In this paper, a MEMS microphone array system scheme is proposed which implements real-time direction of arrival (DOA) estimation for moving vehicles. Wind noise is the primary source of unwanted noise on microphones outdoors. A multiple signal classification (MUSIC) algorithm is used in this paper for direction finding associated with spatial coherence to discriminate between the wind noise and the acoustic signals of a vehicle. The method is implemented in a SHARC DSP processor and the real-time estimated DOA is uploaded through Bluetooth or a UART module. Experimental results in different places show the validity of the system and the deviation is no bigger than 6° in the presence of wind noise.
In this paper, an algorithm of direction finding is proposed in the presence of unknown mutual coupling. The preliminary direction of arrival (DOA) is estimated using the whole array for high resolution. Further refinement can then be conducted by estimating the angularly dependent coefficients (ADCs) with the subspace theory. The mutual coupling coefficients are finally determined by solving the least squares problem with all of the ADCs utilized without discarding any. Simulation results show that the proposed method can achieve better performance at a low signal-to-noise ratio (SNR) with a small-sized array and is more robust, compared with the similar processes employing the initial DOA estimation and further improvement iteratively.
Direction finding systems based on amplitude-comparison algorithms are commonly used today due to their simplicity and robustness. In order to protect the physical structure from lightning strikes, proper lightning protection must be applied. In many cases, due to the complexity of such a system, an internal lightning rod is not feasible. Placed externally, the metal rod influences the antenna patterns and ultimately deteriorates the detection quality of the whole system. In this paper, an analytical model is developed based on the Mie scattering of a perfect conducting cylinder to estimate an affected antenna pattern. Measurements confirm the validity of the analytical model. The impact on the overall bearing error is evaluated for different configurations of the system, and explain the significant errors for practical settings.; http://www.emcsa2011perth.org/home-emcsa2011/home.html; Thomas Kaufmann, Olivier Progin, Christophe Fumeaux
This thesis considers the problem of angle-of-arrival (AOA) estimation in the context of its application to electronic surveillance systems. Due to the operational requirements of such systems, the AOA estimation algorithm must be computationally fast, accurate and will need to be implemented using sparse, large aperture arrays. Interferometry is proposed as a suitable algorithm that meets the operational requirements of electronic surveillance systems. However, for sparse array geometries, phase wrapping effects introduce ambiguities to the phase measurements and so unambiguous AOA estimation requires the use of computationally intensive ambiguity resolution algorithms using three or more antennas. Beamforming and array processing techniques are another class of AOA estimation algorithms that can unambiguously estimate the AOA using sparse, large aperture arrays. While these techniques generally offer better AOA estimation performance than interferometric techniques, they are also comparatively more computationally intensive algorithms. Furthermore, by virtue of using very sparse arrays, high sidelobes in the array beampattern may cause incorrect AOA estimation. This thesis will introduce the concept of using second-order difference array (SODA) geometries which allow unambiguous AOA estimation to be performed in a computationally effcient manner. In the context of interferometry...
A digital implementation of a phase sampling interferometer antenna system based on the Robust Symmetrical Number System (RSNS) is built using commercial-off-the-shelf (COTS) items. The RSNS-based direction finding (DF) system uses short baselines to achieve a high resolution DF capability in a physically compact system for use as stand-in sensors on unmanned aerial vehicles. The RSNS inherent integer Gray code property minimizes the possible encoding errors and adds a robustness to the accuracy of the estimated Angle of Arrival (AOA). A digital architecture using quadrature demodulators and real-time controllers provide grreater flexibility for signal processing and allows for the implementation of a new virtual spacing algorithm. The virtual spacing concept changes the RSNS moduli values to implement a virtual antenna spacing without having to physically change the antenna element spacing. This enables higher resolution DF in circumstances where the Signal-to-Noise Ratio is high enough to provide error free coding of the AOA. Two four element, digital 3-channel interferometer prototype systems were constructed and tested in the NPS anechoic chamber. The first antenna array is designed using pairwise relatively prime (PRP) moduli. When an extension of the virtual spacing concept for application to N-channel systems was successfully resolved...
