Guaranteeing Spoof-Resilient Multi-Robot Networks

Multi-robot networks use wireless communication to provide wide-ranging services such as aerial surveillance and unmanned delivery. However, effective coordination between multiple robots requires trust, making them particularly vulnerable to cyber-attacks. Specifically, such networks can be gravely disrupted by the Sybil attack, where even a single malicious robot can spoof a large number of fake clients. This paper proposes a new solution to defend against the Sybil attack, without requiring expensive cryptographic key-distribution. Our core contribution is a novel algorithm implemented on commercial Wi-Fi radios that can "sense" spoofers using the physics of wireless signals. We derive theoretical guarantees on how this algorithm bounds the impact of the Sybil Attack on a broad class of robotic coverage problems. We experimentally validate our claims using a team of AscTec quadrotor servers and iRobot Create ground clients, and demonstrate spoofer detection rates over 96%

Estimation and Minimization of the Cramer-Rao lower bound for radio direction-finding on the azimuth and elevation of planar antenna arrays

In this paper an approach of obtaining optimal planar antenna arrays consisting of omnidirectional sensors is proposed. The novelty of the proposed approach is to apply an exact expression of the Cramer-Rao lower bound for an arbitrary planar antenna array consisting of a number of omnidirectional elements which has been presented in the further chapters of the paper. The obtained formula describes the influence of antenna elements locations on the direction-of-arrival estimation accuracy. It has been shown that the direction-of-arrival accuracy via planar antenna arrays is determined as the sum of squares of differences between all omnidirectional elements coordinates along x- and y-axis. Thus knowing an expected area or sector of signal source it is very easy to calculate optimal arrangement of antenna elements in order to reduce direction-finding errors, because obtained by that way positions gives the best match according to the maximum likelihood criterion. It is worth nothing that such antenna arrays are useful in the way that they allow estimating the coordinates of radio emission sources in the three-dimensional coordinate space, i.e. in azimuth and elevation. In order to confirm the proposed methodology optimal antenna arrays constructed after minimization of the new formulas are researched. It is found out that the new shapes of antenna arrays based on the analytical expressions have better direction-of-arrival accuracy in comparison with the circular ones

GNSS multiantenna receivers under multiantenna spoofing attacks

The spoofing attack on the GNSS signal began to be investigated in the early 2000s. During the last decade, different attacks have been proposed, but no one to the best of the author's knowledge considered the possibility that the attacker could have a multiantenna system to perform a spoofing attack. This thesis shows a possible attack where one could spoof the GNSS signal, deceiving the receiver about the direction of arrival of the signal

WSR: A WiFi Sensor for Collaborative Robotics

In this paper we derive a new capability for robots to measure relative direction, or Angle-of-Arrival (AOA), to other robots operating in non-line-of-sight and unmapped environments with occlusions, without requiring external infrastructure. We do so by capturing all of the paths that a WiFi signal traverses as it travels from a transmitting to a receiving robot, which we term an AOA profile. The key intuition is to "emulate antenna arrays in the air" as the robots move in 3D space, a method akin to Synthetic Aperture Radar (SAR). The main contributions include development of i) a framework to accommodate arbitrary 3D trajectories, as well as continuous mobility all robots, while computing AOA profiles and ii) an accompanying analysis that provides a lower bound on variance of AOA estimation as a function of robot trajectory geometry based on the Cramer Rao Bound. This is a critical distinction with previous work on SAR that restricts robot mobility to prescribed motion patterns, does not generalize to 3D space, and/or requires transmitting robots to be static during data acquisition periods. Our method results in more accurate AOA profiles and thus better AOA estimation, and formally characterizes this observation as the informativeness of the trajectory; a computable quantity for which we derive a closed form. All theoretical developments are substantiated by extensive simulation and hardware experiments. We also show that our formulation can be used with an off-the-shelf trajectory estimation sensor. Finally, we demonstrate the performance of our system on a multi-robot dynamic rendezvous task.Comment: 28 pages, 25 figures, *co-primary author

