A comparative analysis evaluating Bluetooth, Wi-Fi, Ultra-Wideband, and GPS for contact tracing effectiveness, deployability, and extensibility.
The COVID-19 pandemic has fundamentally changed how we do business.
Negotiating new workplace safety requirements while trying to keep the doors open means all organizations must consider a variety of ways to keep everyone healthy and mitigate downtime. While solutions like mask wearing and increased hand washing are simple to implement, the critical work of contact tracing after an outbreak is more difficult to do.
Contact tracing is a process that identifies people who were in close contact with an infected individual. Quickly finding and notifying all contacts means they can seek quarantine or medical attention faster, slowing the spread of infectious diseases.
Historically, this is a manual and laborious process conducted by trained employees at state organizations, such as the Centers for Disease Control and Prevention (CDC) in the United States. The coarse results obtained from traditional contact tracing can lead employers to send large groups of employees—or even all employees—home to quarantine, resulting in costly shutdowns.
Effective, Accurate Contact Tracing Is Here
Today, there are new means to accomplish contact tracing internally for businesses to reduce the impact of a health-related event. Using wireless technology via wearables to measure each employees’ proximity to one another drastically improves contact tracing accuracy.
The use of wireless technology also expedites the tracing process and reduces the economic burden on employers. However, this comparative analysis will demonstrate not all wireless technologies have the capability to maximize these benefits.
In this analysis, we will:
- discuss how wireless technology can minimize the impact of an event requiring employees to quarantine.
- review two approaches to contact tracing system architecture.
- compare the benefits and challenges of each wireless technology.
- provide a checklist to help you evaluate deployment needs.
- recommend the best technology to utilize for contact tracing.
- consider wireless technology capabilities beyond contact tracing.
A Real-Time Approach to Contact Tracing
A primary task when contact tracing is to determine if two individuals spent a certain amount of time together at a given distance. For example, the CDC defines a close contact as “someone who was within 6 feet [1.83 meters] of an infected person for a cumulative total of 15 minutes or more over a 24-hour period…starting from 2 days before illness onset.”1 For our analysis, we’ll use this definition to help us evaluate each wireless technology.
Clearly it would be impossible for someone to remember the exact distance and time spent at a given distance, especially days afterward. This is where the use of wireless technology to measure this information is critical: avoiding delays and misidentifying contacts.
Real-Time Location Systems and Device-to-Device
There are two main approaches to contact tracing system architecture. The first approach is implementing a Real-Time Location System (RTLS). With an RTLS, the location (X, Y, & Z) of all tracked devices is resolved and compared to determine if two devices are within a particular distance of each other. Rules are then applied to identify and log a contact event if needed. This approach generally requires infrastructure installed throughout the tracking areas—anywhere employees could go.
The second approach is to calculate the device-to-device distance. With this system architecture, data is shared between devices to determine the distance to each device and then determine if a contact event has
occurred. As the devices range to each other, they can also serve as real-time social distancing reminders, notifying the wearers when they come in range.
The only infrastructure required is the hardware needed to offload that data to a cloud server, possibly only a Gateway. As a result, this approach requires less infrastructure and hardware, reducing deployment time and costs. Device-to-device also avoids any “untrackable areas” where there is no coverage, which may occur in mass-deployed RTLS solutions.
Regardless of the system architecture selected, “RTLS infrastructure-based” or “device-to-device,” the business and technology requirements are the same: accuracy and efficiency.
Wireless Location Technology Options for Contact Tracing
Bluetooth Low Energy (Bluetooth LE)
Bluetooth LE is a technology regularly used with our smartphones. For example, Bluetooth can connect our phone to our vehicle or wireless headphones, and it can be used to set your thermostat or open a door.
Devices called Bluetooth “beacons” broadcast an advertisement (data transmission) at an interval that can be received by any Bluetooth LE–enabled device. While Bluetooth LE is still widely used, many cell phone vendors are focused on offering more privacy to consumers by limiting third-party applications’ access to background operation, requiring user permission. This reduction in access has impacted many companies that initially launched real-time location products dependent on the availability of Bluetooth in phones, in particular with background processes.
Wi-Fi is similar to Bluetooth in its capacity and use for real-time location, and a handful of companies offer Wi-Fi–based location services.
