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Showing papers by "Beijing University of Posts and Telecommunications published in 1998"


Journal ArticleDOI
TL;DR: The analysis shows that the multiple-access interference (MAI) of the QS-CDMA system is determined by the cross-correlation between spreading codes around the origin, and the design of a new set of spreading codes to minimize the MAI is designed.
Abstract: A generalized quasi-synchronous code-division multiple-access (QS-CDMA) system for digital mobile radio communications is proposed. In a QS-CDMA system, the relative time delay between the signals of different users is random and restricted in a certain time range, that is, the signals are quasi-synchronous. The analysis shows that the multiple-access interference (MAI) of the QS-CDMA system is determined by the cross-correlation between spreading codes around the origin. To minimize the MAI of the QS-CDMA system, we design a new set of spreading codes. The performance is evaluated according to the criteria of the bit error rate (BER). Analytic results of the BER are obtained by using two methods: Gaussian approximation and characteristic function approaches, which are checked by modified Monte Carlo computer simulations known as "importance sampling." The results indicate that the performance of the QS-CDMA system using the spreading codes we construct is much improved.

102 citations


Journal ArticleDOI
TL;DR: In this paper, the Ginzburg-Landau equation (CGLE) is generalized to include gradient force, and local injections are applied for turbulence control to suppress fully developed turbulence by adding a few injections much less in number than the number of positive Lyapunov exponents.
Abstract: Controlling turbulence in the complex Ginzburg-Landau equation (CGLE) is investigated. The CGLE is generalized to include gradient force. Local injections (pinnings) are applied for turbulence control. It is found that local injections are effective in eliminating turbulence. In particular, for large gradient force, it is possible to suppress fully developed turbulence by adding a few injections much less in number than the number of positive Lyapunov exponents of the system. The high efficiency of controlling is heuristically explained, based on the spatial correlation length and space-time-variable transformation.

68 citations


Journal ArticleDOI
TL;DR: In this paper, the authors derived a new algorithm for the optimal shortening of a channel impulse response in discrete multitone (DMT) transceivers using eigenvalues and eigenvectors to generate the coefficients of the shortening impulse response filter (SIRF).
Abstract: The authors have derived a new algorithm for the optimal shortening of a channel impulse response in discrete multitone (DMT) transceivers. This algorithm uses eigenvalues and eigenvectors to generate the coefficients of the shortening impulse response filter (SIRF). In comparison with the previous approach, this new algorithm can calculate the optimal settings of an SIRF with arbitrary length.

61 citations


Journal ArticleDOI
TL;DR: In this paper, a model of two-dimensional arrays of Chua's circuits is numerically investigated and feedback pinnings are suggested to migrate the system from the spiral wave state to the coherent oscillation.
Abstract: A model of two-dimensional arrays of Chua's circuits is numerically investigated. In a certain parameter region the spatiotemporal system has both synchronized oscillation and spiral wave attractors. Feedback pinnings are suggested to migrate the system from the spiral wave state to the coherent oscillation. The influences of the pinning density, forcing strength, and different pinning distributions on the driving effect are investigated. It is shown that some properly designed control schemes may reach very high control efficiency, i.e., killing a spiral wave consisting of a huge number of cells by injecting only very few cells. The wide applications of the approach are addressed.

37 citations


Journal ArticleDOI
TL;DR: The model-free learning adaptive control (MFLAC) based on new concepts called pseudo-gradient (PG) for a class of non linear systems is presented, and the stability of the regulator and the robustness of the schemes is discussed.

31 citations


Journal ArticleDOI
TL;DR: This paper develops fast algorithms for the construction of a circulant modulated rate process to match with the two primary traffic statistical functions: rate distribution f(x) and autocorrelation R(/spl tau/).
Abstract: This paper develops fast algorithms for the construction of a circulant modulated rate process to match with the two primary traffic statistical functions: rate distribution f(x) and autocorrelation R(/spl tau/). Using existing modeling techniques, f(x) has to be limited to certain forms such as Gaussian or binomial; R(/spl tau/) can only consist of one or two exponential terms which are often real exponentials rather than complex. In reality, these two functions are collected from real traffic traces and generally expressed in a very complicated form. We only consider the traffic whose correlation function can be approximated by the sum of complex exponentials. Our emphasis is placed on the algorithm design for matching complicated R(/spl tau/) in traffic modeling. The typical CPU time for traffic modeling with R(/spl tau/) consisting of five or six complex exponential terms is found to be in the range of a few minutes by the proposed algorithms. Our study further shows an excellent agreement between the original traffic traces and the sequences generated by the matched analytical model. The selection of the measurement-window in traffic statistics collection for queueing performance analysis is also discussed.

