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We present a new technique to mimic an active sonar system with the smartphone’s built-in microphone and speaker, and use this sonar system to evaluate muscle fatigue from the muscle’s surface characteristics that can be measured from the transmitted acoustic signal.

We present a novel design of high-throughput wireless side channel, which operates concurrently with the existing wireless network channel over the same spectrum but dedicates to real-time traffic. Our key idea of realizing such a side channel is to exploit the excessive SNR margin in the wireless network to encode data as patterned interference. We design such patterned interference in the form of energy erasure over specific subcarriers in an OFDM-based wireless network, and achieve a data rate of 1.25 Mbps in the side channel without affecting the existing wireless network links.