- EI核心期刊
Network capacity region is an important character of mobile Ad hoc networks. Using cell-partitioned model, an expression of upper bound of delay-tolerant hybrid mobile Ad hoc network is deduced regardless of coverage of base stations, types of mobile process, scheduling and routing algorithms. The limitation of the upper bound is derived, Analysis of the limitation of upper bound is carried out when the steady-state follows even-distribution law. The relationship among limitation of capacity, the node density and coverage of base station is analyzed.
The problem of key update in sensor network is its slow update, wide range update and energy consumption. In response to these issues, a method of two level key renewal theories is proposed. By update methods, a unicast mode is used between base station and cluster head. The update is unique and different for each cluster head while the polynomial broadcast mode is used between cluster heads and normal nodes. The new method is drawn from slot authentication, it generates the session key by storing key, and has no additional storage overhead. Besides, this method reduces polynomial orders and computation amount of nodes, updates the exposed key quickly, ensures unchanged of key pool size, guarantees the good connectivity of network, and extends the network lifetime at the same time as well. Simulation shows that this method improves the key update speed, and the energy consumption becomes bearable.
To reduce the computational overhead of large-scale network simulation while keeping the simulation fidelity, a network simulation method of focusing on the attention area is presented in which the network topology for simulation is partitioned into two parts: attention area and non-attention area. To keep fidelity, the attention area is simulated by discrete event simulation. And to reduce the computational overhead, the non-attention area is simulated by topology - flow combined abstraction simulation. The simulation fidelity of topology-flow combined abstraction simulation is analyzed. Experiments based on NS2 show that, when the focusing coefficient is 4, compared to the traditional network simulation, this method can decrease the computational overhead of simulation by over 85% at most, also, the average error of simulation results of attention area is only about 2%.
Since there exist redundant sequential patterns in results, such mining runs for a long time. To combat this drawback, a new algorithm, called closed sequential patterns mining algorithm in time order (CloTSP),is proposed. Based on the nature of closed sequential patterns, CloTSP can judge whether a frequent sequential pattern is extended by comparing its time order with each frequent 1-item subsequence. Experiments on the synthetic data produced by International business machines corporation sequential pattern generator show that CloTSP can shorten run-time significantly compared to closed sequential pattern mining (CloSpan). Furthermore, it is also shown that the run-time of CloTSP is not affected by variation of attribute numbers.
A parameter-change maximization sampling method is proposed to capture new user's preference in recommender system. This method produces an item list that maximizes model parameter change based on pure singular value decomposition (PureSVD). By querying new user with specific item list, the ratings are obtained for training the corresponding user's parameter in PureSVD model, it performs prediction for new users in return. A greedy approximation algorithm is presented to produce the item list with an acceptable time bound. Experiments show that the method can learn new user's preference efficiently with small sample size under Top-N metrics.
A two-phase cooperative transmission protocol based on best-relay selection for primary system is proposed in cognitive radio network, which consists of a primary transmitter-receiver pair and K secondary transmitter-receiver pairs. In the proposed protocol, with the transmission quality of service (QoS) constraints of secondary users, one of the secondary users coexisting in the same spectrum as the primary can be selected to serve as a decode-and-forward relay for primary system. The selection criterion is to maximize the ratio of signal to interference plus noise for the primary system. The outage performance of the primary system is analyzed. Simulation confirms that the efficiency of the proposed spectrum sharing protocol, i.e., the primary performance is improved. Meanwhile, the access opportunity for secondary users can be also guaranteed. In addition, it is indicated that the primary user can achieve better outage performance as K increases.
A concept concerning correlation properties of superposition sequences is proposed. And so, an optimized selection method is proposed based on analysis of correlation properties of superposition sequences for Gold sequences. According to the property of the relatively large multiple peaks of the cross-correlation functions, the smaller cross-correlation characteristic peak values of superposition sequences are optimized to decrease mutual interference of superposition sequences in asynchronous system. It is shown that the bit error probability is lower than that of non-optimized selection Gold sequences in additive white Gaussian noise channel of the asynchronous system.
In order to decrease the carbon emission and operator expenditure induced by energy consumption of wireless communication networks, a power allocation scheme achieving optimal energy efficiency is proposed for downlink multiple-input multiple-output system. An energy efficient model is formulated based on realistic power consumption model and beam forming. The existence of unique globally optimal energy efficiency is proved, and the closed-from of the optimal energy efficiency is derived depending on channel state information. Based on the closed-form result, an iterative algorithm achieving optimal energy efficiency adaptively is developed. Simulation shows that the proposed scheme can improve the energy efficiency and spectrum efficiency. Meanwhile, increasing the number of antennas and shrinking cell radius are two important measures to enhance the energy efficiency and the spectrum efficiency.
