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    25 February 2007, Volume 28 Issue 2
    Academic paper
    Novel joint iterative channel estimation and space-frequency decoding algorithm for SFBC-OFDM systems
    Peng ZHOU,Chun-ming ZHAO,Yi-jin YANG,Wei XU
    2007, 28(2):  1-8.  doi:1000-436X(2007)02-0001-08
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    A novel joint iterative channel estimation and space-frequency decoding algorithm was proposed for SFBC-OFDM systems.At first,a new channel estimation algorithm based on time-frequency transforms (TFT) was developed to improve the performance of the initial channel estimator,and then,by exploiting the channel estimated values and the decoded symbols,the joint iterative channel estimation and space-frequency decoding algorithm was advanced.Analyses and simulation results show that the novel joint iterative algorithm improves performance remarkably for the quasi-static,fast time-varying and correlated channels.

    Approach to early detection and defense against internet worms
    Bo CHEN,Bin-xing FANG,Xiao-chun YUN
    2007, 28(2):  9-16.  doi:1000-436X(2007)02-0009-08
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    A distributed defense mechanism was proposed.The main task of defense mechanism was to quickly detect worm attacks and response to constrain their propagation.The defense mechanism was composed of two parts:a date processing centre(DPC) and distributed sensors for defending against worm attacks.DPC is responsible for receiving the result of each distributed sensor and computing the number of infected computer.These distributed sensors monitor the network and detect worm.Once a worm attack was detected,a dropping packet mechanism is used so that the worm propagation was constrained,and the number of interference with normal activity is minimized.The experimental results prove the robustness and efficiency of the proposed defense mechanism.

    Research on stochastic matrix mapping Hash for specific flow matching
    Hong TANG,Yong-jun WU,Guo-feng ZHAO
    2007, 28(2):  17-22.  doi:1000-436X(2007)02-0017-06
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    Because a general Hash algorithm had high collision rate and was not controlled while be used to flow matching,a stochastic matrix mapping Hash algorithm was presented,in which the elements of a large set were mapped into a small set through a pre-choosing stochastic number matrix.Tests show that the algorithm has high operation speed,high storage utilization rate and low collision rate,its flow matching speed is up to 2 million packets per second and it supports 50000 matching rules.

    Channel estimation method for MIMO-OFDM systems based on pilots and modified Kalman filter
    Tie-cheng SONG,Xiao-hu YOU,Lian-feng SHEN,Xiao-jin SONG
    2007, 28(2):  23-28.  doi:1000-436X(2007)02-0023-06
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    A combined channel estimation method of time-frequency-selective fading channels in MIMO-OFDM systems was proposed.The time-varying channel was modeled as an autoregressive (AR) process and a low-dimensional Kalman filter based on pilots was used to estimate the AR parameters,and the LS(least square) algorithm was adopted to track the time-varying channel fading factors.The Kalman estimator explored the time-domain correlation of the channel,and a minimum mean square error (MMSE) combiner was used to modify the Kalman estimates.The proposed solution could reduce the complexity of the high-dimensional Kalman filter and track the channel both in frequency and time domains.The simulation results show that this method improves the LS estimates and has a comparable performance to the complex high-dimensional Kalman channel estimation method.

    Coupled bidirectional flow for adaptive image interpolation
    Shu-jun FU,Qiu-qi RUAN,Cheng-po MU,Wen-qia WANG
    2007, 28(2):  29-32.  doi:1000-436X(2007)02-0029-04
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    An adaptive coupled bidirectional flow process was presenfed,where an inverse diffusion was performed to enhance edges along the normal directions to the isophote lines (edges),while a normal diffusion was done to remove artifacts (“jaggies”) along the tangent directions.The two converse diffusion forces were splitted into a coupled form to stop the cancellation between each other.In order to preserve image features,the nonlinear diffusion coefficients were locally adjusted according to the directional derivatives of the image.And then the above process was applied to image interpolation.Experimental results demonstrate that our interpolation algorithm substantially improves the subjective quality of the interpolated images over conventional interpolations and relative equations.

