Going the Distance: Four Approaches for Expanding the Range of Bluetooth

Design engineers face a conundrum when it comes to Bluetooth Low Energy. BLE is chosen for a design project with full knowledge of its limited range in order to take advantage of the technology’s other strengths. But the implementation, once completed, often requires greater range than BLE can deliver. It’s a Catch-22 that many design engineers face when they work on a BLE-enabled project. BLE is the perfect fit, except for that “minor” detail about how it can’t achieve one of the most important aspects of the project: adequate range to successfully support the product’s core functionality. 

Sometimes engineers know they will face this conundrum going into the project, so they are at least heading into this eyes wide open. Nonetheless, it’s still an unpleasant surprise to engineers who believe they will have enough range based on antenna & module data sheets only to find that those numbers are based on idealized testing environments and are far different from the range that can be achieved in real-world environments. This is not the kind of surprise that engineers appreciate, but fortunately there are ways to extend the range of Bluetooth-enabled products. 

The key is to pick the approach that makes the most sense for your project. This white paper outlines four approaches to extend the range of Bluetooth for wirelessly-connected devices and is designed to use as a practical guide for navigating that process. 

Before I discuss those four approaches in detail, though, I should reiterate the point I made above about taking the published range of an antenna or module with a large grain of salt. Too often, those numbers are based on testing that does not reflect the way real-world environments limit range. Essentially, there is a “hypothetical range” in marketing materials that differs significantly from the “actual range” engineers will see once it is implemented. For that reason, the most important piece of advice I share in this white paper might be to have a healthy skepticism about range data from manufacturers and to conduct your own testing to: 

1) measure the actual range in real-world conditions

2) determine how much you need to extend range to successfully support the device’s use-case. 

To do that, you have to test it in situ. Modeling is not enough to get accurate data. Once you have reliable data about actual range and know how much your team will need to extend that range, there are four approaches to choose from:

• Using the Long-Range Feature in Bluetooth 5
• Amplifying the signal
• Employing a repeater to relay the signal
• Utilizing BLE Mesh 

For engineers who have only tried to increase range through signal amplification in the past, it is important to know that there are far more tools in the toolkit for achieving greater range.

Using the Long-Range Feature in Bluetooth 5 

Bluetooth 5 has an excellent feature for expanding the range of wireless devices, but it has not received as much attention as other enhancements in the most recent release of the Bluetooth standard. The capability is called LE Long Range/Coded PHY, which provides amplification in a novel manner: not by simply increasing power into the antenna or cranking up receive gain settings, but by using “bit repetition” that sends each bit in the data packet as a coded 8-bit byte in order to give more devices at farther distances the opportunity to successfully receive transmissions. It may not seem plausible at first that simple repetition can truly improve the range of listening devices that can successfully receive transmissions – especially since range issues have traditional been solved by pushing more power into antennas.

But there’s a simple analogy that illustrates it in everyday terms: if there is a large room of people at various distances from you, only the closest people will be able to closely follow a story you are telling at a normal speaking voice. Let’s say that is everyone within 8 feet of you. To help more people follow along, you could yell your story (i.e. increase power to the antenna to amplify output), or you could continue speaking at a normal volume but repeat each word 8 times. Each person in the room would simply need to hear 1 of those repetitions to follow your story, which gives the people in the back of the room a far better chance to understand what you’re saying. So even though many of the listeners are yards and yards away, they could successfully follow your very long story about how you got a great deal on the pre-owned 2004 Honda Accord that you bought for far less than the estimated value in  Kelley Blue Book (Parkers for those of you in the UK).

Repetition is remarkably effective at increasing range without the need to “yell across the room,” and testing by the Laird team and other organizations show that LE Long Range/Coded PHY can successfully increase range by 50-100 percent while also improving sensitivity of receiving devices by 4-6dB. There are naturally tradeoffs in terms of speed of transmissions and throughput of data transfer when using LE Long Range/Coded PHY. Essentially, your story about the Honda Accord will take 8 times longer to tell. But this tradeoff may be very worthwhile for many engineering teams in order to achieve up to twice the range. For readers looking for a deeper dive into this feature of Bluetooth 5, please read this blog post and related application note on the Laird Connectivity website or this post by our chip partner Nordic.

