Performance of asynchronous orthogonal multicarrier CDMA system in frequency selective fading channel

An asynchronous multicarrier (MC) direct-sequence (DS) code-division multiple-access (CDMA) scheme for the uplink of the mobile communication system operating in a frequency selective fading channel is analyzed. Bit error rate performance of the system with either equal-gain combining or maximum-ratio combining is obtained. Numerical results indicate that the system performs better than that of the conventional DS-CDMA system and another MC-DS-CDMA system.published_or_final_versio

Memory truncation and crosstalk cancellation for efficient Viterbi detection in FDMA systems, Journal of Telecommunications and Information Technology, 2001, nr 3

In this paper, the design of optimal receive filter banks for frequency division multiple access (FDMA) over frequency selective channels is investigated. A new design strategy based on the principle of memory truncation, rather than equalization, is presented. Through the receive filters, each subchannel is truncated to a pre-defined length, and the final data recovery is carried out via low complexity Viterbi detectors. Both closed form designs and adaptive techniques are discussed. Design examples are presented for high speed transmission over copper wires. The examples show that memory truncation allows significant performance improvements over the often used minimum mean squared error (MMSE) equalization

Orthogonal transmultiplexers : extensions to digital subscriber line (DSL) communications

An orthogonal transmultiplexer which unifies multirate filter bank theory and communications theory is investigated in this dissertation. Various extensions of the orthogonal transmultiplexer techniques have been made for digital subscriber line communication applications. It is shown that the theoretical performance bounds of single carrier modulation based transceivers and multicarrier modulation based transceivers are the same under the same operational conditions. Single carrier based transceiver systems such as Quadrature Amplitude Modulation (QAM) and Carrierless Amplitude and Phase (CAP) modulation scheme, multicarrier based transceiver systems such as Orthogonal Frequency Division Multiplexing (OFDM) or Discrete Multi Tone (DMT) and Discrete Subband (Wavelet) Multicarrier based transceiver (DSBMT) techniques are considered in this investigation. The performance of DMT and DSBMT based transceiver systems for a narrow band interference and their robustness are also investigated. It is shown that the performance of a DMT based transceiver system is quite sensitive to the location and strength of a single tone (narrow band) interference. The performance sensitivity is highlighted in this work. It is shown that an adaptive interference exciser can alleviate the sensitivity problem of a DMT based system. The improved spectral properties of DSBMT technique reduces the performance sensitivity for variations of a narrow band interference. It is shown that DSBMT technique outperforms DMT and has a more robust performance than the latter. The superior performance robustness is shown in this work. Optimal orthogonal basis design using cosine modulated multirate filter bank is discussed. An adaptive linear combiner at the output of analysis filter bank is implemented to eliminate the intersymbol and interchannel interferences. It is shown that DSBMT is the most suitable technique for a narrow band interference environment. A blind channel identification and optimal MMSE based equalizer employing a nonmaximally decimated filter bank precoder / postequalizer structure is proposed. The performance of blind channel identification scheme is shown not to be sensitive to the characteristics of unknown channel. The performance of the proposed optimal MMSE based equalizer is shown to be superior to the zero-forcing equalizer

Filtered Multicarrier Transmission

Orthogonal frequency‐division multiplexing (OFDM) has been adopted as the waveform of choice in the existing and emerging broadband wireless communication systems for a number of advantages it can offer. Nevertheless, investigations of more advanced multicarrier transmission schemes have continued with the aim of eliminating or mitigating its essential limitations. This article discusses multicarrier schemes with enhanced spectrum localization, which manage to reduce the spectral sidelobes of plain OFDM that are problematic in various advanced communication scenarios. These include schemes for enhancing the OFDM waveform characteristics through additional signal processing as well as filter‐bank multicarrier (FBMC) waveforms utilizing frequency‐selective filter banks instead of plain (inverse) discrete Fourier transform processing for waveform generation and demodulation.acceptedVersionPeer reviewe

