Towards ISAC-Empowered mmWave Radars by Capturing Modulated Vibrations

Integrated Sensing and Communication (ISAC) has emerged as a promising technology for next-generation mobile networks. Towards ISAC, we develop mmRipple that empowers commodity mmWave radars with communication capabilities through smartphone vibrations. In mmRipple, a smartphone (transmitter) sends messages by modulating smartphone vibrations, while a mmWave radar (receiver) receives the messages by detecting and decoding the smartphone vibrations. By doing so, a smartphone user can not only be passively sensed by a mmWave radar, but also actively send messages to the radar without any hardware modifications. Although promising, the data rate of mmRipple is limited by Morse-style communication. To address this, we present mmRipple+, which leverages the Pulse Width and Amplitude Modulation (PWAM) technique and suppresses inter-symbol interference to enable faster communication. We prototype mmRipple and mmRipple+ on commodity mmWave radars and different types of smartphones. Experimental results show that mmRipple achieves an average vibration pattern recognition accuracy of 98.60% within a 2 m communication range, and 97.74% within 3 m. The maximum communication range extends to 5 m. Meanwhile, mmRipple+ achieves a bit rate of 100 bps with a BER of less than 3%, improving the data rate by 4× over mmRippe with the same symbol duration. This work pioneers smartphone-to-COTS mmWave radar communication via vibrations, unlocking diverse applications.