In public health, contact tracing is that the method of identification of persons who may have inherit contact with an infected person and subsequent collection of further information about these contacts. By tracing the contacts of infected individuals, testing them for infection, isolating or treating the infected and tracing their contacts successively , public health aims to reduce infections within the population. Diseases for which contact tracing is commonly performed for include tuberculosis, vaccine-preventable infections like measles, sexually transmitted infections (including HIV), blood-borne infections, ebola, some serious bacterial infections, and novel infections (e.g. SARS-CoV, H1N1, and COVID-19).

How does a contact tracing app works?

A contact trace app works by constantly broadcasting and receiving signals following either WiFi (802.11) or BLE (Bluetooth Low Energy) protocols. These signals typically contain a unique identifier (IDs) that helps other apps to identify each user in the area. The unique IDs of all users captured by the app are stored in the list as potential contacts for a particular user.

Three major issues with contact tracing apps.

The elephant in the room is the fact that not all people install the application, and even so, you cannot expect the app to work smoothly in all kinds of phones.

The second issue is that one does not have to be in contact with people in order to get infected. Sharing the same resources with a COVID-19 patient (e.g. a toilet) can lead to an infection.

The third issue is the fact that all contact-tracing apps are collecting signals, not distances. Both protocols operate in radio frequencies and are easily detectable from a receiver in up to 90 meters distance. This means that you may be listed of being in contact with people from another block that may belong to an entirely different company and you may have never seen.

Estimating distance in contact tracing apps

Of course, there are solutions for the contacting apps to calculate distance. The obvious solution is to estimate distance based on the signal attenuation. It is known that signals attenuate predictably with distance. This means that the farther away you are from the broadcast station (i.e. someone else’s smartphone), the weaker the signal will become.

However, the low quality of sensors that all modern smartphones are equipped make this task impossible to accomplish. We will discuss on how applications can be improved at the end of this article.

How smartphones apps could be improved for contact tracing

For the sake of completeness, here we will provide suggestions for the improvement of social distancing application.

A common problem with WiFi and BLE based distance estimation is the fact that signals reflect on surfaces or are blocked by objects. This has as a result to appear much stronger or weaker than they were expected.

A solution here is to emit as many signals as possible, but this is not easy with WiFi and BLE protocols. Moreover, it drains the phone’s battery before it has time to contact someone. That is why UWB (Ultra WideBand) is used for precise localization, but the majority of phones (with the exception of the iPhone 11) are not equipped with it, so it does not need to be discussed.

An alternative option for distance estimation, when the location of all nodes is unknown, can be performed following the round trip time approach. After all, the speed of light is known, and since WiFi and BLE are both wireless electromagnetic signals, they travel at the speed of light. This means that the time it takes for the signal to reach the phone and return must be possible to be estimated.

The obvious problem again is the battery drainage and the second is that we will need to send multiple signals to every phone around us to perform RTT distance. This means that significant delays are expected, and with the speed of light, a delay of 1μs (=0.000001 sec) would cause a 300m offset. The solution to this would be to synchronize our phones as well as our GPS satellites, however this technology is still far from available.

How to use your existing infrastructure to perform contact tracking?

Ariadne Maps is a spin-off company emerged after years of research at the Technical University of Munich. It provides software that can be executed in the existing WiFi infrastructure and can anonymously track smartphones in the surrounding area. Ariadne has successfully solved multiple challenges for enabling your company to perform accurate contact tracing even in the absence of the best infrastructure, such as Cisco or Aruba access points.

Ariadne enables the anonymous tracking of employees with its state-of-the art and mathematically proven anonymization technology that can provide solutions to both key problems, social distancing and contact tracing.

Rather than performing tracking solely based on signal attenuation, Ariadne Maps enables the fusion of the building geometry, topology, and semantics with its patented technology, which improves tracking accuracy compared to existing conditions.

Find more at https://ariadnemaps.com/

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