136 research outputs found
Use of the Wavelet Transform for Interference Detection and Mitigation in Global Navigation Satellite Systems
Radio frequency interference detection and mitigation are becoming of paramount importance due to the increasing number of services and applications based on the position obtained by means of Global Navigation Satellite Systems. A way to cope with such threats is the implementation in the receiver of advanced signal processing algorithm able to raise proper warning or improve the receiver performance. In this paper, we propose a method based on the Wavelet Transform able to split the useful signal from the interfering component in a transformed domain. The wavelet packet decomposition and proper statistical thresholds allow the algorithm to show very good performance in case of multiple pulse interference as well as in the case of narrowband interference, two scenarios in which traditional countermeasures might not be effective
A VHDL-AMS Simulation Environment for an UWB Impulse Radio Transceiver
Ultra-Wide-Band (UWB) communication based on the impulse radio paradigm is becoming increasingly popular. According to the IEEE 802.15 WPAN Low Rate Alternative PHY Task Group 4a, UWB will play a major role in localization applications, due to the high time resolution of UWB signals which allow accurate indirect measurements of distance between transceivers. Key for the successful implementation of UWB transceivers is the level of integration that will be reached, for which a simulation environment that helps take appropriate design decisions is crucial. Owing to this motivation, in this paper we propose a multiresolution UWB simulation environment based on the VHDL-AMS hardware description language, along with a proper methodology which helps tackle the complexity of designing a mixed-signal UWB System-on-Chip. We applied the methodology and used the simulation environment for the specification and design of an UWB transceiver based on the energy detection principle. As a by-product, simulation results show the effectiveness of UWB in the so-called ranging application, that is the accurate evaluation of the distance between a couple of transceivers using the two-way-ranging metho
Compressive Demodulation of Mutually Interfering Signals
Multi-User Detection is fundamental not only to cellular wireless
communication but also to Radio-Frequency Identification (RFID) technology that
supports supply chain management. The challenge of Multi-user Detection (MUD)
is that of demodulating mutually interfering signals, and the two biggest
impediments are the asynchronous character of random access and the lack of
channel state information. Given that at any time instant the number of active
users is typically small, the promise of Compressive Sensing (CS) is the
demodulation of sparse superpositions of signature waveforms from very few
measurements. This paper begins by unifying two front-end architectures
proposed for MUD by showing that both lead to the same discrete signal model.
Algorithms are presented for coherent and noncoherent detection that are based
on iterative matching pursuit. Noncoherent detection is all that is needed in
the application to RFID technology where it is only the identity of the active
users that is required. The coherent detector is also able to recover the
transmitted symbols. It is shown that compressive demodulation requires
samples to recover active users whereas
standard MUD requires samples to process total users with a
maximal delay . Performance guarantees are derived for both coherent and
noncoherent detection that are identical in the way they scale with number of
active users. The power profile of the active users is shown to be less
important than the SNR of the weakest user. Gabor frames and Kerdock codes are
proposed as signature waveforms and numerical examples demonstrate the superior
performance of Kerdock codes - the same probability of error with less than
half the samples.Comment: submitted for journal publicatio
Multi Detector Fusion of Dynamic TOA Estimation using Kalman Filter
In this paper, we propose fusion of dynamic TOA (time of arrival) from
multiple non-coherent detectors like energy detectors operating at sub-Nyquist
rate through Kalman filtering. We also show that by using multiple of these