The traditional web service description language (WSDL) is limited in describing the increasing and changing of dynamic wireless sensor network (WSN) services. The services with similar input and output (IO) interface cannot be distinguished, and thereafter the burden of WSNs for service storage and retrieval is increased. To solve this problem, the WSDL is extended with a service IO relationship characterization based on the logic expression. Accordingly, a service similarity calculation based on Google semantic distance, Levenshtein edit distance and a service IO match algorithm are proposed. Experiments show that the proposed approach can effectively distinguish the services with similar IO and accordingly improve service retrieval efficiency in WSNs.
A composite controller is designed based on the singular perturbation model of one-link flexible manipulators. A dynamic sliding mode controller is designed for the slow subsystem, and optimal controller is designed to stabilize the fast subsystem. Numerical simulation results confirm that the proposed controller not only can perform fast and accurate tracking, but also can reduce the chattering of the sliding-mode control, and the proposed controller can suppress the tip vibration of the flexible manipulators effectively.
A new blind maximum Doppler frequency estimation algorithm is proposed based on channel frequency response envelope power spectral density (PSD) in orthogonal frequency division multiplexing systems. The subcarriers modulated by constant-envelope modulation are utilized. The PSD of received subcarriers magnitude is estimated by classic periodogram method. The maximum Doppler frequency is derived by searching the edge of envelope PSD and noise PSD. It does not need channel estimation used in conventional PSD method. Simulation shows that the estimation precision is increased and the performance is robust in a wide range of Doppler spread values.
The joint maximum likelihood detection (JMLD) in application to non-orthogonal forwarding protocol has higher detection time complexity and poorer detection performance. A new detection method is proposed. The diversity gain of strong signal frame is obtained by maximal ratio combining and detected in advance. The detection result is thereafter used to eliminate interference to weak signal frame. At last, the weak signal frame is detected. Analysis and simulation show that, comparing with JMLD, the proposed method reduces the detection time complexity effectively and improves the bit error performance. The bit error rate of analysis and simulation value tends to be consistent at high signal-to-noise ratio.
To improve the precision of received signal strength indicator(RSSI)wireless localization in traditional indoor positioning technology, using simplex sampling and covariance correction, a method of coordinate position and channel parameter simultaneous estimation is presented based on iterated unscented Kalman filter (IUKF) algorithm. Due to the complexity of indoor environment, there exists a big noise in RSSI signal, so the raw data is calibrated by using kernel smoother. The RSSI localization problem is conveyed into the optimal estimation problem of nonlinear equations. Simulation indicates that SIUKF algorithm has higher estimation accuracy compared with extended Kalman filter (EKF) and unscented Kalman filter (UKF). It shows strong robustness, and the computational complexity is appropriated. The accuracy up to 0.65m is obtained with the proposed method and can meet the needs of indoor positioning.
Limited feedback interference alignment quantizes channel state information to reduce the amount of information of feedback. But classic limited feedback interference alignment algorithms only quantize the channel state information, and limited to theoretical analysis. Considering that the precoding matrix has much greater feedback data than channel state information. A new distributed interference alignment algorithm based on grassmannian codebook is proposed in view of reducing the impact of precoding matrix on feedback channel in distributed interference alignment, precoding matrices and decoding matrices are quantized based on grassmannian codebook, and are optimized for minimizing the interference leakage. The simulation results show that compared with the perfect feedback, when the signal noise rate of transmitters is less than or equal to 15 dB and the numbers of iteration are less than or equal to 10, the algorithm presented in the paper can effectively decrease the feedback data while the capacity close to the system with perfect channel state information.
Widely used in data-intensive computing, the MapReduce model deploys computing to the data side so as to execute in parallel. On this occasion, data layout will not only affect the storage itself, but also affect the computing efficiency. Computing efficiency of node is determined by features of data stored on this node. Therefore, the study on load balancing is accordingly shifted from traditional server management or task scheduling to study of data layout as a purpose to improve parallelism. The data layout characteristics in data-intensive computing and MapReduce environment is analyzed, a load-balanced goal of data layout is proposed, and a load-balanced data layout approach in a specific environment is presented as well. The proposed data layout goal and approach are proved effective through experiments. It is shown that the proposed data layout approach can effectively improve the parallelism of MapReduce applications, thus optimizing the computing efficiency.
