Chunfeng Lv

Performance Evaluation of IEEE 802.15.4 CSMA/CA Scheme Adopting a Modified LIB Model

Since the successful release of the IEEE 802.15.4 standard, a great convenience is offered to applications in low-power and low-rate wireless sensor networks (WSNs) which almost touch upon all aspects in our surrounding circumstances. For time-critical applications, we use a modified Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism called Linear Increase Backoff (LIB) to enhance the performance of packet delay, but not compromise the metrics of energy efficiency and throughput. An accurate and comprehensive Markov model is used to analyze the characteristics of our LIB scheme predicting packet delay, energy consumption and throughput of unsaturated, unacknowledged IEEE 802.15.4 networks in which the unsaturated state is dependent on the traffic condition rather than the depiction by a predetermined length. Simulation results are consistent with the predictions of this model. We also compare the performance of LIB with that of several mechanisms according to the optimal parameters selected from operating point, and find that packet delay is obviously superior to that of other schemes, while energy efficiency and throughput are superior to others for large number of nodes and high traffic arrivals.

Delay Analysis for IEEE 802.15.4 CSMA/CA Scheme with Heterogeneous Buffered Traffic

Analysis of IEEE 802.15.4 CSMA/CA scheme with homogeneous or saturated traffic has received considerable attention recently since a great convenience is offered to applications of low-power and low-rate wireless sensor networks (WSNs) which almost touch upon all aspects of our life. In this paper, we propose a stochastic analysis approach to evaluate the delay performance of CSMA/CA scheme with heterogeneous buffered traffic which is more realistic in our applications. We adopt two modified semi-Markov chain with a macro-Markov chain to present the CSMA/CA process and the theory of queues to character the buffered condition, which are used to evaluate characteristics of our time-critical networks. Packet delay of unsaturated, unacknowledged IEEE 802.15.4 beacon enabled networks is predicted based on these models. Moreover, the impacts of different parameters such as the packet arrival rate, packet size, node’s buffer size and the number of different kinds of nodes are presented in this paper. Comprehensive simulation results are consistent with the predictions of these models.

Analytical modelling for edge effects and impedance characteristics of the transverse eddy current displacement sensors with rectangular coils

Analytical method for eddy current evaluation is an attractive field of learning the concept of electromagnetic phe- nomena. This paper proposes an analytical approach to a transverse eddy current displacement sensor with a rectangular testing coil. Solving domain in the Cartesian coordinate system is limited to finite extents through imposing artificial boundaries at x and y axis, and solutions to the electromagnetic field are expressed as double series. Complete closed-form expressions based on second order vector potential for the electromagnetic field in each region can be obtained from the continuity conditions at the interfaces by mode matching. Closed-form expressions of the eddy current density as well as coil impedance related to the transverse displacement can thus be derived, and the calculated results show good agreement with the experimental results.

Performance improvement for IEEE 802.15.4 CSMA/CA scheme in large-scale wireless multi-hop sensor networks

The hidden-terminal problem and routing establishment or maintenance bring about a tremendous amount of energy consumption in multi-hop wireless sensor networks (WSNs). In this study, the authors propose a carrier sense multiple access with collision avoidance (CSMA/CA) scheme MultiCSMA for multi-hop WSNs adopting two strategies which refer to a novel hidden-terminal list algorithm to avoid the impact of hidden terminals and a parallel access scheme to dispense with taking the routing overhead into account. The accurate statistical performance metrics of throughput and delay of unsaturated, unacknowledged IEEE 802.15.4 beacon enabled networks for one-hop and two-hop scenarios are predicted based on Markov models adopting these two improved strategies, in which nodes are assumed to locate randomly over a circle plane according to Poisson distribution. Comprehensive simulations demonstrate that the analysis results match well with the simulation results, and delay performance of the authors schemes is superior to those of other schemes, whereas throughput is superior to others for relative higher node density.

Analytical Modeling for the Grating Eddy Current Displacement Sensors

Abstract As a new type of displacement sensor, grating eddy current displacement sensor (GECDS) combines traditional eddy current sensors and grating structure in one. The GECDS performs a wide range displacement measurement without precision reduction. This paper proposes an analytical modeling approach for the GECDS. The solution model is established in the Cartesian coordinate system, and the solving domain is limited to finite extents by using the truncated region eigenfunction expansion method. Based on the second order vector potential, expressions for the electromagnetic field as well as coil impedance related to the displacement can be expressed in closed-form. Theoretical results are then confirmed by experiments, which prove the suitability and effectiveness of the analytical modeling approach.

