7 September 2020

Bluetooth Direction Finding: Going Beyond Beacons

This article explores the evolution of Bluetooth® location technology over the years. In particular it shows how the available technologies have evolved from the original Bluetooth beacons to today’s Bluetooth Direction Finding solutions and describes why the newer solutions can provide superior accuracy for tracking results. For a more in depth comparison of the technical details, please also see our article Tags are not Beacons.

They say “the devil is in the detail”. With so many different location-based solutions available on the market, all of which have their uses, it is definitely important to consider the details before selecting a location technology and platform for the use case at hand. This applies to the big picture level of selecting a base technology like Bluetooth, Wi-Fi or Ultra-Wideband (UWB) as well as to the selection of an implementation method from within that technology category, like Bluetooth beacons or the Bluetooth Direction Finding methodologies.

Beacons, introduced around 2010, have become so prevalent that whenever Bluetooth based location services are mentioned, people tend to assume that Beacons are involved. However, since their introduction, Bluetooth positioning technologies have taken significant strides forward, including the introduction of Direction Finding in 2019. While Beacons are by no means an obsolete technology, neither do they represent the most state of the art option for Bluetooth based location technologies in today’s market.

The aim of this article is to give some background as to the differences between Bluetooth based solutions so that the next time someone talks about these solutions as if they are one and the same, you can ask the right questions to figure out which solution best fits your needs.

What are Beacons?

A good way to understand what a Beacon does, is to think of it as a lighthouse that periodically sends out signals from a fixed position, that can be used by the receiver to calculate their own relative position. Where the lighthouse uses a beam of light to signal to passing ships and boats, Beacons broadcast unidirectional signals over the three Bluetooth advertising channels to mobile devices (typically smartphones) that are within range. As the Beacon’s location is fixed and known, the receiving device can compute its relative proximity to that known location by using Received Power Strength Indicator (RSSI) measurements. This unlocks the possibility to provide a wide range of location-based consumable content, such as visualisations of the approximate location on a map, wayfinding, push notifications and other relevant location-based content.

What is Direction Finding?

If Beacons are lighthouses, then Bluetooth Direction Finding is more like a spotlight on a stage illuminating a performer. Think of the spotlight as a fixed infrastructure component that is used to provide access (i.e. visibility) to the performer moving across the stage. In the case of Bluetooth Direction Finding using tags, a fixed infrastructure of Locators (the spotlights) provide access to the Bluetooth signals sent by tags that move around the environment (the performer).

Direction Finding solutions can be set up as either infrastructure-centric (Angle of Arrival, AoA) or mobile-centric (Angle of Departure, AoD) depending on the needs of the use case. These implementations can even be mixed, with the same Locators supporting both AoA and AoD system architectures at the same time. The main difference between the infrastructure-centric and mobile-centric approaches is where the positioning calculations are processed: in the centralised network (AoA) or by the mobile device (AoD). Real-time locating systems (RTLS) for asset tracking typically use a network-centric approach to prolong tag battery life time, while indoor positioning systems (IPS) for wayfinding and mobile applications tend to opt for mobile-centric options to provide increased privacy for their users. This flexibility means that Direction Finding can provide solutions for all kinds of use cases across market segments. For more about the potential of Direction Finding across different markets, read our article Bluetooth AoD as the Technology of Choice for Indoor Positioning Systems (IPS).

Image 1: An illustration of the difference between Bluetooth based positioning methodologies. On the left, a proximity location solution provided by RSSI-based methodology. On the right, a high-accuracy location solution enabled by Direction Finding methodology.

So What are the Main Differences?

Now that we have a basic understanding of what the two technologies are, let’s take a look at some of the key differences between them.

Accuracy

One of the first questions asked of location-based solutions is “how accurate is it?”. Although the accuracy needs vary from use case to use case (for more on this, see our article Location Data – How Accurate is Accurate Enough?), this is one of the key pieces of information customers want to know before they select a technology. It is also one, where Beacons and Direction Finding solutions differ.

