- EI核心期刊
Polarization effect plays a main role in high speed optical communications. The polarization states in fibers must be controlled effectively. The related concepts, the present status of research, the latest progress, and future research trends in the polarization effect controls is presented, including polarization stabilization, demultiplexing for polarization multiplexing system, as well as mitigation or compensation for polarization mode dispersion in fibers. The achievements of these three technologies are also described.
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Based on the proven communications technology, the transmitted electromagnetic pulse/energy standards and testing (TEMPEST) is studied. The propagation model of computer information leakage is compared with conventional communication system model. Then coding and modulation of computer video information is analyzed, and the recovery method is given. Finally, an equivalent communication system model of computer video information leakage, reception, demodulation and decoding is established, indicating that the communication technology is effective in transmitted electromagnetic pulse/energy standards and testing study.
To achieve the frequency reuse of wireless networks, an asynchronous myopic repeated game(AMRG) is modeled, and a corresponding distributed algorithm is proposed. Besides, the existence and convergence of the equilibrium points for the algorithm is analyzed. Simulations show that the number of the frequency that our algorithm required is close to that of the classic greedy coloring algorithms, and the convergence speed of our algorithm is five times that of the greedy coloring ones.
In order to improve signal classification accuracy, a new classification method based on kernel Fisher discriminant analysis (KFDA) is given in the digital modulation signal classification. The higher order cumulants of the received signals are used as the classification vectors firstly, then the kernel thought is used to map the feature vector to the high dimensional feature space nonlinearly and linear Fisher discriminant analysis is applied to signal classification. The multiclass classifier is decomposed to multiple twokinds classifiers, and the classification steps of signal recognition based on kernel Fisher discriminant analysis are described in detail. It is concluded based on experiment that when proper parameters are selected, it will almost get the same classification accuracy as the support vector machine classifier. Meanwhile, support vector machine requires less time and computational complexity is lower because KFDA avoids solving the nonlinear optimization problem.
A Markov chain analysis model is presented to analyze bandwidth request scheme for besteffort and nonreal time polling services in pointtomultipoint mode of IEEE 80216 networks . The average delay of bandwidth request is evaluated by the contention window size, the number of contending subscriber stations(SSs), the number of slots allocated for bandwidth request and the maximum number of retransmission under saturated conditions. Simulations validate its high accuracy under different parameters and the number of SSs.
A subchannel and modulation joint selection method is proposed in dualhop relaying multiinput multioutput (MIMO) systems to improve the system throughput and to cut the signaling overhead. Regarded as an equivalent channel, the channel between source and destination is decomposed into multiple parallel independent subchannels by singular value decomposition. The number of the used subchannels and their modulation schemes are selected and feedback jointly in the proposed algorithm. Simulations show that, compared with the traditional method where each subchannel selects modulation scheme independently, the new selection method can achieve higher throughput and use less signaling bits.
To solve the gateway congestion control problem of wireless Mesh network(WMN), a new congestion control algorithm based on crosslayer loadaware in WMN (CCACL) is proposed based on the existing congestion control strategies. CCACL adaptively adjusts the sending rate of source nodes according to the local congestion information, and it simultaneously, appropriately adjusts the congestion threshold limit of the next hop nodes as well for emptying the buffer faster and to ease the network congestion. In order to ensure the reliability of data transmission, CCACL integrates an endtoend selective acknowledgement mechanism based on the hopbyhop reliability assurance mechanism. Simulation shows that CCACL can increase the network throughput, reduce endtoend delay, and effectively solve the congestion problem in WMN.
In order to represent the invisible electromagnetic environment to commander, the volume visualization based approach of electromagnetic environment in virtual environment is proposed. First, this approach uses the LongleyRice radio propagation model to calculate 3D electromagnetic power volumetric data. And then the data is rendered on virtual environment using coordinate transformation based on hardwareaccelerated volume visualization. Finally, electromagnetic environment of different power is classifiably represented using color mapping tool. The results of the experiment show that this approach can visualize the inner detail of electromagnetic environment, and provide decision supporting and electromagnetic equipments planaiding for users.
To get a better bit error rate (BER) performance of the optical code division multiple access (OCDMA) systems, an OCDMA scheme using 3rd order Chebyshev chaotic sequence is proposed based on the study of the principle of phase shifted superstructure fiber Bragg grating encoder/decoder. The code selecting method using simulated annealing algorithm is investigated. Simulations indicate that the BER performance of the system with chaotic sequences is better than that with Gold sequences, and the proposed code selecting method is effective.
