Norbert Daniele

Impact of NLOS propagation upon ranging precision in UWB systems

The ultra wideband (UWB) radiolocation functionality usually relies on the ability to perform a very precise estimation of the time of flight (TOF). Unfortunately, in spite of the fine performances demonstrated by the UWB systems, indoor dense multipath channels may alter the precision of the range estimate from severe blockage situations. This paper addresses the general problem of non line of sight (NLOS) errors in the specific context of UWB range estimation. Typical ranging errors due to the NLOS propagation are exhibited by deriving experimental results from real indoor VNA measurements into realistic statistical error models.

Performances analysis of a UWB receiver using complex processing

Ultra wideband (UWB) systems are characterized by the transmission of very low power spectral density signals using bandwidths from 500 MHz up to several GHz and propagating through dense multipath channels. Digital communications using UWB impulse radio concern, among others, high data rate transmissions, for instance between 1 Mbps and 1 Gbps. The aim of this analysis is to define a generic UWB model, in terms of signal shape, modulation scheme and channel representation. Then, this model is used to specify and evaluate a brand-new principle of UWB receiver based on a mono band complex processing and maximum ratio combining.

Wireless transmissions in multipath environments benefit from direct sequence spread spectrum techniques

Presents recent radio communications research work carried out by LETI (Laboratoire dElectronique, de Technologie et dInstrumentation), which is a laboratory belonging to the French Atomic Energy Commission. At the outset, a team from the LETI was involved in a programme to develop robot intervention in hostile environments. One of the first problems to be solved was to find a reliable and robust radio modulation technique for multi-path environments. In this type of situation, conventional radio solutions are unsuccessful and provide only extremely low data rates. The performance of wireless transmissions is much poorer than conventional communications using cables and they have to cope with a transmission channel that is subject to much more interference. In particular, multi-path transmission of radio waves leads to interference phenomena such as widening of the channel impulse response, fading and Doppler noise, which reduce the quality of the transmission. A novel reception structure, implementing direct-sequence spread-spectrum techniques combined with a diversity system, actually benefits from the multi-path phenomena which usually damage conventional radio transmissions. The first receivers developed were based on a surface acoustic wave filter and were subsequently replaced by dedicated digital circuits that perform all the base band processing. The resulting flexibility has made the design of CDMA and high-data-rate wireless systems possible. This research has potential applications in a wide variety of areas, e.g. video surveillance and track-to-train communications in underground systems and factory communications for machine synchronisation.

L'étalement de spectre par séquence directe Une solution pour les communications radio en milieu perturbé

Resume La necessite de faire communiquer des robots en environnement hostile (de type centrale nucleaire) a conduit le cea-letl a valoriser ses connaissances de letalement de spectre par sequence directe. Cette technique permet en effet de tirer profit des trajets multiples qui ne manquent pas daffecter les transmissions radio classiques, grâce a une structure de reception originale et un traitement de diversite. Dabord realisees a partir dun filtre a ondes acoustiques de surface, les recepteurs mis au point ont ensuite utilise des circuits numeriques dedies prenant en compte tout le traitement bande de base, La souplesse apportee permet des lors denvisager des structures de reception multiutilisateurs orientees haut debit(jusqua 10 Mbits/s). Toutes ces recherches trouvent ainsi leurs applications dans des domaines varies: la video-surveillance et les communications sol-train dans le metro, les communications tete queue pour les trains hyper-lourds en sont quelques exemples.