Performance Analyses and Improvements for IEEE 802.15.4 CSMA/CA Scheme in Wireless Multihop Sensor Networks Based on HTC Algorithm

Most of analyses for the IEEE 802.15.4 Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme for multi-hop wireless sensor networks (WSNs) focus on how to avoid the impacts of hidden terminal problems rather than how to derive the exact multi-hop characters. In this paper, we propose a novel analysis model to analyze and improve the behaviors of multi-hop WSNs touching upon both avoiding the impacts of hidden terminals and acquiring the exact multi-hop behaviors. At first, a novel Hidden Terminal Couple (HTC) algorithm is proposed to avoid the impacts of hidden terminals, and a parallel access scheme is proposed to dispense with taking the routing overhead into account. Along with these two strategies, the accurate statistical performance metrics of throughput and delay of unsaturated, unacknowledged IEEE 802.15.4 beacon-enabled networks for 1-hop and 2-hop scenarios are then predicted based on the models which contains n modified semi-Markov chains and one macro-Markov chain, in which nodes are assumed to locate randomly over a circle plane according to Poisson distribution. Moreover, performance comparisons between our scheme (called HTC scheme) and other multi-hop CSMA/CA schemes which involve hidden terminal avoiding are also proposed. Comprehensive NS-2 simulations demonstrate that the analysis results of these models match well the simulation results, especially for larger transmission range and relatively higher node density. Besides, the analysis and comparison results show that delay behavior of HTC is improved largely relatively to other schemes, while throughput performance is improved in some cases of more node density and larger transmission range.

A new analysis model for IEEE 802.15.4 MAC with heterogeneous unsaturated conditions

Since the successful release of IEEE 802.15.4 standard, a great convenience is offered to applications in low-power and low-rate wireless sensor networks (WSNs). In this work, a novel CSMA/CA scheme which can be modeled as a renewal process for a node access process and a semi-Markov chain for the macroscopic channel transition process is proposed to analyze and improve the behaviors of heterogeneous unsaturated networks. General performance metrics such as throughput, access delay are predicted through these models. Moreover, performance comparisons of our scheme with other non-priority heterogeneous schemes are presented. Comprehensive analyses and simulations show that the fairness and delay of our scheme are superior to those of other schemes, while throughput is superior to others in more heterogeneous conditions.

Analysis of technical requirements and the self-modification method for a combinatorial code grating eddy-current absolute-position sensor

In order to overcome the shortcomings of the low coarse-localization accuracy of a phase difference grating eddy-current sensor (PDGECS), a combinatorial code grating eddy-current sensor (CCGECS) is presented in this paper. A single-track code localization method is adopted in a CCGECS to realize the coarse localization of a grating eddy-current sensor (GECS). This method is used as a replacement of the multi-track phase difference localization method in a PDGECS. The measurement principle of a CCGECS is introduced in this paper. The relationship between measurement accuracy and main characteristic parameters of sensor is obtained by mathematical deduction and error analysis, which offers theoretical foundation for design and technical requirements analysis of a sensor. A simple and practical self-modification method is also introduced in this paper. Experimental results show that adoption of a single-track code localization method to realize the coarse localization has greatly improved the coarse-localization accuracy of a GECS, resolved the contradiction between the coarse-localization accuracy and the measurement range caused by the multi-track phase difference localization method, realized the absolute-position measurement for a larger range and at the same time reduced the technical requirements, which lays a solid foundation for mass production of a CCGECS.

Research of virtual reality in industrial design manufacture and performance testing

Virtual reality (VR) is a new method of visual operating and interacting of complex data can be realized by computers, in which one would have an immersed sense to observe and operate objects in three dimensions timely and unboundedly. VR is a new developing technique and a complex simulation tool for industry, it builds a simulated environment in which researchers can do many things such as driving, operating, designing and performance test in a unaffected way. Performance test plays an important role in vehicle design. Most of interactive processing in virtual vehicle manufacturing is perfect, but many deep interactive functions are under emphasis such as performance test after manufacturing, variation and recording of performance parameters. Research of VRML combining with JavaScript is presented in this paper, and vehicle designing and manufacturing, testing system are built based on it, in which we can real-time and dynamic control the car through keyboard and mouse, and get the real-time performance parameters.