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    25 May 2007, Volume 28 Issue 5
    academic paper
    Performance analysis of DSSS system with periodic sequence against CW interference
    An-quan WEI,Lian-feng SHEN
    2007, 28(5):  1-6.  doi:1000-436X(2007)05-0001-06
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    Based on the brief account of the performance analysis result of direct sequence spread spectrum (DSSS) system against single tone continuous wave (CW) interference obtained from the traditional stand Gaussian approximation (SGA) hypothesis, the mathematical expression of the interference component of the symbol decision variable in the periodic sequence DSSS system under CW interference was deduced and the actual performance of DSSS system with a periodic sequence against CW interference was researched by theoretical analysis and numerical simulations. The results indicate that the interference component of the symbol decision variable in the periodic sequence DSSS system under CW interference takes on a constant level or a monochromatic fluctuation, which does not approach the standard Gaussian distribution, and the actual performance of DSSS system with a periodic sequence against CW interference is completely different from the analytic result resorted to the stand Gaussian approximation (SGA). The bit error performance is correlative not only with the interference-signal ratio (ISR), with the frequency offset and with phase of the CW interference sensitively, but also with the individual spread spectrum code sequence.

    High energy efficient clock synchronization protocol for sensor networks using time division flooding
    Yi ZENG,Bo HU,Hui FENG
    2007, 28(5):  7-14.  doi:1000-436X(2007)05-0007-08
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    In most synchronization protocols that based on classic flooding scheme, the arrival time of packets couldn't be predicted, so nodes had to keep monitoring the channel. Therefore, idle listening was quite serious which leaded to low energy efficiency. A novel synchronization protocol focusing on reducing idle listening was proposed, where time division flooding scheme was adopted to spread messages. Unique transmitting and receiving slots would be assigned to each individual in localized and distributed way. Higher energy efficiency, lower clock compensation error and faster convergence speed could be achieved, as shown in the simulations. Furthermore, it could be easily modified to co-work with plenty of MAC protocols.

    Improved TCP based on adaptive loss differentiation algorithm over wired-wireless networks
    Jin YE,Jian-xin WANG,Hao GONG
    2007, 28(5):  15-21.  doi:1000-436X(2007)05-0015-07
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    BQM discriminator can not be fit to different network states was pointed and an adaptive BQM, whose key idea is adjusting the important parameters for pattern matching according to network states so that the scheme can keep validity while congestion loss and/or channel error increasing was proposed. The experiment results show that the accuracy of A_BQM discriminator is higher than BQM in different network states and A_BQM can adjust itself adaptively according to network states. A_BQM gets better performance than BQM in some metrics, such as network throughput, fairness, delay jitter, and can be implemented and used easily in wired-cum-wireless networks.

    TCP-friendly streaming medium transmitting mechanism in wireless network
    Zhi-gang CHEN,Xiao-heng DENG,Lian-ming ZHANG,Ming ZHAO
    2007, 28(5):  22-29.  doi:1000-436X(2007)05-0022-08
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    To maintain Streaming media services flows friendly to TCP flows and h/ld the QoS of the streaming service in wireless networks, an adaptive rate control mechanism was proposed. Packet loss between .etwork congestion and wireless link error was distinguished to 'et the accurate state of the networks by the receiver. Occupati/n of the receiver buffer, which reflected how long the temporar)ly stored streaming medium data could be played, was also combined into this algorithm. And tradeoff between TCP-friendly and QoS of streaming media service was achieved through multi-level rate adjustment according to packet loss rate of congestion and queue length of receiver. The results of simulations show that good throughput was gained compared with TCP and TFRC, at most reaching 2M, in condition of 0-0.1 link drop rate, 2 and 32 conncections. As link error and congestion was seperated by WTFCC, therefor, end to end packet drop rate was higher than TCP and TFRC, and also of higer throughput. Nomalized throughput indicated that WTFCC was friendly to TCP.

