- EI核心期刊
YU Tao1, CHEN Shan-zhi2, LI Xin1 ,QIN Zhen3
A new deflection routing scheme is proposed to overcome the drawback of the existing deflection routing scheme ,such as inability to handle node failure and suffering from routing loop problems. A new algorithm for computing backup shortest path tree (SPT) is proposed. And a set of procedures are defined for utilizing the backup SPT in case of a node or link failure. The failure can be promptly handled, meanwhile the backup routes are guaranteed to be loop-free. Experiments show that the backup routes calculated by proposed scheme are closed to the optimal routes by totally recalculating.
ZHANG Long1, LIU Min2，WU Cheng2
For a kind of larger scale Job Shop scheduling problem (JSSP) with the objective of the weighted tardy time, a self-adaptive hybrid genetic algorithm is proposed. First, for the reduction of the solving scale of the scheduling problem, on the basis of the defined scheduling characteristics—resource conflicting probability, all operations of the scheduling problem are divided dynamically into two kinds in the scheduling process: the first kind of operations with greater probability of the resource conflict, and the second kind of operations with less probability of the resource conflict. Furthermore, the chromosome is coded with three gene sequences: the gene sequence which consists of the above first kind of the operations, the gene sequence which consists of heuristic rules for determining the preference order of the second kind of operations, and a token gene sequence. Additionally, a fuzzy logic controller (FLC) is constructed to adjust adaptively the length of the first gene sequence so that the performance of the proposed genetic algorithm (GA) can be improved. The numerical computational results show that the proposed GA is effective for a kind of lager scale JSSP.
A new signal detection method was presented for OFDM (orthogonal frequency division multiplexing) systems with insufficient cyclic prefix (CP). The interchannel interference (ICI) and the residual intersymbol interference (ISI) could be introduced by time varying channel with channel impulse response that exceeds the length of CP, The influence mentioned above would result in error floor. The method proposed, combined with ICI cancellation, uses decisions to estimate the residual ISI through fast Fourier transform（FFT） and inverse fast Fourier transform（IFFT）, and restores the cyclicity of signals. It also can be applied with this algorithm for non-sample spaced channel with a very low computational complexity. Simulations show that the algorithm presented could provide better performance on static and slowly time-varying ISI channels.
An improved selection decode-and-forward method with feedback（FSDF）is proposed in cooperative diversity system, in which both the channel gain of source-to-relay and that of source-to-destination are considered, it is based on the destination’s feedback whether the source terminal adopts the cooperative scheme or not. The formulation of outage probability is derived at high signal-to-noise ratio (SNR). Theoretical analysis and simulation results show that the proposed method can achieve full spatial diversity and will be better than decode-and-forward (DF ) and selection decode-and-forward (SDF) both in reliability and efficiency.
Based on distributed multi-antenna system, a new method for time difference of arrival （TDOA） estimation in multipath environment is proposed. By utilizing advantages of distributed multi-antenna system, the traditional TDOA measurement is converted into the time delay estimation of the first arrival path (FAP) by constructing orthogonal training sequences. Comparing with the non-line-of-sight （NLOS） error induced by traditional timing and synchronization method, numerical simulations are carried out and the results show that the NLOS error imposed on the TDOA estimation can be reduced by 65% with the method proposed. Therefore, the TDOA estimation accuracy can be significantly enhanced.
LI Zhi-tao1, CUI Yi-dong1, XU Ya-jing1, LIU Li-hong2, XU Hui-min1
A new extension header “the time stamp extension header” for IPv6 network is designed in order for recording the time when the packets pass the router. Using the packets, an improved measurement model of link utilization in IPv6 networks is proposed. The source sends probe packets with the time stamp extension header and the current time is recorded in the packets。With the processing of improved link utilization statistic algorithm, the link utilization is therefore obtained. Meanwhile using the special fields in the IPv6 header, the “test level” is designed to eliminate the influence of the current traffic. The approach is verified through simulations
Taking collaborative detection probability of mobile targets as coverage evaluating index in large-scale wireless sensor networks（WSN）, a triangular analytical model（TAM）is proposed to analyze the normalization density of randomly deployed nodes in a 2-dimensional region. Binomial distribution and normalization methods are used to calculate the worst-case upper bounds on the nodes normalized critical density threshold (NNCDT) with 3 collaborative sensors and normalized path length (NPL) less than 1. The effects of sensor nodes normalized density on the collaborative detection performance are discussed. The influences of mobile targets speed, sensor’s measurement time and decision threshold on NNCDT are analyzed. Simulations show that NNCDT can be exactly determined by the collaborative detection probability and NPL, and can provide a reference for determination of sensors density needed for certain performance in random deployment.
