Role of the binder on the failure mechanism of Si nano-composite electrodes for Li-ion batteries

In this work a novel method is used to fabricate uniform thin layer electrodes based on nano-silicon composite material. The manufacture process, based on a combination of Laser assisted Chemical Vapor Pyrolysis and Electro-Spray Deposition, allows the forming of highly uniform and highly porous surface electrodes. By controlling the particle synthesis and deposition parameters it is possible to obtain samples that are highly reproducible in terms of their morphology. Electrosprayed nano-composite electrodes show high specific capacity. The capacity retention of these types of electrodes is strongly dependant on the binder's nature. The capacity fading mechanism has been further investigated and we suggest a simple mechanical model, which is supported by one of the two CMC binding mechanism already proposed in literature.     

Functional equation for the fading correction of imaging plates

Several experiments were performed to investigate the effects of temperature on the fading of the commercial imaging plate, IP (BAS-UR). The fading characteristics were measured under controlled temperatures between 0°C and 60°C after irradiation with ²³⁸U alpha-ray and ⁶⁰Co gamma-ray sources. Applying Arrhenius' equation to the experimental results, we calculated a universal functional equation that includes two variables: elapsed time (t) and temperature (K). The photo-stimulated luminescence (PSL) calculated by this equation showed good agreement with the results of our experimental ones between 0°C and 40°C. From this equation, the activation energies of the fading are estimated to be about 0.9 eV for both ²³⁸U alpha-ray and ⁶⁰Co gamma-ray sources.     

Nakagami衰落信道的仿真方法研究

Nakagami衰落能够描述实际中所遇到的大多数衰落环境。文章提出了一个新的Nakagami衰落信道的仿真方法,用它仿真了Nakagami衰落信道的一阶、二阶统计特性并通过与其理论值进行比较验证了该方法的可靠性。该仿真方法直接基于瑞利衰落信道仿真基础之上,是对Nakagami衰落信道的一种新的研究探讨。     

Commutation Signaling to Combat ISI over Nakagami and Ricean Fading

Bandwidth expanding signaling with quasi-orthogonal short codes is considered. The evaluation of the average probability of error analytically and by simulation is presented, for channels with multipath induced intersymbol interference (ISI) and for two different fading distributions. Namely Nakagami and Ricean fading distributions. The effect of intercell interference due to frequency reuse is also taken into account. Bit error rates (BER) for rake receiver with equal gain combining and postdetection integrator are presented. Both DBPSK and /41 DQPSK modulations with noncoherent demodulation are analysed. The effect of TCM coding, in the expected BER is also evaluated.     

Kalman filtering with faded measurements

This paper considers a sensor network where single or multiple sensors amplify and forward their measurements of a common linear dynamical system (analog uncoded transmission) to a remote fusion center via noisy fading wireless channels. We show that the expected error covariance (with respect to the fading process) of the time-varying Kalman filter is bounded and converges to a steady state value, based on some earlier results on asymptotic stability of Kalman filters with random parameters. More importantly, we provide explicit expressions for sequences which can be used as upper bounds on the expected error covariance, for specific instances of fading distributions and scalar measurements (per sensor). Numerical results illustrate the effectiveness of these bounds.     

Coverage study for broadband wireless systems using link adaptation and diversity combining techniques

A broadband wireless access system is a bi-directional broadband wireless system to fixed networks at millimeter-wave frequencies. The propagation environment at millimeter-wave frequencies is one of the major challenges in delivering broadband services to fixed subscribers. At such high frequencies the signal is attenuated by the obstacles in the radio path between the subscriber and the hub, such as buildings, trees and vehicles in the radio path between the subscriber and the hub.Link adaptation techniques such as adaptive modulation and error control coding have been applied to wireless communication systems to overcome the multipath fading experienced by the transmitted signal. Diversity has long been recognized as an effective technique for combating the effect of channel multipath fading. In this study, we investigate the outage probability improvements due to the employments of various combinations of adaptive modulation, adaptive coding, and diversity techniques in a broadband wireless access system. The results indicate that using adaptive modulation, coding, and maximal ratio combining (MRC) yields significant enhancements in outage probability of the system.     

Complex radio frequency (RF) communications with virtual pulses

A novel complex pulse forming technique has been developed using ultra wideband (UWB) frequency concepts where multiple carriers are modulated by the pulse width of the primary signal source. Specialized modulation of the pulse train provides an effective communication medium with inherent advantages of an UWB system. The multiple frequency nature of the non-traditional “pulse” formation provides a means of implementing UWB without the necessity of complex pulse formation of the classical UWB. The particular example of the research implemented in this paper allows explicit user choice of the specific UWB frequencies, e.g., ISM frequencies, to avoid current restrictions of the Federal Communications Commission (FCC). The reported method also contains an implicit property to support secure information transmission to receivers at known distances.The objective of this technique is an easy to form communication pulse having UWB low energy advantages along with the freedom of implementation without license requirements from regulating authorities, while adhering to the set limits of intentional radiators. The method chosen in this case was based on having the sum of energies from multiple frequencies remain within the restricted radiation limits at the correlated receiver. Included in the implementation technique is the inclusion of the signal fading effect as part of the modulation technique. The relevance of this pulse forming technique is in the simplicity of spreading the transmitted power among multiple frequencies without the issue of decay factor in the current methods. The result presented gives two sets of relative amplitudes of the transmitted frequencies identifying the transmitted character, e.g., 0 or 1. A form of amplitude encryption, due to the RF signal fading effect was also presented as advantage in the technique.     

双衰落信道下OFDM信噪比估计算法

基于最小均方误差方法,在双衰落信道下,提出利用周期PN序列作为导频的信噪比(SNR)估计算法。在导频2侧插入保护间隔降低子载波间干扰对导频的影响,在时域进行相关运算消除噪声干扰,从而得到较精确的信道参数。仿真结果表明,该算法能较准确估计SNR,且可通过改变周期PN序列满足不同信道环境下的性能要求。     

支持向量机在衰落信道预测中的应用

研究信道通信优化控制问题,针对传统衰落信道预测算法中的不足,提出一种改进LSSVM的衰落信道预测。首先通过相空间重构对衰落信道系数序列进行重构,然后采用LSSVM对训练样本集进行学习,并通过自适应遗传算法对LSSVM参数进行优化建立最优衰落信道系数预测模型,最后采用测试集对模型的性能进行验证。仿真结果表明,相对于传统LSS-VM模型,改进模型提高了衰落信道系数预测精度,是一种进行衰落信道非线性预测的有效方法。     

Clipping distortion mitigation in OFDM systems over fading channels by using DFT-based method

Saeedi et al. have recently proposed a DFT-based method (DBM) for Orthogonal Frequency Division Multiplexing (OFDM) systems to compensate for the performance degradation caused by clipping distortion. They have analyzed the performance of the DBM only in an additive white Gaussian noise channel. But, it is known that the main advantage of an OFDM system is its robustness in fading channels where this system turns a frequency selective channel into a set of parallel flat non-selective fading sub-channels. In this paper, we analyze the performance of the DBM over a frequency selective fading channel with flat fading Rician sub-channels. Our results show that similar to additive white Gaussian noise channel case, the DBM can properly mitigate the clipping distortion in OFDM signals over fading channels. Furthermore, the performance of a Hybrid method that consists of a channel coding method and the DBM is also examined over fading channels.