To study the accuracy of magneticdipole position model, the parallelfinite difference time domain (parallelFDTD) arithmetic is presented on a distributed network. The message passing module and space decomposition technique are applied. In FDTD application, simulation of low frequency exciting source is very difficult. The fast Fourier transform arithmetic is introduced to analyze the magnetic characteristic of some special frequency by using Gaussian pulse exciting source. The nearfield position model and the calibration arithmetic are set up based on the Lagendre polynomial. The effects of position distance on magneticdipole position model and parameters position error rule are analyzed. Numerical results validates that the parameters accuracy could be improved by the Lagendre polynomial nearfield calibration model.
Aiming at the lengthy of classical fractal coding algorithm and the problem of fast fractal image coding algorithm based on such as Kmeans clustering, a fast fractal image coding algorithm based on immunity particle swarm optimization（IPSO）and fuzzy kernel clustering is proposed. Firstly, an algorithm of fuzzy kernel clustering based on IPSO is presented. The IPSO algorithm is used to calculate the cluster centers. Then the proposed algorithm of fuzzy kernel clustering based on IPSO is applied to fractal image coding. The range blocks and domain blocks are clustered reasonably by fuzzy kernel method, respectively. Range blocks are searched in the corresponding category of domain blocks. As a result, the encoding time is reduced significantly. The experimental results show that, the encoding time of the proposed algorithm is about six times less than that of the classical algorithm at the cost of slight decrease of peak signaltonoise ratio. Compared with the fast fractal image coding algorithm reported recently based on such as Kmeans clustering and particleswarmoptimization clustering, the proposed algorithm can achieve higher peak signaltonoise ratio in much less encoding time.
When the femotocell technique is utilized in the orthogonal frequency division multiple access (OFDMA) system, the interferences will be increased and the traditional capacity model will not be available. Two kinds of radio resource allocation mechanisms, cochannel and orthogonal, are analyzed for the coexistence of femtocell and macrocell, where the signaltointerference ratio distribution is derived and the closedform outage probability expressions and the corresponding theoretical capacity formulations are presented as well. Analysis and simulation results show that the interference between femtocell and macrocell for the cochannel scenario is worse than that for the orthogonal scenario; however, the throughput in the cochannel scenario is better than that in the orthogonal if the interference can be coordinated.
To solve the complicated problem of analysis of outage performance in cooperative communication system, a theoretical analysis method is proposed. A selection relay model with a direct link over independent identically distributed Nakagamim fading channels is considered based on the power restricted cooperative communication system. An analytical expression of outage probability is derived and the outage performance is analyzed for this model. The optimal power allocation is also investigated and a power allocation factor in a specific relay number is given. Simulations show that the outage performance is evidently improved compared with other selection relay models. The optimal power allocation ia also investigated and a power allocation factor in a specific relay number is given.
A general eigenvalues decomposition (GEVD) aided interference suppression algorithm is proposed based on the minimum meansquared error (MMSE) criterion to improve the precoding gain of multiuser in multiuser multiinput multioutput (MIMO) system. It suppresses the interference and noise, meanwhile, the users precoding gain is taken into account at the same time. The algorithm can maximize the signaltoleakageandnoiseratio at the transmitter and maximize the signalto interference andnoiseratio of each user’s receiver. And how to modify the design in order to account for channel estimation errors is also analyzed. Simulation shows that the algorithm can achieve a better system performance than the general MMSE invension algorithm.
A method to get rid of the complexity redundancy within the fixedcomplexity sphere decoder is proposed, that can reduce the detection complexity greatly in the sense of average, therefore to decrease the power consuming. If the method is well constructed, the reduction of complexity redundancy will cause no loss of diversity order, that means optimal in high signal noise ratio regime. The simulation shows the effect of the method.
For research of the capacity properties and the practical performances of the interference channel with relay, the ability of simultaneously obtaining the multiplexing gain and the diversity gain in the oneside interference channel with relay are analyzed. Based on oneside interference channel with relay with the cognitive relay model, the channel capacity and the outage probability are also analyzed and the expressions are given. The diversity multiplexing tradeoff of the oneside interference channel with relay in the high signal to noise ratio is thereafter derived. Simulation shows that, compared with the one in the Zchannel, the relay can increase both the multiplexing gain and diversity gain simultaneously.
Based on the bilinear pairings, an identitybased signature scheme is presented to overcome the loose security reduction of PatersonSchuldt’s identitybased signature scheme which is proved secure in the standard model. Using the idea of private key generation algorithm in Waters’ and Gentry’s identitybased encryption scheme, the scheme can answer all private key queries and signature queries, which captures tighter secure reduction and weak secure assumption. The scheme is also provably secure in the standard model. A security analysis shows that the proposed scheme is proved secure against existential forgery on the adaptively chosen message attack under the assumption of modify computational DiffieHellman.
To solve the problem of network traffic identification online, a clustering algorithm and a traffic identification scheme is proposed. The scheme uses a few number of the initial data packets in the flows as a subflow, extracts the statistical features from subflows, and extracts the best feature subset of subflows by applying correlationbased filter approach. The network traffic flows are clustered by online density based spatial clustering of applications with noise algorithm, and mapped to application types by the dominant application in clusters. Experiments show that the scheme can identify new application types and encrypted flows, and can be implemented in online network traffic classification.