A primary challenge for contact tracing use is the requirement for infrastructure. Additionally, there is no defined standard for Wi-Fi advertisements that are utilized by Bluetooth LE systems.
In the consumer electronics world, UWB is “that new chip in Apple’s iPhone®,” but UWB technology has been available in the United States for unlicensed commercial use since 2002. UWB has been utilized for real-time location products for over a decade and some early pioneers of UWB products like BlueCats, Zebra, and Qorvo are still innovating new technology today.
The recent inclusion of UWB technology in consumer devices is due to a growing interest in the capability that only UWB can provide. The combination of location information, high data rates, and enhanced security allows vendors to do new things that were previously impossible without UWB. For example, auto manufacturers use UWB in key fobs to increase security and the stop relay station attacks that have become an increasingly common means of auto-related theft.2
Global Positioning System (GPS)
GPS excels in a variety of outdoor applications, such as navigation, real-time asset and personnel tracking for industries like mining and construction, and more. The significant limitation in using GPS for contact tracing is that it is less accurate indoors, and the high cost to achieve the accuracy contact tracing requires.
Due to the outsized cost and reduced indoor accuracy, we are not going to include GPS in this contact tracing analysis despite its usefulness for other wireless location purposes.
There’s several features and performance metrics to consider when comparing wireless technologies, but for the purpose of this analysis we will focus on the capabilities relevant to the specific goal of contact tracing.
Contact Tracing Technology Requirements
For our analysis, we must first understand the basic requirements a wireless technology must meet to provide reliable contact tracing.
To determine our set of requirements, we take our lead from how the CDC measures a close contact: 6 feet (1.83 meters) for a total of 15 cumulative minutes over a 24 hour time period.
For precision, we’ll also measure out a larger range of 5 meters to represent a “nearby” contact: individuals in the vicinity of each other (such as two individuals in the same room) but do not come in any closer proximity.
Signal Strength–based Technologies: Bluetooth LE and Wi-Fi
Bluetooth LE and Wi-Fi–based location rely on Received Signal Strength Indicators (RSSI) to estimate the distance between two devices. There is ongoing interest in using Bluetooth LE and Wi-Fi for contact tracing in part due to their broad availability in consumer devices. However, the research has consistently shown that using Bluetooth LE for contact tracing is particularly challenging and unreliable. As one paper summarized:
“Bluetooth LE received signal strength can vary substantially depending on the relative orientation of handsets, on absorption by the human body, reflection/absorption of radio signals in buildings and trains. Indeed, we observe that the received signal strength need not decrease with increasing distance. This suggests that the development of accurate methods for proximity detection based on Bluetooth LE received signal strength is likely to be challenging.”3
At BlueCats, we’ve confronted these same accuracy challenges in developing our own Bluetooth LE-based location system.
Figure 2 displays the Mean Radial Error of 2D positions calculated with our location engine in a small office. The data represents hundreds of positions solved in each room of the office space. As is clear in the graph, 80% of the calculated positions are within 2 meters of the true position.
Considering the expected Bluetooth LE system performance, two meters Mean Radial Error is impressive and suitable for many applications. However, given the distance resolution requirements for contact tracing, this is nowhere near accurate enough.
As a result, inaccurate data From Bluetooth LE contact tracing could result in:
- false positives: workers who did not come into contact with an infected individual may get identified as a contact and needlessly sent home.
- false negatives: workers who did come into contact with an infected individual may get missed, endangering these workers and everyone who comes into subsequent contact with them.
- inappropriately-sized shutdowns: the chance of any misidentified workers means employers are sending too many or not enough home.
- more frequent shutdowns: if infected workers aren’t sent to quarantine, employers are at risk for another outbreak.
Range-based Technology: UWB
UWB systems utilize precise measurements of time to determine the actual distance between devices. This can be accomplished using the two systems previously described in this paper: RTLS and device-to-device.
A traditional approach to deploying an RTLS solution requires the installation of UWB infrastructure. Stationary and permanently installed devices are calibrated and then used to determine the location of mobile tags. UWB systems using a permanent installation typically achieve better than 1-meter accuracy, with some methods reliably solving to centimeters of accuracy.
