PHY & Radio

Channel Map

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A bitmask indicating which of the 37 data channels are in use for a BLE connection, updated dynamically to avoid interference.

    


    
    
  


  




  
  

    
Channel Map


The channel map is a 37-bit bitmask that indicates which of the 37 BLE data channels (channels 0--36) are currently in use for a specific connection. It is the mechanism through which adaptive frequency hopping avoids channels degraded by interference from Wi-Fi and other 2.4 GHz sources sharing the ISM band.


How the Channel Map Works


When a BLE connection is established, the central device sets the initial channel map, typically with all 37 data channels enabled. As the connection progresses, the central monitors link quality metrics such as packet error rate and CRC failures on each channel. Channels experiencing persistent interference -- for example, from a Wi-Fi access point operating on an overlapping frequency -- are marked as unused in the channel map.


The central communicates channel map updates to the peripheral via the LL_CHANNEL_MAP_IND link layer control PDU. This message specifies the new bitmask and an instant (connection event counter) at which both devices must begin using the updated map. The peripheral must apply the new map at the specified instant to maintain synchronization with the central's hopping sequence.


Minimum Channel Requirements


The Bluetooth specification requires that at least two data channels remain in the channel map at all times. In practice, BLE connections function well with as few as 10--15 channels, though using fewer channels increases the probability of collisions and reduces aggregate throughput in dense deployments with multiple concurrent connections.


Channel Map and Wi-Fi Coexistence


The three BLE advertising channels (37, 38, 39) are fixed and cannot be excluded from use, but they are strategically placed at 2402, 2426, and 2480 MHz to avoid the center frequencies of Wi-Fi channels 1, 6, and 11. The data channel map provides additional protection for connected data transfer by blacklisting any of the 37 data channels that overlap with active Wi-Fi channels.


On SoCs with integrated Wi-Fi and BLE radios (e.g., ESP32, ESP32-C6), the coexistence controller can proactively update the BLE channel map based on which Wi-Fi channels are active, avoiding interference before it causes packet loss rather than reacting after the fact.

  

  

  
  
  




  
  
Related Terms

  

  

    
    Frequency Hopping
    
  





  

  
  

  
  

  
  
  

    
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…is implemented. BLE Adaptive Frequency Hopping The channel map used by a BLE connection can be updated dynamically to…

        
      
      
    

  

  

  
  




  
Frequently Asked Questions


  

    
    

      
      

        
Our glossary covers 90+ BLE technical terms organized by category. Each term includes a definition, related terms, and links to relevant chips and guides.