Bluetooth Does More Than
Connect to AirPods

Methods of AoA and AoD

Before we dive deeper into AoA and AoD, let’s first figure out the implementation mechanism of Bluetooth^® location services prior to the introduction of the direction finding feature.

Different signal strengths are a quality assessment of signal links. The mechanism that a Bluetooth positioning system uses works this way. Before the construction of a Bluetooth positioning system in a certain site, a signal and distance curve will first be built based on the actual situation. Then, according to the signal strength, circles will be drawn according to the three-sided distance represented by different signal strength separately. The place where the circles converge and overlap the most will be the most likely location for this node. This is the principle of Bluetooth LE real-time indoor positioning system based on signal strength.

However, in Bluetooth Direction Finding, AoA, and AoD methods are added.

According to Kai, in the AoA scenario, the Bluetooth transmitter has only one antenna, which periodically transmits Bluetooth wireless communication signals. Meanwhile, at the receiver end, there is an antenna array. This is a significant difference from the previous Bluetooth based signal strength scheme. The antenna array at the receiving end not only has multiple antennas but also has a variety of ways to place the antenna. “The distance between antennas is differential, so even with the same wireless communication signal, when it sweeps over the antenna array, the phase difference is not the same,” said Kai “With the phase difference and the 2.4G wavelength, as well as the distance difference between the antennas, the receiver can calculate an angle of arrival.”

AoD, on the other hand, works the opposite way. There is an antenna array at the transmitter end that has multiple antennas, and the receiver has a single antenna.

Therefore, with the AoA and AoD methods in direction finding, the area where previous Bluetooth technology can figure out by the three-sided measurement will be found out more precisely. The accuracy will be higher.

Kai said the main scenarios for AoA would be RTLS, item tracking, and some Bluetooth beacon applications, while AoD is mainly used in indoor positioning systems.

Direction Finding Feature Aims for More Than Indoor Positioning

Currently, outdoor positioning systems, such as GPS, Beidou Navigation Satellite System, and some others, are all pretty mature. What Bluetooth^® is trying to do with direction finding is to achieve higher positioning accuracy in indoor locations, closed fields, and multi-layer structures. Kai believes that Bluetooth has significant advantages in indoor positioning.

First of all, the vast majority of the devices around us, in terms of hardware or software, all support Bluetooth technology. In terms of cost, the price of Bluetooth chips and Bluetooth solutions is much lower than other solutions.

The rising popularity of smartphones has created the demand for indoor positioning, so the direction finding feature was launched right at this point in time. In the future, Bluetooth Mesh and direction finding will be combined. Lighting systems in hotels and other venues are expected to directly provide Bluetooth indoor positioning and direction finding. What’s more is that today, almost everyone is a consumer of Bluetooth technology. Bluetooth brand awareness and technology maturity are widely recognized.

In fact, the application scenario of Bluetooth Direction Finding is not limited to indoor positioning. It can also be applied in large urban complexes. Kai pointed out that car keyless entry will also be an important area that Bluetooth Direction Finding may apply to in the future.

A Revolutionary Milestone

In 2015, the Bluetooth SIG established the Bluetooth^® Mesh Working Group. Then, in July 2017, Bluetooth SIG released the first version of Bluetooth Mesh.

Now, when two fixed devices exceed wireless communication coverage, if they still need data communication, then Bluetooth Mesh can provide the ability to exchange data between the two nodes that were otherwise outside wireless communication coverage.

“This is a revolutionary milestone for Bluetooth’s network topology. With Bluetooth Mesh, Bluetooth technology is no longer a ‘point-to-point’ or ‘point-to-many’ technology. For any large-scale deployment, whether indoors or outdoors, we can transfer information in this multi-hop way through the mesh,” said Kai. In theory, the maximum network capacity of Bluetooth Mesh can now reach more than 32,000 nodes.

Kai emphasized there was often a misunderstanding about Bluetooth technology, that Bluetooth is a short-range wireless communication technology. “Actually, this is largely due to the battery power and built-in antenna design of our devices today. With the feature of long range in version 5.0 of the Bluetooth Core Specification, some devices can achieve more than 1.5 km of Bluetooth coverage.”

From Lighting to Multi-Scene Applications

Kai said that with the introduction of the Bluetooth^® Mesh, the first everyday application scenario was lighting, “because lighting is an inelastic demand.” Before Bluetooth Mesh came out, Bluetooth low energy was adopted by some lighting companies in the industry, mostly in the connecting area. With Bluetooth Mesh , the large-scale unified operation of this lighting is realized. When people turn on or turn off the lights, or turn them halfway, the command rarely goes to a single light. This is a typical scenario where the Bluetooth Mesh network flooding mechanism is very beneficial.

Meanwhile, Bluetooth Mesh has entered many other areas, including switching and sensor-class applications.

In the field of sensors, temperature sensors, humidity sensors, lighting sensors, etc. can be incorporated into the entire Bluetooth Mesh network. “For example, in a conference room, if there is a Bluetooth Mesh lighting system, and the curtain is Bluetooth Mesh enabled, with the installation of a light sensor, when the light sensor detects that the sun’s irradiance exceeds a certain limit, it would send a command through the lighting system to the curtain’s automatic control system, after which the curtain can achieve an automatic closure and opening. “

Kai told us that lighting can be used as a backbone network to which more and more applications can be added. These applications run in the same network, and the data from the sensor system can be fed back not only to the lighting system but also to the air conditioning system, which can be shared. Provided, of course, that these devices must use standard Bluetooth Mesh specifications.

Bluetooth Mesh Emphasizes Model Standardization

We may use devices from several different vendors In a Bluetooth^® Mesh environment. How do you enable devices from different companies to “understand each other’ and interoperate with each other in a mesh network?

In fact, when the Bluetooth Mesh protocol was introduced, the Bluetooth SIG took this into account and released Bluetooth Mesh models. “Bluetooth Mesh models provide a standardized set of data to define a structure that includes model IDs, status, and related operations,” said Kai “Using the standard Bluetooth model definition released by the Bluetooth SIG, means these devices can communicate with the same language. Company A’s sensor information can be understood by Company B’s lighting products and turned to a related operation. This is what the model does.”

The Bluetooth SIG released the Bluetooth Mesh model 1.0.1 version recently, which includes some of the most basic operations, such as switching and tuning.

“We hope that in the future, through the Bluetooth SIG and our member companies, we will improve the connection capability of Bluetooth Mesh to the extent that Bluetooth headset audio products have right now,” said Kai “Of course, Bluetooth Mesh is just a two-year-old toddler compared to Bluetooth Audio, which is 20 years old. There’s still a long way to go before we can make our connectivity better.”