- EI核心期刊
A joint carrier offset estimation algorithm is proposed to combat the severe inter-symbol interference and sensitivity to the frequency and timing offset of multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM)wireless communication system. The proposed algorithm of carrier offset using flexible correlation and minimum mean square error (MMSE) rule improves the traditional carrier synchronization effects dramatically and has achieved precise estimation performance in the wireless MIMO-OFDM system structure. Analysis and simulations show that, the mean-square error estimation performance of the proposed algorithm can achieve 10-6 under a poor channel circumstance, which reveals that the joint estimation carrier frequency algorithm is suitable for the frequency bias estimation of wireless MIMO-OFDM communication system.
In order to protect the copyright of digital content, an authorization protocol of multimedia digital rights management based on proxy re-encryption is proposed. The proposed protocol allows content providers to encrypt multimedia content on their clients, and allows the users to share the encrypted multimedia content and apply license from license server. After obtaining the license, the users can apply the content encryption key from key proxy server. The key proxy server re-encrypts the content encryption key and sends the encrypted content encryption key to the users, while license server cannot get the content encryption key. Based on the proposed protocol, a content sharing platform for digital TV programs in cloud computing is developed. The comparison results and practical application show that the proposed protocol does not need to re-encrypt content when sharing, and can effectively resist the collision attacks, which is efficient and secure.
In order to authenticate low-cost tag and protect its privacy, a lightweight radio frequency identification mutual-authentication protocol is proposed. The proposed protocol takes advantage of HB# protocol with small amount of transmission and storage, combines with physically unclonable function to protect the tag from cloning, and updates the keys to prevent location tracking. Analysis shows that it realizes mutual-authentication between the reader and the tag, and not only inherits the security properties of HB# protocol, but also can resist clone attack, read memory attack and protect privacy. At the same time, the proposed protocol can also substantially reduce the reader's burden on searching keys.
Nowadays many researchers have proposed different methods to generate test data using genetic algorithm for a specified path.Existing methods primarily focus on the path coverage for sequential programs testing.An approach to construct the fitness function for test case generation in concurrent programs testing is provoked.This approach evaluates the fitness values of the test case by assessing the similarity between the path exercised by a generated input data and the target concurrent path.Algorithm for the fitness function is proposed.Studies indicate that this approach provides guidance for seeking the test case covering small probability target path, and generates fitness function for each target path automatically.
A scheme for efficient multiple signcryption on the conic curve over the ring Zn is presented based on multiple digital signature. The security of the proposed scheme is proved based on the two hard problems of large integer factorization and discrete logarithm on conic curve. As the signcryption and de-signcryption are calculated on conic curve, plaintexts can be embedded easily, and in inverse, the element order and points' operation on conic curve over can be calculated more simply and easily in the proposed scheme. Compared with the exiting scheme in efficiency, the proposed scheme is greatly improved in information computation.
In order to improve the performance of incremental amplify-and-forward cooperative communication systems, a new protocol based on competition scheme and automatic repeat request was proposed, in which the channel state information was estimated by using the feedback transmitted by the destination. The forward manner was determined by the competition between the source node and relay node in case of direct transmission unsuccessfully. The closed-form expression for the outage probability of the proposed scheme was derived in detail. In high signal-to-noise ratio (SNR) regime, the approximation of outage probability was given as well. Meanwhile, based on approximation analysis in high SNR regime, the diversity-multiplexing tradeoff and cooperative diversity were obtained. Analysis and simulation show that the performance of the considered system can be improved effectively in terms of outage probability when applying the proposed strategy to select the optimal forward manner.
An information fusion algorithm was proposed for using both global positioning system (GPS)/base-station positioning system to get high positioning accuracy. The system state was modeled by analyzing the movement features, and the federated Kalman filter was used to fuse the two systems. The effect of information distribution factor was analyzed. A distribution method was proposed by horizontal dilution of precision and carrier to noise ratio. The positioning accuracy was improved by using the proposed algorithm. Simulations and examinations show the effectiveness of the algorithm.
A solution is put forward that makes access point (AP) access into the primary user's channel in the identity of cognitive user under the precondition of guaranteeing primary user's quality of service, so as to share the channel resource of primary user effectively. It models the channel assignment as an integer linear programming issue and puts forward a hybrid optimal channel assignment algorithm (HOCA). Based on minimum spanning tree algorithm of connected weighted graph, the algorithm can allocate the minimum interfered channel for primary user and cognitive AP fast and efficiently in its own frequency band of primary user and cognitive AP. HOCA algorithm and other two channel assignment algorithms, near-optimal opportunistic channel allocation and near optimal frequency assignment-2 are analyzed. It is testified that HOCA algorithm can effectively improve the throughput of cognitive user.