A new interferometer direction finding array architecture based on the optimum symmetrical number system (OSNS) is presented. OSNS arrays are capable of unambiguous high-resolution direction finding with as few as three elements, with multiple baseline options. The OSNS DF antenna architecture being investigated uses the OSNS to decompose the analog spatial filtering operation into a number of parallel sub-operations (moduli) that are of smaller complexity. One two-element interferometer is used for each sub-operation and only requires a precision in accordance with its modulus. A much higher spatial resolution is achieved after the sub-operations are recombined. By incorporating the OSNS concept, the dynamic range of a specific configuration of antenna element spacings and comparator arrangements can be analyzed exactly. In this thesis, the OSNS DF antenna concept was demonstrated experimentally, by designing, fabricating and measuring the performance of a three-element array at 8.5 GHz. These three elements are grouped into two pairs (channels) according to the set of relatively prime moduli (m1 = 6, m2 = 11). A mixer is used to determine the phase difference between each pair of elements. The output voltage from the mixer in each channel is a symmetrical folding waveform that is DC biased and amplified using a summing amplifier. The output voltage of the amplifier is amplitude analyzed using a small comparator ladder. An EEPROM is used to recombine the results of these low precision channels to yield the high resolution direction of arrival (DOA). Simulated and experimental results are presented and compared
To reduce the number of phase sampling comparators in a direction finding (DF) interferometer antenna, a new array based on a robust symmetrical number system (RSNS) is described. The RSNS is used to decompose the spatial filtering operation into a number of parallel sub-operations that are of smaller computational complexity. Each sub-operation (interferometer) symmetrically folds the phase with folding period equal to 2Nm(i) where N is the number of channels that are used and n(i) the channel modulus. A small comparator ladder mid-level quantizes each folded phase response. Each sub-operation only requires a precision in accordance with that modulus. A much higher DF resolution is achieved after the N different RSNS moduli are used and the results of these low precision sub-operations are recombined. The parallel use of phase waveforms increases the antenna resolution without increasing the folding rate of the system. The new antenna is constructed and tested in an anechoic chamber, and the results are compared with the experimental results of a previously tested optimum symmetrical number system (OSNS) array. Although the dynamic range of the RSNS is somewhat less than the OSNS, the inherent Gray code properties make it attractive for error control in phase sampling interferometry.
A new radio direction-finding (DF) technique which applies matched-filter theory to the DF problem is presented. The new technique, called Matched-Filter Doppler Direction Finding (MFD DF) is based on the doppler DF principle in which a rotating antenna, or its equivalent, superimposes periodic frequency modulation on the received carrier. The phase of the induced modulation contains information on the angle of arrival. It is shown that a bandpass filtering operation, which satisfies the phase-matching requirement of a matched filter, converts the frequency-modulated signal to an amplitude-modulated signal whose envelope is a periodic narrow pulse with no sidelobes. The relative time of occurrence of the pulse is a measure of angle of arrival. Included is the description of and results obtained with an experimental system used to confirm the analytical results, to study the effects of noise, and to explore alternatives available in the design of an operating system. Encouraging results were obtained using this same experimental system with a conventional operating doppler DF set. (Author)
Approved for public release; distribution is unlimited.; This thesis suggests a method to estimate the current value of an ionospheric parameter. The proposed method is based on the known variability of the observed current values near path and utilizes data derived from ionospheric sampling measurements. Analysis of errors is provided in Single-Site-Location High-Frequency Direction Finding (SSL-HFDF), arising from ionospheric irregularities such as Es (sporadic E), ionospheric tilts, and traveling ionospheric disturbances (TIDs). The characteristics of Es, tilts and TIDs for mid-latitudes are summarized in tables. The spatial and temporal coherence of ionospheric variabilities and irregularities is analyzed over the electron density. Practical results, measurements, and studies are presented on SSL-HFDF. A survey of characteristics of the ionosphere in the equatorial region is also provided. Finally, some recommendations are given to maximize the applicability of the proposed method.
Several parallel-channel receiver configurations are presented and analyzed. From this background a particular direction-finding system suitable for shipboard use is detailed. Use of three modes of operation of the defined system is shown to provide through 360° coarse and find indications of the bearings of each of several stations transmitting simultaneously. It is also shown that this system will provide measures of amplitude and, with some added circuitry, frequency of each of these received signals. It is shown that the gain characteristics of the antennas for each mode of operation are chosen in a manner which makes the parallel-channel receiving system immune to signals reflected from the ship and its rigging . Two different methods of obtaining independent measures of signal frequency and bearing are presented. A brief history of direction finding and an extensive bibliography are provided.
