Depuis quelques années, le besoin de systèmes de communications plus rapides et plus sures se fait sentir. Le partage entre utilisateurs de la très grande bande passante des fibres optiques nécessite des techniques d'accès adaptées. Afin de répondre à ces besoins, un certain nombre de techniques de multiplexage, dont le CDMA, ont été développées. Cette technique d'accès multiple est déjà largement utilisée dans les systèmes de communications radio-mobiles, que ce soit dans les normes américaines (IS 95), japonaises ou, plus récemment, européenne (UMTS). Ce rapport de thèse traite du DS-CDMA appliqué aux communications optiques. Le premier chapitre permet une mise en contexte et décrit le fonctionnement des techniques de multiplexage utilisées dans les systèmes radiofréquences et les systèmes de transmissions optiques. Le second chapitre présentes les différents types de code utilisés dans les systèmes CDMA. Les codes bipolaires associés aux systèmes radiofréquences sont définis et une présentation des codes optiques est effectuée. Les caractéristiques et contraintes que doivent respecter ces codes optiques, pour être utilisable dans une liaison DS-CDMA optique, sont données. Dans le troisième chapitre, la transmission de signaux CDMA sur un canal optique, passif ou amplifié est abordée et les configurations de décodage électrique et optique, ainsi que les performances du système optique dans ces différentes configurations sont étudies La dernière partie de notre étude concernera l'utilisation de codeurs / décodeurs à réseaux de Bragg dans un système CDMA optique. Des simulations et des montages expérimentaux permettront d'étudier la faisabilité d'une telle implémentation.

A (periodic) correlation function is an important measure to evaluate the effectiveness of pseudorandom sequences. In practice, the sequences are required to have the impulse-like autocorrelation function. Also, crosscorrelation magnitudes of the distinct sequences must be as low as possible. Theoretically, the correlation of sequences has a strong connection with problems of algebraic coding and combinatorics. Namely, the correlation distribution of sequences is related to the weight distribution of codewords in algebraic codes. Furthermore, binary sequences with ideal two-level autocorrelation are equivalent to cyclic Hadamard difference sets in combinatorics. Therefore, a good knowledge of coding theory and combinatorics is helpful for a study of sequences with low correlation. In this thesis, the correlation of binary sequences is studied by the aid of fruitful results of coding theory and combinatorics. From this study, some interesting properties are presented on the correlation of binary sequences, and several new binary sequences with low correlation are discovered. The outline of thesis is as follows. First of all, crosscorrelation properties of binary sequences with ideal two-level autocorrelation are studied. The 3- and 5-valued crosscorrelation properties of several classes of binary sequences with ideal two-level autocorrelation are completely determined by either theoretical proofs or conjectures. Second, new binary sequences of period of a multiple of 4 are proposed by making use of the interleaved structure of sequences. The sequences have three-valued out-of-phase autocorrelation, i.e., {0, -4, +4}, which is optimal with respect to autocorrelation magnitude. Third, a new binary sequence family with low correlation and a large family size is proposed and its asymptotic optimality is examined. With respect to maximum correlation, a family size, and a linear complexity, the sequence family is competitive among all known binary sequence families. Finally, the construction of quadratic bent functions of a special polynomial form is presented by providing necessary and sufficient conditions on the coefficients of the polynomial. The resulting quadratic bent functions can be employed for the linear feedback shift register (LFSR) implementation of a family of bent sequences, which is a potential candidate for future code-division multiple access (CDMA) system.

A (periodic) correlation function is an important measure to evaluate the effectiveness of pseudorandom sequences. In practice, the sequences are required to have the impulse-like autocorrelation function. Also, crosscorrelation magnitudes of the distinct sequences must be as low as possible. Theoretically, the correlation of sequences has a strong connection with problems of algebraic coding and combinatorics. Namely, the correlation distribution of sequences is related to the weight distribution of codewords in algebraic codes. Furthermore, binary sequences with ideal two-level autocorrelation are equivalent to cyclic Hadamard difference sets in combinatorics. Therefore, a good knowledge of coding theory and combinatorics is helpful for a study of sequences with low correlation. In this thesis, the correlation of binary sequences is studied by the aid of fruitful results of coding theory and combinatorics. From this study, some interesting properties are presented on the correlation of binary sequences, and several new binary sequences with low correlation are discovered. The outline of thesis is as follows. First of all, crosscorrelation properties of binary sequences with ideal two-level autocorrelation are studied. The 3- and 5-valued crosscorrelation properties of several classes of binary sequences with ideal two-level autocorrelation are completely determined by either theoretical proofs or conjectures. Second, new binary sequences of period of a multiple of 4 are proposed by making use of the interleaved structure of sequences. The sequences have three-valued out-of-phase autocorrelation, i.e., {0, -4, +4}, which is optimal with respect to autocorrelation magnitude. Third, a new binary sequence family with low correlation and a large family size is proposed and its asymptotic optimality is examined. With respect to maximum correlation, a family size, and a linear complexity, the sequence family is competitive among all known binary sequence families. Finally, the construction of quadratic bent functions of a special polynomial form is presented by providing necessary and sufficient conditions on the coefficients of the polynomial. The resulting quadratic bent functions can be employed for the linear feedback shift register (LFSR) implementation of a family of bent sequences, which is a potential candidate for future code-division multiple access (CDMA) system.

