Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Mind The Gap: Real-time Decentralized Distance Estimation using
  Ultrasound and Bluetooth across Multiple Smartphones   Robust, low-cost solutions are needed to maintain social distancing
guidelines during the COVID-19 pandemic. We establish a method to measure the
distance between multiple phones across a large number of closely spaced
smartphones with a median absolute error of 8.5~cm. The application works in
real-time, using Time of Flight of near-ultrasound signals, providing alerts
with sufficient responsiveness to be useful for distancing while devices are in
users pockets and they are moving at walking speed. The approach is
decentralized, requires no additional hardware, and can operate in the
background without an internet connection. We have no device-specific
requirements nor need any manual calibration or device synchronization. It has
been tested with over 20 different phones models, from both the Android and iOS
systems in the past 5 years. To the best of our knowledge, this is the first
successful such implementation, and has 25000 users at time of publishing.

37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
23
The categories of this paper are: solv-int
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org