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.     

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。     

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.     

Phonon-scattering effects in CNT-FETs with different dimensions and dielectric materials

The impact of acoustic and optical phonon scattering on the performance of CNT-FETs is investigated using a full-quantum transport model within the NEGF formalism. Different gate lengths, dielectric materials and chiralities are considered. It is shown that the use of a high-κ dielectric lowers the off-current dominated by phonon-assisted band-to-band tunneling. The device scalability is demonstrated: with the oxide thickness fixed to 1.5 nm, good performance is obtained with 15 nm and 10 nm gate lengths with SiO₂ and HfO₂ gate dielectrics, respectively. The role of phonon scattering in CNT-FETs of different chiralities is investigated for the HfO₂ devices. A similar analysis has also been carried out for source/drain underlap geometries. The results confirm that the calculation of the off-currents and delay times is strongly influenced by phonon scattering.     

Opportunistic scheduling for multiclass services with different QoS constraints in wireless data networks

In this letter, we focus on the problem with the objective to maximize the system performance, while guaranteeing specified QoS constraints for multiple user classes in wireless data networks. First, we propose two opportunistic scheduling algorithms that exploit time-varying channel conditions for the special two-constraint case, and then propose an opportunistic scheduling algorithm for the general case. Simulation results illustrate that the proposed scheduling algorithms guarantee the different constraints, and achieve high-system performance that is close to the true optimal value using a known general-purpose optimization package, lingo.     

Behaviour of a priority standby redundant system with different types of repair facilities

This paper discusses the stochastic behaviour of a two unit priority standby redundant system, in which priority units gets priority for all operations, with different types of repair facilities. Failure time distributions of Unit are exponential, whereas other distributions are arbitrary.     

Switched-capacitor biquad with low influence of finite gains

The letter describes a switched-capacitor (SC) biquad which exhibits less effect of the finite gains on the Q-factor and centre frequency than other known biquads of this type. The properties of the circuit have been established by extensive simulation studies using a symbolic analysis program.     

Wiener design of adaptation algorithms with time-invariant gains

A design method is presented that extends least mean squared (LMS) adaptation of time-varying parameters by including general linear time-invariant filters that operate on the instantaneous gradient vector. The aim is to track time-varying parameters of linear regression models in situations where the regressors are stationary or have slowly time-varying properties. The adaptation law is optimized with respect to the steady-state parameter error covariance matrix for time-variations modeled as vector-ARIMA processes. The design method systematically uses prior information about time-varying parameters to provide filtering, prediction, or fixed lag smoothing estimates for arbitrary lags. The method is based on a transformation of the adaptation problem into a Wiener filter design problem. The filter works in open loop for slow parameter variations, whereas a time-varying closed loop has to be considered for fast variations. In the latter case, the filter design is performed iteratively. The general form of the solution at each iteration is obtained by a bilateral Diophantine polynomial matrix equation and a spectral factorization. For white gradient noise, the Diophantine equation has a closed-form solution. Further structural constraints result in very simple design equations. Under certain model assumptions, the Wiener designed adaptation laws reduce to LMS adaptation. Compared with Kalman estimators, the channel tracking performance becomes nearly the same in mobile radio applications, whereas the complexity is, in general, much lower     

Patch-based reconstruction of surfaces undergoing different types of deformations

We deal with the reconstruction of surfaces that deform under a variety of conditions. The deformation can range from no extension to a certain degree of extensibility. The deformed surface is reconstructed from a single image, given a 3D reference shape. This shape corresponds to the undeformed state of the surface and can be computed using any appropriate technique. In particular, we use homographies defined from two views of the surface. To proceed with the 3D reconstruction of the deformed surface, we assume that the deformations are locally homogeneous and that the overall surface deformation can be obtained by combining the local homogeneous deformations. For this purpose, the surface is split into small patches. For each patch, a mapping between the undeformed and the deformed shapes is computed. The mapping is specified by using the quadratic deformation model Fayad et al. (Proceedings of British Machine Vision Conference (BMVC), 2004). As a result, given the undeformed shape, we define an optimization procedure whose goal is to estimate the 3D positions of deformed points in each image. The optimization is performed on each patch, independently of the others. The experimental results show that this approach allows precise reconstruction of a wide class of real deformations.     

Harmonic gains of a non-linearity with commensurate input signals

Using the modified non-linearity approach and the recently introduced Fourier superseries, expressions are derived for the harmonic gains of non-linearities with harmonically related inputs. It is also shown that the extension of the problem to the situation where the commensurate sinusoids are contaminated by noise is straightforward. Examples are given to illustrate the computational procedure.     

System performance using different types of in-line optical regenerators

We analytically compare the system performance of various types of in-line optical regenerators in long distance amplified links. The evolution of the probability density function (pdf) of the optical signal intensity is evaluated, and bit error ratio (BER) is estimated numerically. Critical issues of common solutions are found.     

Lifetime analysis of wireless sensor nodes in different smart grid environments

Wireless sensor networks (WSNs) can help the realization of low-cost power grid automation systems where multi-functional sensor nodes can be used to monitor the critical parameters of smart grid components. The WSN-based smart grid applications include but not limited to load control, power system monitoring and control, fault diagnostics, power fraud detection, demand response, and distribution automation. However, the design and implementation of WSNs are constrained by energy resources. Sensor nodes have limited battery energy supply and accordingly, power aware communication protocols have been developed in order to address the energy consumption and prolong their lifetime. In this paper, the lifetime of wireless sensor nodes has been analyzed under different smart grid radio propagation environments, such as 500 kV substation, main power control room, and underground network transformer vaults. In particular, the effects of smart grid channel characteristics and radio parameters, such as path loss, shadowing, frame length and distance, on a wireless sensor node lifetime have been evaluated. Overall, the main objective of this paper is to help network designers quantifying the impact of the smart grid propagation environment and sensor radio characteristics on node lifetime in harsh smart grid environments.     

不同类型光纤对CWDM系统性能的影响

文章比较了目前应用于粗波分复用(CWDM)系统的各类光纤的性能,结合光纤在系统测试中的表现情况对各类光纤的优缺点进行了评价.肯定了标准单模光纤和非零色散位移单模光纤应用于CWDM系统的可靠性,分析了G.652C/D和G.655B/C两类低水峰光纤支持全频谱CWDM传输的优势和在网络升级中的应用潜力,同时与色散位移单模光纤、负色散 (平坦)光纤等非主流光纤的性能作了比较.