Research On Congestion Control And Routing Algorithms In Wireless Sensor Networks And Applications

Since the beginning of the 21 st century,with the rapid development and gradual maturity of sensor technology,embedded systems,distributed computing and wireless communication technology,Wireless Sensor Network(WSNs),an interdisciplinary and multi-technology fusion field that integrates sensing,computing and communication capabilities,has emerged.Wireless sensor nodes are usually powered by batteries,and their service life is restricted by limited power storage.Therefore,how to optimize the routing algorithm in WSNs to select the shortest route for data transmission and reduce network energy consumption is an urgent problem in WSNs.On the other hand,when congestion phenomenon simultaneously occurs in different layers of WSNs,it will result in large transmission delay,high packet loss rate and low throughput.Hence,how to carry out reasonable cross-layer congestion control in WSNs to improve its quality of service is another research focus in WSNs.This dissertation regards cross-layer congestion control in WSNs as the research object,and studies discrete sliding mode control algorithm,adaptive discrete sliding mode control algorithm and fuzzy sliding mode control algorithm respectively.Then,this dissertation also takes routing algorithms in ZigBee wireless sensor network as the research object,and investigates a shortcut tree routing algorithm based on energy perception,and applies this algorithm to a wireless environment monitoring system based on ZigBee technology.The main contributions of this dissertation are as follows:(1)In order to solve the problems of long adjustment time and large steady-state error of traditional congestion control methods in WSNs,this paper investigates the cross-layer congestion control of WSNs based on the sink model and discrete sliding mode.Firstly,by applying water-level control of single-,double-and triple-tank to queue length control of single-,double-and triple-node,a hop-to-hop congestion control model across the link-layer and network-layer of WSNs is presented.Subsequently,a reaching-law-based discrete sliding mode control algorithm(DSMC)is proposed to regulate the inflows and outflows of node’s frame buffer.Finally,simulation results in MATLAB show that compared with conventional congestion control strategies,the proposed DSMC algorithm has advantages such as faster adjustment speed,smaller overshoot and near-zero steady-state error,thus effectively alleviating the congestion phenomenon of WSNs.(2)Aiming at the problems of energy waste,packet loss and short lifespan caused by congestion in WSNs,this paper studies the cross-layer congestion control of WSNs based on fluid model and adaptive discrete sliding mode.Firstly,by regulating incoming and outgoing packets at a particular node,this paper proposes a cross-layer congestion control model which is suitable for node-level congestion in the transport layer and link-level congestion in the data link layer of WSNs.Then,based on this model,an exponential-reaching-law-based adaptive discrete-time sliding mode congestion controller(ADSMC)is designed,which effectively adjusts bottleneck nodes’ queue length to desired value.Extensive NS-2.35 simulation results demonstrate that the proposed ADSMC outperforms conventional algorithms such as Fuzzy control,PID control and Fuzzy-PID control,it controls queue length and avoids congestion well,and has good qualities such as fast convergence,strong stability and long network lifetime.(3)In order to address the shortcomings of traditional sliding mode control algorithms such as large queue chattering and weak anti-interference ability in cross-layer congestion control of WSNs,this paper researches the cross-layer congestion control of WSNs based on fuzzy sliding mode control.Firstly,by applying the signal-to-noise ratio of wireless channel to TCP model,a new cross-layer congestion control model between transmission layer and MAC layer is proposed.Then,by combining fuzzy control with sliding mode control,a fuzzy sliding mode controller(FSMC)is designed,which adaptively regulates the queue length of buffer in congested nodes and significantly reduces the impact of external uncertain disturbance.Finally,numerous simulations are implemented in MATLAB/Simulink and NS-2.35 by comparing with traditional congestion control strategies such as RED,DropTail,Fuzzy,PID and SMC,which show that the proposed FSMC effectively adapts to the change of queue length and has good network performance,such as rapid convergence,lower average delay,less packet loss ratio and higher throughput.(4)Aiming at the drawbacks of poor routing and unequal energy load in ZigBee wireless sensor networks,this paper studies an energy-aware shortcut tree routing algorithm—EASTR.First,by introducing the remaining energy information of neighbor nodes into the neighbor table within one hop,EASTR can perceive the remaining energy of ZigBee nodes.Then,among all neighbor nodes whose remaining energy is greater than the dynamic energy threshold Eth,the one with the least number of hops to the destination node is selected as the next hop node.Many NS-2.35 simulation results show that compared with the existing routing algorithms such as Cluster-Tree,AODV,ZBR,STR,and ETR,the proposed EASTR algorithm significantly enhances the performance of star-shaped,tree-shaped,mesh-shaped and other small-and medium-sized ZigBee networks in terms of average delay,packet loss rate,throughput,total remaining energy,etc.,which provides certain theoretical guidance for improving the quality of service and network lifetime of those ZigBee networks.(5)This paper carries out the application research of EASTR algorithm in ZigBee wireless environment sensing system.First,a small-scale ZigBee wireless environment perception system is designed and implemented.Then,the proposed EASTR algorithm is applied to the system to optimize conventional ZigBee routing strategy.Experimental results show that under the premise of ensuring transmission quality and system stability,EASTR algorithm can effectively reduce the energy consumption and packet loss rate of ZigBee networks,which provides good theoretical significance and practical value for the application of ZigBee technology in the field of wireless environment real-time monitoring,and also brings a new opportunity for the broad development of Internet of Things technology.In the end,the whole thesis is concluded and some future research directions are discussed.