Low energy Bluetooth wireless protocol

Bluetooth low energy technology isn’t just another Bluetooth revision—it’s a whole new technology that can benefit industrial communications.

06/06/2012


There’s considerable interest in Bluetooth low energy technology regarding its possibilities. Bluetooth low energy technology also has some important limitations as well as benefits; it is quite different from Classic Bluetooth technology. It is so different that one carefully needs to consider which technology best fits the application needs.

Bluetooth technology was originally designed for continuous, streaming data applications, including voice, and has successfully eliminated wires in many consumer, industrial, and medical applications. Classic Bluetooth technology will continue to provide a robust wireless connection between devices, such as headsets, cars, industrial controllers, and streaming medical sensors. Many of these connections are not good candidates for new Bluetooth low energy technology, but many other new applications will be.

Bluetooth low energy technology was introduced in 2011 through the Bluetooth Specification v4.0 (Bluetooth v4.0). With its extremely low power consumption, unique characteristics, and new features, Bluetooth low energy technology enables new applications that were impractical with Classic Bluetooth technology. Coin cell battery-operated sensors and actuators in medical, industrial, consumer, and fitness applications (also known as “Smart”) can smoothly connect to Bluetooth low energy technology enabled  smartphones, tablets, or gateways (also known as “Smart Ready.”) Bluetooth low energy technology is ideal for applications requiring episodic or periodic transfer of small amounts of data.

Low power consumption

The key feature of Bluetooth low energy technology is its low power consumption that makes it possible to power a small device with a tiny coin cell battery, such as a CR2032 battery, for 5-10 years. (Click application image for video link.)

Bluetooth low energy technology is implemented in iPhone 4S whereby one can, via an app, read and send data to a Bluetooth low energy device (“smart” device). This demo shows a connectBlue low energy module equipped with temperature sensor, accelerometer,Just as with Classic Bluetooth technology, Bluetooth low energy technology operates in the 2.4 GHz ISM (industrial, scientific, and medical) radio band and has similar radio frequency (RF) output power; however, since a Bluetooth low energy device is in sleep mode most of the time and only wakes up when a connection is initiated, the power consumption can be kept to a minimum. Power consumption is kept low since the actual connection times are of only a few mS. The maximum/peak power consumption is only 15 mA and the average power consumption is only about 1 uA.

Features in common

Many features of Classic Bluetooth technology are inherited in Bluetooth low energy technology including Adaptive Frequency Hopping (AFH) as well as part of the Logical Link Control and Adaptation Protocol (L2CAP) interface.

Bluetooth low energy technology also implements the same link security with simple pairing modes, secure authentication, and encryption.

This inheritance makes Bluetooth low energy technology very easy to set up, robust, and reliable in tough environments.

Data transfer vs. battery

The use of low power consumption and coin cell battery operation also has its limitations. Data transfer rates with Classic Bluetooth technology using Enhanced Data Rate (Bluetooth v2.1 + EDR) can exceed 2 Mbps (actual payload), but practical transfer rates for Bluetooth low energy technology are below 100 kbps (actual payload of roughly 1/20). Therefore, streaming Bluetooth low energy connections will lose a great deal of the huge potential power savings as the use approaches continuous transmission.

In other words, some applications are better served with a Bluetooth low energy connection than others. Use varies depending on the type of device a sensor is connected to. (See geodetic instruments image.) 

Profile support differences

The behavior of a Bluetooth connection, whether Classic or low energy, is determined by the Bluetooth profiles a device has implemented. Devices can only connect if they each have the same Bluetooth profile implemented, and there are some important differences between profiles for Classic Bluetooth technology and those for Bluetooth low energy technology.

A good example of the differences is seen in serial port emulation. Classic Bluetooth technology provides the Serial Port Profile (SPP) for emulation of serial data connections. Bluetooth low energy technology provides no such support in standard Specification v4.0; although suppliers can provide a good level of support.

Many other profiles are not offered for Bluetooth low energy technology because of differences in the connection models. The Classic Bluetooth scenarios that are not part of Bluetooth low energy technology include headset (HSP), object exchange (OBEX), audio distribution (A2DP), video distribution (VDP), and file transfer (FTP). See the following table.

