This thesis considers the use of the tone reservation (TR) technique in orthogonal frequency division multiplexing (OFDM) systems. The nonlinear distortion is usually introduces by the high power amplifiers (HPA) used in wireless communications systems. It orders to reduce the inter-modulation distortion (IMD) in OFDM systems. In addition to the original peak-to-average power ratio (PAPR)-reduction criterion, we propose signal-to-distortion plus noise power ratio (SDNR) criterion and distortion power plus inverse of signal power (DIS) criterion. Based on these criteria, the cross-entropy (CE) algorithm is introduced to determine desired values of the peak reduction carriers (PRCs) to improve the bit error rate (BER) of nonlinearly distorted. Computational complexity is always the major concern of PAPR technique. Therefore, the real-valued PRCs and the modified transform decomposition (MTD) method are introduced here to dramatically decrease complexity of inverse fast Fourier transform (IFFT) operation with slightly performance loss. The simulation results show that the proposed criteria provide a better BER performance and a lower computational complexity.

Orthogonal frequency division multiplexing (OFDM) system is the standard of next generation mobile communication, one of the major drawbacks of OFDM systems is the peak-to-average power ratio (PAPR). In this paper, we proposed a low complexity Selected mapping (SLM) scheme to reduce PAPR. In [27], Wang proposed a low complexity SLM scheme by utilizing conversion vectors having the form of a perfect sequence to solve the problem that phase rotation vectors of the conversion vectors do not usually have an equal magnitude in frequency domain. This paper proposed a low complexity SLM scheme based on perfect sequence and consider the symbol interleaving to reduce the correlation between signals in time domain. It is shown that the (Complementary Cumulative Distribution Function, CCDF) of our proposed scheme are closer to the traditional SLM scheme than Wang¡¦s in [27] but with additional complexity. And the computational complexity is much lower than traditional SLM.

For channel estimation without data-induced interference in data-dependent superimposed training (DDST) scheme, the data sequence is shifted by subtracting a data-dependent sequence before added to training sequence at transmitter. The distorted term causes the data identification problem (DIP) at the receiver. In this thesis, we propose two precoding schemes based on previous work. To maintain low peak-to-average power ratio (PAPR), the precoding matrix is restricted to a diagonal matrix. The first scheme is proposed to enlarge the minimum distance between the closest codewords, termed as efficient diagonal scheme. Conditions to make sure the precoding matrix is efficient for M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) modulation are listed in this paper. The second scheme pursues a lowest complexity at receiver which means the amount of searching set is reduced. It is a trade-off between the better bit error rate (BER) performance and a lower complexity at receiver. The simulation results show that PAPR have been improved and the DIP is solved in both schemes.

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier transmission scheme used in most of the existing wireless standards such as LTE, WiFi and WiMAX. The popularity of OFDM stems from the multitude of benefits it offers in terms of providing high data rate transmission, robustness against multipath fading and ease of implementation. Additionally, OFDM signals are agile in the sense that any subcarrier can be switched on or off to fit the available transmission bandwidth, which makes it well suited for systems with dynamic spectrum access such as cognitive radio systems. Nonetheless, and despite all the aforementioned advantages, OFDM signals have high spectral sidelobes outside the designated band of transmission, that can create severe interference to users in adjacent transmission bands, particularly when there is no synchronization between users. The focus of this dissertation is to propose baseband solutions at the Physical Layer (PHY) of the communications system to address the interference resulting from the high out-of-band (OOB) emissions of OFDM. In the first part of this dissertation, we propose a precoder capable of generating mask compliant OFDM signals with low OOB emissions that are always contained under a given spectrum emission mask (SEM) specified by the OFDM standard. The proposed precoder generates transmitted signals with bit error rate (BER) performance similar to that of classical OFDM and does not reduce the spectral efficiency of the system. In the second part of this dissertation, we introduce a novel and elegant approach, called suppressing alignment (SA), to jointly reduce the OOB interference and peak-to-average power ratio (PAPR) of OFDM systems. SA exploits the unavoidable redundancy provided by the CP as well as the wireless communications channel to generate an OOB/PAPR suppressing signal at the OFDM transmitter. Furthermore, after passing through the wireless channel, the suppressing signal is aligned with the CP duration at the OFDM receiver, essentially causing no interference to the data portion of the OFDM symbol. The proposed approach improves the PAPR of the transmitted OFDM signal and reduces the OOB interference by tens of decibels. Additionally, the proposed approach maintains an error performance similar to that of plain OFDM without requiring any change in the receiver structure of legacy OFDM. In order to reduce the spectral emissions of OFDM, additional blocks, such as linear precoders, are usually introduced in the transmitter leading to a transmitted signal that is drastically different than that of a classical OFDM signal. This distortion is typically quantified by the error vector magnitude (EVM), a widely used metric specified by the wireless standard and is directly related to the BER performance of the system. The receiver can usually decode the information data with acceptable error probabilities if the distortion introduced to the transmitted signal is below the EVM values specified in the OFDM standard. Linear precoders, while capable of achieving significant reduction in the OOB interference, they typically introduce large distortion to the transmitted signal. As such, the receiver needs to know the precoding done at the transmitter to be able to recover the data which usually entails sending large amount of side information that can greatly reduce the spectral efficiency of the system. In the last part of this dissertation, we target the design of precoders for the purpose reducing the OOB interference, in a transparent manner where the receiver does not need to know the changes introduced in the transmitter. We present two precoders capable of significantly reducing the OOB emissions while producing transmitted signals with EVM values below those specified by the wireless standard, thereby guaranteeing acceptable error performance.

