FDMA,TDMAG民CDMA蜂窝系统频谱效率的比较

从理论上分析比较了ＦＤＭＡ，ＴＤＭＡ与ＣＤＭＡ蜂窝网系统的频谱效率，指出了其频谱效率的限制因素和提高方法计算了Ｑ＝ＣＤＭＡ，ＧＳＭ与ＴＡＣＳ三处实用蜒多系统的频谱效率，得和点有用结论。     

4G蜂窝网中移动互联网IP电视服务的优化研究

4G蜂窝网的频谱分配效率难以负担日益增长的移动IPTV服务与大视频流数据,为此提出了蜂窝网支持移动IPTV服务的优化方案,在保持传统语音电话质量的前提下,提高了移动IPTV服务的性能.首先,为语音电话分配较高的频率分配优先级以维护语音电话的QoS(Quality of Service);然后,采用软频谱复用技术来增强频谱的效率,并降低相邻蜂窝之间的频谱干扰;最终,设计了动态频谱分配算法,对相邻蜂窝间边缘频带的频谱分配进行协调与优化,进一步地提高了频谱利用率.仿真结果显示,本频谱分配算法在不降低语音电话服务质量的前提下,明显地提高了移动IPTV服务的性能.     

异构网中基于BD的协作波束赋形算法研究

波束赋形是下一代无线蜂窝网中提高频谱效率的一项重要技术,文中在多用户波束赋形技术的研究基础上,研究了CoMP中的CB技术。针对LTE系统中的小区间干扰严重,且已有的干扰协调技术无法有效解决边缘用户频谱效率低的问题,LTE-A系统引入了多点协作传输/接收技术。该技术通过相邻小区间的联合处理或协作波束赋形,可抑制小区间干扰,提高用户的接收信号质量,使系统容量和小区边缘用户的频谱效率得到有效提高。     

移动通信和个人通信的发展（下）

移动通信和个人通信的发展（下）中国科学院院士张煦３．蜂窝网和微蜂窝网当初为了在城市实行车载移动通信，曾成功地设计和建立无线电蜂窝网，每一蜂窝区的中心各设置无线电基台，使用频谱８００～９００ＭＨｚ，有收发信机和控制设备，覆盖面积的直径一般大于３ｋｍ，视...     

蜂窝系统中基于时延的D2D通信模式选择算法

D2D(Device-to-Device)通信作为蜂窝网的辅助通信方式,可以有效提高系统容量,具有提高频谱效率、减小时延等优势。模式选择是蜂窝网与D2D联合通信的关键问题之一。提出一种基于时延的D2D通信模式选择算法,该算法引入队列状态信息模型,以队列长度为权重的最大加权算法为调度策略,以时延作为模式选择的标准。通过仿真给出本算法与基于系统容量最大化的模式选择算法的性能比较,仿真结果表明与基于系统容量最大化的模式选择算法相比,本算法所需时延和丢包率均减小约20%。     

一种基于传感器网络的认知蜂窝网模型

文中针对未来的蜂窝通信服务提出了一种具体的基于传感器网络的认知蜂窝网模型，并对网络各部分的功能进行了深入分析．该模型能充分的利用现有蜂窝网的基础设施并发挥认知无线电解决频谱资源紧张的特点，具有广泛的应用价值．     

简析CDMA蜂窝系统Erl容量

蜂窝网采用空间频率再用技术大大地缓解了频谱资源有限与用户不断增长之间的矛盾.其中CDMA蜂窝网的容量最大,而且还具有软容量特性.但是由于CDMA是自干扰系统,它在直接应用Erl B定理之前受空间Erl容量概念的制约.本篇文章简要分析了在CDMA系统中计算Erl容量的方法,并涉及了一些针对这一CDMA特有概念的优化工作.     

同频全双工中继协作通信关键技术综述

当前,线性增长的无线蜂窝网容量难以满足按指数规律增长的移动互联网业务量的需求。因此,学术界和工业界要求频谱效率进一步得到提升。与传统的半双工模式相比,同频全双工技术能使得频谱效率显著提高,同时,面临着自干扰的负面影响。文章对同频全双工技术进行了介绍,对相关技术特点进行分析,并对同频全双工所面临的技术挑战进行评述。     

CDMA与TDMA数字蜂窝系统频谱效率的比较

在数字蜂窝系统中频谱效率与频谱利用率有着直接的关系。ＣＤＭＡ与ＴＤＭＡ系统的频谱效率可以由系统的无线电容量所体现。本文将在可比条件下对ＣＤＭＡ与ＴＤＭＡ系统的频谱效率进行比较，从而也必然地导致对频率复用系数Ｋ的比较及共信道干扰减少因子ｑ的计算。作者在对蜂窝概念、系统的频谱效率及ＣＤＭＡ系统无线电容量计算方法进行了研究后，较为系统地归纳并提出了ＣＤＭＡ与ＴＤＭＡ频谱效率的具体比较方法，并对一些关键公式来源进行了推导、分析，最后得出了ＣＤＭＡ与ＴＤＭＡ系统频谱效率比较的结果。     

中继辅助协同通信网

下一代移动通信系统对频谱有效性和功率有效性提出了更高的要求，在现有的蜂窝网结构中引入中继的协作式通信被认为是高速率高覆盖要求下最可行的改进。中继辅助协同通信网与传统蜂窝网相比在覆盖效率、运营成本以及传输容量3方面具有优势。中继辅助通信网络主要有3种典型的传输模型：三终端传输模型、两跳多中继并行传输模型、多跳多中继网络传输模型。中继辅助通信技术已在WiMAX、WINNER和3GPP等通信标准中得到深入研究，具有极为广阔的应用前景。     

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.     

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.     

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.     

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.     

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     

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