Bluetooth Low Energy (BLE) Tutorial: Protocols, Channels & Technology Overview
Bluetooth Low Energy (BLE) is a power-efficient variant of the traditional Bluetooth standard, designed for applications requiring low data rates and minimal power consumption. This tutorial covers the basics of BLE, including handshake protocols for message exchange, BLE channels, BLE protocol layers and key differences between BLE and classic Bluetooth. Learn how BLE achieves energy savings while maintaining reliable communication.
There are various applications of short range wireless communications such as voice, data, audio, video etc. Various standards have been developed to support these application areas such as bluetooth, wifi, zigbee, ANT etc. In bluetooth there are different versions based on data rate and distance coverage requirements such as version 1.2, 2.0, 2.1, 3.0, 4.0 and 4.1. Bluetooth version 4.0 specification is known as Bluetooth Low Energy (BLE). It is also known by the name Bluetooth Smart.
Bluetooth Smart is a low power, low bandwidth and low latency data communication technology. In conventional bluetooth connection is established between bluetooth devices for communication. Once the devices are connected with bluetooth link the connection is maintained even if there is no data to be transferred. Devices go to sleep in sniff mode and hence battery life can be enhanced. Here peak transmit current is less than 25 mA. Though this power is less, it is not low enough to run the coil cell based applications. Bluetooth Low Energy (BLE) standard has been mainly targetted for small chunks of data transfer.
Bluetooth Low Energy-BLE specifications
| Specification | BLE technology Support |
|---|---|
| Channel Frequency | 40 channels (3 advertising, 37 data) |
| Distance coverage | 50 meters (150 meters outdoor) |
| Current Consumption | ~15 mA |
| Data rate of operation | 1Mbps |
| Modulation scheme | GFSK |
| Output Power | 10 dBm |
| Device types | Master and Slave |
| Device Modes | Dual mode(Supports BLE and traditional bluetooth), single mode (Support BLE) |
| Wireless Network Modes | Point to Point and Star |
| System Robustness | Adaptive frequency hopping with 24 bit CRC in the packet |
| Security | 128 bit AES CCM |
| Time for data to be transmitted from one end to the other (i.e. latency) | 3 ms |
| Current consumption during sleep mode | 1 µA |
BLE Network Topology
Fig:1 BLE (Bluetooth Low Energy) Network
As shown in the figure-1 bluetooth low energy supports star and point to point topologies. Point to Point (P2P) is used for pairing two BLE devices. In this mode, one BLE device acts as master and the other BLE device acts as slave device. The other topology star is used when there are multiple BLE nodes. In this topology, one node functions as central node and acts as master while all the other nodes function as slave nodes.
BLE Frequency Channels
Fig:2 Bluetooth Smart (BLE) Frequency Channels
As shown in the figure-2, Bluetooth Smart supports 40 channels, each with spacing of 2 MHz. There are 3 advertising channels and 37 data channels. Advertising channels are allocated in the frequency space other than the 802.11 allocated frequency spectrum space to avoid interference.
BLE Message Exchange
Fig:3 Bluetooth handshake protocol (messages exchanged between BLE devices)
Figure-3 depicts messages exchanged between the BLE devices (master and slave).
• Once connection is established between master and slave using advertising channels
following is done.
• Master informs slave about hopping sequence and when to wake up.
• All the subsequent transactions are performed using 37 data channels.
• Encryption can be applied to the data communicated.
• Both master and slave devices will go to deep sleep mode between
the transactions.
It takes about 3 ms to have complete data transfer including initial message handshake
to complete the connection between bluetooth low energy or bluetooth smart devices.
Bluetooth Smart (BLE) Protocol Stack
Fig:4 Bluetooth Smart or Bluetooth Low Energy or BLE Stack
Figure-4 depicts protocol stack for standard bluetooth device, dual mode device and single mode device. Dual mode device supports both BLE and Standard bluetooth protocols and hence it can interoperate with standard bluetooth devices as well as BLE devices.
Bluetooth Smart/Bluetooth Low Energy/BLE Applications(Apps)
Following are the BLE applications or use cases of Bluetooth Smart/Bluetooth Low Energy/BLE technology:
• Proximity • Time
• Emergency • Network availability
• Personal User Interface • Simple remote control
• Browse over Bluetooth • Generic I/O (automation)
• Temperature Sensor • Humidity Sensor
• HVAC • Battery status
• Heart rate monitor • Physical activity monitor
• Blood glucose monitor • Cycling sensors
• Pulse Oximeter • Body thermometer
There are many more BLE apps other than the one mentioned above.
Conclusion
Bluetooth Low Energy (BLE) has revolutionized wireless communication for battery-operated devices. With its low power consumption and reliable performance, BLE is ideal for IoT applications and wearable technologies. Use this comprehensive guide to implement BLE in your projects, leveraging its unique features and capabilities for power-sensitive applications.
BLE (Bluetooth Low Energy) Links
Bluetooth v5.0 versus v5.1 >>
BLE states and state diagram >>
BLE advertising and data channels >>
BLE protocol stack architecture >>
BLE connection process >>
BLE advertising and data packet formats >>
Difference between Bluetooth and BLE