Bandwidth Efficient Root Nyquist Pulses for Optical Intensity Channels

Indoor diffuse optical intensity channels are bandwidth constrained due to the multiple reflected paths between the transmitter and the receiver which cause considerable inter-symbol interference (ISI). The transmitted signal amplitude is inherently non-negative, being a light intensity signal. All optical intensity root Nyquist pulses are time-limited to a single symbol interval which eliminates the possibility of finding bandlimited root Nyquist pulses. However, potential exists to design bandwidth efficient pulses. This paper investigates the modified hermite polynomial functions and prolate spheroidal wave functions as candidate waveforms for designing spectrally efficient optical pulses. These functions yield orthogonal pulses which have constant pulse duration irrespective of the order of the function, making them ideal for designing an ISI free pulse. Simulation results comparing the two pulses and challenges pertaining to their design and implementation are discussed

Extending the Zn2Z^2_n and HH statistics to generic pulsed profiles

The search for astronomical pulsed signals within noisy data, in the radio band, is usually performed through an initial Fourier analysis to find "candidate" frequencies and then refined through the folding of the time series using trial frequencies close to the candidate. In order to establish the significance of the pulsed profiles found at these trial frequencies, pulsed profiles are evaluated with a chi-squared test, to establish how much they depart from a null hypothesis where the signal is consistent with a flat distribution of noisy measurements. In high-energy astronomy, the chi-squared statistic has widely been replaced by the $Z^2_n$ statistic and the H-test as they are more sensitive to extra information such as the harmonic content of the pulsed profile. The $Z^2_n$ statistic and H-test were originally developed for the use with "event data", composed of arrival times of single photons, leaving it unclear how these methods could be used in radio astronomy. In this paper, we present a version of the $Z^2_n$ statistic and H-test for pulse profiles with Gaussian uncertainties, appropriate for radio or even optical pulse profiles. We show how these statistical indicators provide better sensitivity to low-significance pulsar candidates with respect to the usual chi-squared method, and a straightforward way to discriminate between pulse profile shapes. Moreover, they provide an additional tool for Radio Frequency Interference (RFI) rejection.Comment: 15 pages, 5 figure

Multicarrier Faster-than-Nyquist Signaling Transceivers: From Theory to Practice

The demand for spectrum resources in cellular systems worldwide has seen a tremendous escalation in the recent past. The mobile phones of today are capable of being cameras taking pictures and videos, able to browse the Internet, do video calling and much more than an yesteryear computer. Due to the variety and the amount of information that is being transmitted the demand for spectrum resources is continuously increasing. Efficient use of bandwidth resources has hence become a key parameter in the design and realization of wireless communication systems. Faster-than-Nyquist (FTN) signaling is one such technique that achieves bandwidth efficiency by making better use of the available spectrum resources at the expense of higher processing complexity in the transceiver. This thesis addresses the challenges and design trade offs arising during the hardware realization of Faster-than-Nyquist signaling transceivers. The FTN system has been evaluated for its achievable performance compared to the processing overhead in the transmitter and the receiver. Coexistence with OFDM systems, a more popular multicarrier scheme in existing and upcoming wireless standards, has been considered by designing FTN specific processing blocks as add-ons to the conventional transceiver chain. A multicarrier system capable of operating under both orthogonal and FTN signaling has been developed. The performance of the receiver was evaluated for AWGN and fading channels. The FTN system was able to achieve 2x improvement in bandwidth usage with similar performance as that of an OFDM system. The extra processing in the receiver was in terms of an iterative decoder for the decoding of FTN modulated signals. An efficient hardware architecture for the iterative decoder reusing the FTN specific processing blocks and realize different functionality has been designed. An ASIC implementation of this decoder was implemented in a 65nm CMOS technology and the implemented chip has been successfully verified for its functionality

