Author: H. V. Poor Publisher: ISBN: Category : Languages : en Pages : 7
Book Description
The overall purpose of this research project was to seek new methods for improving the robustness and efficiency of spread-spectrum communications systems operating over non-Gaussian channels. The study was motivated in large part by the fact that modern military radio networks must operate in complex and variable noise environments that are often dominated by impulsive, non-Gaussian man-made noise sources. The research under this contract progressed in three basic areas: (1) optimum multiuser demodulation techniques; (2) direct-sequence spread-spectrum multiple-access (DS/SSMA) signaling through impulsive channels; and (3) improved suppression of narrowband interferers from spread-spectrum signals. The common thread binding these three disparate multiuser-communications research topics is the fact that each involves the processing of signals in non-Gaussian interference. In the first case, the non-Gaussian interference is the multiuser noise interfering with the demodulation of a given user; in the second case, the non-Gaussian interference is the impulsive noise dominating the channel; and in the third case, the non-Gaussian interference is the spread-spectrum signal itself as it interferes with the prediction and consequent excision of the narrowband interferer. (rh).
Author: Publisher: ISBN: Category : Languages : en Pages : 19
Book Description
Based on the theory of locally optimum detection we identified a spread-spectrum receiver architecture that consists of an adaptive non-linear chip-level pre-processor followed by an adaptive linear filter post-processor. The non-linear front-end protects against impulsive, non-Gaussian disturbance. The adaptive linear filter post-processor suppresses unknown highly correlated spread-spectrum (SS) interference. To achieve adaptive, rapid, and effective SS interference suppression from a small number of input observations, we defined a new class of linear filters that we called Auxiliary-Vector (AV) filters. We view this development as a breakthrough in the field of adaptive signal processing theory. When the input autocorrelation matrix is unknown and estimated from a limited set of input data (as in all real-life adaptive signal processing applications), Auxiliary-Vector filters are shown to outperform all other filter estimator means in the literature. We addressed successfully the critical problem of determining an automated, theoretically derived, rule for the selection of the best number of auxiliary vectors (AV's) for a given data record of input observations. We anticipate that this development will attract a great deal of interest in the Auxiliary-Vector filtering technique. Based on the principles of AV-filtering we proposed and analyzed theoretically structures that are self-synchronized in the sense that adaptive synchronization and demodulation are viewed and treated as an integrated receiver operation. As a major application, we addressed the problem of navigation data demodulation by an adaptive jam-resistant GPS receiver that utilizes a bank of linear-tap-delay filters and employs antenna-array reception (one space-time
Author: Amer A. Hassan Publisher: Springer Science & Business Media ISBN: 1461555310 Category : Technology & Engineering Languages : en Pages : 170
Book Description
Perspectives in Spread Spectrum brings together studies and recent work on six exciting topics from the spread spectrum arts. The book gives a wide, collective view of trends, ideas, and techniques in the spread spectrum discipline, due to the authors' extensive work on spread spectrum techniques and applications from different vantage points. The inexorable march of electronics towards ever faster, ever smaller, and ever more powerful electronic and optical circuitry has wrought, and will continue to enable, profound changes in the spread spectrum arts, by allowing increasingly complex signalling waveforms and statistical tests to be implemented as the theory beyond spread spectrum continues to evolve. Perspectives in Spread Spectrum is divided into six chapters. The first chapter deals with sequence spreading design. There is not a single metric for design of spreading sequences; rather, the design is ideally tailored to the specific scenario of usage. This chapter delves into recent and very promising synthesis work. The second chapter deals with OFDM techniques. As channels become wider and trans-channel fading (or jamming) becomes frequency selective across the band, OFDM techniques may provide a powerful alternative design perspective. The third chapter is a generalization of the venerable Walsh functions. A new modulation scheme, Geometric Harmonic Modulation, GHM for short, is reviewed and characterized as a form of OFDM. From GHM, a further generalization of the Walsh functions is derived for non-binary signalling. The fourth chapter is concerned with some new and exciting results regarding the follower jammer paradigm. A counter-countermeasure technique is reviewed, notable for its counterintuitive characteristic which can be understood from a simple yet elegant game framework. The fifth chapter recounts some results pertaining to random coding for an optical spread spectrum link. The technique is based on laser speckle statistics and uses a coherent array of spatial light modulators at the transmitter but allows the receiver to be realized as a spatially distributed radiometric and therefore incoherent structure. The sixth and final chapter looks at an important and interesting application of spread spectrum to accurately locate a wideband, ‘bent pipe’, satellite transponder. It is, in a strong sense, an inverted GPS technique. Perspectives in Spread Spectrum serves as an excellent reference and source of ideas for further research, and may be used as a text for advanced courses on the topic.
Author: Behnaam Aazhang Publisher: ISBN: Category : Languages : en Pages : 148
Book Description
Performance of digital linear and nonlinear correlation receivers is studied in a muli-user environment. There are assumed to be two types of sources interfering with data transmission: multiple-access interference, and additive channel noise, which is attributed to impulsive noise sources in the environment. The contribution of multiple-access interference is examined by considering K users transmitting simultaneously over a linear channel using the binary PSK direct-sequence SSMA technique. Alternatively, the effects of the non-Gaussian impulse channel in such a system are studied by modeling the sample of noise after front-end filtering. The performance of hard-limiting correlation receivers is compared with that of conventional linear correlation receivers in such channels by exact computation of the average bit error probabilities of these two systems. It is seem that hard-limiting correlation receivers can offer substantial improvement over the conventional linear correlator when the additive non-Gaussian channel noise exhibits impulsive behavior.
Author: United States. Army Research Office Publisher: ISBN: Category : Military research Languages : en Pages : 296
Book Description
Vols. for 1977- consist of two parts: Chemistry, biological sciences, engineering sciences, metallurgy and materials science (issued in the spring); and Physics, electronics, mathematics, geosciences (issued in the fall).
Author: H. V. Poor
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Author: Amer A. Hassan
Author: Behnaam Aazhang
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Author: Marvin K. Simon
Author: United States. Army Research Office
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Author: Marvin K. Simon