    Two new color (n, n)-secret sharing schemes
    Feng YI,Dao-shun WANG,Ping LUO,Yi-qi DAI
    2007, 28(5):  30-35.  doi:1000-436X(2007)05-0030-06
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    Two methods of (n, n)-secret sharing scheme for color images were presented. Decryption was processed by XOR operation. The reconstruction complexity of the proposed scheme is equivalent to the visual secret sharing scheme, furthermore the quality of the reconstructed image of the proposed scheme is better than color visual secret sharing scheme.

    Password authentication scheme for mobile computing environment
    Jun LIU,Jian-xin LIAO,Xiao-min ZHU,Chun WANG
    2007, 28(5):  36-42.  doi:1000-436X(2007)05-0036-07
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    By means of IC (integrated circuit) card, RSA cryptography, and discrete logarithm, a password authentication scheme for mobile computing environment was presented. No verification tables were preserved at the server side to consolidate the security. To be applicable for the mobile computing environment, the scheme was designed as a one-roundtrip protocol to meet the computation-constraint terminals and narrow-bandwidth radio interface. Moreover, the passwords in use could be changed by users without any interaction with servers over the radio. The performance of the scheme was measured by making use of M/G/1/N queuing model and compared with that of TLS.

    Waveform interpolation speech coding algorithm at 2.4kbit/s based on wavelet transform
    Jing WANG,Jing-ming KUANG,Xiang XIE
    2007, 28(5):  43-48.  doi:1000-436X(2007)05-0043-06
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    A waveform interpolation speech coding algorithm at 2.4kbit/s based on wavelet transform was proposed, in which characteristic waveform decomposition and reconstruction is processed using biorthogonal wavelet filters. At the encoder, the alignment operation was removed and the amplitude spectrum is decomposed without phase spectrum. Because of the wavelet compression, only the amplitude spectrum of last layer is transmitted. At the decoder, different scale space is reconstructed separately and random or fixed phase was combined to the spectrum based on voice degree at the last. Additionally, based on the time-variable feature of speech, voiced degree flag of each subframe was introduced to indicate the spectrum selection and quantization. Subjective R-A/B listening tests indicated that the synthesis speech quality of the 2.4kbit/s WT-CWI coding algorithm is better than that of standard 2.4kbit/s MELP coder and FS1016 4.8kbit/s CELP coder and is better than traditional 3.8kbit/s CWI coder.

    Pruning automatic sphere decoding algorithm and performance analysis
    Ying LI,Ji-bo WEI
    2007, 28(5):  49-55.  doi:1000-436X(2007)05-0049-06
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    A pruning automatic sphere decoding (PASD) algorithm was presented to reduce the complexity and keep the efficiency of ASD simultaneously. The proposed algorithm efficiently reduced the size of the border node list in ASD by statistical pruning, and obtained the tradeoff between the performance of symbol error ratio (SER) and complexity by setting reasonable parameter's values. Analysis and simulation show that for a higher level (more than 4) modulation, PASD is able to reduce the number of comparisons by at least 30% as compared to ASD without much penalty of the performance in the same SNR region.

    Congestion control protocol design based on delay parameters for layered multicast communication
    Jing BIAN,Ze-qiang WANG,Guang-zhao ZHANG,Yi-qiang YANG
    2007, 28(5):  55-61.  doi:1000-436X(2007)05-0055-07
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    A congestion control mechanism, BDP (based on delay parameters) was presented to be used in receiver-driven layered multicast for multimedia transmission. Based on the dynamic varying of delay parameters, BDP can estimate the path's available bandwidth for adaptive decision of layer join in order to provide guarantee of efficient network resources utilization, and can forecast the network congestion state in quick response to it. The ns2 simulation results show that BDP can achieve scalability, stability, fast convergence and be superior to MRAAR-MT protocol in TCP fairness.

