MMP-DCD-CV based Sparse Channel Estimation Algorithm for Underwater Acoustic Transform Domain Communication System

In this paper, we propose a computationally efficient multipath matching pursuit (MMP) channel estimation algorithm for underwater acoustic (UWA) transform domain communication systems (TDCSs). The algorithm, referred to as the MMP-DCD-CV algorithm, is based on the dichotomous coordinate descent (DCD) iterations and cross validation (CV). The MMP-DCD-CV sparse channel estimator in each iteration searches for multiple promising path candidates most relevant to a residual vector and chooses the best candidate. The DCD iterations are used to solve the corresponding least squares problem with low complexity and numerical stability. The CV provides a stopping criterion of the algorithm without a priori information on the channel sparsity and noise level and examines whether the algorithm overfits its data, thus improving the estimation accuracy. The performance of the proposed algorithm is evaluated under simulated sparse UWA channels. The numerical results show that the algorithm achieves better performance than the original MMP algorithm, has lower complexity, and does not require prior knowledge on the channel sparsity and noise level. We also propose an UWA TDCS with sparse channel estimation based on the proposed MMP-DCD-CV algorithm. The proposed UWA communication system is tested by the Waymark simulator, providing the virtual signal transmission in the UWA channel, with a measured Sound Speed Profile and bathymetry. Numerical results demonstrate that the UWA TDCS with the proposed sparse channel estimator offers considerable improvement in system performance compared to other TDCS schemes

Blood Velocities Estimation using Ultrasound

This thesis consists of two parts. In the rst part, the iterative data-adaptive BIAA spectral estimation technique was extended to estimate lateral blood velocities using ultrasound scanners. The BIAA method makes no assumption on samples depth or sampling pattern, and therefore allows for transmission in duplex mode imaging. The technique was examined on a realistic Field II simulation data set, and showed fewer spectral artifacts in comparison with other techniques. In the second part of the thesis, another common problem in blood velocity estimation has been investigated, namely strong backscattered signals from stationary echoes. Two methods have been tested to examine the possibility of overcoming this problem. However, neither of these methods resulted in a better estimation of the blood velocities, most likely as the clutter characteristics in color ow images vary too rapidly to allow for this form of models. This might be a result of the non-stationary tissue motions which could be caused by a variety of factors, such as cardiac activities, respiration, transducer/patient movement, or a combination of them

MICROPHONE ARRAY OPTIMIZATION IN IMMERSIVE ENVIRONMENTS

The complex relationship between array gain patterns and microphone distributions limits the application of traditional optimization algorithms on irregular arrays, which show enhanced beamforming performance for human speech capture in immersive environments. This work analyzes the relationship between irregular microphone geometries and spatial filtering performance with statistical methods. Novel geometry descriptors are developed to capture the properties of irregular microphone distributions showing their impact on array performance. General guidelines and optimization methods for regular and irregular array design are proposed in immersive (near-field) environments to obtain superior beamforming ability for speech applications. Optimization times are greatly reduced through the objective function rules using performance-based geometric descriptions of microphone distributions that circumvent direct array gain computations over the space of interest. In addition, probabilistic descriptions of acoustic scenes are introduced to incorporate various levels of prior knowledge for the source distribution. To verify the effectiveness of the proposed optimization methods, simulated gain patterns and real SNR results of the optimized arrays are compared to corresponding traditional regular arrays and arrays obtained from direct exhaustive searching methods. Results show large SNR enhancements for the optimized arrays over arbitrary randomly generated arrays and regular arrays, especially at low microphone densities. The rapid convergence and acceptable processing times observed during the experiments establish the feasibility of proposed optimization methods for array geometry design in immersive environments where rapid deployment is required with limited knowledge of the acoustic scene, such as in mobile platforms and audio surveillance applications

Engineering data compendium. Human perception and performance. User's guide

The concept underlying the Engineering Data Compendium was the product of a research and development program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design and military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from the existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by systems designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is the first volume, the User's Guide, containing a description of the program and instructions for its use

Reliable Cognitive Ultra Wideband Communication Systems Under Coexistence Constraints

