Performance Analyses and Improvements for the IEEE 802.15.4 CSMA/CA Scheme with Heterogeneous Buffered Conditions

Studies of the IEEE 802.15.4 Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme have been received considerable attention recently, with most of these studies focusing on homogeneous or saturated traffic. Two novel transmission schemes—OSTS/BSTS (One Service a Time Scheme/Bulk Service a Time Scheme)—are proposed in this paper to improve the behaviors of time-critical buffered networks with heterogeneous unsaturated traffic. First, we propose a model which contains two modified semi-Markov chains and a macro-Markov chain combined with the theory of M/G/1/K queues to evaluate the characteristics of these two improved CSMA/CA schemes, in which traffic arrivals and accessing packets are bestowed with non-preemptive priority over each other, instead of prioritization. Then, throughput, packet delay and energy consumption of unsaturated, unacknowledged IEEE 802.15.4 beacon-enabled networks are predicted based on the overall point of view which takes the dependent interactions of different types of nodes into account. Moreover, performance comparisons of these two schemes with other non-priority schemes are also proposed. Analysis and simulation results show that delay and fairness of our schemes are superior to those of other schemes, while throughput and energy efficiency are superior to others in more heterogeneous situations. Comprehensive simulations demonstrate that the analysis results of these models match well with the simulation results

Characteristics of the transparent fluid assisted in-process measurement method

Coolant fluid is often utilized in precision machining processes. The optical measurement method is a highly accurate method. However, the coolant fluid blocks the light beams from this layer and makes optical measurement impossible. This dissertation describes the fluid and optical characteristics of a new in-process measurement method assisted by a transparent fluid. Fluid model of the transparent window and related experiments are provided. In modeling the motions of the fluids for the transparent window, the transparent flow is simplified as a line source, when it flows into the narrow gap zone between the bottom of the applicator and the workpiece surface. The coolant flow and the line source are combined to a flow potential field. The complex potential theory is utilized to find the boundary line of the two fluid flows. Furthermore, the equations of the transparent window boundary line are obtained, which are functions of the transparent fluid flow rate, the gap, and the velocity of workpiece movement. An experimental setup is developed to simulate the movement of the worktable and workpiece, the coolant fluid condition, and to capture images of the transparent window under various conditions. After analysis, the experimental results are found to correspond with the results of the theoretical model in the effective area of the applicator. There are two assisting layers in the new method, the applicator and fluid layer. These layers are the extra parts for a laser sensor, and change the properties of the sensor, and so as the measurement results. The experimental results show that the laser beam propagation will be changed when it passes through the assisting layers. The effects are governed by the thickness of the applicator and the fluid layer, the refraction indexes of the layers, and the incidence angle of the laser beam. A correction formula has been derived to correct the measurement output. The experiments also indicate that the installation error should be limited to less than 2 degrees for correct measurement. The Reynolds number of the flow in the transparent window region is in the range from 50 to 6000. This makes the flow either laminar or turbulent. The theoretical analysis and experiments show that the deflection of laser beam through a laminar or turbulent flow fluid layer is small under the conditions of the method. However, in the turbulent flow, air bubbles may exist, which will be a serious problem for laser beam propagation in the transparent window. The experiments and analyses show that the effect of the flowing fluid layer can be controlled to an acceptable level. The coolant fluid is opaque for a laser beam. The effects on the optical measurement depend on the density of the coolant and the thickness of the fluid layer. When the density is high, the propagation of the laser beam becomes more difficult, and the diffusion of the laser increases. A large number of the experiments were performed. The results show that, if the thickness of the fluid layer is less than 0.5mm and the density of the coolant in the transparent window is lower than 2%, the measurement error is acceptable

A Nonuniform Sensor Distribution Strategy for Avoiding Energy Holes in Wireless Sensor Networks

The energy hole problem exerts great impact on the energy efficiency and lifetime of wireless sensor networks (WSNs) based on many-to-one communication model. Unequal cluster emerged in recent years is a good way to alleviate the energy hole problem by dispersing cluster heads' burden. However, it fails to address this problem fundamentally due to its inherent characteristics. The single non-uniform nodes distribution strategy can alleviate the energy hole problem well by setting more nodes in networks to achieve energy balance, yet it may result in low energy efficiency and high cost of the networks. In this paper, by analyzing and minimizing intra- and inter-cluster energy consumption, we construct a suboptimal unequal cluster for WSNs. We propose a non-uniform sensor distribution strategy based on the previous unequal cluster in accordance with the energy balance principle. Simulation results show that our proposed non-uniform sensor nodes distribution strategy can not only achieve good energy efficiency as the unequal cluster method, but also ensure the network energy consumption balance and resolve the energy hole problem completely as the non-uniform sensor distribution approach. Furthermore, our algorithm needs fewer sensors to be settled than single non-uniform node distribution

A Hybrid Energy- and Time-Driven Cluster Head Rotation Strategy for Distributed Wireless Sensor Networks

Clustering provides an effective way to extend the lifetime and improve the energy efficiency of wireless sensor networks (WSNs). However, the cluster heads will deplete energy faster than cluster members due to the additional tasks of information collection and transmission. The cluster head rotation among sensors is adopted to solve this problem. Cluster head rotation strategies can be generally divided into two categories: time-driven strategy and energy-driven strategy. The time-driven strategy can balance energy consumption better, but it is not suitable for heterogonous WSNs. The energy-driven cluster head rotation strategy has high energy efficiency, especially in heterogonous networks. However, the rotation will become increasingly frequent with the reduction of the nodes residual energy for this strategy, which causes lots of energy waste. In this paper, we propose a hybrid cluster head rotation strategy which combines the advantages of both energy-driven and time-driven cluster head rotation strategies. In our hybrid rotation strategy, the time-driven strategy or energy-driven strategy will be selected according to the residual energy. Simulations show that the hybrid strategy can enhance the energy efficiency and prolong network lifetime in both homogeneous and heterogeneous networks, compared with either single time-driven or energy-driven cluster head rotation method

An improved localization scheme based on IMDV-hop for large-scale wireless mobile sensor aquaculture networks

Abstract With the hasteful development of ocean economy and the increasing exploiture of ocean resources, offshore water is contaminated seriously. Ocean ecological environment is unprecedentedly faced to threat and destruction. Moreover, the desire for aquatic and marine products is increasing consumedly according to people’s health attention rising. It is extremely urgent to establish and maintain low-cost and high-efficient transmission and localization schemes for real-time large-scale aquaculture surveillance systems. Localization scheme IMDV-hop (Intermittent Mobile DV-hop) embedded in WLS (weighted least square) method, accompanying with HTC (Hidden Terminal Couple), is proposed in this work for the purpose of environment surveillance, object localization for early warning, rescue operations, and restructuring plan, etc. Two critical parameters, correction coefficient k c and weighted coefficient wNx,i $${w}_{N_x,i}$$, are introduced into IMDV-hop scheme for large-scale aquaculture monitoring and localization mobile sensor systems to evaluate the influence on localization behaviors, and subsequently guarantee localization accuracy and time-critical performance. And localization error, delay, and consumption are predicted by comprehensive NS-2 simulations. Besides, performance comparisons of IMDV-hop scheme with other DV-hop-based schemes and MCL-based scheme are also proposed. Analysis and comparison results show that delay behavior of IMDV-hop is improved largely relative to other schemes, while accuracy and energy consumption performance is improved in some cases of more node density and lower mobile velocity