- EI核心期刊
According to timespace conversion relationship of signals and phase coincidence detection technology, a superhigh precision frequency measurement method is proposed based on length vernier in order to improve measurement resolution of signal. High accuracy and stability of the speed of light and electromagnetic signals during the transmission in space or specific medium enable the measurement of short time interval, which uses the coincidence detection of signal’s transmission delay in length. Based on this, measurement precision from ns to 10ps can be easily obtained. The method develops the length vernier utilizing the stability of signal’s transmission delay, minimizes the fuzzy region of phase coincidence between the standard frequency signal and the measured signal, approaches the best phase coincidences, and therefore improves the measurement precision that is higher than the precision provided by the traditional methods based on frequency processing. Besides, the method costs less than the traditional methods and can also solve the problem of the measurement of superhigh frequency.
For study of the source detection areas monitored by wireless sensor network, an algorithm combining low energy adaptive clustering hierarchy（LEACH） algorithm and Bayesian compressive sensing （CS）is proposed. LEACH algorithm divides the sensors into some clusters and chooses the clusterheads. The information in the sensors is collected by the clusterheads. Only the clusterheads are allowed to transmit information to the fusion center. It reduces the number of sensors which send the information to the fusion center. The fusion center utilizes Bayesian CS to recover the source from a little measurement transmitted by clusterheads. At the same time, a threshold is set to optimize the performance of reconstruction when the data volume becomes little. Simulations show that the algorithm proposed can detect the source accurately, and obtain the good performance.
In order to design a high performance miniaturized microstrip filter, a new Φshape defected ground structure (DGS) is proposed. A Lowpass filter is designed using the Φshape DGS with H shape open stubs line. A one single, twocascaded and threecascaded Φshape DGS lowpass filters is designed, simulated, fabricated and measured repectively. The transmission characteristics of the twocascaded Φshape DGS lowpass filter shows its advantages of compact size, high selectivity, low insertion loss and excellent passband performance. The frequency response of the threecascaded Φshape DGS lowpass filter presents the advantages of compact size; high selectivity; low insertion loss; better passband performance and high outband suppression of more than 40dB. Measurement shows a good agreement with the simulated results. It also validates the requirements of miniaturization and high performance for filters.
In order to extend the scope of zero correlation zone (ZCZ) sequence in quasisynchronous code division multiple access system, an almost perfect punctured binary sequence pairs is used in zero correlation zone (ZCZ) sequence pairs, a new construction method for ZCZ signals is presented. ZCZ punctured sequence pairs set can be generated from the periodic product of unitary matrix and the original ZCZ punctured sequence pairs set. The almost perfect punctured binary sequence pairs and the unitary matrix can be easily obtained, so the capacity of ZCZ punctured sequence pairs set constructed by the proposed method is so large that they can satisfy requirements of engineering applications.
A linear correct total least squares method by semidefinite programming global algorithm (LCTLSSDP) is proposed for robust 3D acoustic source localization model considered time difference of arrival. The new algorithm finds the optimal solution of this ratio of quadratic functions model with a equality constraint by solving a nonconvex homogenous quadratic optimization problem with inequality constraints. The dual theory is also used when designing.
By extracting the edge information of the target object in single digital image, the light direction can be estimated. In order to improve the efficiency of the estimated light direction, the image edge detection operators are brought in which achieves the accurate orientation of the target object in the fake image. With the combination of border fitting and data analysis, thus a procedure of detecting image tampering which is based on the inconsistencies in light source direction is formed. Experimental results show that edge detection operators optimize the detecting process, also improve the feasibility and expandability of this forensic technology.
In general, the fault detection in wireless sensor networks (WSNs) could be happened in additional communication and computation load. Considering the feature of WSNs that those nodes in the same coverage range have the close reading data, a neighbordata analysis based fault detection schema is proposed. The confidence level of sensor nodes is taken by analyzing the history reading data in the first place. Comparing the node’s reading data with that of neighbor nodes results in good confidence level to determine that whether this node is failure or not. Simulations show that the proposed schema can catch a good performance in fault detection accuracy and transient fault tolerance, but do not bring any communication and computation overhead to sensor nodes.