GAN Dong-ming, LIAO Qi-zheng , WEI Shi-min
A new parallel mechanism 2CCC-4SPS that has distance and angle constraints was described in this paper. The analysis of degree of freedom and forward kinematics were given. Sylvester’s resultant and Groebner basis theory were used and the problem of forward kinematics analysis was reduced to a 32nd degree polynomial equation in a single unknown, from which 32 different locations of the platform can be derived, numerical example confirms these theoretical results.
ZHANG Xue-dan 1, HONG Jun 1, ZHANG Lin 1, LI Victor On Kwok1,2, SHAN Xiu-ming 1
The transmission scheduling of wireless mesh networks (WMNs) is modeled as a problem of conflict graph coloring. a new distributed time division multiple access（TDMA） medium access control（MAC） algorithm based on parallel graph coloring is proposed. The algorithm utilizes the advantages of mesh routers and backbone networks, and only depends on local topology and traffic load information. Simulation demonstrates that the proposed scheme achieves significant throughput enhancement approaching optimal scheduling in WMNs, and enjoys very low communication overhead.
Previous researches on collocation extraction considered that lexical combination was simply to put terms together, but ignored the collocation preference. To solve that problem, the collocation preference statistic model based on relative conditional entropy is brought up in this paper to measure dependence between headword and co-occurrence words in context. Then the linguistic heuristic rule is integrated to identify the border of collections, by part-of-speech filter and sliding window. Finally, an approach of collocation extraction is formulated. The approach is able to effectively disclose the internal mechanism of collocation and it is more understandable. It is proved the collocation preference strength could be considered as mutual information corrected by directions.
By analysis of the flooding features of open shortest path first (OSPFv3) and the shortages of its link-state advertisement (LSAs) flooding multi-metric, the performances of average flooding efficiency (FE) and average flooding packets number (FPN) in regular 3,4,6-neighbor and n-neighbor networks are researched. Simulations resulted from arbitrary-node-distribution IPv6 networks show that the increases of the network scale, neighbor nodes and metrics can make the flooding efficiency lower and bring more network loads. The conclusions are very useful in selecting routing metrics and constructing future IPv6 quality of service (QoS) routing networks.
A new error temporal concealment algorithm for recovering the loss or erroneously received motion vectors is presented. To alleviate the effect of transmission errors, an error tracking model is adopted to estimate the mean square error (MSE) of each pixel in the decoder. Then, the MSE is added into the boundary matching algorithm to evaluate the goodness of boundary matching and interior pixel reliability of recovered macroblocks. Simulation shows that the proposed technique is superior to conventional temporal concealment techniques and demonstrates fairly good robustness in various lost rates of inter-coded macroblocks.
XU Ya-jing, LI Zhi-tao, ZHONG Xiu-fang, XU Hui-min
Based on traffic prediction, a new adaptive bandwidth request mechanism for real-time traffic in worldwide interoperability for microwave access （WiMAX） is proposed. According to historical traffic of system, this algorithm combines exponential estimation with cumulative mean errors; therefore it can estimate the arrival of packets next time and request extra bandwidth for them in advance. Hence it can decrease time lags and reduce buffer for real-time traffic. Simulation results show that the proposed adaptive algorithm can provide better performance of average delay and buffer
The performance of the high symbol rate intersymbol interference (ISI) transmission with maximum likelihood sequence detection (MLSD) utilized at receiver is researched. Compared with the Mary-quadrature amplitude modulation (M-QAM) non-ISI system that has the same spectral efficiency, the bit error rate performance of the ISI system outperforms gradually with the spectral efficiency increasing. The optimal algorithm of the coded ISI system is proposed that is iteratively soft-in soft-out joint detection and decoding under maximum a posterior (MAP) criterion. Simulation results show that optimal algorithm obtains the optimal coding gain for it fully utilizing the encoding constraints formed by ISI.
An analogue phase-alternative line (PAL) co-channel interference cancellation algorithm is proposed to improve the robustness of orthogonal frequency division multiplexing （OFDM ）based digital television terrestrial broadcasting（DTTB）systems. The proposed algorithm estimates interference in frequency domain using the similarity between two adjacent scanning lines. Simulation shows that the algorithm can effectively improve the bit error rate (BER) performance of the OFDM-DTTB receiver in presence of PAL co-channel interference.
For the weakness of low string matching speed, a fast algorithm to perform multiple pattern matching in a string, based on finite state automaton combined with Boyer-Moore(BM) algorithm and an improved quick search(QS) algorithm, was presented. In general, the algorithm described does not need to test each character in the string. By making full use of the results of matching successes and failures, the algorithm can often bypass inspection of as many characters as possible and get all matching locations after one quick search. Experimental results demonstrate that the proposed algorithm has achieved excellent performance in the cases of both short patterns and long patterns and effectively improved the performance of keyword detection and filtering.