    Proxy caching algorithm based on segment popularity for mobile streaming media
    Ge YANG,Jian-xin LIAO,Xiao-min ZHU,Bo YANG,Hai HUANG
    2007, 28(2):  33-39.  doi:1000-436X(2007)02-0033-07
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    A novel dynamic scheduling algorithm P2CAS2M2(proxy caching algorithm based on segment popularity for mobile streaming media)based on segment popularity for mobile streaming media was proposed.Proxy caching admission and replacement algorithm based on the object segment popularity for mobile streaming media was implemented.The principle was obeyed that the data cached for each mobile streaming media object were in proportion to their popularity at the proxy server.The cache window size was updated periodically according to the average access time of the clients.Simulation results show that this algorithm is more adaptive than A2LS (adaptive and lazy segmentation algorithm) for the variety of the proxy server cache.It can gain more average number of cached mobile streaming media objects and less delayed requested ratio while byte-hit ratio of P2CAS2M2is close to or exceeds A2LS under the circumstance of the same proxy cache space.

    Blind tracking based on Monte Carlo algorithm over MIMO fast time-varying channels
    Ming-yan JIANG,Dong-feng YUAN
    2007, 28(2):  40-44.  doi:1000-436X(2007)02-0040-05
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    The Monte Carlo algorithm was applied for time-varying channel tracking in communication system and in multi-antenna channels with space time block coding (STBC).The algorithm was compared with Kalman filtering method under the same condition,the tracking performance was discussed when the system had carrier frequency offset.Simulation results show that the proposed method has good performance in tracking the time-varying channel.

    Network traffic nonlinear prediction combined with mutifractal
    Sheng-hui WANG,Zheng-ding QIU
    2007, 28(2):  45-50.  doi:1000-436X(2007)02-0045-06
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    By analyzing the correlation structure of multifractal tree,it was found that multifractal has the ability to convert the non-stationary long-range dependence (LRD) trace to a series of short-range dependence (SRD) sequence.Based on this property,a FIR neural network traffic predictor combined with multifractal was proposed.Because the LRD feature of trace is used,the multi-step performance of proposed method is much better than traditional methods.

    Deterministic upper bounds on performance of generalized processor sharing based on fractal regulators
    Lian-ming ZHANG,Zhi-gang CHEN,Ming ZHAO,Lei WANG
    2007, 28(2):  51-56.  doi:1000-436X(2007)02-0051-07
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    In order to get exact bounds problems encountered in networking with self-similar input traffic,a fractal regulator was introduced into the ingress of a generalized processor sharing (GPS) system for regulating the self-similar traffic,and a model was presented based on fractal regulator and GPS.The deterministic bounds on queue length,delay,delay jitter and effective bandwidth of the system with self-similar input traffic were derived using network calculus.Numerical simulations demonstrate that the bound models of a GPS system based on fractal regulators using network calculus are suited for the networks with self-similar input traffic.

    Novel coding and decoding scheme for modified optical duobinary signal transmission
    Yu-feng SHAO,Lin CHEN,Shuang-chun WEN,Jiang-zhang ZHU
    2007, 28(2):  58-63.  doi:1000-436X(2007)02-0058-06
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    A novel pre-coding scheme for modified optical duobinary signals was proposed.It could be applied to transmit high speed data rate signals (≥ 10Gbit/s).Through analyzing the process of coding and decoding,It was demonstrated that modified optical duobinary signals have capability in reduction of pulse-to-pulse interaction,and could be directly measured through a conventional binary intensity modulation direct detection (IM-DD) receiver.Two modified optical duobinary signals’ formats were simulated to generate.Simulation results show that MD-NRZ and MD-RZ signals’ formats can avoid the eye diagrams’ distortion for long-distance transmission,if the dispersion can be compensated in each amplifier span.Moreover,the MD-RZ signal has lower BER than the MD-NRZ signal after long-distance communication.

    Parlay and OGSA based framework for service creation in NGN
    Zhen LIU,Jing YANG,Guo-jie LI,Guo-qing ZHANG
    2007, 28(2):  64-74.  doi:1000-436X(2007)02-0064-11
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    A parlay and open grid services architecture (OGSA) based framework for service creation in NGN was proposed,which not only provided uniform access to heterogeneous network capabilities,but also built effective distributed convergence mechanisms beyond them.Then a service-oriented method for communication between Parlay and OGSA was further proposed.It was a new and significant attempt to apply grid technologies to telecommunication service creation.The validity of the proposed framework for flexible service creation spanning heterogeneous networks is verified by simulations.Moreover,the proposed framework can support legacy communication terminals without upgrading on client.

