The water analogy is hard to understand. As I said below: At a fundamental level, backscatter modulation is little more than a reflector that modulates its ra

The water analogy is hard to understand. As I said below: At a fundamental level, backscatter modulation is little more than a reflector that modulates its radar cross section. You could imagine building massive spinning reflectors to serve the same purpose at very low datarates. Basically, you're looking for the presence (or absence) of reflections over time. Your "baffle" needs to be able to change it's state to change how much of the wave it's reflecting, and the receiver needs to be able to detect the minute changes in the reflections. On the receiving side, you'd have another "duck" that generates waves to exactly cancel out the incoming "big" (direct) waves through destructive interference (but this new duck's waves don't propagate to the rest of the system). Then, all you're left with at the receiver are the small reflection waves, which you measure changes in over time. [See, it's hard to visualize for water.] For RF signals, this is done by mixing with a local copy of the carrier, low-pass (or bandpass) filtering the baseband signals, and then running symbol correlators. For ambient backscatter... I presume they have to do carrier recovery for their own LO.