— Many sensor network applications exploit the mobility of sensor nodes and the location-awareness plays an important role in these applications. However, it is too expensive to equip special hardware in each sensor node for localization, thus a distributed range-free localization scheme in mobile sensor network is highly desired. Several such localization techniques have been developed but few of them consider leveraging the feature of node mobility. Leveraging node mobility, in this paper, both static constrain set by transmission range and velocity constrain set by node movement are introduced. Based on these two types of constrain, we propose a range-free Mobile Inequality Localization (MIL) algorithm, which uses ring inequalities to restrict and estimate the possible location in numerical method. Our approach is distributed, quickly relocalizable and works well when all sensors are moving uncontrollably. We analyze the theoretical bound for the accuracy of position estimation an...