  State-of-the-art device-free localization systems infer presence and location
of users based on received signal strength measurements of line-of-sight links
in wireless networks. In this letter, we propose to enhance device-free
localization systems by exploiting multipath propagation between the individual
network nodes. Particularly indoors, wireless propagation channels are
characterized by multipath propagation, i.e., received signals comprise
multipath components due to reflection and scattering. Given prior information
about the surrounding environment, e.g., a floor plan, the individual
propagation paths of multipath components can be derived geometrically.
Inherently, these propagation paths differ spatially from the line-of-sight
propagation path and can be considered as additional links in the wireless
network. This extended network determines the novel multipath-enhanced
device-free localization system. Using theoretical performance bounds on the
localization error, we show that including multipath components into
device-free localization systems improves the overall localization performance
and extends the effective observation area significantly.
