Dissertations / Theses on the topic 'Turbo-equalization'
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Konuskan, Cagatay. "Turbo Equalization for HSPA." Thesis, Linköping University, Department of Electrical Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-54640.
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New high quality mobile telecommunication services are offered everyday and the demand for higher data rates is continuously increasing. To maximize the uplink throughput in HSPA when transmission is propagated through a dispersive channel causing self-interference, equalizers are used. One interesting solution, where the equalizer and decoder exchange information in an iterative way, for improving the equalizer performance is Turbo equalization.
In this thesis a literature survey has been performed on Turbo equalization methods and a chosen method has been implemented for the uplink HSPA standard to evaluate the performance in heavily dispersive channels. The selected algorithm has been adapted for multiple receiving antennas, oversampled processing and HARQ retransmissions. The results derived from the computer based link simulations show that the implemented algorithm provide a gain of approximately 0.5 dB when performing up to 7 Turbo equalization iterations. Gains up to 1 dB have been obtained by disabling power control, not using retransmission combining and utilizing a single receiver antenna. The algorithm has also been evaluated considering alternative dispersive channels, Log-MAP decoding, different code rates, number of Turbo equalization iterations and number of Turbo decoding iterations.
The simulation results do not motivate a real implementation of the chosen algorithm considering the increased computational complexity and small gain achieved in a full featured receiver system. Further studies are needed before concluding the HSPA uplink Turbo equalization approach.
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Lee, Kah Ping. "Turbo equalization in wireless communication." Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/5844.
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Thesis (M.S.)--University of Missouri-Columbia, 2005.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 11, 2006) Includes bibliographical references.
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Kurkoski, Brian M. "Algorithms and schedules for turbo equalization /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3137222.
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Monfet, Frederic. "Turbo equalization using frequency-domain shortening filter." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99527.
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Turbo equalization provides excellent performance but the complexity associated with this technique prohibits its use in application with severe inter-symbol interference (ISI) channel; the turbo equalizer complexity increases exponentially with the length of the channel impulse response (CIR) and the modulation level used for data transmission. In this work, a combined frequency-domain pre-equalizer with a turbo equalizer is proposed in an attempt to reduce the length of the CIR used by the turbo equalizer and hence the complexity of the receiver. The optimum selection of coefficients of the frequency-domain pre-equalizer and desired channel impulse response is discussed. With the proposed receiver, the complexity of the turbo equalizer can be controlled by pre-selecting the length of the desired channel impulse response. This complexity reduction is achieved at the cost of an increase in the noise level, which degrades the performance. The effect on the performance of such pre-equalizer is studied analytically. The overall performance of the proposed receiver for different length of the desired channel impulse response is studied via analytical comparison and simulation. Simulation results on performance in various frequency-selective fading channels indicate a substantial performance gain when compared to a conventional feed-forward equalizer (FFE) plus decision-feedback equalizer (DFE) receiver. Finally, in cases where a large alphabet is used for modulation, the reduced-search BCJR (Bahl, Cocke, Jelinek, and Raviv) [1] algorithm is utilized in the proposed receiver to further reduce the complexity of the receiver.
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Mysore, Naveen. "Combined turbo coding and turbo equalization for wireless systems with antenna diversity." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33983.
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Emerging wireless communication systems strive for very high data rates, increased coverage and good quality of service. To achieve these goals under harsh conditions on many wireless channels (e.g., due to fading, multipath interference, power constraints and bandwidth limitations), both antenna diversity schemes and channel coding should be utilized.This thesis focuses on achieving reliable transmission over a class of multi-input multi-output Rayleigh faded channels at very low Signal-to-Noise Ratios (SNRs). The transmitter and receiver designs are based on turbo coding, multiple transmit/receive antennas and turbo equalization. Simulation studies were performed for systems with different coding rates, numbers of antennas and interleaving strategies. They show the ability to achieve small bit error rates (10-4--10-5) for negative values of SNR.
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Oletu, Grace Ogheneruonano. "Turbo coding and equalization for wireless communication systems." Thesis, University of Greenwich, 2013. http://gala.gre.ac.uk/11626/.
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Turbo coding, a forward error correcting coding (FEC) technique, has made near Shannon Limit performance possible when Iterative decoding algorithms are used. Intersymbol interference (ISI) is a major problem in communication systems when information is transmitted through a wireless channel. Conventional approaches implement an equalizer to remove the ISI, but significant performance gain can be achieved through joint equalization and decoding. In this thesis, the suitability of turbo equalization as a means of achieving low bit error rate for high data communication systems over channels with intersymbol interference was investigated. A modified decision feedback equalizer algorithm (DFE) that provides significant improvement when compared with the conventional DFE is proposed. It estimates the data using the a priori information from the SISO channel decoder and also a priori detected data from previous iteration to minimize error propagation. Investigation was also carried out with Iterative decoding with imperfect minimum mean square error (MMSE) decision feedback equalizer, assuming soft outputs from the channel decoder that are independent identically distributed Gaussian random variables. The prefiltering method is considered in this thesis, where an all-pass filter is employed at the receiver before equalization to create a minimum phase overall impulse response. The band limited channel suffers performance degradation due to impulsive noise generated by electrical appliances. This thesis analysed a set of filter design criteria based on minimizing the bit error probability of impulse noise using digital smear filter.
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Shiao, Fu-Sheng. "Combined Channel Estimation and Turbo Equalization for Wireless Channels." Thesis, University of Canterbury. Electrical and Computer Engineering, 2007. http://hdl.handle.net/10092/1189.
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Single-carrier linear modulation techniques combined with frequency-domain equalization provide a viable alternative to multicarrier techniques for combating multipath fading in channels with large delay spread. Such modulations tolerate frequency offset and have well controlled peak to average power ratio. They have comparable complexity to orthogonal frequency division multiplexing (OFDM) systems, and are more robust to synchronization errors. If error correction coding is used, then information can be iteratively passed between the equalizer and the decoder to improve performance. This is referred to as turbo equalization. To date, several turbo equalization schemes have been proposed, but little work has been done to address the problem of channel estimation for the turbo equalization process. The work in this thesis considers frequency-domain turbo equalization with imperfect channel state information (CSI) at the receiver for different wireless channels. A receiver structure incorporating joint frequency-domain turbo equalization and time- domain channel estimation is developed. The novelty of this scheme lies in the combination of time-domain channel estimation and frequency-domain turbo equalization, and in its extension to high level modulation formats. The performance of the system is investigated by a combination of analysis and computer simulation. It is found that the system performs well over a range of dispersive channels.
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Chesnutt, Elizabeth. "Novel Turbo Equalization Methods for the Magnetic Recording Channel." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6867.
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Novel Turbo Equalization Methods for the Magnetic Recording Channel
Elizabeth Chesnutt
95 Pages
Directed by Dr. John R. Barry
The topic of this dissertation is the derivation, development, and evaluation of novel turbo equalization techniques that address the colored noise problem on the magnetic recording channel. One new algorithm presented is the noise-predictive BCJR, which is a soft-output detection strategy that mitigates colored noise in partial-response equalized magnetic recording channels. This algorithm can be viewed as a combination of the traditional BCJR algorithm with the notion of survivors and noise prediction.
Additionally, an alternative equalization architecture for magnetic recording is presented that addresses the shortcomings of the PRML approach, which dominates magnetic recording. Specifically, trellis-based equalizers are abandoned in favor of simple equalization strategies based on nonlinear filters whose complexity grows only linearly with their length. This research focuses on the linear-complexity SFE algorithm and on investigating the possibility of lowering the SFE filter calculation complexity. The results indicate that with using the proposed novel SFE method, it is possible to increase the information density on magnetic media without raising the complexity. The most important result presented is that partial-response equalization needs to be reconsidered because of the amount of noise enhancement problems that it adds to the overall system. These results are important for the magnetic recording industry, which is trying to attain a 1 Tb/cm2 information storage goal.
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Yildirim, Recep Ali. "Mmse Based Iterative Turbo Equalization For Antenna Switching Systems." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612480/index.pdf.
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In this thesis, we study the performance of an antenna switching (AS) system in comparison to an Alamouti coded system. We analyze the outage probabilities and propose minimum mean-squared error based iterative equalizers for both systems. We see from the outage probability analysis of both systems that the AS system may achieve the same diversity order of the Alamouti coded scheme contingent on the transmission rate and constellation size. In the proposed receiver, MMSE equalization and channel decoding are jointly carried out in an iterative fashion. We use both hard and soft decision channel decoders in our simulations. It is observed that the Alamouti based scheme performs better when the channel state information is perfect. The Alamouti scheme also performs better than the AS scheme when the channel state information is imperfect in hard decision channel decoder case and a random interleaver is used. On the other hand, if a random interleaver is not used, AS scheme performs remarkably better than the Alamouti scheme in hard decision channel decoder case. In a soft decision channel decoder case, when the channel state information is imperfect, the AS scheme performs approximately a 2 dB better than the Alamouti scheme. Moreover, there is approximately a 3 dB performance gain if a soft decision channel decoder is used instead of hard decision.
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Franz, Volker. "Turbo-detection for GSM-systems channel estimation, equalization and decoding /." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=96205772X.
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Kansanen, K. (Kimmo). "Wireless broadband single-carrier systems with MMSE turbo equalization receivers." Doctoral thesis, University of Oulu, 2005. http://urn.fi/urn:isbn:9514279336.
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Abstract
Broadband single-carrier modulated signals experience severe multipath distortion when propagating through the physical medium. Correcting the distortion with channel equalization is the foremost task of the detector. Prior information about the transmitted signals in the form of channel decoder feedback can significantly enhance equalization accuracy. An algorithm that iteratively performs channel decoding and equalization with prior information is generally denoted a turbo equalizer. This thesis focuses on turbo equalization with prior information using the principle of interference cancellation followed by minimum mean squared error (MMSE) filtering. Receiver algorithms, receiver convergence, and coding and modulation in the context of MMSE turbo equalization are studied.
