  The problem of sequentially detecting an abrupt change in a sequence of
independent and identically distributed (IID) random variables is addressed.
Whereas previous approaches assume a known probability density function (PDF)
at the start of the sequence, the problem addressed is the detection of a
single change in distribution among a finite number of known 'equal-energy'
PDFs, but where the initial and final distributions are not known a priori. A
Bayesian multiple hypothesis approach is proposed where (i) unlike previous
threshold policies, the minimum cost hypothesis is tracked through time, (ii)
under an exponential delay-cost function that satisfies an upper bound
determined by the distances between hypotheses, the probability of detecting a
change from an incorrect initial distribution asymptotically vanishes with
time, (iii) computation is recursive and constant per unit time, and (iv) the
unknown initial state gives rise to unavoidable incorrect detections that be
made to vanish with a constant test threshold with negligibly small effect on
correct detection delay for change times beyond a lower bound. Simulations
illustrate the analysis and reveal that average delay approaches that of the
optimal CUSUM test after an initial transient period determined by an incorrect
detection probability constraint.
