What frequency does Bluetooth use?

Since its inception, Bluetooth technology, as a core standard for short-range wireless communications, has permeated every aspect of consumer electronics, industrial control, healthcare, and other fields. From wireless earbuds in smartphones to sensor networks in smart homes, Bluetooth's frequency design directly determines its anti-interference capabilities, transmission efficiency, and device compatibility.

Globally Harmonized 2.4GHz ISM Band

Bluetooth technology operates in the globally unlicensed ISM (Industrial, Scientific, and Medical) band of 2.400 GHz to 2.4835 GHz, covering 83.5MHz of bandwidth. While this band does not require a license, it is subject to national regulatory requirements. For example, Japan restricts the use of the 2.402-2.473 GHz band, and countries like France have additional transmission power restrictions. Bluetooth divides the frequency band into multiple channels, enabling concurrent communication among multiple devices.

Classic Bluetooth (BR/EDR)'s 79 1MHz Channels

Classic Bluetooth uses frequency-hopping spread spectrum (FHSS) technology, dividing the 2.4GHz band into 79 1MHz-wide channels. The center frequency is calculated as:

f = 2.402 GHz + k × 1 MHz (k = 0, 1, ..., 78).

The device hops 1600 times per second (i.e., switches channels every 625 microseconds), dynamically adjusting the channel sequence to avoid interference. For example, if Wi-Fi channel 6 (2.437 GHz) is detected to be occupied, the Bluetooth master updates the frequency hopping map using the LMP_set_AFH message, disabling the affected channel.

Bluetooth Low Energy (BLE)'s 40 2MHz Channels

To optimize energy efficiency for IoT devices, BLE uses wider 2MHz channels, for a total of 40 channels:

Three advertising channels (37/38/39): with center frequencies of 2.402 GHz, 2.426 GHz, and 2.480 GHz, respectively. These channels intentionally avoid Wi-Fi's commonly used channels 1 (2.412 GHz), 6 (2.437 GHz), and 11 (2.462 GHz) to reduce conflicts during the advertising phase.

37 data channels: These are used for data transmission after connection. They use a pseudo-random frequency hopping algorithm (such as CRC16) to select the next channel, avoiding long-term channel occupancy with Classic Bluetooth or other BLE devices.

 

Frequency Conflict and Coexistence Strategies

The 2.4GHz band is a crowded area for wireless technologies. In addition to Bluetooth, Wi-Fi, ZigBee, cordless phones, and even microwave ovens operate in this frequency band. Bluetooth achieves coexistence through the following technologies:

Dynamic Adaptation of Frequency Hopping Spread Spectrum (FHSS)

Classic Bluetooth's frequency hopping mechanism ensures extremely short channel occupancy (625 microseconds per hop). Even when overlapping with Wi-Fi channels, the probability of collision is only approximately 2% (1 in 79). For example, when a Bluetooth device coexists with a Wi-Fi router, AFH technology dynamically marks channels occupied by Wi-Fi as "disabled." The master device then instructs slave devices to skip these channels and prioritize uninterrupted frequency bands.

BLE Channel Selection Algorithm (CSA)

BLE 5.0 and above introduce an enhanced channel selection algorithm that analyzes historical channel quality data to prioritize channels with minimal interference for data transmission. For example, in a smart factory, hundreds of BLE sensors can use CSA to automatically avoid interfering frequency bands with industrial wireless devices, ensuring reliable data transmission.

Physical Isolation and Band Migration

5GHz Wi-Fi Migration: By switching Wi-Fi devices to the 5GHz band, contention in the 2.4GHz band can be completely eliminated. Antenna Design Optimization: Utilizing directional antennas or MIMO technology reduces signal overlap through spatial isolation. For example, Apple AirPods Max utilizes a customized antenna module that combines Bluetooth signal directionality with head tracking algorithms to reduce environmental interference.

 

The Future of Frequency Allocation

With the release of the Bluetooth 6.0 standard, frequency management has entered a new era of intelligence:

Channel Sounding

Bluetooth 6.0 introduces millimeter-level positioning technology, which accurately calculates the distance and angle between devices by analyzing channel response time differences. For example, in smart home scenarios, routers can use channel sounding to identify the physical location of Bluetooth devices and dynamically adjust transmit power to reduce interference.

AI-Driven Dynamic Spectrum Management

Qualcomm and other manufacturers are developing machine learning-based spectrum sensing algorithms that automatically optimize channel allocation strategies by analyzing 2.4GHz band occupancy in real time (such as Wi-Fi signal strength and Bluetooth frequency hopping patterns). For example, at a concert, AI systems can coordinate channel usage among thousands of Bluetooth headsets to avoid widespread disconnection.

 

From classic Bluetooth's 79-channel frequency hopping to BLE's intelligent channel selection, and then to Bluetooth 6.0's channel detection and AI integration, frequency management has always been at the core of Bluetooth technology's evolution. In the era of the Internet of Everything, Bluetooth has continuously optimized its frequency allocation strategy, not only achieving peaceful coexistence with technologies like Wi-Fi and ZigBee, but also driving the explosion of emerging scenarios such as smart wearables, the Industrial Internet of Things, and high-precision positioning.