Wavelet based design of digital multichannel communications systems

The huge penetration of the personal communications systems in the market is constantly presenting new challenges to the research, aimed at satisfying people's needs and requirements for effective communication systems. At present, the cellular telephone network is perhaps the most evident example of communication system that has had a great impact on the lives of ordinary people and, at the same time, is the subject of interest of many researchers both at academic and industrial level. For the future, one of the main challenges in telecommunications will be the provision of ubiquitous broadband tetherless integrated services to mobile users. Such a pretentious goal cannot be achieved without a continuous research facing such problems as service quality, complete mobility support, and affordable complexity that are still open problems. However, present telecommunication problems are not only a matter of implementation or development of new services, exploiting a totally assessed doctrine. In order to respond to the mobility of the users personal communication systems have to deal with the wireless communication channel whereby mobility and non-stationarity of the propagation conditions require a stochastic description of the channel parameters. While this fact can be viewed as strong limitation to the development of a solid theory whose validity can be assesed in practice, on the other hand allows for an investigation and study of novel communication schemes, sometimes encompassing basic aspects of digital communications. This thesis, is the result of a research work that has investigated one of the basic building block of every communication systems, the modulation scheme, and the design of the pulse shape carrying the digital information. We have studied the design of multichannel communication scheme exploiting the mathematical theory of wavelets. Such a theory, developed recently, has had a great impact in many fields of engineering and of other scientific disciplines. In particular, wavelet theory has become very popular in the signal processing area; in fact it is a flexible toolbox for signal analysis allowing effective representation of signals for features extraction purposes. The main features that make wavelet waveforms suitable to be used as shaping pulses for modulation are their substantial compact support both in the time and frequency domains, and the fact that they are ISI-free pulses over frequency flat channels. The study presented in this thesis is focused on application of wavelet theory to design high-efficiency multichannel communication schemes and to the performance evaluation over linear and non-linear channels. We present a general method to design wavelet based multichannel communication schemes that we denoted Wavelet Orthogonal Frequency Division Multiplexing (WOFDM). We show that such schemes, having a largerspectral efficiency for a small number of channels, are a valid alternative to the classical OFDM. Potential advantage of wavelet modulation are shown presenting other applications examined in this thesis: a joint use of WOFDM and Trellis Coded Modulation to shape the power spectrum in order to match a frequency selective channel and minimize distortion, and application to spread spectrum modulation. Particular attention has been devoted to the timing recovery problem in multichannel communication schemes, exploiting the timing information of the different subchannels to improve the error variance in estimation of the sampling instant leading to a reduction of the adjacent channels interferenc

Etude et évaluation d un multiplexage fréquentiel basé sur l OFDM/OQAM

Cette thèse est consacrée à l étude de la modulation OFDM/OQAM en tant qu alternative à la modulation OFDM. Nous traitons plus particulièrement le contexte multiusagers. De ce point de vue, les aspects de synchronisation sont déterminants. Les différentes options plus le choix de la forme d onde sont donc examinés de ce point de vue. Un autre objectif est de montrer de manière précise comment la modulation OFDM/OQAM peut s adapter à une transmission de type cellulaire, en prenant comme référence le système 3GPP/LTE. Les principales contributions que nous avons apportées sont : 1) Une analyse des phénomènes de désynchronisation : nous analysons l effet de la désynchronisation, suivant les axes temporel et fréquentiel, sur les performances de l OFDM/OQAM au récepteur. 2) Méthode de synchronisation : nous analysons une méthode de synchronisation temporelle définie dans un contexte de transmission OFDM/OQAM mono-usager et nous l adaptons à un scénario de type multi-usagers. 3) Proposition d un schéma d accès multiple : nous proposons un schéma d accès multiple basé sur la modulation OFDM/OQAM, alternatif aux techniques connues OFDMA et SC-FDMA, pour la transmission en liaison montante dans un contexte de type 3GPP/LTE.This thesis is dedicated to the study of the OFDM/OQAM modulation as an alternative to the OFDM modulation. We treat more especially the multi-user environment. In this respect, synchronization aspects are crucial. The different options plus the choice of the waveform are examined in this point of view. Another objective is to precisely show how the OFDM/OQAM can be adapted to a cellular transmission type, taking as reference the 3GPP/LTE system. The main contributions we have made are : 1) Analysis of the desynchronization phenomena : we analyze the effect of desynchronization, according to the time and frequency axes, on the performance of OFDM/OQAM at the receiver side. 2) Synchronization method : we analyze a method of temporal synchronization defined in a single user OFDM/OQAM transmission and we adapt it to a multi-user scenario type. 3) Proposing for a multiple access scheme : we propose a multiple access scheme based on theOFDM/OQAM modulation, alternative to the known techniques OFDMA and SC-FDMA, for the UL transmission in a 3GPP/LTE context.PARIS-CNAM (751032301) / SudocSudocFranceF

Journal of Telecommunications and Information Technology, 2001, nr 3

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Comments on "Orthogonal multiple carrier data transmission"

In a paper from 1992, Fliege introduced a novel multicarrier modulation scheme claiming to obtain an implementation that is computationally more efficient and has a simpler filter bank structure with respect to those previously presented in the literature. Being understood the correctness and valuability of the ideas expressed in that paper, nevertheless we would like to point out that an implementation with the same computational complexity had already been presented by Hirosaki in 1981, and that the optimization of the filter bank structure is based on an incorrect ste