The performance of two novel interferometer antenna architectures for high resolution, wideband direction finding are investigated. The first configuration incorporates a Symmetrical Number System (SNS) encoding of the interferometer amplitude response (symmetrical folding waveform). The second configuration incorporates a Residue Number System (RNS) encoding of the interferometer phase response (saw tooth waveform). The residue architectures serve as a source for resolution enhancement in an interferometer array by decomposing the analog spatial filtering operation into a number of parallel sub-operations (moduli) that are of smaller computational complexity. Each sub- operation only requires a precision in accordance with the size of the modulus. A much higher resolution is achieved after the N moduli are used and the results of these low precision sub-operations are recombined. A four-element, 3 channel array using the moduli set m1 = 3, m2 = 4 and m3 = 5 was constructed in a ground plane using rectangular waveguide elements with a center frequency of 8.5 GHz. Experimental results are compared with the simulation results to demonstrate the advantages of this approach. The frequency response of the RNS array is investigated numerically. To correct the quantization errors due to any frequency offset...
Approved for public release; distribution is unlimited; Several advances are made toward a microelectromechanical (MEMS) acoustic direction-finding sensor based on the Ormia ochracea fly’s ear. First, linear elastic stiffness models are presented and then validated by using a nanoindenter to measure the sensor’s stiffness directly. The measured stiffness is highly linear, and the resonant frequencies are correctly predicted by the models presented. Additional nanoindenter results suggest that the sensor can be exposed to at least 162 decibel sound pressure level with no loss of function. Next, an improved capacitive readout system using branched comb fingers is presented. This design is shown to double electrical sensitivity to motion. Finally, it is shown that residual stress-induced curvature in the sensors greatly reduces their sensitivity by effectively shrinking the readout capacitors. A simple model of this curvature is presented and then verified by measurements. This model offers an extremely straightforward means of predicting curvature in similarly fabricated structures. It is also shown that perforations in the sensor’s structure have no effect on curvature. The results presented here provide several essential tools for the continued development of the MEMS acoustic direction-finding sensor.
Approved for public release; distribution is unlimited; Includes supplementary materials.; The collection of signals intelligence via passive direction finding and geolocation of radio frequency signals is of great concern to the military for its contribution to the development of battlespace awareness. Basic subspace direction finding techniques provide a method of determining the direction-of-arrival (DOA) of multiple signals on an array of receivers, but they have an inherent limitation in that they are narrowband by design. The impact of various signal frequencies, bandwidths, and signal to noise ratios present in the source signals received by a sparse array using the multiple signals classification (MUSIC) subspace direction-finding algorithm are evaluated in this thesis. Additionally, two performance enhancements are presented: one that reduces the MUSIC computational load and one that provides a method of utilizing collector motion to resolve DOA ambiguities.
Approved for public release, distribution is unlimited; The objective of this thesis is to investigate and evaluate the effectiveness of modern estimation methods with different array geometries as they apply to the problem of bearing estimation. The algorithms were selected from those that apply to multidimensional direction finding, and include MUSIC, PHD, minimum norm, and Capon's beam-former. These four techniques based on their high resolution capability, and their ability to deal with three-dimensional non-uniform arrays and to estimate both azimuth and elevation angle of arrival (AQA). Computer simulations were run linear arrays, circular array, and combinations of the two. The test conditions included: (1) two closely spaced emitters, and (2) various levels of additive white Gaussian noise.; http://www.archive.org/details/comparisonofsupe00link; Civilian, Chung-Shan Institute of Science and Technology
Approved for public release; distribution is unlimited.; An important resource for Signal Intelligence activity in High Frequency Direction Finding (HFDF) is the use of Single Site Location (SSL) systems. Present research and development is aimed at developing tactical, mobile, easy to deploy SSL systems for locating hostile HF transmitters. These systems can detect, determine azimuth and elevation angles of incoming signals, and using ionospheric height information can calculate emitter location. The success or failure of SSL systems is dependent on many different factors, some of which are associated with site effects. System operation over different ground parameters can affect the accuracy of locating emitters. In this thesis, the performance of an 'X' shaped interferometer HF SSL system is examined using the Numerical Electromagnetics Code (NEC). Performance in the presence of two different types of lossy ground conditions are investigated. .; Lieutenant, Hellenic Navy
Approved for public release; distribution is unlimited.; Approved for public release; distribution is unlimited.; This applied research project has designed, simulated, constructed and tested the performance of a processing system for a prototype direction finding antenna. A mixed signal architecture to derive the direction of arrival from a Robust Symmetrical Number System (RSNS) encoded direction finding array is based on a new phase sampling interferometer approach that can be easily incorporated into established techniques to provide a high resolution, small-baseline array with few number of phase sampling comparators. The approach is based on preprocessing the received signal using the RSNS. The preprocessing is used to decompose the spatial filtering operation into a number of parallel suboperations (moduli) that are of smaller computational complexity. A much higher direction finding spatial resolution is achieved after the N different moduli are used and the results of the low precision suboperations are recombined, in addition to the reduction of the number of possible encoding errors due to the RSNS' inherent Gray-coding properties. This has resulted in a four inch antenna array being able to attain an angular resolution of less than 1.8 degrees with a continuous field of view of 120 degrees. The accompanying electronics occupy two 6 inch by 8 inch printed circuit boards...
