Spatial dissection of a soundfield using spherical harmonic decomposition

A real-world soundfield is often contributed by multiple desired and undesired sound sources. The performance of many acoustic systems such as automatic speech recognition, audio surveillance, and teleconference relies on its ability to extract the desired sound components in such a mixed environment. The existing solutions to the above problem are constrained by various fundamental limitations and require to enforce different priors depending on the acoustic condition such as reverberation and spatial distribution of sound sources. With the growing emphasis and integration of audio applications in diverse technologies such as smart home and virtual reality appliances, it is imperative to advance the source separation technology in order to overcome the limitations of the traditional approaches. To that end, we exploit the harmonic decomposition model to dissect a mixed soundfield into its underlying desired and undesired components based on source and signal characteristics. By analysing the spatial projection of a soundfield, we achieve multiple outcomes such as (i) soundfield separation with respect to distinct source regions, (ii) source separation in a mixed soundfield using modal coherence model, and (iii) direction of arrival (DOA) estimation of multiple overlapping sound sources through pattern recognition of the modal coherence of a soundfield. We first employ an array of higher order microphones for soundfield separation in order to reduce hardware requirement and implementation complexity. Subsequently, we develop novel mathematical models for modal coherence of noisy and reverberant soundfields that facilitate convenient ways for estimating DOA and power spectral densities leading to robust source separation algorithms. The modal domain approach to the soundfield/source separation allows us to circumvent several practical limitations of the existing techniques and enhance the performance and robustness of the system. The proposed methods are presented with several practical applications and performance evaluations using simulated and real-life dataset

Theory and Design of Spatial Active Noise Control Systems

The concept of spatial active noise control is to use a number of loudspeakers to generate anti-noise sound waves, which would cancel the undesired acoustic noise over a spatial region. The acoustic noise hazards that exist in a variety of situations provide many potential applications for spatial ANC. However, using existing ANC techniques, it is difficult to achieve satisfying noise reduction for a spatial area, especially using a practical hardware setup. Therefore, this thesis explores various aspects of spatial ANC, and seeks to develop algorithms and techniques to promote the performance and feasibility of spatial ANC in real-life applications. We use the spherical harmonic analysis technique as the basis for our research in this work. This technique provides an accurate representation of the spatial noise field, and enables in-depth analysis of the characteristics of the noise field. Incorporating this technique into the design of spatial ANC systems, we developed a series of algorithms and methods that optimizes the spatial ANC systems, towards both improving noise reduction performance and reducing system complexity. Several contributions of this work are: (i) design of compact planar microphone array structures capable of recording 3D spatial sound fields, so that the noise field can be monitored with minimum physical intrusion to the quiet zone, (ii) derivation of a Direct-to-Reverberant Energy Ratio (DRR) estimation algorithm which can be used for evaluating reverberant characteristics of a noisy environment, (iii) propose a few methods to estimate and optimize spatial noise reduction of an ANC system, including a new metric for measuring spatial noise energy level, and (iv) design of an adaptive spatial ANC algorithm incorporating the spherical harmonic analysis technique. The combination of these contributions enables the design of compact, high performing spatial ANC systems for various applications

Theory and Design of Feasible Active Noise Control Systems for 3D Regions

This thesis advances Active Noise Control (ANC) over three-dimensional (3D) space using feasible loudspeaker and microphone array systems. By definition, ANC reduces unwanted acoustic noise by generating an anti-noise signal(s) from secondary loudspeakers. The concept of spatial ANC aims to reduce unwanted acoustic noise over a continuous 3D region, by utilizing multiple microphones and multiple secondary loudspeakers to create a large-sized quiet zone for listeners in three-dimensional space. However, existing spatial ANC techniques are usually impractical and difficult to implement due to their strict hardware requirements and high computation complexity. Therefore, this thesis explores various aspects of spatial ANC, seeking algorithms and techniques to promote the reliability and feasibility of ANC over space in real-life applications. The spherical harmonic analysis technique is introduced as the basis of conventional spatial ANC systems. This technique provides an accurate representation of a given spatial sound field using higher-order microphone (spherical microphone array) recordings. Hence, the residual noise field in a spatial ANC system can be effectively captured spatially by applying the spherical harmonic technique. Incorporating conventional spatial ANC methods, we developed a series of algorithms and methods that optimize conventional methods regarding array geometries and ANC algorithms, towards improving the feasibility of a conventional spatial ANC system involving the spherical harmonic analysis. Overall, motivated by feasible and realistic designs for spatial ANC systems, work included in this thesis mainly solves the three problems of: (i) the impracticality of realizing spherical microphone and loudspeaker arrays, (ii) achieving secondary channel estimation with microphones remote from their desired locations, and (iii) unreasonable delays inherent to frequency domain spatial ANC methods. Based on our work, we have stepped towards achieving a spatial ANC system in a real-world environment for people to enjoy silence in the control region with the reliable usage of resources and algorithms. Several contributions of this work are: (i) designing a 3D spatial ANC system using multiple circular microphone and loudspeaker arrays instead of spherical arrays, (ii) proposing a 3D spatial ANC method with remote microphone technique such that noise reduction over a region is achieved with microphones remote from the region, (iii) proposing a secondary channel estimation method using a moving higher-order microphone such that usage of an error microphone array is not necessary, (iv) deriving a time domain spherical harmonic analysis method for open spherical microphone array recording with less delay than in the frequency domain, and (v) designing a feed-forward adaptive spatial ANC algorithm incorporating the time domain spherical harmonic analysis technique to better minimize the noise in the region of interest

Advanced Radio Frequency Antennas for Modern Communication and Medical Systems

The main objective of this book is to present novel radio frequency (RF) antennas for 5G, IOT, and medical applications. The book is divided into four sections that present the main topics of radio frequency antennas. The rapid growth in development of cellular wireless communication systems over the last twenty years has resulted in most of world population owning smartphones, smart watches, I-pads, and other RF communication devices. Efficient compact wideband antennas are crucial in RF communication devices. This book presents information on planar antennas, cavity antennas, Vivaldi antennas, phased arrays, MIMO antennas, beamforming phased array reconfigurable Pabry-Perot cavity antennas, and time modulated linear array

Towards 6G MIMO: Massive Spatial Multiplexing, Dense Arrays, and Interplay Between Electromagnetics and Processing

The increasing demand for wireless data transfer has been the driving force behind the widespread adoption of Massive MIMO (multiple-input multiple-output) technology in 5G. The next-generation MIMO technology is now being developed to cater to the new data traffic and performance expectations generated by new user devices and services in the next decade. The evolution towards "ultra-massive MIMO (UM-MIMO)" is not only about adding more antennas but will also uncover new propagation and hardware phenomena that can only be treated by jointly utilizing insights from the communication, electromagnetic (EM), and circuit theory areas. This article offers a comprehensive overview of the key benefits of the UM-MIMO technology and the associated challenges. It explores massive multiplexing facilitated by radiative near-field effects, characterizes the spatial degrees-of-freedom, and practical channel estimation schemes tailored for massive arrays. Moreover, we provide a tutorial on EM theory and circuit theory, and how it is used to obtain physically consistent antenna and channel models. Subsequently, the article describes different ways to implement massive and dense antenna arrays, and how to co-design antennas with signal processing. The main open research challenges are identified at the end.Comment: Submitted to Proceedings of the IEEE, 36 pages, 23 figure

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression