TIME-REVERSAL MIRRORING FOR NEAR-ULTRASONIC INDOOR COMMUNICATION
Résumé
We present the first use of a Time-Reversal Mirror (TRM) for near-ultrasonic indoor communication and discuss its advantages over existing techniques. For indoor applications where radio-frequency telecommunications are not suitable, acoustic solutions can indeed be a viable alternative. In this work, we experimentally evaluate the performance of a new acoustic communication system operating between the audible spectrum and near-ultrasounds, a range seldom studied for communication purposes. This choice allows us to take advantage of consumer transceivers while limiting users' hearing discomfort. To design a robust communication system and improve its overall bit rate, we combine a linear-frequency-modulation spread-spectrum technique and TRM. For testing purposes , we have developed a prototype array of speaker-microphones and implemented a TRM-based communication protocol. We first characterize this TRM device in an anechoic chamber. We then evaluate its focusing effectiveness in typical indoor environments and receiver-transmitter configurations. The quality of transmission is assessed via measurements of bit-error rates, with and without TRM, as a function of the signal-to-noise ratio. We also study how indirect paths impact communication robustness during changes in the environment. Finally, we present a concrete communication application between our TRM device and a consumer device, namely a smartphone.
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