    Study of transmitter individual identification based on bispectra
    Zhong-wei CAI,Jian-dong LI
    2007, 28(2):  75-79.  doi:1000-436X(2007)02-0075-05
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    Based on the bispectra and RBF,a new method for identifying different transmitters of the same model was presented.The selected spectra and parameters significant for classification of the received signal form the identification feature vector,and RBF was used to realize the individual identification.Experiment results show that the method is able to classify the same model transmitter with an accuracy rate of no less than 90% under the environment of lower SNR.

    Robust DWT-HMM image watermarking algorithm optimized with content-adaptive approach
    Chun-tao WANG,Jiang-qun NI,Ji-wu HUANG,Rong-yue ZHANG,Xi-zhang LUO
    2007, 28(2):  80-87.  doi:1000-436X(2007)02-0080-08
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    A robust watermarking algorithm based on content-adaptive approach was proposed to optimize the tradeoff between robustness and imperceptibility,which was characterized as follows:the entropy masking proposed by Watson etc.was constructed in wavelet domain,which was then used to constitute the integrated HVS model;three different measures,namely,energy,entropy and integrated HVS,for content-adaptive selection were constructed and investigated;repeat-accumulate (RA) code with erasure and error correction was used to tackle the synchronization issue of the exact positions for watermark embedding;and a posteriori DWT-HMM detector was utilized for watermark detection.Simulation results show that the proposed content-adaptive watermarking algorithm,under the same imperceptibility,has considerable improvement in robustness performance over the traditional one with stochastic approach.

    Technical Report
    DDoS attacks detection based on link character
    Hong-jie SUN,Bin-xing FANG,Hong-li ZHANG
    2007, 28(2):  88-93.  doi:1000-436X(2007)02-0088-06
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    A new method based on link character was proposed for DDoS attacks detection.Maximum likelihood estimation was used to estimate the distribution of link character.SOM neural network is used for link activity profile learning and anomaly link detection.Experiment results indicate that the technique is effective and of a definite practicability.It has a further develop potential for DDoS attacks detection.

    Blind estimation of MPSK carrier frequency
    Zhen-miao DENG,Yu LIU
    2007, 28(2):  94-100.  doi:1000-436X(2007)02-0094-07
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    The blind carrier frequency estimation of multi-phase shift keying (MPSK) signals was discussed.The carrier frequency was coarsely estimated without the prior knowledge of received signals.Consequently the signals were transformed to the baseband-modulated PSK signals by correlation to estimate the symbol rate.With the estimations of the carrier frequency and the symbol rate,the problem of carrier frequency estimation was converted to that of frequency offset.Because the phase of baseband-modulated PSK signal is a piecewise linear function and the slope coefficient of every segment is a linear function of frequency offset,the multi-segment line can be transformed to a straight-line and then the least squares fitting method was applied to estimate the slope coefficient.The simulation results show that this method can accurately estimate the carrier frequency without the prior knowledge.

    summarize
    Survey of cache technology for VoiceXML-based voice platform
    Wen-lin WANG,Jian-xin LIAO,Xiao-min ZHU
    2007, 28(2):  101-108.  doi:1000-436X(2007)02-0101-08
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    The basic elements and perfect attributes of cache system in VoiceXML-based voice platform were presented,and the difference between WWW environment and VoiceXML-based voice platform was introduced.The cache content selection,cache replacement algorithm,cache consistency control algorithm and content prefetch and theirs applications in VoiceXML-based voice platform were analyzed.Finally,the further researches of cache technology in VoiceXML-based voice platform are addressed.

    Short essay
    Novel blind audio watermarking algorithm in the hybrid domain
    Xiang-yang WANG,Hong-ying YANG,Pan-pan NIU
    2007, 28(2):  109-114.  doi:1000-436X(2007)02-0109-06
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    A new robust digital audio watermarking against desynchronization attack using DWT and DCT was proposed.Firstly,the origin digital audio was segmented and then each segment was cut into two sections.Secondly,with the spatial watermarking technique,synchronization code was embedded into the first section.Finally,the DWT and DCT were performed on the second section,and then the watermark was embedded into the low frequency components by quantization.Experiment results show that the proposed watermarking scheme is inaudible and robust against various signal processing such as noise adding,re-sampling,re-quantization,random cropping,MPEG audio layer 3 (MP3) compression,time-scale modification,frequency-scale modification.

