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.

FEATURED

How Bluetooth® Technology Makes Wireless Communication Reliable

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

LEARN MORE

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.

FEATURED DOWNLOAD

Understanding Reliability in Bluetooth Technology

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

INSTANT DOWNLOAD

New Core Specification v5.3 Feature Enhancements

One of the key reasons why Bluetooth® technology has emerged as the global wireless…

Bluetooth® Core Specification Version 5.3 Feature Enhancements

Bluetooth® Core Specification version 5.3 includes several feature enhancements with the potential to improve…

10 Resources That Showcase the Range and Reliability of Bluetooth Technology

Despite the overwhelming adoption of Bluetooth® technology across a wide range of global solutions…

Bluetooth Range and Reliability: Myth vs Fact

For years, Bluetooth® technology enhanced the lives of millions of people around the world, becoming…

Connect: Car Access Demo

In this demo, Texas Instruments will discuss and demonstrate Bluetooth 5.1 and its cutting…

Wireless Connectivity Options for IoT Applications - Commercial Lighting

Industry 4.0 is no longer a thing of the future. The term describes the…

4 Essential Tools for Every Bluetooth Low Energy Developer

One of the biggest challenges of learning any new technology is knowing which tools…

Understanding Reliability in Bluetooth® Low Energy Communication

Achieving reliability in wireless communication systems presents some serious engineering challenges and the job…

Reliable Industrial Communication Using Bluetooth® Technology

As early as 2005, Bluetooth® technology had found its way into control applications in…

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…

IoT Now: Bluetooth technology is reliable by design

Wireless communication systems usually employ radio as the underlying, physical basis to transport data…

Designing and Developing Bluetooth® Internet Gateways

Design and implement your own Bluetooth® Internet working prototype and see for yourself how BIGs allow applications to exchange data with Bluetooth devices from anywhere in the world.

Reliability in the Context of Bluetooth Positioning Systems

“When we invest in infrastructure, we need it to be reliable!” – said every buyer…

Understanding Reliability in Bluetooth® Technology

Download this detailed discussion of the issues and factors that impact the reliability of…

Bluetooth Mesh for Industrial IoT

Bluetooth Mesh lays a framework for large-scale industrial deployments using technology that is already…

Bluetooth AoD as the Technology of Choice for Indoor Positioning Systems (IPS)

This article discusses how GPS and Location Based Services became so ubiquitous that we…

How to Deploy BlueZ on a Raspberry Pi Board as a Bluetooth Mesh Provisioner

This step-by-step study guide will teach you: How to rebuild the kernel on a…

The Bluetooth LE Security Study Guide

Learn about fundamental security concepts, the security features of Bluetooth Low Energy, and gain some hands-on experience using those features in device code.

 Get Help