Beaconing solutions use the RSSI methodology for calculating location. In other words, the positioning calculations are based on distance measurements taken by evaluating the received signal strength. While a significant leap for technology when Beacons were introduced, this methodology is somewhat limited in the accuracy that it can provide, typically about 2 to 10 meters. This is because the power of the received signal can fluctuate based on radio propagation phenomena such as multipaths and obstructions such as objects moving around the environment. There are some well-known methods to mitigate these challenges, such as averaging and fingerprinting methods, but relying on calibration measurements is both time-consuming and inefficient, especially in environments that are constantly evolving.

Although the level of accuracy provided by Beacons is perfectly acceptable for many use cases, it is not enough to compete with high-accuracy location system providers like UWB. However, this does not mean that Bluetooth based locations solutions on the whole cannot compete in the high-accuracy arena. A competitive Bluetooth based solution, using the Direction Finding methodology, is already available on the market, providing the same level of accuracy as UWB.

Instead of RSSI methodologies, Direction Finding solutions use calculation based on angular measurements for determining location, which can robustly handle the challenges posed by radio propagation phenomena and obstructions in the environment. This means that system implementations can also operate reliably in harsh environments like industrial plants, warehouses, and manufacturing facilities. The Direction Finding approach makes it possible to attain much higher accuracy, even down to a few centimeters, with latency of a small fraction of a second. This enhancement makes it possible to implement location-based solutions for use cases that truly require high accuracy, low latency and a high degree of scalability, all at a reasonable cost.

Image 2: An illustration of the architectural difference between Bluetooth based positioning methodologies. On the left the network-centric AoA method. On the right the mobile-centric AoD method.

One of the best examples showcasing the accuracy of Direction Finding in action is ice hockey. Currently two of the major ice hockey leagues, Liiga (Finnish Elite League) and KHL (Kontinental Hockey League), have implemented the Quuppa Intelligent Locating System™, which uses the Direction Finding methodology to track games and provide statistics for both the teams and their supporters. In ice hockey, both the puck and the players move at tremendous speed and the details really matter so accuracy is a must. Having a system that can be configured to reach ten centimeter accuracy with a latency of just 150 milliseconds is a must to provide valuable data. To see this display of accuracy in action, take a look at this video recording of Wisehockey’s solution in use at a live game. If Direction Finding can provide the level of performance required by ice hockey, just imaging what it can do for you?

Reliability

The robustness of the system is also typically of interest to potential customers. Deploying a location-based system is an investment into at least one use case, and naturally the reliability of the system and the expected maintenance for operating the system once it is set up are factors that affect the investment decision. So how do Beacons and Direction Finding solutions differ from this perspective?

Beaconing solutions are relatively simple to set up and deploy and rely on the Beacon being in a fixed and known location. In some cases, the simplicity of setting up the system is a key selling point. However, when selecting a technology, it is important to also factor in the maintenance required, which adds to the total cost of ownership, and how it fits with your existing processes. For example, in hospitals, Beacons are commonly attached to power plugs or placed on shelves at a reachable height. While this may be convenient in many ways, it also makes the devices easy to move, e.g. by the cleaning crew as they work through the space. This is no problem if measures are taken to ensure that Beacons are not moved and maintenance is done to check that all installed Beacons are where they should be, but it is important to identify these needs to ensure that the reliability of the positioning results are not unintentionally eroded over time.

On the other hand, Direction Finding solutions really shine when it comes to robustness. The Locators are typically installed on the ceiling, where they are unlikely to be disturbed by staff that require access to the power plug or shelves. Direction Finding solutions, such as are offered by Quuppa, are also practically maintenance free once deployed in other ways. For example, enhancements made to Bluetooth radio chips in recent years make it possible for tags to operate for several years without running out of power, reducing the total cost of ownership. The methodology enables the positioning engine to achieve superior system performance even if the environment changes over time with no need for fingerprinting or other calibration methods. It also ensures that the overall system retains robustness when operating in harsh environments as each Locator works independently (no need for trilateration) to provide data for the positioning engine’s positioning calculation. This fundamental benefit makes Direction Finding solutions much more robust and also easy to deploy, even in challenging metallic environments.

Real-Time

Another common requirement for location-based solutions is that they provide data in real-time. Like with accuracy, many use cases do not really require real-time data, but for those that do, the value of the system is significantly reduced if it cannot deliver, making this an important factor in deciding which solution is right for your use case. Cases that typically require real-time data are, for example, the sports and access control use cases mentioned earlier, but also very topical ones such as social distancing and collision avoidance.

