Array signal processing robust to pointing errors

The objective of this thesis is to design computationally efficient DOA (direction-of- arrival) estimation algorithms and beamformers robust to pointing errors, by harnessing the antenna geometrical information and received signals. Initially, two fast root-MUSIC-type DOA estimation algorithms are developed, which can be applied in arbitrary arrays. Instead of computing all roots, the first proposed iterative algorithm calculates the wanted roots only. The second IDFT-based method obtains the DOAs by scanning a few circles in parallel and thus the rooting is avoided. Both proposed algorithms, with less computational burden, have the asymptotically similar performance to the extended root-MUSIC. The second main contribution in this thesis is concerned with the matched direction beamformer (MDB), without using the interference subspace. The manifold vector of the desired signal is modeled as a vector lying in a known linear subspace, but the associated linear combination vector is otherwise unknown due to pointing errors. This vector can be found by computing the principal eigen-vector of a certain rank-one matrix. Then a MDB is constructed which is robust to both pointing errors and overestimation of the signal subspace dimension. Finally, an interference cancellation beamformer robust to pointing errors is considered. By means of vector space projections, much of the pointing error can be eliminated. A one-step power estimation is derived by using the theory of covariance fitting. Then an estimate-and-subtract interference canceller beamformer is proposed, in which the power inversion problem is avoided and the interferences can be cancelled completely

Advanced array processing techniques and systems

Research and development on smart antennas, which are recognized as a promising technique to improve the performance of mobile communications, have been extensive in the recent years. Smart antennas combine multiple antenna elements with a signal processing capability in both space and time to optimize its radiation and reception pattern automatically in response to the signal environment. This paper concentrates on the signal processing aspects of smart antenna systems. Smart antennas are often classified as either switched-beam or adaptive-array systems, for which a variety of algorithms have been developed to enhance the signal of interest and reject the interference. The antenna systems need to differentiate the desired signal from the interference, and normally requires either a priori knowledge or the signal direction to achieve its goal. There exists a variety of methods for direction of arrival (DOA) estimation with conflicting demands of accuracy and computation. Similarly, there are many algorithms to compute array weights to direct the maximum radiation of the array pattern toward the signal and place nulls toward the interference, each with its convergence property and computational complexity. This paper discusses some of the typical algorithms for DOA estimation and beamforming. The concept and details of each algorithm are provided. Smart antennas can significantly help in improving the performance of communication systems by increasing channel capacity and spectrum efficiency, extending range coverage, multiplexing channels with spatial division multiple access (SDMA), and compensating electronically for aperture distortion. They also reduce delay spread, multipath fading, co-channel interference, system complexity, bit error rates, and outage probability. In addition, smart antennas can locate mobile units or assist the location determination through DOA and range estimation. This capability can support and benefit many location-based services including emergency assistance, tracking services, safety services, billing services, and information services such as navigation, weather, traffic, and directory assistance

Experimental evaluation of synchronization errors on the performance of smart antenna algorithms for CDMA

The CDMA and smart antennas are two promising approaches to increase system capacity and spectrum efficiency for mobile communication services. In a CDMA system, frequency offset between local oscillator and the carrier of impinging signal, timing offset between local generated PN sequence and received PN sequence, imperfect power control may exist and this degrades the performance of the smartantenna algorithms. In this thesis, the effects of frequency and timing offsets on smart antenna performance is presented. A smart antenna system has been set up to implement blind adaptive algorithms for W-CDMA in a laboratory environment. The blind adaptive algorithms implemented on the smart antenna system are Least- Squares Despread-Respread Multi Target Array (LS-DRMTA) and Least- Squares Despread-Respread Multi Target Constant Modulus Algorithm (LSDRMTCMA). Since both LS-DRMTA and LS-DRMTCMA algorithms utilize users PN sequence, they have several advantages compared to other blind adaptive algorithms for CDMA. BER and beamforming performances of LS-DRMTA and LSDRMTCMA algorithms in a two-user and two- element-antenna array system is evaluated for systems with timing offset and frequency offset. Experimental results show that frequency and timing offset degrades the performance, however they still give reasonable BER. In all test conditions LS-DRMTA and LS-DRMTCMA outperforms conventional receiver, moreover LS - DRMTCMA can generate deeper nulls and outperforms LS-DRMTA

