Finally, the system performs key labeling of each cluster to recover each keystroke by examining the distance difference between the mean TDoA of each cluster to that of the theoretical TDoAs.
we conduct following experiments: as shown in Figure 16(a), we first use the Samsung Galaxy Note 3 to play a pre-recorded chirp sound signal via a earbud, which is to make sure the sound comes below neighboring key caps and thus has multipath effects, for 20 times at each target key’s position on a regular keyboard.