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| 2. |
- Karlsson, Johan, 1976, et al.
(författare)
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Glöm inte Dawit Isaak
- 2004
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Ingår i: Göteborgs-Posten.
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 5. |
- Nilsson, Rickard, et al.
(författare)
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A rank-reduced LMMSE canceller for narrowband interference suppression in OFDM-based systems
- 2003
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 51:12, s. 2126-2140
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Tidskriftsartikel (refereegranskat)abstract
- We present a narrowband interference (NBI) canceller that suppresses spectral leakage in an orthogonal frequency-division multiplexing (OFDM)-based system caused by a narrowband (NB) signal. We assume that the spectrum of the NB signal is within the spectrum of the OFDM signal. This can be the case, e.g., on digital subscriber lines (DSL) and in new unlicensed frequency bands for radio transmission. The canceller makes linear minimum mean-square error estimates of the spectral leakage by measuring the NBI on a few modulated or unmodulated OFDM subcarriers. It uses a model of the NB signal's power spectral density as a priori information. Using a frequency invariant design, it is possible to cancel NBI from signals that are changing their frequency location with significantly reduced complexity overhead. The operational complexity of the canceller can be lowered by using the theory of optimal rank reduction and using the time-bandwidth product of the NB signal. Analytical performance evaluations, as well as Monte Carlo simulations, show that, without perfect a priori information, this canceller can suppress the spectral leakage from a strong NB signal (e.g., with equal power as the OFDM signal) to well below the background noise floor for typical applications where it causes negligible signal-to-noise ratio and symbol error rate degradation.
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| 6. |
- Nilsson, Rickard, et al.
(författare)
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Autonomous synchronization of a DMT-VDSL system in unbundled networks
- 2002
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 20:5, s. 1055-1063
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Tidskriftsartikel (refereegranskat)abstract
- We present an algorithm that autonomously synchronizes all DMT-Zipper based VDSL modems in an unbundled access network, solving the problem with nonorthogonal NEXT that appears in systems with unsynchronized modems. The algorithm we present runs autonomously in each VDSL-modem in the central office or in the street cabinet. We determine the other modems ' relative frame offsets by exploiting their NEXT signal using the inherent cyclic redundancy found in DMT signals. By estimating the relative frame offsets of the other users, we can adjust a given user's own frame-timing relative to the mean of the others. With our method all modems in the network will be synchronized to within a small fraction of the total DMT frame-length, suppressing the nonorthogonal NEXT to a level far below the background noise-floor. This means that we can achieve the same performance in an unbundled access network without any master clock reference as in a system where all modems are perfectly synchronized using a master clock. Index Terms-Discrete multitone, frame synchronization, subscriber loops.
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| 7. |
- Nilsson, Rickard, et al.
(författare)
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Self-synchronizing a DMT-based VDSL system
- 2001
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Ingår i: Where minds meet. - Piscataway, NJ : IEEE Communications Society. ; , s. 1249-1253
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Konferensbidrag (refereegranskat)abstract
- We present an algorithm for self-synchronizing all modems in a discrete multitone (DMT)-based very high-speed digital subscriber line (VDSL) system using the Zipper duplex method. This solves the problem with non-orthogonal near-end crosstalk (NEXT) that appears in systems with unsynchronized modems. The algorithm we present runs autonomously in each VDSL-modem. It uses the auto-correlation of the DMT-signal to determine the frame-offset of other users, and adjusts the own frame-timing to be better aligned with the other users. With our method all modems will be self-synchronized to within a small fraction of the total DMT frame-length. This self-synchronization suppresses the NEXT to a level far below the background noise-floor. This means that our self-synchronized system has the same performance as a system where all modems are perfectly synchronized to a master clock
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| 8. |
- Sjöberg, Frank, et al.
(författare)
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Digital RFI Suppression in DMT-based VDSL Systems
- 2004
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Ingår i: IEEE Transactions on Circuits and Systems Part 1. - 1549-8328 .- 1558-0806. ; 51:11, s. 2300-2312
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we propose a method for suppressing radio frequency interference (RFI) in discrete multitone (DMT) based very high bit rate digital subscriber line (VDSL) systems. The method operates in the frequency domain of a DMT system. First, we derive a model of how an unknown narrow-band RF signal is mapped onto the DMT carriers. Then, by measuring the RFI on a few unused DMT carriers we are able to subtract RFI estimates from every modulated subcarrier. Simulation results show that this method, applied to an RFI signal with the same average power as the VDSL signal, suppresses the RFI with 40-50 dB, which reduces the average SNR loss from about 20 to less than 0.3 dB.
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| 9. |
- Sjöberg, Rickard L
(författare)
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Children's testimony
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Most cases of child sexual use are identified through statements made by children and in many cases such statements constitute the only evidence available that abuse occurred. Despite its importance the use of children's testimonies is however complicated by the fact that a substantial proportion of victims delay disclosure of abuse or even deny such experiences when asked for them directly. A further complicating factor, highlighted by an abundance of experimental research, performed mainly on English speaking populations, is that autobiographical statements by young children appear to be more susceptible to suggestion than older children and adults. The primary aims of the studies described in the present thesis were first to identify possible mechanisms behind delayed disclosure and non-disclosure of child sexual abuse among Swedish children, second to test the hypothesis that age related differences in suggestibility can be found in archival material from different historical and cultural contexts than that of 20th century English speaking countries and third to identify and describe possible mechanisms of suggestion in these contexts. Methods: Archival data describing forensic interviews with 10 children with histories of child sexual abuse which were video-taped by the perpetrator; archival data describing 47 cases child sexual abuse which were corroborated by confessions from the perpetrator, archival data describing the making of false allegations of Satanist abductions during the 17 th century as made by some 500 children and experimental data from one study performed on 48, 5-7 year old children were used to address these issues. Results: Young children showed an increased tendency to delay disclosure of child sexual abuse and an increased susceptibility to suggestion when compared to older children. Both cognitive and social factors seem to determine these results. Conclusion: The cognitive and social context in which a child's testimony is given may be important to the validity of the testimony.
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