Computationally efficient versions of the receiver algorithm through approximate time-average filtering, matched filtering, square-root time-variant filtering and frequency-domain filtering are studied. The frequency-domain turbo equalizer (FDTE) is found to exhibit both superior convergence and low computational complexity among the compared equalizer algorithms.
Multi-dimensional extrinsic information transfer (EXIT) charts are introduced for the purpose of tracking the convergence of the turbo equalization of layered MIMO transmissions. Generic properties of the equalizer EXIT functions defining the equalizer convergence are analyzed. The principles for detector ordering, maximum sum-rate code design and maximum rate symmetric design are derived from the properties of the multidimensional EXIT functions.
Semi-analytical EXIT charts are developed for the convergence analysis of the FDTE. The effects of channel parameters and the channel code are analyzed with semi-analytical methods. A new approach for the design of irregular low-density parity-check (LDPC) codes using a convergence outage principle is proposed. A performance gain is demonstrated in a single-input multiple output (SIMO) channel over non-optimized regular LDPC codes and irregular LDPC codes optimized for the AWGN channel. The outage convergence based design, which takes advantage of the semi-analytical convergence analysis method, is also extended to layered MIMO transmissions.
Quadrature amplitude modulation using multilevel bit-interleaved coded modulation (MLBICM) is studied as an alternative to regular bit-interleaved coded modulation (BICM) for highly bandwidth-efficient transmission in MMSE turbo equalized systems. A linear bit-to-symbol mapping is introduced that enables the use of a computationally efficient MMSE turbo equalizer at the receiver. The proposed coded modulation is compared with BICM in channel measurement data based simulations and found to exhibit superior robustness against changes in spatial channel parameters. An automatic repeat request (ARQ) configuration using one ARQ controller for each equally performing group of code levels is proposed. The configuration takes advantage of the unequal error protection (UEP) property of the coded modulation. The semi-analytical convergence analysis is extended to the multilevel modulated case and applied in a channel measurement based convergence evaluation. The construction of the MLBICM is found to have an inherently better convergence behavior than BICM. Finally, the outage convergence based channel code design is extended to the layered MIMO multilevel signalling case.
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Otnes, Roald. "Improved Receivers for Digital High Frequency Communications : Iterative Channel Estimation, Equalization, and Decoding (Adaptive Turbo Equalization)." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-86.
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We address the problem of improving the throughput and the availability of digital communications in the High Frequency (HF, 3-30 MHz) band. In standardized military waveforms, the data is protected by an error-correcting code (ECC), and the code bits are shuffled by an interleaver and mapped onto a signal constellation for modulation onto a single carrier. Training sequences are multiplexed into the stream of transmitted symbols to aid the receiver in tracking the channel variations. The channel imposes severe time-varying intersymbol interference (ISI) as well as additive noise. Conventional receivers for such a system would first perform adaptive equalization (to mitigate the ISI) and symbol demapping, deinterleave the received code bits, and finally perform decoding, where the redundancy of the ECC is used to make high-quality decisions on the transmitted data bits even when bit errors have been introduced by the channel. Such a receiver is suboptimal because the equalizer does not make use of the redundancy introduced by the ECC, and is outperformed by an iterative scheme called turbo equalization. In turbo equalization, a.k.a. iterative equalization and decoding, soft information on the code bits is fed back from the decoder to the equalizer in an iterative fashion, and by performing the equalization and decoding tasks several times the bit error rates become significantly smaller than for a conventional “single-pass” receiver. Since we are dealing with an unknown time-varying channel, we must also perform channel estimation. We include channel estimation in the iterative loop of the turbo equalizer, using soft information fed back from the decoder as “training sequences” between the ordinary transmitted training sequences. Then, the receiver performs iterative channel estimation, equalization, and decoding, which can also be called adaptive turbo equalization. We have proposed a receiver using adaptive turbo equalization, and performed simulations using the MIL-STD-188-110 waveform at 2400 bps, transmitted over an ITU-R poor channel (a commonly used channel to test HF modems). We find that the proposed receiver outperforms a conventional receiver by 2-3 dB in terms of required signal-to-noise ratio to achieve a certain bit error rate. In this dissertation, we give an introduction to the fields of HF communications and standardized HF waveforms, channel modelling, and turbo equalization. We present an analysis of measured channel data to motivate our research in turbo equalization. We then present our research contributions to the field of turbo equalization: A low-complexity soft-in soft-out equalizer for time-varying channels, a comparative study of channel estimation algorithms using soft information as the input signal, and an investigation of adaptive turbo equalization using a technique known as EXIT charts. Finally, we present our main practical result, which is our proposed receiver and the corresponding simulation results.
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Karjalainen, J. (Juha). "Broadband single carrier multi-antenna communications with frequency domain turbo equalization." Doctoral thesis, Oulun yliopisto, 2011. http://urn.fi/urn:isbn:9789514295027.
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Abstract This thesis focuses on advanced multi-antenna receiver and transmission techniques to improve the utilization efficiencies of radio resources in broadband single carrier communications. Special focus is devoted to the development of computationally efficient frequency domain (FD) turbo equalization techniques for single and multiuser MIMO frequency selective channels. Another special emphasis is given to transmission power optimization for single user MIMO communications, which takes into account the convergence properties of the iterative equalizer. A new iterative FD soft cancellation (SC) and minimum mean square error (MMSE) filtering based joint-over-antenna (JA) multiuser MIMO signal detection technique for multiuser MIMO uplink transmission in frequency-selective channels is proposed. The proposed FD multiuser MIMO detection technique requires significantly lower computational complexity than its time-domain counterpart. Furthermore, significant performance gains can be achieved with the proposed JA turbo receiver compared to an antenna-by-antenna (AA) turbo receiver when the total number of transmitter antennas and users is larger than the number of receiver antennas, as well as in the presence of spatial correlation. The impact of existing linear precoding techniques, e.g, maximum information rate (MaxRate) and minimum sum mean square error (MinSumMSE), on the performance of frequency domain turbo equalization is investigated by utilizing extrinsic information transfer (EXIT) chart analysis. A novel transmission power minimization framework based on an EXIT analysis of single carrier MIMO transmission with iterative FD SC-MMSE equalization is then proposed. The proposed optimization framework explicitly takes into account the convergence properties of the iterative equalizer. The proposed convergence constrained power allocation (CCPA) technique decouples the spatial interference between streams using singular value decomposition (SVD), and minimizes the transmission power while achieving the mutual information target for each stream after iterations at the receiver side. The transmission power allocation can be formulated as a convex optimization problem. A special case having only two mutual information constraints is considered, for which the Lagrange dual function is derived and its dual problem is solved. Inspired by the Lagrange duality, two CCPA based heuristic schemes are developed. The numerical results demonstrate that the proposed CCPA schemes outperform the existing power allocation schemesTiivistelmä Tässä työssä tutkitaan edistyksellisten moniantennivastaanotto- ja lähetysmenetelmien käyttöä radioresurssien tehokkuuden parantamiseen laajakaistaisessa yhden kantoaallon kommunikaatiossa. Työssä keskitytään erityisesti laskennallisesti tehokkaiden taajuustasossa suoritettavien iteratiivisten kanavakorjaintekniikoiden kehittämiseen yhden ja usean käyttäjän multiple-input multiple-output (MIMO) -kommunikaatiossa taajuusselektiivisen radiokanavan yli. Toinen tutkimuksen painopiste on lähetystehon optimointi yhden käyttäjän MIMO-kommunikaatiossa, jossa iteratiivisen kanavakorjaimen konvergenssiominaisuudet otetaan huomioon. Työssä ehdotetaan uudenlaista iteratiivista taajuustasossa suoritettavaa soft-cancellation (SC) ja minimum mean square error (MMSE) -suodatukseen pohjautuvaa joint-over-antenna (JA) monen käyttäjän ilmaisumenetelmää nousevan siirtokanavan tiedonsiirtoon taajuusselektiivisessa radiokanavassa. Ehdotettu tajuustasossa suoritettava usean käyttäjän MIMO-lähetyksen ilmaisumenetelmä vaatii selvästi vähemmän laskentatehoa verrattuna aikatason menetelmään. Tämän lisäksi ehdotetulla menetelmällä voidaan saavuttaa merkittävää suorituskykyhyötyä verrattuna antenna-by-antenna (AA) -pohjaiseen iteratiiviseen vastaanottimeen kun lähetysantennien ja käyttäjien kokonaislukumäärä on suurempi kuin vastaanotinantennien. Suorituskykyhyöty pätee myös tilakorrelaation tapauksessa. Työssä tutkitaan lisäksi olemassa olevien lineaaristen esikoodaustekniikoiden, esim. maximum information rate (MaxRate) and minimum sum mean square error (MinSumMSE), vaikutusta taajuustasossa suoritettavaan iteratiivisen kanavakorjaimen konvergenssiominaisuuksiin xtrinsic information transfer (EXIT) -analyysin avulla. Työssä ehdotetaan uudenlaista EXIT-analyysi-pohjaista lähetystehon minimointimenetelmää yhden kantoaallon MIMO-lähetykseen käyttäen iteratiivista taajuustason SC-MMSE-kanavakorjainta. Menetelmä ottaa huomioon iteratiivisen kanavakorjaimen konvergenssiominaisuudet. Ehdotettu convergence constrained power allocation (CCPA) -menetelmä erottaa tilatason häiriön lähetteiden välillä hyödyntäen singular value decomposition (SVD) -tekniikkaa ja minimoi lähetystehon ja saavuttaa samalla keskinäisinformaatiotavoitteet jokaiselle lähetteelle iteraatioiden jälkeen vastaanottimessa. Lähetystehon minimointiongelma voidaan muotoilla konveksiksi optimointiongelmaksi. Kahden keskinäisinformaatiorajoitteen erityistapaukselle johdetaan Lagrangen duaalifunktio ja ratkaistaan sen duaalifunktio. Työssä kehitetään lisäksi kaksi CCPA-pohjaista heuristista menetelmää. Numeeriset tulokset osoittavat ehdotettujen CCPA-pohjaisten menetelmien suoriutuvan paremmin verrattuna olemassa oleviin menetelmiin
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Iltis, Ronald A. "Decoding and Turbo Equalization for LDPC Codes Based on Nonlinear Programming." International Foundation for Telemetering, 2010. http://hdl.handle.net/10150/605945.
