  The radio interferometric positioning system (RIPS) is a novel positioning
solution used in wireless sensor networks. This letter explores the ranging
accuracy of RIPS in two configurations. In the linear step-frequency (LSF)
configuration, we derive the mean square error (MSE) of the maximum likelihood
(ML) estimator. In the random step-frequency (RSF) configuration, we introduce
average MSE to characterize the performance of the ML estimator. The simulation
results fit well with theoretical analysis. It is revealed that RSF is superior
to LSF in that the former is more robust in a jamming environment with similar
ranging accuracy.
