We address the problem of localising a mobile terminal ("blind" node) in unknown position from a set of "anchor" nodes in known positions. The proposed method does not require any form of node synchronisation nor measurement (or control) of the transmission times, which is difficult or anyway costly to achieve in practice. It relies exclusively on reception timestamps collected by the anchor nodes, according to their local clocks, that overhear packets transmitted by the blind node and by (at least one) other transmitting node(s) in known position, e.g., other anchors. The clock differences between the nodes are not eliminated ex-ante through clock synchronisation, as in traditional ToA and TDoA methods. Instead, they are counteracted ex post, during the data processing stage, leveraging the data redundancy that is intrinsic to the multiple reception of the same packet by different (anchor) nodes. We validate the proposed method in two experimental setting, indoor and outdoor, using exclusively low-cost Commercial-Off-The-Shelf WiFi devices, and obtain sub-meter accuracy in Line-of-Sight conditions. The proposed method does not require that the blind node participate actively to the localisation procedure and can use "opportunistically" any legacy signal or packet available over-the-air for communication purposes. Considering the very minimal requirement on the system - basically, only that anchors in known positions are able to collect and share reception timestamps - the proposed approach can enable practical adoption of opportunistic and/or cooperative localisation on top of existing radio communication systems.
If you want to either test the localisation system by yourself on your testbed, or if you want to have access to the data we collected in our experiments for designing new localisation algorithms, please send an email to firstname.lastname@example.org.
The research leading to these results was partially funded by the EU's 7th Framework Programme under grant n.258301 (CREW).