We consider real zero-crossing analysis of the real/imaginary parts of the spectrum, namely, spectral zero-crossings (SZCs). The two major contributions are to show that: (i) SZCs provide enable temporal localization of transients; and (b) SZCs are suitable for modeling transient signals. We develop a spectral dual of Kedem’s result linking temporal zero-crossing rate (ZCR) to the spectral centroid. The key requirement is stationarity, which we achieve through random-phase modulations of the time-domain signal. Transient signals are not amenable to modelling in the time domain since they are bursts of energy localized in time and lack structure. We show that the spectrum of transient signals have a rich modulation structure, which leads to an amplitude-modulation – frequency-modulation (AM-FM) model of the spectrum. We generalize Kedem’s arc-cosine formula for lags greater than one. For the specific case of a sinusoid in white Gaussian noise, He and Kedem devised an iterative filtering algorithm, which leads to a contraction mapping. An autoregressive filter of order one is employed and the location of the pole is the parameter that is updated based on the filtered output. We use the higher-order property, which relates the autocorrelation to the expected ZCR of the filtered process, between lagged ZCR and higher-lag autocorrelation to develop an iterative higher-order autoregressive-filtering scheme, which stabilizes the ZCR and consequently provides robust estimates of the autocorrelation at higher lags. Next, we investigate ZC properties of critically sampled outputs of a maximally decimated M-channel power complementary analysis filterbank (PCAF) and derive the relationship between the ZCR of the input Gaussian process at lags that are integer multiples of M in terms of the subband ZCRs. Based on this result, we propose a robust autocorrelation estimator for a signal consisting of a sum of sinusoids of fixed amplitudes and uniformly distributed random phases. Robust subband ZCRs are obtained through iterative filtering and the subband variances are estimated using the method-of-moments estimator. We compare the performance of the proposed estimator with the sample auto-correlation estimate in terms of bias, variance, and mean-squared error, and show through simulations that the performance of the proposed estimator is better than the sample auto- correlation for medium to low SNR. We then consider the ZC statistics of the real/imaginary parts of the discrete Fourier spectrum. We introduce the notion of the spectral zero-crossing rate (SZCR) and show that, for transients, it gives information regarding the location of the transient. We also demonstrate the utility of SZCR to estimate interaural time delay between the left and right head-related impulse responses. The accuracy of interaural time delay plays a vital role in binaural synthesis and a comparison of the performance of the SZCR estimates with that of the cross-correlation estimates illustrate that spectral zeros alone contain enough information for accurately estimating interaural time delay. We provide a mathematical formalism for establishing the dual of the link between zero-crossing rate and spectral centroid. Specifically, we show that the expected SZCR of a stationary spectrum is a temporal centroid. For a deterministic sequence, we obtain the stationary spectrum by modulating the sequence with a random phase unit amplitude sequence and then computing the spectrum. The notion of a stationary spectrum is necessary for deriving counterparts of the results available in temporal zero-crossings literature. The robustness of location information embedded in SZCR is analyzed in presence of a second transient within the observation window, and also in the presence of additive white Gaussian noise. A spectral-domain iterative filtering scheme based on autoregressive filters is presented and improvement in the robustness of the location estimates is demonstrated. As an application, we consider epoch estimation in voiced speech signals and show that the location information is accurately estimated using spectral zeros than other techniques. The relationship between temporal centroid and SZCR also finds applications in frequency-domain linear prediction (FDLP), which is used in audio compression. The prediction coefficients are estimated by solving the Yule-Walker equations constructed from the spectral autocorrelation. We use the relationship between the spectral autocorrelation and temporal centroid to obtain the spectral autocorrelation directly by time-domain windowing without explicitly computing the spectrum. The proposed method leads to identical results as the standard FDLP method but with reduced computational load. We then develop a SZCs-based spectral-envelope and group-delay (SEGD) model, which finds applications in modelling of non-stationary signals such as Castanets. Taking into account the modulation structure and spectral continuity, local polynomial regression is performed to estimate the GD from the real spectral zeros. The SE is estimated based on the phase function computed from the estimated GD. Since the GD estimate is parametric, the degree of smoothness can be controlled directly. Simulation results based on synthetic transient signals are presented to analyze the noise-robustness of the SE-GD model. Applications to castanet modeling, transient compression, and estimation of the glottal closure instants in speech are shown.

