4G关键技术研究

随着用户对移动通信系统的速率要求不断提高,3G系统实际所能提供的最高速率已不能满足未来市场的实际需求,因而在3G系统还没有大规模投入商用的情况下,国内外移动通信领域的专家已经在进行4G系统的研究和开发工作.4G是多功能集成的宽带移动通信系统,具有许多关键优势,因而已成为移动通信领域的研究热点.文章给出了4G的体系结构,并对4G相关技术的原理进行了详细分析.     

Integrated Planar Waveguide Demultiplexers for High-Density WDM Applications

A review is presented of state-of-the-art optical planar waveguide demultiplexers (DEMUXes), that is, phasars (arrayed waveguide) and etched grating devices designed for high-density (narrow channel spacing) wavelength division multiplexing (WDM) systems. Their advantages and disadvantages are discussed in comparison with other techniques for demultiplexing WDM signals. The advances made in their performance are reviewed, and ultimate limitations, set by technological constraints, are proposed. Finally, a comparison is made of the advantages and disadvantages of etched grating as opposed to phasar planar waveguide DEMUXes.     

Anti-inflammatory chromone alkaloids and glycoside from Dysoxylum binectariferum

Herein we report isolation of a new chromone alkaloid chrotacumine K (12) from fruits and a chromone glycoside schumaniofioside A (13) from leaves of Dysoxylum binectariferum Hook f. Schumaniofioside A is reported for the first time from Meliaceae family. Other known alkaloids isolated include rohitukine (1) and chrotacumine E (6). The structure of new alkaloid 12 was elucidated on the basis of extensive 1D and 2D NMR analysis, synthesis and chemical hydrolysis. Chemically, chrotacumine K (12) is a 3′-O-acetyl rohitukine which on chemical or enzymatic hydrolysis produces rohitukine. The new alkaloid 12 is also present in seeds and stem-barks of this plant. The glycoside schumaniofioside A (13) is present only in leaves, and in abundance (～1% w/w of dried leaves). The isolated compounds and extracts were evaluated for in vitro effect on the proinflammatory cytokines (TNF-α and IL-6) in human monocytic THP-1 cells. The alkaloid 12 displayed potent inhibition (57%) of TNF-α at 0.3 µM, and was non-toxic to THP-1 cells up to 40 µM, indicating its excellent therapeutic window. Furthermore, a nitrobenzoyl ester analog 15e showed better inhibition of IL-6 than parent natural product chrotacumine K.     

光缆传输设备工程配套设施安装设计探讨

简要阐述了光缆传输系统工程设计界面的划分;根据中国移动集团提倡的标准化建设管理思路,从光缆传输设备工程特点和实践工作经验出发,对相关配套设施的安装设计进行了探讨,并提出了初步实用方案     

P N IFFT FOR OFDM-BASED UWB SYSTEM

In this letter, P × N-point IFFT is proposed to replace the N-point IFFT and analog frequency conversion in an Orthogonal Frequency Division Multiplexing (OFDM)-based Ultra-WideBand (UWB) system, and a new algorithm, named fast P × N-point IFFT, is designed to reduce the complexity of the P × N-point IFFT in the proposed scheme.     

第四代移动通信露曙光

本文介绍了第四代（4G）移动通信的概念和技术要求，着重讨论了正交频分复用（OFDM）在第四代移动通信中的应用，最后简要的介绍了第四代移动通信的研发状况。     

一种新的地面数字多媒体/电视广播传输系统

针对传输信道线性时变的宽带传输信道特性，设计了一种时域同步正交频分复用（简称TDS－OFDM）的多载波调制方式。这种调制方式既适用于具有多径干扰和多普勒频移的地面数字电视广播传输信道，也适用于其它宽带数字传输系统。为了进一步提高传输效率，提出的地面数字多媒体／电视广播DMB－T传输系统还采用了最新的纠错编码和交织编码技术，在额定的8MHz带宽中，净载数据传输率可达32．511Mbps。     

Free groups in a normal subgroup of the field of fractions of a skew polynomial ring

Let k(t) be the field of rational functions over the field k, let σ be a k-automorphism of K = k(t), let D = K(X;σ) be the ring of fractions of the skew polynomial ring K[X;σ], and let D^? be the multiplicative group of D. We show that if N is a noncentral normal subgroup of D^?, then N contains a free subgroup. We also prove that when k is algebraically closed and σ has infinite order, there exists a specialization from D to a quaternion algebra. This allows us to explicitly present free subgroups in D^?.     

新型太赫兹光子晶体OAM光纤设计

太赫兹通信兼具微波通信和光波通信的优势,是解决通信容量紧缺难题的最有效技术手段之一。针对太赫兹波段吸收损耗严重及抗外在扰动差,难以支持长距传输问题,设计了一种基于环形光子晶体光纤(PCF)结构的新型太赫兹光纤。以现有常见材料作为光纤基底材质,通过创新光纤结构中空气孔排布方式,抵消材料高吸收损耗,以支持高性能轨道角动量(OAM)模式传输。选择最优参数,实现6个OAM模式群的高模式质量、低限制损耗和宽带宽的稳定传输。在0.2~0.9 THz宽波段内,实现模式纯度超过88.9%,限制损耗小于10^-7 dB/m。通过软件仿真实验设计,解决了太赫兹与OAM技术相结合的关键问题,为模分复用(MDM)技术在太赫兹通信系统的应用奠定了理论研究基础。