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




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