Higher-order spectral analysis of acoustical waveforms can provide phase information that is not retained in calculations of power spectral density. In the propagation of high intensity sound, nonlinearity can cause substantial changes in the waveform as frequency components interact with one another. The bispectrum, which is one order higher than power spectral density, may provide a useful measure of nonlinearity in propagation by highlighting spectral regions of interaction. This thesis provides a review of the bispectrum, places it in the context of nonlinear acoustic propagation, and presents spectra calculated as a function of distance for numerically propagated acoustic waveforms. The calculated spectra include power spectral density, quad-spectral density, bispectrum, spatial derivative of the bispectrum, bicoherence, and skewness function. / text

La finesse de la résolution spectrale des images hyperspectrales en télédétection permet une analyse précise de la scène observée, mais leur résolution spatiale est limitée, et un pixel acquis par le capteur est souvent un mélange des contributions de différents matériaux. Le démélange spectral permet d'estimer les spectres des matériaux purs (endmembers) de la scène, et leurs abondances dans chaque pixel. Les endmembers sont souvent supposés être parfaitement représentés par un seul spectre, une hypothèse fausse en pratique, chaque matériau ayant une variabilité intra-classe non négligeable. Le but de cette thèse est de développer des algorithmes prenant mieux en compte ce phénomène. Nous effectuons le démélange localement, dans des régions bien choisies de l'image où les effets de la variabilité sont moindres, en éliminant automatiquement les endmembers non pertinents grâce à de la parcimonie collaborative. Dans une autre approche, nous raffinons l'estimation des abondances en utilisant la structure de groupe d'un dictionnaire d'endmembers extrait depuis les données. Ensuite, nous proposons un modèle de mélange linéaire étendu, basé sur des considérations physiques, qui modélise la variabilité spectrale par des facteurs d'échelle, et développons des algorithmes d'optimisation pour en estimer les paramètres. Ce modèle donne des résultats facilement interprétables et de meilleures performances que d'autres approches de la littérature. Nous étudions enfin deux applications de ce modèle pour confirmer sa pertinence. / The fine spectral resolution of hyperspectral remote sensing images allows an accurate analysis of the imaged scene, but due to their limited spatial resolution, a pixel acquired by the sensor is often a mixture of the contributions of several materials. Spectral unmixing aims at estimating the spectra of the pure materials (called endmembers) in the scene, and their abundances in each pixel. The endmembers are usually assumed to be perfectly represented by a single spectrum, which is wrong in practice since each material exhibits a significant intra-class variability. This thesis aims at designing unmixing algorithms to better handle this phenomenon. First, we perform the unmixing locally in well chosen regions of the image where variability effects are less important, and automatically discard wrongly estimated local endmembers using collaborative sparsity. In another approach, we refine the abundance estimation of the materials by taking into account the group structure of an image-derived endmember dictionary. Second, we introduce an extended linear mixing model, based on physical considerations, modeling spectral variability in the form of scaling factors, and develop optimization algorithms to estimate its parameters. This model provides easily interpretable results and outperforms other state-of-the-art approaches. We finally investigate two applications of this model to confirm its relevance.

