[AD 15] Poisson-distributed SWD

We now assume that the bead displacement d_n during time interval n is the sum of k_n unresolved microsteps, each of (average) width w_1:


Let the k_n fluctuate according to a Poisson-distribution with average event number lambda (given by some event rate times the discretization time interval):


which has a variance of


Then one obtains for the mean bead displacement per discretization time interval


and for the variance