A cross-lingual pseudo relevance feedback model based on bilingual topics is proposed for cross language information retrieval task. The latent Dirichlet allocation (LDA) model is extended to the bilingual topic model, each topic could generate a source language token and a target language token. A strategy on how to choose topics and words for cross language query expansion is given, and the secondary retrieval is performed on the basis of the refined query translation. Experiments show that this model outperforms monolingual LDA-based feedback method as well as classical techniques based on vector space model.
Considering that the channel capacity sharply declines when the array element spacing is relatively small and the average direction of arrival (DOA) is large in multiple-input multiple-output (MIMO) antenna array, a new MIMO receiving antenna model is put forward based on Y-shaped array structure. Utilizing equivalent network model of antenna array's mutual coupling effects, the general closed form expressions is deduced for correlations of Y-shaped array mode and mutual coupling so as to clarify the relations between the correlation with its array mutual coupling effects and the correlation without mutual coupling effects. The influences of incident signal's central DOA and angular spread on the channel capacity of Y-shaped array MIMO is analyzes respectively. Comparing with analysis and performance of MIMO circular array receiving antenna, it is found that Y- shaped MIMO antenna array is of a relatively stable channel capacity and better than that of the circular antenna array. It can effectively improve the array mutual coupling effects so as to enhance the system performance.
The current dispatching schemes for memory-space-memory (MSM) Clos-network switches provide 100% throughput under admissible traffics but with higher algorithm complexity. A low-complexity and distributed scheduling algorithm, called randomized weight matching dispatching scheme (RWMD), is proposed. Under this approach, each input module balances requests among central modules, and each central module can carry out scheduling algorithm concurrently and independently, where the memory and the randomness of the arrival process are used for matching. With single iteration and less information exchange between stages, RWMD reduces the communication overhead greatly. Simulation shows that RWMD can achieve 100% throughput under uniform and non-uniform traffics.
An improved space-time coded transmission scheme with limited feedback is proposed in order to eliminate interference for two-user multi-input multi-output multiple access channels (MIMO-MAC). Each user employs rate-2 space-time block code with phase rotation, which requires a phase feedback. The multiuser interference is eliminated through simple addition of the received signal, and full diversity is realized. The signal to noise ratio is increased in the proposed scheme and the system performance is improved compared with the existing space-time coded transmission scheme with limited feedback.
The regenerative Hash key chain mechanism is adopted for the secure routing protocol named as secure efficient distance vector routing (SEAD) in Ad hoc networks in order to enhance the security performance. Based on (t, n)-threshold scheme, a new regenerative Hash chain method is designed, in which as the sender sends one key value of the current Hash chain, and then it sends a shadow of public key of the new Hash chain as following. This method effectively verifies the signature of the tail value of the new Hash chain after receiving total t key values of the old Hash chain and simultaneously makes the new Hash chain to be used correctly continuing to ensure the routing protocol's security and reliability. Compared with the two methods proposed by Zhao Yuanchao, NS-2 simulation shows that the method has higher security and success rate on transmission of cbr packets, makes some improvements on energy consumption at the same time.
To evaluate the influence of X2 interface time delay in long term evolution-advanced (LTE-A) system, we establish the channel model with time delay and conduct the system level simulation of three typical coordinated multipoint transmission/reception(CoMP) schemes. Finally, we evaluate the system performance at different time delay with different complexity of negotiation. It can be seen that the system performance will degrade with time delay increasing and the system will be more sensitive to delay when the negotiation becomes more complex. What's more, if the X2 interface time delay grows to a certain threshold, it's better not to apply CoMP in LTE-A system.
Sensor data is modeled and Gaussian sum particle filter method is used for probabilistic inference based on model-driven methods for saving energy. First, the correlations on different sensor nodes and constructed probabilistic models from historical data are exploited. Then, the particle filter method is adopted to infer values for one sensor node from values acquired from real world by other sensor nodes, which saves energy of sensors efficiently. Finally, according to the fact that the sensor data generally satisfies Gaussian distribution, Gaussian particle filters and Gaussian sum particle filters are utilized for probabilistic inference respectively. Experiments show that the proposed Gaussian sum particle filter method is of high accuracy and efficiency.
In wireless sensor networks (WSNs), the effective network organization and nodes deployment are essential to the network lifetime and the budget. A new network deployment with node alternate operation scheme is put forward to prolong the network lifetime and decrease the number of nodes. An accurate analytical non-linear battery model is presented for evaluating the energy consumption of nodes. Time division multiple address is applied for data transmission and reception between the nodes. Optical frequency shift keying is introduced, and the constellation size is optimized for node energy efficiency. Furthermore, non-uniform deployment with varied number of nodes in different layer is considered for network energy balance. Simulation shows that the proposed method requires less number of nodes for the network deployment and achieves longer network lifetime at meantime.