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.

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.

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.

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, Nevada / OFDM 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.

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 Gaussien. / In 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.

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.

<p>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.</p><p>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.</p><p>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.</p>

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.

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.

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.