Accelerometer first-order Markov chain model
That is a discrete-time differential equation. It models the progress of \$^sa_t\$ through time: it has a contribution from the previous time instant (weighed by \$c_a\$) and is deviated by an exogenous factor \$\epsilon_{a,t}\$.

Disconsidering exogenous influence, one can affirm that, if \$|c_a| &lt; 0\$, the signal will decay in amplitude with time. If \$|c_a| &gt; 0\$, the signal will gain magnitude until it becomes unbounded. We can then call \$c_a\$ a "natural decay" constant.

To obtain this constant, one could perform some sort of experiment in which exogenous influences are nullified and the signal has an initial value different from zero. By sampling the signal \$^sa_t\$ along time, the rate of decay of the signal can be estimated. Sorry, but I can't read korean, so these generic concepts are as good as I can provide.