Comparison of Bit Error Rate and Power Spectral Density on the Ultra Wideband Impulse Radio Systems

Ultra-Wideband (UWB) is defined as a wireless transmission scheme that occupies a bandwidth of more than 25% of its center frequency. UWB Impulse Radio (UWB-IR) is a popular implementation of the UWB technology. In UWB-IR, information is encoded in baseband without any carrier modulation. Pulse shaping and baseband modulation scheme are two of the determinants on the performance of the UWB-IR. In this thesis, both temporal and spectral characteristics of the UWB-IR are examined because all radio signals exist in both the time and frequency domains. Firstly, the bit error rate (BER) performance of the UWB-IR is investigated via simulation using three modulation schemes: Pulse position modulation (PPM), on-off shift keying (OOK), and binary phase shift keying (BPSK). The results are verified for three different pulse shaping named Gaussian first derivative, Gaussian second derivative, and return-to-zero (RZ) Manchester. Secondly, the effects of the UWB-IR parameters on the power spectral density (PSD) are investigated because PSD provides information on how the power is distributed over the radio frequency (RF) spectrum and determines the interference of UWB-IR and the existing systems to each other in the spectrum. The investigated UWB-IR parameters include pulse duration, pulse repetition rate, modulation scheme, and pseudorandom codes

Localisation dans les milieux confinés: combinaison de l'UWB et les réseaux de neurones dans un algorithme de localisation par signature

Le travail de ce rapport porte sur la localisation dans les milieux internes et plus précisément dans les milieux non conventionnels, les mines par exemple. L'UWB (Ultra Wide Band) présente un niveau physique idéal pour une telle application en raison de ses caractéristiques. Parmi les avantages de l'UWB citons: une résolution temporelle élevée qui fournit une meilleure précision temporelle dans un système de localisation; une grande largeur de bande qui permet de mieux contrôler les effets sélectifs d'un canal; une résolvabilité des différentes parties d'une même transmission et provenant du phénomène multi-trajet. D'autre part, la localisation par signature se base généralement sur la formation d'une empreinte qui est directement liée à une position donnée et cela d'une manière unique et reproductible. En conséquence, le choix du signal UWB devient évident pour la prise des signatures et pour l'application dans le système de localisation sous étude. Plusieurs analyses et campagnes de mesure concernant une transmission UWB ont été effectuées. Pour cela, un analyseur de réseau a été utilisé. Ce dernier réalise les mesures dans le domaine fréquentiel en effectuant un balayage de fréquences sur toute la largeur de bande choisie. Ces mesures sont ensuite transformées dans le domaine temporel utilisant les transformations de Fourier. Nous avons réussi à couvrir des distances allant de 36 à 40 mètres, alors que la plupart des travaux dans la littérature couvrent une distance maximale de 10 m. Ce qui a nécessité l'addition de matériel pour augmenter la portée du système. Jusqu'aux limites de nos connaissances, ce travail (au LRTCS) est l'un des rares se focalisant sur les mines et les environnements hostiles. Enfin, trois scénarios différents ont été réalisés: i) le cas de visibilité directe sans aucune source d'interférence; ii) le cas de visibilité directe avec plusieurs sources de bruit (interférence); iii) le cas d'absence de ligne de vue. Après avoir construit les bases de données requises, des analyses ont été effectuées sur les réponses impulsionnelles collectées afin de trouver une empreinte qui représente au mieux le milieu choisi et qui offre donc la meilleure performance de l'algorithme de localisation. L'erreur étudiée représente la différence entre la position bidimensionnelle réelle et celle estimée par l'algorithme. Les résultats obtenus sont comparables à ceux trouvés dans la littérature