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ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, CaliforniaDecoding and Turbo Equalization (TEQ) algorithms based on the Sum-Product Algorithm (SPA) are well established for LDPC codes. However there is increasing interest in linear and nonlinear programming (NLP)-based decoders which may offer computational and performance advantages over the SPA. We present NLP decoders and Turbo equalizers based on an Augmented Lagrangian formulation of the decoding problem. The decoders update estimates of both the Lagrange multipliers and transmitted codeword while solving an approximate quadratic programming problem. Simulation results show that the NLP decoder performance is intermediate between the SPA and bit-flipping algorithms. The NLP may thus be attractive in some applications as it eliminates the tanh/atanh computations in the SPA.
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Le, Bidan Raphaël. "Turbo-equalization for bandwidth-efficient digital communications over frequency-selective channels." Rennes, INSA, 2003. http://www.theses.fr/2003ISAR0012.
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Cette thèse traite de la combinaison des fonctions d'égalisation et décodage pour les transmissions haut-débits avec modulations codées sur canaux sélectifs en fréquence. Nous considérons la Turbo-Egalisation, qui instaure un échange itératif d'information entre l'égaliseur et le décodeur. Nous étudions dans un premier temps le turbo-égaliseur reposant sur le critère maximum-a-posteriori, et montrons que ce récepteur offre des gains de performances importants en comparaison avec les récepteurs traditionnels. Nous considérons ensuite une seconde classe de turbo-égaliseurs de moindre complexité reposant sur des égaliseurs à base de filtres linéaires, optimisés selon le critère de la minimisation de l'erreur quadratique moyenne (MEQM). Nos études montrent que ce récepteur constitue une solution attractive pour les transmissions à grande efficacité spectrale sur canaux sélectifs en fréquence. Finalement, nous présenterons la mise en oeuvre d'un turbo-égaliseur MEQM sur un DSP virgule-fixe.
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Doan, Dung Ngoc. "Design and analysis of iteratively decodable codes for ISI channels." Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/2754.
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Recent advancements in iterative processing have allowed communication systems to perform close to capacity limits withmanageable complexity.For manychannels such as the AWGN and flat fading channels, codes that perform only a fraction of a dB from the capacity have been designed in the literature. In this dissertation, we will focus on the design and analysis of near-capacity achieving codes for another important class of channels, namely inter-symbol interference (ISI)channels. We propose various coding schemes such as low-density parity-check (LDPC) codes, parallel and serial concatenations for ISI channels when there is no spectral shaping used at the transmitter. The design and analysis techniques use the idea of extrinsic information transfer (EXIT) function matching and provide insights into the performance of different codes and receiver structures. We then present a coding scheme which is the concatenation of an LDPC code with a spectral shaping block code designed to be matched to the channel??s spectrum. We will discuss how to design the shaping code and the outer LDPC code. We will show that spectral shaping matched codes can be used for the parallel concatenation to achieve near capacity performance. We will also discuss the capacity of multiple antenna ISI channels. We study the effects of transmitter and receiver diversities and noisy channel state information on channel capacity.
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Iltis, Ronald A. "Turbo Equalization for OFDM over the Doubly-Spread Channel using Nonlinear Programming." International Foundation for Telemetering, 2011. http://hdl.handle.net/10150/595779.
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ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, NevadaOFDM has become the preferred modulation format for a wide range of wireless networks including 802.11g, 802.16e (WiMAX) and 4G LTE. For multipath channels which are time-invariant during an OFDM symbol duration, near-optimal demodulation is achieved using the FFT followed by scalar equalization. However, demodulating OFDM on the doubly-spread channel remains a challenging problem, as time-variations within a symbol generate intercarrier interference. Furthermore, demodulation and channel estimation must be effectively combined with decoding of the LDPC code in the 4G-type system considered here. This paper presents a new Turbo Equalization (TEQ) decoder, detector and channel estimator for OFDM on the doubly-spread channel based on nonlinear programming. We combine the Penalty Gradient Projection TEQ with a MMSE-type channel estimator (PGP-TEQ) that is shown to yield a convergent algorithm. Simulation results are presented comparing conventional MMSE TEQ using the Sum Product Algorithm (MMSE-SPA-TEQ) with the new PGP-TEQ for doubly-spread channels.
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Fuchs-Lautensack, Martin. "Advances in multi-user scheduling and turbo equalization for wireless MIMO systems." Ilmenau ISLE, 2009. http://d-nb.info/995974241/04.
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Assegu, Wannaw, and Ibrahim Fofanah. "Performance of Turbo Coded OFDM Modulation over an Aeronautical Channel." International Foundation for Telemetering, 2012. http://hdl.handle.net/10150/581818.
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The main objectives of Integrated Network Enhanced Telemetry (iNET) are increased data rate and improved spectral efficiency. In this paper we propose the transmission scheme for the physical layer to be coded Quadrature Amplitude Modulation-Orthogonal Frequency Division Multiplexing (QAM OFDM) which enables high data rates and spectrum efficiency. However in high mobility scenarios, the channel is time-varying the receiver design is more challenging. In this paper pilot-assisted channel estimation is used at the receiver, with turbo coding to enhance the performance; while the effect of inter symbol interference (ISI) is mitigated by cyclic prefix. The focus of this paper is to evaluate the performance of OFDM with QAM over an aeronautical channel. The M-QAM with OFDM provides a higher data rate than QPSK hence it is chosen in this paper. The implementation is done using Inverse Fast Fourier Transform (IFFT) and the Fast Fourier Transform (FFT). This paper considers how the performance of Coded QAM OFDM can be enhanced using equalization to compensate for inter symbol interference, and using turbo coding for error correction.
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Silva, Fábio José. "Design and performance evaluation of turbo FDE receivers." Master's thesis, Faculdade de Ciências e Tecnologia, 2010. http://hdl.handle.net/10362/4975.
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Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Electrotécnica e de ComputadoresIn recent years, block transmission techniques were proposed and developed for broadband wireless communication systems, which have to deal with strongly frequency-selective fading channels. Techniques like Orthogonal Frequency-Division Multiplexing (OFDM)and Single Carrier with Frequency Domain Equalization (SC-FDE) are able to provide high bit rates despite the channel adversities. In this thesis we concentrate on the study of single carrier block transmission techniques considering receiver structures suitable to scenarios with strongly time-dispersive channels. CP-assisted (Cycle Pre x) block transmission techniques are employed to cope with frequency selective channels, allowing cost-e ective implementations through FFT-based (Fast Fourier Transform) signal processing. It is investigated the impact of the number of multipath components as well as the diversity order on the asymptotic performance of SC-FDE schemes. We also propose a receiver structure able to perform a joint detection and channel estimation method, in which it is possible to combine the channel estimates, based on training sequences, with decision-directed channel estimates. A study about the impact of the correlation factor estimation in the performance of Iterative Block-Decision Feedback Equalizer (IB-DFE) receivers is also presented.
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Fuchs-Lautensack, Martin [Verfasser]. "Advances in multi-user scheduling and turbo equalization for wireless MIMO systems / Martin Fuchs-Lautensack.ISLE." Ilmenau : ISLE, 2009. http://d-nb.info/99975128X/34.
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Wavegedara, Kapila Chandika B. "Advanced receivers for space-time block-coded single-carrier transmissions over frequency-selective fading channels." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/620.
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In recent years, space-time block coding (STBC) has emerged as an effective transmit-diversity technique to combat the detrimental effects of channel fading. In addition to STBC, high-order modulation schemes will be used in future wireless communication systems aiming to provide ubiquitous-broadband wireless access. Hence, advanced receiver schemes are necessary to achieve high performance. In this thesis, advanced and computationally-efficient receiver schemes are investigated and developed for single-carrier space-time (ST) block-coded transmissions over frequency-selective fading (FSF) channels.
First, we develop an MMSE-based turbo equalization scheme for Alamouti ST block-coded systems. A semi-analytical method to estimate the bit error rate (BER) is devised. Our results show that the proposed turbo equalization scheme offers significant performance improvements over one-pass equalization. Second, we analyze the convergence behavior of the proposed turbo equalization scheme for Alamouti ST block-coded systems using the extrinsic information transfer (EXIT)-band chart technique.
Third, burst-wise (BW)-STBC is applied for uplink transmission over FSF channels in block-spread-CDMA systems with multiuser interference-free reception. The performances of different decision feedback sequence estimation (DFSE) schemes are investigated. A new scheme combining frequency-domain (FD) linear equalization and modified unwhitened-DFSE is proposed. The proposed scheme is very promising as the error-floor behavior observed in the existing unwhitened DFSE schemes is eliminated.
Fourth, we develop a FD-MMSE-based turbo equalization scheme for the downlink of ST block-coded CDMA systems. We adopt BW-STBC instead of Alamouti symbol-wise (SW)-STBC considered for WCDMA systems and demonstrate its superior performance in FSF channels. Block spreading is shown to be more desirable than conventional spreading to improve performance using turbo equalization. We also devise approximate implementations (AprxImpls) that offer better trade-offs between performance and complexity. Semi-analytical upper bounds on the BER are derived.