京都大学 / 0048 / 新制・課程博士 / 博士(情報学) / 甲第21915号 / 情博第698号 / 新制||情||120(附属図書館) / 京都大学大学院情報学研究科数理工学専攻 / (主査)教授 梅野 健, 教授 山下 信雄, 教授 守倉 正博 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

The number of mobile wireless devices on the market has increased substantially over the last decade. The frequency spectrum has become crowded due to the number of devices demanding radio traffic and new modulation schemes have been developed to accommodate the number of users. These new modulation schemes have caused very poor efficiencies in power amplifiers for wireless transmission systems due to high peak-to-average power ratios (PAPR). This thesis first presents the issue with classical power amplifiers in modern modulation systems. A brief overview of current attempts to mitigate this issue is provided. A new RF power amplifier topology is then presented with supporting simulations. The presented amplifier topology utilizes the concept of negative conductance and load modulation. The amplifier operates in two stages, a low power stage and a high power stage. A negative conductance amplifier is utilized during peak power transmission to modulate the load presented to the input amplifier. This topology is shown to greatly improve the power added efficiency of power amplifiers in systems with high PAPR.

No description available.

Massive data centers housing thousands of computing nodes have become commonplace in enterprise computing, and the power consumption of such data centers is growing at an unprecedented rate. Exacerbating such costs, data centers are often over-provisioned to avoid costly outages associated with the potential overloading of electrical circuitry. However, such over provisioning is often unnecessary since a data center rarely operates at its maximum capacity. It is imperative that we realize effective strategies to control the power consumption of the server and improve the energy efficiency of data centers. Adding to the problem is the inability of the servers to exhibit energy proportionality which diminishes the overall energy efficiency of the data center. Therefore in this dissertation, we investigate whether it is possible to achieve energy proportionality at the server- and cluster-level by efficient power and resource provisioning. Towards this end, we provide a thorough analysis of energy proportionality at the server and cluster-level and provide insight into the power saving opportunity and mechanisms to improve energy proportionality. Specifically, we make the following contribution at the server-level using enterprise-class workloads. We analyze the average power consumption of the full system as well as the subsystems and describe the energy proportionality of these components, characterize the instantaneous power profile of enterprise-class workloads using the on-chip energy meters, design a runtime system based on a load prediction model and an optimization framework to set the appropriate power constraints to meet specific performance targets and then present the effects of our runtime system on energy proportionality, average power, performance and instantaneous power consumption of enterprise applications. We then make the following contributions at the cluster-level. Using data serving, web searching and data caching as our representative workloads, we first analyze the component-level power distribution on a cluster. Second, we characterize how these workloads utilize the cluster. Third, we analyze the potential of power provisioning techniques (i.e., active low-power, turbo and idle low-power modes) to improve the energy proportionality. We then describe the ability of active low-power modes to provide trade-offs in power and latency. Finally, we compare and contrast power provisioning and resource provisioning techniques. This thesis sheds light on mechanisms to tune the power provisioned for a system under strict performance targets and opportunities to improve energy proportionality and instantaneous power consumption via efficient power and resource provisioning at the server- and cluster-level. / Ph. D.