energy detectors, we can achieve the performance of a digital matched filter
implementation in the AWGN (additive white Gaussian noise) setting. We derive
analytical expression for number of energy detectors needed to achieve the
matched filter performance. We demonstrate in simulation the validity of our
analytical approach. Results indicate that number of energy detectors needed
will be high at low SNRs and converge to a constant number as the SNR
increases. We also study the performance of the strategy proposed using IEEE
802.15.4a CM1 channel model and show in simulation that two sub-Nyquist
detectors are sufficient to match the performance of digital matched filter
Ultra-wideband indoor communications using optical technology
La communication ultra large bande (UWB) a attirĂ© une Ă©norme quantitĂ© de recherches ces derniĂšres annĂ©es, surtout aprĂšs la prĂ©sentation du masque spectral de US Federal Communications Commission (FCC). Les impulsions ultra-courtes permettent de trĂšs hauts dĂ©bits de faible puissance tout en Ă©liminant les interfĂ©rences avec les systĂšmes existants Ă bande Ă©troite. La faible puissance, cependant, limite la portĂ©e de propagation des radios UWB Ă quelques mĂštres pour la transmission sans fil Ă lâintĂ©rieur dâune piĂšce. En outre, des signaux UWB reçu sont Ă©tendus dans le temps en raison de la propagation par trajet multiple qui rĂ©sulte en beaucoup dâinterfĂ©rence inter-symbole (ISI) Ă haut dĂ©bit. Le monocycle Gaussien, lâimpulsion la plus commune dans UWB, a une mauvaise couverture sous le masque de la FCC. Dans cette thĂšse, nous dĂ©montrons des transmet- teurs qui sont capables de gĂ©nĂ©rer des impulsions UWB avec une efficacitĂ© de puissance Ă©levĂ©e. Une impulsion efficace rĂ©sulte dans un rapport de signal Ă bruit (SNR) supĂ©rieur au rĂ©cepteur en utilisant plus de la puissance disponible sous le masque spectral de la FCC. On produit les impulsions dans le domaine optique et utilise la fibre optique pour les transporter sur plusieurs kilomĂštres pour la distribution dans un rĂ©seau optique pas- sif. La fibre optique est trĂšs fiable pour le transport des signaux radio avec une faible consommation de puissance. On utilise les Ă©lĂ©ments simples comme un modulateur Mach-Zehnder ou un rĂ©sonateur en anneau pour gĂ©nĂ©rer des impulsions, ce qui permet lâintĂ©gration dans le silicium. Compatible avec la technologie CMOS, la photonique sur silicium a un potentiel Ă©norme pour abaisser le coĂ»t et lâencombrement des systĂšmes optiques. La photodĂ©tection convertit les impulsions optiques en impulsions Ă©lectriques avant la transmission sur lâantenne du cĂŽtĂ© de lâutilisateur. La rĂ©ponse frĂ©quentielle de lâantenne dĂ©forme la forme dâonde de lâimpulsion UWB. Nous proposons une technique dâoptimisation non-linĂ©aire qui prend en compte la distorsion dâantenne pour trouver des impulsions qui maximisent la puissance transmise, en respectant le masque spectral de la FCC. Nous travaillons avec trois antennes et concevons une impulsion unique pour chacune dâentre elle. LâamĂ©lioration de lâĂ©nergie des impulsions UWB amĂ©liore directement la SNR au rĂ©cepteur. Les rĂ©sultats de simulation montrent que les impulsions optimisĂ©es amĂ©liorent considĂ©rablement le taux dâerreur (BER) par rapport au monocycle Gaussien sous propagation par trajet multiple. Notre autre contribution est lâĂ©valuation dâun filtre adaptĂ© pour recevoir efficacement des impulsions UWB. Le filtre adaptĂ© est synthĂ©tisĂ© et fabriquĂ© en technologie microstrip, en collaboration avec lâUniversitĂ© McGill comme un dispositif de bande interdite Ă©lectromagnĂ©tique. La rĂ©ponse frĂ©quentielle du filtre adaptĂ© montre une ex- cellente concordance avec le spectre ciblĂ© de lâimpulsion UWB. Les mesures de BER confirment la performance supĂ©rieure du filtre adaptĂ© par rapport Ă un rĂ©cepteur Ă conversion directe. Le canal UWB est trĂšs riche en trajet multiple conduisant Ă lâISI Ă haut dĂ©bit. Notre derniĂšre contribution est lâĂ©tude de performance des rĂ©cepteurs en simulant un systĂšme avec des conditions de canaux rĂ©alistes. Les rĂ©sultats de la simulation montrent que la performance dâun tel systĂšme se dĂ©grade de façon significative pour les hauts dĂ©bits. Afin de compenser la forte ISI dans les taux de transfert de donnĂ©es en Gb/s, nous Ă©tudions lâalgorithme de Viterbi (VA) avec un nombre limitĂ© dâĂ©tats