Rake, Peel, Sketch:The Signal Processing Pipeline Revisited

The prototypical signal processing pipeline can be divided into four blocks. Representation of the signal in a basis suitable for processing. Enhancement of the meaningful part of the signal and noise reduction. Estimation of important statistical properties of the signal. Adaptive processing to track and adapt to changes in the signal statistics. This thesis revisits each of these blocks and proposes new algorithms, borrowing ideas from information theory, theoretical computer science, or communications. First, we revisit the Walsh-Hadamard transform (WHT) for the case of a signal sparse in the transformed domain, namely that has only K †N non-zero coefficients. We show that an efficient algorithm exists that can compute these coefficients in O(K log2(K) log2(N/K)) and using only O(K log2(N/K)) samples. This algorithm relies on a fast hashing procedure that computes small linear combinations of transformed domain coefficients. A bipartite graph is formed with linear combinations on one side, and non-zero coefficients on the other. A peeling decoder is then used to recover the non-zero coefficients one by one. A detailed analysis of the algorithm based on error correcting codes over the binary erasure channel is given. The second chapter is about beamforming. Inspired by the rake receiver from wireless communications, we recognize that echoes in a room are an important source of extra signal diversity. We extend several classic beamforming algorithms to take advantage of echoes and also propose new optimal formulations. We explore formulations both in time and frequency domains. We show theoretically and in numerical simulations that the signal-to-interference-and-noise ratio increases proportionally to the number of echoes used. Finally, beyond objective measures, we show that echoes also directly improve speech intelligibility as measured by the perceptual evaluation of speech quality (PESQ) metric. Next, we attack the problem of direction of arrival of acoustic sources, to which we apply a robust finite rate of innovation reconstruction framework. FRIDA â the resulting algorithm â exploits wideband information coherently, works at very low signal-to-noise ratio, and can resolve very close sources. The algorithm can use either raw microphone signals or their cross- correlations. While the former lets us work with correlated sources, the latter creates a quadratic number of measurements that allows to locate many sources with few microphones. Thorough experiments on simulated and recorded data shows that FRIDA compares favorably with the state-of-the-art. We continue by revisiting the classic recursive least squares (RLS) adaptive filter with ideas borrowed from recent results on sketching least squares problems. The exact update of RLS is replaced by a few steps of conjugate gradient descent. We propose then two different precondi- tioners, obtained by sketching the data, to accelerate the convergence of the gradient descent. Experiments on artificial as well as natural signals show that the proposed algorithm has a performance very close to that of RLS at a lower computational burden. The fifth and final chapter is dedicated to the software and hardware tools developed for this thesis. We describe the pyroomacoustics Python package that contains routines for the evaluation of audio processing algorithms and reference implementations of popular algorithms. We then give an overview of the microphone arrays developed

Design and Implementation of System Components for Radio Frequency Based Asset Tracking Devices to Enhance Location Based Services. Study of angle of arrival techniques, effects of mutual coupling, design of an angle of arrival algorithm, design of a novel miniature reconfigurable antenna optimised for wireless communication systems

The angle of arrival estimation of multiple sources plays a vital role in the field of array signal processing as MIMO systems can be employed at both the transmitter and the receiver end and the system capacity, reliability and throughput can be significantly increased by using array signal processing. Almost all applications require accurate direction of arrival (DOA) estimation to localize the sources of the signals. Another important parameter of localization systems is the array geometry and sensor design which can be application specific and is used to estimate the DOA. In this work, various array geometries and arrival estimation algorithms are studied and then a new scheme for multiple source estimation is proposed and evaluated based on the performance of subspace and non-subspace decomposition methods. The proposed scheme has shown to outperform the conventional Multiple Signal Classification (MUSIC) estimation and Bartlett estimation techniques. The new scheme has a better performance advantage at low and high signal to noise ratio values (SNRs). The research work also studies different array geometries for both single and multiple incident sources and proposes a geometry which is cost effective and efficient for 3, 4, and 5 antenna array elements. This research also considers the shape of the ground plane and its effects on the angle of arrival estimation and in addition it shows how the mutual couplings between the elements effect the overall estimation and how this error can be minimised by using a decoupling matrix. At the end, a novel miniaturised multi element reconfigurable antenna to represent the receiver base station is designed and tested. The antenna radiation patterns in the azimuth angle are almost omni-directional with linear polarisation. The antenna geometry is uniplanar printed logspiral with striplines feeding network and biased components to improve the impedance bandwidth. The antenna provides the benefit of small size, and re-configurability and is very well suited for the asset tracking applications

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

Spatiotemporal arrayed MIMO radar

In the last decade, Multiple Input Multiple Output (MIMO) radar has emerged as a leading candidate for stimulating major new advancement in radar theory. A fundamental challenge in MIMO radar is to identify a theoretical framework within which the radar system may be represented and analysed. In the relatively well-established field of Single Input Multiple Output (SIMO) array signal processing, this task has already been achieved using the array manifold (which is a geometric object that completely characterises the array system). A central objective of this thesis is therefore to bridge the gap between SIMO and MIMO by developing a manifold representation of the MIMO radar system. A new differential geometric framework, based on the complex Cartan matrix, is exploited in this thesis for characterising array manifold curves. New formulas are presented for recursively calculating the strictly orthonormal moving frame, U(s), and corresponding complex Cartan Matrix, C(s), for arbitrary array geometries. The circular approximation of the array manifold is derived under this new framework and compact closed-form expressions are provided for the popular uniform linear array geometry. Based on a number of approximations derived using the circular approximation of the array manifold, the performance capabilites of various popular detection and parameter estimation algorithms are investigated. The figure of merit "C" is then used to place these capabilities into the context of the theoretically ideal algorithm. The concept of a virtual SIMO array system is used as a basis for characterising the full MIMO radar configuration using a single equivalent response vector. By tracing out this response vector across the whole parameter space, a manifold is formed that fully characterises the MIMO radar system. In the important case of orthogonal transmit waveforms, the fundamental performance bounds of the MIMO radar system are studied. A space-time receiver architecture is proposed which exploits the virtual SIMO structure as part of a subspace-based joint Doppler, delay and direction of arrival (DOA) estimation framework. Due to the great computational burden of an exhaustive 3-parameter search, the joint Doppler-delay-DOA estimation is partitioned into an equivalent two-stage algorithm. The proposed approach is evaluated via computer simulation studies and shown to outperform existing methods.Open Acces

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion