Bluetooth Low Energy 101
Part 1 of a two-part series. Read part two here.
By Allen Henley, LitePoint
The Bluetooth low energy standard was introduced almost six years ago, but it recently has experienced a major resurgence. Some key factors driving this Bluetooth low-energy boom include ease of development and simple deployment.
Bluetooth low energy has emerged as an ideal wireless technology for the Internet of Things (IoT). Bluetooth low energy chipset manufacturers provide turnkey chipsets and development tools, allowing for fast and low-cost development. Additionally, almost every smartphone today supports Bluetooth low energy, making it easy to build a device and deploy it with a simple Android or iOS application.
While it is true that Bluetooth low energy leverages the smartphone installed base and the brand recognition of Bluetooth, Bluetooth low energy applications are much different than classic Bluetooth. Thus, they require different tools and test methodology to ensure they will perform as expected when they reach consumers. Verification and testing need to take place throughout the product lifecycle, from development through manufacturing.
However, the constraints of Bluetooth low energy products’ size, cost, and battery life make it fundamentally more difficult to achieve good RF performance in these systems. At the same time, there is considerable pressure on designers to include built-in, reliable RF on Bluetooth low energy devices. This is because, in many cases, consumers can’t use these products if there’s a problem with the wireless link — and a marginal product will provide a marginal experience for the consumer.
To ensure that devices meet the standard, the Bluetooth Special Interest Group (SIG) mandates that product designs must pass conformance testing before they are permitted to use the Bluetooth low energy brand mark. While these tests ensure that product engineering meets the established standards, they are performed in a lab, with wires and cables attached to the device, and generally are accomplished with special “test firmware” installed. This is not how consumers will experience the product, and therefore these tests do not accurately reflect many real-world performance characteristics that are important to consumers.
For example, important factors like battery life and antenna efficiency will directly or indirectly impact consumer perception of the product, and these need to be fleshed out as part of a complete design verification. This essential step needs to be performed in an environment that is as close to the consumer experience as possible. For this reason, over-the-air testing systems are necessary to supplement the Bluetooth SIG tests, and to provide critical insight into true, real-world performance, which reflects actual customer experience.
This two-part article will provide product designers with the information they need to develop quality Bluetooth low energy products, starting with an understanding of the standard.
Bluetooth low energy, also known as Bluetooth Smart, was introduced with the Bluetooth 4.0 specification in 2010. While earlier versions of Bluetooth, known as Bluetooth Classic, were commonly used in streaming content applications (like headphones or wireless speakers), Bluetooth low energy is intended primarily for short-range, low data rate, long battery life applications. These applications include smart watches, IoT sensors, fitness monitors, beaconing, and home automation.
As the name indicates, the low power aspect of the technology is its defining feature, allowing sensors in some applications to run multiple years on a single button battery. Bluetooth low energy chips consume scant power and spend much of their time in sleep mode — until there is a need to communicate data, at which point the chip will wake up, advertise a need to communicate with the host device, send its data, and then return to sleep mode.
Bluetooth low energy is not designed for high data rate transmission but, during bursts, that data is transferred at roughly 1 Mbps. These devices operate within the unlicensed 2.4 GHz-2.4835 GHz industrial, scientific, medical frequency band, and use a frequency hopping spread spectrum (FHSS) scheme to minimize interference with other devices that may share that spectrum.
Bluetooth low energy is designed to use only 40 2 MHz channels, with a maximum transmit power of 10 mW (increasing with the 5.0 version of the technology). Connection setup and data transfer times are as short as 3 ms, providing a low-latency mode of operation that is very efficient for short data bursts.
In many applications, the required range will be just a few meters — such as from a wearable to a smartphone in a purse or pocket — but factors like device orientation and interference-causing nearby objects can have a significant impact on true effective range. New packet coding methods are being added to the Bluetooth 5.0 standard to provide a long-range option, reducing the data rate and adding more coding gain to improve devices’ useful range. This will be valuable for applications like home automation, beaconing, or checking a mobile patient-monitoring device that needs to communicate with a fixed sensor.
Bluetooth is capable of providing robust security by leveraging its AES-128 encryption and device-pairing capabilities. Initially, Bluetooth low energy supported Secure Simple Pairing, which allowed developers to implement no pairing, passkey pairing, or out-of-band pairing. The LE Secure Connections pairing model — introduced in Bluetooth Core Specification version 4.2 — offers even more security through the addition of new numeric comparison methods and a new, more secure, anonymous key agreement algorithm.
Currently, Bluetooth Core Specification technology is supported by all major mobile operating systems, and the Bluetooth SIG expects that, by 2018, more than 90 percent of all mobile handsets will support Bluetooth low energy. In addition, the technology is supported natively in macOS, Windows, and Linux.
Common Use Cases
To simplify development, the Bluetooth SIG has published a list of general attribute profile use cases for Bluetooth low energy — such as alert notification, battery service, or time profiles — that can be adapted to specific applications. These profiles define a variety of characteristics (a single value requested for the application) and services (a defined collection of characteristics). Also listed are the application program interfaces (APIs) to assist developers in reading and writing data and other functions suited to these applications. Some of the emerging use cases include:
Beaconing — Sending alerts or promotions to a mobile device as the user passes a sensor. The short range of Bluetooth low energy makes it an ideal proximity sensor, pushing specific promotions or information to a consumer, based on their location.
Wireless Tether — Battery operated devices, such as smart watches, motion sensors, or temperature monitors, need to communicate with a smartphone or other controller to share data. Bluetooth low energy technology conserves battery and provides sufficient data rates for these low data rate applications.
Smart Sensor — Sometimes, attaching a wire isn’t an option. One novel application is the smart soccer ball, which features built-in sensors to monitor distance traveled, spin, speed, and acceleration. Bluetooth low energy transfers this data from the ball for real-time or post-processing analysis.
Medical Devices — Bluetooth low energy is showing up in diabetic blood kits, blood pressure cuffs, and other medical systems. These sensors are connected to a user’s smart phone, but the data can be relayed online to a doctor.
With its low energy consumption, low cost, easy development, and sufficient data rates, Bluetooth low energy is helping IoT developers get to market quickly with successful products. In the next article, we’ll look at what IoT design engineers need to know about testing systems to ensure quality operation of their Bluetooth low energy devices.
About The Author
Allen Henley is senior product manager at LitePoint where he is responsible for cellular, Wi-Fi, Bluetooth and IoT test solutions. Prior to LitePoint, Allen held product management roles at Fluke, Agilent Technologies and Hewlett-Packard. He earned a BS in electrical engineering from California Polytechnic State University-San Luis Obispo and an MSEE from Washington State University. Allen is actively involved with his local school district STEM education programs to encourage high school students to pursue rewarding careers in engineering.