Good shout. I checked the actual paper (here: https://arxiv.org/pdf/2301.00250.pdf, link in the article is broken), and seems you would need multiple routers:
> [...] three WiFi transmitters and three aligned receivers [...]. It should be noted that many WiFi routers, such as TP-Link AC1750, come with 3 antennas, so our method only requires 2 of these routers.
So basically, one on each side of the subject, one to transmit the signal, the other to receive, and then you can work out the interference pattern. It may be possible to do the same with the transmitters and receivers on the same physical device by measuring the reflected signal, but that doesn't seem to be what they were testing.
It seems that the person needs to be between the transmitter and receiver, so I'm not even sure if triangulation would work, although figure 2 implies that you need the 'line of sight' between the routers to be blocked (three 'transmitter' routers and three 'receiver' routers).
> (three 'transmitter' routers and three 'receiver' routers).
Three Tx antennas and three Rx antennas.
You need 3 of them to make a 3d point, otherwise you would have 2d/1d only. Even 1cm difference between antennas placement is more than enough.
> It seems that the person needs to be between the transmitter and receiver
You receive the direct signal earlier than the reflected one. If you find a way to capture both/only reflections then you can do it without LoS and consequently from only one device (though you would still need at least 3 Tx/Rx pairs.)
> [...] three WiFi transmitters and three aligned receivers [...]. It should be noted that many WiFi routers, such as TP-Link AC1750, come with 3 antennas, so our method only requires 2 of these routers.
So basically, one on each side of the subject, one to transmit the signal, the other to receive, and then you can work out the interference pattern. It may be possible to do the same with the transmitters and receivers on the same physical device by measuring the reflected signal, but that doesn't seem to be what they were testing.
It seems that the person needs to be between the transmitter and receiver, so I'm not even sure if triangulation would work, although figure 2 implies that you need the 'line of sight' between the routers to be blocked (three 'transmitter' routers and three 'receiver' routers).