Position estimation for IR-UWB systems using compressive sensing

One major challenge in IR-UWB signal processing is the requirement of high sampling rate, which renders standard analog-to-digital converter (ADC) costly and even impractical. Compressive Sensing (CS) provides a solution to this problem by allowing to sample UWB signals at a rate significantly lesser than the Nyquist sampling limit.Ultra-Wideband (UWB) technology, thanks to its high time resolution, arises as an excellent candidate to provide accurate positioning information in cluttered environments. However, the dense multipath and strong attenuation of the Line-of-Sight (LOS) present in UWB channels poses additional challenges to positioning algorithms. Therefore, in this thesis we have mainly focused on designing an algorithm robust to these problems. Specifically, we have developed two different techniques based on a frequency domain receiver. The first one is based on a Direct Position Estimation (DPE) approach, that is, estimating the position directly from the observed signals, while the second is based on ?soft? two-steps approach, where more than one estimated Time of Arrival (TOA) is estimated on each anchor, then in the second stage the best estimators are used to find the position. Simulation results proof the accuracy of the proposed algorithms. Besides, the proposed methods have also been tested while using Compressive Sensing (CS). CS is a new sensing paradigm that allows compressing signals while they are being sampled, thus it allows to sample at a lower rather than the Nyquist limit.La tecnología Ultra-Wideband (UWB), gracias a su alta resolución temporal, se presenta como un candidato ideal per proporcionar información de la posición precisa en ambientes muy densos. Sin embargo, la gran concentración de propagación multi camino, así como la fuerte atenuación del camino de visión directa (LOS) característica de los canales UWB conlleva grandes dificultades a la hora de estimar la posición. Por esta razón, en esta tesis nos hemos centrado principalmente en diseñar algoritmos robustos a la problemática que presenten los canales UWB. Concretamente, hemos desarrollado dos técnicas basadas en un receptor en el dominio de la frecuencia. La primera está basada en una estimación directa de la posición (DPE) a partir de las señales recibidas, mientras que la segunda está basada en una estimación en dos etapas pero con la diferencia que en la primera etapa se proporcionen diversos estimadores del tiempo de vuelo (TOA) y en la segunda se seleccionen los mejores estimadores para estimar la posición. Los resultados de les simulaciones demuestran la precisión del los algoritmos propuestos. Además, los métodos propuestos también se han probado utilizando Compressive Sensing (CS). El CS es un nuevo paradigma en la teoría del muestreo que permite comprimir una señal al mismo tiempo que se está muestreando, permitiendo así muestrear per debajo del límite de Nyquist.La tecnologia Ultra-Wideband (UWB), gràcies a la seva alta resolució temporal, es presenta com un candidat ideal per proporcionar informació de la posició precisa en ambients molt densos. Tanmateix, la gran concentració de propagació multi camí, així com la forta atenuació del camí de visió directa (LOS) característica del canals UWB comporta grans dificultats a l?hora d?estimar la posició. Per aquesta raó, en aquesta tesis ens hem centrat principalment en dissenyar algoritmes robusts a la problemàtica que presenten els canals UWB. Concretament, hem desenvolupat dues tècniques basades en un receptor en el domini freqüencial. La primera està basada en una estimació directa de la posició (DPE) a partir dels senyals rebuts, mentre que la segona està basada en una estimació en dues etapes però amb la diferència que en la primera etapa es proporcionen diversos estimadors del temps de vol (TOA) i en la segona es seleccionen els millors estimadors per trobar la posició. Els resultats de les simulacions demostren la precisió dels algoritmes proposats. A més a més, els mètodes proposats també s?han provat fent servir Compressive Sensing (CS). CS és un nou paradigma en la teoria del mostreig que permet comprimir una senyal mentre s?està mostrejant, permetent així mostrejar per sota del límit de Nyquist

Doctor of Philosophy

dissertationWireless communications pervade all avenues of modern life. The rapid expansion of wireless services has increased the need for transmission schemes that are more spectrally efficient. Dynamic spectrum access (DSA) systems attempt to address this need by building a network where the spectrum is used opportunistically by all users based on local and regional measurements of its availability. One of the principal requirements in DSA systems is to initialize and maintain a control channel to link the nodes together. This should be done even before a complete spectral usage map is available. Additionally, with more users accessing the spectrum, it is important to maintain a stable link in the presence of significant interference in emergency first-responders, rescue, and defense applications. In this thesis, a new multicarrier spread spectrum (MC-SS) technique based on filter banks is presented. The new technique is called filter bank multicarrier spread spectrum (FB-MC-SS). A detailed theory of the underlying properties of this signal are given, with emphasis on the properties that lend themselves to synchronization at the receiver. Proposed algorithms for synchronization, channel estimation, and detection are implemented on a software-defined radio platform to complete an FB-MC-SS transceiver and to prove the practicality of the technique. FB-MC-SS is shown through physical experimentation to be significantly more robust to partial band interference compared to direct sequence spread spectrum. With a higher power interfering signal occupying 90% of its band, FB-MC-SS maintains a low bit error rate. Under the same interference conditions, DS-SS fails completely. This experimentation leads to a theoretical analysis that shows in a frequency selective channel with additive white noise, the FB-MC-SS system has performance that equals that obtained by a DS-SS system employing an optimal rake receiver. This thesis contains a detailed chapter on implementation and design, including lessons learned while prototyping the system. This is to assist future system designers to quickly gain proficiency in further development of this technology