Performance evaluation of underwater wireless optical CDMA system for different water types

In this paper, an analytical approach is presented to investigate the bit error rate (BER) performance of underwater wireless optical code division multiple access system for different water types. Optical orthogonal codes (OOC) are used as the user-specific address sequence to encode and decode the user’s data. LED with an operating wavelength of 532 nm is used as the optical source, and silicon avalanche photodiode is used as the optical detector. The system BER performance is analyzed on account of transmission distance, transmitted power, number of simultaneous users, and other system parameters where different water types (i.e., pure sea water, clear ocean water, and coastal ocean water) are considered as the communication channel qualities. It is found that the BER performance of this system significantly depends on the water types. However, the best overall system performance is achieved in pure sea water where clear ocean water provided better results than coastal ocean water.

     

Design of IIR notch filters with different passband gains

A method is proposed for the design of infinite-duration impulse response (IIR) notch filters with different passband gains using the standard lowpass IIR digital-filter design methods. This method satisfies the notch-frequency specification exactly and realises a rejection bandwidth, defined by the frequencies at which the gain is 3 dB below the lower of the two passband gains, which is smaller than that specified. Illustrative examples are given     

不同光源对激光尘埃粒子计数器性能的影响

使用Beam Profile2350光束诊断仪测量了氦氖激光和半导体激光两种典型光源的光束特性,并分析了将它们作为激光尘埃粒子计数器的光源时,其在光敏区所产生光场的不均匀性。同时讨论了光场不均匀对计数器性能的影响,计算了两种不同光源下,计数器计数效率和分辨比率的差异。结果表明,以半导体激光作为计数器光源时,光敏区的光强均匀性更好,计数效率更高,粒径的分辨比率较氦氖激光作用时提高了17％,增大了粒径的有效测量范围。     

On the tradeoff between two types of processing gains

One of the features characterizing almost every multiple-access (MA) communication system is the processing gain. Through the use of spreading sequences, the processing gain of random code-division multiple-access (RCDMA) systems, or any other code-division multiple-access (CDMA) systems, is devoted to both bandwidth expansion and orthogonalization of the signals transmitted by different users. Another type of MA system is impulse radio (IR). IR systems promise to deliver high data rates over ultra-wideband channels with low-complexity transmitters and receivers. In many aspects, IR systems are similar to time-division MA systems, and the processing gain of IR systems represents the ratio between the actual transmission time and the total time between two consecutive transmissions (on-plus-off-to-on ratio). While CDMA systems, which constantly excite the channel, rely on spreading sequences to orthogonalize the signals transmitted by different users, IR systems transmit a series of short pulses, and the orthogonalization between the signals transmitted by different users is achieved by the fact that most of the pulses do not collide with each other at the receiver. In this paper, a general class of MA communication systems that use both types of processing gain is presented, and both IR and RCDMA systems are demonstrated to be two special cases of this more general class of systems. The bit-error rate of several receivers as a function of the ratio between the two types of processing gain is analyzed and compared, under the constraint that the total processing gain of the system is large and fixed. It is demonstrated that in non-intersymbol interference (ISI) channels, there is no tradeoff between the two types of processing gain. However, in ISI channels, a tradeoff between the two types of processing gain exists. In addition, the suboptimality of RCDMA systems in frequency-selective channels is established.     

Prolonging the lifetime of wireless sensor networks by utilizing feedback control

A new algorithm aiming to prolong the lifetime of wireless sensor networks (WSNs) is proposed to balance energy depletion. Using a feedback control combined with a discrete nonlinear programming method to adjust the transmission radii of sensor nodes located in different locations, makes network load redistribution possible and balances energy consumption, further prolongs the lifetime of the entire network. A data distribution model which specific to WSNs with sensor nodes that can adjust transmission radii is proposed to analyze the load spread of the network. This model contributes to predicting and analyzing energy consumption balance effectively. Compared with two other algorithms, dynamic transmission range adjustment and SP, respectively, the experimental results show that the proposed algorithm can lengthen the lifetime of WSNs by up to 22.7 and 27.2 %.     

CRLB analysis of wireless cognitive location with different short-range measurements

Because of the wide application and great market potential of location-aware services, the research of wireless location techniques for the fourth generation （4G） mobile communications is being paid more attention. Wireless cognitive location （WCL） techniques for next generation wireless networks have been proposed in recent years. This article investigates the changes of the positioning accuracy of WCL algorithm when different methods are adopted to measure the short-range （SR） information. By fJrst completing Cramer-Rao lower bound （CRLB） analysis of the WCL algorithm with SR measurements based on time of arrival （TOA） and received signal strength （RSS）, it is discovered that TOA-based or time difference of arrival （TDOA） -based SR measurement can make WCL algorithms achieve higher accuracy than RSS mode, which is also verified by numerical simulation in the article. The conclusions can instruct the design of novel WCL-based location algorithms.     

