Bluetooth Radio

[admin]

Introduction

Bluetooth is one of the 2 default secondary wireless protocol supported by all Private Cyberspaces. Bluetooth is used in situations where WiFi is not practical or feasible.

Wireless technology	Link distance	Power consumption	Connection speed
WiFi	medium	high	high
Bluetooth	low	medium	medium
LoRa	high	low	low

1. Bluetooth Versions

Minimum supported version is Bluetooth 4.0 from 2010, also known as Bluetooth LE (Bluetooth Low Energy).

Bluetooth 4.0 - Bluetooth Low Energy
Bluetooth 4.1 - direct IoT connection
Bluetooth 4.2 - direct IPv6 connection
Bluetooth 5.0 - higher speed longer range
Bluetooth 5.1 - direction finding
Bluetooth 5.2 - improved audio
Bluetooth 5.3 - better signal quality and security

2. Bluetooth Assigned Numbers

Assigned Numbers | Bluetooth® Technology Website

3. Reverse Bluetooth Detection

Personal Console uses the mobile phone to scan for emitted bluetooth signals to determine current position. It is also possible to do it the other way round - use other nearby Bluetooth devices to scan for bluetooth signals emitted by the the mobile phone.

This way is NOT receommneded, as we believe our way is substantially more private, however it is interesting to know there are alternatives available:

• https://espresense.com/
• ESP32-mqtt-room | An ESP32 based presence detection node for use with the Home Assistant mqtt_room component for localized device presence detection.

[admin]

Bluetooth Positioning

1. Bluetooth Timing

Setting of Bluetooth Advertising Interval, Scan Interval and Scan Window is important, as they must overlap for discovery to happen (those tall dotted boxes shown in diagram below).

Source: Microchip

Note Bluetooth 4.0 onwards has 40 channels, all needs to be scanned.

2. Direction Finding

Bluetooth 5.1 direction finding is very nice, by attaching Constant Tone Extension (CTE) data sequence behind the CRC in a Bluetooth packet in order to get Angle of Departure (AoD) or Angle of Arrival (AoA) with multiple antennas at either transmitter or receiver.

That would be great for our indoor positioning, unfortunately it is not readily available yet, so we will be using the Received Signal Strength Indication (RSSI) and triangulation from multiple fixed Bluetooth sources instead.