How Bluetooth Mesh Enables
Scalable, Reliable Low-Power
Wireless Networks

Can you explain the proactive retransmission technique that Bluetooth Mesh utilizes and how it contributes to the reliability of a Bluetooth Mesh network?

The traditional approach to reliability was to use acknowledged messages, have the sender wait for the acknowledgment to come back, and, if it did not, send the original message once again. I call this reactive; you react to the timeout while awaiting the acknowledgment, and you react by retrying. This results in very bad performance and large latency, and the acknowledgments consume radio bandwidth, effectively reducing the network capacity by half. This approach is also impossible to use in multicast (group) communication. A message sent to a group of 50 lights would result in a sudden storm of 50 acknowledgments coming back, most of them colliding with each other, resulting in total network saturation, or even a collapse.

Bluetooth^® Mesh takes a proactive approach; instead of sending a single copy of a message, it sends multiple copies. A mesh message is by default sent as a set of three independent radio transmissions (each on a separate radio channel), and then the whole set may be repeated several times. Statistics is what gives us reliability. Assuming the probability of message loss on a single delivery attempt is 10%, adding a single retransmission brings that number down to 1 percent (10 percent of 10 percent). After two retransmissions, we are at 0.1 percent message loss probability, bringing the reliability to 99.9 percent (three nines). With four retransmissions, we get five nines of reliability. And these five transmissions are still only 10 percent of the load of the 50 acknowledgments in the reactive approach.

On top of that, we have multi-path delivery over multiple hops. In a mesh network, messages may travel over different paths from source to destinations, extending this proactive approach to address events, such as strong, long-lasting local interference or a potential loss of a relaying node. All that without any impact on latency, which in the end makes Bluetooth^® Mesh very reliable as products using it do not exhibit any lags, popcorn effects, and message losses.

What should technical decision makers, product managers, and the like consider when evaluating wireless protocols for their emerging commercial and industrial projects?

You need to do proper due diligence and analyze the facts as well as understand the physics of wireless communication. This will help you understand the qualities which are critical with regard to your requirements. If reliability is one of them, you will find out why packet size and multipath delivery are important and that Bluetooth^® Mesh scores best in both aspects. Talk to companies who have a track record of dealing with different wireless technologies and selected Bluetooth technology as the foundation for their products.

What would you say to change the perception of someone who thinks Bluetooth is still an unreliable wireless technology for use in the device networks space?

I would present them with a collection of case studies. I believe the customers’ and end-users’ opinions speak for themselves. We are fortunate to have reached the point when there is enough public evidence for Bluetooth^® technology being the preferred technology for device networks.