Effect of different types of carbon on microstructure and arcing behavior of Ag/C contact materials

Silver-carbon (Ag/C) contact materials with different types of carbon, including diamond, graphite, carbon black, and carbon nanotubes were fabricated by high-energy ball milling and hot-pressing. Their microstructures, arcing properties, and stability of the carbon structures were investigated. The results show that Ag/C nanotubes material displays a scallop-like morphology, which is significantly different from the microstructure of other Ag/C materials with dispersed particles. During the process of discharge, the diamond and carbon black in Ag/C materials are partially graphitized, while the morphology and crystal structure of graphite component have little change, indicating the graphite structure of Ag/C materials is the most stable of all.     

Synthesis of dibenzothiophene-based host materials and their blue phosphorescent device performances

Two structural isomeric host materials, 9-(4-(dibenzo[b,d]thiophen-4-yl)phenyl)-9H-pyrido-[2,3-b]indole (pDBTCb) and 9-(3-(dibenzo[b,d]thiophen-4-yl)phenyl)-9H-pyrido-[2,3-b]indole (mDBTCb), were designed and synthesized, incorporating dibenzothiophene (DBT) and α-carboline moieties via phenyl linkages and their device performances of phosphorescent organic light-emitting diodes (PHOLEDs) were also investigated. The different linkages between DBT and α-carboline on central phenyl spacer play an important role in the structure–property correlations. Although their photophysical properties were similar regardless of different linkage positions, the bis[2-(4,6-difluorophenyl)pyridinato-C²,N](picolinato)iridium(III)-based blue device with mDBTCb, which adopted a meta-linkage showed a significantly higher maximum quantum efficiency of 19.8% as compared to its para-linkage analog, pDBTCb (16.2%). A high quantum efficiency of 19.8% and only ca. 10% reduction of quantum efficiency at 1000 cd/m² were demonstrated from the blue PHOLEDs with the mDBTCb host material.     

不同粒型小麦品种胚乳淀粉体的扫描电镜观察

对3个不同粒型小麦品种胚乳淀粉体的大小，形状、分布和发育等特性进行了扫描电镜观察。结果表明，3个品种胚乳细胞淀粉体均为单粒淀粉，可根据淀粉体的大小分为三种类型：Ⅰ、Ⅱ，Ⅲ，型。Ⅰ型为椭球形，大粒淀粉；Ⅱ型为椭球形或橄榄球型，中粒淀粉；Ⅲ型为近圆球形，小粒粉，鄂恩1号Ⅱ型淀粉体多为橄榄球型，明显异于其它品种。各品种颖果腹部Ⅰ、Ⅱ型淀粉体多，排列紧密，背部Ⅲ型淀粉体较多，中间胚乳细胞淀粉体以Ⅰ、Ⅲ型为主，排列疏松。颖果腹部淀粉的发育和排列明显优于背部和中间，小粒型品种胚乳细胞淀粉体育好，淀粉充实度高；大粒型品种相反，淀粉体排列疏松，发育差，大粒淀粉体通过网状膜与中小淀粉体相连。     

多种无线制式的网络容量规划

随着LTE网络的大规模建设,2G/3G和LTE网络将在一定时期内长期并存。对各种制式的网络容量进行协调规划,首先需要对各种制式的网络配置数据和参数进行分析;其次是预测不同类型业务量的增长和网络负荷情况;最后,基于不同的驱动环境制定容量规划方案。本文总结了基于市场驱动、覆盖、容量和无线频谱等场景的容量规划方法。基于市场驱动的容量规划,网络为市场服务,业务需求预测成为对网络容量规划的依据;基于覆盖驱动的容量规划,首先满足覆盖要求,分步建站,逐步提高系统容量;基于容量驱动的容量规划,需要满足用户的服务质量要求,用户的业务需求和服务质量等级成为容量规划的依据;基于无线频谱的容量规划,需要在不同制式系统之间合理分配容量,以达到频率效率最优。     