    Channel shortening in IFDMA-SIMO system
    Lan XU,Zong-xin WANG
    2007, 28(2):  115-119.  doi:1000-436X(2007)02-0115-05
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    In high-speed IFDMA systems,the increase of channel memory can lead to serious multi-path interference.After a brief introduction to IFDMA system,a new channel shortening algorithm based on the presented IFDMA-SIMO system model was proposed.Simulation results show that the proposed algorithm can effectively suppress multi-path interference while maintaining the orthogonality among the signals from different users.

    New method of channel multiplexing:prime-number division multiple
    Xiu-lin HU,Jun-qiang WANG
    2007, 28(2):  120-123.  doi:1000-436X(2007)02-0120-04
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    For increased channel utilization,based on the unique factorization character of prime-numbers’ product,a new method of channel multiplexing:prime-number division multiple was presented,the work principe and it’s characters were discussed.It is especially useful to user terminals multiplexing or functions multiplexing.

    Method to calculate the diameter of undirected double-loop networks G(N;±1,±s)
    Mu-yun FANG,Bao-hua ZHAO
    2007, 28(2):  124-129.  doi:1000-436X(2007)02-0124-06
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    A new method,step-search-diameter,to calculate the diameter of undirected double-loop networks G(N;±1,±s) was presented.A new diagram,spiral ring whose attributes were studied,was obtained by this method.A simple formula to express the d(N;±1,±s) of undirected double-loop networks was presented.The algorithm to calculate the diameter of undirected double-loop networks whose N,s were fixed and the algorithm to calculate the diameter of undirected double-loop networks whose N was fixed but s varied from 2 to N?1 were both given.VB6.0 and SQL Server 2000 were used to simulate the latter algorithm.The diameters of such family of undirected double-loop networks had such characters:maximum values,minimum values,symmetry.For any given N,many s made G(N;±1,±s) tight optimal or nearly tight optimal.The limited bound of diameter of undirected double-loop networks G(N;±1,±s) presented by Boesch and Wang is certified.A new formula to calculate the upper bound of the diameter of undirected double-loop networks is presented.

    Academic communication
    Improving DSSS signal PN code phase measurement precision by 3-points quadratic interpolation
    Guo-hui GONG,Si-kun LI
    2007, 28(2):  130-133.  doi:1000-436X(2007)02-0130-04
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    A method using 3-points quadratic interpolation to process correlation spectrum peak data was proposed to improve precision of DSSS signal PN code phase measurement.The method used data points around correlation spectrum peak to determine a quadratic interpolation function,then located the maximum point of the function so as to determine the precise position of correlation spectrum peak,thus effectively increased the precision of measurement.Experiments show that the method reaches the goal of greatly increasing the precision of DSSS signal PN code phase measurement.

    Optimized method of generating the spread-spectrum sequences based on Logistic-map
    Ping LIU,Chuan YAN,Xian-gao HUANG
    2007, 28(2):  134-140.  doi:1000-436X(2007)02-0134-07
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    Based on the Logistic-map,an optimized method of generating the spread-spectrum sequences was proposed.An initial value was given and iterated in the Logistic map,then L bit qualification was done to every point,in this way,new spread spectrum sequence would be achieved by shorten.It was compared with conventional chaotic code and Gold code and finally simulated in the DS-CDMA systems.Experiment results show that the iterative times are reduced,the calculating speed is improved,the spread-spectrum sequences can be reshaped with any length and the number of these sequences is larger than Gold sequence in being.The best quantification order is got too.

Copyright Information
Authorized by: China Association for Science and Technology
Sponsored by: China Institute of Communications
Editor-in-Chief: Zhang Ping
Associate Editor-in-Chief:
Zhang Yanchuan, Ma Jianfeng, Yang Zhen, Shen Lianfeng, Tao Xiaofeng, Liu Hualu
Editorial Director: Wu Nada, Zhao Li
Address: F2, Beiyang Chenguang Building, Shunbatiao No.1 Courtyard, Fengtai District, Beijing, China
Post: 100079
Tel: 010-53933889、53878169、
53859522、010-53878236
Email: xuebao@ptpress.com.cn
Email: txxb@bjxintong.com.cn
ISSN 1000-436X
CN 11-2102/TN
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