21 citations


Journal ArticleDOI
TL;DR: Every sequence of 2n−¼k2+k−2 elements in G assuming k distinct values has an n-subsequence with sum zero, which settles a conjecture of Bialostocki and Lotspeich.
Abstract: Let k be a positive integer and G a finite abelian group of order n, where n≥k2−4k+8. Then every sequence of 2n−¼k2+k−2 elements in G assuming k distinct values has an n-subsequence with sum zero. This settles a conjecture of Bialostocki and Lotspeich.

19 citations


Journal ArticleDOI
TL;DR: In this paper, a mathematical model is developed by treating the dopant ions in glass host as partially anisotropic oscillators, and both the signal and the pump effects are taken into account.
Abstract: Polarization-dependent gain (PDG) in fiber amplifiers is studied theoretically. A mathematical model is developed by treating the dopant ions in glass host as partially anisotropic oscillators, and both the signal and the pump effects are taken into account. It is illustrated that PDG includes two components. One arises from polarization-selective excitation of the dopant ions by the pump; the other originates from polarization-selective deexcitation of the lasing ions by the saturating signal, known as polarization hole burning (PHB). PDG depends strongly on the operating state of the amplifiers such as the level of gain compression, the anisotropy of the dopant ions, and the relative polarization orientations of the signal and the pump. In a small-signal regime, PDG is induced only by the pump while in large-signal condition it is the sum of the two components. The good agreement between the theoretical calculations and the reported results confirms the validity of the model.

16 citations


Proceedings ArticleDOI
26 Oct 1998
TL;DR: In this paper, a specially made lubricant was used which dramatically lowered the contact resistance in sliding and fretting electric contact behavior on tin platings on phosphorous bronze substrates when the coupons were cross-sectioned to show the growth of intermetallic compounds.
Abstract: An intermetallic compound (IMC) Cu/sub 6/Sn/sub 5/ is formed in tin platings on phosphorous bronze substrates when the coupons are subjected to thermal shocks. The coupons were cross-sectioned to show the growth of Cu-Sn IMC which was identified by X-ray diffraction method. Sliding and fretting electric contact behavior were studied on such surfaces. Previous studies in other laboratories found that the contact resistance in such experiments was quite high. In the present experiments, however, a specially made lubricant was used which dramatically lowered the contact resistance. It was found that the oxide and other contaminant particles normally located in the contact area of the probe were removed by the lubricant. But in agreement with earlier studies, obvious cracks could easily be seen on the surface of the substrate after sliding or fretting experiments. Thus the main beneficial effect of the lubricant in these kinds of experiments was to reduce the contact resistance.

15 citations


Proceedings ArticleDOI
26 Oct 1998
TL;DR: A comprehensive analysis of the organic compounds of the airborne dust collected in Beijing University of Post and Telecommunications has been carried out by combined application of four analytic methods including infrared spectroscopy, gas chromatography-mass spectrometry (GC/MS), high performance liquid chromatography mass spectrometer (LC/MS) and thermogravimetric analysis as discussed by the authors.
Abstract: A comprehensive analysis of the organic compounds of the airborne dust collected in Beijing University of Post and Telecommunications has been carried out by combined application of four analytic methods including infrared spectroscopy, gas chromatography-mass spectrometry (GC/MS), high performance liquid chromatography-mass spectrometry (LC/MS) and thermogravimetric analysis. The aim is to gain a better understanding of the main organic constituents in the dust and seek an efficient method for analysis of the organic compounds. The results show that weight percentage of the organic compounds and "black" carbon is about 20% of the dust. The main constituents of the organic compounds are a series of alkanes (C/sub 7/-C/sub 40+/) and two ortho-benzendicarboxylic acid esters. These materials probably are from the chimney of the central heating station and exhaust gas of vehicles. Evidences show that the organics in dust may also contribute to electrical contact failures of connectors and cannot be ignored.

12 citations


Proceedings ArticleDOI
22 Oct 1998
TL;DR: The image theory is used in this paper to calculate the value of magnetic field near high voltage transmission lines and electronic trains and magnetic pollution of high voltage power transmission line and electronic railways is discussed.
Abstract: The image theory is used in this paper to calculate the value of magnetic field near high voltage transmission lines and electronic railways. Areas in which the magnetic field is less than 0.002 Gauss is given and magnetic pollution of high voltage power transmission line and electronic railways is discussed.