Triaxial seismic direction finding can be performed by eigenanalysis of the complex coherency matrix (or cross power matrix). By splitting the symmetric Hermitian coherency matrix C to D + E (where det(E) = 0 and D is diagonal), we shift unpolarized (or inter-channel uncorrelated) data into D and then E becomes 'random noise free'. Without placing any restrictions on the signal set—P, S, Rayleigh—matrix E has only one non-zero eigenvalue (at least for the case of a single mode arriving from a single direction). But for real data (polychromatic transients with correlated noise), it will have two non-zero eigenvalues. By rotating one axis of the triaxial geophone recorded signals to lie normal to the principal eigenvector, it is possible to reduce the coherency matrix from a 3 × 3 to a 2 × 2 matrix. For the case of a perfectly polarized monochromatic signal, we interpret this to mean that the particle trajectory can only be elliptical. It seems as though particles can only move in a plane: they cannot move in three dimensions. In practice, the signal is made up of a band of frequencies, there are multiple arrivals in the time window of interest, and noise is invariably present, which causes the ellipse to wobble in a 3D orbit. Explicit analytical expressions are derived in this paper to yield the eigenvalues and eigenvectors of the coherency matrix in terms of the triaxial signal amplitudes and phases.; S Greenhalgh...
A new ESPRIT-based algorithm is proposed to estimate the direction-of-arrival
of an arbitrary degree polynomial-phase signal with a single acoustic vector
sensor. The proposed approach requires neither a priori knowledge of the
polynomial-phase signal's coefficients nor a priori knowledge of the
polynomial-phase signal's frequency-spectrum. A pre-processing technique is
also proposed to incorporate the single-forgetting-factor algorithm and
multiple-forgetting-factor adaptive tracking algorithm to track a
polynomial-phase signal using one acoustic vector sensor. Simulation results
verify the efficacy of the proposed direction finding and source tracking
We propose and implement a novel indoor localization scheme, Swadloon, built
upon an accurate acoustic direction finding. Swadloon leverages sensors of the
smartphone without the requirement of any specialized devices. The scheme
Swadloon does not rely on any fingerprints and is very easy to use: a user only
needs to shake the phone for a short duration before walking and localization.
Our Swadloon design exploits a key observation: the relative shift and velocity
of the phone-shaking movement corresponds to the subtle phase and frequency
shift of the Doppler effects experienced in the received acoustic signal by the
phone. A novel method is designed to derive the direction from the phone to the
acoustic source by combining the velocity calculated from the subtle Doppler
shift with the one from the inertial sensors of the phone. Then a real-time
precise localization and tracking is enabled by using a few anchor speakers
with known locations. Major challenges in implementing Swadloon are to measure
the frequency shift precisely and to estimate the shaking velocity accurately
when the speed of phone-shaking is low and changes arbitrarily. We propose
rigorous methods to address these challenges, then design and deploy Swadloon
in several floors of an indoor building each with area about 2000m^2. Our
extensive experiments show that the mean error of direction finding is around
2.1 degree when the acoustic source is within the range of 32m. For indoor