| 1. |
- Bengtsson, Daniel, et al.
(författare)
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Trellis coding in a discrete multitone modulation system
- 1996
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Ingår i: Proceedings of the 1996 SNRV and NUTEK Conference on Radio Sciences and Telecommunications in Luleå and Kiruna June 3-6, 1996. - Luleå : Luleå tekniska universitet. - 9163044552 ; , s. 668-672
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Konferensbidrag (refereegranskat)abstract
- Discrete Multitone (DMT) modulation is a multicarrier technique which makes efficient use of the channel, maximizing the throughput by sending different numbers of bits on different subchannels. The number of bits on each subchannel depends on the Signal-to-Noise Ratio of the subchannel. The performance of a DMT system can be further increased by using powerful coding techniques. This paper investigates an implementation of trellis coded modulation in a DMT system intended for transmission over short copper cables, less than 1000m. We suggested trellis code is Wei's 4-dimensional 16-state coder combined with trellis shaping. A single encoder is used which codes across the tones of each DMT-symbol. At a bit error probability of 10-7, the suggested code gains 4-5 dB over uncoded transmission.
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| 2. |
- Edfors, Ove, et al.
(författare)
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An introduction to orthogonal frequency-division multiplexing
- 1997
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report is an introduction to orthogonal frequency-division multiplexing (OFDM). The focus is on signal processing areas pursued by our research group at Luleå University of Technology. We present an historical background and some frequently used system models. Typical areas of applications are also described, both wireless and wired. In addition to the general overview, the addressed areas include synchronization, channel estimation and channel coding. Both time and frequency synchronization are described, and the effects of synchronization errors are presented. Different types of channel estimators are described, where the focus is on low-complexity algorithms, and in this context, advantages and disadvantages of coherent and differential modulation are also discussed. Channel coding is described, both for wireless and wired systems, and pointers are included to evaluation tools and bitloading algorithms. An extensive bibliography is also included.
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| 3. |
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| 4. |
- Johansson, Stefan, et al.
(författare)
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Implementation of an OFDM Synchronization Algorithm
- 1999
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Ingår i: 42nd Midwest Symposium on Circuits and Systems, 1999.. - 0780354915 ; 1, s. 228-231
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Konferensbidrag (refereegranskat)abstract
- In this paper, a implementation of an OFDM synchronization algorithm is presented. Both time and frequency offsets are estimated simultaneously, using the cyclic prefix. The algorithm is implemented on a commercial DSP, an FPGA and as an ASIC. It is shown that although the algorithm is too complex to be implemented on a standard DSP, a hardware architecture that is optimized for the algorithm can be implemented with moderate complexity
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| 5. |
- Johansson, Stefan, et al.
(författare)
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Silicon realization of an OFDM synchronization algorithm
- 1999
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Ingår i: The 6th IEEE International Conference on Electronics, Circuits and Systems, Proceedings of ICECS '99.. - 0780356829 ; 1, s. 319-322
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Konferensbidrag (refereegranskat)abstract
- n this paper a hardware architecture for an OFDM synchronizer is presented. The proposed synchronization unit can be used in any OFDM system that uses a cyclic prefix. The algorithm is based on the correlation introduced by the cyclic prefix, which is exploited in the time domain where both time and frequency offset are estimated simultaneously. The synchronization unit also performs frequency correction, which means that no feedback to the analog parts is necessary. Although the algorithm is too complex to be implemented on today's most powerful standard DSP, a hardware architecture that is optimized for the algorithm can be implemented with moderate complexity. The unit contains 32 kbit RAM and 5000 gates and the sample rate is 25 Msamples/s
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| 6. |
- Landström, Daniel, et al.
(författare)
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Symbol time offset estimation in coherent OFDM systems
- 1999
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Ingår i: IEEE International Conference on Communications. - Piscataway, NJ : IEEE Communications Society. - 078035284X ; , s. 500-505
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Konferensbidrag (refereegranskat)abstract
- This paper presents a symbol time offset estimator for coherent OFDM systems. This estimator exploits both the redundancy in the cyclic prefix and the pilot symbols used for channel estimation. The estimator is robust against frequency offsets and is suitable for use in dispersive channels. We base the estimator on the ML estimator for the AWGN channel. Simulations of an example system indicate a system performance as close as 0.3 dB to a perfectly synchronized system. Compared to an estimator not using pilots, our estimator's performance could allow a shorter cyclic prefix and thus a more spectrally efficient system.
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| 7. |
- Landström, Daniel, et al.
(författare)
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Symbol time offset estimation in coherent OFDM systems
- 2002
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Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778. ; 50:4, s. 545-549
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a symbol time offset estimator for coherent orthogonal frequency division multiplexing (OFDM) systems. The estimator exploits both the redundancy in the cyclic prefix and available pilot symbols used for channel estimation. The estimator is robust against frequency offsets and is suitable for use in dispersive channels. We base the estimator on the maximum-likelihood estimator for the additive white Gaussian noise channel. Simulations for an example system indicate a system performance as close as 0.6 dB to a perfectly synchronized system.
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| 8. |
- Landström, Daniel
(författare)
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Synchronization for Multicarrier Systems
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis has synchronization of Multicarrier systems, more specifically Orthogonal Frequency Division Multiplexing (OFDM) systems, as the main theme. The thesis addresses two areas, the first proposing and analyzing time and frequency estimators for OFDM systems, the second investigating more practical issues around these estimators. The practical part addresses implementation and applies the estimators in an OFDM-based mobile multiuser communication system, one of the proposals for the Universal Mobile Telecommunication System (UMTS/IMT-2000). Estimation of time and frequency offsets is a core issue in synchronizing an OFDM system. We address this issue with a family of new time and frequency offset estimators using the signal redundancy provided by the cyclic prefix. The estimators are all based on the Maximum Likelihood (ML) criterion, but for different system models, e.g., with different channels, with and without pulse shaping, with and without using pilot information, and under different implementational constraints. Furthermore, the design of an OFDM-based multiuser mobile communications system using both time and frequency division multiple access has been attempted. A standardization proposal for UMTS has been developed and submitted, suggesting, among other things, a synchronization method and parameter values describing the time and frequency grid. The work documented here has been performed at Lund Institute of Technology, Luleå University of Technology, Telia Research AB, and the Telecommunications Research Center Vienna (ftw.). Financial support has been received from NUTEK (The Swedish National Board for Industrial and Technical Development), Vetenskapsrådet (The Swedish Research Council), Telia Research AB, and VINNOVA through the Eureka/Medea+ A106 INCA and A110 MIDAS programs.
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| 9. |
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| 10. |
- Landström, Daniel, et al.
(författare)
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Time and frequency offset estimation in OFDM systems employing pulse shaping
- 1997
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Ingår i: Bridging the way to the 21st century. - Piscataway, NJ : IEEE Communications Society. - 0780337778 ; , s. 279-283, s. 279-283
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Konferensbidrag (refereegranskat)abstract
- Time and frequency offset estimation is addressed in an OFDM system that uses a cyclic prefix and pulse shaping. Earlier work has presented a method that avoids the use of pilots by exploiting the inherent correlation in the cyclically extended OFDM symbol. In this paper this technique is extended to include systems with pulse shaping. The joint Maximum Likelihood estimator of time and frequency offsets for such systems is presented and evaluated. An implementable structure of the extended estimator is given. Simulations show that it is possible to maintain the performance when introducing pulse shaping into an OFDM system.
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