DiSync: Accurate distributed clock synchronization in mobile ad-hoc networks from noisy difference measurements

To perform clock synchronization in mobile ad-hoc networks, nodes need to estimate current time of a global clock based on the readings of their local clocks along with time-stamped messages from their neighbors. We formulate the problem as nodes simultaneously estimating skews and offsets of their own clocks with respect to a global clock from noisy difference measurements of logarithm of skews and that of offsets. These measurements can be obtained by exchanging time stamped messages. A leader-following consensus-based algorithm is proposed to estimate these parameters in a distributed manner. Ideas from stochastic approximation are used to ensure mean square convergence of estimation error under certain conditions. A sequence of scheduled update times is used to meet the requirement of specific decreasing time-varying gains that need to be synchronized across nodes with unsynchronized clocks. Simulations indicate that high accuracy of global time estimation can be maintained for long time duration with the proposed algorithm. Performance of the proposed algorithm is compared through simulations with the virtual clock synchronization algorithm ATS [1]. It is seen that the proposed algorithm is more robust than ATS to measurement noise resulting from random delays in message exchange.