When a sensor has continuous measurements but sends limited messages over a
data network to a supervisor which estimates the state, the available packet
rate fixes the achievable quality of state estimation. When such rate limits
turn stringent, the sensor's messaging policy should be designed anew. What are
the good causal messaging policies ? What should message packets contain ? What
is the lowest possible distortion in a causal estimate at the supervisor ? Is
Delta sampling better than periodic sampling ?
We consider a well defined joint detection and parameter estimation problem.
By combining the Baysian formulation of the estimation subproblem with suitable
constraints on the detection subproblem we develop optimum one- and two-step
test for the joint detection/estimation case. The proposed combined strategies
have the very desirable characteristic to allow for the trade-off between
detection power and estimation efficiency. Our theoretical developments are
then applied to the problems of retrospective changepoint detection and MIMO
radar.
For the most popular sequential change detection rules such as CUSUM, EWMA,
and the Shiryaev-Roberts test, we develop integral equations and a concise
numerical method to compute a number of performance metrics, including average
detection delay and average time to false alarm. We pay special attention to
the Shiryaev-Roberts procedure and evaluate its performance for various
initialization strategies.
In several interesting applications one is faced with the problem of
simultaneous binary hypothesis testing and parameter estimation. Although such
joint problems are not infrequent, there exist no systematic analysis in the
literature that treats them effectively. Existing approaches consider the
detection and the estimation subproblems separately, applying in each case the
corresponding optimum strategy. As it turns out the overall scheme is not
necessarily optimum since the criteria used for the two parts are usually
incompatible.
The CUSUM procedure is known to be optimal for detecting a change in
distribution under a minimax scenario, whereas the Shiryaev-Roberts procedure
is optimal for detecting a change that occurs at a distant time horizon. As a
simpler alternative to the conventional Monte Carlo approach, we propose a
numerical method for the systematic comparison of the two detection schemes in
both settings, i.e., minimax and for detecting changes that occur in the
distant future.
We present a test for the problem of decentralized sequential hypothesis
testing, which is asymptotically optimum. By selecting a suitable sampling
mechanism at each sensor, communication between sensors and fusion center is
asynchronous and limited to 1-bit data. The proposed SPRT-like test turns out
to be order-2 asymptotically optimum in the case of continuous time and
continuous path signals, while in discrete time this strong asymptotic
optimality property is preserved under proper conditions. If these conditions
do not hold, then we can show optimality of order-1.