The working principle of Bluetooth in data transmission is as follows:
1. Frequency Band and Channel
Bluetooth operates on the 2.4GHz ISM band. Classic Bluetooth has 79 channels (with a 1MHz bandwidth), while low-power Bluetooth has 40 channels (with a 2MHz bandwidth). Through adaptive frequency hopping technology, the two communicating parties jump 1,600 times per second between channels to avoid interference.
2. Modulation method
The Gaussian Frequency Shift Keying (GFSK) technology is adopted to convert digital signals into radio frequency signals. Classic Bluetooth represents "0" and "1" through carrier frequency offset, while low-power Bluetooth has an offset of ±185kHz.
3. Data packet format
The classic Bluetooth data packet contains the access address, header, data bit and CRC check, with a maximum of 357 bytes. The low-power Bluetooth data packet contains pre-complement code, access address, data bit and CRC check, with a maximum of 261 bytes.
4. Networking mode
Classic Bluetooth adopts a master-slave mode, with a master device capable of connecting up to seven slave devices at most. Low-power Bluetooth supports point-to-point, broadcast and Mesh networking. Mesh networking can achieve many-to-many communication.
5. Transmission process
- Device discovery: The device periodically broadcasts identity information, which is scanned and recorded by other devices.
- Establish a connection: Both parties negotiate parameters such as the channel, protocol version, and key.
- Data transmission: Data is encapsulated through Logical Link Control and Adaptation Protocol (L2CAP), supporting segmented recombination and QoS control.
- Disconnect: Release resources and end communication.
Bluetooth achieves short-range and low-power data transmission through frequency band division, frequency hopping technology, data packet encapsulation and flexible networking methods, and is widely used in audio, Internet of Things and other fields.
