I am having two timeseries which are input and output of a linear time discrete system (LDS) , I need to know whether they are jointly widesense stationary, I know that the input and output of a LDS are jointly WSS, if the input is WSS. But here again I am having only on instance of the ensemble.
Can anyone suggest what is the best possible method I can follow? Can somebody please help me if I assume the sequence to be ergodic how can I proceed?