Conventional Global Positioning System Receivers Research Articles

Detection and mitigation of GPS Spoofing Attacks on Phasor Measurement Units using deep learning

The widespread use of Phasor Measurement Units (PMUs) is considered one of the most important contributions to the quality of power system monitoring. PMUs are digital devices that provide synchronized phasor measurements time-referenced by the Global Positioning System (GPS). The lack of encryption in conventional GPS receivers used in PMUs makes them vulnerable to GPS Spoofing Attacks (GSAs) that cause the GPS receiver to lose track, resulting in a phase shift of all measurements of the affected PMU. Even small phase shifts can downgrade the performance of the state estimator, indicating their ability to propagate throughout the entire system. Therefore, ensuring the integrity of PMU measurements is of utmost importance. State-of-the-art statistical methods are insensitive to small phase shifts, and they become computationally intensive as the system size and the number of simultaneous attacks increase. This paper presents the first application of deep learning to simultaneously detect and mitigate the effects of GSAs against PMUs. The performance of the proposed method is evaluated on IEEE 14-, 57-, and 118-bus systems and compared to state-of-the-art statistical and deep learning methods.

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.

Receiver-channel based adaptive blind equalization approach for GPS dynamic multipath mitigation

Aiming at mitigating multipath effect in dynamic global positioning system (GPS) satellite navigation applications, an approach based on channel blind equalization and real-time recursive least square (RLS) algorithm is proposed, which is an application of the wireless communication channel equalization theory to GPS receiver tracking loops. The blind equalization mechanism builds upon the detection of the correlation distortion due to multipath channels; therefore an increase in the number of correlator channels is required compared with conventional GPS receivers. An adaptive estimator based on the real-time RLS algorithm is designed for dynamic estimation of multipath channel response. Then, the code and carrier phase receiver tracking errors are compensated by removing the estimated multipath components from the correlators’ outputs. To demonstrate the capabilities of the proposed approach, this technique is integrated into a GPS software receiver connected to a navigation satellite signal simulator, thus simulations under controlled dynamic multipath scenarios can be carried out. Simulation results show that in a dynamic and fairly severe multipath environment, the proposed approach achieves simultaneously instantaneous accurate multipath channel estimation and significant multipath tracking errors reduction in both code delay and carrier phase.

Performance limits of channel parameter estimation for joint communication and positioning

Recently, a system concept for joint communication and positioning has been proposed by the authors. Channel parameter estimation (CPE) is the core part of this system proposal. Parameters of the physical channel, which can be exploited for positioning, are estimated based on the assumption that a priori knowledge about pulse shaping and receive filtering is available. At the same time, channel estimates of the equivalent discrete-time channel model, which are needed for data detection, are obtained inherently. This article focusses on the positioning part of the system proposal. Performance limits for CPE in terms of Cramer-Rao lower bounds are determined for different channel models. The influence of oversampling and of different channel characteristics is investigated. Oversampling proves especially helpful in dense multipath scenarios, which are most challenging. Based on the presented results, oversampling with a factor of two is recommended in order to improve the positioning accuracy. Excessive oversampling like in conventional global positioning system receivers is not necessary.

Experimental Application of Global Positioning system To Locate Motor Vehicle Crashes: Impact on Time and Accuracy

Motor vehicle crash countermeasures often are selected after an extensive data analysis of the crash history of a roadway segment. The value of this analysis depends on the accuracy or precision with which the crash itself is located. yet this crash location only is as accurate as the estimate of the police officer. Global Positioning System (GPS) technology may have the potential to increase data accuracy and decrease the time spent to record crash locations. Over 10 months, 32 motor vehicle crash locations were determined by using both conventional methods and hand-held GPS receivers, and the timeliness and precision of the methods were compared. Local crash data analysts were asked how the improved precision affected their consideration of potential crash countermeasures with regard to five crashes selected from the sample. On average, measuring a crash location by using GPS receivers added up to 10 extra minutes, depending on the definition of the crash location, the technology employed, and how that technology was applied. The average difference between conventional methods of measuring the crash location and either GPS or a wheel ranged from 5 m (16 ft) to 39 m (130 ft), depending on how one defined the crash location. Although there are instances in which improved precision will affect the evaluation of crash countermeasures, survey respondents and the literature suggest that problems with conventional crash location methods often arise from human error, not a lack of precision inherent in the technology employed.