Dans la recherche de modulations adaptées à la voie descendante des réseaux cellulaires 4G, i.e. permettant le transfert de données à haut débit tout en garantissant une grande mobilité aux utilisateurs, les systèmes MC-CDMA s'affirment aujourd'hui comme des solutions à fort potentiel. Ces techniques reposent sur la combinaison des modulations à porteuses multiples et l'étalement de spectre qui permet l'accès multiple par répartition de code. En parallèle, les sytèmes MIMO constituent une nouvelle voie très prometteuse améliorant notablement l'efficacité spectrale des systèmes hertziens via la dimension spatiale. Cette thèse porte sur l'optimisation des systèmes MIMO/MC-CDMA par l'étude des codes temps-espace en blocs (STBC)ou en treillis (STTC).<br /><br />Après un état de l'art relativement exhaustif des systèmes MIMO en général et des codes temps-espace en particulier, nous proposons de nouveaux codes STBC orthogonaux, puis une représentation polynômiale permettant la comparaison des codes STTC existants. La combinaison STBC/MC-CDMA étudiée ensuite améliore sensiblement les performances d'un système MC-CDMA SISO tout en autorisant un décodage relativement simple. Leur optimisation repose sur des techniques de détection mono-utilisateurs ou multi-utilisateurs. Leur performances sont évaluées dans des configurations MISO ou MIMO, aussi bien sur des canaux théoriques que sur des canaux réalistes. Enfin, la combinaison STTC/MC-CDMA est étudiée.

No description available.

Nowadays most communication networks like GSM, WLan or WiMAX are based on pre-existing infrastructure. These infrastructures are complicated, costly and difficult to deploy in very short time. Whereas Wireless Ad Hoc Networks are infrastructure-free self organizing networks which consist of co-operating nodes. These networks are highly desirable for various emerging applications for military and to extend the range and capacity of infrastructure based wireless networks. One critical issue that we face in Ad Hoc Network is the problem of scheduling. Scheduling algorithms in an Ad Hoc Network allows the nodes to share the wireless channel efficiently. But on the other hand, the scheduling algorithm needs to be easily implementable in a distributed fashion with little, if any, coordination between nodes in the network. Spread spectrum technologies allow interference averaging and therefore are employed in Ad Hoc networks. There are two major types of spread spectrum physical layer, which are frequency hopping (FH) spread spectrum and direct sequence (DS) spread spectrum. FH-CDMA divides the bandwidth into M sub channels, the receiver only sees the interference from the transmitter side which is on the same sub channel whereas in DS-CDMA we increase the spreading code M to decrease the signal to interference plus noise ratio (SINR) requirement. The purpose of research is to study a hybrid spread spectrum based on physical layer, in which the direct sequence signal is also frequency hoped. The DS will reduce the region of dominating interferes, while frequency hopping will be used within this region intelligently and allow the dominating interferes to transmit on different frequencies. First the system bounds on the transmission capacity of the proposed scheme is evaluated, and than a comparative analysis of different multiple access schemes is done with our proposed model with respect to their transmission capacity to evaluate its performance.

