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• • 1999, Vol. 22 No. 2 Published date:10 March 1999 Last issue Next issue

  • Performance Analysis of TCP over ATM with Asymmetric Links
  • Zhang Peng, Cheng Shiduan
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 1-5.
  • Abstract ( 214 )     HTML     　　
  • The TCP performance in the case of ATM asymmetric links is analgzed.Our goaal is to investigate the impact of asymmetry on TCP performace.By defining the asymmetry parameter and building the model, we deduce theformula to calculate the TCP perfomance.Effectiveness of the deduction is verified by simulation studies.We conclude that asymmetry has a direct impact on TCP performance and the mean throughput is linear to the asymmetry parameter under the same condition.
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  • Correlation Functions of GMW-Geometric Sequences(1)
  • Sun Wei, Yang Yixian
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 6-10.
  • Abstract ( 245 )     HTML     　　
  • Families of periodic sequences with good correlationproperty are important for code division multiple access (CDMA) communication systems.A family of GMW-sequences constructed, which are derived fromGMW-sequences, and calculates their correlation functions.The results show their correlation function values can be controlled by choosing suitable parameters.
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  • The Tunable Fiber Bragg Grating Device with a PZT
  • Huang Yongqing, Liu Kai, Guo Wei, Ren Xiaomin
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 11-15.
  • Abstract ( 220 )     HTML     　　
  • The tuning characteristics of the fiber Bragg gratings are analyzed on theory and experiment, and a tunable fiber Bragg grating device with a PZT has been realized, which can be tuned about 1.344 nm. Compared with other types of tunable fiber Bragg grating, this device has the advantages ofsimple structure, easy realization and stable performance. By the way, the tuning characteristics of the fiber Bragg grating are also studied when bending it inexperiment, and the tuning range is about 1.68 nm.
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  • State-Dependent Routing with a Neural Networks Algorithm
  • Xin Zhanhong, Zhang Haijun
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 16-20.
  • Abstract ( 233 )     HTML     　　
  • A state-dependent routing algorithm based on Hopfield's neural networks model is given, which takes advantage of other dynamic routing methods for the circuitswitched network. The model fully integrates the traffic data, network states and circuits reservation policy monitored by the network management center, and optimizes dynamic routes for the whole network on the bases of short period forecasting of trunk congestion probabilities. The design of the model is ascloser to the real world as possible, and also takes the hardware realization into consideration. Computer simulations show that the algorithm is much better than the classical fixed routing methods, therefore the model could be a solutionfor the applications of neural networks to the dynamic routing.
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  • The Testing Method about Communication Protocols with “Activity”
  • Luo Hong, Gao Wenchang
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 21-24.
  • Abstract ( 230 )     HTML     　　
  • In order to test communication protocols with “activity”, AFSM model and it's fault model for these protocols are established first.Two testing methods are preferred then.The first is establishing software tester and hardware tester apart.The second is transforming AFSM to FSM by adding activity messages, then testing activities with signals.Test system's framework using the second method and transform method are analyzed emphasized.At last, an application in CDMA BSC tester is described.
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  • Investigation of Stimulate Raman Scattering Spectrum in Silica Optic Fibers
  • Zhao Xiaohong, Jia Xindong
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 25-29.
  • Abstract ( 259 )     HTML     　　
  • According to characteristic of the Raman gain curve,the Raman spectral region of interest was divided into a number of small frequency intervals.The Stocks spectrum of every frequency interval was pumped by those of higher frequency and pumped those of lower frequency.The effcet between them can be described by coupled differential equation.Solving the equationgroup of the entire frequency range, the Raman spectrum in different length fiber pumped by diff-
    erent intersity be calculated and the threshold pump intensitybe obtained by study the calculated spectrum.
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  • ElGamal's Multisignature Digital Signature Scheme
  • Li Zichen, Yang Yixian
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 30-34.
  • Abstract ( 262 )     HTML     　　
  • Based on ElGamal's digital signature scheme, a new sequential digital multisignature and a new broadcasting digital multisignature which based on DLP are proposed. The initial stage of the schemes is simple and the signatures of the schemesare random, so the schemes are highly application and security.
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  • A New Algorithm of Wavelength Assignment in Wavelength-Routed Optical Networks
  • Wei Xuesong, Zhang Ji, Gu Wanyi, Li Guorui
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 35-38.
  • Abstract ( 212 )     HTML     　　
  • The assignment of wavelength in the design of opticalpath layer of wavelength-routed network is discussed and a new mathematical description is proposed. According to the characteristics of the wavelength-routed optical network and the concept of pathgraph, a new algorithm for wavelength assignment is proposed.The assignment of wavelength is result fromthe resolve of the vertices coloring problem of the pathgraph. Simulation on computer is carry out to compare this algorithm with a used one on random network, the higher wavelength efficiency is acquired by new algorithm . This algorithmcan be used to exploit the wavelength resources effectively under the conditionof static services.
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  • Functionality and Operations of Security Server in UPT System
  • Zhu Yujun, Wang Bai, Chen Junliang
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 39-43.
  • Abstract ( 235 )     HTML     　　
  • The domain structure of UPT system raises the need for interworking and complexes the security management thereof. To provide a solution in a centralized, flexible and effective way, a security server is introduced inthe intelligent network based UPT system.The functionality and operations of the security server are discussed in detail, including the authentication of a roaming UPT user, the access control, UPT service subscription and key management.
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  • Analysis and Realization of H.223 and H.245
  • Liu Yong
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 44-48.
  • Abstract ( 266 )     HTML     　　
  • Protocols of H.223 and H.245 for multimedia communications on PSTN are discussed. It analyses the main functions and theoretically the main design problems forthe protocols.The main program flow charters are given, and the methods for design problems are also given. According to the above program flow charters and design methods, we realize the protocols, and verify that the protocols are basically in accordance with ITU-T specifications.
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  • The System Design of Diffuse Infrared Communications and Its Anti-Interference Technology
  • Wang Yong, Xu Daxiong
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 49-53.
  • Abstract ( 226 )     HTML     　　
  • The calculations of the lowest radiant intensity of transmitter of the wireless diffuse infrared data communications are introduced which satisfy the request of error rate according to the receiver's lowest sensibility . This communication system is applied to the infrared fuse in one complex form. In consideration of internal and external interference in its practical application, which are solved by combining software and hardware.
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  • Protection Analysis of Self-Healing Ring for Optical Access Networks
  • Ning Fan, Shou Guochu, Qian Zongjue
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 54-57.
  • Abstract ( 261 )     HTML     　　
  • Based on the introduction of the general concept ofthe protection for optical access networks, the architecture of self-healing ring is discussed. Analysis of the features of 2 fiber bi-directional path switching ring are made. The calculating result shows that the number of switching time of 2 fiber Path switching ring is related to the number of nodes and independent of the transmitting direction of the traffic signal. According to the resultabove, issues on the application of the Self-Healing Ring for optical access networks are briefly discussed.
  • References | Supplementary Material | Related Articles

