- EI核心期刊
Ultrawideband (UWB) systems must coexist with narrow band systems and implement adaptive use of available bandwidth for cognitive UWB radio. To deal with these challenges, a cognitive UWB adaptive pulse design method based on the eigenvectors of Hermite matrix and bipolar Gaussian combined signal is presented for narrow band interference (NBI) suppression. Simulations show that the proposed adaptive UWB pulses met with the federal communications commission indoor and outdoor spectral mask and produced arbitrary spectral notches with flexible cognitive avoid ability. Furthermore, through the MonteCarlo simulation of pulse position modulationtime hopping and pulse amplitude modulationtime hopping systems, the proposed adaptive UWB pulses are proved to have stronger multiuser interference and NBI suppression abilities than Scholtz pulse.
An adaptive chaos genetic annealing algorithm is proposed to solve the mapping problem of lowenergy consumption networkonchip (NoC) subject to the constraints of bandwidth and communication latency. Based on Boltzmann update mechanism, the algorithm makes a selection of genetic individuals. Individuals with poor fitness are optimized by the adaptive chaos method, while the optimum individuals are optimized by the strategy of multineighborhood annealing. Experiments suggest that the proposed algorithm is able to avoid premature convergence and increase the convergence speed. Compared with the standard genetic algorithm and the chaos genetic algorithm, 45% and 226% energy savings are achieved on average, respectively, thus effectively reducing the energy consumption of NoC system communications.
Logical system PC(T) based on 0level universal operation models is proved an integrity logical system when generalized correlative coefficient is from 0 to 05. An integrity propositional logic PC(T) based on 0level universal operation models is built. When generalized correlative coefficient is from 05 to 075 moreover, propositional logic system PC(T) based on 0level universal operation models is proved an integrity logical system if P is equal to 0 or 1 and an integrity propositional logic PC(T) based on 0level universal operation models is given if P is not equal to 0 or 1 when generalized correlative coefficient is from 075 to 1.
The principle of relevancy for auxiliary problems (APs) selection is proposed to further improve the classification results in alternating structure optimization algorithm. Many kinds of APs are created by taking examples of Chinese syntactic chunking and Chinese semantic role labeling. Experiments demonstrate that the APs created can help target problems to obtain better classification results.
To maintain the global asymptotic stability control for space manipulator in the influence of manipulator actuator input saturation, a new output feedback antisaturation nonlinear proportionintegraldifferential(PID) control law is proposed by using a kind of tangent hyperbolic nonlinear function as the antisaturation function. Based on Lyapunov theory and LaSalle’s invariance principle, the global asymptotic stability of the space manipulator closedloop controller is proved, and the explicit conditions on the regulator gains is concluded. Simulations carried on a planar 2degree of freedom space manipulator demonstrate the effectiveness of the proposed approach.
With indepth study and analysis about the existing parallel packet switching (PPS) scheduling mechanism, a PPS scheduling for differentiated quality of service (QoS) based on identifier is proposed which is introduced to switch fabric. The network data flow in denomination of traffic classes is managed by the mechanism. The packets sequence for each traffic stream by queuing in order is ensured by the scheme. At the same time, if set a small amount of buffer in the multiplexer, double pointer round robin scheduling algorithm could be adopted to provide differentiated QoS guarantee for different traffics,which ensured the switch provide effective support for different highlevel traffic classes. Simulation indicates that the throughput of the mechanism reaches up to 99% at full load, and can be accordance to the reservation bandwidth to allocate the bandwidth of output links, and ensure that packets have an upper delay bound, and also can balance the load to the exchange planes.
Traditional wireless token protocols are unavoidable with failure detection mechanism. Token passing protocols for spatial multiplexing such as Ripple and improved wireless token ring protocol could not synchronize their passing tokens, while not any failure detection mechanisms are included too. A concept of token autoregeneration is introduced, cooperated with fixed token holding time mechanism and timer queue, multiple parallel token passing is allowed in token protocols with spatial reuse. Based on that, a failure detection algorithm based on neighbor monitor is provided, analytical and simulation results of quality of service performances of this algorithm indicate that it can detect failures in limited time while the correct detection probability is quite high. This failure detection algorithm is suitable for wireless token protocol with spatial reuse.
The antenna number in distributed multiple input multiple output（MIMO）system is much larger than that in centralized MIMO system. Therefore adopting existent antenna selection algorithms with excellent performance will make the system hardly realized because of the increase of its complexity. To deal with the problem, an enhanced elimination antenna selection algorithm based on port selection is proposed according to characteristics of the distributed structure. The algorithm decreases the antenna search range via numberlimited dynamic port selection and uses iterative optimizingparameter computation instead of matrix inversion during the elimination process. Analysis and simulation show that the computation complexity of the proposed algorithm is largely decreased, while the capacity performance is still very close to that of the optimal algorithm.