Antenna array geometries and algorithms for direction of arrival estimation

Direction of arrival (DOA) estimation with the antenna array was a forever topic of scientist. In this dissertation, a detailed comparison of the direction of arrival (DOA) estimation algorithms, including three classic algorithms as MUSIC, Root-MUSIC and ESPRIT, was performed and an analysis of various array geometries’ (configurations) properties in DOA estimation was demonstrated. Cramer-Rao Bound (CRB) was used for theoretic analysis and Root Mean Square Error (RMSE), which determined the best performance for a given geometry, regardless the specific estimation algorithm used, was implemented in simulation comparison. In the first part, MUSIC, Root-MUSIC and ESPRIT were illustrated, where theoretic underlying of the algorithms were expressed by revisited, paseudo code algorithms, and compared in the aspects of accuracy and computational efficiency. Consequently, ESPRIT was found more efficient than the other two algorithms in computation. However, the accuracy of MUSIC was better than ESPRIT. In the second part, four particular array geometries, including Uniform Circular Array (UCA), L Shaped Array (LSA), Double L Shaped Array (DLSA) and Double Uniform Circular Array (DUCA), were analyzed in the area of directivity, accuracy and resolving ability. A simulation comparison of DOA estimation with these four array geometries by MUSIC algorithm in two dimensions was made then, since MUSIC had the best accuracy in these three algorithms. According to the analysis and comparison, it was found that L Shaped Array (LSA) and Double L Shaped Array (DLSA) were more accurate than others, considering both azimuth and elevation estimation. Also, in the case of two dimensional DOA estimation, the Double L Shaped Array (DLSA) was shown a theoretically relative isotropy to other array geometries. From the simulation, the detection ability of Double L Shaped Array (DLSA) was proved the best in the array geometries discussed in this dissertation. These findings had significant implications for the further study of the array geometry in DOA estimation

Antenna array geometries and algorithms for direction of arrival estimation

Direction of arrival (DOA) estimation with the antenna array was a forever topic of scientist. In this dissertation, a detailed comparison of the direction of arrival (DOA) estimation algorithms, including three classic algorithms as MUSIC, Root-MUSIC and ESPRIT, was performed and an analysis of various array geometries’ (configurations) properties in DOA estimation was demonstrated. Cramer-Rao Bound (CRB) was used for theoretic analysis and Root Mean Square Error (RMSE), which determined the best performance for a given geometry, regardless the specific estimation algorithm used, was implemented in simulation comparison. In the first part, MUSIC, Root-MUSIC and ESPRIT were illustrated, where theoretic underlying of the algorithms were expressed by revisited, paseudo code algorithms, and compared in the aspects of accuracy and computational efficiency. Consequently, ESPRIT was found more efficient than the other two algorithms in computation. However, the accuracy of MUSIC was better than ESPRIT. In the second part, four particular array geometries, including Uniform Circular Array (UCA), L Shaped Array (LSA), Double L Shaped Array (DLSA) and Double Uniform Circular Array (DUCA), were analyzed in the area of directivity, accuracy and resolving ability. A simulation comparison of DOA estimation with these four array geometries by MUSIC algorithm in two dimensions was made then, since MUSIC had the best accuracy in these three algorithms. According to the analysis and comparison, it was found that L Shaped Array (LSA) and Double L Shaped Array (DLSA) were more accurate than others, considering both azimuth and elevation estimation. Also, in the case of two dimensional DOA estimation, the Double L Shaped Array (DLSA) was shown a theoretically relative isotropy to other array geometries. From the simulation, the detection ability of Double L Shaped Array (DLSA) was proved the best in the array geometries discussed in this dissertation. These findings had significant implications for the further study of the array geometry in DOA estimation

Planar array design and analysis on direction of arrival estimation for mobile communication systems