Fifth, turbo multicode detection is investigated for ST block-coded downlink transmission in DS-CDMA systems. We propose symbol-by-symbol and chip-by-chip FD-MMSE-based multicode detectors. An iterative channel estimation scheme is also proposed. The proposed turbo multicode detection scheme offers significant performance improvements compared with non-iterative multicode detection. Finally, the impact of channel estimation errors on the performance of MMSE-based turbo equalization in ST block-coded CDMA systems is investigated.
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Tamma, Raja Venkatesh. "Iterative equalization and decoding using reduced-state sequence estimation based soft-output algorithms." Texas A&M University, 2004. http://hdl.handle.net/1969.1/283.
Full textAbstract:
We study and analyze the performance of iterative equalization and decoding (IED) using an M-BCJR equalizer. We use bit error rate (BER), frame error rate simulations and extrinsic information transfer (EXIT) charts to study and compare the performances of M-BCJR and BCJR equalizers on precoded and non-precoded channels. Using EXIT charts, the achievable channel capacities with IED using the BCJR, M-BCJR and MMSE LE equalizers are also compared. We predict the BER performance of IED using the M-BCJR equalizer from EXIT charts and explain
the discrepancy between the observed and predicted performances by showing that the extrinsic outputs of the $M$-BCJR algorithm are not true logarithmic-likelihood ratios (LLR's). We show that the true LLR's can be estimated if the
conditional distributions of the extrinsic outputs are known and finally we design a practical estimator for computing the true LLR's from the extrinsic outputs
of the M-BCJR equalizer.
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Minkov, Lyubomir L. "EXPERIMENTAL DEMONSTRATION OF MITIGATION OF LINEAR AND NONLINEAR IMPAIRMENTS IN FIBER-OPTIC COMMUNICATION SYSTEMS BY LDPC-CODED TURBO EQUALIZATION." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/194082.
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The ever-increasing demands for transmission capacity are the cause for the quick evolution of optical communication systems. Channel transmission at 100 Gb/s is already being considered by network operators. The major transmission impairments at these high rates are intra-channel and inter-channel nonlinearities, nonlinear phase noise, and polarization mode dispersion. By implementing LDPC-coded modulation schemes with soft decoding and Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm for equalization we have demonstrated significant improvements in system performance experiencing several impairments simultaneously. The new turbo-equalization scheme is used as a mean to simultaneously mitigate both linear and nonlinear impairments. This approach is general and applicable to both direct and coherent detection.We provide comprehensive study of LDPC codes suitable for implementation in high-speed optical transmission systems. We determine channel capacity based on the forward step of the BCJR algorithm and show that by using LDPC codes we can closely approach the maximum transmission capacity that is possible. We propose the multilevel maximum a posteriori probability (MAP) turbo equalization scheme based on multilevel BCJR algorithm and an LDPC decoder, which considers independent symbols transmitted over both polarizations as two dimensional super-symbols. The use of multilevel modulation schemes provide higher spectral efficiency, while all related signal processing is performed at lower symbol rates, where dealing with PMD compensation and fiber nonlinearities mitigation is more manageable. We show significant improvement in system performance over a system employing an equalizer that considers symbols transmitted in different polarizations as independent.
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Großmann, Marcus [Verfasser], Reiner [Akademischer Betreuer] Thomä, Volker [Akademischer Betreuer] Kühn, and Werner [Akademischer Betreuer] Teich. "Transmission strategies for broadband wireless systems with MMSE turbo equalization / Marcus Großmann. Gutachter: Volker Kühn ; Werner Teich. Betreuer: Reiner Thomä." Ilmenau : Universitätsbibliothek Ilmenau, 2012. http://d-nb.info/1065829183/34.
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Großmann, Marcus Verfasser], Reiner [Akademischer Betreuer] [Thomä, Volker [Akademischer Betreuer] Kühn, and Werner [Akademischer Betreuer] Teich. "Transmission strategies for broadband wireless systems with MMSE turbo equalization / Marcus Großmann. Gutachter: Volker Kühn ; Werner Teich. Betreuer: Reiner Thomä." Ilmenau : Universitätsbibliothek Ilmenau, 2012. http://nbn-resolving.de/urn:nbn:de:gbv:ilm1-2012000014.
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Radhakrishnan, Rathnakumar. "Detection and Decoding for Magnetic Storage Systems." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/194396.
Full textAbstract:
The hard-disk storage industry is at a critical time as the current technologies are incapable of achieving densities beyond 500 Gb/in2, which will be reached in a few years. Many radically new storage architectures have been proposed, which along with advanced signal processing algorithms are expected to achieve much higher densities. In this dissertation, various signal processing algorithms are developed to improve the performance of current and next-generation magnetic storage systems.Low-density parity-check (LDPC) error correction codes are known to provide excellent performance in magnetic storage systems and are likely to replace or supplement currently used algebraic codes. Two methods are described to improve their performance in such systems. In the first method, the detector is modified to incorporate auxiliary LDPC parity checks. Using graph theoretical algorithms, a method to incorporate maximum number of such checks for a given complexity is provided. In the second method, a joint detection and decoding algorithm is developed that, unlike all other schemes, operates on the non-binary channel output symbols rather than input bits. Though sub-optimal, it is shown to provide the best known decoding performance for channels with memory more than 1, which are practically the most important.This dissertation also proposes a ternary magnetic recording system from a signal processing perspective. The advantage of this novel scheme is that it is capable of making magnetic transitions with two different but predetermined gradients. By developing optimal signal processing components like receivers, equalizers and detectors for this channel, the equivalence of this system to a two-track/two-head system is determined and its performance is analyzed. Consequently, it is shown that it is preferable to store information using this system, than to store using a binary system with inter-track interference. Finally, this dissertation provides a number of insights into the unique characteristics of heat-assisted magnetic recording (HAMR) and two-dimensional magnetic recording (TDMR) channels. For HAMR channels, the effects of laser spot on transition characteristics and non-linear transition shift are investigated. For TDMR channels, a suitable channel model is developed to investigate the two-dimensional nature of the noise.
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Charaf, Akl. "Etudes de récepteurs MIMO-LDPC itératifs." Phd thesis, Télécom ParisTech, 2012. http://pastel.archives-ouvertes.fr/pastel-00913457.
Full textAbstract:
L'objectif de cette thèse est l'étude de récepteurs MIMO LDPC itératifs. Les techniques MIMO permettent d'augmenter la capacité des réseaux sans fil sans la nécessité de ressources fréquentielles additives. Associées aux schémas de modulations multiporteuses CP-OFDM, les techniques MIMO sont ainsi devenues la pierre angulaire pour les systèmes sans fil à haute efficacité spectrale. La réception optimale peut être obtenue à l'aide d'une réception conjointe (Egalisation/Décodage). Étant très complexe, la réception conjointe n'est pas envisagée et l'égalisation et le décodage sont réalisés disjointement au coût d'une dégradation significative en performances. Entre ces deux solutions, la réception itérative trouve son intérêt pour sa capacité à s'approcher des performances optimales avec une complexité réduite. La conception de récepteurs itératifs pour certaines applications, de type WiFi à titre d'exemple doit respecter la structure du code imposée par la norme. Ces codes ne sont pas optimisés pour des récepteurs itératifs. En observant l'effet du nombre d' itérations dans le processus itératif, on montre par simulation que l'ordonnancement des itérations décodage LDPC/Turbo-égalisation joue un rôle important dans la complexité et le délai du récepteur. Nous proposons de définir des ordonnancements permettant de réduire la complexité globale du récepteur. Deux approches sont proposées, une approche statique ainsi qu'une autre dynamique. Ensuite nous considérons un système multi-utilisateur avec un accès multiple par répartition spatiale. Nous étudions l'intérêt de la réception itérative dans ce contexte tenant en compte la différence de puissance signale utile/interférence.
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Abelló, Barberán Albert. "Turbo égalisation à haute performance pour la transmission par satellite au-delà de la cadence de Nyquist." Thesis, Toulouse, ISAE, 2018. http://www.theses.fr/2018ESAE0025/document.
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Le contexte de ces travaux de thèse est la transmission dite faster-than-Nyquist (FTN). Cette technique propose d’augmenter l’efficacité spectrale en augmentant lerythme de transmission au-delà de la bande occupée par le signal émis, indépendamment de laconstellation choisie. Il a été montré que le FTN offre des taux d’information supérieurs à ceuxdes systèmes de Nyquist. Toutefois, le non respect du critère de Nyquist entraîne l’apparitiond’interférence entre symboles et des techniques de réception appropriées doivent être utilisées.La technique de réception dite channel shortening consiste à filtrer la séquence reçue puis àcalculer des probabilités symbole a posteriori approximatives à l’aide de l’algorithme BCJRen considérant une réponse de canal modifiée, de longueur réduite. Dans la littérature, enprésence d’information a priori, les filtres du récepteur channel shortening sont optimiséssous critère de maximisation de l’information mutuelle généralisée (IMG) en utilisant desméthodes numériques. Nous proposons dans ces travaux de thèse une solution analytiquepour l’ensemble des filtres channel shortening sous critère de maximisation de l’IMG lorsquele récepteur dispose d’information a priori. Nous démontrons ensuite que l’égaliseur au sens dela minimisation de l’erreur quadratique moyenne (MMSE) est un cas particulier de l’égaliseurchannel shortening. Dans le cadre de la turbo égalisation, nous étudions ensuite un estimateurpermettant d’obtenir l’information a priori à partir de l’information en sortie du décodeurcorrecteur d’erreurs. Finalement, nous évaluons les performances du système complet aveccodage correcteur d’erreurs sur canal à bruit additif blanc GaussienIn order to increase the spectral efficiency of digital communications systems,the faster-than-Nyquist (FTN) approach increases the symbol rate beyond the occupied bandwidthof the transmitted signal independently of the constellation type and size. It has beenshown that information rates of FTN systems are greater than those of Nyquist systems.However, the non-compliance of the Nyquist criterion causes inter-symbol interference to appearand therefore appropriate reception techniques must be used. At reception, the channelshortening approach consists on a receiving filter followed by a BCJR algorithm computingapproximate a posteriori symbol probabilities by considering a modified channel response ofreduced length. In the literature, the channel shortening receiving filters are chosen to maximizethe generalized mutual information (GMI). Such optimization is performed by usingnumerical optimization methods. In this PhD thesis, we propose a closed-form solution forall channel shortening filters considering the GMI maximization criterion. We show that theminimum mean square error (MMSE) equalizer is a particular case of the channel shorteningapproach. Within the frame of turbo equalization, we then study a suitable estimator allowingto obtain symbols a priori information from the information provided by the a decoder. Finally,we study the performance of the complete system with channel coding over an additivewhite Gaussian noise channel
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Deleu, Thibault. "Digital predistortion and equalization of the non-linear satellite communication channel." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209212.