Le positionnement d'objets sous-marins représente un enjeu stratégique pour des applications militaires, industrielles et scientifiques. Les systèmes de positionnement reposent sur des signaux de type SONAR « Sound Navigation and Ranging ». Plusieurs émetteurs synchrones avec des temps d'émission connus sont alors considérés, l'objectif étant que la position d'un récepteur se fasse en fonction des positions des émetteurs. Nous avons la main mise sur la détection des signaux en réception d'une part, et sur le choix des formes d'ondes à l'émission d'autre part. La méthode de détection, basée sur le filtrage adapté, se veut robuste aux différentes perturbations engendrées par le canal de propagation (pertes par transmission, multi-trajets) et par le système lui-même (environnement multi-émetteurs). De plus, la détection restreinte à une somme de tests d'hypothèses binaires, nécessite un fonctionnement en temps réel. A l'émission, les formes d'ondes doivent permettre d'identifier indépendamment les émetteurs les uns des autres. Ainsi les travaux portent essentiellement sur les modulations FHSS, les paramètres de construction de ces signaux étant alors choisis de sorte à optimiser la méthode de détection étudiée. Enfin, l'implémentation des algorithmes issus de ces travaux sur des systèmes embarqués a permis leur validation sur des données enregistrées, puis en conditions réelles. Ces essais ont été réalisés avec l'entreprise ALSEAMAR, dans le cadre de la thèse CIFRE-DGA. / There is an increasing interest in underwater positioning system in industry (off-shore, military, and biology). In order to localize a receiver relative to a grid of transmitters, thanks to the knowledge of positions and transmission time, it needs to detect each signal and estimate the TOA (Time Of Arrival). Thus, a range between a transmitter and receiver can be deduced by estimation of TOA. When receiver knows three ranges at least, it can deduce its position by triangulation. This work takes into account signal detection, and waveform choice. Detection method, based on matched filter, needs to be robust face to propagation channel (transmission loss, multi-paths) and to the system (multi-users environment). Moreover, the detection structure, being a combination of binary hypothesis testing, must work in real time. In a CDMA context which requires to distinguish each transmitter, the FHSS (Frequency Hopped Spread Spectrum) modulation, allocating one code per user, is adapted. FHSS signals performance, depending of the number of frequency shifts N and the time-bandwidth product, are analyzed from detection criterion point of view. Moreover, detection method and adapted signal is tested in a shallow water environment.The research was supported by ALSEAMAR and DGA-MRIS scholarship.

No description available.

Le réseau de radio communications mobiles professionnelles (PMR), qui est utilisé pour le fonctionnement de la sécurité publique, doit évoluer pour les solutions à large bande pour satisfaire les demandes des utilisateurs à l’avenir. Dans les technologies à large bande actuels, Long Term Evolution (LTE), développé par le 3GPP (3rd Generation Partnership Project), est considéré comme l’un des candidats potentiels pour la prochaine génération de PMR. Malgré le fait que la technologie LTE en charge la transmission de données à haute vitesse et prend en charge différentes tailles de paquets en utilisant la modulation et le codage adaptatifs (AMC), le LTE n’est pas encore optimisée pour la communication vocale à bas débit, en particulier en cas d’utilisation LTE pour la radio communications mobiles professionnelles (PMR ) contexte. Par conséquent, dans cette thèse, nous présentons des solutions pour renforcer la capacité de la voix de la technologie LTE dans le cadre PMR à la fois la liaison montante et la transmission de liaison descendante. Les nouvelles propositions, basées sur la technologie de norme LTE existant avec des adaptations, permettent la réduction de les frais généraux de données et les frais généraux de contrôle sur LTE (VoLTE) dans le contexte PMR / The Professional Mobile Radio (PMR) network, which is used for public safety operation, has to evolve to the broadband solutions to satisfy the user demands in the future. In the current broadband technologies, Long Term Evolution (LTE) standard, developed by the 3GPP (3rd Generation Partnership Project), is considered one of the potential candidates for the next generation of PMR. Despite the fact that LTE supports high-speed data transmission and supports different packet sizes by using Adaptive Modulation and Coding (AMC), LTE is not yet optimized for low bit rate voice communication, especially in case of using LTE in Professional Mobile Radio (PMR) context. Therefore, in this dissertation, we present several new solutions for enhancing the voice capacity of LTE in the PMR context for both uplink and downlink transmission. The new propositions, based on existent LTE standard technology with adaptations, allow reducing both control and data overhead issues of Voice over LTE (VoLTE) in PMR context

