In this paper, an improved joint time-frequency (TF) analysis method based on a reassigned smoothed pseudo Wigner–Ville distribution (RSPWVD) has been proposed in interference detection for Global Navigation Satellite System (GNSS) receivers. In the RSPWVD, the two-dimensional low-pass filtering smoothing function is introduced to eliminate the cross-terms present in the quadratic TF distribution, and at the same time, the reassignment method is adopted to improve the TF concentration properties of the auto-terms of the signal components. This proposed interference detection method is evaluated by experiments on GPS L1 signals in the disturbing scenarios compared to the state-of-the-art interference detection approaches. The analysis results show that the proposed interference detection technique effectively overcomes the cross-terms problem and also preserves good TF localization properties, which has been proven to be effective and valid to enhance the interference detection performance of the GNSS receivers, particularly in the jamming environments.

Since radio frequency interference (RFI) seriously degrades the performance of a global navigation satellite system (GNSS) receiver, interference detection becomes very important for GNSS receivers. In this paper, a novel rearranged wavelet–Hough transform (RWHT) method is proposed in GNSS interference detection, which is obtained by the combination of rearranged wavelet transform and Hough transform (HT). The proposed RWHT method is tested for detecting sweep interference and continuous wave (CW) interference, the major types of GNSS interfering signals generated by a GNSS jammer in a controlled test bench experiment. The performance of the proposed RWHT method is compared with the conventional techniques such as Wigner–Ville distribution (WVD) and Wigner–Hough transform (WHT). The analysis results show that the proposed RWHT method reduces the influence of cross-item problem and improves the energy aggregation property in GNSS interference detection. When compared with the WHT approach, this proposed RWHT method presents about 90.3% and 30.8% performance improvement in the initial frequency and chirp rate estimation of the GNSS sweep interfering signal, respectively. These results can be further considered to be the proof of the validity and effectiveness of the developed GNSS interference detection method using RWHT.

This paper has proposed a new and efficient Global Navigation Satellite System (GNSS) anti-interference method using fractional Fourier Transform (FrFT) and notch filtering. An effective optimal fractional order determination model based on generalized time fractional bandwidth product (GTFrBP) of the FrFT has been developed in the detection of GNSS interfering signal, which can be realized using efficient one-dimensional search scheme and provide estimated interfering parameters. The GNSS interference mitigation can be realized through dechirping and notch filtering operations based on the obtained GNSS interference detection and estimation results. These proposed techniques in interference detection and mitigation are verified using real GPS L1-C/A signal interfered by the sweep interference. The results demonstrate that the developed GTFrBP search model delivers satisfactory precision in the determination of the optimal fractional order of the FrFT in the GNSS interference detection procedure; and the GNSS anti-interference experimental results have proven that the developed GNSS anti-interference method can successfully suppress the sweep interference present in the received GPS L1-C/A signal, which ensures that the acquisition performance of the GNSS receiver can be greatly improved in the interfering environments. The validity and effectiveness of the developed anti-interference method for GNSS receivers can be further verified by the carrier power-to-noise power density ratio (C/N0) curve and jamming tolerance analysis results, which have proven that the proposed FrFT and notch filtering based method is capable of providing significantly improved GNSS anti-interference performance in the interfering environments. Furthermore, the proposed GNSS anti-interference method has been tested in positioning experiments, which provides very satisfactory positioning results under interfering conditions, confirming the proposed method’s reliability and effectiveness in handling GNSS interference.

Interference is a major threat to the safe and secure operation of global navigation satellite system (GNSS) receivers particular in disturbing scenarios. Therefore, correct detection and reliable mitigation of interfering signals is critical to the delivery of mission critical positioning, navigation and timing services. In this paper, an effective interference detection and mitigation (ID&M) method based on the fractional Fourier transform (FrFT) has been proposed for GNSS receivers. This paper addresses the problem of inefficient search methods and unreliable interference detection and mitigation of the current techniques. Firstly, it develops an efficient optimal fractional order determination model First Order Moment of Magnitude (FOMM) of the FrFT to reduce the computational complexity compared with the traditional FrFT's maximum magnitude (MM) and generalized time fractional bandwidth product (GTFrBP) approaches. Secondly, an effective GNSS interference excision method using FrFT filtering has been developed to suppress GNSS interference. These proposed methods are tested in a controlled test bench experiment, for detecting and mitigating sweep interference, a major type of GNSS interfering signal generated by a GNSS jammer. The jamming tolerance analysis results show that the proposed FrFT filtering method is more than 25 dB higher than the state-of-the-art two-pole notch filter technique; the reliability of the proposed FrFT method has been further consolidated using effective carrier power-to-noise power density ratio analysis; and therefore, the proposed anti-interference method using FrFT filtering is recommended for use in GNSS receivers

Interference detection is very important for Global Navigation Satellite System (GNSS) receivers. Current work on interference detection in GNSS receivers has mainly focused on time-frequency (TF) analysis techniques, such as spectrogram and Wigner–Ville distribution (WVD), where the spectrogram approach presents the TF resolution trade-off problem, since the analysis window is used, and the WVD method suffers from the very serious cross-term problem, due to its quadratic TF distribution nature. In order to solve the cross-term problem and to preserve good TF resolution in the TF plane at the same time, in this paper, a new TF distribution by using a reassigned spectrogram has been proposed in interference detection for GNSS receivers. This proposed reassigned spectrogram method efficiently combines the elimination of the cross-term provided by the spectrogram itself according to its inherent nature and the improvement of the TF aggregation property achieved by the reassignment method. Moreover, a notch filter has been adopted in interference mitigation for GNSS receivers, where receiver operating characteristics (ROCs) are used as metrics for the characterization of interference mitigation performance. The proposed interference detection method by using a reassigned spectrogram is evaluated by experiments on GPS L1 signals in the disturbing scenarios in comparison to the state-of-the-art TF analysis approaches. The analysis results show that the proposed interference detection technique effectively overcomes the cross-term problem and also keeps good TF localization properties, which has been proven to be valid and effective to enhance the interference Sensors 2015, 15 22168 detection performance; in addition, the adoption of the notch filter in interference mitigation has shown a significant acquisition performance improvement in terms of ROC curves for GNSS receivers in jamming environments.

The next generation Global Navigation Satellite Systems (GNSS), such as Galileo and Global Positioning System (GPS) modernization, will use signals with equal code and bit periods, resulting in a potential bit sign transition in each primary code period of the received signal segments. A bit sign transition occurring within an integration period usually causes a splitting of the Cross Ambiguity Function (CAF) main peak into two smaller side lobes along the Doppler shift axis in the search space and it may lead to an incorrect Doppler shift estimate, which results in a serious performance degradation of the acquisition system. This paper proposes a novel two steps based bit sign transition cancellation method which can overcome the bit sign transition problem and remove or mitigate the CAF peak splitting impairments. The performance of the proposed technique has been comprehensively evaluated with Monte Carlo simulations in terms of detection and false alarm probabilities, which are presented by Receiver Operating Characteristic (ROC) and Signal-to-Noise-Ratio (SNR) curves. The test results show that the proposed acquisition technique can provide improved performance in comparison with the state-of-the-art acquisition approaches.