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In satellite communications, non-linear interference is created by the non-linear power amplifier aboard the satellite. Even in the case of a memoryless power amplifier, the channel is a non-linear system with memory due to the presence of linear filters on ground and aboard the satellite. The non-linear interference degrades the system performance, especially when considering high-order modulations or in case of several signals being amplified by the same power amplifier. In this thesis, we have proposed algorithms at the transmitter and at the receiver to digitally compensate this interference. In particular, a new predistortion algorithm has been proposed, which significantly improves state-of-the-art algorithms. Since the complexity of this algorithm is an issue, low-complexity algorithms have also been proposed and achieve almost the same performance as the initial algorithm. We have also proposed joint predistortion and turbo-equalization algorithms to further improve the system performance. / En communications par satellite, de l’interférence non-linéaire est créée par l’amplificateur de puissance non-linéaire à bord du satellite. Même si l’amplificateur peut être considéré comme sans mémoire, le canal est malgré tout un système non-linéaire avec mémoire de par la présence de filtres linéaires au sol ou à bord du satellite. L'interférence non-linéaire dégrade les performances du système, en particulier lorsqu’on considère des modulations d’ordre élevé ou plusieurs signaux amplifiés par le même amplificateur de puissance. Dans cette thèse, nous avons proposé des algorithmes à l’émetteur et au récepteur pour compenser numériquement cette interférence. En particulier, nous avons proposé un nouvel algorithme de prédistorsion qui améliore de façon significative les algorithmes de l’état-de-l’art. La complexité de l’algorithme étant très élevée, nous avons proposé des algorithmes de plus faible complexité atteignant pratiquement les mêmes performances par rapport à l’algorithme initial. Nous avons aussi proposé des algorithmes de prédistorsion et d’égalisation conjointes, permettant d'atteindre des performances plus élevées qu'avec la prédistorsion seule.Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Nhan, Nhat-Quang. "Optimisation de précodeurs linéaires pour les systèmes MIMO à récepteurs itératifs." Thesis, Brest, 2016. http://www.theses.fr/2016BRES0062/document.
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Les standards « Long-term evolution » (LTE) et LTE-Advanced (LTE-A) devraient influencer fortement l’avenir de la cinquième génération (5G) des réseaux mobiles. Ces normes exigent de hauts débits de données et une qualité de service de très bon niveau, ce qui permet d’assurer un faible taux d’erreur, avec une faible latence. Par ailleurs, la complexité doit être limitée. Dans le but de déterminer des solutions technologiques modernes qui satisfont ces contraintes fortes, nous étudions dans la thèse des systèmes de communication sans fil MIMO codés. D’abord, nous imposons un simple code convolutif récursif systématique (RSC) pour limiter la complexité et la latence. En considérant des récepteurs itératifs, nous optimisons alors la performance en termes de taux d’erreur de ces systèmes en définissant un précodage linéaire MIMO et des techniques de mapping appropriées. Dans la deuxième partie de la thèse, nous remplaçons le RSC par un LDPC non-binaire (NB-LDPC). Nous proposons d’utiliser les techniques de précodage MIMO afin de réduire la complexité des récepteurs des systèmes MIMO intégrant des codes NB-LDPC. Enfin, nous proposons également un nouvel algorithme de décodage itératif à faible complexité adapté aux codes NB-LDPCThe long-term evolution (LTE) and the LTE-Advanced (LTE-A) standardizations are predicted to play essential roles in the future fifth-generation (5G) mobile networks. These standardizations require high data rate and high quality of service, which assures low error-rate and low latency. Besides, as discussed in the recent surveys, low complexity communication systems are also essential in the next 5G mobile networks. To adapt to the modern trend of technology, in this PhD thesis, we investigate the multiple-input multiple-output (MIMO) wireless communication schemes. In the first part of this thesis, low-complex forward error correction (FEC) codes are used for low complexity and latency. By considering iterative receivers at the receiver side, we exploit MIMO linear precoding and mapping methods to optimize the error-rate performance of these systems. In the second part of this thesis, non-binary low density parity check (NB-LDPC) codes are investigated. We propose to use MIMO precoders to reduce the complexity for NB-LDPC encoded MIMO systems. A novel low complexity decoding algorithm for NB-LDPC codes is also proposed at the end of this thesis
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Gazi, Orhan. "Parallelized Architectures For Low Latency Turbo Structures." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608110/index.pdf.
Full textAbstract:
In this thesis, we present low latency general concatenated code structures
suitable for parallel processing. We propose parallel decodable serially concatenated
codes (PDSCCs) which is a general structure to construct many
variants of serially concatenated codes. Using this most general structure we
derive parallel decodable serially concatenated convolutional codes (PDSCCCs).
Convolutional product codes which are instances of PDSCCCs are
studied in detail. PDSCCCs have much less decoding latency and show almost
the same performance compared to classical serially concatenated convolutional
codes. Using the same idea, we propose parallel decodable turbo
codes (PDTCs) which represent a general structure to construct parallel concatenated
codes. PDTCs have much less latency compared to classical turbo
codes and they both achieve similar performance.
We extend the approach proposed for the construction of parallel decodable
concatenated codes to trellis coded modulation, turbo channel equalization,
and space time trellis codes and show that low latency systems can be
constructed using the same idea. Parallel decoding operation introduces new problems in implementation. One such problem is memory collision which occurs when multiple decoder units attempt accessing the same memory device. We propose novel interleaver structures which prevent the memory collision problem while achieving performance close to other interleavers.
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Gulmez, Baskoy Ulku. "A Turbo Detection Scheme For Egprs." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1259415/index.pdf.
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Enhanced Data Rates for Global Evolution (EDGE) is one of the 3G wireless communication standards, which provides higher data rates by adopting 8-PSK modulation in TDMA system infrastructure of GSM. In this thesis, a turbo detection receiver for Enhanced General Packet Radio Services (EGPRS) system, which is the packet switching mode of EDGE, is studied. In turbo detection, equalization and channel decoding are performed iteratively. Due to 8-ary alphabet of EGPRS modulation, full state trellis based equalization, as usually performed in GSM, is too complex not only for turbo detection but even for conventional equalizationso suboptimum schemes have to be considered. The Delayed Decision Feedback Sequence Estimation (DDFSE) is chosen as suboptimal and less complex trellis based scheme and it is examined as a conventional equalization technique firstly. It is shown that the DDFSE has a fine tradeoff between performance and complexity and can be a promising candidate for EGPRS. Then it is employed to reduce the number of the trellis state in turbo detection. Max-log-MAP algorithm is used for soft output calculations of both SISO equalizer and SISO decoder. Simulation results illustrate that proposed turbo detection structure improves bit error rate and block error rate performance of the receiver with respect to the conventional equalization and decoding scheme. The iteration gain varies depending on modulation type and coding rate of Modulation Coding Scheme (MCS) employed in EGPRS.
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Arthur, Rangel 1977. "Novas propostas para otimização de receptores de TV digital baseados em OFDM em ambientes de redes de frequencia unica regionais." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/261230.
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Orientador: Yuzo IanoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
Made available in DSpace on 2018-08-08T10:21:08Z (GMT). No. of bitstreams: 1 Arthur_Rangel_D.pdf: 3675976 bytes, checksum: 65350df75e5a9588b1366325ac95ef62 (MD5) Previous issue date: 2007
Resumo: Esta tese trata da otimização de receptores de TV Digital baseados em OFDM, com avaliação de desempenho em redes de retransmissão em freqüência única (SFN . Single Frequency Networks) regionais. Tal ambiente facilita a distribuição de canais, porém possui características que dificultam o trabalho do receptor. São tratados, inicialmente, de projetos de filtros canceladores de elos de realimentação em estações retransmissoras, que ocorrem quando a antena de transmissão interfere na antena de recepção. Um novo filtro, baseado em técnicas que utilizam informação temporal é proposto. Novas propostas são feitas para as partes de sincronismo, estimação e equalização de canal, e codificação/decodificação. Uma técnica, vinda da teoria de reconhecimento de padrões, é aplicada para diminuição da complexidade no processo de sincronismo temporal. Um sistema de estimação de canal 2D e equalização adaptativa, usando o LMS (Least Mean Square), é comparado com técnicas clássicas da literatura, e um ganho significativo é encontrado. Como novo esquema de codificação e decodificação é proposto um esquema iterativo, baseado em códigos turbo, com número reduzido de iterações. Tal código melhora o desempenho do sistema em relação ao uso combinado dos decodificadores Viterbi e Reed Solomon. Todas as propostas são combinadas para se avaliar o desempenho do receptor diante de condições típicas de SFN e multicaminhos típicos em recepção de TV do Brasil
Abstract: This thesis deals with the optimization of Digital TV receivers based on OFDM, with performance evaluation in regional single frequency networks (SFN). Such environment facilitates the channel distribution, however its characteristics degrade the receiver operation. Initially, projects of loop canceller filters in relay stations are treated, and they are necessary when the transmission antenna causes interference on reception antenna. A new filter, based on time information is proposed. New proposals are made for the synchronism, channel estimation and equalization, and coding/decoding. One technique, coming from the pattern recognition theory, is applied for complexity reduction in the process of time synchronism. A 2D channel estimation system and adaptive equalization, using LMS (Least Mean Square), is compared to classical techniques in the literature, and a significant gain is achieved. As a new coding and decoding scheme, an iterative system based on turbo codes is used with reduced number of iterations. Such code improves the system performance when compared to the Viterbi and Reed Solomon concatenated decoders. The proposals are combined and the performance of the proposed receiver is evaluated on typical conditions of SFN and on typical multipaths for TV reception in Brazil
Doutorado
Telecomunicações e Telemática
Doutor em Engenharia Elétrica
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Charaf, Akl. "Etudes de récepteurs MIMO-LDPC itératifs." Electronic Thesis or Diss., Paris, ENST, 2012. http://www.theses.fr/2012ENST0017.
