无线传感器网络MAC协议的研究与改进

研究和分析了当前无线传感器网络(WSN)中介质访问控制(MAC)协议、IEEE802.11和IEEE802.15.4 MAC协议的各种性能,并结合传感网络介质访问协议(S-MAC)中低占空比休眠机制对IEEE802.15.4介质访问协议进行改进.用NS-2仿真软件对各种协议进行仿真,仿真结果表明改进后的MAC协议可大...     

基于FPGA无线传感器网络MAC控制器的设计

给出了一种由FPGA实现的无线传感器网络MAC控制器的设计方法,采用自顶向下的方法设计各个模块,并在QuartusⅡ 8.0完成了仿真,该控制器主要支持IEEE802.15.4协议.测试结果表明,该MAC控制器支持20～250 kb·s<'-1>数据传输速率,适应IEEE802.15.4协议要求.     

基于GAF的无线传感器网络MAC协议

节能是无线传感器网络介质访问控制(MAC)协议的首要目标,综合近年来MAC协议的研究成果,针对S-MAC、T-MAC等几种典型协议进行分析,研究出将拓扑结构控制机制引入MAC协议,可进一步降低能耗。给出了一种基于GAF拓扑控制思想的MAC协议、GS-MAC协议。GS-MAC协议可以降低处于空闲侦听状态的节点数量,是一种高效节能的协议。仿真表明,引入拓扑控制后可以达到进一步节约能耗的目的。     

Jennic JN5139 ZigBee解决方案

方案简余 JN5139是IEEE802.15.4和ZigBee低成本低功耗微控制器,集成了32位RISC处理器、完全兼容的2.4GHz IEEE802.15.4收发器、192KBROM、96KB RAM以及丰富的模拟和数字外设.成本敏感的ROM/RAM架构支持系统软件存储,包括协议堆栈、路由表格以及应用代码/数据.每个器件都集成了硬件MAC和AES加密加速器、节电模式和定时睡眠模式以及安全键和程序代码加密.     

无线传感器网络MAC层协议浅析

文章简述了无线传感器网络中MAC层协议设计所需要考虑的要素,并详细介绍了S-MAC、T-MAC、PCSMAC、CoLaNet以及ACSEMAC等五种已经提出的MAC协议。通过介绍这些协议的细节,展示了近几年来无线传感器网络MAC层协议的部分研究成果。最后,文章还分析了这些协议的优势和缺陷。     

无线传感器网络MAC协议的实现与分析

介绍了无线传感器网络中2种重要的基于竞争的MAC协议(IEEE802.11和S-MAC)原理。从平台的整体架构和运行环境2个方面对无线传感器网络测试平台的设计进行了详细介绍。对于IEEE802.11和S-MAC协议的实现,具体描述了通信接口的定义和组件重用技术,从状态机的角度阐述了协议的运行流程。根据测试数据从不同方面对IEEE802.11和S-MAC协议进行了对比分析。实验结果真实地反映了协议的性能,对无线传感器网络MAC协议的研究有着积极的推动作用。     

基于网络编码的IEEE 802.15.4 MAC协议优化

针对应用网络编码的多信源节点双向中继网络,在IEEE 802.15.4 MAC传输协议的基础上进行了优化.IEEE802.15.4 MAC协议在整个超帧的竞争访问周期均处于收发状态,优化后的MAC协议,在超帧的竞争访问周期,当信源节点接收到确认帧后,就关闭收发机制,信源节点进入睡眠状态,大大的节约了能量消耗.仿真结果表明优化后的MAC协议在完成系统功能的同时更好的节约了能耗.     

甚低功耗无线通信技术——ZigBee

ZigBee技术作为无线传感器网络的主要支撑技术获得人们广泛的关注.完整的ZigBee协议套件由高层应用规范、应用会聚层、网络层、数据链路层和物理层组成.网络层以上协议由ZigBee联盟制订,物理层和媒体访问控制(MAC)层采用IEEE 802.15.4标准.IEEE802.15.4物理层简单采用比特到符号映射技术、符号到码片序列转换技术、偏移正交相移键控(OQPSK)调制技术,无须信道编码等复杂算法;MAC层采用载波监听多址-冲突避免技术,支持休眠模式.整个协议的设计使得ZigBee技术具有数据传输速率低、功耗低、成本低等特点,更加适合于工业监控系统、传感器网络、家庭监控系统、安全系统等应用.     

