How do these ToF systems deal with multiple sensors pointing at the same scene? I've seen it work with two ToF sensors, but haven't been able to find a good explanation for how it works.
There are three different methods.
1) TDMA (Time division multiplexing). Some sync system so only one camera is emitting light at a given time. The Microsoft Azure Kinect uses this with the 3.5mm sync cable, this enables up to 3 cameras to illuminate at different times.
2) Frequency domain. iToF cameras use different modulation frequencies, you can set different modulation frequencies and the signals won't interfere. The other cameras photon's will contribute to photon shot noise. Or randomly change modulation frequencies by a small amount during the integration time, which is supported by some sensors.
3) Randomly change timing during integration time, this is more common with pulsed ToF cameras. Analog devices had an example of this in their booth at CES in 2020.
if the measurement time is short enough, (<1us capturing at 60 fps), the probability of interaction is low even with large number of cameras. Even then, some temporal filtering and intelligent time offsetting to separate signals, can usually fix the problem.
If the other emitter/sensor pairs are uncorrelated with our own, and if we integrate over enough transmit/receive cycles, then the other pairs will contribute approximately equally to both of our own two sensor phase detectors. The method descibed here uses the difference between the sensor phase detectors, so any competing interference should cancel out. It will (just) raise the background noise floor a bit.
2) Frequency domain. iToF cameras use different modulation frequencies, you can set different modulation frequencies and the signals won't interfere. The other cameras photon's will contribute to photon shot noise. Or randomly change modulation frequencies by a small amount during the integration time, which is supported by some sensors.
3) Randomly change timing during integration time, this is more common with pulsed ToF cameras. Analog devices had an example of this in their booth at CES in 2020.