Journal ArticleDOI
TL;DR: In this article, a novel phase-lock type clock recovery technique based on a terahertz optical asymmetric demultiplexer (TOAD) is proposed, which is compatible with the conventional time-division multiplexing (TDM) timing techniques but does not require the ultrahigh-speed optical detector nor ultrafast electrical components.
Abstract: A novel phase-lock type clock recovery technique based on a terahertz optical asymmetric demultiplexer (TOAD) is proposed. The technique is compatible with the conventional time-division multiplexing (TDM) timing techniques but does not require the ultrahigh-speed optical detector nor ultrafast electrical components. Further, it can readily be used to achieve frame synchronization, upon which a complete self-timing demultiplexer can be demonstrated.

Proceedings ArticleDOI
26 Oct 1998
TL;DR: In this paper, the experiments for erosion behavior of AgCdO, AgSnO/sub 2/ and AgZnO contacts by breaking arcs were carried out in an accelerated testing machine.
Abstract: The experiments for erosion behavior of AgCdO, AgSnO/sub 2/ and AgZnO contacts by breaking arcs were carried out in an accelerated testing machine. The surface undergone melting temperature range was examined by SEM, and the element compositions of the surface were analyzed by EDS. The microstructure and composition of the surface after melting range were analyzed. The mechanism of hole formation is described. Finally, the arc erosion and microstructure as well as composition of the surface after melting range are discussed. With increasing operations, two stages named as adjustment state and quasi steady state are discussed.

Proceedings ArticleDOI
07 Jun 1998
TL;DR: In this article, a fuzzy traffic predictor using nearest neighborhood clustering learning algorithm is presented, which can reduce cell loss ratio, buffer requirement and improve the bandwidth utilization remarkably, and the results show that the traffic predictor is accurate and flexible.
Abstract: Traffic prediction is a new research subject in ATM traffic management. It is the basis of dynamic and adaptive traffic control. This paper, based on the theory of fuzzy system, presents a fuzzy traffic predictor using nearest neighborhood clustering learning algorithm. We examine its prediction effect through autoregressive (AR) process and real video traffic. The results show that the approximator/predictor is accurate and flexible. The applications of the traffic predictor in ATM networks include dynamic bandwidth allocation, traffic shaping, traffic smoothing, service synchronization etc. We mainly discuss dynamic bandwidth allocation based on the fuzzy traffic prediction. The research results show that the dynamic bandwidth allocation can reduce cell loss ratio, buffer requirement and improve the bandwidth utilization remarkably.

Journal ArticleDOI
TL;DR: In this paper, the diffusion mechanism of nitrogen atoms in ThMn12-type crystal structure compounds was investigated by using x-ray diffraction, Mossbauer spectroscopy measurements, thermopiezic analysis, and differential thermal analysis.
Abstract: The diffusion mechanism of nitrogen atoms in ThMn12-type crystal structure compounds was investigated by using x-ray diffraction, Mossbauer spectroscopy measurements, thermopiezic analysis, and differential thermal analysis. The studies indicate that the distribution of nitrogen atoms in a R(Fe,M)12 particles with intermediate N content is characterized by a nitrided region and an unnitrided region. The results confirmed that this two-phase region is stable, and the nitrogen atoms do not diffuse further into the particle. Based on the characteristics of the nitrogenation, a trapping diffusion model is applied to the R(Fe,M)12 system. On the basis of this study high performance magnetic powders of NdFe10.5Mo1.5Nx were successfully prepared.

Proceedings ArticleDOI
22 Oct 1998
TL;DR: F-TCP reduces ATM buffer oscillation, since most of the time the TCP is in a congestion avoidance phase after short period of the slow start phase, the flow is fairly smooth and the ATM buffer utilization is improved.
Abstract: The essential idea of fast TCP (F-TCP) is to delay TCP acknowledgment (ACK) traveling towards its TCP source through a node where its forward channel is congested. By the analysis of the simulation results of a simple example, it can be seen that: (1) F-TCP smoothes the peak of the TCP flow, consequently F-TCP reduce the requirement of the ATM buffer; (2) with the same size of ATM buffer, F-TCP reduces the probability of overflow and as a result, improve the TCP throughput; and (3) F-TCP reduces ATM buffer oscillation, since most of the time the TCP is in a congestion avoidance phase after short period of the slow start phase, the flow is fairly smooth and the ATM buffer utilization is improved.

