BLE Overview

This is a quick overview covering the highlights of Bluetooth® Low Energy (BLE) referenced in one place.

As with all first-time Bluetooth blogs, there is a mandatory requirement to describe the story of how Bluetooth earned its name.  The name ‘Bluetooth’ is a head-nod to King Harold Blatand of Denmark.  King Harold was reported to have united dissonant warring factions in Norway, Sweden, and Denmark.   He was rumoured to have snacked on so many blueberries that he stained his teeth blue.  An alternate, more likely, theory was that he had a “dead tooth” which appeared as a black or “bluish tooth”.  The name Bluetooth was proposed in 1997 by Jim Kardach of Intel.  While reading the novel “The Long Ships”, Jim developed a protocol that allowed mobile devices to communicate with computers. The novel contained descriptions of Vikings and King Harold Bluetooth.  The Bluetooth symbol comes from the combination of Furthak runes Harold’s initials: Hagall () and Bjarkan (), as shown below.

 

 

Bluetooth Low Energy is part of the Bluetooth standard maintained by the Bluetooth SIG (Special Interest Group) founded in 1998.  Low energy was first introduced in 2011 in version 4.0 of the standard.  Today there are over 30,000 members in the Bluetooth SIG with a shared vision of “A connected world, free from wires.”

 

Bluetooth operates using the ISM 2.4GHz band (2.400 – 2483.5MHz) band and is based on the IEEE 802.15.1™ – Wireless medium access control (MAC) and physical (PHY) specifications for wireless personal area networks (WPANs). 

 

BLE brings the following features:

  • Introduced in V4.0 when launched in 2011
  • Primary benefit is lower power consumption
  • Very short connection time (~3ms)
  • High data rate (1Mbps), up to 2Mbps with BT5.0
  • Sleep mode
  • 128-bit AES CCM encryption, 24-bit CRC
  • Receiver sensitivity -87 to -93dBm (typical)
  • Allows for short bursts of long-range radio connection
  • Asynchronous – doesn’t require continuous connections
  • Ideal for Internet of Things (IoT) applications

 

The table below comes from https://www.bluetooth.com/bluetooth-technology/radio-versions and contrasts key differences between traditional Bluetooth and BLE:

  Bluetooth Low Energy (LE) Bluetooth Basic Rate / Enhanced Data Rate (BR/EDR)
Optimized for Short burst data transmission Continuous data streaming
Frequency Band 2.4 GHz ISM Band (2.402 – 2.480 GHz Utilized) 2.4 GHz ISM Band (2.402 –2.480 GHz Utilized)
Number of Channels 40 channels with 2MHz spacing (3 advertising channels/37 data channels) 79 channels with 1MHz spacing
Channel Width/Spacing 2 MHz 1 MHz
Channel Usage Frequency-Hopping Spread Spectrum (FHSS) Frequency-Hopping Spread Spectrum (FHSS)
Modulation GFSK GFSK, π/4 DQPSK, 8DPSK
Data Rate LE 2M PHY: 2 Mb/s
LE 1M PHY: 1 Mb/s
LE Coded PHY (S=2): 500 Kb/s
LE Coded PHY (S=8): 125 Kb/s
HS: 24 Mb/s**

EDR PHY (8DPSK): 3 Mb/s
EDR PHY (π/4 DQPSK): 2 Mb/s
BR PHY (GFSK): 1 Mb/s

Max Tx Power* Class 1: 100 mW (+20 dBm)
Class 1.5: 10 mW (+10 dbm)
Class 2: 2.5 mW (+4 dBm)
Class 3: 1 mW (0 dBm)
Class 1: 100 mW (+20 dBm)
Class 2: 2.5 mW (+4 dBm)
Class 3: 1 mW (0 dBm)
Network Topologies Point-to-Point (including piconet)
Broadcast
Mesh
Point-to-Point (including piconet)

* Devices shall not exceed the maximum allowed transmit power levels set by the regulatory bodies that have jurisdiction over the locales in which the device is to be sold or intended to operate. Implementers should be aware that the maximum transmit power level permitted under a given set of regulations might not be the same for all modulation modes.

