Propagation Parameter Estimation, Modeling and Measurements for Ultrawideband MIMO Radar

Ultrawideband (UWB) radar is a promising method for reliable remote monitoring of vital signs. The use of multiple antennas at transmitter and receiver (MIMO) allows not only improved reliability, but also better accuracy in localization and tracking of humans and their various types of movement. This paper describes an experimental demonstration of localizing a test subject and tracking his breathing under ideal conditions. The UWB MIMO channel, which includes the test subject as well as other objects, is modeled as a superposition of multipath components (MPCs). From the measured data one can extract the parameters of the MPCs, including their directions and delays, which allows localization of the test subject as well as tracking the breathing motion. Since the breathing pattern of the test subject induces delay variations of the diaphragm-reflected MPC that are much smaller than the Fourier resolution limits, the high-resolution RIMAX algorithm (iterative maximum-likelihood estimation scheme) is employed together with a path detection scheme for determining and tracking the MPC parameters. Furthermore, it is illustrated that with a wideband array model, the requirements for antenna spacing are not as limited as for conventional narrowband array processing. Through controlled experiments with a vector network analyzer and a virtual antenna array observing both an artificial “breathing” object as well as a human subject, it is shown that one can accurately estimate the small scale movement from human respiratory activity. This is achieved both for line-of-sight between transmitter, receiver, and objects, as well as for non-line-of sight.