Une perte auditive neurosensorielle est généralement associée à uneréduction de l’intelligibilité de la parole, et ce tout particulièrement dans le bruit.Les contributions respectives d’une réduction de l'audibilité et de déficitssupraliminaires sont encore débattues.L'objectif principal de cette thèse était d'évaluer l'effet spécifique desdéficits supraliminaires sur l’intelligibilité de la parole. L'effet de l'audibilité étaitcontrôlé en mesurant l’intelligibilité de signaux de parole sans signification filtrésdans les régions basses et moyennes fréquences au sein desquelles la détection desons purs était normale chez des auditeurs malentendants présentant par ailleursune perte auditive en hautes fréquences. Dans ces régions fréquentielles oùl’audibilité est supposée normale, des déficits d'intelligibilité de la parole légers àsévères ont été observés dans le silence comme dans le bruit chez les auditeursmalentendants. Les déficits étaient similaires dans les bruits masquantstationnaires et fluctuants. Ces résultats démontrent l’influence des déficitsauditifs supraliminaires sur l’intelligibilité de la parole.Le second objectif de cette thèse était d'étudier l'origine de ces déficitssupraliminaires. Les résultats indiquent qu’une réduction de la sélectivitéfréquentielle cochléaire ne peut pas expliquer entièrement les déficitsd’intelligibilité de la parole des auditeurs malentendants. L'influence de lasensibilité à la structure temporelle fine reste incertaine / Speech intelligibility is reduced for listeners with sensorineural hearingloss, especially for speech in noise. The extent to which this reduction is due toreduced audibility or to supra-threshold deficits is still debated.The main goal of this PhD work was to investigate the specific influenceof supra-threshold deficits on speech intelligibility. The effect of audibility wascontrolled for by measuring speech intelligibility for hearing-impaired listenersusing nonsense speech signals filtered in low- and mid-frequency regions wherepure-tone sensitivity was normal. Hearing-impaired listeners with hearing loss inhigh-frequency regions showed mild to severe intelligibility deficits for speechboth in quiet and in noise in these frequency regions of normal audibility. Similardeficits were obtained for speech in steady and fluctuating masking noises. Thisprovides additional evidence that speech intelligibility may be strongly influencedby supra-threshold auditory deficits.The second aim of this PhD work was to investigate the origin of thesesupra-threshold deficits. Results showed that reduced frequency selectivity cannotentirely explain the speech intelligibility deficits of the hearing-impaired listeners.The influence of temporal fine structure sensitivity remained unclear

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / This paper considers the use of Amplitude-Phase Shift Keying (APSK) for a telemetry system. Variable rate turbo codes are used to improve the power efficiency of 16- and 32-APSK. We discuss compensation techniques for power amplifier nonlinearities. Simulation results show the improved spectral efficiency of this modulation scheme over those currently defined in telemetry standards.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Shaped Offset Quadrature Shift Keying (SOQPSK) is a spectrally efficient modulation that has been promoted in the airborne telemetry community as a more spectrally efficient alternative for legacy PCM/FM. First generation demodulators for SOQPSK use coherent detectors which achieve good bit error rates at the expense of long synchronization times. This paper examines the performance of a noncoherent SOQPSK detector which significantly improves the signal acquisition times without impacting BER performance in the AWGN environment. The two detection methods are also compared in their ability to combat other channel impairments, such as adjacent and on-channel interference.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Modern telemetry systems require flexible bit rate telemetry encoders in order to optimize mission formats for varying data rate requirements and/or signal to noise conditions given a fixed transmitter power. Implementing a variable bit rate telemetry encoder requires consideration of several possible architectural topologies that place different system requirements on data acquisition modules within the encoder in order to maintain adequate signal fidelity of sensor information. This paper focuses on the requirements, design considerations and tradeoffs associated with differing architectural topologies for implementing a variable bit rate encoder and the resulting implications on the encoder systems data acquisition units.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Since the 1970s PCM/FM has been the dominant modulation scheme used for RF telemetry. However more stringent spectrum availability as well as increasing data rates means that more advanced transmission methods are required to keep pace with industry demands. ARTM Tier-I and Tier-II are examples of how the PCM/FM link can be enhanced. However these techniques require a significant increase in the complexity of the receiver/detector for optimal recovery. This paper focuses on a quantitative approach to improving the rate and quality of data using existing PCM/FM links. In particular ACRA CONTROL and BAE SYSTEMS set themselves the goal of revisiting the pre-modulation filter, diversity combiner and bit-sync. By implementing programmable adaptive hardware, it was possible to explore the various tradeoffs offered by modifying pulse shapes and spectral occupancy, inclusion of forward error correction and smart source selection. This papers looks at the improvements achieved at each phase of the evaluation.

