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  • Parkvall, Stefan, et al. (författare)
  • Sensitivity Analysis of Linear DS-CDMA Detectors to Propagation Delay Estimation Errors
  • 1995
  • Ingår i: Proceedings IEEE Global Telecommunications Conference. ; s. 1872-1876
  • Konferensbidrag (refereegranskat)abstract
    • An asynchronous direct-sequence code division multiple access (DS-CDMA) communication system operating over an additive white Gaussian noise (AWGN) channel is considered. In many applications, the near-far problem can be the limiting factor. Several near-far resistant receivers have therefore been proposed (e.g., the decorrelating receiver). These receivers assume perfect knowledge of the propagation delay from all users to the receiver. In practice, the delays are estimated and therefore subject to estimation errors. The performance penalty these errors impose on linear detectors, especially the decorrelating detector, is evaluated
  • Ström, Erik G, et al. (författare)
  • DS-CDMA synchronization in time-varying fading channels
  • 1996
  • Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716. ; 14:8, s. 1636-1642
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, the problem of estimating propagation delays of the transmitted signals in a direct-sequence code-division multiple access (DS-CDMA) system operating over fading channels is considered. Even though this study is limited to the case when the propagation delays are fixed during the observation interval, the channel gain and phase are allowed to vary in time. Special attention is given to the near-far problem which is catastrophic for the standard acquisition algorithm. An estimator based on subspace identification techniques is proposed, and the Cramer-Rao bound, which serves as an optimality criterion, is derived. The Cramer-Rao bound is shown to be independent of the near-far problem, which implies that there is no fundamental reason for propagation delay estimators to be near-far limited. Furthermore, the proposed algorithm is experimentally shown to be robust against the near-far problem.
  • Ström, Erik G, et al. (författare)
  • Near-Far Resistant Propagation Delay Estimators for Asynchronous Direct-Sequence Code Division Multiple Access Systems
  • 1994
  • Ingår i: Lecture Notes in Computer Science: Mobile Communications, Proceedings 1994 International Zurich Seminar on Digital Communications. - Springer-Verlag. ; s. 251-260
  • Konferensbidrag (refereegranskat)abstract
    • This paper considers an asynchronous direct-sequence code division multiple access (DS-CDMA) communication system over an AWGN channel. We are interested in estimating the propagation delay from the different users to the receiver. The Cram'er-Rao bound for such an estimator is derived and compared with the measured variance of three algorithms. The performance of the classical correlation-based estimator is demonstrated to be quite good in a noise-limited scenario. However, in a near-far situation, i.e., when the multiple access interference becomes dominant, the performance of the classical method is severely degraded. We therefore propose two new algorithms which are shown to be near-far resistant.
  • Ström, Erik G, et al. (författare)
  • Propagation delay estimation in asynchronous direct-sequence code-division multiple access systems
  • 1996
  • Ingår i: IEEE Transactions on Communications. - 0090-6778. ; 44:1, s. 84-93
  • Tidskriftsartikel (refereegranskat)abstract
    • In an asynchronous direct-sequence code-division multiple access CDS-CDMA) communication system, the parameter estimation problem, i.e., estimating the propagation delay, attenuation and phase shift of each user's transmitted signal, may be complicated by the so-called near-far problem. The near-far problem occurs when the amplitudes of the users' received signals are very dissimilar, as the case might be in many important applications, In particular, the standard method for estimating the propagation delays will fail in a near-far situation, Several new estimators, the maximum likelihood, an approximative maximum likelihood and a subspace-based estimator, are therefore proposed and are shown to be robust against the near-far problem, No knowledge of the transmitted bits is assumed, and the proposed estimators can thus be used for both acquisition and tracking. In addition, the Cramer-Rao bound is derived for the parameter estimation problem.
  • Kaiser, Thomas, et al. (författare)
  • When will smart antennas be ready for the market? : Part II - results
  • 2005
  • Ingår i: IEEE signal processing magazine (Print). - 1053-5888. ; 22:6, s. 174-176
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • The aim of this two-part forum is to shed more light on the future of smartantennas (SA) through discussions among a balanced group of experts from academia and industry. In part I, which appeared in the March 2005 issue of IEEE Signal Processing Magazine, each of the experts stated his own opinion after exchanging some thoughts by e-mail. Then, a panel session took place at ICAS-SP'05 and a public poll followed. Now, in part II, the results are summarized by the experts. The central topic of the forum was the expectedmarket breakthrough of SA.
  • Ottersten, Björn, 1961-, et al. (författare)
  • Analysis of Subspace Fitting and ML Techniques for Parameter Estimation from Sensor Array Data
  • 1992
  • Ingår i: IEEE Transactions on Signal Processing. - 1053-587X. ; 40:3, s. 590-600
  • Tidskriftsartikel (refereegranskat)abstract
    • It is shown that the multidimensional signal subspace method, termed weighted subspace fitting (WSF), is asymptotically efficient. This results in a novel, compact matrix expression for the Cramer-Rao bound (CRB) on the estimation error variance. The asymptotic analysis of the maximum likelihood (ML) and WSF methods is extended to deterministic emitter signals. The asymptotic properties of the estimates for this case are shown to be identical to the Gaussian emitter signal case, i.e. independent of the actual signal waveforms. Conclusions concerning the modeling aspect of the sensor array problem are drawn.
