Spatial imaging using a communication system's channel state information

Abstract

We investigate the use of a communication system's channel state information (CSI) for spatial imaging. The CSI provides the the magnitude and phase of the link between pairs of (transmit and receive) antennas in sub-bands operating in the overall system bandwidth. Since these links are sensitive to the system's electromagnetic environment, information regarding physical objects in that environment are, to some extent, encoded in the CSI. In particular, the time history of objects (such as people) in the environment is partly encoded in the time history of the CSI. Combined with suitable prior information, useful facts regarding the dynamics of moving objects may be extracted using the methods of computational sparse imaging. Prior information can include a detailed characterization of the static electromagnetic environment (or boundary conditions) and the electromagnetic signature of the objects that are to be tracked. Specifically, we perform experiments using an 802.11n Wifi system operating at 2.4GHz, and which has been modified to allow acquisition of the CSI. Experimental results are compared with computational results (using CST Microwave Studio) for comparable electromagnetic environments. Image reconstructions are attempted, both experimentally and computational, to correctly locate a human sized reflective object.