithms are implemented on 1.25MHz signal data of one millisecond period, sampled at 5MHz. For the sampled data, the proposed algorithm uses 5000 samples insted of number of samples raised to nearest power of 2 i.e. 8192 samples as in the case of radix2 FFT search method to compute FFT. Performance of the algorithms are compared based on computational time and correlation peak magnitude.

GPS 수신기에서 간섭신호에 대응하기 위한 배열 안테나기반 능동 간섭 제거 방안

GPS (global positioning system) is a popular system that provides location information by measuring arrival time difference at the receiver between several GPS satellite signals. GPS is widely used in commercial area as well as military systems. Reliable GPS signal reception is more important in the military systems. However, since the carrier frequencies of the GPS signals are well known, the GPS receivers are vulnerable to intentional jamming attacks. To remove jammers but maintain GPS signals at the received signals, a popular technique is an adaptive beam steering method based on array antenna. Among adaptive beam steering techniques, this paper considers MVDR (minimum variance distortionless response) algorithm, and proposes a new adaptive technique that preserves the received signals at desired direction, but removes the jamming signals adaptively. The performance of the proposed method is verified through computer simulation. 키워드 : GPS 수신기, 어레이 안테나, 적응 빔 제어, MVDR Key word : GPS receiver, array antenna, adaptive beam steering, MVDR Journal of the Korea Institute of Information and Communication Engineering 한국정보통신학회논문지(J. Korea Inst. Inf. Commun. Eng.) Vol. 19, No. 7 : 1539~1545 Jul. 2015

Jamming mitigation in global positioning system receivers using wavelet packet coefficients thresholding

In this paper, the authors describe a new pre-correlation mitigation technique for global positioning system (GPS) receivers. Proposed mitigation technique is based on wavelet packet coefficients thresholding. This technique employs adaptive thresholding to mitigate GPS jammers. The authors compare proposed technique against discrete wavelet coefficient thresholding method. In this paper, the interferers are generated by an RF signal generator. The received GPS signal and interference are combined in a combiner. Then, the combined signal is processed by a software GPS receiver which includes the proposed mitigation technique. Simulation results show benefits of the proposed method in terms of signal-to-noise power ratio improvement and mean square error (MSE) in contrary to previous methods. Comparison of presented method and the discrete wavelet method illustrates that the average improvement is 50% and 80% in terms of SNR improvement and MSE, respectively.

대역제한 백색잡음 재밍환경에서 GPS L1 C/A 신호를 위한 유효 반송파 대 잡음 전력비 추정치의 CRLB

In this paper, we derive the CRLB (Cramer-Rao Lower Bound) of effective carrier-to-noise power ratio (<TEX>$C/N_0$</TEX>) estimation for a GPS (Global Positioning System) L1 C/A (Coarse/Acquisition) signal under band-limited white noise jamming environments. The quality of a received GPS signal is commonly described in terms of its <TEX>$C/N_0$</TEX>, implying that the noise is white and thus can be described by scalar noise density. However, if some intentional interference is received to a victim GPS receiver, then the <TEX>$C/N_0$</TEX> is no longer the efficacious performance indicator. The correct and straightforward measurement to analyze the receiving situation is the effective <TEX>$C/N_0$</TEX>. In this paper, we consider a band-limited white noise jamming whose bandwidth is 2MHz and is the same as one of the first null-to-null bandwidth of the GPS L1 C/A signal.

A multipath mitigation discriminator for GPS receiver

A novel technique for mitigating the multipath-induced code delay estimation error in Global Positioning System (GPS) is proposed. In contrast to conventional methods that aim to eliminate multipath signals, the proposed method exploits them to enhance the direct signal without affecting the accuracy of GPS code delay estimates. To achieve this, coherent accumulation of the received GPS signals is first done by transforming the received data into frequency domain and the parameters of multipath signals are then estimated by sparse reconstruction algorithm. Subsequently, a modified local reference signal is employed in delay lock loop (DLL) of the GPS receiver, which mitigates the pseudo-range estimation error and increases the correlation value of direct GPS signal. Simulation results demonstrate the performance and robustness of the proposed method.