For general encoding algorithm of low density parity check (LDPC) codes over GF(q), a Tanner graph and research encoding algorithm is presented based on lower upper (LU) decomposition. In order to keep sparsity of matrix, three pivot selection criterias named row pivot, rowcolumn pivot and product of rowcolumn pivot are deduced and analyzed. Simulations show that the new algorithm could be lower than one half density compared with existing algorithm. The conclusion is useful to application of universal encoding algorithm for LDPC codes over GF(q).
Based on the particle swarm optimization (PSO) algorithm with gradient, a new design is proposed to optimize the degree distribution in the procedure of Luby transform(LT) encoding. The importance sampling approach is employed to construct an objective function. The estimation for the gradient is obtained by the objective function. And then, the degree distribution can be optimized by PSO with gradient. At last, forms with sparse degree distributions and soliton distributions are optimized with the proposed method respectively. Simulations show that the degree distributions obtained by the proposed method are more efficient compared with that of Robust soliton distribution and importance sampling approach, it can reduce the overhead packets in LT codes with short codelength.
A hybrid protocol with relay selection(HPRS) is derived to improve the cognitive performance. What a cooperative protocol is chosed is rest with the the source signal relay decoding. The relay with the highest relaydestination signaltonoise ratio is selected to forward the data. The approximated outage probability formulation and diversity for HPRS is given. Simulation shows that amplifyandforward with relay selection(SAF), decodeandforward with relay selection(SDF) protocol and HPRS can achieve full space diversities, but the HPRS is better than that of both SAF and SDF in outage performance.
A network coding (NC) based twosubscribercooperation scheme in a fullduplex transmission mode of orthogonal frequencydivision multiple access system is proposed to further improve the network throughput. And a double level Nash bargaining solution (DL_NBS) game is adopted to resolve the interuser resource bargaining problem. In the interuser pair, the pairwise capacity based NBS is utilized to allocate subcarrier and distribute power between the cooperative subscribers. Simulations show that the proposed CoNC achieves a system capacity of 491% higher than the normal cooperative transmission, and 464% higher than the direct transmission. Meanwhile, compared with the traditional resource allocation algorithms, the twolevel NBS solution achieves a well tradeoff between fairness and efficiency, and perfectly suits the distributed subscriber cooperation scenario as well.
Based on analysis of internet topology model and metrics, five topology generators are compared on both autonomous system （AS） level and router level. The accuracy of these generators is checked by counting several topology metrics of the generated graphs and with indicators. Evaluation of their performance is given on the basis of comparison. It is shown that new Internet topology has the best performance on AS level, and TopGen generates most accurate topology on router level.
Malwares and their resulting threats are growing urgently. A method at the file system level is provided for analysis and defense against malwares with reducing the loss as possible, and implements a file system for malware analysis and protection (MAPFS). With checkpoint and file versioning technology, MAPFS can record the modifications in file systems during the process. These records are important for analysis of malware behavior, and may be used to recover the files damaged by the malwares. Experiments show that this method is effective in analysis and defense of malwares, and MAPFS only brings a little loss lower than 10 percent.
For solving the questions of complexities, high computationconsumings and applications limited for the direct anonymous attestation(DAA), a new DAA scheme is proposed based on bilinear maps under the assumption of q strong DiffieHellman and decisional DiffieHellman so as to match the limited computational resource of trusted platform module（TPM）. It is shown that the secured scheme can efficiently relieve the computation bottleneck of trusted platform and enable TPM to be used in embedded and other resourceconstrained environments.