    Interference suppression in GPS receiver using space-time subspace projection techniques
    Yi GUO,Er-yang ZHANG,Rong-jun SHEN
    2007, 28(5):  62-66.  doi:1000-436X(2007)05-0062-05
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    A new approach was proposed for interference suppression in GPS receiver. It combines subspace projection with space-time processing based on the characters of GPS signal, noise and jammers. Space-time interference subspace is constructed using the multistage decomposition structure of the MWF based on the correlation subtractive architecture. Then the optimal filter is educed. Comparing with conventional eigenvalue decomposition technique, the method proposed avoids the estimation of receive data covariance matrix and its eigenvalue decomposition, reduces the computation while the anti-jammer performance is not affected. The performance in numerical simulation demonstrates that it is effective and efficient to both narrowband and wideband interference.

    New method for adaptive echo cancellation in communication systems
    You-lian ZHU,You-hong LU,Guo-dong SHI
    2007, 28(5):  67-72.  doi:1000-436X(2007)05-0067-06
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    The advent of packetized audio transmission system has resulted in challenging requirements for echo cancellation technology. One key aspect of this technology is the need to estimate, quickly and accurately, the delay in an echo path in the transmission media. Delay estimation based on direct application of cross-correlation has poor performance and high implementation cost for the echo cancellation. A new method was presented in this paper. Input signals are bandpass filtered, downsampled, and cross-correlation function is computed via using the whitened signals. Theoretical analysis and experiment results show that the new delay estimation has resulted in higher performance and lesser computation cost than the traditional delay estimation. This method has a broad application in communication systems.

    Domain component interface identifier matching based on semantic
    Zheng ZHANG,Chun ZUO,Yu-guo WANG,Yu-bao CAI
    2007, 28(5):  73-79.  doi:1000-436X(2007)05-0073-07
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    A domain component interface identifier matching method based on semantic was provided. The original interfaces in component library were parsed based on naming rule base, DRM (dimension record model), root base, operation classification and environment classification. Then the parsed component library was generated. The proposed method searched in parsed component library based on environment, object and operation information provided by user. First, the method filtered interface by environment and object, then the name similarity and construction similarity are calculated by defined threshold, matching degree is got. The tool based on the way was applied in practical work and have achieved good results.

    technical report
    Approach to worm early warning based on local victim behavior
    Jun-feng TIAN,Chi ZHANG,Tao LIU,Ning LI
    2007, 28(5):  80-89.  doi:1000-436X(2007)05-0080-10
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    Traditional algorithm to scanning worms early warning can't be used to distinguish P2P activity which can produce infection-like traffic, it also can't be used to forecast the multivector worms which propagation by exploits several vulnerabilities. To settle this problem, an improved algorithm was developed and an early warning model was established based on the algorithm. At last, the feasibility of this method was analysed, by comparing with existing methods, the new approach become more efficient, and had the characteristic of issuing warning at the early stage of worm propagation.

    Analysis for channel capacity of BPSK-based optical wireless communication system
    HENJun C,De-xiu HUANG,Xiu-hua YUAN
    2007, 28(5):  90-93.  doi:1000-436X(2007)05-0090-04
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    The atmospheric turbulence intensity is analyzed by the Γ model based on the theory of information, and the channel capacity of optical wireless communication system based BPSK is calculated by Monte Carlo integral, the detailed analysis of the channel capacity versus the signal-noise-rate(SNR) in different turbulence intensity is given, it is a key theoretical basis for the designs of optical wireless communication.

    Bare-hand alphabets gesture recognition based on VCM and ROI segmentation
    Hang ZHOU,Qiu-qi RUAN
    2007, 28(5):  94-101.  doi:1000-436X(2007)05-0094-08
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    A bare-hand gesture location and tracking system with single camera in real-time was introduced. By employing improved difference method,restrictions of hand are used to location region of Interesting(ROI). Then on the basis of relatively satisfied segment result the thesis analyzed and extracted the hand features combined with the improved vector coherence mapping (VCM) whose constraint was enhanced to overcome the illegibility for robust results. Furthermore, a time-correlation forecasting model proved the demand of real-time and the consistency of the results now and before. The experiment results show the system has a high recognition rate up to 99% in different illuminations and backgrounds and has more efficient performance compared with existing other systems.

