Multichannel MLSE equalizer with parametric FIR channelidentification

We propose a parametric finite impulse response (FIR) channel identification algorithm, apply the algorithm to a multichannel maximum likelihood sequential estimation (MLSE) equalizer using multiple antennas, and investigate the improvement in the overall bit error rate (BER) performance. By exploring the structure of the specular multipath channels, we are able to reduce the number of channel parameters to provide a better channel estimate for the MLSE equalizer. The analytic BER lower bounds of the proposed algorithm as well as those of several other conventional MLSE algorithms in the specular multipath Rayleigh-fading channels are derived. In the derivation, we consider the channel mismatch caused by the additive Gaussian noise and the finite-length channel approximation error. A handy-to-use simplified BER lower bound is also derived. Simulation results that illustrate the BER performance of the proposed algorithm in the global system for mobile communications (GSM) system are presented and compared to the analytic lower bounds     

三网融合下视频业务质量评估体系的研究

随着三网络融合的推进,由电信运营的IPTV、手机影视等视频业务必将加速发展,对视频业务的质量评估和质量保障将日趋紧迫。本文探讨了基于用户主观体验的的视频质量评估模型和指标体系,并根据IPTV业务的特点,提出了适用的关键指标和指标阈值。视频质量评估模型和指标是构建IPTV等视频业务监测手段的关键,是提升视频质量监测评估不可或缺的重要前提。     

源特定组播的研究

自网络层组播技术出现以来，得到了广泛的关注和深入的研究。但由于传统的任意源组播模型先天不足，商业应用进展缓慢。分析了源特定组播产生的背景，讨论了源特定组播模型的体系结构和特点，比较了PIM—SM协议和PIM—SSM协议的不同。最后对网络层组播的研究现状作了介绍。     

WAP移动网络关键技术

WAP这一使无线设备访问互联网的关键技术,被称为移动数据服务领域继短信之后又一金矿,越来越受到业界关注。本文通过对这一技术发展状况进行介绍,技术特点的分析,得出WAP涉及的安全问题,并对应用价值进行预估,总结出发展前景。     

非相干散射雷达探测空间碎片实验研究

这是我国首次用欧洲非相干散射雷达探测空间碎片的实验。根据非相干散射探测原理和空间碎片高度分布的规律,采用匹配滤波方法处理了2010年3月25日15小时实验数据,每小时平均24个碎片,用统计方法分析了碎片高度分布。结果表明:大部分碎片分布在高度为800~1000 km之间,与碎片高度分布理论一致,与中国科学院国家天文台空间碎片预测理论模型比对,比较2010年3月25日10点31分05秒目标信息,高度误差仅为0.97 km,确认为碎片国际标识为1965-016F的美国报废业余通信卫星,证实了非相干散射雷达设备直接探测碎片的可行性。     

Atomic Ni Anchored Covalent Triazine Framework as High Efficient Electrocatalyst for Carbon Dioxide Conversion

Electrochemically driven carbon dioxide (CO₂) conversion is an emerging research field due to the global warming and energy crisis. Carbon monoxide (CO) is one key product during electroreduction of CO₂; however, this reduction process suffers from tardy kinetics due to low local concentration of CO₂ on a catalyst's surface and low density of active sites. Herein, presented is a combination of experimental and theoretical validation of a Ni porphyrin‐based covalent triazine framework (NiPor‐CTF) with atomically dispersed NiN₄ centers as an efficient electrocatalyst for CO₂ reduction reaction (CO₂RR). The high density and atomically distributed NiN₄ centers are confirmed by aberration‐corrected high‐angle annular dark field scanning transmission electron microscopy and extended X‐ray absorption fine structure. As a result, NiPor‐CTF exhibits high selectivity toward CO₂RR with a Faradaic efficiency of >90% over the range from ?0.6 to ?0.9 V for CO conversion and achieves a maximum Faradaic efficiency of 97% at ?0.9 V with a high current density of 52.9 mA cm^?2, as well as good long‐term stability. Further calculation by the density functional theory method reveals that the kinetic energy barriers decreasing for *CO₂ transition to *COOH on NiN₄ active sites boosts the performance.     