To predict endtoend available bandwidth accurately, a autonomous system (AS) topologybased available bandwidth prediction algorithm Taware is proposed. Taware employs the AS topology information to choose landmarks for ultrametricconstraint nodes and unultrametricconstraint nodes respectively, and then predicts the endtoend available bandwidth accordingly. Experiments with HP scalable sensing service dataset show that the Taware can predict endtoend available bandwidth over ten percent precisely than the PathGuru algorithm.
To overcome the shortcomings of the existing schemes such as strong hardness assumption,long signatures and high compution cost, a new transformation is proposed. It can convert any simulativepartitioned identitybased signature with existentially unforgeable security to a strongly unforgeable signature. And a concrete strongly unforgeable identitybased signature based on Paterson’s scheme is constructed in the standard model. Under computational DiffieHellman assumption, the proposed signature scheme is provably secure against strongly existential forgery under adaptive chosen message attacks. In addition, the new scheme has some advantages over the available schemes, such as short signatures, low computation cost and high security.
In order to reduce the outage probability of cooperative communication, a hybrid forwarding scheme for cooperative communication system in symmetric wireless networks is proposed. In this scheme, each relay is decided to use either “amplify and forward (AF)” or “decode and forward (DF)” according to the instantaneous signal to noise ratio conditions between the source and the relay. Thus, the different relay nodes may use different communication protocols to carry out cooperative communication. An expression of the average outage probability on the hybrid forwarding scheme is derived. Furthermore, the simulation shows that the proposed hybrid forwarding scheme outperforms conventional cooperative relaying with AF and DF in reducing the outage probability.
In order to sign the vary age value and check its verification. A new secure protection mechanism for open shortest path first (OSPF) routing protocol is proposed through utilizing the sanitizable signature scheme. Enhanced sanitizable signature schemes, combines with the security property of weak transparence on the sanitizable signature algorithm,to protect the routing massage on the OSPF protocol. Security analysis shows, the proposed OSPF protocol can avoid the MaxAge attack and premature MaxAge attack.
The effective bandwidth, acting as an economic production function of network service, is commonly used to impose admission control on realtime traffic. Yet the allocation of bandwidth and buffer remains as a technical problem and an economic one as well. A pricedriven resource composition algorithm is proposed based on Courcoubetis effective bandwidth formula, aiming to keep the allocation of bandwidth and buffer in step while following the objective of charge minimization. Then an adaptive pricing mechanism for bandwidth and buffer allocation is presented to improve the resource utilization ratio, in which prices are adjusted relatively and absolutely at different time scales respectively. Simulation results show that the proposed scheme could effectively improve the resource utilization ratio and keep the call blocked ratio at reasonable level.
In the existing trust models of peer to peer network, the internal situations and external environments of nodes are not considered in the process of calculating the trust value that will affect the rationality and objectivity of models. To solve this problem effectively, a new trust model based on the deviation factor (TMDF) is proposed. Introducing the structure concepts of selfcapacity and externalcapacity, the model gives a multidimensional evaluation vector, it comes from construction approach of trust relations in the social network, in which, a peer’s trust value is calculated according to two aspects. TMDF calculates the recommended trust value of the recommended nodes using the deviation factor and calculate the trust value of nodes by the direct trust value and the recommended trust value. Analysis and simulation show that the new model can provide the more real trust services, identify and resist the malicious acts, such as slander and conspirator.
To collect passenger flow information of public transit from the widely applied smart card fare payment systems, a new method is proposed to infer the stops at which passengers holding smart cards board the bus from smart card fare data and bus schedules. The method first classifies two sequential swipes to decide whether they occur at the same stop with naive Bayes classifier. Travel times are then estimated from the naive Bayes classifier results using maximum likelihood estimation, dynamic programming and quadratic programming methods. To solve the problem with imprecise initial parameters, a coordinate descent method is applied. It updates parameters and estimates values alternatively until convergence. An experiment is designed to test this algorithm with realworld data, and it proves that the error of this method is small and the convergence is fast.