Amplifying the Signal

This second approach is the one that most engineers have direct experience with, and it continues to be a viable option for increasing the range of Bluetooth. It involves increasing the strength of the signal by increasing the power being channeled into the antenna to produce a stronger RF output. To continue the Honda Accord analogy above, this is about talking at a far louder volume so even the people at the back of the room can follow along. It is essentially a “brute force” method that achieves greater range, but with some caveats. The first caveat with this approach is that certification standards have firm limits on how much power amplification can be utilized while still staying within the limits set by certifying bodies in the U.S., the E.U., and internationally.

For example, the U.S. permits maximum BLE power of +20dBm while the E.U. only permits a maximum of +10dBm. The varying limits are important for engineering teams to be cognizant of if they are planning to utilize signal amplification, particularly for products that will be deployed worldwide. Pushing amplification too hard can therefore put your device at risk of failing certifications. Assuming you are within those certification guidelines, though, there are other caveats with this approach. Amplifying the signal uses more battery than operating a device, and the drop in energy efficiency could be significant enough to make the battery life impractical for the device’s use case. It is important to calculate and test this tradeoff between signal amplification and battery life to ensure that extending range will not undermine longevity of the device’s power source. With all of that said, signal amplification works well when it will not lead to unacceptable loss of battery life and when the certification constraints are acceptable for your use of the product in a global application.

Employing a Repeater to Relay the Signal 

This third approach is made possible with the Bluetooth 5 protocol, which gives product engineers more options for increasing range beyond the “brute force” approach above. With this approach, the Bluetooth device does not use internal signal amplification, which enables engineers to preserve battery life by not seeking increased range through more power being channeled into the antenna. Instead, a repeater device serves as a go-between that can expand the distance between two Bluetooth devices that need to communicate – repeating the message until it is received by the target device. This extends the effective range of a Bluetooth device without engineering changes that affect battery life or have certification tradeoffs.

Repeating the signal works best when the physical layout of devices and repeaters do not change, when physical objects in the environment do not change over time, and when the RF landscape is static. In that scenario, engineers can plan where to place devices and repeaters and know they will continue performing as designed. But in a more dynamic environment, this approach can underperform over time. Engineers should therefore take into consideration what kind of environment the use case will be deployed in in order to determine if this route to extended range is the best of the four tools in the toolkit. Assuming a relatively static environment, repeating the signal has a number of advantages over signal amplification that will make it the best option for many implementations.

However, I should point out an important caveat with this repeater option is utilized: Commissioning gets more complex in deployments that utilize repeaters, because of the additional burdens it puts on engineers to maintain secure communications. In order to repeat messages through this approach, all of the devices in the network need to be commissioned with security protocols that have levels of trust with the repeater device. That, in and of itself, adds complexity to the commissioning process, but it becomes even more complex if the repeating device ever fails and needs to be replaced. In that common situation, every device in the network would need to be re-commissioned to have a secure connection with the new repeating device.

Utilizing BLE Mesh 

This last approach may be the least familiar to design engineers, but it has a significant advantage over the three above: BLE Mesh networks can achieve extended ranges without concern for how much the physical environment and RF landscape changes over time. In a BLE Mesh network, messages are relayed across the network of interconnected devices until it reaches intended recipients, enabling engineers to achieve extended range not through power amplification or repeaters but via the BLE devices themselves. For an introduction to BLE Mesh and best practices for designing these devices and networks, please see two prior white papers I wrote that jointly serve as a practical guide to working with BLE Mesh: “Making BLE Mesh Simple” and “BLE Mesh: Friends are the Key to a Long [Battery] Life.”

