Ali Broumandan

GPS Vulnerability to Spoofing Threats and a Review of Antispoofing Techniques

Article deposited according to Hindawi Publishing Corporation policy for the International Journal of Navigation and Observation: http://www.hindawi.com/journals/ijno/guidelines/, August 22, 2012.

GNSS spoofing detection in handheld receivers based on signal spatial correlation

Spoofing and jamming in the form of transmitting counterfeit location information and denying services are an emerging threat to GNSS receivers. In general, spoofing is a deliberate attack that aims to coerce GNSS receivers into generating false navigation solutions. The spoofing attack is potentially more hazardous than jamming since the target receiver is not aware of this threat and it is still providing position/navigation solutions which seem to be reliable. One major limitation of spoofers is that they are required to transmit several highly correlated GNSS signals simultaneously often from a single source in order to present a truthful navigation solution to the receiver. Different GNSS signals sourced from a single transmitter have essentially the same spatial signature, which as shown in this paper, can be utilized to discriminate the spoofing signals. In this paper a moving antenna is investigated to discriminate between the spatial signatures of the authentic and the spoofing signals based on monitoring the amplitude and Doppler correlation of the visible satellite signals. The effectiveness of this detection method is studied and verified based on a set of experiments.

GPS spoofer countermeasure effectiveness based on signal strength, noise power, and C/N0 measurements

SUMMARY Spoofing sources can effectively disrupt a GPS receiver during the acquisition phase by generating multiple false correlation peaks and increasing the noise floor. Such deceptive correlation peaks can mislead the GPS receiver into acquiring the spoofer generated signals rather than the authentic signals. Also, the spoofer can increase the receiver noise floor to bury the authentic signals in the noise and at the same time generate correlation peaks with amplitudes commensurate with reasonable C/N0 expectations. The main focus of this paper is on assessment of the reduced effectiveness of the GPS spoofer countermeasure during acquisition where the GPS receiver utilizes C/N0 discrimination. As shown, whereas the C/N0 discrimination is of limited effectiveness, with a modest circuit modification, the receiver can measure the absolute power of the correlation peaks, which is an effective means of detecting and discriminating spoofer sources. It will be shown that employing absolute power monitoring technique considerably reduces the vulnerability region of the receiver compared with the C/N0 monitoring techniques. Copyright

Indoor GNSS Signal Acquisition Performance using a Synthetic Antenna Array

GNSS (Global Navigation Satellite System) signal reception in indoor environments is susceptible to spatial fading and signal attenuation. An antenna array utilizing spatial diversity can be implemented to improve detection performance which reduces the required fading margin. However for the typical handheld GNSS receiver, constrained to a single antenna, spatial processing gain is possible only if the antenna is physically translated as the signal is being captured by the receiver. This is equivalent to realizing a spatially distributed synthetic array (SA) antenna. An investigation of the indoor detection performance of a GNSS receiver based on SA processing with optimized combining algorithms is made and compared with the detection performance of the equivalent static antenna. The processing gain achievable through spatial combining of a synthetic antenna is considered from a general theoretical perspective and validated with an extensive set of experimental measurements satisfying statistical significance criteria. The performance of the proposed method is theoretically analyzed in terms of the probability of false alarm (PFA) and probability of detection (PD). It is shown that the significant processing gain resulting from randomly moving the antenna relative to a stationary position can be large, exceeding 10 dB in practically encountered usage cases for a GNSS handset.

Practical Results of Hybrid AOA/TDOA Geo-Location Estimation in CDMA Wireless Networks

This paper describes a hybrid AOA/TODA mobile station (MS) location estimation method based on the CDMA wireless communications signals. The method utilized estimates the angle of arrival (AOA) and time difference of arrival (TDOA) of downlink pilot channel. In this paper, signal parameter estimations including AOA and TDOA, and position estimation challenges in real wireless communications systems are denoted. For position estimation, the mathematical model and its linearized model for a hybrid TDOA/AOA method based on the Taylor series expansion are derived. The performance analysis of the high-resolution MUSIC angle and double delta delay estimators using field measurements from a typical outdoor IS-95 CDMA radio propagation channel are demonstrated. In this paper, practical considerations on the implementation of a standalone positioning system are described. The performance of TDOA and hybrid AOA/TDOA positioning system when the receiver has access to minimum LOS signals are compared.

