  The paper proposes a multi-body electromagnetic (EM) model for the
quantitative evaluation of the influence of multiple human bodies in the
surroundings of a radio link. Modeling of human-induced fading is the key
element for the development of real-time Device-Free (or passive) Localization
(DFL) and body occupancy tracking systems based on the processing of the
Received Signal Strength (RSS) data recorded by radio-frequency devices. The
proposed physical-statistical model, is able to relate the RSS measurements to
the position, size, orientation, and random movements of people located in the
link area. This novel EM model is thus instrumental for crowd sensing,
occupancy estimation and people counting applications for indoor and outdoor
scenarios. The paper presents the complete framework for the generic N-body
scenario where the proposed EM model is based on the knife-edge approach that
is generalized here for multiple targets. The EM-equivalent size of each target
is then optimized to reproduce the body-induced alterations of the free space
radio propagation. The predicted results are then compared against the full EM
simulations obtained with a commercially available simulator. Finally,
experiments are carried out to confirm the validity the proposed model using
IEEE 802.15.4-compliant industrial radio devices.
