- EI核心期刊
Information overload is one of most critical problems in big data, and recommendation systems which are powerful methods to solve this problem are coming under growing attention by industry and academia. The main task of recommendation systems in big data is to improve the performance and accuracy along with user satisfaction utilizing user feedback, social network and other information. A survey of the recommendation systems in the big data is proposed, which includes the summarization of big data and recommendation systems, the differences between the recommendation systems in traditional environment and in big data, key techniques, evaluation and typical applications according to a hierarchical framework. Finally, the prospects for future development and suggestions for possible extensions are also discussed.
Considering that hexagonal signal constellation (HSC) demodulation algorithm is not optimal, a low-complexity demodulation algorithm of HSC based on non-orthogonal vectors projection was proposed. On the basis of overview of the typical hexagonal constellation structure, the projection coefficients of hexagonal signal vectors and computational complexity of the algorithm were analyzed and calculated. The effect of noise on the received signal was researched and the signal to noise ratio thresholds were given combined with Gauss-Legendre numerical analysis method. It is shown that the demodulation algorithm is only about 30% of base vector projection demodulation algorithm in terms of computational complexity when it performs effectively.
Device-to-device (D2D) communications can improve spectral efficiency, but it may generate interference onto the cellular networks at the same time. The improving proportional fairness (IPF) scheme is proposed to optimize resource allocation and power control between cellular and D2D connections which share the same resources. Simulation results show that the IPF scheme can significantly improve the fairness and throughput of the cellular system.
In order to enhance system capability and reliability in diverse scenarios of smart grid traffic with different quality of service requirements, a cognitive technology of double path maintenance for wireless smart meters is proposed using causality tree. The causality tree performs efficient reasoning by using the underlying causal relationships between metrics and events which are defined in the program of smart meters. Path maintenance metrics identify routing design issues about link states, link qualities, and correlated dynamics transitions in terms of received signal strength indicator and packet reception rate. Physical experiments are used to evaluate the reliable performance of the wireless smart meters in the scenarios of channel and electromagnetic interference.
Nowadays, the development of wireless communications technology makes vehicle-road communication possible. Building vehicle-road communication based cooperative intersection collision avoidance systems can ensure the safety of vehicles traveling at an intersection and improve the passing rate of the intersection, however, vehicle collision warning system needs accurately estimating the vehicle's route, when vehicle's in danger, giving the safe speed range and informing the vehicle to decelerate or brake. A grid-based space-time synchronization algorithm for vehicle collision avoidance warning is proposed, which will divide the intersection into several grids. Roadside unit through the vehicle velocity, direction and attribute to determine the vehicle trajectory, which is the vehicle occupied grid number. If two vehicles occupy the same grid at the same moment, the risk of collision will occur. Then the unit gives a safe speed based on the state of motion of the vehicle to the vehicle to avoid the collision. To test the algorithm, the algorithm is simulated and truly tested in the scenario of intersection with signal lights and intersection without signal lights. Experimental results demonstrate the proposed algorithm can accurately detect the vehicles which are in potential collision in the intersection and give the advised speed. The results also demonstrate the effectiveness and accuracy of the system.
A method of high dynamic Doppler shift simulation with time-varying sampling interval on intermediate frequency simulator was presented. Based on satellite movement model, the high dynamic frequency shift characteristic of the signal was researched and a Pseudo-code and carrier Doppler shift simulated method was proposed as well based on variable frequency dynamic samplings. A design scheme of high-precision Doppler simulation was given, it reduces the system hardware complexity by omitting the code numerically controlled oscillator module in conventional methods. With analysis on error accuracy of pseudo-code frequency, the closed-form solution of the main parameters was derived. Simulation shows that the method can effectively improve the accuracy of the Doppler shift simulation, and provide high stability under high dynamic environment, with which, the frequency of the received signal will reach a finite second-order change rate.
The traditional network security events analysis methods depend more on human interventions. To address this problem, an automatic and self-adaptive method is presented. The neural network models are used to classify amounts of security events according to various attack scenarios, which can reduce much human intervention. The rule items are extracted from the classification results. And the correlation rules are generated automatically from these items using genetic algorithm. Experiments demonstrate that the method can classify the network security events and generate association rules automatically, so that the degree of automation can be improved. It is an effective enhancement and improvement to the traditional methods.
A fuzzy identity-based signature scheme based on short integer solution problem was designed. in 2013. Two weaknesses about its security proof are illustrated as follows: 1) the response to private key extraction queries leads to hash function collision; 2) for identities who have same bits with the target identity, and the number of same bits is larger than the threshold value, the challenger couldn't response to signature queries. The modifications were given to improve the above mentioned items. In addition, the lattice basis delegation with fixed dimension was used. A new fuzzy identity-based lattice signature scheme was obtained with smaller lattice dimension. The security proof of new signature scheme was proposed as well.
