A FULL-DUPLEX ULTRASONIC THROUGH-WALL COMMUNICATION AND POWER DELIVERY SYSTEM WITH FREQUENCY TRACKING

摘要

A method and apparatus provide simultaneous bi-directional communications through a barrier using a pair of piezoelectric transducers. Outside-to-inside transmission of differentially encoded binary data is only sampled at the inside when a known repeated bit in a Barker sequence is transmitted in the other direction. Differentially encoded data is translated based on the absolute value of differences between each signal envelope sample and the previous signal envelope sample. Inside-to-outside data is transmitted by varying an electrical load on the inside transducer to vary the proportion of a continuous wave signal it reflects. The reflected portion of the continuous wave changes the electrical impedance of the outside transducer and this change is measured and interpreted as binary data. Two frequency selection algorithms select minimally sufficient and then optimal frequencies for power and data transmission by a frequency stepping process.