BLE Mesh is able to achieve far greater potential range than both power amplification and signal repeating. I should make an important point here for engineers working with battery-powered devices: in order for wireless devices to achieve their desired battery life, these BLE Mesh deployments should utilize the Low Power Node feature in the Mesh protocol as well as utilize the “Friend” mode for some nearby devices in the network. This conserves battery power because the Friend device is responsible for the active listening role that captures incoming messages, while the Low Power Node can maximize its time in sleep mode and check with the Friend for relevant messages only occasionally. Not utilizing that feature and deployment strategy will drain battery life by having all device radios listening 100% of the time, which can consume about 3mA current continuously hence a steady drain on batteries.

With that said, BLE Mesh can greatly extend signal range. Many engineers may be new to working with BLE Mesh, but the design and commissioning are actually quite simple and intuitive when using a module like Laird’s BL654 that abstracts the inherent complexity of how BLE Mesh works and allows engineers to use existing skills to take advantage of Mesh capabilities.One final thought: It may even be possible to have your LECODED and BLE Mesh cake and eat it, too, by leveraging both capabilities in a single implementation. This would be possible with the deployment of a “proprietary solution” where the mesh adverts are sent as LE_CODED messages. There are pros and cons to this approach. One downside is that networks utilizing a proprietary setup like this would have interoperability issues with normal Mesh deployments, but there may be scenarios where an engineering team would choose this in order to take advantage of upsides such as the strong security of Mesh. 

There will continue to be projects where signal amplification is clearly the best approach to extending range, but having three additional approaches to extending Bluetooth range gives design engineers more options for achieving that goal while mitigating engineering tradeoffs in ways that are optimized for the use case and the environment of the application.

Laird Connectivity’s Bluetooth Modules

Laird Connectivity provides a full suite of Bluetooth modules that deliver robust performance, easy global certification and simple implementation to accelerate your entire new product development cycle.

Laird Connectivity’s Bluetooth 5 modules include the BL654PA Series of Bluetooth modules, which provides all of the benefits of Laird’s popular BL654 modules but with the extended PA/LNA support that enables even greater range. Key features of the BL654PA Series include an integrated Skyworks Power Amplifier capable of up to +18 dBm output.

The BL654 Series, including BL654PA, is a complete multi-protocol embedded wireless offering with exceptional processing capability, all at a micro power budget. Powered by Nordic’s nRF52840 silicon, the small form factor BL654 modules, DVKs and USB Dongle provide for a secure, robust BLE and Cortex -M4F CPU for any OEM’s product design. The BL654 provides you with maximum development flexibility with programming options for the Nordic SDK, a simple, intuitive AT Command Set, as well as Laird’s own smartBASIC environment. The BL654 series brings out all nRF52840 hardware features and capabilities including USB access, up to 5.5V supply considerations, and 802.15.4 (Thread) implementation. Complete regulatory certifications enable faster time to market and reduced development risk completes.

Organizations designing and implementing BLE Mesh devices and networks can dramatically simplify that process using Laird Connectivity’s BL654 Series of Bluetooth modules. The BL654 allows device designers and provisioners to bypass the complexity of BLE Mesh’s internal working and focus on achieving their end goals. Laird Connectivity’s BL654 Series builds upon the field-proven BL600 and BL652 Series, reducing engineering burden and design risk, and speeding time-to-market when integrating BLE, as well as Thread (802.15.4) and NFC capabilities into an OEM design. In addition to the stand-out Bluetooth 5 features of enhanced data rates and LE Long Range, the BL654 also integrates BLE Mesh capabilities in a high TX power platform, providing innovative new application possibilities for low power, long-range sensor networks.

Laird Connectivity also provides a range of other solutions that utilize earlier iterations of the Bluetooth standard, including Bluetooth 4.0 and 4.2 and Bluetooth 2.0, 2.1 and 3.0. A full range of solutions that combine the capabilities of Bluetooth with other wireless technologies such as Wi-Fi and LoRA are also available from Laird Connectivity.

About the Author

Jonathan Kaye is the Senior Director of Product Management at Laird Connectivity. In this role at the company, Kaye is a lead developer of Laird’s embedded wireless connectivity solutions. He has more than 20 years of experience in the embedded wireless and product design field, including positions at EZURiO and Lever Technology before joining Laird a decade ago.