The widespread application of wireless services and the requirements of ubiquitous access have recently triggered rapidly booming energy consumption in wireless communications networks. Such escalation of energy consumption in wireless networks causes high operational expenditure from electricity bills for operators, unsatisfactory user experience due to limited battery capacity of wireless devices, and a large amount of greenhouse gas emission. Green radio (GR), which emphasizes both energy efficiency (EE) and spectral efficiency (SE), has been proposed as an effective solution and is becoming the mainstream for future wireless network design. Unfortunately, EE and SE do not always coincide and may even sometimes conflict. In this dissertation, we focus on energy-efficient transmission and resource allocation techniques for orthogonal frequency division multiple access (OFDMA) networks and the joint energy-efficient design of OFDMA and other promising wireless communications techniques, such as cognitive radio (CR) and two-way relay. Firstly, we investigate the principles of energy-efficient design for pure OFDMA networks. As the first step, we study the fundamental interrelationship between EE and SE in downlink OFDMA networks and analyze the impacts of channel gain and circuit power on the EE-SE relationship. We establish a general EE-SE optimization framework, where the overall EE, SE and per-user quality-of-service (QoS) are all considered. Under this framework, we find that EE is quasiconcave in SE and decreases with SE when SE is large enough. These findings are very helpful guidelines for designing energy- and spectral-efficient OFDMA. To facilitate the application of energy-efficient resource allocation, we then investigate the energy-efficient resource allocation in both downlink and uplink OFDMA networks. For the downlink transmission, the generalized EE is maximized while for the uplink case the minimum individual EE is maximized, both under prescribed per-user minimum data rate requirements. For both transmission scenarios, we first provide the optimal solution and then develop an computationally efficient suboptimal approach by exploring the inherent structure and property of the energy-efficient design. Then we study energy-efficient design in downlink OFDMA networks with effective capacity-based delay provisioning for delay-sensitive traffic. By integrating information theory with the concept of effective capacity, we formulate and solve an EE optimization problem with statistical delay provisioning. We also analyze the tradeoff between EE and delay, the relationship between spectral-efficient and energy-efficient designs, and the impact of system parameters, including circuit power and delay exponents, on the overall performance. Secondly, we consider joint energy-efficient design of OFDMA and CR and two-way relay, respectively, to further enhance the EE and SE of wireless networks. We study energy-efficient opportunistic spectrum access strategies for an OFDMA-based CR network with multiple secondary users (SUs). Both worst EE and average EE of the SUs are considered and optimized subject to constraints including maximum transmit power and maximum interference to primary user (PU) system. For both cases, we first find the optimal solution and then propose a low-complexity suboptimal alternative. The results show that the energy-efficient CR strategies significantly boost EE compared with the conventional spectral-efficient CR ones while the low-complexity suboptimal approaches can well balance the performance and complexity. Then we study energy-efficient resource allocation for OFDMA-based two-way relay, which aims at maximizing the aggregated EE utility while provisioning proportional fairness in EE among different terminal pairs. Different from most exist energy-efficient design, we consider a new circuit power model, where the dynamic circuit power is proportional to the number of active subcarrier. For low-complexity solution, we propose an EE-oriented sequential subchannel assignment policy and discover the sufficient condition for early termination of the sequential subchannel assignment without losing the EE optimality. It is found that the energy-efficient transmission does not necessarily make all the subcarriers active, which is another useful principle for practical energy-efficient system design.

International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada / A simple, low cost radio frequency (RF) power and spectrally efficient integrated transceiver/modem architecture employing Feher’s patented Quadrature Phase Shift Keying (FQPSK) is described. The FQPSK signals presented in this paper are obtained by using additional post low-pass filters in the FQPSK architecture. This implementation significantly improves the spectral efficiency of the worldwide commercially standardized Gaussian Minimum Shift Keying (GMSK) systems. The Bit Error Rate (BER) performance of FQPSK in additive white Gaussian noise (AWGN) channel has been investigated by means of computer simulation and hardware prototype measurements. The results of the hardware and software simulations are compared to GMSK and QPSK/OQPSK performance. These results show that the filtered FQPSK modulated signal passing through a non-linear amplifier (NLA) can achieve a spectral efficiency improvement of about 60% over NLA filtered OQPSK and an integrated spectral efficiency improvement of 50% over GMSK and a better BER performance. In particular, 100 kb/s to 34 Mb/s hardware experimental results over 2.4 GHz NLA (saturated) 1 Watt system confirmed that FQPSK hardware systems attain a BER=f(Eb/N0) performance within 1 dB to 2 dB of predicted theoretical results.