Full textAbstract:
L’objectif de cette thèse est l’étude de récepteurs MIMO LDPC itératifs. Les techniques MIMO permettent d’augmenter la capacité des réseaux sans fil sans la nécessité de ressources fréquentielles additives. Associées aux schémas de modulations multiporteuses CP-OFDM, les techniques MIMO sont ainsi devenues la pierre angulaire pour les systèmes sans fil à haute efficacité spectrale. La réception optimale peut être obtenue à l’aide d’une réception conjointe (Egalisation/Décodage). Étant très complexe, la réception conjointe n’est pas envisagée et l’égalisation et le décodage sont réalisés disjointement au coût d’une dégradation significative en performances. Entre ces deux solutions, la réception itérative trouve son intérêt pour sa capacité à s’approcher des performances optimales avec une complexité réduite. La conception de récepteurs itératifs pour certaines applications, de type WiFi à titre d’exemple doit respecter la structure du code imposée par la norme. Ces codes ne sont pas optimisés pour des récepteurs itératifs. En observant l’effet du nombre d' itérations dans le processus itératif, on montre par simulation que l’ordonnancement des itérations décodage LDPC/Turbo-égalisation joue un rôle important dans la complexité et le délai du récepteur. Nous proposons de définir des ordonnancements permettant de réduire la complexité globale du récepteur. Deux approches sont proposées, une approche statique ainsi qu'une autre dynamique. Ensuite nous considérons un système multi-utilisateur avec un accès multiple par répartition spatiale. Nous étudions l’intérêt de la réception itérative dans ce contexte tenant en compte la différence de puissance signale utile/interférenceThe aim of this thesis is to address the design of iterative MIMO receivers using LDPC Error Correcting codes. MIMO techniques enable capacity increase in wireless networks with no additional frequency ressources. The associationof MIMO with multicarrier modulation techniques OFDM made them the cornerstone of emerging high rate wireless networks. Optimal reception can be achieved using joint detection and decoding at the expense of a huge complexity making it impractical. Disjoint reception is then the most used. The design of iterative receivers for some applications using LDPC codes like Wifi (IEEE 802.11n) is constrained by the standard code structure which is not optimized for such kind of receivers. By observing the effect of the number of iterations on performance and complexity we underline the interest of scheduling LDPC decoding iterations and turboequalization iterations. We propose to define schedules for the iterative receiver in order to reduce its complexity while preserving its performance. Two approaches are used : static and dynamic scheduling. The second part of this work is concerns Multiuser MIMO using Spatial Division Multiple Access. We explore and evaluate the interest of using iterative reception to cancel residual inter-user interference
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Hwang, Sung Jun. "Communication over Doubly Selective Channels: Efficient Equalization and Max-Diversity Precoding." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1261506237.
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Lahbabi, Naila. "Faster than Nyquist transceiver design : algorithms for a global transmission-reception enhancement." Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2017. http://www.theses.fr/2017IMTA0017/document.
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La croissance exponentielle du trafic de données sans fils, causée par l'Internet mobile et les smartphones, contraint les futurs systèmes radio à inclure des modulations/formes d'ondes plus avancées offrant un débit plus élevé et une utilisation efficace des ressources spectrales. Les transmissions dites Faster-Than-Nyquist (FTN), introduites en 1975, sont parmi les meilleurs candidates pour répondre à ces besoins. En transmettant les symboles à une cadence plus rapide que celle définie par le critère de Nyquist, FTN peut théoriquement augmenter le débit mais en introduisant des interférences en contrepartie. Dans cette thèse, nous explorons le concept des transmissions FTN à travers un canal AWGN (Additive White Gaussian Noise) dans le contexte des modulations OFDM/OQAM (Orthogonal Frequency Division Multiplexing with Offset Quadrature Amplitude Modulation).L'objectif principal de cette thèse est de présenter un système OFDM/OQAM qui permet de transmettre l'information au-delà de la cadence de Nyquist tout en tenant en compte la complexité globale du système. Tout d'abord, nous proposons une nouvelle implémentation efficace des systèmes OFDM/OQAM appliquant le concept FTN, désignée ici par FTN-OQAM, qui garde la même complexité que les systèmes OFDM/OQAM et qui permet un gain en débit très proche du gain théorique. Vu que la condition de Nyquist n'est plus respectée, le signal transmis est maintenant perturbé par des interférences. Pour remédier à ce problème, nous proposons un récepteur basé sur le principe de l'égalisation linéaire sous le critère minimum erreur quadratique moyenne avec annulation d'interférences appelé MMSE LE-IC. Le but de notre système est d'augmenter le débit de transmission, ce qui signifie que des constellations d'ordres élevés seront ciblées. Dans ce contexte, le MMSE LE-IC, dont la complexité est indépendante de la constellation, représente un bon compromis entre efficacité et complexité. Puisque la modulation OFDM/OQAM utilise différents types de formes d'ondes, nous proposons pour plusieurs d'entre elles un algorithme pour déterminer la valeur minimale du facteur d'accélération, en fonction de l'ordre de constellation, qui apporte un gain en efficacité spectrale tout en gardant les mêmes performances que les systèmes respectant le critère de Nyquist à un SNR fixé. Ensuite, nous étudions l'amélioration du traitement itératif de l'émetteur-récepteur. La méthode proposée consiste à combiner un précodeur avec le système FTN-OQAM afin de réduire les interférences causées par du FTN à l'émission. Nous proposons un modèle de précodage dispersé, car il est difficile de précoder conjointement tous les symboles transmis. Nous présentons trois familles de précodeurs avec les récepteurs correspondants. En outre, nous modifions différents blocs de l'émetteur FTN-OQAM tels que le codage canal, le mappage des bits et le mappage des symboles afin d'améliorer davantage le transmetteur FTN-OQAM. Les résultats présentés révèlent le potentiel important des systèmes proposésThe exponential growth of wireless data traffic driven by mobile Internet and smart devices constrains the future radio systems to include advanced modulations/waveforms offering higher data rates with more efficient bandwidth usage. One possibility is to violate the well known Nyquist criterion by transmitting faster than the Nyquist rate, i.e., using a technique also known as Faster-Than-Nyquist (FTN) signaling. Nyquist-based systems have the advantage of simple transmitter and receiver architectures at the detriment of bandwidth efficiency. The idea of signaling beyond the Nyquist rate to trade the interference-free transmission for more throughput goes back to 1975. In this dissertation, we investigate the concept of FTN signaling over Additive White Gaussian Noise (AWGN) channel in the context of Orthogonal Frequency Division Multiplexing with Offset Quadrature Amplitude Modulation OFDM/OQAM modulation.The main objective of our work is to present an OFDM/OQAM system signaling faster than the Nyquist one and explore its potential rate improvement while keeping under consideration the overall system complexity. First, we propose a new efficient FTN implementation of OFDM/OQAM systems, denoted by FTN-OQAM, that has the same complexity as OFDM/OQAM systems, while approaching very closely the FTN theoretical rate improvement. As the Nyquist condition is no longer respected, severe interference impacts the transmitted signals. To deal with the introduced interferences, we propose a turbo-like receiver based on Minimum Mean Square Error Linear Equalization and Interference Cancellation, named MMSE LE-IC. The aim of our system is to boost the transmission rate, which means that high constellation orders will be targeted. In this respect, the MMSE LE-IC, whose complexity is independent of the constellation, turns out to be a good candidate. Since OFDM/OQAM modulation can be equipped with different types of pulse shapes, we propose an algorithm to find, for different constellation orders, the minimum achieved FTN packing factor for various pulse shapes. Then, we aim at improving the iterative processing of the introduced transceiver. The proposed method involves combining a precoder with the FTN-OQAM system in order to remove FTN-induced interference at the transmitter. We also present a sparse precoding pattern as it is difficult to jointly precode all the transmitted symbols. We introduce three families of precoders along with the corresponding receivers. Furthermore, we propose several modifications of the FTN-OQAM transmitter concerning different blocks such as channel coding, bits mapping and symbols mapping to further enhance the FTN-OQAM transceiver design. Presented results reveal the significant potential of the proposed methods
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Nayak, Aravind Ratnakar. "Iterative Timing Recovery for Magnetic Recording Channels with Low Signal-to-Noise Ratio." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5018.
Full textAbstract:
Digital communication systems invariably employ an underlying analog communication channel. At the transmitter, data is modulated to obtain an analog waveform which is input to the channel. At the receiver, the output of the channel needs to be mapped back into the discrete domain. To this effect, the continuous-time received waveform is sampled at instants chosen by the timing recovery block. Therefore, timing recovery is an essential component of digital communication systems.
A widely used timing recovery method is based on a phase-locked loop (PLL), which updates its timing estimates based on a decision-directed device. Timing recovery performance is a strong function of the reliability of decisions, and hence, of the channel signal-to-noise ratio (SNR). Iteratively decodable error-control codes (ECCs) like turbo codes and LDPC codes allow operation at SNRs lower than ever before, thus exacerbating timing recovery.