et un Ă©galiseur DFE (decision feedback equalizer). Nous examinons le nombre dâĂ©tats requis dans le VA, et le nombre de coefficients du filtre dans le DFE pour une transmission fiable de UWB en Gb/s dans les canaux en ligne de vue. LâĂ©valuation par simulation de BER confirme que lâĂ©galisation amĂ©liore considĂ©rablement les performances par rapport Ă la dĂ©tection de symbole. La DFE a une meilleure performance par rapport Ă la VA en utilisant une complexitĂ© comparable. La DFE peut couvrir une plus grande mĂ©moire de canal avec un niveau de complexitĂ© relativement rĂ©duit.Ultra-wideband (UWB) communication has attracted an enormous amount of research in recent years, especially after the introduction of the US Federal Communications Commission (FCC) spectral mask. Ultra-short pulses allow for very high bit-rates while low power eliminates interference with existing narrowband systems. Low power, however, limits the propagation range of UWB radios to a few meters for indoors wireless transmission. Furthermore, received UWB signals are spread in time because of multipath propagation which results in high intersymbol interference at high data rates. Gaussian monocycle, the most commonly employed UWB pulse, has poor coverage under the FCC mask. In this thesis we demonstrate transmitters capable of generating UWB pulses with high power efficiency at Gb/s bit-rates. An efficient pulse results in higher signal-to-noise ratio (SNR) at the receiver by utilizing most of the available power under the FCC spectral mask. We generate the pulses in the optical domain and use optical fiber to transport the pulses over several kilometers for distribution in a passive optical network. Optical fiber is very reliable for transporting radio signals with low power consumption. We use simple elements such as a Mach Zehnder modulator or a ring resonator for pulse shaping, allowing for integration in silicon. Being compatible with CMOS technology, silicon photonics has huge potential for lowering the cost and bulkiness of optical systems. Photodetection converts the pulses to the electrical domain before antenna transmission at the user side. The frequency response of UWB antennas distorts the UWB waveforms. We pro- pose a nonlinear optimization technique which takes into account antenna distortion to find pulses that maximize the transmitted power, while respecting the FCC spectral mask. We consider three antennas and design a unique pulse for each. The energy improvement in UWB pulses directly improves the receiver SNR. Simulation results show that optimized pulses have a significant bit error rate (BER) performance improvement compared to the Gaussian monocycle under multipath propagation. Our other contribution is evaluating a matched filter to receive efficiently designed UWB pulses. The matched filter is synthesized and fabricated in microstrip technology in collaboration with McGill University as an electromagnetic bandgap device. The frequency response of the matched filter shows close agreement with the target UWB pulse spectrum. BER measurements confirm superior performance of the matched filter compared to a direct conversion receiver. The UWB channel is very rich in multipath leading to ISI at high bit rates. Our last contribution is investigating the performance of receivers by simulating a system employing realistic channel conditions. Simulation results show that the performance of such system degrades significantly for high data rates. To compensate the severe ISI at gigabit rates, we investigate the Viterbi algorithm (VA) with a limited number of states and the decision feedback equalizer (DFE). We examine the required number of states in the VA, and the number of taps in the DFE for reliable Gb/s UWB trans- mission for line-of-sight channels. Non-line-of-sight channels were also investigated at lower speeds. BER simulations confirm that equalization considerably improves the performance compared to symbol detection. The DFE results in better performance compared to the VA when using comparable complexity as the DFE can cover greater channel memory with a relatively low complexity level
A built-in self-test technique for high speed analog-to-digital converters
Fundação para a CiĂȘncia e a Tecnologia (FCT) - PhD grant (SFRH/BD/62568/2009
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