The demand of wireless communication has increased significantly in the past few decades due to huge demand to deliver multimedia content instantly. The expansion of mobile content paired with affordable mobile devices has opened a new trend for having access to the latest information on mobile devices. This trend is made possible by the technology of smart antenna systems as well as array signal processing algorithms. Array signal processing is not limited to wireless communication, but also found in other applications such as radar, sonar and automotive. One of the important components in array signal processing is its ability to estimate the direction of incoming signals known as directional-of-arrival (DOA). The performance of DOA algorithms depends on the steering vector since it contains information about the direction of incoming signals. One of the main factors to affect the DOA estimation is the array geometries since the array factor of the array geometries determines the definition of the steering vector. Another issue in DOA estimation is that the DOA algorithms are designed based on the ideal assumption that the antenna arrays are free from imperfection conditions. In practice, ideal conditions are extremely difficult to obtain and thus the imperfect conditions will severely degraded the performance of DOA estimation. The imperfect conditions include the presence of mutual coupling between elements and are also characteristic of directional antenna. There are three topics being discussed in this thesis. The first topic being investigated is new geometry of antenna array to improve the performance of DOA estimation. Two variants of the circular-based array are proposed in this thesis: semi-circular array and oval array. Another proposed array is Y-bend array, which is a variant of V-shape array. The proposed arrays are being put forward to offer a better performance of DOA estimation and have less acquired area compared with the circular array. It is found out that the semi-circular array has 5.7% better estimation resolution, 76% lower estimation error, and 20% higher estimation consistency than the circular array. The oval array improves the estimation resolution by 33%, estimation error by 60%, and estimation consistency by 20% compared with the circular array. In addition, for the same number of elements, the oval array requires 12.5% to 15% less area than the circular array. The third proposed array, Y-bend array, has 23% smaller estimation resolution, 88% lower estimation error, and 7% higher estimation consistency than the V-shape array. Among the proposed arrays, the semi-circular possessed the best performance with 25% smaller estimation resolution, ten times smaller estimation error, and 5% higher estimation consistency over the other proposed arrays. Secondly, this thesis investigates the DOA estimation algorithm when using the directional antenna array. In this case, a new algorithm is proposed in order to suit the characteristics of the directional antenna array. The proposed algorithm is a modified version of the Capon algorithm, one of the algorithms in beamforming category. In elevation angle estimation, the proposed algorithm achieves estimation resolution up to 1°. The proposed algorithm also manages to improve the estimation error by 80% and estimation consistency by 10% compared with the Capon algorithm. In azimuth angle estimation, the proposed algorithm achieves 20 times lower estimation error and 20% higher estimation consistency than the Capon algorithm. These simulation results show that the proposed algorithm works effectively with the directional antenna array. Finally, the thesis proposes a new method in DOA estimation process for directional antenna array. The proposed method is achieved by means of modifying covariance matrix calculation. Simulation results suggest that the proposed method improves the estimation resolution by 5° and the estimation error by 10% compared with the conventional method. In summary, this thesis has contributed in three main topics related to DOA estimation; array geometry design, algorithm for the directional antenna array, and method in DOA estimation process for the directional antenna array

Applications of Continuous Spatial Models in Multiple Antenna Signal Processing

This thesis covers the investigation and application of continuous spatial models for multiple antenna signal processing. The use of antenna arrays for advanced sensing and communications systems has been facilitated by the rapid increase in the capabilities of digital signal processing systems. The wireless communications channel will vary across space as different signal paths from the same source combine and interfere. This creates a level of spatial diversity that can be exploited to improve the robustness and overall capacity of the wireless channel. Conventional approaches to using spatial diversity have centered on smart, adaptive antennas and spatial beam forming. Recently, the more general theory of multiple input, multiple output (MIMO) systems has been developed to utilise the independent spatial communication modes offered in a scattering environment. ¶ ..