In view of the energy limits and synchronization requirements of sensor nodes of Internet of Things (IoTs)

a low-energy-consumption time synchronization algorithm LECTS is proposed

and the energy consumption's reduction is performed from average synchronization message amount

synchronization period and duty cycle aspects.The network is divided into several parent-child groups and for each group one or more PS nodes are chosen.The intra-group nodes are synchronized continuously and the out-group nodes are synchronized on-demand.In each parent-child group

the parent node and PS nodes exchange synchronous me

ssage

N

times given synchronization period and duty cycle

and other intra-group nodes passively overhear those messages.The clock skew and offset respected to the parent node are estimated jointly based on the maximum likelihood estimation

and thus the intra-group nodes are all synchronized to the parent node.With the given synchronization precision

the network synchronization error is periodically evaluated by the sink node.Synchronization period and duty cycle are adjusted by synchronization controller according to the synchronization precision error.Simulation results show that LECTS method can guarantee synchronization precision and reduce energy consumption effectively

thus it can improve the network's lifetime.