This thesis studies advanced error control schemes using turbo-like codes, turbo-like coded modulations, turbo hybrid-ARQ (Automatic Repeat reQuest) schemes, and rate compatible puncturing techniques for reliable and adaptive commercial and tactical spread-spectrum communications, especially for code-division multiple access (CDMA) cellular systems and direct-sequence (DS) and frequency-hopping (FH) anti-jam systems. Furthermore, we utilize both the maximum-likelihood (ML) bounding techniques and convergence analysis to design and analyze various turbo-like coding schemes that show different behaviors in error performance from conventional trellis coding schemes. In the area of DS-CPM, we propose a DS concatenated coded CPM system for pulse-noise jamming channels and an anti-jam iterative receiver utilizing jammer state information. We also design a mixed concatenated CPM system that mixes CPM schemes with different convergence characteristics. In addition, we present the ML bound and convergence analysis for the jamming channel. In the area of FH-CPM, we propose anti-jam serially concatenated slow FH-CPM systems, whose phase is continuous during each hop interval, along with coherent and non-coherent iterative receivers. We also propose an iterative jamming estimation technique for the iterative receiver. In the area of multi-h CPM, we propose a power- and bandwidth-efficient serially concatenated multi-h CPM along with an appropriate iterative receiver structure. Serially concatenated multi-h CPM is shown to outperform single-h CPM. To design adaptive and versatile error control schemes using turbo-like codes for packet-data networks, we propose turbo hybrid-ARQ (HARQ) and rate compatible puncturing techniques for retransmission. In the area of turbo hybrid-ARQ, we propose a Type-I turbo HARQ scheme using a concatenated RS-turbo code and a packet combining technique for W-CDMA system to improve the performance of error and decoding latency. The W-CDMA system including the fast power control and coherent Rake receiver with a channel estimation technique for multipath fading channels is considered. Finally, in the area of rate compatible punctured turbo-like codes, we propose rate compatible punctured turbo (RCPT) codes and rate compatible punctured serially concatenated convolutional (RCPS) codes along with their puncturing methods. In addition, we propose Type-II RCPT-HARQ and RCPS-HARQ schemes to perform an efficient incremental redundancy retransmission.

The analysis of this thesis concerns various problems associated with adaptive CDMA multi-user detection in asynchronous multi-path channels. Starting with some simple concept of Wiener filtering and correlating detector, we construct a novel adaptive decorrelating transversal filter suitable for CDMA multi-user detection in uplink channels. Then, we make use of the LMS and RLS algorithms to replace the traditional decorrelating transversal filter (which is also called inverse matrix based decorrelating detector) to make the scheme work fully adaptively. In this way, a great advantage in terms of computation load reduction is made possible. To further improve the detection efficiency, we will also make use of RAKE receiver to enhance the overall decision reliability in the proposed adaptive CDMA MUD scheme. Although the focus of this thesis is put on analysis, we will also use computer simulations to counter-check the results obtained from theoretical analysis, showing a very good match between the two. In the last part of the thesis, we will also discuss the various issues on fully blind implementation of the proposed adaptive CDMA MUD scheme with some useful multipath channel delay and amplitude estimation algorithms.

In this thesis, the feasibility of complete complementary code based OFDM CDMA system is studied. The complete complementary code is composed of several sets of auto-complementary codes, any two of which are cross-complementary codes. The perfect correlation between code sets is the distinguishing feature of complete complementary code. In this thesis, we designed a new OFDM CDMA system architecture according the property of complete complementary code. The most obvious characteristic is that the bit stream in the new system is no longer aligned one bit after another in time. Instead, a new bit will start only after one chip delay relative to the previous bit, which is spread by an element code of complete complementary code. The proposed new CDMA architecture can offer an MAI-free operation in both down-link (synchronous channel) and up-link (asynchronous channel) transmission under the AWGN channel, because of the use of the CC-codes. However, due to the special spreading modulator-offset stacking modulator (OSM), we¡¦ll encounter a ¡§ multi-level ¡¨ problem . If we can¡¦t solve this problem , the linear power amplifier will not be able to support the whole system . Hence , we try to clip the multilevel into a smaller magnitude . And also , we try some other mapping methods to solve the multilevel problem .

In this thesis, we propose a modified MT-CDMA system, which can improve channel estimation accuracy by using transmit diversity of pilot signals. We not only expound the principles and structures of the system we proposed, but analyze its performance in slow Rayleigh fading channel environment. According to different ways to assign data symbols of transmitted signals, we have two different bit error rate results. At the same transmit power, the simulation results show that when we combine comb-type pilot signals of two parallel channels to estimate channel gains, we can recover the drawbacks of comb-type pilot arrangement, which can not perform well in frequency selective fading channel. Finally, the numerical results will be also shown.

Because using the perfect orthogonal code in CDMA system means elimination of multi-path interference and multiple access interference, we will discuss this aspect in this thesis. At first, we address a algorithm to how to search a flock of perfect orthogonal code, which consisting of many codes have a characteristic of perfect auto-correlation and perfect cross-correlation to each other. Following, we will compare perfect orthogonal code we find with the present complementary codes include complete complementary code (CCC), super complementary code (SCC), and two-dimensional orthogonal variable spreading code (2D-OVSF code). Considering that the run time of searching perfect orthogonal code is long in case of high processing gain (PG), we construct a PC cluster based Linux O.S or Windows O.S for the operation of parallel program to faster our production of perfect orthogonal code.

First, we proved that the - Columnwise Complementary codes is better than - Columnwise Complementary code in time selective channel by explaining the probability of happening MAI elimination in frequency domain and proposing a method to use - Columnwise Complementary codes in one cell. Furthermore, we proposed the method to increase the capability of resisting of frequency selective fading channel without decreasing the capability of resisting of time selective fading channel. Finally, we showed some simulation results about receiver velocity and MAI elimination in frequency domain.

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