Ce travail de thèse concerne le développement de sources femtoseconde de forte puissance moyenne ou de forte énergie avec des matériaux pompés par diodes laser, dopés à l’ytterbium. Plus particulièrement au cours de cette thèse deux types de matrices ont été utilisés, le CALGO (CaGdAlO4) et les fluorures, possédant le potentiel de générer des impulsions courtes (100aine de femtoseconde). Les caractéristiques spectroscopiques et thermiques du CALGO dopés à l’ytterbium permettent d’envisager le développement d’oscillateur femtoseconde court de forte puissance moyenne. Dans ce contexte, la technologie des disques minces permet d’obtenir avec d’autres matrices, des résultats très intéressants. C’est pourquoi durant cette thèse le choix de maitriser cette nouvelle technologie, avec l’utilisation de ce cristal, a été fait. Dans ce cadre, des résultats très prometteurs ont été obtenus. L’oscillateur femtoseconde Yb :CALGO de plus forte puissance moyenne a en effet été développé (28 W), pour une énergie non négligeable, supérieure au µJ et une durée d’impulsions de 300 fs. Des améliorations sont à prévoir avec l’utilisation de nouveaux cristaux plus dopés et plus fins, mais d’hors et déjà les résultats obtenus sont au niveau de l’état de l’art des oscillateurs femtoseconde de forte puissance moyenne.Le cristal de CaF2 quant à lui, possède un grand intérêt pour le développement d’amplificateurs énergétiques courts, puisqu’il a la capacité de stocker beaucoup d’énergie. Deux types d’amplificateurs ont alors été développés, avec des objectifs bien différents. Le premier permet d’obtenir un fort gain (~106), avec une énergie extraite proche du mJ (amplificateur régénératif), alors que le second a pour but d’extraire le maximum d’énergie (amplificateur multipassage), dans notre cas jusqu’à 160 mJ, avec un gain plus faible (~10).Le potentiel de ces matériaux pour la génération d’impulsions courtes et/ou de forte puissance moyenne a alors été démontré. / This work concerns the development of high average power or high energy laser with diode-pumped ytterbium-doped materials. Two host matrices were studied, CALGO (CaGdAlO4) and fluoride, which permit the generation of ultra-short pulses. Spectroscopic and thermal properties of ytterbium doped CALGO crystals are adapted for the development of high average power oscillator. In this area, thin disk technology seems to be particularly interesting for the development of such oscillator. That’s why we choose to master this technology with ytterbium-doped CALGO crystals. Thus, Yb:CALGO oscillator with the highest average power was developed (28 W), with more than µJ energy and pulse duration of 300 fs. Using more doped and thinner crystals should permit to improve our performances, however they are already at the state of the art of high average power oscillator.Ytterbium doped CaF2 has a great interest for short-pulse high energy amplifier, thanks to its capacity to store energy. Two types of amplifier were developed. A regenerative amplifier with high gain (~106), mJ energy level, and a multipass amplifier with lower gain (~10) but permitting to extract really high energy (up to 160 mJ).Potential of these materials for the development of short pulse high average power and/or high energy system was demonstrated.

The proliferation of portable systems and mobile computing platforms has increased the need for the design of low power consuming integrated circuits. The increase in chip density and clock frequencies due to technology advances has made low power design a critical issue. Low power design is further driven by several other factors such as thermal considerations and environmental concerns. In low-power design for battery driven portable applications, the reduction of peak power, peak power differential, average power and energy are equally important. In this dissertation, we propose a framework for the reduction of these parameters through datapath scheduling at behavioral level. Several ILP based and heuristic based scheduling schemes are developed for datapath synthesis assuming : (i) single supply voltage and single frequency (SVSF), (ii) multiple supply voltages and dynamic frequency clocking (MVDFC), and (iii) multiple supply voltages and multicycling (MVMC). The scheduling schemes attempt to minimize : (i) energy, (ii) energy delay product, (iii) peak power, (iv) simultaneous peak power and average power, (v) simultaneous peak power, average power, peak power differential and energy, and (vi) power fluctuation. A new parameter called "Cycle Power Function" (CPF) is defined which captures the transient power characteristics as the equally weighted sum of normalized mean cycle power and normalized mean cycle differential power. Minimizing this parameter using multiple supply voltages and dynamic frequency clocking results in the reduction of both energy and transient power. The cycle differential power can be modeled as either the absolute deviation from the average power or as the cycle-to-cycle power gradient. The switching activity information is obtained from behavioral simulations. Power fluctuation is modeled as the cycle-to-cycle power gradient and to reduce fluctuation the mean power gradient (MPG) is minimized. The power models take into consideration the effect of switching activity on the power consumption of the functional units. Experimental results for selected high-level synthesis benchmark circuits under different constraints indicate that significant reductions in power, energy and energy delay product can be obtained and that the MVDFC and MVMC schemes yield better power reduction compared to the SVSF scheme. Several application specific VLSI circuits were designed and implemented for digital watermarking of images. Digital watermarking is the process that embeds data called a watermark into a multimedia object such that the watermark can be detected or extracted later to make an assertion about the object. A class of VLSI architectures were proposed for various watermarking algorithms : (i) spatial domain invisible-robust watermarking scheme, (ii) spatial domain invisible-fragile watermarking scheme, (iii) spatial domain visible watermarking scheme, (iv) DCT domain invisible-robust watermarking scheme, and (v) DCT domain visible watermarking scheme. Prototype implementation of (i), (ii) and (iii) are given. The hardware modules can be incorporated in a "JPEG encoder" or in a "digital still camera".