We propose iterative timing recovery, where the timing recovery block, the equalizer and the ECC decoder exchange information, giving the timing recovery block access to decisions that are much more reliable than the instantaneous ones. This provides significant SNR gains at a marginal complexity penalty over a conventional turbo equalizer where the equalizer and the ECC decoder exchange information. We also derive the Cramer-Rao bound, which is a lower bound on the estimation error variance of any timing estimator, and propose timing recovery methods that outperform the conventional PLL and achieve the Cramer-Rao bound in some cases.
At low SNR, timing recovery suffers from cycle slips, where the receiver drops or adds one or more symbols, and consequently, almost always the ECC decoder fails to decode. Iterative timing recovery has the ability to corrects cycle slips. To reduce the number of iterations, we propose cycle slip detection and correction methods. With iterative timing recovery, the PLL with cycle slip detection and correction recovers most of the SNR loss of the conventional receiver that separates timing recovery and turbo equalization.
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Bayramoglu, Muhammet Fatih. "Sub-graph Approach In Iterative Sum-product Algorithm." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/3/12606550/index.pdf.
Full textAbstract:
Sum-product algorithm can be employed for obtaining the marginal probability
density functions from a given joint probability density function (p.d.f.). The sum-product
algorithm operates on a factor graph which represents the
dependencies of the random variables
whose joint p.d.f. is given.
The sum-product algorithm can not be operated on factor-graphs that contain
loops. For these factor graphs iterative sum-product algorithm is used.
A factor
graph which contains loops can be divided in to loop-free sub-graphs. Sum-product
algorithm can be operated in these loop-free sub-graphs and results of these sub-graphs can
be combined for obtaining the result of the whole factor graph in an iterative manner.
This method may increase the convergence rate of the algorithm significantly
while keeping the complexity
of an iteration and accuracy of the output constant.
A useful by-product of this research that is introduced in this thesis is a good
approximation to message calculation in factor nodes of the inter-symbol interference
(ISI) factor graphs. This approximation has a complexity that is linearly proportional with
the number of neighbors instead of being exponentially proportional. Using this
approximation and the sub-graph idea we have designed and simulated joint
decoding-equalization (turbo equalization) algorithm and obtained good results
besides the low complexity.
40
Nangare, Nitin Ashok. "Non-iterative joint decoding and signal processing: universal coding approach for channels with memory." Texas A&M University, 2003. http://hdl.handle.net/1969.1/3899.
Full textAbstract:
A non-iterative receiver is proposed to achieve near capacity performance on intersymbol
interference (ISI) channels. There are two main ingredients in the proposed
design. i) The use of a novel BCJR-DFE equalizer which produces optimal soft
estimates of the inputs to the ISI channel given all the observations from the channel
and L past symbols exactly, where L is the memory of the ISI channel. ii) The
use of an encoder structure that ensures that L past symbols can be used in the
DFE in an error free manner through the use of a capacity achieving code for a
memoryless channel. Computational complexity of the proposed receiver structure
is less than that of one iteration of the turbo receiver. We also provide the proof
showing that the proposed receiver achieves the i.i.d. capacity of any constrained
input ISI channel. This DFE-based receiver has several advantages over an iterative
(turbo) receiver, such as low complexity, the fact that codes that are optimized for
memoryless channels can be used with channels with memory, and finally that the
channel does not need to be known at the transmitter. The proposed coding scheme
is universal in the sense that a single code of rate r; optimized for a memoryless
channel, provides small error probability uniformly across all AWGN-ISI channels of
i.i.d. capacity less than r:
This general principle of a proposed non-iterative receiver also applies to other
signal processing functions, such as timing recovery, pattern-dependent noise whiten ing, joint demodulation and decoding etc. This makes the proposed encoder and
receiver structure a viable alternative to iterative signal processing. The results show
significant complexity reduction and performance gain for the case of timing recovery
and patter-dependent noise whitening for magnetic recording channels.
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Petit, Paul. "Turbo-equalization for QAM constellations." 2002. http://arrow.unisa.edu.au:8081/1959.8/46699.
Full textAbstract:
While the focus of this work is on turbo equalization, there is also an examination of equalization techniques including MMSE linear and DFE equalizers and Precoding. The losses and capacity associated with the ISI channel are also examined. Iterative decoding of concatenated codes is briefly reviewed and the MAP algorithm is explained.
42
Lin, Yung-Che, and 林雍哲. "Minimum Delay Scheduling for Turbo Equalization with Turbo Codes." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/r2j536.
Full textAbstract:
碩士國立高雄第一科技大學
電子與資訊工程研究所
96
The traditional turbo equalization basically is composed by a equalization series a Error-Correcting Codes decoder. When low SNR, the EXIT chart that the convergence tunnel to be unable to open, and the bit error rate can display not good. Above question can be solved effectively if the turbo equalization union turbo code( hereafter refers to as the double turbo equalization). Different the traditional turbo equalization, the double turbo equalization is a kind of turbo signal processor merges three soft processes which decoding way is complex and non-only. How to find the best decoding way, according to all kinds of demand is an interesting and important question. Brannstrom succeeded proposed the optimal scheduling of decoding way under the restriction that can only start a soft processor in once. Based on real time and the demand of high speed communication, how to find the minimum delay decoding way is an important subject and still a question not solved so far. Brannstrom’s proposed the best decoding way which has not still achieved the minimum delay and still had reduces the detention the space, due to the restriction can only start a soft processor in once. In this article, we have relaxed the limit of starting the number of the soft processor, and changes advance route of the double turbo equalization on the three domain EXIT chart, and proposed one kind of scheduling of minimum delay decoding way which be suitable for the double turbo equalization. The simulation result showed that, we proposed minimum delay scheduling can achieve restrains shorter than Brannstrom’s optimal scheduling. In turbo equalization union parallel (seriers) turbo code configuration, our method may effective reduce 12.5% (15%) delay time, when Es/No is equal 2dB(2.2dB) at a bit-error rate of 10-2.
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Lin, Yu-Cheng, and 林育丞. "Turbo Equalization And Turbo coding for MIMO-OFDM System." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/xr5qu7.
Full textAbstract:
碩士國立交通大學
電信工程系所
95
In this thesis, we focus on the outer receiver design for multiple-input-multiple output (MIMO) OFDM systems. The outer receiver mainly consists of a soft-bit demapper and an outer code decoder. The conventional approach considers these two devices separately, and cannot achieve true optimum performance. In the first part of the thesis, we study the application of turbo equalization technique in MIMO-OFDM systems. Using this approach, we can combine demapping and decoding in an iterative way. The conventional communication system often uses the bit-interleaved-coding modulation (BICM) scheme. However, the BICM scheme treats coding and modulation separately, and does not exploit the MIMO structure constraint. Tone-interleaved- coding-modulation (TICM) has been proposed to solve the problem. However, only the convolution code was considered. In the second part of the thesis, we propose to use the turbo code in the TICM scheme. Simulations with the IEEE 802.11n systems show that both the turbo equalization and the TICM schemes can significantly outperform conventional approaches.
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Myburgh, Hermanus Carel. "Low complexity turbo equalization using superstructures." Thesis, 2013. http://hdl.handle.net/2263/32814.
Full textAbstract:
In a wireless communication system the transmitted information is subjected to a number of impairments,
among which inter-symbol interference (ISI), thermal noise and fading are the most prevalent.
Owing to the dispersive nature of the communication channel, ISI results from the arrival of multiple
delayed copies of the transmitted signal at the receiver. Thermal noise is caused by the random
fluctuation on electrons in the receiver hardware, while fading is the result of constructive and destructive
interference, as well as absorption during transmission. To protect the source information,
error-correction coding (ECC) is performed in the transmitter, after which the coded information is
interleaved in order to separate the information to be transmitted temporally.
Turbo equalization (TE) is a technique whereby equalization (to correct ISI) and decoding (to correct
errors) are iteratively performed by iteratively exchanging extrinsic information formed by optimal
posterior probabilistic information produced by each algorithm. The extrinsic information determined
from the decoder output is used as prior information by the equalizer, and vice versa, allowing for
the bit-error rate (BER) performance to be improved with each iteration. Turbo equalization achieves
excellent BER performance, but its computational complexity grows exponentially with an increase in
channel memory as well as with encoder memory, and can therefore not be used in dispersive channels
where the channel memory is large. A number of low complexity equalizers have consequently been developed to replace the maximum a posteriori probability (MAP) equalizer in order to reduce the
complexity. Some of the resulting low complexity turbo equalizers achieve performance comparable
to that of a conventional turbo equalizer that uses a MAP equalizer. In other cases the low complexity
turbo equalizers perform much worse than the corresponding conventional turbo equalizer (CTE)
because of suboptimal equalization and the inability of the low complexity equalizers to utilize the
extrinsic information effectively as prior information.
