Fifty Years of Noise Modeling and Mitigation in Power-Line Communications.

Building on the ubiquity of electric power infrastructure, power line communications (PLC) has been successfully used in diverse application scenarios, including the smart grid and in-home broadband communications systems as well as industrial and home automation. However, the power line channel exhibits deleterious properties, one of which is its hostile noise environment. This article aims for providing a review of noise modeling and mitigation techniques in PLC. Specifically, a comprehensive review of representative noise models developed over the past fifty years is presented, including both the empirical models based on measurement campaigns and simplified mathematical models. Following this, we provide an extensive survey of the suite of noise mitigation schemes, categorizing them into mitigation at the transmitter as well as parametric and non-parametric techniques employed at the receiver. Furthermore, since the accuracy of channel estimation in PLC is affected by noise, we review the literature of joint noise mitigation and channel estimation solutions. Finally, a number of directions are outlined for future research on both noise modeling and mitigation in PLC

Analysis performance of wavelet OFDM in mobility platforms

Wavelet orthogonal frequency division multiplexing (OFDM) is one of the medium access techniques recommended by the IEEE 1901 working group for broadband communications over electrical networks, and is under consideration for IoT applications. This standard provides a flexible architecture supporting integrated access, smart grid, building, in-home, and mobility platform (vehicle) applications. Wavelet OFDM is a filter bank multicarrier system based on the extended lapped transform, in which the transmitting and receiving filters are obtained from a waveform provided by the standard. In this paper, we explore system performance when other waveforms are employed, studying the trade-off between stopband attenuation and transition band width. Furthermore, an alternative and more efficient way of obtaining the theoretical expressions of the achievable data rate is shown, assuming realistic power line communication noise other than additive white Gaussian noise. To demonstrate the capabilities of wavelet OFDM, the results of simulation of the symbol error rate and the data rate in several systems in platform scenarios (in-vehicle and in-aircraft) are shown.Comunidad de MadridUniversidad de Alcal

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

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

Interference mitigation techniques for wireless OFDM

Orthogonal Frequency Division Multiplexing (OFDM) is a promising multicarrier wireless system for transmission of high-rate data stream with spectral efficiency and fading immunity. Conventional OFDM system use efficient IFFT and FFT to multiplex the signals in parallel at the transmitter and receiver respectively. On the other hand, wavelet based OFDM system uses orthonormal wavelets which are derived from a multistage tree-structured wavelet family. The Fourier based and wavelet based OFDM systems are studied in this dissertation. Two types of QAM schemes, circular and square modulations are used to compare the performance in both OFDM systems. A new approach of determining exact BER for optimal circular QAM is proposed. In addition, the presence of narrowband interference (NBI) degrades the performance of OFDM systems. Thus, a mitigation technique is necessary to suppress NBI in an OFDM system. Recent mitigation techniques can be broadly categorized into frequency domain cancellation, receiver windowing and excision filtering. However, none of the techniques considers wavelet based OFDM. Therefore, an interference cancelation algorithm has been proposed to work for both OFDM platforms. The performance results of two OFDM schemes applicable to digital video broadcasting (DVB)-terrestrial system and under the effect of impulsive noise interference are also studied. BER performances are obtained in all results. It has been shown that wavelet based OFDM system has outperformed Fourier based OFDM system in many cases

Space-time-frequency methods for interference-limited communication systems

textTraditionally, noise in communication systems has been modeled as an additive, white Gaussian noise process with independent, identically distributed samples. Although this model accurately reflects thermal noise present in communication system electronics, it fails to capture the statistics of interference and other sources of noise, e.g. in unlicensed communication bands. Modern communication system designers must take into account interference and non-Gaussian noise to maximize efficiencies and capacities of current and future communication networks. In this work, I develop new multi-dimensional signal processing methods to improve performance of communication systems in three applications areas: (i) underwater acoustic, (ii) powerline, and (iii) multi-antenna cellular. In underwater acoustic communications, I address impairments caused by strong, time-varying and Doppler-spread reverberations (self-interference) using adaptive space-time signal processing methods. I apply these methods to array receivers with a large number of elements. In powerline communications, I address impairments caused by non-Gaussian noise arising from devices sharing the powerline. I develop and apply a cyclic adaptive modulation and coding scheme and a factor-graph-based impulsive noise mitigation method to improve signal quality and boost link throughput and robustness. In cellular communications, I develop a low-latency, high-throughput space-time-frequency processing framework used for large scale (up to 128 antenna) MIMO. This framework is used in the world's first 100-antenna MIMO system and processes up to 492 Gbps raw baseband samples in the uplink and downlink directions. My methods prove that multi-dimensional processing methods can be applied to increase communication system performance without sacrificing real-time requirements.Electrical and Computer Engineerin