Proceedings ArticleDOI
31 May 1998
TL;DR: A new algorithm based on Hopfield neural networks is presented to optimize the multicast tree with delay and delay variation constraints to meet the quality of service (QoS) requirements of real-time interactive applications operated in high-speed packet-switched environments.
Abstract: This paper studies the problem of constructing minimum-cost multicast trees with end-to-end delay and delay variation constraints to meet the quality of service (QoS) requirements of real-time interactive applications operated in high-speed packet-switched environments. The paper first discusses the routing problem with bounded delay along the paths from the source to each destination and bounded variation among the delays along these paths, and then presents a new algorithm based on Hopfield neural networks to optimize the multicast tree with delay and delay variation constraints. The simulations show that the proposed algorithm achieves its best performance in constructing constrained multicast tree in computer networks.

Proceedings ArticleDOI
22 Oct 1998
TL;DR: This works gives the general formula for calculating the electric fields around a 3-/spl Phi/, symmetrical power transmission line when the heights of its conductors are different from each other.
Abstract: This works gives the general formula for calculating the electric fields around a 3-/spl Phi/, symmetrical power transmission line when the heights of its conductors are different from each other. It gives also the method for calculating the electric fields around single phase and 3-/spl Phi/ asymmetrical lines. The minimum permissible separation distance between the power line and resident has been given.

Journal ArticleDOI
TL;DR: The achievements and history of telecommunications development in China are reviewed, the development of the telecommunications services market in China is analyzed, and development targets for the future are given.
Abstract: This article reviews the achievements and history of telecommunications development in China, and analyzes the development of the telecommunications services market in China. The analysis is mainly focused on total turnover of telecommunications services, the development of telecommunications services, and competition in the market. Finally, it analyzes issues on policies and regulations for telecommunications, and gives development targets for the future.

Journal ArticleDOI
TL;DR: In this paper, a model of globally coupled bistable systems consisting of two kinds of sites, subject to periodic driving and spatially uncorrelated stochastic force, is investigated.
Abstract: A model of globally coupled bistable systems consisting of two kinds of sites, subject to periodic driving and spatially uncorrelated stochastic force, is investigated. The extended system models the competing process of activators and suppressers. Analytical computations for linear response of the system to the external periodic forcing is carried out. Noise-induced Hopf bifurcation is revealed, and stochastic resonance, sensitively depending on the frequency of the external forcing, is predicted under the Hopf bifurcation condition. Numerical simulations agree with the analytical predictions satisfactorily.

Proceedings ArticleDOI
30 Jun 1998
TL;DR: This work presents a two-level concurrency model of the SCP software, and gives the implementation of this model in the multi-task environment, and discusses in detail the issues of the SFT based on this model, and the corresponding strategies and algorithms to achieve the specified whole FT targets.
Abstract: Fault tolerance (FT) is a feature of top importance in the long-life real-time systems. The service control point (SCP) in the intelligent network (IN) is just one of this type of systems. Its dependability affects directly the quality of service (QoS) of the whole network. We give an overview on the software fault tolerance (SFT) at first, and decide to adopt the time-redundancy approach to implement the SFT of the SCP according to the special features of the IN application. Based on the processing mechanism of IN calls and with the consideration of the load-balance, software fault-tolerance and software upgrading on-line, we present a two-level concurrency model of the SCP software, and give our implementation of this model in the multi-task environment. Furthermore, we discuss in detail the issues of the SFT based on this model, and give the corresponding strategies and algorithms to achieve the specified whole FT targets. Finally, we discuss the system effectiveness of the SCP software, and provide a method of computing the effectiveness of the SCP software based on the Markov model.

Journal ArticleDOI
TL;DR: In this article, a novel OTDM frame synchronization scheme based on an electrical tank circuit incorporating an asymmetric nonlinear optical loop mirror (NOLM) as an optical nonlinearity is proposed and analyzed theoretically.