A limited feedback scheme is proposed based on differential normalized matched channel matrix for downlink multiuser multiple input multiple output systems. By distinguishingly normalizing the elements of the matched channel matrix, the proposed scheme avoids the range of the elements in the Frobenius normbased normalized matrix converging to zero with the number of transmitter antennas increasing, and maintains the precision of uniform quantization under different number of transmitter antennas. Simulations show that, comparing with conventional Frobenius normbased normalized scheme, the proposed one could effectively decrease the mean squire quantization error, and improve the reliability of precoding.
To improve the efficiency of spectrum sensing and to maximize the system sensing efficiency with meeting interference avoidance constraint, a parameters optimization algorithm for cooperative spectrum sensing in resourcelimited cognitive radio networks is proposed. By operating the optional weights between the channel utilization efficiency and system resources usage efficiency, the proposed algorithm can figure out the optimal sensing parameters for each licensed channel with the unique usage characteristic. Simulation shows that using the optimal sensing parameters can maximize the sensing efficiency and satisfy the interference avoidance requirement for protecting the primary users.
In order to optimize allocation of the limited bandwidth resources and maximize the operators profit in environment of multiservices sharing network resources, some typical services’ traffic characteristics and quality requirements are firstly analyzed, and the quality of service (QoS)based pricing objective of operators’ revenue maximization is proposed. Based on necessary and sufficient conditions of maximizing the objective function, the binary search algorithm for optimal solution is proposed. The case analysis and experiments show that the pricing mechanism proposed can achieve better revenue compared with resource usage based one.
In order to make the ultrawideband (UWB) signal received efficiently and stably, an ultrawideband channel estimation algorithm with low complexity based on the features in frequency domain is proposed. With the help of recursive least squares, the blind channel estimating is achieved based on the onedimensional statistical stationary feature of time hoppingpulse position modulation signal. The algorithm is of low complexity. Simulation shows the promising gain reaches 3dB when the bit error rate is 10-4, compared to maximum likelihood blind channel estimation. The algorithm can perform estimations for multiple channels, and there is no ambiguity in both the amplitude and the phase of the estimated channel.
To enhance the precision of wireless localization in the traditional mobile network, a wireless cooperative localization algorithm is proposed for the nextgeneration mobile communication system by employing the cooperative communication between the mobile stations (MS). The cooperative localization problem is solved by nonlinear optimization theory. With that this problem is converted to the linear least square problem, finally the location is estimated by the GaussNewton algorithm. Simulation shows that, when GaussNewton algorithm is applied in the cooperative localization, it is almost converged and the times for convergence (the converging speed) is about 2~3. When there are two or more than two reference terminals (RT) involved in the cooperative localization, and the standard deviation of the distance measured by RT is less than 50m, the root mean square error of the location estimate is less than 100m.
Based on the existing solution for spam over Internet telephony (SPIT) detection, a method using human conversational model to describe the call pattern of human telephone call is proposed. A conversational pattern state sequence is generated through the conversational model from a call. Via using Bayesian probability model, the possibility that the call is malicious is calculated. The possibility can be used to detect the spam phone calls generated by robot, and can be applied in our perimeter defense system. Experiments on the border defense system indicate that the false negative rate of detection is less 10% while the false positive rate remains low at about 2%. It demonstrates that conversation pattern can be used as a feature to detect behavior of SPIT as the other features.
Based on improved Lyapunov function, a new method is proposed to analyze the problem of decentralized static output feedback control for a class of nonlinear interconnected systems composed with a number of TakagiSugeno fuzzy bilinear subsystems with interconnections. By constructing a new Lyapunov function, some sufficient stabilization conditions are derived for the whole closeloop fuzzy interconnected systems. The stabilization conditions got by loosing the restricted conditions in the proving have less conservativeness than the existing methods. The corresponding decentralized fuzzy controller design is converted into a convex optimization problem with linear matrix inequality constraints. Analysis and simulation show that the proposed wethod has a better stabilization property.
In order to study an information hiding technology of keyhole markup language (KML) file, an information hiding algorithm based on KML file is proposed. Firstly the difference between the characteristics of the KML document and the extensible markup language document is analyzed, and the status of the information hiding algorithm is studied. Then the information embedding algorithm and detection algorithm are proposed in KML file based on latitude and longitude coordinates. In these algorithms the values are classified by means of counting values for unimportant position, and then the information is hidden into the position which has been counted. The detection algorithm is the same as the embedding part, and information is extracted by using the classification. Experimental results show that the proposed algorithm has the higher robustness for resistance to addition and deletion attacks and rotation attacks on carrier data.