  Integrating millimeter wave (mmWave)technology in both communication and
sensing is promising as it enables the reuse of existing spectrum and
infrastructure without draining resources. Most existing systems piggyback
sensing onto conventional communication modes without fully exploiting the
potential of integrated sensing and communication (ISAC) in mmWave radios (not
full-fledged). In this paper, we design and implement a full-fledged mmWave
ISAC system Gemini; it delivers raw channel states to serve a broad category of
sensing applications. We first propose the mmWave self-interference
cancellation approach to extract the weak reflected signals for near-field
sensing purposes. Then, we develop a joint optimization scheduling framework
that can be utilized in accurate radar sensing while maximizing the
communication throughput. Finally, we design a united fusion sensing algorithm
to offer a better sensing performance via combining monostatic and bistatic
modes. We evaluate our system in extensive experiments to demonstrate Gemini's
capability of simultaneously operating sensing and communication, enabling
mmWave ISAC to perform better than the commercial off-the-shelf mmWave radar
for 5G cellular networks.