Proceedings ArticleDOI
19 Jun 1998
TL;DR: In this paper, a simple method for transformation of a uniform fiber grating into a linear chirped grating and realization of independent tuning of the grating's central wavelength and chirp degree is presented.
Abstract: A simple method is reported for transformation of a uniform fiber grating into a linear chirped grating and realizationof independent tuning of grating's linear chirp degree (or spectral width) and central wavelength. This methodinvolves embedding a uniform grating into a textile laminated beam and creating an odd-symmetrical linear straindistribution along the grating versus its center with a three-point-bending and stretching setup. The grating's central wavelength and chirp degree can be tuned by adjusting the horizontal stretching range and vertical bending displacement on the beam independently. A simulating experiment for compensating the dispersion of a standardsingle-mode fiber (G652) over 100km for lOGbit/s signal at 1550nm window is successfully demonstrated using sucha tunable chirped grating with 10 cm in length.Keywords: chirped fiber grating, dispersion compensation1. IntroductionSince the first observation of photo-induced refractive-index changes in optical fiber1 and development of UV-writingtechniques for fiber Bragg gratings (FBG's)2, there has been much interest in the application of the such devices forthe compensation of fiber dispersion and linearity-induced pulse chirp. Linearly chirped gratings have been used in a

Proceedings ArticleDOI
31 May 1998
TL;DR: Detailed analyses demonstrate some modifications of Hestenes SVD method and Franklin SVD algorithm can make them more suitable for array processing since the array architecture may be substantially simplified.
Abstract: In the study of array signal processing, the extensively researched MUSIC (Multiple Signal Characterization) algorithm can be realized based on SVD (Singular Value Decomposition) and many advantages are expected to be achieved. In the application of SVD, how to compute SVD on a parallel array becomes a key issue. In this paper, we discussed several SVD algorithms and their implementation on array processors. Detailed analyses demonstrate some modifications of Hestenes SVD method and Franklin SVD algorithm can make them more suitable for array processing since the array architecture may be substantially simplified.

Proceedings ArticleDOI
22 Oct 1998
TL;DR: By introducing the basic concept of TMN, the requirement and related MIB in the ATM NMS are discussed and the implementation is discussed.
Abstract: By introducing the basic concept of TMN, the requirement and related MIB in the ATM NMS are discussed in the paper. This paper also discusses the design consideration for the ATM NMS and describes the software structure of the ATM NMS. The implementation is discussed.

Journal ArticleDOI
TL;DR: In this paper, the effects of channel separation, cross-phase modulation and input power on nonlinear WDM systems with conventional single-mode fiber combined with dispersion-compensating fiber were analyzed.

Proceedings ArticleDOI
04 May 1998
TL;DR: A probabilistic neural network is proposed and applied for implementation of a maximum likelihood detector and classifier and significantly outperforms the conventional matched filter detector.
Abstract: A probabilistic neural network is proposed and applied for implementation of a maximum likelihood detector and classifier. The network is trained using the algorithm based on Parzen probability density function estimation theory for detection of signals in CDMA multi-user communications Gaussian channel. By viewing these multi-user detector's problem as a nonlinear classification decision problem, we apply this algorithm which has the abilities of arbitrary nonlinear transformations, adaptive learning and tracking to implement this decision optimally and adaptively. The performance of the proposed neural networks detector is evaluated via extensive computer simulations and compared with other detectors and neural classifiers' schemes in a multi-user environment. The neural detector is shown to exhibits some desirable properties and significantly outperforms the conventional matched filter detector.

Proceedings ArticleDOI
22 Oct 1998
TL;DR: A new multi-mode architecture of the 3G mobile system based on software radio is produced, and some issues on realizing this kind of flexible3G mobile are discussed.
Abstract: It is requested that the 3G mobile system should support multi-mode operation, especially multi-mode terminals. This paper, on the basis of evaluating the software radio technology, produces a new multi-mode architecture of the 3G mobile system based on software radio, and discusses some issues on realizing this kind of flexible 3G mobile.

Journal ArticleDOI
TL;DR: In this paper, the authors extended the results about the ambiguity functions of the TFHC-EQC from aperiodic cases to periodic cases and proved that the tight upper bound for the periodic auto-ambiguity function of TFHC EQC is 6.
Abstract: The time-frequency hop codes based upon extended quadratic congruences (TFHC-EQC) were developed previously (1988, 1991). The known results about the ambiguity functions of the TFHC-EQC are extended from aperiodic cases to periodic cases. Precisely, the following new results are proved: (1) The tight upper bound for the periodic auto-ambiguity function of the TFHC-EQC is 6; (2) the periodic cross-ambiguity upper bound of the TFHC-EQC is at least (N-1)/2; (3) there exists a subset TFHC-EQC of volume (N-1)/2 such that its periodic cross-ambiguity is tightly upper bounded by 8.

Journal ArticleDOI
TL;DR: In this paper, the relationship of the crystallographic structure and the intrinsic magnetic properties to the nitrogen content was investigated, and it was found that the Nitrogen content is vital to obtain high-performance magnetic powders based on NdFe10.5V1.5Nx.