Interference is one of the biggest challenges for any wireless technology in providing reliable data communication. Since wireless technologies like Bluetooth®, Wi-Fi, and 802.15.4 devices share a transmission medium, it’s possible for a data packet that is being transmitted to be corrupted or lost if it collides with another packet being transmitted at the exact same time and on the same frequency channel.

One of the techniques Bluetooth technology uses to overcome interference and find a clear transmission path that avoids packet collision is the application of a form of frequency-hopping spread spectrum (FHSS) called adaptive frequency hopping (AFH). Bluetooth divides the frequency band into smaller channels (e.g. 40 channels in the case of Bluetooth Low Energy) and rapidly hops between those channels when transmitting packets. To further reduce the chance of interference, Bluetooth adapts its hopping sequence. Channels that are noisy and busy are dynamically tracked and avoided when sending packets.

Recently, Martin Woolley, developer relations manager with the Bluetooth Special Interest Group (SIG), released a paper on Understanding Reliability in Bluetooth Technology. In this deep dive into Bluetooth reliability, Woolley explains how Bluetooth technology uses adaptive frequency hopping to lower the probability of collisions and offset inevitable packet loss.

Below is an excerpt from that section of Woolley’s paper.

Adaptive Frequency Hopping

One of the major challenges in radio communications concerns collisions, which are particularly problematic in busy radio environments. Earlier we explored collisions and explained that a collision occurs when two or more devices transmit data on the same radio channel in overlapping time periods, and that different radio technologies such as Bluetooth® technology and Wi-Fi can interfere with each other if their use of the radio spectrum overlaps.

Bluetooth technology mitigates the risk of collisions through its use of spread spectrum techniques. When two devices are connected, this involves a specific technique known as adaptive frequency hopping.

At each connection event, a pair of connected devices have the opportunity to use their radios to exchange packets at precisely timed intervals. But in addition to this, at the start of each connection event, frequency hopping occurs, with a radio channel being deterministically selected from the set of available channels using a channel selection algorithm. Each device in the connection will then switch to the selected channel and over time and a series of connection events, communication will take place using a frequently changing series of different channels, distributed across the 2.4 GHz band, thereby significantly reducing the probability of collisions occurring.

Of the 40 channels defined for use by Bluetooth Low Energy (LE), 37 of these channels (known as the general purpose channels) are available for use during connected communication.


How Bluetooth® Technology Makes Wireless Communication Reliable

Learn about the challenge of wireless interference and the techniques Bluetooth technology uses to overcome it.


Frequency hopping makes a great contribution to reliability in communication between connected devices but Bluetooth goes one step further.

In a given environment, some Bluetooth® radio channels might not be functioning well, perhaps because interference is impacting them, whereas other channels are working reliably. Over time, the list of reliable channels and unreliable channels may change, as other wireless communication devices in the environment come and go.

The primary device in a connection maintains a channel map which classifies each channel that is working well as used or otherwise as unused. The channel map is shared with the second device using a link layer procedure so that they each have the same information about which channels will be used and which will be avoided.

Devices use implementation-specific techniques to monitor how well each channel is functioning. If it is determined that one or more previously working channels are no longer working well enough, the channel map is updated. Conversely, if a previously bad channel is found to be working well now, its status will also be updated in the channel map. Channel map updates are then shared with the second device. In this way, Bluetooth ensures that it uses only known good channels, avoids problematic channels and keeps the channel map up to date so that it is always the optimal subset of channels that are being used. This is the adaptive aspect of the Bluetooth adaptive frequency hopping system.

Figure 10 – Adaptive Frequency Hopping distributing communication across channels

Figure 10 shows the way the Bluetooth channels were used by two connected devices during testing and illustrates the highly effective way in which radio use is spread across the ISM 2.4 GHz spectrum. At the bottom of the chart you can see the channel index and frequencies in MHz. 

To learn more about reliability in Bluetooth® connection-oriented and connectionless communication systems as well as how to achieve reliability in Bluetooth mesh networks, check out Woolley’s in-depth paper on Understanding Reliability in Bluetooth Technology.


Understanding Reliability in Bluetooth Technology

Download this detailed discussion on reliability in wireless data communication and the techniques Bluetooth technology uses to increase reliability.


Bluetooth® Mesh Feature Enhancements Summary

This paper summarizes the recent Bluetooth® Mesh feature enhancements and provides references to other…

Bluetooth® Mesh Subnet Bridging - Technical Overview

This paper examines subnet bridging, a new feature introduced in the Bluetooth® Mesh protocol…

Bluetooth® Mesh Remote Provisioning - Technical Overview

This paper provides an overview of remote provisioning, a new Bluetooth® Mesh feature that…

Bluetooth® Mesh Private Beacons - Technical Overview

This paper examines private beacons, a type of beacon that can be used to…

Bluetooth® Mesh Directed Forwarding - Technical Overview

This paper provides an overview of directed forwarding, a new Bluetooth® Mesh feature that…

Bluetooth® Mesh Device Firmware Update - Technical Overview

This paper examines the new device firmware update (DFU) feature of Bluetooth® Mesh that…

Bluetooth® Mesh Certificate-Based Provisioning - Technical Overview

This paper provides an overview of the certificate-based provisioning feature that allows digital certificates…

The Latest in HADM with Bluetooth LE

HADM, or high accuracy distance measurement using Bluetooth does exactly what it says –…

Bluetooth® Certificate-based Provisioning - A Technical Overview

This paper details the capabilities and benefits of certificate-based provisioning. Provisioning is the procedure…

Silicon Labs Bluetooth Low Energy Devices Now Support Bluetooth Core Specification 5.4

The release of Bluetooth® Core Specification Version 5.4 earlier this year was met with…

Mr. Beacon Podcast: Snapdragon Sound with Mike Canevaro

This episode of the Mr. Beacon Podcast explores the revolutionary world of Bluetooth audio.…

The Importance of Commissioning in NLC

With constant technology advancements and growing market awareness, we are all getting more and…

Large Scale Bluetooth Mesh Testing

Reliability and latency are the key parameters to be optimized to achieve a seamless…

Top 10 Auracast™ Resources

It’s been almost a year since the Bluetooth Special Interest Group (SIG) released Auracast™…

Features and Benefits of Bluetooth Mesh 1.1 for Wireless Mesh Networking

Commercial and industrial applications like lighting require large-scale, low-power device networks where thousands of…

Bluetooth ESL – The Global Standard for the Electronic Shelf Label MarketBluetooth ESL – 電子棚札市場のためのグローバル規格

Electronic shelf label (ESL) systems have historically relied on proprietary protocols for wireless communication,…

The Bluetooth® Low Energy Primer

Are you new to Bluetooth Low Energy? Learn about its constituent parts, features, and how it works.

Bluetooth® Technology for Linux Developers

Learn how to use the interprocess communication system D-Bus and the BlueZ APIs to create Bluetooth applications for Linux computers.

Bluetooth Range and Reliability: Myth vs Fact

As Bluetooth is becoming more and more ubiquitous in smart homes, buildings, and factories,…

The Path to Reliable Wireless Connections in the Industrial and Commercial IoT

Internet of Things technologies offer opportunities for companies to capitalize on applications in new…

Viewpoint: Reliability, and Bluetooth overcoming interference with AFH

Martin Woolley, Senior Developer Relations Manager, EMEA, at Bluetooth SIG, considers how Bluetooth technology…

Designing and Developing Bluetooth® Internet Gateways

Learn about Bluetooth internet gateways, how to make them secure and scalable, and design and implement your own working prototype gateway and web application for use with either Bluetooth LE Peripherals or with Bluetooth mesh networks.

 Get Help