Classic vs. low energy Bluetooth

Attribute

 

Classic Bluetooth technology

 

Bluetooth low energy technology

 

Data payload throughput (net)

 

2 Mbps

 

~100 kbps

 

Robustness

 

Strong

 

Strong

 

Range

 

Up to 1000m

 

Up to 250m

 

Local system density

 

Strong

 

Strong

 

Large scale network

 

Weak

 

Good

 

Low latency

 

Strong

 

Strong

 

Connection setup speed

 

Weak

 

Strong

 

Power consumption

 

Good

 

Very strong

 

Cost

 

Good

 

Strong

 

New Bluetooth technology

In several key aspects, Bluetooth low energy technology is a totally new technology. For instance, the technology features very efficient discovery and connection setup, short data packages, and asymmetric design for small devices.

Just as with Classic Bluetooth technology, Bluetooth low energy technology is based on a master connected to a number of slaves. However, in Bluetooth low energy technology the number of slaves can be very large; how large depends on the implementation and available memory. The new “advertising” functionality makes it possible for a slave to announce that it has something to transmit to other devices that are “scanning.” “Advertising” messages can also include an event or a measurement value.

There also are differences in software structure. In Bluetooth low energy technology all parameters have a state that is accessed using the Attribute Protocol. Attributes are represented as characteristics that describe signal value, presentation format, client configuration, etc. The definitions of these attributes and characteristics along with their use make it possible to build numerous basic services and profiles like Proximity, Battery, Automation I/O, Building Automation, Lighting, Fitness, and Medical Devices. These nuances make the implementation seamless and compatible between devices from different manufacturers.

Single, dual modes

Because the two technologies are fundamentally different, there are the two following options for implementations:

  • Single-mode devices are stand-alone Bluetooth low energy devices (also known as “Smart” devices) optimized for small battery-operated devices with low cost and low power consumption in focus. Since the sensors have limited resources they may not be able to support the sensor role and the collector role. One example of a single-mode device is a heart-rate sensor.
  • Dual-mode devices (also known as “Smart Ready” devices) include both Bluetooth low energy technology and Classic Bluetooth technology. Dual-mode devices will rarely gain in power saving since they need to support both technology implementations; the power savings will only be achieved with the single-mode option. Dual-mode device examples include mobile phones and PCs.

 

Application selection

In other words, even if both technologies have a common name in “Bluetooth,” it is important to understand that the addition of Bluetooth low energy technology is not the same thing as when new versions of the Bluetooth Specification have been released in the past.  For some applications “Classic” is the best choice, and for others “low energy” is the best choice. Bluetooth low energy technology does not replace Classic Bluetooth technology—it is a whole new game.

- Rolf Nilsson is CEO and Bill Saltzstein is the U.S. president of connectBlue. Edited by Mark T. Hoske, content manager CFE Media, Control Engineering, Plant Engineering, and Consulting-Specifying Engineer, mhoske(at)cfemedia.com.

See connectBlue wireless technology comparisons

ONLINE extra

About the authors: Rolf Nilsson is the CEO and founder of connectBlue with more than 30 years of thorough insight and know-how from industrial automation and communication. Before founding connectBlue, Rolf was the President of Eurotherm Scandinavia, and before that he was in leading positions at Alfa Laval Automation/ABB Automation Products.

Bill Saltzstein is the U.S. president and the medical business development manager of connectBlue. with over 25 years of experience in medical device development and wireless technology.Prior to joining connectBlue, Bill worked as a wireless medical expert through his own company, Code Blue Communications, and product management and development positions at Medtronic Physio-Control, Instromedix, and Hewlett-Packard.

About connectBlue: connectBlue is a leading provider of robust industrial and medical wireless solutions, designed and tested for the most demanding applications and environments. Based on Bluetooth technology, Wireless LAN (WLAN) and IEEE 802.15.4 / ZigBee, connectBlue provides ready-to-use products and modules as well as custom design solutions. connectBlue has its head office in Sweden and local offices in Germany and the U.S.; connectBlue is a registered trademark of connectBlue AB.

http://www.connectblue.com

See controleng.com/wireless for more about industrial wireless. 



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