The spectrum sensor and transceiver can be jointly designed for the orthogonal frequencydivision multiplexing(OFDM)based cognitive radio. Which does spectrum sensing and transmission alternatively. Furthermore, it can sense multiple licensed bands simultaneously. The time length of sensing can be decided according to the sensing performance requirement. The choice of the sensing period is modeled as a nonlinear optimization problem with the constraint of the probability of interference with the licensed users. Through the sensing period optimization, the OFDMbased cognitive radio can take full advantage of the spectrum opportunity and guarantee the lower interference with the licensed users.
An eigenvalue based coordinated beamforming algorithm is proposed to mitigate the intercell interference aroused by beam collision in beamforming systems. Assuming the scheduling of users has been done in each cell, the users suffering serious interference require their serving cell cooperatively working with their strongest aggressor. The two cells calculate the beamforming vectors for the subcarriers adopted by this user together. With this coordinated multipoint technique, the intercell interference is mitigated and the sum of achievable rate of users adopt the same frequency is maximized. Compared with the classical independent beamforming techniques, the proposed algorithm can greatly improve system performance.
In order to automatically map algorithms onto reconfigurable multimedia processor and improve the parallel efficiency of algorithms, a task compiler frontend is designed. The kernel loop unrolling is introduced to improve the degree of parallelism; and the scalar replacement technique based on data dependence analysis is used to optimize the cost of data transmission. Experiments show that the task compiler frontend improves the degree of parallelism effectively, its performance can be, compared with the frontend of Garp C compiler, sharply increased up to 2~4 times in the whole system.
In order to compensate polarization mode dispersion (PMD) in high speed optical communication systems, an analysis of the principle of PMD monitoring with degree of polarization （DOP） as monitoring signal is proposed. Utilizing DOP method, a high precision and high response rate realtime inline PMD monitoring unit is designed and implemented. The range of input optical power is -20~0dBm, the response time reaches 1μs and the detection accuracy is 1%. An experimental system is set up to adaptively compensate the PMD of 43Gbit/s return to zero differential quadrature phase shift keying system with PMD monitoring unit. Experiments show that the adaptive PMD compensation can be completed in 1 ms and the compensation effect is significant well.
Three electromagnetic simulators：high frequency structure simulator (HFSS), FEKO and computer simulation technology microwave studio(CST MS) are applied in dualband cylindershape antenna analysis. Simulations show that HFSS provides good agreement with the measured return loss, while FEKO presents good agreement with the measured far field gain. The simulated results by using CST MS agree well with the measured results for both return loss and farfield gain. The measured results show that it has 150MHz (820～970MHz) bandwidth at the lower band and 600MHz (17～23GHz) at the upper band under the condition of voltage standing wave ratio less than 15, and far field gain is 18dBi at 900MHz and 49dBi at 2GHz.
A network selfprotection mechanism based on abnormality analysis is presented aiming at deficiencies of current network security protection technologies. To improve the ability of detection and protection against network attacks, a network attack detection algorithm based on the multivariate abnormality analysis is proposed. The algorithm uses a metric of abnormal distance to classify the network flow into different types and prioritize the routing of the different network flow packets. In this way, the normal traffic flows can suffer the least impact from network attacks. Experiments show that our mechanism can significantly improve the network system’s protection ability against distributed denial of service attacks.
A carrier sensing multiple access collision avoidance (CSMA/CA) and hidden node effect integrated system modeling method is proposed to study the optimum sustained application traffic of multihop Ad hoc network. The coexistence of CSMA scheme and hidden node effect in multihop environment makes the nodes competition for channel occupation more complicated. Firstly, we set up the optimum throughput model of the system by analyzing the modes competing action for accessing the channel. Then we deduce the mathematical expression of system optimum throughput under both CSMA effect and hidden node effect. Finally, numerical results are given based 802.11 b/g media access control mechanism in both analysis and simulation. Simulation of different chain hops and different packet size verifies that the modeling method and the model expression could accurately evaluate the traffic supporting situation in multihop Ad hoc networks.