A Channel Estimation Method for Ultrasonic Through-Metal Communication

A piecewise suboptimal threshold (PSOT) is proposed to select the most significant samples (MSSs) of the channel impulse response (CIR) for channel estimation of ultrasonic through-metal (UTM) communication. We analyze the correlation of echoes in the UTM channel, i.e., the periodicity and the exponential decay of echoes. The summation of mean-square error (MSE) is partitioned using the periodicity of the echoes so that each partitioned MSE contains only one echo. The PSOT is derived by setting the first derivative of the partitioned MSE to zero. Channel tap energies, namely, the received energies of ultrasonic waves, are required to calculate the PSOT, which can be estimated using the exponential decay of echoes. After selecting MSSs by PSOT, we propose a further selection approach to get rid of possible noise samples in MSS using the correlation of echoes. The simulation results show that the proposed method is robust. Specifically, the performance of the proposed method does not depend on ultrasonic velocity, is unaffected by the estimated number of the echoes at a low signal-to-noise ratio (SNR), and can be applied to UTM channels with different metal thicknesses. The simulation also shows that the proposed method has a lower MSE than other methods, especially at low SNR.