For the problem of handoff service in high-speed railway communication (HSRC) systems prone to drop, a priority-based admission control (PB-AC) scheme is proposed, where adaptive resource reservation algorithm and spring-based resource preemption model are jointly adopted to guarantee handoff service dropping probability (HSDP) requirement. The adaptive resource reservation algorithm can dynamically reserve bandwidth resource for handoff service according to their traffic intensity. Under the condition of minimizing the influence of resource preemption on on-going service, the spring-based resource preemption model can enable handoff service to preempt bandwidth resource from on-going vary bit rate service to further improve HSDP performance. Simulation results show that the proposed PB-AC scheme can effectively improve HSDP performance while maintaining desirable new service blocking probability performance.
Using the available outdated channel quality indicator (CQI), an optimized long term evolution downlink resource allocation method is proposed. The key is a neural network based on CQI prediction model and algorithm, which can predict the current CQI from the outdated CQIs. The scheduler uses the predicted CQI to allocate radio resources and decide on proper modulation and coding scheme. Simulation shows that the proposed prediction model and algorithm have practical effects on solving the degradation of scheduling efficiency due to the outdated CQI.
In order to study the social network users' emotional behavior, the massive sina micro-blogging data is graded by emotional stage, and the group emotional behavior is analyzed as well. An emotional stage posting model is established and model simulation is done. Analysis shows that the posting amount of users obeys power-law distribution at a certain emotional stage, and the exponent increases as the emotional stage tends to calm. Most of posts are peaceful when users express emotion through the micro-blogging, and the user participation rates will also decrease when the intense emotions need to be expressed. In the emotional stage posting model, the impact of the around emotional environmental factors of the poster is considered, and also the randomly changing of poster's own emotion. Finally the previous experiments are verified by model simulation.
A joint transceiver optimization is proposed for downlink multiuser multiple-input multiple-output (MIMO) relay systems. The proposed method is based on minimum mean-square error criterion. Using high signal-to-noise ratio approximation, the error covariance matrix is decomposed into two individual error matrices, which leads to two simple problems for the optimization, the simple traditional MIMO optimization and the traditional multiuser optimization. Moreover, the closed-form solution of the source precoding matrix can be obtained. The decomposition greatly degrades the complexity of the joint transceiver design and mitigates the feedback overhead. Simulations verify the effectiveness of the proposed method.
Analyzing the relation among energy efficiency, spectrum efficiency, the number of antennas at the base station and cell radius is helpful to the parameter design of the practical communication system. When zero-forcing detector was adopted in the uplink massive multiple-input multiple-output system, the closed-form expression among energy efficiency, the spectrum efficiency, the number of receiving antennas and the cell radius were derived according to the realistic power consumption model. Further, the optimal energy efficiency, corresponding spectrum efficiency and power consumption were deduced based on the closed-form. It is shown that the setting up of rational spectrum efficiency, the deploying of more receiving antennas at the base stations and the shrinking of cell radius are three key measures to enhance the system energy efficiency.
The selection of relay node will directly affect the data forwarding performance of opportunity network. Therefore the cost-efficient routing mechanism with delivery probability perception (DPP-CERM) in opportunistic networks is proposed. The probability of comprehensive encounter between nodes by combining the probability of direct encounter and indirect encounter is estimated and evaluated by indirect inter-meeting time between nodes. The relay node reasonably and forward data with very lower cost were chosen thereafter. It is shown that DPP-CERM can reduce the average overhead ratio of data forwarding at least 64.9%.
The anomaly detection methods based on measurement attributes relationship analysis is proposed. The correlation between the measurement attributes in space grid structure is calculated, and hereby the relationship network model of measurement attributes is established. The network segmentation method is put forward based on hidden Markov model. The anomaly detection algorithm for distributed systems is designed by using the newest monitoring attributes correlation. The anomaly detection experiments demonstrate the effectiveness of the proposed method.
A packet-level variable service rate queuing system is established to model the process that the long-term evolution (LTE) network works for heterogeneous services traffic. The system reflects packets switching and variable service rate of LTE. The main research target is to explore the way that heterogeneous services share a common server. Heterogeneous services can be divided into two types, human to human (H2H) services and machine to machine (M2M) services. Based on network of LTE and its service characteristics, two queuing models MMPP/M/1/KM+ARQ and M/M/1/KH are established to depict different LTE network services under M2M and H2H traffic arrival respectively. Two kinds of services sharing the same server and the service process are controlled by the queue length threshold of H2H queue. The average service rate changes exponentially or in a linear fashion, while the total service rate remains constant. By deducing three-dimensional Markov chain and generator matrix of queuing system, the queuing model is solved. Algorithm simulation shows the system performance in several circumstances, including different service modes and different burst features of M2M arrival.