Spoofing detection, classification and cancelation (SDCC) receiver architecture for a moving GNSS receiver

Abstract Spoofing in the form of transmitting fake GNSS signals is a deliberate attack that aims to mislead GNSS receivers into generating false position/time solutions. Current work on GNSS spoofing has mainly focused on spoofing detection where the proposed algorithms only indicate the presence of spoofing attacks. A new architecture consisting of spoofing detection, authentic/spoofing signal classification and spoofing cancelation known as spoofing detection, classification and cancelation for moving GNSS receivers is proposed. Predespreading and acquisition level analysis are performed to detect the presence of spoofing interference. The receiver motion is then used to classify the signals tracked into two groups, namely spoofing and authentic signal sets. A successive spoofing cancelation method is then developed to remove the spoofing signals from the raw digitized samples. It is shown that canceling out the spoofing signals removes multiple access interference and significantly improves the authentic signals’ detectability and tracking performance. Finally, after spoofing cancelation, authentic signals are acquired and tracked and their corresponding measurements are passed to a PVT engine for a reliable position solution. The proposed receiver architecture is analyzed in the acquisition, tracking and positioning layers.

GNSS space-time interference mitigation and attitude determination in the presence of interference signals.

The use of Space-Time Processing (STP) in Global Navigation Satellite System (GNSS) applications is gaining significant attention due to its effectiveness for both narrowband and wideband interference suppression. However, the resulting distortion and bias on the cross correlation functions due to space-time filtering is a major limitation of this technique. Employing the steering vector of the GNSS signals in the filter structure can significantly reduce the distortion on cross correlation functions and lead to more accurate pseudorange measurements. This paper proposes a two-stage interference mitigation approach in which the first stage estimates an interference-free subspace before the acquisition and tracking phases and projects all received signals into this subspace. The next stage estimates array attitude parameters based on detecting and employing GNSS signals that are less distorted due to the projection process. Attitude parameters enable the receiver to estimate the steering vector of each satellite signal and use it in the novel distortionless STP filter to significantly reduce distortion and maximize Signal-to-Noise Ratio (SNR). GPS signals were collected using a six-element antenna array under open sky conditions to first calibrate the antenna array. Simulated interfering signals were then added to the digitized samples in software to verify the applicability of the proposed receiver structure and assess its performance for several interference scenarios.

GNSS Multipath Mitigation with a Moving Antenna Array

Besides the size and shape of antenna arrays, the correlation between multipath components and a desired signal restricts the use of array processing techniques for Global Navigation Satellite System (GNSS) multipath mitigation. A new method, based on a moving antenna array, to synthesize a larger array and increase its degree of freedom is proposed. Furthermore, a spatial filter is applied to this synthesized array to prevent the signal cancellation phenomenon and mitigate the multipath components.

Overview of Spatial Processing Approaches for GNSS Structural Interference Detection and Mitigation

GNSS-dependent positioning, navigation, and timing synchronization procedures have a significant impact on everyday life. Thus, such an extensively used system progressively become an attractive target for illegal exploitation and attacks. Position and timing solutions provided by GNSS receivers can be threatened by structural interference such as spoofing threats. This paper provides an overview of recent research work on GNSS signal authentication utilizing spatial processing methods. Different spatial processing approaches for spoofing detection, classification and mitigation are characterized and compared. Three different processing methods, namely antenna array processing, moving receiver and cloud based spoofing countermeasure are analyzed in details. The benefits and disadvantages of each are discussed.

A GNSS structural interference mitigation technique using antenna array processing

Position solutions provided by Global Navigation Satellite Systems (GNSS) can be completely misled by structural interference or spoofing threats. An approach utilizing an antenna array is proposed in order to suppress spoofing attacks. The proposed method is based on the assumption that all spoofing signals are transmitted from a single point source. A spatial domain processing technique is proposed to extract the spoofing signal steering vector and consequently to discard the spoofing signals. This method is implemented before despreading and acquisition stage of a GNSS receiver. Hence, it does not impose a heavy computational load on the receiver operational process since it does not require any extensive search in the code and Doppler domains to separately despread individual authentic and spoofing signals. Moreover, the proposed method does not require any antenna array calibration process. This pre-despreading interference mitigation technique is further extended to maximize signal-to-noise ratio (SNR) of each individual authentic GNSS signal. Simulation results show that the proposed method effectively countermeasures spoofing attacks for a wide range of received spoofing power.