Page 111 - ITU Journal, Future and evolving technologies - Volume 1 (2020), Issue 1, Inaugural issue

ITU Journal on Future and Evolving Technologies, Volume 1 (2020), Issue 1

microphone for distance measurement. This feature can culate the distance by using Equation (1), where is
be used very easily. Ultrasound-based distance measure- the sound speed, and , or , is the distance from
1
ment is promising, and it has been shown to achieve a one phone’s speaker to its microphone respectively . Fi-
centimeter-level accuracy, e.g. BeepBeep [16]. It can nally, in Step », two devices disconnect Bluetooth when
help to improve the performance of mobile contact trac- the transmissions of other types of data for contact trac-
ing systems. According to the CDC guidelines [6], for ing finish.
the purpose of Covid transmission, it can be assumed Integrated Contact Tracing with WiFi.
that two individuals are in close contact (and hence Besides the above mobile phone based contact tracing
likely to spread infection) if the distance between them approaches, we can also use WiFi logs. Different from
is within 6 feet. Clearly, with an accuracy of a few the above approaches, the WiFi based solution does not
centimeters, ultrasound is a very reliable and accurate require app installation on mobile phones, and relies
technique for the purpose of mobile contact tracing. upon widely deployed WiFi access points. It also does
Note that ultrasound cannot penetrate solid walls, and not require active involvement of mobile phones for ex-
hence it can also help us to rule out those “false con- changing the required information. The basic principle
tacts” that have been declared by the Bluetooth con- is described as follows: WiFi networks log all the associ-
nections occurring across walls.Using ultrasound for dis- ations and disconnections of devices connected to access
tance measurement requires a pair of devices to ex- points. We can analyze these WiFi logs to know where
change data between each other [16]. Fortunately, and when the devices (and hence their users) are close
Bluetooth-based mobile contact tracing systems have al- to each other. This provides information about the con-
ready implemented such an information exchange mech- tacts of device users.
anism, and hence developers can easily extend these sys- One of the advantages of such a WiFi-based solution is
tems in order to support ultrasound distance measure- that the WiFi log data is always available as long as
ment. This means that we can conveniently deploy both WiFi networks are active. Such networks allow both a)
ultrasound and Bluetooth technologies. reactive and b) proactive techniques for contact tracing.
An illustration of how we can integrate ultrasound and Let’s take the example of a university campus in order
Bluetooth for improved contact tracing is presented in to illustrate this. In reactive contact tracing, once a stu-
Fig. 1. The scheme is composed of six steps for the im- dent is confirmed to be infected, the university health
proved data exchange. In particular, when two smart- administration can use the WiFi MAC addresses of the
phones encounter, they first use Bluetooth to discover student’s mobile phone and his/her other computing de-
each other and initiate connections. At the beginning, vices such as laptop and Apple watch etc. to search
in Step ¶, one smartphone keeps advertising BLE pack- in the WiFi logs of campus networks, thereby deter-
ets to nearby devices. Meanwhile, another smartphone mining the locations where the student visited during a
scans its environment for any possible advertising pack- certain time period, and also his/her contacts at these
ets from its nearby devices, and initiates the connection locations. In proactive contact tracing, the university
in Step ·. After a connection has been established, two health administration can proactively analyze WiFi logs
devices emit ultrasound signals in turns (Step ¸ and ¹). to identify potential high risk users such as super spread-
When both devices have received signals from the other ers, and hot-spots (such as big gathering) in the cam-
device, they record the information that is required by pus. The university health administration can proac-
algorithms in order to measure distances, and then ex- tively pull WiFi logs and determine if the number of
change this information amongst each other via Blue- students in a gathering exceeds the limit that social dis-
tooth in Step º. For example, when using the algorithm tancing allows, and take appropriate measures.
from BeepBeep [16] for distance measurement, in Step The WiFi based contact tracing technique described
¸, alongside emitting an ultrasound signal, the phone above has its own limitations, for example the AP as-
( ) will record the timestamp 1 when it senses the sociation logs can generate false alarms. In order to

signal sent by itself, and the other phone ( ) will also overcome these, we might consider using Received Sig-

store the timestamp 1 when it receives such a sig- nal Strength Indicator (RSSI) and Channel State Infor-
nal. Similarly, in Step ¹, phone records the times- mation (CSI) to reduce the errors. WiFi based solu-
tamp for signal emitting as 2 and phone stores the tion cannot be applied in areas without WiFi connec-

timestamp 2 when receiving signal. Next, in Step º, tivity. We should consider enhancing contact tracing by
phone has to send both 1 and 2 to phone , integrating multiple solutions such as Bluetooth, WiFi

and phone also needs to share its two timestamps and acoustic symbiotically, where one helps or replaces
(i.e., 1 and 2 ) with . the other depending on user preferences, environmental
dynamics, and resource availability. For example, in a

( , ) = WiFi-AP dense area such as a campus academic build-

(1) ing, the WiFi-based solution can play a dominant role,
2 × (( 2 − 1 ) − ( 2 − 1 )) + , + , while the mobile app running Bluetooth and acoustic
When each phone has these four timestamps, it can cal- 1 For more details, please refer to BeepBeep [16]

© International Telecommunication Union, 2020 91