Evaluation of node importance in command information system (CIS) is of important effects on information warfare. A new evaluation method on node importance is presented, since the traditional evaluation methods could not be well used in CIS. Both mission requirement and network topology are taken into account, and node importance is calculated by indices of reliance and influence. An experiment is designed and conducted in two different missions. The change of node importance in the process of attack is also researched. Experiment shows the rationality and availability of this method.
A recognition method of downlink telemetry (TM) transfer frame of consultative committee for space data systems(CCSDS) is presented. A detection algorithm of (2,1,6) convolutional code based on check polynomial is examined. A node synchronization technique based on patternmatching is proposed for convolutional code. The frame length is used to roughly judge the interleaving depth of ReedSolomon(255,223), then the galoias field Fourier transform is introduced to verify the recognition results. Simulation is given according to different bit error rates and the TM transfer frame can be recognized effectively.
According to difference set and difference set pairs multiplier theorem and multiplier conjecture, the method by onorbit can determine the nonexistence of difference set and difference set pairs. The orbit created by prime p in Abelian group G by order v is discussed. Two kinds of orbit discipline are presented and proved. The one is order described by only one prime number, another is order described by the product of two prime numbers. Nonexistence of difference set or difference set pairs with the specific parameters is determined.
A differential transmit scheme based on multiplerelay cooperating is proposed in broadband communication environment. By exploiting several technologies including differential unitary modulation, amplifyandforward and maximum ratio combining, the scheme can acquire full spatial and frequency diversity gains in the manner of decoupling. Compared to the differential spacefrequency block codes, the proposed scheme not only reduces coding and decoding complexity but also easyly adjusts diversity gain. In addition, it can acquire higher spatial and frequency diversity gains with the same relay node numbers and block length. Simulation consists with theoretical analysis.
A study on approach multiple access channel capacity by means of power allocation and low density parity check (LDPC) codes optimization is presented. The power allocation scheme is designed based on the maximization of mutual information and then the power profile is obtained. The probability density function of message on factor graph is obtained by Gaussian approximation. The optimized LDPC code degree profiles are obtained by using the power profile. Iterative detection and decoding algorithm is also applied to combat multiple access interference. Simulation showes that the bit error probability performance can be improved by 16dB at 10-5 with the proposed method compared with that of only optimization of LDPC code.
The detection performance of the four Network Radar operating models to spherical targets is researched when the total power of single pulse of the transmitters is definite. Analysis and simulation show that the more the node number is, the better the detection performance of rephased coherent netted radar (RPNR) and multiinput multioutput (MIMO) model is, and show that mobile windows (MW) and coherent metted radar (NR) is opposite. When the node number is definite, the detection performance of RPNR model is better than that of MIMO model, but the latter is better than that of MW and NR model. The MW model is the worst when the signaltonoise ratio (SNR) is lower, also the NR model is the worst when the SNR is higher.
An optimal order cycle algorithm is put forward to maximize the spare expense utility. An order point algorithm and an order quantity algorithm are introduced as well, they assure that the spare part is available whenever the device fails down. An evaluation method is brought forward, verifying that the new control method has better performances than “3A” spare part inventory control method.
To eliminate redundant features in original fault feature space, a novel feature selection algorithm based on support vector data description (SVDD) and modified genetic algorithm is proposed. Firstly, it constructs a complete acoustical fault feature space through theoretic analysis and experiments. According to established criterion of feature separation and SVDD classifier prediction accuracy, prior knowledge is extracted from training data set and used as initialization to improve the efficiency of genetic algorithm. Inner and intraclass distance criterion and classifier prediction accuracy are introduced to establish fitness function and evaluate the degree of importance of every gene, thus the optimized feature subset is obtained. Experiments with unbalancefault data set simulated on rotor vibration testbed show that the proposed algorithm can improve the diagnosis accuracy.
A new viewpoint is proposed for the energyefficient power control games framework. Under the assumption that more intelligent users present, The Stackelberg equilibrium (SE) is introduced to represent the game results. It is proved that SE is superior to Nash equilibrium (NE) in terms of efficiency without any more network assistance. The proposed viewpoint and scenario can be regarded as a case that system overall performance is improved with help of cognitive knowledge being exploited by cognitive user. Simulation shows that, when in SE, all users can get more remarkable utility increase with decreased power than in NE.
In order to tackle the problem appeared in dynamic and stochastic nature of web service, a new web service selection algorithm based on interval quality of service (QoS) is proposed. The uncertainty is described by interval QoS with probability distribution. The probability distribution can be computed in terms of the sample data. By comparing the probability density in the confidence interval of QoS, it can more accurately describe the degree with which the QoS is affected by the open environment. Integrating this comparison method with interval QoS model of composite web service, a web service composition algorithm with the interval QoS guaranteed is designed. Experiment shows the interval numbers contribute to reduce the effect imposed by the dynamic environment and enhance the correctness of service selection.
