Yes.
Since there is no central coordination, every device has to listen basically all the time to hear new devices that come within range. If they don’t, then they potentially miss the appearance of a new device within their reception range. For UWB, that depletes the battery very rapidly. A device that is recharged every day can possibly manage this with a sufficiently big battery, but anything else is a non starter using a straightforward UWB implementation.
Low power UWB requires being in SLEEP or DEEPSLEEP most of the time. The primary way to do that is to have central coordination to determine a time when devices wake up exchange packets, and go to sleep again. This use case doesn’t have that.
There are two viable solutions that I can see presently:
One, daily charging with a big battery, as mentioned before. The device listens on UWB basically all the time and they transmit periodically.
Two, use a low power alternate radio to determine your neighboring devices and then coordinate a time to do UWB. BLE could work, and that’s built into the nRF52832 on the DWM1001C, for example. nRF52832 BLE receive is about 17 mW versus UWB receive about 300 mW, so a big power difference. This approach requires some heavy duty firmware development to make that all work.
Once you solve the power problem, then you are confronted with the O(n^2) problem, that is, your distance matrix grows as the square of in range devices. The problem is easy with 10 devices, complex with 40, intractable with 100. That is, the system falls down exactly when you most need it. Be skeptical of anyone who claims they have that solved.
Using BLE RSSI as a first filter, or at least as a sorting mechanism, could be a good way to reduce the O(n^2) problem. Basically, only do UWB distance to a maximum of 10 devices which have the highest BLE RSSI you have seen. This doesn’t solve the O(n^2) problem, since that now exists at the BLE level.
This use case is an example of a seemingly trivial problem, measure distance between two devices, which is ultimately extremely difficult to realize in a practical way.
There is a lot of enthusiasm about using UWB for social distancing, we get an inquiry about this use case literally about once a day. But the enthusiasm rarely turns into the dedication and funding to do this right. This is a hard problem and the gap between the expectation and reality is discouraging to the inquirers.
Mike Ciholas, President, Ciholas, Inc
3700 Bell Road, Newburgh, IN 47630 USA
mikec@ciholas.com
+1 812 962 9408