  Acoustic signal acts as an essential input to many systems. However, the pure
acoustic signal is very difficult to extract, especially in noisy environments.
Existing beamforming systems are able to extract the signal transmitted from
certain directions. However, since microphones are centrally deployed, these
systems have limited coverage and low spatial resolution. We overcome the above
limitations and present ChordMics, a distributed beamforming system. By
leveraging the spatial diversity of the distributed microphones, ChordMics is
able to extract the acoustic signal from arbitrary points. To realize such a
system, we further address the fundamental challenge in distributed
beamforming: aligning the signals captured by distributed and unsynchronized
microphones. We implement ChordMics and evaluate its performance under both LOS
and NLOS scenarios. The evaluation results tell that ChordMics can deliver
higher SINR than the centralized microphone array. The average performance gain
is up to 15dB.