IEEE802.15.4标准的自适应GTS调度机制

介绍了IEEE 802.15.4协议的GTS调度机制。基于现有的IEEE802.15.4MAC协议,提出了一种针对传输时延和公平性问题的自适应GTS调度(Adaptive GTS Allocation,AGA)算法。建立相应的自适应GTS仿真模型,对GTS算法的性能进行评估,并用网络演算理论对GTS进行理论分析。结果表明,提出的GTS调度机制在传输时延和公平性上明显优于现有的GTS调度方案。     

IEEE 802.15.4轻量级网络层路由设计及实现

IEEE 802.15.4是低速率、低功耗的无线个人区域网络协议标准。分析了IEEE 802.15.4的特点,在其上设计了轻量级网络层路由协议并在ZigBit 900平台上实现。路由协议对AODV进行了简化,利用MAC层的应答机制检测链路是否连通。最后对路由协议进行了测试,结果表明本路由设计具有良好的性能和扩展性。     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

Critical Stage Rule-Based Real Time Dispatch（RTD）System in Highly-Mixed-Products （HMP） FAB

An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB.     

GaAsSb/InAlAs PA DHBTs Grown by Production MBE

The epi material growth of GaAsSb based DHBTs with InAlAs emitters are investigated using a 4 × 100mm multi-wafer production Riber 49 MBE reactor fully equipped with real-time in-situ sensors including an absorption band edge spectroscope and an optical-based flux monitor. The state-of-the-art hole mobilities are obtained from 100nm thick carbon-doped GaAsSb. A Sb composition variation of less than ± 0.1 atomic percent across a 4 × 100mm platen configuration has been achieved. The large area InAlAs/GaAsSb/InP DHBT device demonstrates excellent DC characteristics,such as BVCEO＞6V and a DC current gain of 45 at 1kA/cm2 for an emitter size of 50μm × 50μm. The devices have a 40nm thick GaAsSb base with p-doping of 4. 5 × 1019cm-3 . Devices with an emitter size of 4μm × 30μm have a current gain variation less than 2% across the fully processed 100mm wafer. ft and fmax are over 50GHz,with a power efficiency of 50% ,which are comparable to standard power GaAs HBT results. These results demonstrate the potential application of GaAsSb/InP DHBT for power amplifiers and the feasibility of multi-wafer MBE for mass production of GaAsSb-based HBTs.     

Noise character analysis and the restraint of self-pulsation laser diodes

We calculate the Langevin noise sources of self-pulsation laser diodes, analyze the effects of active region noise and saturable-absorption region noise on the power fluctuation as well as period fluctuation, and propose a novel method to restrain the noise effects. A visible SIMULINK model is established to simulate the system, The results indicate that the effects of noise in absorption region can be ignored; that with the increase of DC injecting current, the noise effects enhance power jitter, and nevertheless, the period jitter is decreased; and that with external sinusoidal current modulating the self-pulsation laser diode, the noise-induced power jitter and period jitter can be suppressed greatly. This work is valuable for clock recovery in all-optical network.     

High-quality single-crystal CdSe nanoribbons and their optical properties

Large-scale synthesis of single-crystal CdSe nanoribbons is achieved by a modified thermal evaporation method, in which two-step-thermal-evaporation is used to control CdSe sources＇ evaporation. The synthesized CdSe nanoribbons are usually several micrometers in width, 50 nm in thickness, and tens to several hundred micrometers in length. Studies have shown that high-quality CdSe nanoribbons with regular shapes can be obtained by this method. Room-temperature photolumines-cence indicates that the lasing emission at 710 nm has been observed under optical pumping （266 nm） at power densities of 25-153 kW/cm^2. The full width half maximum （FWHM） of the lasing mode is 0.67 nm     

Propagation of hermite-cosh-gaussian beams passing through ABCD optical system with an annular aperture

By using the expansion of the aperture function into a finte sum of complex Gaussian functions, the corresponding analytical expressions of Hermite-cosh-Gaussian beams passing through annular apertured paraxially and symmetrically optical systems written in terms of ABCD matrix were derived, and they could reduce to the cases with squared aperture. In a similar way, the corresponding analytical expressions of cosh-Gaussian beams through annular apertured ABCD matrix were also given. The method could save more calculation time than that by using the diffraction integral formula directly.     

Influence of polarization extinction ratio on distributed polarization coupling detection

Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited.     

Call for Papers

正Communications—VLSI Researches and industries of telecommunications have been growing rapidly in the last 20 years and will keep their high growing pace in the next decade.The involved researches and developments cover mobile communications,highway and last-mile broadband communication,domain specific communications,and emerging D2D M2M communications.Radio communication steps into its