  • Analysis on Hopfield Neural Networks Solution to TSP
  • Chen Ping, Guo Jinfeng
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 58-61.
  • Abstract ( 274 )     HTML     　　
  • To study the effection of network parameters and topology of city on Hopfield NN on solving TSP, computer simulation is used and theidea and algorithm of Hopfield NN on solving TSP is carried out.According to the calculating results on parameters and topology of city, the correspondent conclusion have been given.First, the premised values to network parameters made byHopfield are not the best values.The parameter D has a major influence on the performance on network.When D equals to 100, the convergence ration of network enhanced largely.There are no obvious rules to tell the influence on performance of network made by parameters A, B, C.A and B could be defined between 400 and 700.C could be set among150 to 250.Second, the topology of a city is one of the most important factorsto the influence on network performance, which mean both the convergence ratio and the quality of the path.
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  • Comparison of Buffer Allocation Strategies in Shared Buffer ATM Switches ——under VBR Traffic
  • Yu Hao, Zhan Zhiqiang, Ding Wei, Zhu Xianghua
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 62-66.
  • Abstract ( 217 )     HTML     　　
  • To enhance the performance and buffer usage of ATM switch, we compares the performance of buffer allocation strategies in shared buffer ATM switches under VBR load by computer simulation. We compare the four strategies from two aspects: cell loss ratio (R), mean delay(D). By the comparison,we find that the performances of buffer allocation strategies in shared buffer ATM switches are relate to traffic measure of the ATM switches. In general, the strategies that have buffer sharing are better than that have no buffer sharing.The strategy that has some measures used to prevent some output ports from occupying almost all buffer are better.
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  • Single Chip DSP Implementation of MPEG Audio Encoding
  • Lin Sheng, Men Aidong
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 67-71.
  • Abstract ( 259 )     HTML     　　
  • To develop a low-priced audio encoder using single fix-point DSP.The requirements of calculation and memory of MPEG audio encoding reference algorithm are analysed. Taking both the encoding quality and speed of processor into consideration, along with the result of simulation, the critical problem of single fix-point DSP implementation are point out. Fully using the property of the hardware optimized for audio processing, we have designed the software and hardware of a real-time MPEG audio layer 2 encoding implementation based ADSP-2181 of Analog Device Corp. The test result shows that both encoding quality and real-time property can be achieved when MAC based precision extension filter and modified psychoacoustic model are used.
  • References | Supplementary Material | Related Articles

