Collaborative Research: Sensing by Leveraging Cellular Communication Networks: A Framework of Medium Distance Baseline Interferometry

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There is a long history of reusing communication signals for radar sensing, in which the illumination by communication signal is not intended for radar sensing, thus being a `bonus' of communications. In 5G communication networks, the signals from densely deployed base stations provide substantial illumination over the region served by the network, similar to the way that densely-placed streetlamps illuminate an area. In particular, the base stations form a large virtual antenna, where large distances between the base station antennas can help improve the sensing resolution, since the spatial resolution is inversely proportional to the antenna size. A motivating example for the use of a large virtual antenna to improve sensing resolution is the milestone achievement in radio astronomy, namely the first successful imaging of black hole in 2019. The black hole is 550 light years away from the earth, thus requiring an angle resolution of 20 microarcseconds. Due to the full reuse of the waveforms and infrastructure to achieve both communications and sensing, various applications are expected for the proposed communication-signal-based sensing scheme, such as outdoor positioning, wide-area imaging for surveillance, and remote sensing using communication satellites. The function of sensing with high resolution is achieved at the marginal cost of computation, without requiring extra radio or sensing hardware for implementation. The project is extended to education purposes, including K-12 outreach, and undergraduate/graduate level course development. The achievements of the proposed research are disseminated to academia and industry communities.The key technique in the imaging of black hole is the very long baseline interferometry (VLBI). It is based on the principle of interferometry, which stems from optics: two coherent beams from the same source interfere with each other at a receiver and form a fringe (namely the pattern of intensity); the fringe experiences substantial changes when the source has a tiny displacement, thus yielding high sensitivity of sensing. Due to the much shorter propagation distance for communication signals, the proposed scheme is called Medium Distance Baseline Interferometry (MDBI). Major challenges in the proposed MDBI scheme are addressed, including: (1) the near field analysis, in contrast to the far field in VLBI, (2) limited number of baselines, (3) time/frequency synchronization errors in base stations, and (4) interference/clutter. The proposed MDBI scheme is tested using software and hardware testbeds.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.