不同极性聚合物材料的THz-TDS光谱测量研究

为探讨聚合物分子的极性对其介电性质的影响,采用太赫兹时域光谱研究了5种聚合物材料,高密度聚乙烯、聚对苯二甲酸乙二醇酯、聚氨酯、聚偏氟乙烯和聚乙烯吡咯烷酮在太赫兹波段的吸收色散性质,并尝试采用De-bye模型对实验结果进行了理论分析.研究发现,聚合物的偶极弛豫运动随极性的增强而加剧,导致吸收系数(α)、介电常数虚部(ε")和弛豫强度(△ε)均随之增大;由于弛豫运动受介质阻尼的影响落后于太赫兹电场的周期性变化,折射率(n)和介电常数实部(ε')呈现反常的色散现象,即n和ε随频率的增大而降低;Debye模拟结果还表明弛豫时间(T)随偶极子尺寸的增大和分子刚性的增强而显著增大.     

Enhanced photovoltaic performances of the dye-sensitized solar cell by utilizing rare-earth modified tin oxide compact layer

Multifunctional and ultrathin tin oxide (SnO₂) compact layer is modified by europium ion doped ytterbium fluoride (YbF₃:Eu³⁺), which is first designed and fabricated by a facile spin-coating method for the dye-sensitized solar cell (DSSC). The device with SnO₂/YbF₃:Eu³⁺ compact layer exhibits enhanced long-term stability and photoelectric conversion efficiency (PCE) compared to those of the device without compact layer. The enhanced long-term stability is due to the SnO₂/YbF₃:Eu³⁺ compact layer can transform ultraviolet (UV) light into visible light to mitigate dye degradation. The enhanced PCE is associated with the reduced recombination rate of electrons, the enhanced short-wavelength light response, and the high transparency of the compact layer. Moreover, the novel strategy of preparation SnO₂/YbF₃:Eu³⁺ compact layer is an universal method to adjust rare-earth species to achieve up- or down-conversion functions, and the multifunctional compact layer can be widely applied in the photovoltaic device.     

Wideband directional antenna system with different polarizations for wireless communication system

A novel directional antenna system with different polarizations is proposed for wireless communication system application in this paper. The proposed antenna employs modified E-shaped rectangular patch for vertical polarization and crossed dipoles for ±45° slant polarization. The vertically polarized (VP) element is formed by inserting a pair of wide slits at the boundary of rectangular patch with edge folded. The VP element is fed by using an L-probe feed, designed to work at the frequency range of 773–1013 MHz for GSM900 and other wireless communication systems such as GSM850 and LTE700 bands. Dual slant polarized (SP) elements are formed with two orthogonally situated dipoles with corner cut and slots on the patch, which yields a wide impedance bandwidth of 55.5% covering the frequency bands for 3G and LTE communication systems. A wideband diplexer is used to connect VP element and +45° SP element, forming a compact structure. Simulated and measured results show that peak gains of 8.0 dBi for VP element and 9.5 dBi for ±45° SP element, an isolation better than 26 dB over the working frequency bands are achieved. The cross-polarization levels in the azimuth plane for triple polarization states are lower than −14 dB.     

利用联合调制提高移动无线网络信息传输的可靠性

文章简要介绍了在移动无线传输信道中提高数据传输可靠性的几种方法,并利用联合调制思想和自适应均衡技术,提出了一种能够提高无线传输可靠性的尝试性方法。     

Electron-optical analog study of image tubes with different types of cathodes

Electron trajectory analog measurements for image tubes show that the serious aberrations of distortion and curvature of the image field, inherent to flat unipotential photocathodes, can be reduced by using a flat gradient cathode. Similar potential distributions as with curved cathodes are thus established. The resulting curvatures of the equipotential surfaces in the vicinity of the flat gradient cathode can be changed within a relatively wide range by varying the potentials at the gradient-cathode terminals. Pincushion distortion rapidly vanishes and even becomes barrel-shaped with increasing cathode center potential. Adequate reduction of the imagefield defect can be achieved only at the cost of introducing barrel-shaped distortion.     

Exploring the design space of reliable multicast protocols for wireless mesh networks