In this thesis the author develops two novel iterative low complexity turbo equalizers. The turbo equalization
problem is modeled on superstructures, where, in the context of this thesis, a superstructure
performs the task of the equalizer and the decoder. The resulting low complexity turbo equalizers
process all the available information as a whole, so there is no exchange of extrinsic information
between different subunits. The first is modeled on a dynamic Bayesian network (DBN) modeling
the Turbo Equalization problem as a quasi-directed acyclic graph, by allowing a dominant connection
between the observed variables and their corresponding hidden variables, as well as weak connections
between the observed variables and past and future hidden variables. The resulting turbo equalizer is
named the dynamic Bayesian network turbo equalizer (DBN-TE). The second low complexity turbo
equalizer developed in this thesis is modeled on a Hopfield neural network, and is named the Hopfield
neural network turbo equalizer (HNN-TE). The HNN-TE is an amalgamation of the HNN maximum
likelihood sequence estimation (MLSE) equalizer, developed previously by this author, and an HNN
MLSE decoder derived from a single codeword HNN decoder. Both the low complexity turbo equalizers
developed in this thesis are able to jointly and iteratively equalize and decode coded, randomly interleaved information transmitted through highly dispersive multipath channels. The performance of both these low complexity turbo equalizers is comparable to that of the conventional
turbo equalizer while their computational complexities are superior for channels with long
memory. Their performance is also comparable to that of other low complexity turbo equalizers, but
their computational complexities are worse. The computational complexity of both the DBN-TE and
the HNN-TE is approximately quadratic at best (and cubic at worst) in the transmitted data block
length, exponential in the encoder constraint length and approximately independent of the channel
memory length. The approximate quadratic complexity of both the DBN-TE and the HNN-TE is
mostly due to interleaver mitigation, requiring matrix multiplication, where the matrices have dimensions
equal to the data block length, without which turbo equalization using superstructures is
impossible for systems employing random interleavers.Thesis (PhD)--University of Pretoria, 2013.
gm2013
Electrical, Electronic and Computer Engineering
unrestricted
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Gaffar, Mohammed Yusuf Abdul. "MMSE equalizers and precoders in turbo equalization." Thesis, 2003. http://hdl.handle.net/10413/4155.
Full textAbstract:
Transmission of digital information through a wireless channel with resolvable multipaths or a bandwidth limited channel results in intersymbol interference (1SI) among a number of adjacent symbols. The design of an equalizer is thus important to combat the ISI problem for these types of channels and hence provides reliable communication. Channel coding is used to provide reliable data transmission by adding controlled redundancy to the data. Turbo equalization (TE) is the joint design of channel coding and equalization to approach the achievable uniform input information rate of an ISI channel. The main focus of this dissertation is to investigate the different TE techniques used for a static frequency selective additive white Gaussian noise (AWGN) channel. The extrinsic information transfer (EXIT) chart is used to analyse the iterative equalization/decoding process and to determine the minimum signal to noise ratio (SNR) in order to achieve convergence. The use of the Minimum Mean Square Error (MMSE) Linear Equalizer (LE) using a priori information has been shown to achieve the same performance compared with the optimal trellis based Maximum A Posterior (MAP) equalizer for long block lengths. Motivated by improving the performance of the MMSE LE, two equalization schemes are initially proposed: the MMSE Linear Equalizer with Extrinsic information Feedback (LE-EF (1) and (U)). A general structure for the MMSE LE, MMSE Decision Feedback Equalizer (DFE) and two MMSE LE-EF receivers, using a priori information is also presented. The EXIT chart is used to analyse the two proposed equalizers and their characteristics are compared to the existing MAP equalizer, MMSE LE and MMSE DFE. It is shown that the proposed MMSE LE-EF (1) does have an improved performance compared with the existing MMSE LE and approaches the MMSE Linear Equalizer with Perfect Extrinsic information Feedback (LE-PEF) only after a large number of iterations. For this reason the MMSE LE-EF is shown to suffer from the error propagation problem during the early iterations. A novel way to reduce the error propagation problem is proposed to further improve the performance of the MMSE LE-EF (I). The MAP equalizer was shown to offer a much improved performance over the MMSE equalizers, especially during the initial iterations. Motivated by using the good quality of the MAP equalizer during the early iterations and the hybrid MAP/MMSE LE-EF (l) is proposed in order to suppress the error propagation problem inherent in the MMSE LE-EF (I). The EXIT chart analysis reveals that the hybrid MAP/MMSE LE-EF (l) requires fewer iterations in order to achieve convergence relative to the MMSE LE-EF (l). Simulation results demonstrate that the hybrid MAP/MMSE LE-EF (I) has a superior performance compared to the MMSE LE-EF (I) as well as approaches the performance of both the MAP equalizer and MMSE LE-PEF at high SNRs, at the cost of increased complexity relative to the MMSE LEEF (I) receiver. The final part of this dissertation considers the use of precoders in a TE system. It was shown in the literature that a precoder drastically improves the system performance. Motivated by this, the EXIT chart is used to analyse the characteristics of four different precoders for long block lengths. It was shown that using a precoder results in a loss in mutual information during the initial equalization stage. However" we show by analysis and simulations that this phenomenon is not observed in the equalization of all precoded channels. The slope of the transfer function, relating to the MAP equalization of a precoded ISI channel (MEP), during the high input mutual information values is shown to play an important role in determining the convergence of precoded TE systems. Simulation results are presented to show how the precoders' weight affects the convergence of TE systems. The design of the hybrid MAP/MEP equalizer is also proposed. We also show that the EXIT chart can be used to compute the trellis code capacity of a precoded ISI channel.Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.
46
Zhang, Yuan-Kai, and 張廖元凱. "Low-complexity Fuzzy-Filter-Assisted Turbo Equalization." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/87428896228596257666.
Full textAbstract:
碩士國立雲林科技大學
電子與資訊工程研究所
93
Turbo equalizer (TEQ) was shown to against inter symbol interference (ISI) and multipath Rayleigh fading channel effective. That had been implement using linear filter, Logarithm-Maximum a-posteriori algorithm (Log-MAP), Soft Output Viterbi algorithm (SOVA), and Radial Basis Function algorithm (RBF). In RBF-TEQ, which has high computational complexity, in order to reduce computational complexity, we can use Jacobian logarithmic algorithm and Decision-feedback technology, but in high order equalizer, the number of adder is exponential increase, so the computational complexity still too high for materializing. In this paper, we present fuzzy algorithm to reduce computational complexity. We joint fuzzy-filter equalizer and log-MAP decoder (Fuzzy-TEQ). The fuzzy equalizer is shown to perform close to the Bayesian equalizer (RBF). Using different membership function, we get different performance. However, in first iteration, the RBF-TEQ performance is better than Fuzzy-TEQ . After several iteration, the fuzzy-TEQ just need increase one iteration, the performance will be very close RBF-TEQ, almost same performance, but computational complexity can be reducing effective.
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"Turbo equalization and turbo estimation for multiple-input multiple-output wireless systems." Université catholique de Louvain, 2006. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-09112006-173121/.
Full text
48
Peng, Jun-Hua, and 彭俊豪. "Combination of Turbo Trellis Coded Modulation and Turbo Equalization for Wireless Communication." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/81534015190901259784.
Full textAbstract:
碩士國立臺灣科技大學
電子工程系
95
Because of the rapid and widespread development of communication technique, transmission style has developed from wire communication to wireless communication. Wireless communication has become a popular topic in recent mobile communication. It is necessary that we apply channel equalization and channel coding techniques in data transmission when we transmit data in multi-path fading channels, which typically suffer serious signal degradation. In this thesis, we consider an iterative system, turbo equalization, which consists of equalization and decoding. Finally, the performances of these techniques mentioned above are evaluated by computer simulation in multi-path fading channels In the part of channel coding, turbo trellis-coded modulation is considered. Encoded signals are transmitted in wireless fading channel; we employ turbo equalization, which consists of trellis equalizer and decoder in the receiver. The form of equalizer is not the same as the form of decoder. Because the forms of exchange of extrinsic information for equalizer and decoder in different forms, we have to use some methods to help transfer the extrinsic information as each other’s soft-input information. Because the computation load of equalizer is high, we also try to use T-BCJR algorithm to reduce the computation complexity of equalizer.
49
"Combating channels with long impulse response using combined turbo equalization and turbo decoding." 2000. http://library.cuhk.edu.hk/record=b5890402.
Full textAbstract:
by Chan Yiu Tong.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.
Includes bibliographical references (leaves 56-[59]).
Abstracts in English and Chinese.
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Communications and Coding Technology --- p.2
Chapter 1.2 --- The Emerge of Turbo Codes --- p.3
Chapter 1.3 --- The Extension of Turbo Principle --- p.3
Chapter 1.4 --- Receiver Structures for Practical Situations --- p.4
Chapter 1.5 --- Thesis Overview --- p.5
Chapter 2 --- ISI Channel Model and Channel Equalization --- p.6
Chapter 2.1 --- A Discrete Time ISI Channel Model --- p.6
Chapter 2.1.1 --- Optimum Maximum Likelihood Receiver --- p.8
Chapter 2.1.2 --- The Whitened Matched Filter --- p.11
Chapter 2.2 --- Equalization Techniques for Combating ISI --- p.13
Chapter 2.2.1 --- Linear MMSE Equalizer --- p.13
Chapter 2.2.2 --- MLSE Equalizer in Viterbi Algorithm --- p.15
Chapter 3 --- An Overview of Turbo Codes --- p.18
Chapter 3.1 --- The Turbo Encoder --- p.19
Chapter 3.2 --- The Turbo Interleaver --- p.21
Chapter 3.3 --- The Iterative Decoder --- p.22
Chapter 3.3.1 --- The MAP Algorithm --- p.23
Chapter 3.3.2 --- The Max-Log MAP Algorithm --- p.25
Chapter 3.3.3 --- The Log-MAP Algorithm --- p.28
Chapter 4 --- Receivers for Channels with Long Impulse Responses --- p.29
Chapter 4.1 --- Shortcomings for the Existing Models --- p.30
Chapter 4.2 --- Proposed System Architecture --- p.30
Chapter 4.2.1 --- Optimized Model for Channel Shortening Filter --- p.31
Chapter 4.2.2 --- Method One - Separate Trellises for EQ and DEC --- p.35
Chapter 4.2.3 --- Method Two - Combined Trellises for EQ and DEC --- p.37
Chapter 5 --- Performance Analysis --- p.40
Chapter 5.1 --- Simulation Model and Settings --- p.40
Chapter 5.2 --- Performance Expectations --- p.43
Chapter 5.3 --- Simulation Results and Discussions --- p.49
Chapter 6 --- Concluding Remarks --- p.55
Bibliography --- p.56
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"Novel turbo-equalization techniques for coded digital transmission." Université catholique de Louvain, 2004. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-12042004-160602/.
Full text