Call drop will occur when no satellite can be visible, handoff is not real-time and the corresponding response is lost in satellites constellations communication system. If the call drop terminating request cannot be sent to network management center in time, the channel resource cannot be released. Then the rate of call blocked may increase. In order to solve this problem, two tactics: broadcast the terminating request and use the location paging information to route the terminating request are put forward. Both of the tactics can decrease the rate of call blocked. The results of the simulation prove that the additional signaling cost of both tactics is far from the cost of the system call signaling, and the dealing delay is acceptable as well.
HUANG Hai1, YIN Chang-chuan1, PENG Duan2, YUE Guang-xin1
For the case of symbol timing in nonlinear and non-Gaussian orthogonal frequency division multiplexing (OFDM) systems, it is usually difficult to directly utilize Kalman filter. Thereafter, a feasible structure known as sequential Monte Carlo ( SMC) is brought forward. Estimation and tracking the symbol timing offset in frequency selective multi-paths fading channels based on the application of SMC technique is investigated. The problems of symbol timing offset and system observation function are represented as dynamic state-space models and recursive computation of relevant probability distributions using the concepts of importance sampling and approximation of probability distributions with discrete random measures. The performance of the SMC technique and extend Kalman filter (EKF) are compared in terms of bit error rate (BER) and mean square error (MSE) obtained by simulations and SMC superior outperforms EKF for the considered SNR.
In order to analyze the operational efficiencies and the influencing factors of telecommunication operators, the method to evaluate the firms with productive efficiency was proposed. The firms’ technical efficiencies, pure technical efficiencies, scale efficiencies, and the types of scale efficiency were analyzed with the data envelopment analysis (DEA). And the impacts of environment variable on the productive efficiency were analyzed also by using Tobit regression method. Finally, some suggestions are given to maximize productive efficiency. It is shown better to evaluate by efficiency since it avoids the weakness of the evaluating while focused on “quantity”.
YU Yan-hua, SONG Mei, PAN Yang-fa, SONG Jun-de
Evaluation of the performance of mobile network and its elements is the basis of network optimization. According to the problems existing in the applications of the methods applied at present, a new method based on dimension transformation and support vector machines was proposed. The steps were that, firstly, transforming the n related indicators to another n independent indicators, and secondly, using support vector machines (SVM) to model the transformed data. Theoretical analysis shows that this method can conquer the problems of back propagation（BP） neural network: overfitting,and the danger of getting stuck into local minima. The information loss occurring in the application of primary component analysis was avoided. Experimental results show that compared to BP neural network, the training process of support vector machines is more controllable, and the relative error of evaluation score based on support vector regression machines is smaller. Furthermore, the evaluation differences of the samples are maintained better.
For the weakness of qualitative performance at the speed in secure sockets layer/ transport layer security（SSL/TLS）protocol, an improved SSL/TLS safety system was proposed. Based on the typical SSL connection model, the system was indeed improved on algorithm and whole system model by using the SSL proxy and the improved SSL/TLS handshake protocol based on client-aided road safety authority（RSA）algorithm. Compared with the typical SSL connection method, the test result shows that the new safety system model can greatly increase the processing speed, meanwhile, it can clearly improve the systematic quality with the the enhancement of RSA secret key length.
A new software reliability model (SRM) which combines maintenance policy and failure correlation is proposed to resolve the problem of current SRM. According to the characteristic of maintenance policy and six mode of state conversion, Markov renewal process of three class points including successful run and failed run as well as version update is used to establish the SRM respectively in discrete time and in continuous time. On this basis, a layer idea is introduced into the model: modeling dependent successive software runs at each layer and maintenance policy between two layers. Finally , some important reliability measurements including the distribution function of the time to failure, software reliability etc are concluded by applying this model. Through model comparison and analysis, the intrinsic consistency between the proposed model and other SRMs is validated, and the model itself can be also considered as a more flexible SRM framework.
DENG Yu, ZHANG Pei, LI Bin, GU Wan-yi
A new pre-configure cycle (p-cycle) algorithm named unidirectional p-cycle is proposed when considering the single span failure in mesh networks with directional capacity. Unidirectional p-cycle includes clockwise and counterclockwise p-cycle by adding direction to traditional p-cycle. The new evaluation criteria and approach for determining and configuring candidate p-cycles according to the proposed algorithm are presented. Extensive simulations show that the proposed unidirectional p-cycle outperforms conventional p-cycle algorithms in mesh networks with directional capacity in terms of protection success ratio, protecting capacity proportion and protecting capacity utilization.
