基于拥塞估计的TCP窗口在线学习方法

针对传统TCP拥塞窗口更新、控制机制所导致的Ad Hoc网络吞吐量下降的问题,利用机器学习算法来改善TCP在Ad Hoc网络中的性能。该方法利用确认帧的时间间隔,通过连续动作集(CALA)算法快速学习并估计当前网络链路中的拥塞状况,从而能够迅速调整TCP拥塞窗口。仿真实验表明:当Ad Hoc网络环境较好时,学习型TCP的吞吐量略优于TCP-Few、TCP-Reno协议,但在环境较差的情况下,学习型TCP的吞吐量远远优于TCP-Few和TCP-Reno协议。     

一种改进的TCP over OBS网络拥塞控制策略

首先深入分析了TCP over OBS网络中造成TCP性能下降的各种原因.在此基础上,考虑将近年来提出的GAIMD算法与OBS网络的特点相结合,提出了一种改进的拥塞控制策略.该策略能在一定程度上改善OBS网络由于随机竞争丢包给TCP性能带来的负面影响.     

前向主动网络拥塞控制算法及其性能分析

本文提出了一种基于主动式网络(Active Networks)技术的拥塞控制算法FACC(Forward Active Networks Congestion Control).与传统的TCP(Transport Control Protocol)相比,FACC算法通过在网络结点直接提供拥塞检测和拥塞控制机制,大大缩短源端点的拥塞反应时间,从本质上提高了网络拥塞检测和控制的性能,从而提高了终端用户的平均吞吐量.文中还利用计算机仿真研究了FACC算法在各种网络条件下的性能,并与传统的Tahoe,Reno,NewReno及SACK TCP协议做了对比.结果表明无论网络中存不存在非受控数据流时,FACC控制算法均能明显地提高用户终端的平均吞吐量,并且由于采用FACC控制算法而增加的网络结点运算迟延也很小.     

网络中的拥塞控制管理算法分析与比较

随着网络技术的发展,网络拥塞日益严重,如何解决拥塞,充分、高效地利用网络资源,成为当今急需解决的问题.由于Internet上大多数业务都采用TCP协议,因此TCP的拥塞控制机制对控制网络拥塞具有特别重要的意义.本文介绍了TCP基于窗口的拥塞控制策略和目前常用端到端拥塞控制算法,并对它们的性能进行比较.     

光突发交换网络中的传输控制协议性能

光突发交换(OBS)是IP over WDM核心网络采用的交换技术。在OBS网络中,送往同一边缘节点的IP分组汇聚成传输和交换的基本单元———数据突发(DB),DB丢弃会导致大量IP分组丢失,显著影响传输层的性能。文中分析OBS网络的参数对传输控制协议(TCP)吞吐量和时延的影响。仿真结果表明,DB丢包率越高,TCP性能越差。在低丢包率情况下,随着DB长度的增加,TCP吞吐量和端到端时延明显增加,高丢包率情况下则不明显;随着汇聚周期的增加,TCP吞吐量逐渐下降,端到端时延逐渐增加。     

MPLS网络主动式流量和拥塞控制机制及性能分析

MPLS是具有大带宽一时延迟的网络,用传统的TCP解决MPLS拥塞问题显得十分困难,该文结合MPLS的网络特点,提出了一种适合MPLS网络的主动式流量和拥塞控制机制,在网络边缘节点引入拥塞反馈处理,对实验模型进行了性能仿真分析,实验证明,与传统的TCP协议相比,该机制将流量和拥塞控制从用户端点扩展到MPLS边缘路由器,能够更及时地检测和控制网络拥塞,缩短了控制时延,可以进行较精确的流量调节,实现了提高吞吐量和改善缓冲区利用率的目的。     

基于Gilbert丢包机制的TCP吞吐量模型

 丢包机制是推导TCP吞吐量模型的关键,直接影响模型的准确性.本文利用四状态Gilbert丢包机制来描述端到端路径上的丢包行为,对TCP的拥塞控制过程进行建模,在此基础上提出了一种更精确的TCP吞吐量模型.实验表明,改进的模型能较好的与实际值相拟合,可以更精确地预测实际TCP数据流的吞吐量性能.     

一种3GPP LTE网络的TCP拥塞控制方法

现有的传输控制协议(TCP)拥塞控制机制源自有线网络,未考虑无线基站介质访问控制(MAC)层调度器的特性,影响了TCP协议在长期演进(LTE)系统上的传输性能。提出一种跨层的TCP拥塞控制方法,由MAC层和TCP共同解决TCP虚假超时问题。此方法中,MAC层提供超时信息,TCP层识别出虚假超时后调整数据速率,从而避免系统性能损失,保证MAC层稳定工作。仿真结果表明,在保证用户公平性的同时,新方法可以有效解决虚假超时问题,提高用户实际吞吐量。     

基于主动网络的分层组播机制研究

分层组播是解决组播通信当中底层网络结构异构性,适应网络动态变化的一种最佳解决方案。本论文分析了现有的分层组播技术,介绍了采用主动网进行接收方驱动的分层组播的新方案(RLM-AN)。不同于大多数的分层组播方法的端到端的拥塞控制机制,RLM-AN是分布式的TCP友好的拥塞控制机制。方案中把组播树看成是一组虚拟链路,在每个虚拟链路上进行TCP友好的拥塞控制。通过在网络内部的主动节点处进行拥塞控制,传输系统可以得到更为平滑的和更为TCP友好的吞吐量,以及对网络内部拥塞的快速响应。同时,本论文对RLM-AN在技术细节实现上的若干问题进行了讨论。     

基于主动网络的分层组播机制研究

分层组播是解决组播通信当中底层网络结构异构性，适应网络动态变化的一种最佳解决方案。本论分析了现有的分层组播技术，介绍了采用主动网进行接收方驱动的分层组播的新方案(RLM-AN)。不同于大多数的分层组播方法的端到端的拥塞控制机制，RLM-AN是分布式的TCP友好的拥塞控制机制。方案中把组播树看成是一组虚拟链路，在每个虚拟链路上进行TCP友好的拥塞控制。通过在网络内部的主动节点处进行拥塞控制，传输系统可以得到更为平滑的和更为TCP友好的吞吐量，以及对网络内部拥塞的快速响应。同时，本论对RLM-AN在技术细节实现上的若干问题进行了讨论。     

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