| The high cost and security problems of industrail wired network makes industrial go for "wireless".Though the limitation of hardware resource and energy supply of industrial devices and the demands of real-time transportation for burst event challedges the deployment of industrial wireless network.As the tenique selected by major industrial wireless network standards,time slotted channel hopping(TSCH)enables the low power and high reliable transportation feature,which statisfied the needs of industrial devices and network deployment.The two foundamental mechanisms of TSCH,time synchronization and resource allocation,are the key techniques affecting the performance of power consumption and transportation reliability.Those two key techniques are classified as centralization-oriented and distributed-oriented.The trend of interconnection of industrial wireless network and the extension of scalability tends to the distributed strategy as its low communication overhead and fast responding speed.This thesis studies distributed time synchronization and resource allocation in TSCH network.The mainly work and contribution are shown below:First,this thesis proposed an adaptive time compensation synchronizing algorithm,depending on the relationship between "Guard Time" and synchronization interval,exponentially increasing the synchronization interval and reducing 98%and 80%synchronization packet communication in indoor and outdoor scenario,meanwhile maintaining under 100 micro synchronization accuracy.Also,adaptive time compensation protocol reset its process to defend the changing of clock drift caused by the variation of temperature in different environments.Second,we proposed a multi-hop time cooperating synchronization algorithm.Through organizing the synchronization point between nodes,the algorithm allows to form a 10 hops depth network with 100 micro second per hop.The protocol solved the problem that the time offset will be accumulated along with the routing path and the node far away from the network time source would get de-synchronized because of exceeding "Guard Time".Through adding the synchronization interval information to advertisement packet,the node knows its time source neighbor's time to synchronize and synchronizes to time source neighbor right after that point to get the most accurate time.Besides,this algorithm has combined the adaptive time compensation protocol which only deal with one-hop synchronization,to keep the time offset at each hop a low level,hence increased the accuracy of whole networks.Third,this thesis proposes a slot chain allocation strategy to reduce the end-to-end latency:low latency scheduling function(LLSF).The adjacent nodes on the same routing path,through choosing the first slot right after the slot for receiving from previous hop as the transmission slot to next hop,reduce the latency of one hop to one slot duration.Besides,the end-to-end latency of LLSF doesn't increase along with the increasing of slotframe length,which reduces the radio duty-cycle hence reduces the power consumption.This slot chain allocation strategy satisfied the application requirement of low power and low latency in high real-time industrial diagnosing system.At the end,this thesis proposes a slot relocation policy,through applying the"Equivalence of Cell" in TSCH,relocating the potential collision cells to increase the link quality of TSCH network.Comparing to no-relocation slot scheduling policy,31.8%number of slots can be reduced through this relocation policy,hence the radio duty cycle can be reduced for saving power.The equivalence of cell(all slots have the same average communication quality)in TSCH network provides a way to detect collision slot.Once the communication quality is lower than average level,the respond slot is marked as collision.The node decides whether to relocate denpending on the communication cost.In the end,the thesis concludes the proposed algorithm in this thesis and the contribution of the work for the standalization of 6TiSCH protocol stack. |
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