Matthew Trinkle

Reconfigurable Adaptive Array Beamforming by Antenna Selection

Traditional adaptive array beamforming with a fixed array configuration can lead to significant inefficiencies and performance loss under different scenarios. As antennas become smaller and cheaper relative to front-ends, it becomes important to devise a reconfigurable adaptive antenna array (RAAA) strategy to yield high signal to noise and interference ratio using fewer antennas. This is achieved by selecting K from N antennas to minimize the Spatial Correlation Coefficient (SCC) between the desired signal and the interference. The lower bound of optimum SCC is formulated with two relaxation methods to give information about the suitable number of selected antennas K. A Correlation Measurement (CM) method is proposed to select the optimum subarray with K antennas, thereby reducing complexity. We carry out performance analysis and show that a 1/K2-suboptimum solution can be guaranteed with arbitrary shaped arrays. Furthermore, a Difference of Convex Sets (DCS) method is proposed to select the optimum subarray with controlled quiescent pattern in order to reduce the effect of interference during the reconfiguration time. The utility of the proposed array reconfiguration for performance improvement without increasing the cost is demonstrated using both simulated and experimental data.

A Cross-Layer Defense Mechanism Against GPS Spoofing Attacks on PMUs in Smart Grids

Recent investigations have revealed the susceptibility of phasor measurement units (PMUs) to the time synchronization attack by spoofing its global positioning system (GPS). This paper proposes a cross-layer detection mechanism to fight against simultaneous attacks toward multiple PMUs. In the physical layer, we propose a GPS carrier-to-noise ratio (C/No) based spoofing detection technique. We apply the patch-monopole hybrid antenna to two GPS receivers and compute the difference between the standard deviation of each receivers C/No. The priori probability of spoofing is calculated from the distributions of the difference. A counter is embedded in the physical layer to identify the most suspicious PMU. In the upper layer, the spoofing attack is considered similarly to the bad data injection toward the power system. A trustworthiness evaluation, which is based on both the physical layer information and power grid measurements, is applied to identify the PMU being attacked. An experiment has been carried to validate the proposed algorithm.

Combating time synchronization attack: a cross layer defense mechanism

A novel time synchronization attack (TSA) on wide area monitoring systems in smart grid has been identified recently. A cross layer detection mechanism is proposed to combat TSA in this paper. In the physical layer, we propose a G PS carrier carrier to noise ratio (C/No) based spoofing detection technique. In addition, a patch-monopole hybrid antenna is applied to receive GPS signal. By computing the standard deviation of the C/No difference from two GPS receivers, the a priori probability of spoofing detection is fed to the upper layer, where power system state is estimated and controlled. A trustworthiness based evaluation method is applied to identify the PMU being under TSA. Both the physical layer and upper layer algorithms are integrated to detect the TSA, thus forming a cross layer mechanism. Experiment is carried out to verify the effectiveness of the proposed TSA detection algorithm.

Quickest detection of GPS spoofing attack

GPS is being increasingly used in critical infrastructures in modern society. Therefore, the reliability of GPS is extremely important. Recently, the vulnerability of GPS to a spoofing attack has been discussed in the literature. A malicious attacker may spoof a GPS receiver, causing it to provide incorrect navigation and timing information, which may lead to serious damage. Therefore, it is extremely important to detect spoofing attacks as quickly as possible. In this paper, we propose a quickest spoofing detection algorithm to combat GPS spoofing attacks. The experimental results demonstrate that the proposed algorithm can effectively detect the spoofing attack quickly after it occurs.

Automatic microphone array position calibration using an acoustic sounding source

This paper presents a sensor array position calibration algorithm for determining the positions of individual microphones in a linear array automatically from time-difference of arrival measurements obtained from a mobile sounding source. The algorithm uses a nonlinear least squares method to determine the interspacing of microphones that are located along a fixed axis of a linear array. This method provides a means of establishing the positions of microphones for the purposes of acoustic localization and other beamforming applications, without the need to measure these distances by manual means. Simulations and some live experiments illustrate the method.

GPS spoofing based time stamp attack on real time wide area monitoring in smart grid

Many operations in power grids, such as fault detection and event location estimation, depend on precise timing information. In this paper, a novel time stamp attack (TSA) is identified in smart grid. Since many applications in smart grid utilize synchronous measurements and most of the measurement devices are equipped with global positioning system (GPS) for precise timing, it is highly probable to attack the measurement system by spoofing the GPS. The effectiveness of TSA is demonstrated by time synchronized transmission line fault detection, as well as regional disturbing event location. To defend against TSA, we proposed a multi-antenna based quickest GPS spoofing detection algorithm. By exploiting the theory of quickest detection, we apply the probabilistic metric of the carrier signal to noise ratio from two receive antennas to conduct the quickest GPS spoofing detection. Experiment results demonstrate that the proposed defense scheme can effectively detect and prevent GPS spoofing attack.

DOA Estimation under Unknown Mutual Coupling and Multipath with Improved Effective Array Aperture

Subspace-based high-resolution direction of arrival (DOA) estimation significantly deteriorates under array manifold perturbation and rank deficiency of the covariance matrix due to mutual coupling and multipath propagation, respectively. In this correspondence, the unknown mutual coupling can be circumvented by the proposed method without any passive or active calibration process, and the DOA of the coherent signals can be accurately estimated accordingly. With a newly constructed matrix, the deficient rank can be restored, and the effective array aperture can be extended compared with conventional spatial smoothing. The proposed method achieves a good robustness and DOA estimation accuracy with unknown mutual coupling. The simulation results demonstrate the validity and efficiency of the proposed method.

Fast-time STAP Performance in pre and post Range Processing Adaption as applied to Multichannel SAR

Hot-clutter cancellation using fast-time space time adaptive processing (STAP) can occur either pre or post range processing (RP) and to date, there has not been a direct comparison on which method offers the best results. This paper provides an analytic comparison which is verified with simulation and aims to provide insight into the location of the adaptive filter which would provide the best hot-clutter suppression. The covariance models are tested with signal models used in a multichannel synthetic aperture radar (SAR).

GPS bistatic radar using phased-array technique for aircraft detection

A study has been made into using a 32-elements phased-array receiver to detect the echo of GPS signals from a moving target. This paper mainly proposes the methods that improve the performance of GPS bistatic radar with phased-array receiver and allow it to properly perform aircraft detection. Among these methods are antenna array phase error calibration, array gain optimization and interference signal cancellation technique. Also, the detection technique of using PRN codes that are directly acquired by phased-array receiver is also proposed in this paper to search for the correlation of GPS signals.

Dynamic range considerations for wideband Zero-IF receivers

This paper considers the suitability of the Zero-IF architecture for wideband receivers in modern radar and communication systems. The main performance measures are the overall system dynamic range including the effects of phase and amplitude I/Q imbalances. An adaptive I/Q channel mismatch calibration algorithm is used to reduce the I/Q mismatch, and the suitability of this calibration algorithm for wideband system has been tested. The results indicate that the dynamic range of more than 50dB is achievable in a 100MHz bandwidth system after I/Q mismatch calibration.