Bluetooth® Low Energy Channels

As described in the physical layer, Bluetooth® Low Energy (BLE) uses 40 channels, divided into two types. A frequency hopping scheme is implemented for robust operation.

# Channels

There are two types of link layer channels: advertising channels and data channels:

• Device discovery
• Connection establishment

## Data Channel Usage

• Bidirectional communication between connected devices
• Adaptive frequency hopping used for subsequent connection events

When in a data connection, a frequency hopping algorithm is used to cycle through the 37 data channels:

(1)
\begin{align} {f}_{n+1} = \left({f}_{n} + hop \right) mod\, 37 \end{align}

Where fn+1 is the frequency (channel) to use on the next connection event and hop is a value that can range from 5-16 and is set when the connection is created. It is added onto the last frequency module 37.

The following diagram depicts three active BLE connections, showing the frequency hopping sequence (frequency hopping on Link 3 is outlined for clarity):

The diagram shows that frequency hopping provides a robust method for maintaining a connection in the presence of interference or many other devices in the radio range.