Interference management in impulse-radio ultra-wide band networks

We consider networks of impulse-radio ultra-wide band (IR-UWB) devices. We are interested in the architecture, design, and performance evaluation of these networks in a low data-rate, self-organized, and multi-hop setting. IR-UWB is a potential physical layer for sensor networks and emerging pervasive wireless networks. These networks are likely to have no particular infrastructure, might have nodes embedded in everyday life objects and have a size ranging from a few dozen nodes to large-scale networks composed of hundreds of nodes. Their average data-rate is low, on the order of a few megabits per second. IR-UWB physical layers are attractive for these networks because they potentially combine low-power consumption, robustness to multipath fading and to interference, and location/ranging capability. The features of an IR-UWB physical layer greatly differ from the features of the narrow-band physical layers used in existing wireless networks. First, the bandwidth of an IR-UWB physical layer is at least 500 MHz, which is easily two orders of magnitude larger than the bandwidth used by a typical narrow-band physical layer. Second, this large bandwidth implies stringent radio spectrum regulations because UWB systems might occupy a portion of the spectrum that is already in use. Consequently, UWB systems exhibit extremely low power spectral densities. Finally IR-UWB physical layers offer multi-channel capabilities for multiple and concurrent access to the physical layer. Hence, the architecture and design of IR-UWB networks are likely to differ significantly from narrow-band wireless networks. For the network to operate efficiently, it must be designed and implemented to take into account the features of IR-UWB and to take advantage of them. In this thesis, we focus on both the medium access control (MAC) layer and the physical layer. Our main objectives are to understand and determine (1) the architecture and design principles of IR-UWB networks, and (2) how to implement them in practical schemes. In the first part of this thesis, we explore the design space of IR-UWB networks and analyze the fundamental design choices. We show that interference from concurrent transmissions should not be prevented as in protocols that use mutual exclusion (for instance, IEEE 802.11). Instead, interference must be managed with rate adaptation, and an interference mitigation scheme should be used at the physical layer. Power control is useless. Based on these findings, we develop a practical PHY-aware MAC protocol that takes into account the specific nature of IR-UWB and that is able to adapt its rate to interference. We evaluate the performance obtained with this design: It clearly outperforms traditional designs that, instead, use mutual exclusion or power control. One crucial aspect of IR-UWB networks is packet detection and timing acquisition. In this context, a network design choice is whether to use a common or private acquisition preamble for timing acquisition. Therefore, we evaluate how this network design issue affects the network throughput. Our analysis shows that a private acquisition preamble yields a tremendous increase in throughput, compared with a common acquisition preamble. In addition, simulations on multi-hop topologies with TCP flows demonstrate that a network using private acquisition preambles has a stable throughput. On the contrary, using a common acquisition preamble exhibits an effect similar to exposed terminal issues in 802.11 networks: the throughput is severely degraded and flow starvation might occur. In the second part of this thesis, we are interested in IEEE 802.15.4a, a standard for low data-rate, low complexity networks that employs an IR-UWB physical layer. Due to its low complexity, energy detection is appealing for the implementation of practical receivers. But it is less robust to multi-user interference (MUI) than a coherent receiver. Hence, we evaluate the performance of an IEEE 802.15.4a physical layer with an energy detection receiver to find out whether a satisfactory performance is still obtained. Our results show that MUI severely degrades the performance in this case. The energy detection receiver significantly diminishes one of the most appealing benefits of UWB, specifically its robustness to MUI and thus the possibility of allowing for parallel transmissions. This performance analysis leads to the development of an IR-UWB receiver architecture, based on energy detection, that is robust to MUI and adapted to the peculiarities of IEEE 802.15.4a. This architecture greatly improves the performance and entails only a moderate increase in complexity. Finally, we present the architecture of an IR-UWB physical layer implementation in ns-2, a well-known network simulator. This architecture is generic and allows for the simulation of several multiple-access physical layers. In addition, it comprises a model of packet detection and timing acquisition. Network simulators also need to have efficient algorithms to accurately compute bit or packet error rates. Hence, we present a fast algorithm to compute the bit error rate of an IR-UWB physical layer in a network setting with MUI. It is based on a novel combination of large deviation theory and importance sampling