结合Chirp信号的单向广播机制水下无线传感器网络时间同步算法

Time synchronization algorithm for UWSNs based on unidirectional broadcast mechanism of Chirp signal

水下无线传感器网络(underwater wireless sensor networks, UWSNs)的时间同步主要面临两大挑战,分别是水声传播时延较长和节点的移动性.针对水下无线传感器网络时间同步问题,提出了一种结合Chirp信号的单向广播机制的跨层时间同步(Chirp-based broadcasting time synchronization, CB-Sync)算法. CB-Sync算法在物理层利用Chirp扩频信号的时钟频偏与相偏来减少因节点移动性带来的误差.此外, CB-Sync算法采用周期性的单向广播机制来同步邻居节点,邻居节点根据收到的广播信息,通过两次线性回归得到时钟的初始频偏与相偏,最后利用最小梯度下降算法来减少多普勒频移带来的误差,以提高最终的时间同步精度.仿真实验结果表明, CB-Sync算法具有更为高效的能量利用效率和时间同步精度.

Time synchronization in mobile underwater wireless sensor networks(UWSNs)faces two major challenges,namely,long propagation delay and node mobility.In this paper,a Chirp-based broadcasting time synchronization(CB-Sync)algorithm based on unidirectional broadcast mechanism of a spread spectrum signal,i.e.,Chirp,is proposed.The CB-Sync algorithm uses the clock frequency offset and phase offset of the Chirp at the physical layer to reduce errors caused by mobility of the nodes.Furthermore,CB-Sync algorithm uses a periodic one-way broadcast mechanism to synchronize neighboring nodes.According to the received broadcast information,the neighboring node obtains the initial frequency clock skew and offset by two linear regressions.Finally,a minimum gradient descent algorithm is used to reduce errors caused by Doppler shift to improve accuracyof time synchronization.Simulation results show that the CB-Sync algorithm can achievehigher energy efficient and better time synchronization accuracy.