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

将通信信号重新用于雷达感测有着悠久的历史，其中通信信号的照射并不打算用于雷达感测，因此是通信的“附加物”。在5G通信网络中，来自密集部署的基站的信号在网络所服务的区域上提供大量照明，类似于密集放置的路灯照亮区域的方式。特别地，基站形成大的虚拟天线，其中基站天线之间的大距离可以帮助提高感测分辨率，因为空间分辨率与天线尺寸成反比。使用大型虚拟天线来提高传感分辨率的一个激励性例子是射电天文学的里程碑式成就，即2019年首次成功成像黑洞。黑洞距离地球550光年，因此需要20微弧秒的角度分辨率。由于波形和基础设施的充分重用，以实现通信和传感，各种应用预计所提出的通信信号为基础的传感方案，如户外定位，广域成像监视，和遥感使用通信卫星。以计算的边际成本实现具有高分辨率的感测功能，而不需要额外的无线电或感测硬件来实现。该项目扩展到教育目的，包括K-12推广和本科/研究生课程开发。黑洞成像的关键技术是甚长基线干涉测量（VLBI）。它基于干涉测量原理，该原理源于光学：来自同一光源的两束相干光束在接收器处相互干涉并形成条纹（即强度图案）;当光源有微小位移时，条纹会发生实质性变化，从而产生高灵敏度的传感。由于通信信号的传播距离要短得多，所提出的方案被称为中距离基线干涉测量（MDBI）。提出了MDBI方案的主要挑战，包括：（1）与VLBI远场分析相比，近场分析;（2）基线数量有限;（3）基站的时间/频率同步误差;（4）干扰/杂波。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.