An alternate approach is for each device to calculate its distance to another device without the need for permanent infrastructure. For example, Qorvo produces Ultra Wideband chipsets that implement this technological approach. Leveraging UWB’s speed and accuracy, a Two-Way Ranging (TWR) functionality is used in industry for time on tool, safety, asset location, and more. In our analysis, we found that the real-world accuracy of the DW3110 chipset was not only consistent with the published accuracy specifications for the market, but offered best in class battery performance compared to traditional TWR based systems.
Figure 3 displays the measured range error of the BlueCats contact tracing tag utilizing the DW3110 chipset.
Approximately 90% of the mean range error, across hundreds of tags, falls within 10 centimeters. In a real-world scenario, we would expect the results to be slightly worse due to factors like human interaction and body blockage. However, even if the results were ten times worse, UWB still has a distinct advantage over signal strength–based solutions.
As a result, accurate data from UWB contact tracing results in:
- correct identification of contacts: with centimeter-level accuracy, UWB wearable tags minimize the potential for false positives or negatives.
- known per-contact and cumulative time of exposure: UWB provides timing in range down to the second. Given the updated CDC guidance for 15 minutes of cumulative exposure, seconds add up.
- improved social distancing: workers become more aware of their position relative to others.
- faster notification: in the event of an outbreak, UWB data can be quickly referenced so the affected contacts can be notified to quarantine immediately.
- sending home only the affected contacts: eliminate the guesswork about a worker’s exposure.
- avoiding repeat shutdowns: by sending home the right contacts the first time, employers prevent multiple shutdowns.
- an enhanced culture of workplace safety: employers demonstrate their commitment to protecting workers, and empowers everyone to enforce safety measures.
Deployment Costs and Challenges
Deployment should be a serious consideration when evaluating contact tracing technologies. If accuracy and precision are the foundation of contact tracing, deployment makes up the framing.
Deployment considerations should look at costs but also longevity. If deployment costs are affordable and there is potential for system utilization growth, there can be a realized ROI for companies. Without the potential for utilization in future work processes, a contact tracing system stops at exactly that purpose and may simply be a risk mitigation cost not so different from liability insurance.
Other factors in deployment are employee training, ease of use, and reliability. A contact tracing system must provide transparent feedback to users that it is functioning properly: it must be easy and quick to use, and must operate reliably.
Review the questions in the following Deployment Evaluation Checklist to consider the reliability, user experience, and extensibility of a contact tracing solution.
Deployment Evaluation Checklist
- How long will the device’s batteries last on a single charge?
- What sort of enclosure is the device in?
- Is the device safe for use in my environment?
- What is the process for linking a device to an employee? How long does it take?
- Can the user wear the device comfortably?
- How does a user know if the device is functional?
- How does a user know if they are generating a contact event?
- What other uses can the device provide beyond contact tracing?
Real-Time Contact Tracing, and Beyond
Considering the CDC guidelines for close contact, any contact tracing solution must accurately measure distance and record time in contact outdoors and indoors.
In our analysis we’ve seen that signal strength–based solutions, while popular and ubiquitous, are not accurate enough to support a reliable contract tracing solution. In contrast, our results show the centimeter-level accuracy of UWB is well within contact range, and offers multiple approaches to implementation. As a result, employers and workers can feel more confident returning to work every day trusting the system to provide accurate data as well as real-time distance alerts coming from their wearable UWB device.
Both RTLS and device-to-device systems are also fully extensible, supporting contact tracing and other use cases. In addition to evaluating technology, other critical ROI decisions are deployment, product usability, and long-term growth potential. While the urgent need for contact tracing is most impactful during a pandemic, a UWB-based solution provides additional value when used for asset and personnel tracking, time on tool, and more.
- “Appendices,” Centers for Disease Control and Prevention, 21 October 2020, https://www.cdc.gov/coronavirus/2019-ncov/php/contact-tracing/contact-tracing-plan/appendix.html#contact
- “Wireless car keys migrating to ultra-wide band (UWB) for better connectivity,” Simmtester. 15 November 2019, https://www.simmtester.com/News/IndustryArticle/21619
- Douglas J. Leith and Stephen Farrell, “Coronavirus Contact Tracing: Evaluating The Potential Of Using Bluetooth Received Signal Strength For Proximity Detection,” arXiv:2006.06822v1 [eess.SP], 2020.