Beta Solutions Blog

Author: Siddharth Venkatesh, Intern

Bluetooth 5.1 is the latest iteration of the wireless technology, and introduces the ability to detect the Angle Of Arrival of the wireless signal. Such disruptive technology introduces a vast range of new opportunities - such as going a long way to solve the present issues with Local Positioning Systems.

Bluetooth Technology - A Quick Recap

Bluetooth is no doubt a word we have all heard. Since the advent of version 1.0 in 1999, the technology has become synonymous with short range wireless communication found in consumer electronics today. Indeed, whether it is to transfer files between devices or listen to our favorite songs using wireless headphones - Bluetooth is often the technology of choice.

Bluetooth operates by using (short range) UHF radio waves at a frequency band of 2.4GHz to 2.48GHz. Incidentally, this is the same frequency band as another popular wireless communication protocol - Wi-Fi. However, these are two very different protocols and intended for very different applications. Bluetooth technology devices transmit a much weaker signal than Wi-Fi and therefore are intended for short range applications. The upside of this is significantly reduced power consumption, and therefore longer battery life.

Bluetooth has evolved markedly over the years.

• Versions 1-3 (now known as “Bluetooth Classic”) was a point to point (1:1) topology - enabling various devices to pair together and exchange data.
• Version 4 (known as “Low Energy”), introduced in 2010 - is a point to many (1:M) topology. That is, Beacons can “broadcast” their data to many Receiver Nodes. Additionally, the technology was designed to be ultra low power - enabling low power wireless sensing.
• Version 5 (“Mesh”) was first introduced in 2016, and is a many to many (M:M) topology. Any nodes can talk to any other nodes, enabling large device networks. You can read more about this in our Blog A Closer Look at the New Bluetooth Mesh from 2017.
• Version 5.1, as we will see, is a further advancement on the BT Mesh protocol - and introduces a very exciting new feature.

Bluetooth 5.1

Bluetooth Special Interest Group (SIG) announced in January 2019 that 5.1 would include new “direction finding” technology. Undoubtedly, being able to determine the position of an object will unlock a wide range of commercial opportunities.

While Global Navigation Satellite Systems (GNSS) are relatively good at resolving positions, they will only work if the GNSS receiver can “see” 3 or more satellites - making them unsuitable for indoors.

Current Indoor Positioning Systems use the Received Signal Strength Indication (RSSI) technology to triangulate the position of other Bluetooth devices. This often requires multiple receivers (more the better) to “resolve” the transmitter’s location - and the end results are still often not highly accurate.

This new direction-finding technology, however, calculates the angle of transmission of the Bluetooth device to accurately pinpoint its location. This technology is three times more accurate than RSSI technology¹.

There are two methods for direction finding, the Angle of Arrival (AoA) and Angle of Departure (AoD) methods - which are briefly described as follows:

Angle of Arrival (AoA):

• The Angle of Arrival method consists of an antenna array on the receiver end. At least two antennas are required - but more antennas will enable more direction precision.
• The transmitter emits what is called a “Constant Tone Extension” packet, which is received by the receiver's antennas and ultimately sampled and digisited both In-phase and Quadrature components (IQ) - and by the Bluetooth receiver’s circuitry.
• Essentially, as each of the antennas will receive the packet at a different phase, this phase delay can be used to determine the AoA of the transmission.