We did experiments with varying numbers of anchors deliberately sending packets at very precisely the same time, and with identical and random payloads. We even adjusted launch times to account for time of flight to the tag to make sure the packets overlapped at the tag within +/- 4 ns (the DW1000 launch time quantization).
What we found is that the DW1000 is pretty remarkable in locking onto one sender and retrieving the packet despite the overlap. This comes about mostly because the UWB modulation is a series of pulses and the receiver can find the stream of pulses that fit the packet pretty well even with a lot of other pulses happening at the same time. Signal strength was not necessarily a prime factor in which packet made it through, it seemed to be whichever packet correlated best during the preamble, or maybe whichever packet had the first pulse that arrived.
There were times and places where multiple transmitters did disrupt the ability to receive at least one of the packets, lowering packet reliability below, say, 25% (that is, the tag got at least one packet from some anchor 25% of the time). This seemed to be more position dependent than anything else as other tag positions were close to 100% reception rate.
In summary: the DW1000 tends to lock onto one sequence of pulses from one sender and get the packet received even in the face of multiple packets in the air at the same time.
These experiments were part of our research into using multiple anchors to increase range to send one message to a tag. While we can use physically large and directional antennas on anchors, tags must have small and omni antennas which limit their reception range. The goal was to get a signal to such tags without each individual anchor exceeding regulatory limits, but the combination of multiple signals would get through. Tags that operate in scheduled networks need to hear the anchors every so often to maintain network time lock.
That research is on hiatus as we do other things now, but it did result in a patent application for the idea which should issue soon.
Mike Ciholas, President, Ciholas, Inc
3700 Bell Road, Newburgh, IN 47630 USA
+1 812 962 9408