  The accurate and low-cost localization of sensors using a wireless sensor
network is critically required in a wide range of today's applications. We
propose a novel, robust maximum likelihood-type method for distributed
cooperative received signal strength-based localization in wireless sensor
networks. To cope with mixed LoS/NLoS conditions, we model the measurements
using a two-component Gaussian mixture model. The relevant channel parameters,
including the reference path loss, the path loss exponent and the variance of
the measurement error, for both LoS and NLoS conditions, are assumed to be
unknown deterministic parameters and are adaptively estimated. Unlike existing
algorithms, the proposed method naturally takes into account the (possible)
asymmetry of links between nodes. The proposed approach has a communication
overhead upper-bounded by a quadratic function of the number of nodes and
computational complexity scaling linearly with it. The convergence of the
proposed method is guaranteed for compatible network graphs and compatibility
can be tested a priori by restating the problem as a graph coloring problem.
Simulation results, carried out in comparison to a centralized benchmark
algorithm, demonstrate the good overall performance and high robustness in
mixed LoS/NLoS environments.
