Bluetooth (Bluetooth) is abbreviated as BT, and is a wireless communication technology jointly announced by five world-renowned companies: Ericsson, Nokia, Toshiba, IBM, and Intel in May 1998. From the introduction of Bluetooth 1.0 in 1999 to the latest Bluetooth 5.3 standard, the evolution of Bluetooth technology has gone through a long process. Below is a comparative introduction to various Bluetooth versions:
Bluetooth technology stipulates that for communication between each pair of devices, one must be the master role, while the other must be the slave role, in order to communicate. During communication, the master must search for and initiate pairing. Once the connection is successfully established, both parties can send and receive data. Theoretically, a Bluetooth master device can communicate with up to 7 Bluetooth slave devices simultaneously. A device with Bluetooth communication capabilities can switch between the two roles, usually operating in slave mode, waiting for other master devices to connect. When needed, it switches to master mode to initiate a call to other devices. When a Bluetooth device initiates a call in master mode, it must know the Bluetooth address of the other party, the pairing password, and other information. Once paired, it can directly initiate a call. During Bluetooth communication, the master device initiates the call by first searching for nearby discoverable slave devices. After the master device finds a slave device, pairing is conducted, during which the PIN code of the slave device may need to be entered; some devices do not require a PIN code. Once pairing is complete, the slave device records the trust information of the master device, allowing the master device to initiate a call to the slave device. Devices that have been paired do not need to re-pair during subsequent calls. A paired device, as a slave, can also initiate a communication request. After a communication link is successfully established, bidirectional data or voice communication can occur between the master and slave devices. During the communication state, both master and slave devices can initiate and disconnect links.
Bluetooth operates in the free ISM frequency band: 2400~2483.5MHz, using GFSK modulation. There is a protective bandwidth at both the front and back of the frequency band, specifically 2.4~2.4019GHz and 2.481~2.4835GHz. Versions after Bluetooth 4.0 are divided into Classic Bluetooth and Bluetooth Low Energy (BLE). Classic Bluetooth is divided into 79 channels, with a channel spacing of 1MHz, supporting only point-to-point communication. Bluetooth Low Energy has a total of 40 channels (3 advertising channels + 37 data channels), with a channel bandwidth of 2MHz, supporting point-to-point, point-to-multipoint, and multipoint communication forming a MESH. Whether Classic Bluetooth or Bluetooth Low Energy, both support frequency hopping technology. This is because the ISM frequency band is an open licensed band, so there are many other devices operating in the same frequency band. To avoid interference with other devices, Bluetooth automatically hops to frequencies with less interference, greatly improving the reliability and stability of Bluetooth operation. The power levels of Bluetooth devices are divided into three classes: power class 1, power class 2, and power class 3. Below are the power limits for different power levels:
In addition, Bluetooth chip manufacturers are continuously innovating to enhance the user experience of Bluetooth products. For example, Qualcomm’s XPAN technology is a Bluetooth personal area network technology that can enhance Bluetooth signals through Wi-Fi signals. The XPAN technology seamlessly switches to a Wi-Fi connection before the Bluetooth signal drops or attenuates to a noticeable level for the user. This way, even when beyond the effective range of Bluetooth, users can still transmit audio signals via Wi-Fi, ensuring that music playback does not stutter or interrupt, greatly improving the user experience.