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- Guio, P., et al.
(author)
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Phase space vortices in collision-less plasmas
- 2003
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In: Nonlinear processes in geophysics. - 1023-5809 .- 1607-7946. ; 10:1/2, s. 75-86
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Journal article (peer-reviewed)abstract
- Results on the formation and propagation of electron phase space vortices from laboratory experiments are summarized. The electron phase space vortices were excited in a strongly magnetized Q-machine plasma by applying a pulse to a segment of a waveguide surrounding the plasma. Depending on the temporal variation of the applied pulse, one or more phase space vortices can be excited, and their interaction can be followed in space and time. We were able to demonstrate, for instance, an irreversible coalescence of two such vortices. These results are extended by numerical simulations, showing how electron phase space vortices can also be formed by beam instabilities. Furthermore, a study of ion phase space vortices is performed by numerical simulations. Both codes allow for an externally applied magnetic field in three spatial dimensions. Ion phase space vortices are formed by the nonlinear saturation of the ion-ion two-stream instability, excited by injecting an ion beam at the plasma boundary. By following the evolution of the ion distribution of the velocity perpendicular to the direction of propagation of the injected ion beam, we find a significant ion heating in the direction perpendicular to the magnetic field associated with the ion phase space vortices being formed. The results are relevant, for instance, for the interpretation of observations by instrumented spacecraft in the Earth's ionosphere and magnetosphere.
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| 5. |
- Alexander, Paul D., et al.
(author)
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Filter structure for iterative signal processing
- 2002
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Patent (pop. science, debate, etc.)abstract
- The present invention relates to improved multiple access communications. In one form, the invention relates to an improved signal processing method and apparatus for an iterative method of determining the reception of a signal in a multi user packet based wireless OFDM (Orthogonal Frequency Division Multiplexing) communication system. In other forms the present invention provides recursive filtering for joint iterative decoding in a variety of systems and functions such as linear multiple access channel decoders, iterative equalisation, iterative joint channel estimation and detection/decoding, iterative space-time processing, iterative multi user interference cancellation and iterative demodulation.; In one particular form the present invention provides an iterative decoding circuit for a wireless multiuser communications receiver comprising a first signal processing means for receiving at least one received signal, said first signal processing means comprising at least two linear iterative filters such that the first linear iterative filter provides an estimate of a selected received signal to an estimated signal output and a second linear iterative filter provides estimates of at least one other received signal, delayed by one iteration cycle, to an input of said first linear iterative filter, a second signal processing means for receiving the estimated signal output of the first linear iterative filter and providing a further received signal estimate to the input of the first signal processing means in a succeeding iteration cycle of the decoding circuit.
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| 6. |
- Alexander, Paul D., et al.
(author)
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Filter structure for iterative signal processing
- 2002
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Patent (pop. science, debate, etc.)abstract
- The invention is an iterative signal processing arrangement having one or more pairs of first and second signal processing components. These pairs are in iterative configuration with each of the first signal processing components having as its input one or more received signals dependent upon one or more transmitted signals. For each said signal processing component pair the output of said first signal processing component is an estimate of a characteristic of a selected transmitted signal based on the current and one or more previous input signals received by said first signal processing component. This estimate is input to said corresponding second signal processing component which provides a further estimate of said selected transmitted signal. The outputs of all said second components of respective pairs are input to their corresponding first components in a succeeding iteration cycle.
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| 9. |
- Brännström, Fredrik, 1974, et al.
(author)
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Convergence analysis of iterative detectors for narrow-band multiple access
- 2002
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In: IEEE Global Telecommunications Conference (GLOBECOM '02), Taipei, Taiwan, Nov. 2002. ; , s. 1373-–1377
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Conference paper (peer-reviewed)abstract
- Convergence analysis of iterative detectorsfor narrow-band multiple access is performed by usingextrinsic information transfer charts. The system has nobandwidth expansion, so K users are using the same bandwidthas one single user. The load (the number of bitsper channel use) of the system is therefore higher than theload in, for example, conventional CDMA systems. Theanalysis provide useful guidelines how to combine outercodes with the chosen mapper for different loads of thesystem. Both memoryless mappers and differential mappersare evaluated. The limitations of the system measuredin the maximum number of users and the requiredSNR for different scenarios are presented.
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| 10. |
- Brännström, Fredrik, 1974, et al.
(author)
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Optimal puncturing for multiple parallel concatenated codes
- 2004
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In: IEEE International Symposium on Information Theory. - 0780382803 ; , s. 154-, s. 154-
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Conference paper (other academic/artistic)abstract
- Optimal puncturing ratios for parallel concatenated codes with two or more constituentcodes are found using extrinsic information transfer functions. These ratios minimise the signal-to-noise ratio convergence threshold and provide additional degrees of freedom for constructing codes with low thresholds over a wide range of code rates.
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