Most of developers protect their Java programs by code obfuscation, and opaque predicates act as tools for obfuscating control flow logic embedded within code. A new method of using congruent equation to construct a family of opaque predicates for Java programs is presented. Additionally, key and Diophantine equation is first exploited for estimating output of opaque predicates. The opaque predicates are trapdoor one-way being more resilient, stealthier and cheaper. The opaque predicates are dynamic and secure against all usual types of static attacks and dynamic attacks, and also secure against cryptanalysis.
Image retrieval based on texture in discrete cosine transform （DCT） compressed domain is proposed by introducing the spatial information of DCT blocks and taking the DCT coefficients into the feature extraction. Firstly, the definition of complex is introduced. Secondly, a complex histogram is presented to extract the texture information. Meanwhile, the effect of the DCT coefficients on the retrieval precision is discussed, the weighting values for histograms are presented. The statistical distribution of DCT blocks and the spatial distribution of DCT coefficients are taken into account as well, thus avoiding the mistaken retrieval and losing retrieval. Experiments show that the new method will show a good performance both in retrieval efficiency and effectiveness.
ZHAO Cheng-shi1,2, WANG Shu-bin1,2, YANG Cheng1,2, KWAK Kyung Sup3, ZHOU Zheng1,2
Through the specification analysis of xMax technique, a realization method of xMax is elaborated. On this basis, a new method to realize the xMax by the way of sine-like wave modulation is proposed. This modulation technique realizes the information carrying through the method of single cyclical modulation to a kind of sine-like wave signal. The technique can achieve the xMax requirements of narrow bandwidth, low sideband power spectral density, extremely low emissive power and high transmission speed. Analysis and simulation show that the bandwidth of peak power spectrum is 300 kHz, the sideband power spectral density is 40 dB lower than peak value of power spectrum density, which enables the sideband to be able to hide well in the background noise; and transmission speed may be achieved to 7.5 Mbit/s.
SONG Xing-hua, HE Zhi-qiang, NIU Kai, WU Wei-ling
The resource allocation problem for the downlink of orthogonal frequency division multiple access-spatial division multiple access (OFDMA-SDMA) systems is studied. A simple and efficient algorithm is proposed, it jointly takes the constraints posed by the physical layer (in terms of bit error rate (BER) performance and spatial orthogonality) and the constraints posed by the media access control layer (in terms of quality of service requirements and user fairness). The resource allocation is divided into two steps: user selection and power allocation. Simulations show that the proposal enjoys a low implementation complexity. It improves the spectral efficiency significantly while maintaining quality of service (QoS) guarantees and certain fairness.
A space-frequency equalization receiver scheme is proposed for space-time block-coded multiple-input multiple-output (STBC-MIMO) systems. The scheme exploits transmit diversity through grouping of the transmit antennas of MIMO systems and implementation of block level space-time block-coding for each group. Subsequently, the processed independent signals of each group are radiated from the respective two transmit antennas. Also, at the receiver, the single-carrier frequency-domain equalization and the successive interference cancellation (SIC) are used to combat with various interferences resulting from the frequency selective MIMO - code division multiple access (CDMA) channels. In addition, the channel estimation errors and the computational complexities are considered. It is shown that the proposed systems significantly outperform the traditional ones while the receiver is still simple.
In order to analyze the process capability of telecommunication services, to improve quality of telecommunication service and to enhance customer satisfaction and loyalty, the concept of telecommunication service process capability index (TSCP) is defined. First, the service blueprint technology is used to describe the existing telecommunications services process and to locate and identify the contact points of services process. Second, the capability of the service contact points is acquired by comprehensive analysis. At last the TSCP model is established to deal with the data of the contact points capability based on the grey system theory.
WANG Zhao-xiang1，2, MIAO Jian-song2, DING Wei2
In Ad hoc networks, the low priority flows have significant influence on high priority flows because the cooperative mechanism does not exist in medium access control (MAC) layer. To resolve the problem, a new MAC protocol based on fuzzy logic is proposed. It can protect the high priority flows maintain high end-to-end throughput and low delay under heavy background loads, through cooperating relative flows using fuzzy logic mechanism in MAC layer. The new protocol can better protect the end-to-end delay and throughput of high priority data flows when the networks’ background load is over 20% in simulation.
Proposed a puncturing scheme for finite-length low density parity check code （LDPC） codes. According to the rule of making the average girth maximum, we got the indices of the punctured bits. Simulation results show signal to noise ratio(SNR) gain has been achieved compared to random puncturing scheme. The proposed scheme alleviates the error floor and resolves the puncturing problem in the practice system.