    Research on the fairness of QoS degradation in multimedia wireless networks
    HANGXue Z
    2007, 28(5):  102-108.  doi:1000-436X(2007)05-0102-07
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    The fairness of QoS degradation of multi-class and multi-priority adaptive multimedia applications in wireless/mobile multimedia networks was studied. A degradation principle minimizing the weighted sum of degradation factor's square (MWSDFS) was proposed, considering not only inter-class and intra-class priority but also user's QoS degradation degree. Then, the degradation principle of MWSDFS is proved satisfying the generalized proportional fairness for discrete multimedia applications, and proportional fairness for continuous adaptive multimedia applications. At last, quantum genetic algorithm is used to solve the given problem, and the results further validate the effectiveness of the proposed algorithm.

    overview
    Survey on ring signature
    Guo-yin ZHANG,ANGLing-ling WANG,Chun-guang MA
    2007, 28(5):  109-117.  doi:1000-436X(2007)05-0109-09
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    The achievements of ring signature and its applications were surveyed. The majority of the schemes were generalized. The advantages and disadvantages of these schemes were analyzed. Some problems in the study of this field were presented, and several main research directions were pointed out as well.

    short essay
    Further study of the trace representation of Bent sequences families
    Pin-hui KE,Jie ZHANG,Qiao-yan WEN
    2007, 28(5):  118-121.  doi:1000-436X(2007)05-0118-04
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    Linear onto mapping satisfying certain conditions plays an important role in the generation of Bent sequences families. Further discussions were made A well-rounded characterization of these mapping were presented, and known results were showed to be a subcase of our general results.

    Improved model for multiple uncorrelated Rayleigh fading channels
    Xin WANG,Guang-zeng FENG
    2007, 28(5):  122-125.  doi:1000-436X(2007)05-0122-04
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    An improved model for multiple uncorrelated Rayleigh channels was proposed. Compared with other models, this new model satisfied not only the stochastic characters of Rayleigh channel but also the uncorrelation between different fading channels. The simulation results show that the statistics for single channel of the new model is the same as other models and its uncorrelation is obviously better.

    Performance analysis of packet dropping probability under error-prone channel in WLAN
    Yuan CHENG,Yuan ZHANG,Xi-qi GAO
    2007, 28(5):  126-131.  doi:1000-436X(2007)05-0126-06
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    The packet dropping probability of DCF in WLAN under AWGN and Rayleigh fading channel was analyzed. The closed form of optimum packet length maximizing the throughput under error-prone channel was derived and the uniqueness was verified. Study results show that both modulation scheme and packet length have a great effect on packet dropping probability under error-prone channel. By changing packet length according to different channel conditions, maximized throughput can be obtained.

    academic communication
    Analyses for initiative defense based on cost
    Wei-hua ZHANG,Zhi-hua FAN
    2007, 28(5):  132-136.  doi:1000-436X(2007)05-0132-05
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    Based on state-analysis and cheat technology, a improving scheme was brought out based on several initiative defense methods. By applying the state transition to network defense, the method and the steps of cost-calculating was put forward, a case of inform action deception was also been introduced. The method was verified by simulation results that it can divert direction of intrusion effectively.

    Error concealment algorithm for entire frame loss based on optical flow estimation
    Ning CAO,Jian-rong HU,Yin-song MA
    2007, 28(5):  137-141.  doi:1000-436X(2007)05-0137-04
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    The whole frame loss in wireless environment and a specific and applicable solution was presented with better performance based on optical flow estimation, which was testified by experimental results.

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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