210 research outputs found
Theoretical optimal modulation frequencies for scattering parameter estimation and ballistic photon filtering in diffusive media
The efficiency of using intensity modulated light for estimation of
scattering properties of a turbid medium and for ballistic photon
discrimination is theoretically quantified in this article. Using the diffusion
model for modulated photon transport and considering a noisy quadrature
demodulation scheme, the minimum-variance bounds on estimation of parameters of
interest are analytically derived and analyzed. The existence of a
variance-minimizing optimal modulation frequency is shown and its evolution
with the properties of the intervening medium is derived and studied.
Furthermore, a metric is defined to quantify the efficiency of ballistic photon
filtering which may be sought when imaging through turbid media. The analytical
derivation of this metric shows that the minimum modulation frequency required
to attain significant ballistic discrimination depends only on the reduced
scattering coefficient of the medium in a linear fashion for a highly
scattering medium
Robust Control Barrier Functions with Uncertainty Estimation
This paper proposes a safety controller for control-affine nonlinear systems
with unmodelled dynamics and disturbances to improve closed-loop robustness.
Uncertainty estimation-based control barrier functions (CBFs) are utilized to
ensure robust safety in the presence of model uncertainties, which may depend
on control input and states. We present a new uncertainty/disturbance estimator
with theoretical upper bounds on estimation error and estimated outputs, which
are used to ensure robust safety by formulating a convex optimization problem
using a high-order CBF. The possibly unsafe nominal feedback controller is
augmented with the proposed estimator in two frameworks (1) an uncertainty
compensator and (2) a robustifying reformulation of CBF constraint with respect
to the estimator outputs. The former scheme ensures safety with performance
improvement by adaptively rejecting the matched uncertainty. The second method
uses uncertainty estimation to robustify higher-order CBFs for safety-critical
control. The proposed methods are demonstrated in simulations of an uncertain
adaptive cruise control problem and a multirotor obstacle avoidance situation
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