Research On Synchronization And Accessing Technology In Wireless Sensor Networks

Wireless Sensor Networks (WSN), a technology exhibiting the characteristics ofrapid deployment, self-structuring network, and the ability to be remotely controlled,has not only generated much attention academically, but researchers from the public andprivate sectors have all been very interested. Contemporary research and developmentin this field has been rapid and intense. Limited by issues with node power consumptionand widely distributed information processing, accompanied by other issues withchannel mobility, some key supporting technologies of the WSN, such as thenode-precise clock synchronization technology and efficient medium access control(MAC) protocol have not yet been perfected. Therefore, to keep the accessibility ofwireless sensor node, optimize task dispatch and increase the service quality have beenput on the first priority to deal with; Furthermore, as the new technologies of MWSN(Mobile Wireless Sensor Networks) has been becoming increasingly popular, thetechnology of enabling massive nodes connected at the same time and increasing theefficiency of access rate of MWSN have to be developed as well.Aimed at the resolution of these problems, this report will approach them throughfour aspects of research:(1) Synchronization protocols of clocks based upon packetinteractions or distributed synchronization signal process algorithm;(2) Employing asingle channel control strategy based upon Game Theory’s Multi-node parallel;(3)Resolving the issue based upon mobile perception’s mobile node.(4) A GuaranteedTime Slot (GTS) allocation scheme with delay requirement and slot utilizationguaranteed in vehicular sensor networks. Detailed results of the research report arecontained below.The first topic of research was conducted on WSN’s distributed clocksynchronization problem. In regards to the synchronization accuracy, energyconsumption and other practical conditions of the clock synchronization mechanism,while making comparisons and analysis on a few existing problems of clocksynchronization algorithm within the field of area broadcasting, we have come across alow cost, multi-hop clock synchronization algorithm. This algorithm utilizes a pair ofnodes that have already been synchronized to transmit information to all peer nodes,thus synchronizing all nodes within the specific physical area. A tree structure with adual root node will be created to spread the algorithm throughout the network. Results from simulations have shown that under circumstances where synchronization accuracyis low and the suggested algorithm is able to effectively reduce the synchronizationcosts of the whole network.Research was also conducted on problems with single-channel multi-node paralleltransmission. Based on the interface-aware model signal interference ratio, informationmay be assembled from multiple nodes using a stochastic parallel and into a singlechannel control strategy, modeling it into a channel access matrix. Afterwards, the Nashequilibrium of the matrix will be the network’s transmission threshold; this suggests atype of single channel multi-node transmission agreement that transmits all parallelinformation. Simulations have shown that an increase in throughput; transmissionthreshold can also be adjusted according to the activity of nodes, interface ratio,transmission cost and wireless receiver sensitivity. This strategy allows multiple nodesto transmit information in a single channel in parallel: lowing costs while increasingnetwork throughput.The next topic of research was conducted on problems with accessing mobilenodes in WSNs. To resolve the issue of weak signal within wireless sensor networks, wesuggest utilizations of a network of wireless sensor that contain multiple mobile nodes,in order to widen the GTS of the nodes connectivity. First, by using the Kalman FilterPrediction Model, the location of the user in the next stage of transmission could bedetermined. Next, introducing a type of cognitive speed and taking into considerationthe direction of the transmissions and their respective mobility, to calculate thereservation priority of each signal. The next step is in determining the most appropriatereservation sequences based on the feed backs of the appointed slots of mobile nodes.Lastly, determining the GTS’s order of use based on the priority level of each node, aswell as the utilization of all slack time. Simulations have shown that in a network thatcontains multiple mobile nodes, the suggested allocation strategy is able to improve therate of node successfully accessing the network while keeping failure rate at a lowerlevel even when there is high delay in node group delivery ratio. Furthermore, byutilizing a self adjusting reservation priority strategy based on a feedback mechanism,the accuracy of network time slot reservation priority can be significantly improved.The final topic of our research was conducted on a GTS allocation scheme withdelay requirement and slot utilization guaranteed in vehicular sensor networks. TheIEEE802.15.4protocol can provide a flexible solution to support both real-time andcontention-based services. When beacon model is enabled, the Guaranteed Time Slot(GTS) scheduling can give a contention-free access to those latency-sensitive services based on time division multiple access mechanism. This characteristic makes IEEE802.15.4the appropriate candidate for vehicular sensor networks in which nodesgenerally should exchange packets with roadside units within given delay limitconsidering their mobility. We first analyze the relation between slots utilization andcorresponding access parameters, such as packets arrival rate, burst size and mobilitylevel etc. Then, for a given number of vehicles ready to access the roadside unit, wepropose a Time-Sensitive Weighted Round Robin scheduler with service delayrequirements, packets arrival rates and vehicles’ mobility levels into account. Bydetailed analysis to our scheduler, the weights setting method and time slots allocationstrategy is presented. Numerical results show the performance of transactions delayrequirement guarantee and GTS utilization maximization in Vehicular Sensor Networks.