A Denavit-Hartenberg (D-H) quaternion transformation method for kinematics analysis of serial mechanisms was presented. Firstly, the point mapping is described with quaternion. Then a D-H quaternion transformations method for motion transformation between adjacent linkages was proposed. Moreover, the matrix operation method of D-H quaternion transformations was illustrated to construct the classical D-H homogeneous transformation matrix in robotics, which can be theoretically proven that the proposed D-H quaternion transformation method is correct. Based on the above D-H quaternion transformation formula of motion transformation between adjacent linkages, the D-H quaternion transformation method for kinematics analysis of serial mechanisms with any number of linkages was further proposed. By analyzing the kinematics of PUMA robot, the effectiveness and correctness of the proposed method was validated as well. The D-H quaternion transformation method has clear geometric meaning and the computation process is simple. The method is proved effective for kinematics analysis of serial mechanisms.
In order to improve the energy consumption efficiency of the distributed antenna system, a model of the cooperative multipoint transmission (CoMP) system was established. The channel propagation model, the energy consumption evaluation index and the system coverage, and the relationship existed in the distance between base stations and system energy efficiency were analyzed as well. The expressions between the distance between the base station and energy consumption efficiency were derived. Simulation was performed by Monte Carlo method. It is shown that, with increase of the distance between base stations in CoMP systems, there appears a trend that the energy consumption per unit area appears from large to small and then gradually become large. Meanwhile, the absolute contribution that the growth of the unit area contributes to the energy consumption per unit area also is seen from large to small and then gradually becomes large. Furthermore, the impaction of the energy consumption decrease per unit area on the system Spectrum efficiency seems relatively low. The distributed antenna deployment strategy of the minimum energy consumption per unit area in CoMP systems is therefore developed.
An affine-interval arithmetic-based method for the feasible region evaluation of function or electronic circuits was presented. This method uses affine-interval arithmetic to analyze the bounds of the function, and use branch and bound method divided these intervals into three kinds: accept regions, refuse regions and those of uncertain regions. All the uncertain regions were re-divided and the bounds calculation and classification performed again until the subintervals small enough. The statistics on each of accept regions was performed thereafter to get the sum of the accept regions. The proposed technique guarantees an efficient, reliable and accurate evaluation of the yield, even for non-convex and not simply connected feasible region. The examples presented show the features of the approach.
Considering the reliable broadcast communication problem of quantum network nodes in the environment with complicated information channels, the error control issue of this problem was investigated. A communication protocol with broadcast error control for quantum networks was proposed based on forward error correction. For networks containing N+1 quantum nodes, the error counts of N slave nodes are calculated respectively when the master node sends quantum information to N slave nodes, that determine that the slave nodes are retained in or removed from the information list according to the calculated error counts. For states of those retained slave nodes, the errors of bit flips and phase flips of the remaining slave nodes were corrected using the intrinsic characteristic of error-correcting code. Due to the different measuring sequences of the N slave nodes, each slave node has different quantum key. The problem of network leak resulted from the leak of single slave node, if all slave nodes have the same quantum key, can be amended. Finally, analyses of throughput efficiency of information channels as well as the protocol security were presented.
A new heuristic process scheduling strategy was proposed on the basis of a memory sharing mechanism. Based on software defined networking (SDN) architecture, A workload model and a memory energy consumption model were designed. Two heuristic process scheduling algorithms were designed to save the memory energy consumption. The algorithms come from physical memory nodes. The key idea of the above proposed algorithms is to achieve the largest sharing ratio of memory which assures workload balance through scheduling processes reasonably. The least number of active memory nodes means the least memory energy consumption of data center. Simulations verify that these strategies can reduce the energy consumption effectively.
A generalized Bayesian information criterion (GBIC) based wideband spectrum sensing scheme was proposed for cognitive radios. The proposed algorithm first estimates the number of subbands occupied by primary users in the licensed frequency band under the GBIC mechanism. Subsequently, their positions in the wide spectrum are identified. In this way, the idle subbands can be dynamically accessed by the secondary users. Simulations illustrate that the proposed wideband sensing scheme of GBIC, is capable of significantly improving the spectrum sensing performance and very close to the conventional energy detection scheme.
A perceptual hashing algorithm for speech content authentication based on correlation coefficient of mel-frequency cepstrum coefficients (MFCC) was proposed. The MFCC of the framed speech signal is extracted as perceptual feature. The correlation coefficients between MFCC and a pseudo-random sequence, which is generated by keys for security, were calculated. Hash sequence is generated by quantifying the correlation coefficients and then scrambling. For audio authentication procedure, a new method, similarity metric, was used to measure the distance of hashes, which is compared with the hamming distance method. Simulations show that the algorithm is robust against content-preserving manipulations such as re-sampling, MP3 compression, and so on. It is very sensitive to tamper of speech by similarity metric.