  • The Telecom Network Routing Optimization Algorithm for Sudden Failures
  • Zhang Bin, Xin Zhanhong, Huo Yumei, Zhao Xinyan, Meng Ye
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 72-76.
  • Abstract ( 259 )     HTML     　　
  • In the condition that fixed and non-hierarchical routing which will practiced soon in our country's toll telecom network , we bring up a new optimization algorithm with mathematical model for sudden failures of telecom network solving the problem of service restoration .The optimization model aims at the maximum living rate . Through practice simulation we show that the algorithm of routing modification is better than the algorithm of routing a new design for its practicality.
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  • The Fast Packet Switching Technology Used in CDMA Base Station
  • Duan Shiping, Wang Wenbo, Yang Dacheng
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 77-80.
  • Abstract ( 265 )     HTML     　　
  • To the problem of unsuitable use in narrow band realtime service with ATM and frame-relay, A scheme of fast variable length packet switching through hardware implementation which combine with the advantages ofATM and frame-relay is given to support narrow band real time voice services andwide band data services effectively. In scheme, the variable length frame structure is used, the maximum length is limited less than 120 bytes, packets are transfered and switched according to DLCI located in the head of the frame. To implement the system, we designed the entire relative switching chipset. Now the scheme is used successfully in CDMA base station developed by ourselves.
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  • Performance Analysis of Multiuser Detection with Channel Estimation
  • Wu Jun, Wang Yi, Zhang Hong, Wu Weiling
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 81-84.
  • Abstract ( 205 )     HTML     　　
  • A new method which use the Kalman filter as the Rayleigh flat fading channel estimator is presented, and the performance analyses of decorrelator,two-stage detector and decision-feedback detector with the channel estimator are conducted.The simulated results show the performance of two-stage detector and decision-feedback detector is better than that of decorrelator in low SNR region, but for high SNR,the former have higher bit error rate.
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  • Controlling Chaos in the Complex Ginzburg-Landau Equation
  • Wang Shihong, Xiao Jinghua
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 85-88.
  • Abstract ( 277 )     HTML     　　
  • Controlling chaos in the complex Ginzburg-Landau equation(CGLE) is studied and chaos is controllable to the stable plane waves by negative feedback. It is found that the distance between two adjacent controlling points and feedback intensity is effective in controlling. When the CGLE is included gradient force, controlling local numbers are smaller as gradient force is larger.
  • References | Supplementary Material | Related Articles

  • Compression of Multiple Signals Source with Lynch-Davisson Code
  • Li Xiangming, Yue Guangxin
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 89-91.
  • Abstract ( 221 )     HTML     　　
  • For compressing the multiple signal sources by Lynch-Davisson code, an extended method is presented.It is not necessary for the newmethod to split the original sources to two sequences any longer. It is showedthat as the sequence length N approaches infinity, the number of code bits per symbol approaches the entropy of the statistically independent symbol source.
  • References | Supplementary Material | Related Articles

  • The Design of Intelligent Communication Module of RFID System
  • Shen Yuchao, Shen Shuqun, Wang Haibo, Xu Daxiong
  • Journal of Beijing University of Posts and Telecommunications. 1999, 22(2): 92-94.
  • Abstract ( 233 )     HTML     　　
  • Based on electrical design automation(EDA) technique, a design method of CPLD, which represents complex programmable logic devices (CPLD), is described. Its application in design of intelligent communication module of radio frequency identification (RFID) system is proposed. The advantage is that the developing periodcould be reduced and the physical size of PCB could be smaller.
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