====== BT Versions ======

Bluetooth versions:

  * BT 5.4: ESL (Electronic Shelf Label)
    * PAwR
    * EAD

  * BT 5.3
    * Peripherals can list preferred channels with a central device. Previously, only the central device could set channels. 

  * BT 5.2
    * LE Isochronous Channels
    * LE Audio
    * LE power control (LEPC) provides adjustable power that can be requested by peer devices.

  * BT 5.1
    * Angle of Arrival (AoA), Angle of Departure (AoD) for tracking
    * generic attribute (GATT) profile caching makes pairing quicker by retraining requirements. 

  * BT 5
    * 2Mbit/s PHY for LE
    * Coded PHY: with ECC
    * More antennas provide greater tracking accuracy, and generic attribute (GATT) profile caching makes pairing quicker by retraining requirements. 

  * BT 4.2:
    * Designed for the Internet of Things (IoT), BT 4.2 increased the payload size in the Bluetooth packet by 10x, dramatically lowering the overhead to yield 2.5 times more data.
    * The low-power wireless personal area network (WPAN) version of IPv6 (6LoWPAN) is supported, which enables billions of devices to have a unique IP address.
    * It also supports beacon privacy, which prevents retail shops from sensing a user's presence (see iBeacon).

  * BT 4.0: Introduced low-power Bluetooth Low Energy, branded as "Bluetooth Smart."
    * BLE

  * BT 3+HS: Branded as Bluetooth 3.0 + HS (High Speed), it started the connection via Bluetooth but transmitted data over Wi-Fi

  * BT 2.1: Secure Simple Pairing (SSP) was added to make pairing faster and more secure. Encryption was made mandatory, security was improved, and less power was used. 

  * BT 2.0+EDR (Enhanced Data Rate)
    * π/4-DQPSK (2Mbit) and 8-DPSK (3Mbit) modulations
    * Apple: 4 (HDR4) and 8 (HDR8) Mbit/s using π/4-DQPSK modulation on 4 MHz channels with FEC.
    * Interference handling was improved, and less power was used. 

  * BT 1.2: 
    * BT 1.2 (Basic Data Rate) was the first widely used Bluetooth technology.
    * Adaptive frequency hopping (AFH) helped avoid interference with Wi-Fi and other technologies in the same frequency.
    * Pairing speed was improved. 

  * BT 1.1: Improvements to reliability and interoperability; mostly backward compatible but not 100%. 

  * BT 1.0
    * 1Mbit GFSK modulation - BR (Basic Rate)