Leveraging Multi-AP Diversity for Transmission Resilience in Wireless Networks: Architecture and Performance Analysis

With the increasing development of IEEE 802.11 based wireless local area network (WLAN) devices, large-scale multi-cell WLANs with a high density of users and access points (APs) have emerged widely in various hotspots. Providing resilient data transmission has been a primary challenge for scaling the WLANs because the high density of users and APs results in too many collisions. In this paper, we analyze and point out the defect of the single association mechanism defined in IEEE 802.11 on transmission reliability from a network perspective. Then, we propose a "multi-AP" architecture with which a MAC layer device called an AP controller (AC) is employed to enable each user to associate and cooperate with multiple APs. In this way, the users can benefit from the diversity effect of multipaths with independent collisions and transmission errors. This paper concentrates on the theoretical analysis of performance comparison between the proposed ldquoMulti-APrdquo architecture and that in IEEE 802.11. Extensive simulation results show that the proposed ldquomulti-APrdquo architecture can obtain much better performance in terms of the throughput per user and the total throughput, and the performance gain is position dependent. Moreover, the unfairness issue in traditional WLANs due to capture effect can be alleviated properly in the ldquomulti-APrdquo framework.     

Porous alumina nano-membranes: Soft replica molding for large area UV-nanoimprint lithography

High-density ordered arrays of h-PDMS nanopillars were fabricated using an anodic aluminium oxide (AAO) template. The pore diameter and the interpore distance of the replica h-PDMS molding are well consistent with that of AAO template. The inverse h-PDMS has the surface characteristic of hydrophobic and surface energy of 130°. Hexagonally arranged array can be obtained by UV-nanoimprint lithography using our proposed h-PDMS mold, and their morphologies can be transferred truly. Besides, the h-PDMS mold has been used to fabricate photonic crystal structure on GaN by nanoimprint process, which could be found an application in the light output of GaN LED.     

关于电信企业电子渠道发展若干问题的思考

对于电信企业（这里主要讨论移动运营商）而言,电子渠道涵盖的范围广泛,种类丰富,包括10086热线、短信渠道、网站渠道、WAP渠道、自助终端、USSD,KJAVA等多种类型。本文将聚焦于两大热点渠道,即网站和WAP渠道,探讨目前电信企业在实际运营中所遇到的难点及困惑。其内容包括网站及WAP渠道目标用户的界定、对电子渠道“增量不分流”现象的思考,以及电子渠道与用户、业务的匹配性研究。通过以上问题的探讨希望能为运营商电子渠道的发展带来一定的参考价值及启示。     

沟道应力对GaAs PHEMT材料电性能的影响

设计并用分子束外延(MBE)法制备了不同沟道结构的GaAs PHEMT材料,采用高分辨率X射线双晶衍射仪(DCXRD)、应力测试仪和霍尔测试仪对样品的结晶质量、薄层组分和厚度偏差、应力以及电子迁移率进行了分析表征。探讨了外延片应力与沟道结构的相关性,研究了沟道失配应力对电性能的影响机理。建立了GaAs PHEMT材料热应力引起电子传输特性退化的试验方法,进行了高温和低温存储后材料电性能的演化行为测试,并归纳了热应力引起材料电特性退化的实验结果。结果表明GaAs PHEMT材料经高、低温存储并恢复室温后仍能保持原有电性能,沟道应力对材料电性能的影响主要表现为失配应力。     

一种光纤通信系统中帧同步电路的设计

描述了一种光纤通信系统中基于FPGA实现的全数字通信系统同步电路的原理.在MAX PLUSⅡ环境下结合原理图和VHDL语言进行了综合、仿真和配置,该电路实现了同步电路的全数字化.测试结果表明,该设计方法能比较准确地恢复同步信号.     

双沟道实空间电子转移晶体管的设计、研制和特性测量

采用双沟道结构和GaAs衬底,成功设计研制了双沟道实空间电子转移晶体管.它具有RSTT典型的"A"形负阻I-V特性和较宽的平坦谷值区.通过栅压可改变各种负阻参数值,当栅压从0.6V增至1.0V时,PVCR的变化范围是2.1～10.6峰值电流跨导约为3×10-4 S.负阻参数VP,VV和开始产生负阻的栅极阈值电压都小于国际上同类器件的报道值,因此更适合低功耗的运用.     

Study on the failure temperature of Ti/Pt/Au and Pt5Si2-Ti/Pt/Au metallization systems

The Ti/Pt/Au metallization system has an advantage of resisting KOH or TMAH solution etching. To form a good ohmic contact, the Ti/Pt/Au metallization system must be alloyed at 400℃. However, the process temperatures of typical MEMS packaging technologies, such as anodic bonding, glass solder bonding and eutectic bonding, generally exceed 400℃. It is puzzling if the Ti/Pt/Au system is destroyed during the subsequent packaging process. In the present work, the resistance of doped polysilicon resistors contacted by the Ti/Pt/Au metallization system that have undergone different temperatures and time are measured. The experimental results show that the ohmic contacts will be destroyed if heated to 500℃. But if a 20 nm Pt film is sputtered on heavily doped polysilicon and alloyed at 700℃ before sputtering Ti/Pt/Au films, the Pt₅Si₂-Ti/Pt/Au metallization system has a higher service temperature of 500℃, which exceeds process temperatures of most typical MEMS packaging technologies.     

Defect-related visible luminescence of ZnO nanorods annealed in oxygen ambient

ZnO nanorods prepared by a solution-phase method are annealed at different temperatures in oxygen ambient.The luminescence properties of the samples are investigated.In the same excitation condition,the photoluminescence(PL) spectra of all samples show an ultraviolet(UV) emission and a broad strong visible emission band.The asymmetric visible emis-sion band of annealed samples has a red-shift as the annealing temperature increasing from 200 ℃ to 600 ℃ and it can be deconvoluted into two subband emissions centered at 535 nm(green emission) and 611 nm(orange-red emission) by Gaussian-fitting analysis.Analyses of PL excitation(PLE) spectra and PL spectra at different excitation wavelengths reveal that the green emission and the orange-red emission have a uniform initial state,which can be attributed to the electron transition from Zn interstitial(Zni) to oxygen vacancy(Vo) and oxygen interstitial(Oi),respectively.     

基于寄生振子的多频印刷天线

RFID技术近年来发展迅猛,但是各国使用的频段却不统一。为了增强RFID系统的兼容性,本文设计一款应用于RFID标签的3频印刷天线。采用加载寄生振子实现天线的3频工作。使用ADS仿真软件对本文所设计的天线进行了仿真研究,结果表明反射损耗小于-15dB时天线的工作带宽分别为782.5～851.1MHz,919.3～995.5MHz,2.446～2.577GHz,满足设计要求。这3个频段分别覆盖了中国划分的两个RFID频段以及国际通用的2.45GHz频段。