A chirp-FFT approach to mitigate multipath influence on Radio Tomographic Imaging

Radio Tomographic Imaging (RTI) uses the Received Signal Strength (RSS) loss due to the target´ s obstruction to locate the target in the area of interest surrounded by wireless sensor nodes. In cluttered environment rich in multipath, RSS loss cannot reflect the true attenuation of power loss of LOS path, thus the performance of RTI deteriorates greatly. In this paper, we propose a new method referred to chirp-FFT approach to mitigate the multipath influence. In this approach, the nodes transmit wideband chirp signal to resolve the multipath. Because that the time of arrival (TOA) of paths are different, the received signal will contain multiple frequency components after demodulation. Then the demodulated signal can be transformed by FFT to separate the components and the first component corresponds to the LOS path. And we use an interpolator based estimator to accurately obtain the amplitude of LOS path. We simulate the performance of chirp-FFT approach in an environment with two paths. The results show that traditional RTI fails to locate the target at low SMR (signal to multipath ratio) while chirp-FFT approach works well at SMR up to -30dB.