[pt] As comunicações sem fio são um dos pilares do desenvolvimento das novas gerações de comunicações móveis. Cada geração tem usado alguma técnica de acesso múltiplo para aproveitar os recursos do canal. Esta dissertação apresenta uma análise de duas técnicas de multiplexação ortogonal. Ambas técnicas implementam a transmissão em blocos, onde uma delas se combina com a abordagem Code Division Multiple Access (CDMA), enquanto a outra usa a técnica de transmissão multiportadora Orthogonal Frequency Division Multiplexing (OFDM). O desempenho e a ocupação espectral de ambas técnicas e as suas vantagens são analisados neste trabalho. Expressões analíticas para a Densidade Espectral de Potência dos sinais foram obtidas e permitiram estabelecer comparações entre os dois métodos. O estudo dessas técnicas de multiplexação é realizado em diferentes canais de propagação para avaliar o comportamento de ambos sistemas de uma forma geral. Os três tipos de canais avaliados neste trabalho são: linear e invariante no tempo, linear e variante no tempo e, finalmente, não linear e invariante no tempo. Cada tipo de canal foi modelado em forma matricial para ambos sistemas de forma independente. As simulações consideram os equalizadores Zero Forcing e Minimum Mean Square Error, assumindo um canal conhecido. / [en] Wireless communications are one of the pillars of the development of the new generations of mobile communications. Each generation has used some multiple access technique to take advantage of the channel s resources. This dissertation presents an analysis of two orthogonal multiplexing techniques. Both techniques implement block transmission, where one is combined with the Code Division Multiple Access (CDMA) approach, while the other uses the multicarrier transmission technique Orthogonal Frequency Division Multiplexing (OFDM). The performance and spectral occupation of both techniques and their advantages are analyzed. Analytical expressions for the Power Spectral Density of the signals were obtained, which allowed establishing comparisons between both methods. The study of these multiplexing techniques is carried out in different propagation channels to evaluate the behavior of both systems in general. The three types of channels evaluated in this work are linear and time-invariant, linear and time-variant and, finally, non-linear and time-invariant. Each type of channel was modeled in matrix form for both systems independently. The simulations consider the Zero Forcing and Minimum Mean Squared Error equalizers, assuming a known channel.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / With the recent broadband upgrades to various cellular infrastructures and the myriad new emerging wireless broadband standards and services offered by carriers, it is often difficult to navigate this sea of technology. In deciding the best choice for broadband telemetry applications, one must look not only at the technology, but also at the economics, market timing, bandwidths, legacy issues, future expandability and coverage, security, protocols, and the requirements of the specific application. This paper reviews the technology roadmap of cellular providers keeping these issues in perspective as they apply to TCP/IP data for images, audio, video, and other broadband telemetry data using CDMA 1xRTT, EV-DO, and EV-DO Rev A systems as well as GSM GPRS/EDGE, UMTS/W-CDMA, HSDPA, and HSUPA networks. Lastly, issues seen by system integrators when using cellular channels for telemetry applications are examined, and a case is presented for overcoming many of these issues through the use of cellular routers.

Iraq may be considered as the largest wireless market in the Gulf region. A key driving factor in the market of wireless communication, it has seen enormous growth in the mobile phone market over the last five years leading to almost 24 million subscribers in 2011. Moreover, there are several technologies and services working in Iraq; three GSM Operators, three CDMA national operators and three CDMA provinces operators. The recent growth in the mobile phone market is based on the Global System for Mobile (GSM) communications and Code Division Multiple Access (CDMA) standards creating the next-generation wireless technologies in the Iraqi Wireless Communication market. One of the essential issues of this research is to investigate the performance of the decreased Quality Of Service (QoS) caused by interferences in the services on GSM/CDMA operators in Iraq. Many issues should be studied and taken into consideration, such as; does the Multi-Coalition Forces cause the interferences, jamming, higher rate of calls drop and false ringing; or are they caused by bad design and planning? Do we need to optimise our network due to the large number of users? All these factors are investigated and the measurements of most service providers and government agencies will be gathered. A detailed analysis was included from the providers with measurements of performance and the reasons for the deterioration of wireless services. The novel contributions of this thesis is the extensive radio measurement campaign over the three mobile an CDMA operator networks and the analysis and recommendations that were drawn to suggest the best approach to improve the QoS of Wireless communication technologies. Awareness of actual reasons behind the deterioration of services will be raised to the Iraqi Government, CMC and the wireless service providers.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / At present, multiple mobile targets will be remote controlled in many remote control and telemetry system, in which multiple access technology will be applied. This paper proposes a communication scheme to remote control multiple mobile targets using Coded-Division Multiple Access(CDMA) technique. It's feasibility, advantage and shortcoming are analyzed. Moreover, the key techniques of Direct-Sequence Spread Spectrum(DS/SS) system, i.e. the correlation detection and delay lock-on techniques, are studied and stimulated on the experimental model. The results of theoretical analysis show that the CDMA system has the peculiar advantage over the conventional multiple access system, such as FDMA and TDMA.