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Search Results: 1 - 10 of 9825 matches for " Lichun BAO "
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UWB-Based Localization in Wireless Sensor Networks  [PDF]
Di WU, Lichun BAO, Renfa LI
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2009, DOI: 10.4236/ijcns.2009.25046
Abstract: Localization has many important applications in wireless sensor networks, such as object searching and tracking, remote navigation, location based routing etc. The distance measurements have been based on a variety of technologies, such as acoustic, infrared, and UWB (ultra-wide band) media for localization pur-poses. In this paper, we propose UWB-based communication protocols for distance estimation and location calculation, namely a new UWB coding method, called U-BOTH (UWB based on Orthogonal Variable Spreading Factor and Time Hopping), an ALOHA-type channel access method and a message exchange protocol to collect location information. U-BOTH is based on IEEE 802.15.4a that was designed for WPANs (wireless personal area networks) using the UWB technology. We place our system in coal mine environ-ments, and derive the corresponding UWB path loss model in order to apply the maximum likelihood esti-mation (MLE) method to compute the distances to the reference sensors using the RSSI information, and to estimate the coordinate of the moving sensor using least squares (LS) method. The performance of the sys-tem is validated using theoretic analysis and simulations. Results show that U-BOTH transmission technique can effectively reduce the bit error rate under the path loss model, and the corresponding ranging and local-ization algorithms can accurately compute moving object locations in coal mine environments.
Scheduling Heterogeneous Wireless Systems for Efficient Spectrum Access
Bao Lichun,Liao Shenghui
EURASIP Journal on Wireless Communications and Networking , 2010,
Abstract: The spectrum scarcity problem emerged in recent years, due to unbalanced utilization of RF (radio frequency) bands in the current state of wireless spectrum allocations. Spectrum access scheduling addresses challenges arising from spectrum sharing by interleaving the channel access among multiple wireless systems in a TDMA fashion. Different from cognitive radio approaches which are opportunistic and noncollaborative in general, spectrum access scheduling proactively structures and interleaves the channel access pattern of heterogeneous wireless systems, using collaborative designs by implementing a crucial architectural component—the base stations on software defined radios (SDRs). We discuss our system design choices for spectrum sharing from multiple perspectives and then present the mechanisms for spectrum sharing and coexistence of GPRS+WiMAX and GPRS+WiFi as use cases, respectively. Simulations were carried out to prove that spectrum access scheduling is an alternative, feasible, and promising approach to the spectrum scarcity problem.
Scheduling Heterogeneous Wireless Systems for Efficient Spectrum Access
Lichun Bao,Shenghui Liao
EURASIP Journal on Wireless Communications and Networking , 2010, DOI: 10.1155/2010/736365
Abstract: The spectrum scarcity problem emerged in recent years, due to unbalanced utilization of RF (radio frequency) bands in the current state of wireless spectrum allocations. Spectrum access scheduling addresses challenges arising from spectrum sharing by interleaving the channel access among multiple wireless systems in a TDMA fashion. Different from cognitive radio approaches which are opportunistic and noncollaborative in general, spectrum access scheduling proactively structures and interleaves the channel access pattern of heterogeneous wireless systems, using collaborative designs by implementing a crucial architectural component—the base stations on software defined radios (SDRs). We discuss our system design choices for spectrum sharing from multiple perspectives and then present the mechanisms for spectrum sharing and coexistence of GPRS+WiMAX and GPRS+WiFi as use cases, respectively. Simulations were carried out to prove that spectrum access scheduling is an alternative, feasible, and promising approach to the spectrum scarcity problem.
New Channel Access Coordination Functions in Large Scale Wireless LAN Systems
Lichun Bao,Shih-Hsien Yang
Network Protocols and Algorithms , 2009,
Abstract: Large-scale wireless LAN systems based on the IEEE 802.11 standards have become the most successful wireless networks deployed in large organizations, such as educational campuses and corporate warehouses. However, the suite of IEEE 802.11 MAC protocols, including DCF, PCF and EDCA mechanisms, was unable to meet the challenges to provide collision freedom and differentiated quality of services. We propose a channel access scheduling protocol based on Latin squares, called DCLASS (Distributed Coordination based on LAtin SquareS), that provisions a set of highly desirable features to large scale wireless networks with stringent performance demands. DCLASS is scalable, fair, and co-exists with IEEE 802.11 nodes with traditional DCF mechanisms. The performance of DCLASS is evaluated using an IEEE standards compliant simulation toolkit, QualNet 4.5, in distributed WLAN systems. The experiment results show the near-optimum performance of DCLASS in contrast to IEEE 802.11 DCF under various scenarios.