Due to high flexibility to different channels, fountain codes with hard-decoding algorithm are used in many applications such as the board-band Internet. However, hard-decoding suffers from the delay and jitter caused by the randomness of encoding. The delay and jitter were minimized with analysis and computational optimization. Firstly, expressions of delay and jitter determined by degree distribution were deduced under any erasure probability. Secondly, several short-length fountain codes with small delay and jitter were developed from previous work through simulation and optimization. As a significant improvement, two raptor codes with length at 1 024 will offer minimized delay and jitter as 9.56% and 3.22%.
The extra-high frequency measurement is a hot issue of research in the field of current international time-frequency measurement and control. Aiming at difficult measurement and uncertain precision of extra-high frequency in time and frequency measurement domain and combining time and space conversion relations, an extra-high frequency measurement in picoseconds was proposed. Utilizing different frequency phase detection principle, a precise short time interval measurement was changed into the measurement of frequency. By introducing conversion relations of the time and space and using stability of signal delay in the course of transmission, a phase difference of delay time was obtained based on measuring space length value. Furthermore, an extra-high frequency measurement could be achieved in the proposed method. Experiment shows that the measurement resolution of 10-12 within 1 s can be reached in radio frequency range. Comparing the traditional frequency measurement method, the proposed method features simple structure, low cost and high measurement precision.
A risk assessment approach for threat scenario (TS) was proposed. Firstly, hierarchical index system of venture evaluation was constructed for TS, and a new index called uncontrollability was proposed to describe the uncontrollability of relationship between safety measures and risk formation, meanwhile, integrality of index system was enhanced. Secondly, membership function of indicators based on Gaussian function was defined, thereafter, an improved fuzzy comprehensive evaluation model based on membership matrix constructor method was given to reduce the influence of subjective factors. Finally, a combining method of fuzzy algorithm above and analytic hierarchy process were adopted to calculate the degree of risk quantitatively. The case study shows that this method is beneficial to risk size sort.
Power allocation was formulated as the system capacity maximization problem and a strategy to solve the problem in its equivalent form was proposed. Based on genetic algorithm and particle swarm optimization, the path loss threshold to select the cooperative base stations for each user and maximize system capacity was set by the proposed power allocation strategy. Numerical results show that when the number of mobile users is 100, the proposed power allocation strategies based on genetic algorithm and particle swarm optimization will increase system capacity about 5.25 bit·s-1·Hz-1 and 7.38 bit·s-1·Hz-1 in the same conditions of adopting equal power allocation of multi-base cooperative communication system, respectively. Moreover, the algorithm performance of power allocation strategy based on particle swarm optimization is better than the power allocation strategy based on genetic algorithm.
Certificate-based cryptosystem combines the merits of public key infrastructure (PKI)-based cryptosystem and identity-based cryptosystem, which can not only simplify the public key management, but also avoid the key escrow problem. A certificate-based signature scheme without pairing is analyzed, and shown to be forgeable by a type Ⅱ attacker. In the proof, there exists a security flaw, which is improved by means of binding random number to hash function. The improved scheme is proven to be unforgeable in the strongest security model of certificate-based signature scheme under discrete logarithm assumption. Without any time-consuming bilinear pairing operations, it shows efficient and applicable to power-constrained devices, such as wireless sensor networks.
A relay node selection strategy was proposed to improve the long-term throughput and extend the lifetime of system. Based on decode-and-forward relay protocol, the secondary user was pretended as a relay node of the primary system to assist the primary user pair to communicate. Meanwhile, data transmission for the secondary system was achieved. The proposed strategy introduces three factors, i.e. the transmit power required for each data transmission, the remaining energy of relay nodes as well as the probability of system outage. Therefore, the long-term throughput can be improved and the lifetime of system can be extended effectively.
An algorithm was proposed, which can choose secondary users and estimate signal to noise ratio (SNR) in order to improve the accuracy of cooperative spectrum sensing. The algorithm constructs a correlation matrix by means of the related characteristics of the signals of secondary users. According to the properties of matrix elements, some parameters of channels, e.g. ratio of channels gain, SNR and variance of noise were estimated. The realization of the algorithm was only based on the sampled signals of secondary users without any prior knowledge of primary users. The number of secondary users must be greater than three in cooperative spectrum sensing network. Simulations testify the effects of the algorithm about SNR and the ratio of channel gain.