Many important applications in wireless mesh networks require reliable multicast communication, i.e., with 100% packet delivery ratio (PDR). Previously, numerous multicast protocols based on automatic repeat request (ARQ) have been proposed to improve the packet delivery ratio. However, these ARQ-based protocols can lead to excessive control overhead and drastically reduced throughput. In this paper, we present a comprehensive exploration of the design space for developing high-throughput, reliable multicast protocols that achieve 100% PDR.Motivated by the fact that 802.11 MAC layer broadcast, which is used by most wireless multicast protocols, offers no reliability, we first examine if better hop-by-hop reliability provided by unicasting the packets at the MAC layer can help to achieve end-to-end multicast reliability. We then turn to end-to-end solutions at the transport layer. Previously, forward error correction (FEC) techniques have been proved effective for providing reliable multicast in the Internet, by avoiding the control packet implosion and scalability problems of ARQ-based protocols. In this paper, we examine if FEC techniques can be equally effective to support reliable multicast in wireless mesh networks. We integrate four representative reliable schemes (one ARQ, one FEC, and two hybrid) originally developed for the Internet with a representative multicast protocol ODMRP and evaluate their performance.Our experimental results via extensive simulations offer an in-depth understanding of the various choices in the design space. First, compared to broadcast-based unreliable ODMRP, using unicast for per-hop transmission only offers a very small improvement in reliability under low load, but fails to improve the reliability under high load due to the significantly increased capacity requirement which leads to congestion and packet drop. Second, at the transport layer, the use of pure FEC can significantly improve the reliability, increasing PDR up to 100% in many cases, but can be inefficient in terms of the number of redundant packets transmitted. In contrast, a carefully designed ARQ–FEC hybrid protocol, such as RMDP, can also offer 100% reliability while improving the efficiency by up to 38% compared to a pure FEC scheme. To our best knowledge, this is the first in-depth study of high-throughput, reliable multicast protocols that provide 100% PDR for wireless mesh networks.     

High-current stressing of organic light-emitting diodes with different electron-transport materials

We conducted accelerated reliability tests of electron-only devices (EODs) and organic light-emitting diodes (OLEDs) differing only in their electron-transport material (ETM). High current stressing of EODs at 50 mA/cm² showed that Bphen ~ Alq₃ > TPBi > TAZ in terms of intrinsic material stability. In addition, the lowest unoccupied molecular orbital (LUMO) level and electron mobility have been identified as two other key material factors affecting the degradation rate of OLEDs. TAZ has a low electron mobility, a LUMO level misaligned with the Fermi level of the cathode, and poor material stability, leading to extremely poor reliability of devices with a TAZ electron-transport layer (ETL). In contrast, the OLED with a Bphen ETL exhibited more stable operation and a 76 × longer luminance lifetime. Due to its relatively high electron mobility and good stability as well as perfect energy level alignment with the cathode, Bphen has proven to be the most desirable ETM from the standpoint of OLED reliability.     

Electrical conductivity of organic single-nanofiber devices with different contact materials

The electrical characteristics of morphologically completely defined individual para-hexaphenylene (p6P) nanofibers are investigated with different electrode materials Au, Al, and Cr. Simple quadratic fitting of the I–V measurements along the Mott–Gurney law results in a large range of mobility values, suggesting that the tested contact materials lead to injection limited conduction. We find that Au exhibit the best charge injection properties. A method for fabricating single-nanofiber devices with different anode and cathode materials is applied, with the aim of investigating the electroluminescent properties.     

High-brightness blue organic light emitting diodes with different types of guest-host systems

We demonstrate high-brightness blue organic light emitting diodes (OLEDs) using two types of guest-host systems. A series of blue OLEDs were fabricated using three organic emitters of dibenz anthracene (perylene), di(4-fluorophenyl) amino-di (styryl) biphenyl (DSB) and 4,4''-bis[2-(9-ethyl-3-carbazolyl)vinyl]biphenyl (BCzVBi) doped into two hosting materials of 4,4''-bis(9-carbazolyl) biphenyl (CBP) and 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) as blue emitting layers, respectively. We achieve three kinds of devices with colors of deep-blue, pure-blue and sky-blue with the Commission Internationale de L''Eclairage (CIE) coordinates of (0.16, 0.10), (0.15, 0.15) and (0.17, 0.24), respectively, by employing PBD as host material. In addition, we present a microcavity device using the PBD guest-host system and achieve high-purity blue devices with narrowed spectrum.     

Fabrication of grid type dye sensitized solar modules with 7% conversion efficiency by utilizing commercially available materials

A process to fabricate a parallel connection dye‐sensitized solar cell (DSSC) module has been developed using commercially available materials and screen printed silver grid. The process is not only simple but also easy to manipulate and therefore facilitates researchers in evaluating new materials in a module platform. By changing the design of the silver grid pattern, it was found that the performance of DSSC modules can be controlled. With the silver grid, DSSC modules have shown that a 7% conversion efficiency can be reached. Modules fabricated by this process, but with a non‐volatile electrolyte system, passed a 60 °C, 1000 h thermal aging test. Copyright © 2012 John Wiley & Sons, Ltd.