  • Ottersten, Björn, 1961-, et al. (författare)
  • Direction-of-Arrival Estimation for Wideband Signals using the ESPRIT Algorithm
  • 1990
  • Ingår i: IEEE Transactions on Acoustics, Speech and Signal Processing. - IEEE Signal Processing Society. - 0096-3518. ; 38:2, s. 317-327
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel direction-of-arrival estimation algorithm is proposed that applies to wideband emitter signals. A sensor array with a translation invariance structure is assumed, and an extension of the ESPRIT algorithm for narrowband emitter signals is obtained. The emitter signals are modeled as the stationary output of a finite-dimensional linear system driven by white noise. The array response to a unit impulse from a given direction is represented as the impulse response of a linear system. The measured data from the sensor array can then be seen as the output of a multidimensional linear system driven by white noise sources and corrupted by additive noise. The emitter signals and the array output are characterized by the modes of the linear system. The ESPRIT algorithm is applied at the poles of the system, the power of the signals sharing the pole is captured, and the effect of noise is reduced. The algorithm requires no knowledge, storage, or search of the array manifold, as opposed to wideband extensions of the MUSIC algorithm. This results in a computationally efficient algorithm that is insensitive to array perturbations. Simulations are presented comparing the wideband and ESPRIT algorithm to the modal signal subspace method and the coherent signal subspace method.
  • Ottersten, Björn, 1961-, et al. (författare)
  • Exact and Large Sample ML Techniques for Parameter Estimation and Detection in Array Processing
  • 1993
  • Ingår i: Radar Array Processing. - Berlin ; New York : Springer Berlin/Heidelberg. - 3-540-55224-3 (Berlin : acid-free paper) - 978-3-540-55224-6 (Berlin : acid-free paper) - 0-387-55224-3 (New York : acid-free paper) - 978-0-387-55224-8 (New York : acid-free paper) ; s. 99-151
  • Bokkapitel (övrigt vetenskapligt)abstract
    • Sensor array signal processing deals with the problem of extracting information from a collection of measurements obtained from sensors distributed in space. The number of signals present is assumed to be finite, and each signal is parameterized by a finite number of parameters. Based on measurements of the array output, the objective is to estimate the signals and their parameters. This research area has attracted considerable interest for several years. A vast number of algorithms has appeared in the literature for estimating unknown signal parameters from the measured output of a sensor array.
  • Ottersten, Björn, 1961-, et al. (författare)
  • Spatio-Temporal Processing in Wireless Communications
  • 1999
  • Ingår i: RadioVetenskap och Kommunikation (RVK). ; s. 402-406
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Herein, we provide an overview of the research conducted in the project "Spatio-Temporal Processing in Wireless Communications" supported by NUTEK's telecommunications program. Spatio-temporal processing at the base stations of a wireless system can provide processing gain which may be used to extend range and improve coverage of the network and/or improve signal quality and lower terminal power requirements. Furthermore, with spatially selective reception and transmission, the capacity in wireless communication systems can be increased without exploiting additional bandwidth. We will give an overview of the results of this research project to date. 
  • ROY, R, et al. (författare)
  • ESPRIT and Uniform Linear Arrays
  • 1989
  • Ingår i: Proceedings of the 33rd SPIE International Technical Symposium : Advanced Algorithms and Architectures for Signal Processing IV. ; s. 370-380
  • Konferensbidrag (refereegranskat)abstract
    • ESPRIT is a recently developed and patented technique for high-resolution estimation of signal parameters. It exploits an invariance structure designed into the sensor array to achieve a reduction in computational requirements of many orders of magnitude over previous techniques such as MUSIC, Burg's MEM, and Capon's ML, and in addition achieves performance improvement as measured by parameter estimate error variance. It is also manifestly more robust with respect to sensor errors (e.g. gain, phase, and location errors) than other methods as well. Whereas ESPRIT only requires that the sensor array possess a single invariance best visualized by considering two identical but other-wise arbitrary arrays of sensors displaced (but not rotated) with respect to each other, many arrays currently in use in various applications are uniform linear arrays of identical sensor elements. Phased array radars are commonplace in high-resolution direction finding systems, and uniform tapped delay lines (i.e., constant rate A/D converters) are the rule rather than the exception in digital signal processing systems. Such arrays possess many invariances, and are amenable to other types of analysis, which is one of the main reasons such structures are so prevalent. Recent developments in high-resolution algorithms of the signal/noise subspace genre including total least squares (TLS) ESPRIT applied to uniform linear arrays are summarized. ESPRIT is also shown to be a generalization of the root-MUSIC algorithm (applicable only to the case of uniform linear arrays of omni-directional sensors and unimodular cisoids). Comparisons with various estimator bounds, including CramerRao bounds, are presented.
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