RÉSUMÉ La croissance rapide des systèmes de communication sans fil et la rareté du spectre ont motivé les industries et les fournisseurs ouvrant dans le domaine de communication sans fil de développer des stratégies et des technologies de communication qui peuvent utiliser efficacement les ressources spectrales. La réutilisation pacifique du spectre sous-licence et sous-utilisé peut être une solution prometteuse pour certaines initiatives en cours telles que la communication mobile à haut débit, la communication machine-à-machine, et la connectivité WiFi. Un des plus gros facteurs qui empêche l'approche de cette réutilisation de fréquences est l'effet d'environnements bruyants sur les dispositifs coexistent dans la même bande de fréquence. Par conséquent, la demande pour une stratégie de coexistence pacifique entre les utilisateurs du spectre, des défis et des questions techniques qu'elle engêndre, motive notre recherche. Il est à noter que dans cette thèse, nous considérons un système pratique appelé MB-OFDM UWB (en anglais multiband orthogonal frequency division multiplexing ultra wideband) pour donner un aperçu pratique de ce concept. Pour atteindre cet objectif, d'abord nous examinons le problème d'interférence des utilisateurs secondaires sur les utilisateurs principaux. A cet effet, tenant compte d'un système secondaire OFDM, nous proposons des méthodes de mise en forme du spectre pour les applications de transmission à antennes simples et multiples. Nous présentons une technique débit-efficace nommée “Enhanced active interference cancellation (E - AIC)qui est en effet capable de créer des encoches ayant des caractéristiques flexibles. Afin de résoudre le problème de dépassement du spectre causé pas la technique classique-AIC, nous utilisons une approche multi-contraintes qui à son tour cause un problème multi-contrainte de minimisation (en anglais multi-constraint minimization problem, MCMP). Cependant, un nouvel algorithme itératif basé sur la technique SVD (en anglais singular value decomposition) est proposé, permettant ainsi de réduire la complexité de la solution de MCMP. Les résultats de simulation obtenus montrent que la technique E-AIC proposée fournit de meilleures performances en termes de suppression des lobes latéraux avec 0 dB de dépassement, moins de complexité de calcul et moins de perte de débit par rapport aux méthodes AIC précédentes. Quant aux antennes multiples, nous proposons deux nouvelles techniques AIC, qui utilisent l'idée principale des approches de sélection d'antennes d'émission (en anglais transmit antenna selection, TAS). Bien que les résultats montrent que les deux techniques permettent la création d'encoche identique, la technique per-tone TAS-AIC a la plus grande efficacité spectrale. Après avoir obtenu une emission sans interférence pour le système MB-OFDM UWB, nous analysons, modélisons et atténuons le bruit impulsif au récepteur MB-OFDM UWB. Pour ce faire, d'abord, nous proposons un cadre analytique qui décrit les principales caractéristiques d'interférence d'un système à ultra large bande et saut temporel (en anglais time-hopping UWB, TH-UWB) niveau de ces paramètres de signalisation. Les résultats montrent que la distribution d'interférence dépend fortement aux paramètres de saut temporel du système TH-UWB.----------ABSTRACT The rapid growth of wireless communication systems along with the radio spectrum's scarcity and regulatory considerations have put the onus on the wireless industries and service providers to develop wireless communication strategies and technologies that can efficiently utilize the spectral resources. Hence, peaceful reuse of underutilized licensed radio frequencies (by secondary users) can be a promising solution for some ongoing initiatives such as mobile broadband, machine-to-machine applications and WiFi connectivity. One of the biggest factors that prevents the spectrum reusing approach to effectively address the spectrum scarcity, is noisy environments result from coexistence of different devices in the same frequency band. Therefore, the request for a peaceful coexistence strategy between spectrum users, which leads to various challenges, and technical issues, motivates our research. It is worth noting that, in this thesis, we consider a practical system called multiband orthogonal frequency division multiplexing ultra wideband (MB-OFDM UWB) as an underlay system to provide a practical insight into this concept. However, all the obtained results and contributions are applicable to other OFDM-based communication systems. Towards this goal, we first investigate the problem of the interference from secondary users to the primary users. For this purpose, considering an OFDM-based secondary communication system, we propose spectrum-shaping methods for single and multiple transmit antennas applications. For single antenna scenario, we present a throughput-efficient enhanced active interference cancellation (E-AIC) technique, which is indeed capable of creating notches with flexible characteristics. In order to address the spectrum overshoot problem of conventional-AIC techniques, we employed a multi-constraint approach, which leads to a multi-constraint minimization problem (MCMP). Hence, a novel iterative singular value decomposition (SVD) based algorithm is proposed to reduce the complexity of the MCMP's solution. The obtained simulation results show that the proposed enhanced-AIC technique provides higher performance in terms of sidelobes suppression with 0 dB overshoot, less computational complexity and less throughput-loss compared to previous constrained-AIC methods. For multiple transmit antennas, we propose two novel AIC techniques employing main ideas behind bulk and per-tone transmit antenna selection (TAS) approaches. Simulation results show that although both techniques provide identical notch creation, the per-tone TAS-AIC technique has higher spectral efficiency

Blind source separation for interference cancellation in CDMA systems

Communication is the science of "reliable" transfer of information between two parties, in the sense that the information reaches the intended party with as few errors as possible. Modern wireless systems have many interfering sources that hinder reliable communication. The performance of receivers severely deteriorates in the presence of unknown or unaccounted interference. The goal of a receiver is then to combat these sources of interference in a robust manner while trying to optimize the trade-off between gain and computational complexity. Conventional methods mitigate these sources of interference by taking into account all available information and at times seeking additional information e.g., channel characteristics, direction of arrival, etc. This usually costs bandwidth. This thesis examines the issue of developing mitigating algorithms that utilize as little as possible or no prior information about the nature of the interference. These methods are either semi-blind, in the former case, or blind in the latter case. Blind source separation (BSS) involves solving a source separation problem with very little prior information. A popular framework for solving the BSS problem is independent component analysis (ICA). This thesis combines techniques of ICA with conventional signal detection to cancel out unaccounted sources of interference. Combining an ICA element to standard techniques enables a robust and computationally efficient structure. This thesis proposes switching techniques based on BSS/ICA effectively to combat interference. Additionally, a structure based on a generalized framework termed as denoising source separation (DSS) is presented. In cases where more information is known about the nature of interference, it is natural to incorporate this knowledge in the separation process, so finally this thesis looks at the issue of using some prior knowledge in these techniques. In the simple case, the advantage of using priors should at least lead to faster algorithms.reviewe