Computational Time-Division and Code-Division Channel Access Scheduling in Ad Hoc Networks
Lichun Bao,J.J. Garcia-Luna-Aceves
Journal of Networks , 2008, DOI: 10.4304/jnw.3.8.26-34
Abstract: Using two-hop neighborhood information, we present the hybrid activation multiple access (HAMA) protocol for time-division channel access scheduling in ad hoc networks with omni-directional antennas. Different from other approaches, HAMA is a node-activation channel access protocol that also maximizes the chance of link activations using time- and code-division schemes. The throughput and delay characteristics of HAMA in randomly-generated multihop wireless networks are studied by analyses and simulations. The results of the analyses show that HAMA achieves higher channel utilization in ad hoc networks than previous similar works, namely, the node activation multiple access (NAMA), the link activation multiple access (LAMA) and pair-wise link activation multiple access (PAMA). In addition, HAMA achieves better throughout than an existing scheduling algorithm based on complete topology information, and much higher throughout than the ideal CSMA and CSMA/CA protocols. The main contribution of this work is to computationally derive channel access schedules according to local network topology information instead of on-demand negotiations or static global coordinations.
Stock Selection Based on a Hybrid Quantitative Method  [PDF]
Lichun Tang, Qimin Lin
Open Journal of Statistics (OJS) , 2016, DOI: 10.4236/ojs.2016.62030
Abstract: Quantitative stock selection has become a research hotspot in the field of investment decision. As the data mining technology becomes mature, quantitative stock selection has made great progress. From the perspective of value investment, this paper selects top 200 stocks of A share in terms of market value. With the random forest (RF), financial characteristic variables with significant impact on SVR are screened out. At the same time with quantum genetic algorithm (QGA) superior to the traditional genetic algorithm (GA), SVR parameters are deeply and dynamically sought for, so as to build the RF-QGA-SVR model for year-to-year stock ranking. The quantitative stock selection model is built, and the empirical analysis of its stock selection performance is conducted. The conclusion is as follows: 1) Optimizing SVR with QGA has higher precision than the traditional genetic algorithm, and is more excellent than the traditional GA optimization; 2) SVR after RF optimization of characteristic variables more significantly improves the accuracy of stock ranking and prediction; 3) In the stock ranking obtained from the RF-QGA-SVR model, the yields of top stock portfolios are much higher than the market benchmark yield. At the same time, the yields of the top 10 stock portfolios are the highest, and the top 30 stock portfolios are the most stable. This study has positive reference significance on quantitative stock selection in the field of quantitative investment.
A Study on Design of Enterprise Internal Control System
Lichun Wu
International Journal of Business and Management , 2009,
Abstract: Increased attention has been devoted to enterprise internal control system by academe and business world. The main reasons for this can be divided into two aspects: first, it is a result of compulsion by relating laws and regulations, for example, Accounting Law attaches much importance to the establishment of enterprise internal control system, Internal Accounting Control Criteria and Several Regulations Concerning the Reinforcement of Accounting Control on Money Capital issued by Ministry of Finance as well as the Regulation of Public Information Disclosure for Securities Companies issued by China Securities Regulatory Commission all make hard rules for enterprises to establish and improve their internal control systems; secondly, internal control system is propitious to the internal management of enterprises so as to help them achieve the aims of high efficiency and measuring up to standards. Design of enterprise internal control system is the conundrum and end result of study on internal control of enterprises, so this paper probed into the design of enterprise internal control system based on the fact that most Chinese enterprises have no strict internal control system or have poorly performed internal control.
Similarity Form, Similarity Variational Element and Similarity Solution to (2+1) Dimensional Breaking Solition Equation
Lichun Pu
Journal of Mathematics Research , 2012, DOI: 10.5539/jmr.v4n4p81
Abstract: In this paper, the thoughts and methods of ordinary deferential equation of dimensional non-linear partial deferential equation with (2+1) dimensional non-linear partial deferential equation will be analysed first, then the authors deduce the universal similarity form and similarity variational element of (2+1) dimensional breaking solution equation and its suitable deferential equation and find the similarity solition to (2+1) dimensional breaking solition equation.
New evolution: Inhibitors of fatty acid synthase and fat-reducing study
Lichun Li,Weixi Tian
Chinese Science Bulletin , 2002, DOI: 10.1007/BF02901308
Abstract:
Application of Nonlinear Mixed-Effects Modeling Approach in Tree Height Prediction
Lichun Jiang,Yaoxiang Li
Journal of Computers , 2010, DOI: 10.4304/jcp.5.10.1575-1581
Abstract: A nonlinear mixed-effects modeling approach was used to model the individual tree height–diameter relationship based on Chapman-Richards function for dahurian larch (Larix gmelinii. Rupr.) plantations in northeastern China. The study involved the estimation of fixed and random parameters, as well as procedures for determining random effects variance-covariance matrices to reduce the number of the parameters in the model. The mixed-effects model provided better model fitting and more precise estimations than the fixed-effects model. Techniques for calibrating the height-diameter model for a particular plot of interest were also explored. The greatest reductions in bias and root mean square error (RMSE) were obtained when comparing the calibration from one randomly selected tree with the calibration from two randomly selected trees. Substantial reductions were obtained with the inclusion of two randomly selected trees, which could reduce the bias and RMSE of the predictions by almost 73% and 63%, respectively. An important characteristic of mixed-effects models is that they permit both mean response prediction and calibrated prediction. The fixed-effects parameters alone can be used to obtain the mean response prediction. More accurate estimates can be obtained by calibration for individual prediction.
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