Modeling propagation into collapsed buildings for radio-localization-based rescue search missions

The retrieval of people trapped in buildings in fire or partially destroyed is a priority for rescue teams. Given the widespread use of mobile phones by the general public, an innovative idea to retrieve victims or to track rescue teams consists in capturing, via an antenna array acting as subrogated base station, the signals transmitted by cell phones (even if these are in idle mode). Real-time postprocessing then allows localizing the victim using a robust localization algorithm. The receive antenna array may be mounted under a helicopter for a first rough localization, while a second step involves a pedestrian rescue team equipped with portable versions of the same antenna array, providing in real-time localization data of the victim. In order to evaluate the performance of localization algorithms, a precise channel characterization is however required. Collapsed building structures constitute a very complex environment, for which no model exists so far. Also, there is a huge variety of possible scenarios because many different material can be involved; the electromagnetic properties of any given material strongly depends on the structure, humidity, compression, etc., so that the values of permittivity and conductivity are hardly known with precision; and the shape and dimensions of each rubble is highly variable. The goal of the present communication is to propose a channel model to predict the propagation characteristics between an outdoor unit and a buried terminal.