With enough input of low resolution video sequences, the algorithm of spacetime superresolution reconstruction proposed by Shechtman E et al. can achieve satisfactory result. Because it’s hard to obtain enough low resolution video sequences of the same dynamic scene in practice, the application of this algorithm is limited. A new algorithm of spacetime superresolution reconstruction is proposed, in which, a high temporal resolution video sequence is reconstructed by utilizing the algorithm proposed by Shechtman E et al, and the spatial resolution of the high temporal resolution video sequence is improved by utilizing the improved iterative back projection algorithm. Experiments show that the proposed algorithm can effectively reconstruct a high spacetime resolution video sequence with limited low resolution video sequences.
In overlay sharing cognitive radio networks, an optimal scheme is proposed for improving cognitive system performance, it proves to minimize the outage probability on the premise of guarantee fixed detection performance. Analysis and simulation show that the optimal scheme can improve outage performance of cognitive system and enhance transmission reliability of cognitive network.
When transmission control protocol (TCP) connections are reset, the buffered data in the network will still be forward to the destination based on the current TCP mechanism. A new approach is proposed to solve this problem by monitoring the TCP reset message and dropping the buffered data of the TCP connection before forwarding the message in the last hop. To verify the effectiveness, a long term evolution (LTE) network model is implemented in NS2. Extensive numerical experiment is carried out. Eimulation shows that the proposed mechanism can greatly improve the network performance in terms of packet loss rate, network throughput, as well as average packet delay and jitter.
The estimation method of phase difference between multipath signals and the elimination technique of loss factor caused by noncoherent demodulation are investigated firstly. With the phase difference estimation method, a noncoherent demodulation Rake receiver implementation scheme is proposed, in which the loss factor caused by noncoherent demodulation is eliminated in base band. By using the presented estimation method of phase difference, we can not only eliminate the impact of the loss factor in base band, but also realize the perfect coherent demodulation in radio frequency. The performance analysis shows that the presented scheme is effective.
For the distributed coordination function (DCF) defined in the IEEE 80211 standard, the nodes is obtained an access rights to the wireless medium by contention method. As a result, the service time of the data frame becomes larger than the transmission time. Based on analysis of the transition between the status of frame transmitting, frame collision and idle, the medium status can be described by the binomial distribution; moreover, the service time for the given network status can be estimated. Simulations show that the estimated results are accurate.
Based on the cryptanalysis of multivariate public key cryptosystems the hidden fields equations (HFE) system with some external variables (HFEv) and internal perturbation of HFE (IPHFE), a hybrid multivariate signature scheme is proposed. In this scheme, both methods of the external perturbation in HFEv and the internal perturbation in IPHFE are used, with which the existing attacks against HFEv and IPHFE become invalid. Thus the security of the proposed scheme have been enhanced, while the total amount of computation does not increase too much. Furthermore, the security of the proposed signature scheme can be improved by the method of minus, or by multiplying two perturbations to produce mutual effect.
In order to attain the signature characteristics rapidly and detect unknown botnets precisely, an automated extracting signatures algorithm and a system designing framework are presented according to the distribution of the botnet signature characteristics, they can selfadaptively extract the signature characteristics on data flows of different functions. Experiment shows that the improved algorithm acquires far more effective signatures than before and so it can detect the numerous variants of the botnet efficiently.
null
As for the shortcoming that the participants cant carry out secure multiparty protocol, an extended proxy multiparty is proposed. The model has higher security comparing to the related models, it is formally described from functionality, protocol and security. A secure union set protocol is designed under this model, furthermore, the protocols efficiency, security and correctness are discussed.
Elastohydrodynamic lubrication (EHL) traction behavior of a kind of chlorphenyl silicone oil (CSO) used in spacecraft mechanisms is studied. The Carreau viscosity model is used to describe the shearthinning behavior encountered in EHL. Rheological tests are performed in order to determine the rheological parameters of the CSO. Tribological tests are carried out on a balldisk traction rig to measure the traction coefficient for different operating conditions. Experiments are compared with theoretical ones. It is shown that the traction coefficient of CSO increases steeply with an initial increase in slide to roll ratio followed by a relatively gradual increase and finally a decreasing trend. Traction coefficient of CSO is less sensitive to load compared with two other spatial liquid lubricants and decreases with an increase in rolling velocity at high slide to roll ratios. Therefore the tribological components lubricated with CSO will present longer service life and consume lower power. But the viscosity variation of CSO is about 5 magnitude orders in the wide temperature range，so it is unfit to cryogenic operating conditions.
To solve the high peaktoaverage power ratio (PAPR) problem of waveletbased orthogonal frequency division multiplexing (WOFDM), an optimizing PAPR algorithm based on linear programming is proposed. On conditional that the number of the wavelet filter banks level is fixed, the best wavelet packer basis is chosen by constructing the linear programming model and the optimal PAPR of the system can be obtained by utilizing the best wavelet packer basis to modulate signals. The analysis and simulations show the bit error rate performance of the system can be ensured, at the same time, the PAPR of the system can be mitigated by implementing the algorithm.