Designing a Bluetooth bracelet system for contact tracing

Article By : Asem Elshimi

Here is how a bracelet system design can send data to the server and detect proximity with each other using RSSI and RTLS technologies.

Governments and organizations in quest of strategies to manage the COVID-19 pandemic are deploying a wide variety of technological solutions. One technology that has been gaining a lot of traction is Bluetooth contact tracing. This wireless protocol is ubiquitous, cost-effective, and simple to use.

Initially, developers were utilizing smartphone Bluetooth technology to perform contact tracing, but this approach proved problematic as not everybody in the world has (and operates) a smartphone. The alternative to smartphones are Bluetooth bracelets, which can be as cheap as a few dollars, making them affordable to large populations. Bracelets also provide a privacy advantage over smartphones. Many countries and political establishments are already wary of the user data collected by smartphones, but bracelets don’t require any information from users and can simply be assigned identification numbers that users can keep to themselves.


Special Projects Editor’s Note: This article is part of an AspenCore Special Project, a collection of interrelated articles that explores the anatomy of designs tackling the coronavirus pandemic. See all the articles in this Special Project below.

 


Bracelets have already been deployed in several different regions around the world. Singapore deployed tracing bracelets to its 5.7 million residents in June while Bahrain announced a similar bracelet distribution to its citizens back in April. While these events are positive indicators of the potential of such tracing technology, there are many elements to take into consideration in order to best implement Bluetooth bracelet contact-tracing systems.

For instance, the privacy concerns are legitimate, so we need to be careful as we approach the design problem. This tutorial covers some important design considerations for Bluetooth bracelets. However, this tutorial by no means reflects a public acceptance or shows health impact analysis of the bracelets.

Bracelet system overview

Like the Internet, consisting of servers and personal computers, the Bluetooth bracelet system consists of a database/server and end-nodes aka bracelets. To maximize users’ confidentiality, all user information can be excluded from the database. The database acts as the hub for all the information gathered by individual bracelets. The complexity of the bracelets can vary based on the design goal. Important questions to address from the beginning are:

  • Are the bracelets built for a centralized or a decentralized approach?
  • What is the cost margin?
  • Are we looking at minimal tracing devices or are we considering integrating more health gadgets on the bracelets to detect wearers’ symptoms?

An important aspect of the system is how the bracelets send their data to the server. Bluetooth bracelets can detect the proximity of each other using received signal strength indicator (RSSI) or real-time location system (RTLS) technology. However, they ultimately need to connect to the Internet to forward their data to the server. They also need to get readings from the server to figure out if one of the bracelets they’ve previously contacted has tested positive.

So how do they connect to the server? There are a few options here. The very same bracelet that carries the Bluetooth chip and manages contact tracing can carry another chip that performs LTE and communicates with the server through the cellular infrastructure. This approach might raise the cost a bit.

Another alternative could be connecting the bracelets to the server through smartphones. Every smartphone has Bluetooth technology and can act as a bridge for the bracelet to connect to the Internet and access the database. The downside of this scenario is the need for smartphones.

One last possibility is adding gateways to the bracelet infrastructure. Gateways are enabled with Bluetooth radios and exchange data with the bracelets on one end. On the other end, the gateways have access to the Internet through Wi-Fi, LTE, or Ethernet. In this case, users would be asked to walk nearby or drive through gateway kiosks, so their data can be collected. The gateways would be deployed all around urban and suburban areas so users could access them seamlessly. Of course, creating these gateway kiosks would increase cost.

diagram of a Bluetooth bracelet systemThe Bluetooth bracelet system consists of a server, gateways, and end-points (the bracelets).

Decommissioning and expiration

Another system decision to be made early on is the decommissioning date. The bracelets will hopefully go into action and do their work in saving lives and helping to revive the economy, however, it is essential that we place limits on these systems built for emergencies. The best way to do so is to decommission the system once the emergency is over, guaranteeing that users’ data will not be used against them. This applies to the server and bracelets as well. The bracelets could potentially have an expiration date, at which point, the device would deactivate.

This brings up another important issue: waste management. Where will the bracelets actually go once the emergency is over? Are people going to dispose of them? In that case, disposal should be considered when deciding which materials to use. An alternative to disposal is recycling. In a simple design, the bracelets are made of a Bluetooth system-on-chip (SoC), an antenna, a coin cell battery, and the plastic material of the bracelet itself. For a small financial incentive, it would be a feasible option to have people return the bracelets once their mission is over, reducing electronic waste and enabling suppliers to use the intricate electronics for other applications.

Building blocks available

Bluetooth bracelets offer an intriguing solution for contact tracing and many are already in use. Engineering teams with access to semiconductor hardware design as well as packaging and material science are well-positioned to build out this solution further to assist populations during this health crisis. As imminent as the need is for this type of technology, developers need to incorporate privacy, security, and a decommissioning strategy into the product design to ensure its holistic success.

The fourth and final part of this series about Bluetooth-centric contact tracing solutions for COVID-19 provides a detailed treatment of the key building blocks of Bluetooth bracelets.

Editor’s Note: This article is for general information purposes only and provides an overview of a specific developing situation that continually evolves. It is not intended to, and should not be construed, for public-health guidance. — Majeed Ahmad

Asem Elshimi is an RFIC design engineer for IoT wireless solutions at Silicon Labs.

For further insights into the designs tackling the coronavirus pandemic, check out the other articles in this AspenCore Special Project:

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