The traditional trajectories compression methods handle each trajectory individually, but it does not take into account the actual route situations, so it shows limited space performance. To solve this problem, the route network model is designed, and regulations of these trajectories are deeply explored. The main contributions include: 1) proposing the distance measure SRTD (shadow reference trajectory distance) which incorporates the space and time information of trajectories together; 2) proposing an algorithm called SDTC (SRTD distance based trajectory compression), which compresses dual-layer trajectories based on SRTD distance similarities. Experiments show that, compared with traditional methods, SDTC algorithm significantly reduces the storage consumption, and is of good precision.
A distributed cooperative caching strategy was proposed for content-centric networking, in which the popular contents can be cached and the distributed cooperation is allowed within the cache nodes to ensure a longer sojourn period of caching. By utilizing the tracker node, the location of cached contents can be found during the content request process. Moreover, the content requesters can acquire the contents from all cache nodes that participate in the cooperation to achieve the goal of distributed cooperative caching, so as to improve the utilization of cache resources in the network, and to reduce the average time of acquiring contents for the requesters. Simulation shows that the proposed strategy can reduce the average round trip time in the network effectively.
A compact dual-band bandpass filter was designed and developed based on asymmetrical stepped impedance resonators (SIR) for the realization of miniature dual-band bandpass filtering in mobile base station. The two central passband frequencies and bandwidths of the proposed filter can be adjustable by geometric parameters. A folded stepped impedance resonator modified by adding an inner quasi-lumped SIR stub was used as the basic module of a new configuration of dual-band bandpass filter to produce two different passbands. The first pass-band of the filter only depends on the dimensions of the external SIR, while the second passband depends on both the external SIR and the quasi-lumped stub. A dual-band filter operating at 0.9 GHz and 1.8 GHz was designed, fabricated and measured for the application of mobile phone base stations. The dimension of the proposed filter is 24.76 mm × 13.5 mm. The experimental results show that the measured S parameter fits very well with the simulation. The effectiveness of the proposed design method was validated.
A 3-5 GHz ultra-wideband (UWB) low noise amplifier based on common source (CS) with inductive-source and quarter-wave impedance convertor was proposed. The quarter-wavelength impedance convertor provides wideband input matching without noise figure (NF) degradation. The proposed UWB low noise amplifier was verified and implemented with packaged GaAs PHEMT device for 3.1-5 GHz UWB system. The measurement demonstrates a 12±1.5 dB in-band gain, a minimum NF of 1.8 dB. Good input and output matching are obtained.
The trust evaluation is one of the key issues that need to be resolved in credible trust management for trust-based access control in open networks. Referring to the complexity of trust relationships in human society, some relevant concepts on trust and proposes a dynamic comprehensive trust evaluation method for open networks was introduced. This method establishes a trust-based access control framework and introduces a balanced weight factor in trust evaluation to solve the problem for determining the weights between direct trust which includes historical information to improve accuracy and recommendation trust which includes the bonus-penalty factor as well as the reliability of evaluation to improve reliability and efficiency. Experiment shows that the proposed method can achieve certain robustness and better dynamic self-adaptability.
As a result of Contourlet transform can be effectively applied in the field of image enhancement, the characteristics of Contourlet transform in image fusion algorithm has been widely attention. Remote sensing image fusion algorithm based on Contourlet transform always utilize frequency domain linear weighted and swap high frequency to low frequency. By particle swarm optimization algorithm,the different weighting coefficients of different sub-band image by Contourlet transform is optimization. Using multivariate analysis method to set the objective function realizes the panchromatic image and multispectral image fusion. Compared with traditional Contourlet transform, (principal component analysis) algorithm, high-pass filter for remote sensing image fusion algorithm,the new algorithm with improving the definition of image have obvious advantages in terms of spectral fidelity than other methods.
In high-speed circuit, crosstalk is one of the bottlenecks hindering system rate to continue rising. In a 50-Ohm bus, with a spacing equal to the line width, 95% of all the crosstalk on any victim line comes from the nearest two traces on either side of the victim line. However, the current methods only consider the crosstalk from the first nearest traces, which means the crosstalk can be suppressed 75% at most. In order to solve the crosstalk from the second nearest traces, a new circuit structure was proposed, in which the position and the number of inverters could be changed according to the principle of crosstalk phase cancellation to suppress the crosstalk from the nearest two traces at same time. Simulation shows that in range of 0.1~4 GHz, far crosstalk from the second nearest trace can be eliminated about 10 dB.
Due to the shortages of the analytical model and simulation model, hierarchical stochastic colored Petri net has been proposed to model the media access control layer of IEEE 802.11p, which is used for investigating the broadcast performance of vehicular ad hoc networks. The proposed model has been used to describe the generation, retransmission, backoff and internal collision process. Then, the performance metrics have been simulated and analyzed. The results show that the higher priority access category has the shorter time delay and delay jitter. Moreover, the operation of the IEEE 802.11p can be intuitively understood by using the hierarchical stochastic colored Petri net(HSCPN) model, which is helpful for the protocol improvement, and it can also provide theoretical basis for the deployment of VANETs.