ワイヤレス通信のための先進的な信号処理技術を用いた非線形補償法の研究

The inherit nonlinearity in analogue front-ends of transmitters and receivers have had primary impact on the overall performance of the wireless communication systems, as it gives arise of substantial distortion when transmitting and processing signals with such circuits. Therefore, the nonlinear compensation (linearization) techniques become essential to suppress the distortion to an acceptable extent in order to ensure sufficient low bit error rate. Furthermore, the increasing demands on higher data rate and ubiquitous interoperability between various multi-coverage protocols are two of the most important features of the contemporary communication system. The former demand pushes the communication system to use wider bandwidth and the latter one brings up severe coexistence problems. Having fully considered the problems raised above, the work in this Ph.D. thesis carries out extensive researches on the nonlinear compensations utilizing advanced digital signal processing techniques. The motivation behind this is to push more processing tasks to the digital domain, as it can potentially cut down the bill of materials (BOM) costs paid for the off-chip devices and reduce practical implementation difficulties. The work here is carried out using three approaches: numerical analysis & computer simulations; experimental tests using commercial instruments; actual implementation with FPGA. The primary contributions for this thesis are summarized as the following three points: 1) An adaptive digital predistortion (DPD) with fast convergence rate and low complexity for multi-carrier GSM system is presented. Albeit a legacy system, the GSM, however, has a very strict requirement on the out-of-band emission, thus it represents a much more difficult hurdle for DPD application. It is successfully implemented in an FPGA without using any other auxiliary processor. A simplified multiplier-free NLMS algorithm, especially suitable for FPGA implementation, for fast adapting the LUT is proposed. Many design methodologies and practical implementation issues are discussed in details. Experimental results have shown that the DPD performed robustly when it is involved in the multichannel transmitter. 2) The next generation system (5G) will unquestionably use wider bandwidth to support higher throughput, which poses stringent needs for using high-speed data converters. Herein the analog-to-digital converter (ADC) tends to be the most expensive single device in the whole transmitter/receiver systems. Therefore, conventional DPD utilizing high-speed ADC becomes unaffordable, especially for small base stations (micro, pico and femto). A digital predistortion technique utilizing spectral extrapolation is proposed in this thesis, wherein with band-limited feedback signal, the requirement on ADC speed can be significantly released. Experimental results have validated the feasibility of the proposed technique for coping with band-limited feedback signal. It has been shown that adequate linearization performance can be achieved even if the acquisition bandwidth is less than the original signal bandwidth. The experimental results obtained by using LTE-Advanced signal of 320 MHz bandwidth are quite satisfactory, and to the authors’ knowledge, this is the first high-performance wideband DPD ever been reported. 3) To address the predicament that mobile operators do not have enough contiguous usable bandwidth, carrier aggregation (CA) technique is developed and imported into 4G LTE-Advanced. This pushes the utilization of concurrent dual-band transmitter/receiver, which reduces the hardware expense by using a single front-end. Compensation techniques for the respective concurrent dual-band transmitter and receiver front-ends are proposed to combat the inter-band modulation distortion, and simultaneously reduce the distortion for the both lower-side band and upper-side band signals.電気通信大学201

Third Order Nonlinear Optics in Solids

Nonlinear optical effects occur when strong electromagnetic waves induce changes in a medium that affect its own propagation or that of another wave. Third order optical nonlinearities scale linearly with irradiance and lead to effects like two-photon absorption and nonlinear refraction. This work focuses on the experimental and theoretical study of two-photon absorption in crystalline solids. We begin by detailing the quantum mechanical states of electrons in solids along with the computational approaches to calculate their band structure. Next, a theoretical model for the linear and nonlinear optical interaction of light with matter is presented in a many-body formalism. This first-principles approach derives first and third order nonlinear optical coefficients directly from the many-body Schrödinger equation coupled to the electromagnetic wave equation through the current densities excited by incident electromagnetic fields. The following work examines nondegenerate two-photon absorption in semiconductor quantum well waveguides to determine their suitability as a two-photon lasing medium under population inversion. Experimental pump-probe measurements are presented for a structure comprising GaAs/32% AlGaAs quantum wells. The data is first analyzed by devising a theoretical model for the co-propagation of a strong pump and weak probe pulse within the wave guide sample. After, we present a quantum mechanical model for the electronic states and corresponding optical response of our system to compare to the two-photon absorption coefficients determined from the experimental investigation. The model\u27s excellent agreement with the measured results allows us to extrapolate to the extremely nondegenerate regime, predicting large enhancements in the nondegenerate two-photon absorption coefficients when one pulse has a mid-infrared wavelength. Next, we detail phonon-assisted nondegenerate two-photon absorption in silicon, with the goal of determining which transition pathway best explains the dispersion of ND-2PA coefficients near the band gap energy. After discovering many cases where simplified models break down, we introduce a tool to calculate linear and nonlinear optical properties of materials using density functional theory. This work focuses on the efficient calculation of one- and two-photon absorption, as well as the nonlinear effects arising from excited carrier populations. Finally, a theoretical model is proposed to determine the exact many-body quantum states of materials including electron-electron Coulomb interactions

B(2): P(M) DUAL RADIX SYSTEMS - THEORY, DESIGN, AND I(SQUARE)L IMPLEMENTATION.

The upward compatibility of binary Boolean algebra with Post algebra was examined. There exists in a Post algebra, P(m), a single two-element Boolean algebra, B(2) {4}. If the complement operation in P(m) is the pseudo-complement or strong negation, then more than one B(2) to P(m) mapping is possible. For m = 2('N), N an integer greater than one, there are 2('N-1) homomorphic mappings of B(2) into P(m). Standard B(2):P(4) building blocks were designed and constructed with integrated injection logic to demonstrate the practical aspects of the dual radix concept. An algorithm for finding the maximum compatible mapping from B(2) to P(m) for completely and incompletely specified functions was developed. Finally, memory elements, bus design, and basic architecture to support a B(2):P(4) processor were considered and comments concerning a B(2) machine operating in a P(m) host were made

Perturbative light–matter interactions; from first principles to inverse design

Our experience of the world around us is governed almost entirely by light–matter interactions. At the most fundamental level, such interactions are described by quantum electrodynamics (QED), a well-established theory that has stood up to decades of experimental testing to remarkable degrees of precision. However, the complexity of real systems almost always means that the quantum electrodynamical equations describing a given scenario are often infeasible or impractical to solve. Thus, a sequence of approximations and idealisations are made, in order to build up from the simple case of an isolated electron interacting with a gauge field leading to the deceptively simple laws governing reflection and refraction at mirrors and lenses. This review provides a pedagogical overview of this journey, concentrating on cases where external boundary conditions can be used as a control method. Beginning from the fundamental Lagrangian, topics include gauge freedom, perturbative macroscopic QED descriptions of spontaneous decay, Casimir–Polder forces, resonant energy transfer, interatomic Coulombic decay, all of which are described in terms of the dyadic Green’s tensor that solves the Helmholtz equation. We discuss in detail how to calculate this tensor in practical situations before outlining new techniques in the design and optimisation of perturbative light–matter interactions, highlighting some recent advances in free-form, unconstrained inverse design of optical devices. Finally, an outlook towards the frontiers in the interaction of quantum light with matter is given, including its interface with chemical reactivity via polaritonic chemistry and quantum chemistry via quantum electrodynamical density functional theory (QEDFT)