As we have discussed, Beaconing solutions are based on distance estimates based on signal strength. As power measurements are affected by other radio noise, the RSSI can vary significantly due to various radio propagation phenomena such as multipaths, reflections and shadowing even in static scenarios. This means that in order to compute stable distance measures and mitigate the radio noise, filtering needs to be applied over time, resulting in a delay for location estimates. A typical delay of 10 to 30 seconds is fine for many use cases, such as automated inventory management, but imagine having to wait in front of a locked door for 30 seconds every time before you can enter an access controlled room or getting the alert that a forklift is likely to hit you 20 second too late. Selecting the right technology for the job at hand is key to getting the desired value out of the system.

With Direction Finding solutions, real-time tracking is a realistic option for Bluetooth based location solutions. Tags can now communicate continuously with the system, meaning that the system always knows where the tracked items are with a system latency as low as a fraction of a second. Furthermore, embracing the angular methodologies has made it possible to design extremely responsive tracking systems that can successfully track fast moving objects with a high degree of accuracy and low latency. This makes the technology solution applicable to even those more challenging use cases that truly do need real-time solutions. In more technical terms, while UWB technologies can resolve the multipath challenges in the time domain, Direction Finding solutions resolve it equally as effectively in the spatial domain.

Versatility & Scalability

The versatility and scalability of a solution also play a part in selecting the right technology for the use case. If the system can grow and adapt with the needs of the use case, then it can continue to provide value to those using it, no matter what changes the market brings their way. This is a key advantage of Bluetooth based technologies when compared to others as Bluetooth can provide both device compatibility with a wide range of options as well as easily adapt to different levels of accuracy (for more on this, see Quuppa’s 3Ps of Location: Presence, Proximity & Positioning article).

While the technical limitations of traditional Beacon-based solutions tend to limit their adoption for large-scale infrastructure projects, Direction Finding solutions are well equipped to face the versatility and scalability requirements of the market without compromising on performance. They can be implemented across use cases and markets due to their ability to provide accurate and reliable location data in real time. The use of Bluetooth as the technology of choice provides an additional benefit as Bluetooth is widely deployed across devices in many vertical markets, providing interoperability benefits. Furthermore, in infrastructure-centric applications, moving the system intelligence from the smartphone application to the centralised network opened up new possibilities for the tags. It is now possible to design options that are simpler and more tailored to form-specifications for the use case (for more specifics, see our Tags are not Beacons article). The customisation options make Direction Finding solutions much more accessible for a range of industries.

Image 3: Example of Bluetooth tags used with the Quuppa Intelligent Locating System, a Direction Finding RTLS system.

Conclusion

In summary, we can see that Bluetooth technology offers a variety of location methodologies. There are many differences between the original Beacons and today’s state of the art Direction Finding. The table below summarises the main differences discussed in this article.

Bluetooth Beacons Bluetooth Direction Finding
Accuracy Typically 2 – 10 meters Typically submeter, down to few centimeters
Robust and Consistent  Low High
Real-Time Tracking Typically around 10 seconds Down to 150 milliseconds
Trackable Devices Any Bluetooth device Any Bluetooth device (soon to come)

Both technologies are very much in use today and provide value to the use cases where they are best suited, but it is important to make the distinction when discussing Bluetooth based location technology so as not to misdirect the conversation. Beacons paved the way and work great for proximity use cases, while the technological advances since their introduction have made it possible for Direction Finding to provide for a broader array of use cases from presence to proximity and even positioning (i.e. high-accuracy). This additional range makes it possible for Bluetooth based solutions to truly reach the full potential of what indoor positioning can offer for both real-time locating systems (RTLS) and indoor positioning solutions (IPS).

Now, Bluetooth based solutions can provide high-accuracy (down to centimeters), real-time (latency of only a fraction of a second) and scalable (robust and versatile) location solutions at an affordable price. This makes it possible to compete directly with the perceived market leader for accuracy, UWB. All the while, Bluetooth carries with it a long list of other significant advantages that push it ahead of UWB-based system implementations, including a lower price point, successful market penetration, interoperability across devices, global adoption running on standard ISM radio channels and lower power consumption. Bluetooth Direction Finding is the leading technology on the market and it is well-equipped to provide the location solutions that the market wants.

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