Both in nature and engineered systems, many signals are modulated onto carriers.  This provides some immunity to baseline noise and DC level shifts.  We see many of these modulated signals in various position and velocity sensors (as well as others).  Unfortunately, most control engineers are not taught enough about how to efficiently demodulate these signals so as to minimize the noise, nonlinearities, and time delay in the extracted information.  This topic covers some of the ways in which control engineers can use coherent demodulation to minimize these negative effects on the returned signal.