A novel range-free localization approach-smallest enclosing circle based localization （SECL） has been pro- posed. This approach estimates the position of target by the center of smallest enclosing circle of neighboring anchor nodes. Comparing to centroid

SECL considers the geometrical coverage center of anchors rather than the geometrical mass center of them. Consequently

SECL is more robust when the topology of anchors is not uniform. Simulation results show that SECL outperforms centroid by an average of 10%

and even better when the topology is not uniform.