Salt‐Assisted Growth of P‐type Cu9S5 Nanoflakes for P‐N Heterojunction Photodetectors with High Responsivity

P‐n junctions based on two dimensional (2D) van der Waals (vdW) heterostructure are one of the most promising alternatives in next‐generation electronics and optoelectronics. By choosing different 2D transition metal dichalcogenides (TMDCs), the p‐n junctions have tailored energy band alignments and exhibit superior performance as photodetectors. The p‐n diodes working at reverse bias commonly have high detectivity due to suppressed dark current but suffer from low responsivity resulting from small quantum efficiency. Greater build‐in electric field in the depletion layer can improve the quantum efficiency by reducing recombination of charge carriers. Herein, Cu₉S₅, a novel p‐type semiconductor with direct bandgap and high optical absorption coefficient, is synthesized by salt‐assisted chemical vapor deposition (CVD) method. The high density of holes in Cu₉S₅ endows the constructed p‐n junction, Cu₉S₅/MoS₂, with strong build‐in electric field according to Anderson heterojunction model. Consequently, the Cu₉S₅/MoS₂ p‐n heterojunction has low dark current at reverse bias and high photoresponse under illumination due to the efficient charge separation. The Cu₉S₅/MoS₂ photodetector exhibits good photodetectivity of 1.6 × 10¹² Jones and photoresponsivity of 76 A W^?1 under illumination. This study demonstrates Cu₉S₅ as a promising p‐type semiconductor for high‐performance p‐n heterojunction diodes.     

Salt‐Assisted Synthesis of 2D Materials

2D materials have demonstrated good chemical, optical, electrical, and magnetic characteristics, and offer great potential in numerous applications. Corresponding synthesis technologies of 2D materials that are high‐quality, high‐yield, low‐cost, and time‐saving are highly desired. Salt‐assisted methods are emerging technologies that can meet these requirements for the fabrication of 2D materials. Herein, the recent process for the salt‐assisted synthesis of 2D materials and their typical applications are summarized. First, the properties of salt crystals and molten salts are briefly introduced, and then some examples of 2D materials synthesis with the assistance of salt as well as their representative applications are presented. The underlying mechanisms of salts with different states on the formation of 2D morphology are discussed to aid in the rational design of synthetic route of 2D materials. At last, the challenges and future perspectives for salt‐assisted methods are briefly described. This review provides guidance for the controllable synthesis of 2D materials based on the salt‐assisted approaches.     

扫描型红外探测系统指向精度的测量

描述和分析了扫描型红外探测系统指向精度测量的必要性,并提出了一种扫描型红外探测系统指向精度的测量方法.该方法综合了内场测量和外场测量的优点,降低了系统在整个测量过程中由于检测设备的误差和检测方法不当所引起的偏差.并对误差产生的原因以及造成的结果进行了分析.有利于扫描型红外探测系统指向精度的高精度测量和校正.     

混合激励线性预测低速率语音编码研究

为了满足数字通信及其他商业应用的需求,语音压缩编码技术得到迅速发展。近年来主流的低速率语音编码方案主要基于LPC-10,混合激励线性预测（MELP）,多带激励编码（MBE）,正弦变换编码（SCI）,波形内插编码（WI）。大多都工作在2．4kb／s速率下。作为一种重要的低速率语音编码算法。MELP算法对LPC-10编码方案进行大量改进,引入混合激励,非周期脉冲,残差付氏幅度谱,脉冲散布和自适应谱滤波5个特征。实验结果表明,该混合激励线性预测编码在2．4kb／s上得到了更好的合成语音,并使得合成语音能更好地拟合自然语音。