With the introduction of Bluetooth low energy technology, considerable interest has been seen in media and the market 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 needs to carefully 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 as well as industrial and medical applications. Classic Bluetooth technology will continue to provide a robust wireless connection between devices ranging from headsets and cars to industrial controllers and streaming medical sensors. Many of these connections are not good candidates for the 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 not practical with Classic Bluetooth technology. Coin cell battery-operated sensors and actuators in medical, industrial, consumer and fitness applications (also known as “Smart”) can now smoothly connect to Bluetooth low energy technology enabled smart phones, 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.
Extremely 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.
Figure 1: Bluetooth low energy technology is implemented in iPhone 4S whereby one can, via an “App”, read up and send data to a Bluetooth low energy device (“smart” device). This demo shows a connectBlue low energy module equipped with temperature sensor, accelerometer and embedded application software forming a complete product/application.
Just as with Classic Bluetooth technology, Bluetooth low energy technology operates in the 2.4 GHz ISM 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 milliseconds. The maximum/peak power consumption is only 15 mA and the average power consumption is of only about 1 uA.
Strong, common features
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.
Limitations
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 utilization approaches continuous transmission.
In other words, some applications are better served with a Bluetooth low-energy connection than others. The use varies depending on the type of device a sensor is connected to.
Figure 2: In a Bluetooth application where streaming data is used, Classic Bluetooth technology is the preferred choice as it achieves substantially greater throughput than Bluetooth low-energy technology. This application is such a situation and shows geodetic instruments used in construction environments, provided by Leica Geosystems.
Differences in bluetooth profile support
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 both have the same Bluetooth profile implemented and there are some important differences between what profiles are available for Classic Bluetooth technology and 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 the standard Specification v4.0, although suppliers like connectBlue can provide a good level of support.
Many other profiles are not offered for Bluetooth low energy technology because of the 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).
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 set-up speed
Weak
Strong
Power consumption
Good
Very strong
Cost
Good
Strong
Table 1: Comparison of classic Bluetooth and Bluetooth low energy technologies.
Bluetooth low energy technology is completely new
In several key aspects, Bluetooth low-energy technology is a totally new technology. For instance, the technology features very efficient discovery and connection set-up, 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 are also 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. All these nuances are needed in order to make the implementation seamless and compatible between devices from different manufacturers.
“Single-mode” and “Dual-mode” – what does that mean?
Because the two technologies are fundamentally different, there are the two following options for implementations:
- Single-mode devices: These 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 sensors have limited resources, they may not be able to support both roles. A typical single-mode device is for example a heart rate sensor.
- Dual-mode devices: These 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. Typical dual-mode devices include mobile phones and PCs.
Conclusion
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. For a complete listing of connectBlue parts available from Digi-Key, follow this link.
