隠れ端末問題及びフロー内干渉キャンセルを考慮したワイヤレスアドホックネットワークに関する研究

Performance of CSMA/CA (carrier sense multiple access/collision avoidance) wireless ad hoc network is severely affected by hidden terminal (HT) problem that results in the failure of carrier sense and causes the packet error due to collision. This thesis proposes a method of improving the performance of multi-hop ad hoc network by 4 steps which can be summarized as follows. First, the thesis analyzes HT effect on CSMA/CA unicast communication taking into account actual radio environments including both fading and capture effect. Based on the analysis results, it is predicted that multi-hop transmission is vulnerable to HT problem because of intra-flow interference (IFI). Regarding to this issue, as the second step, a CINR (carrier to interference and noise ratio) -based analysis method is proposed that can precisely estimate the packet delivery probability for CSMA/CA multi-hop transmission suffering from HT-caused IFI under fading environment. The results prove that conventional CSMA/CA media access control cannot achieve efficient multi-hop transmission. Therefore, as the third step, this thesis further proposes IFI-canceling multi-hop transmission (IFIC-MHT) scheme that enables efficient relaying with the highest traffic load for half-duplex multi-hop networks. The interference cancellation (IC) technique employs adaptive signal processing with a normalized least mean square (NLMS) algorithm for channel estimation and has good BER (bit error rate) and PER (packet error rate) performance under a wide range of SNR (signal to noise ratio) and SIR (signal to interference ratio) conditions. A multi-hop packet transmission frame format dedicated to the IFIC is designed. Finally, this thesis studies the effect of IFIC on large-scale ad hoc network where both intra-flow interference and inter-flow interference take place and together affect the multi-hop transmission.電気通信大学201

On properties of positive solutions to nonlinear tri-harmonic and bi-harmonic equations with negative exponents

In this paper, we investigate various properties (e.g. nonexistence, asymptotic behavior, uniqueness and integral representation formula) of positive solutions to nonlinear tri-harmonic equations in [Formula: see text] ([Formula: see text]) and bi-harmonic equations in [Formula: see text] with negative exponents. Such kind of equations arise from conformal geometry

Data from: Electrochemical performance of ZnO-coated Li4Ti5O12 composite electrodes for lithium-ion batteries with the voltage ranging from 3 to 0.01 V

Oxide is widely used in modifying cathode and anode materials for lithium ion batteries. In this work, a facial method of radio magnetron sputtering is introduced to deposit a thin film on Li4Ti5O12 composite electrodes. The pristine and modified Li4Ti5O12 electrodes are characterized at an extended voltage range of 3-0.01 V. The reversible capacity reach a high level of 286 mAh g-1, which is a little less than its theoretical capacity (293 mAh g-1). Electrodes modified by ZnO thin films with various thickness show elevated rate capability and improved cycle performance

Enhanced Interfacial Kinetics and High-Voltage/High-Rate Performance of LiCoO₂ Cathode by Controlled Sputter-Coating with a Nanoscale Li₄Ti₅O₁₂ Ionic Conductor

The selection and optimization of coating material/approach for electrode materials have been under intensive pursuit to address the high-voltage induced degradation of lithium ion batteries. Herein, we demonstrate an efficient way to enhance the high-voltage electrochemical performance of LiCoO₂ cathode by postcoating of its composite electrode with Li₄Ti₅O₁₂ (LTO) via magnetron sputtering. With a nanoscale (∼25 nm) LTO coating, the reversible capacity of LiCoO₂ after 60 cycles is significantly increased by 40% (to 170 mAh g^–1) at room temperature and by 118% (to 139 mAh g^–1) at 55 °C. Meanwhile, the electrode’s rate capability is also greatly improved, which should be associated with the high Li⁺ diffusivity of the LTO surface layer, while the bulk electronic conductivity of the electrode is unaffected. At 12 C, the capacity of the coated electrode reaches 113 mAh g^–1, being 70% larger than that of the uncoated one. The surface interaction between LTO and LiCoO₂ is supposed to reduce the space-charge layer at the LiCoO₂–electrolyte interface, which makes the Li⁺ diffusion much easier as evidenced by the largely enhanced diffusion coefficient of the coated electrode (an order of magnitude improvement). In addition, the LTO coating layer, which is electrochemically and structurally stable in the applied potential range, plays the role of a passivation layer or an artificial and friendly solid electrolyte interface (SEI) layer on the electrode surface. Such protection is able to impede propagation of the in situ formed irreversible SEI and thus guarantee a high initial columbic efficiency and superior cycling stability at high voltage

Improved Electrochemical Performance of LiCoO₂ Electrodes with ZnO Coating by Radio Frequency Magnetron Sputtering

Surface modification of LiCoO₂ is an effective method to improve its energy density and elongate its cycle life in an extended operation voltage window. In this study, ZnO was directly coated on as-prepared LiCoO₂ composite electrodes via radio frequency (RF) magnetron sputtering. ZnO is not only coated on the electrode as thin film but also diffuses through the whole electrode due to the intrinsic porosity of the composite electrode and the high diffusivity of the deposited species. It was found that ZnO coating can significantly improve the cycling performance and the rate capability of the LiCoO₂ electrodes in the voltage range of 3.0–4.5 V. The sample with an optimum coating thickness of 17 nm exhibits an initial discharge capacity of 191 mAh g^–1 at 0.2 C, and the capacity retention is 81% after 200 cycles. It also delivers superior rate performance with a reversible capacity of 106 mAh g^–1 at 10 C. The enhanced cycling performance and rate capability are attributed to the stabilized phase structure and improved lithium ion diffusion coefficient induced by ZnO coating as evidenced by X-ray diffraction, cyclic voltammetry, respectively

Extending the High-Voltage Capacity of LiCoO₂ Cathode by Direct Coating of the Composite Electrode with Li₂CO₃ via Magnetron Sputtering

Surface coating of composite electrode has recently received increasing attention and has been demonstrated to be effective in enhancing the electrochemical performance of lithium ion battery (LIB) materials. In this work, an electronic-insulating but ionic-conductive lithium carbonate (Li₂CO₃) is rationally selected as the unique coating material for commercial LiCoO₂ (LCO) cathode. Li₂CO₃ is a well-known constitute in conventional solid electrolyte interface (SEI) layer, which can electrochemically protect the electrode. The carbonate coating layer is deposited on LCO composite electrodes via a facial magnetron sputtering approach. The sputtered Li₂CO₃ layer serves as an artificial SEI layer between the active material and electrolyte and can impede the formation of the primary SEI layer, which will permanently consume Li⁺ and reduce the reversible capacity of the electrode. After a 10 min Li₂CO₃ coating, the capacity retention of the composite electrode is improved from 64.4% to 87.8% when cycled at room temperature in the potential range of 3.0–4.5 V vs Li/Li⁺ for 60 cycles. The obtained discharge capacity is extended to 161 mAh g^–1, which is 36% higher than the uncoated one (118 mAh g^–1). When further increasing the charging potential up to 4.7 V, or elevating the operation temperature to 55 °C, the Li₂CO₃-coated LCO electrodes still display remarkably improved cycling stability