** Bluetooth is used to negotiate session establishment while high speed data rates are carried over a collocated 802.11 link.

 

In the diagram below, image (a) shows traditional Bluetooth using 79 channels with 1MHz width.  Image (b) highlights BLE with versions 4.0-4.2 contrasted against version 5.0 exposing differences in power levels.  BLE uses 40 channels – spaced 2MHz apart and are 2MHz wide.  37 of the 40 channels are used to transfer data with three channels reserved as ‘advertisement channels’.  These three special channels are strategically selected across the 2.4GHz band with center frequencies of 2402MHz, 2426MHz, and 2480MHz.  The careful selections are intended to minimize interference and avoid overlap with commonly used IEEE 802.11 b/g/n channels.  Image (c) represents the 16 channels used with many IEEEE 802.15.4 based networks such as ZigBee.  Finally, for comparison, image (d) represents IEEE 802.11b™ channels using DSS with 22MHz wide channels.

 

Image from IEEE Access: “Low-Power Wireless for the Internet of Things: Standards and Applications. https://www.researchgate.net/publication/328843842_Low-Power_Wireless_for_the_Internet_of_Things_Standards_and_Applications

 

Gaussian Frequency-Shift Keying (GFSK) was originally the only modulation scheme defined. It was referred to as basic rate (BR) with an instantaneous data rate of 1 Mbit/s.  FSK directly modulates wave forms with different frequency to the digital data symbols, changing the frequency at the beginning of each symbol period as necessary based on the bit sequence to be transmitted.  Gaussian frequency-shift keying (GFSK) smooths transitions between data pulses using filters.  Advantages from smoother transitions in filtering include reducing spectral width and reducing interference with neighbouring channels.  The tradeoff, however, comes at the expense of increasing intersymbol interference.   Later, modulation techniques using DQPSK and 8PPSK were added, referred to as enhanced data rate (EDR) providing increased data rates of 2 and 3 Mbit/s.  Version 3.0 of the standard introduced the highest data rate of 24 Mbit/s.

 

The table below captures the changes across different versions within the Bluetooth standard.

Bluetooth Version Name Data Rate (Mbps) Notes
1.0 Basic rate (BR) 1 Release 1999
1.2      
2.0 Enhanced Data Rate (EDR) 2 & 3 Released 2004
2.1     Released 2007

Simplified pairing

3.0 High speed (HS) Up to 24 Released 2009
4.0   BT (Up to 24)

BLE (1)

Released 2010

Added LE

4.1   BT (Up to 24)

BLE (1)

Released 2013
4.2   BT (Up to 24)

BLE (1)

Released 2014

IPv6 support

5.0   BT (Up to 24)

BLE (1 & 2)

Released 2016

Higher output power

Doubled data rate for LE

5.1   BT (Up to 24)

BLE (1 & 2)

Released 2019

Improved AoA, AoD for location

Added mesh

5.2   BT (Up to 24)

BLE (1 & 2)

Released 2020

LE Audio

 

When version 4.2 was released in 2014, the payload size was increased from 27 bytes to 251 bytes.  This change allowed for the support of IPv6; however, IPv6 was not specifically supported in the core specifications.  Fortunately, the IETF stepped in and published RFC 7668: “IPv6 over BluetoothÒ Low Energy” to provide IPv6 support over BLE with adaptation of the 6LoWPAN protocol stack.  Bluetooth 5 was released with the goal of increasing range/distance, size of advertisement payload, and throughput.

 

BLE advertising channels in a SpecA capture as shown below using Ekahau Pro + Sidekick:

Source: @Marcel_koedijk | @TomVanDriessche

 

BLE advertising channels in a SpecA capture as shown below using AirMagnet Spectrum XT:

Source: Peter Mackenzie | Design for IoT | WLPC Prague 2019

 

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