  This paper studies the positioning problem based on two-way time-of-arrival
(TW-TOA) measurements in asynchronous wireless sensor networks. Since the
optimal estimator for this problem involves difficult nonconvex optimization,
we propose two suboptimal estimators based on squared-range least squares and
least absolute mean of residual errors. The former approach is formulated as a
general trust region subproblem which can be solved exactly under mild
conditions. The latter approach is formulated as a difference of convex
functions programming (DCP), which can be solved using a concave-convex
procedure. Simulation results illustrate the high performance of the proposed
techniques, especially for the DCP approach.
