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Which Bluetooth flavour suits your taste?

13 Feb 2013  | Karl Helmer Torvmark

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Not immediately apparent from the Bluetooth specifications is the fact that the relaxed requirements allow IC vendors to do a lot of optimisations that are difficult or impossible to make with "classic" Bluetooth, lowering sleep and active currents and shortening switching times. These optimisations enable single-mode chips to be lower power, simpler and lower cost than dual-mode or classic chips.

There are also differences at the profile layer. Bluetooth low energy profiles so far are all layered over GATT, using the GATT/ATT protocol to exchange data. In "classic" Bluetooth, profiles often define their own protocols. This is more flexible, but renders the implementation more complex and increases the amount of code that needs to run.

Figure 3: Comparison of Bluetooth low energy (left) and Bluetooth "classic" (right) architecture.

So, which one should you choose?
Newer ICs are generally dual-mode rather than "classic," so from a hardware perspective, the choice will often be made for you. Certain application-specific devices might continue to be BR- or BR/EDR-only if the application they are targeted at does not make use of Bluetooth low energy. From a software perspective, many commonly-available Bluetooth stacks include low energy support at this point, although again, there may be some that will not.

When it comes to choosing between dual-mode and single-mode ICs or system-on-chips (SoCs), it depends on what application you are targeting. If you need to communicate with "classic" devices, then the choice is simple – you need to use a dual-mode device. If you have flexibility on both sides of the link, then the most important criteria are determined by what and how much data you are moving over the wireless link.

If you are moving a lot of data or streaming media, then you should go with a BR/EDR solution. An example of this type of IC would the CC2564 from TI. This IC contains the Bluetooth v4.0 stack up to the HCI level, with the rest of the stack running on the host microcontroller (MCU).

If you are only transmitting smaller amounts of data then Bluetooth low energy may be a better choice. Bluetooth low energy can provide very long battery life when used in the types of use-cases it was designed for. For example, a sensor communicating with a phone once every second 24/7 will last for more than a year on a CR2032 coin cell. Power consumption (and therefore battery life) scales with the communication period used.

The minimum supported period in BLE is 7.5 ms, the maximum is 16 seconds. The 16 second limit is related to a communications time-out; if longer times are needed, it is possible to drop the connection and then reconnect every time as needed. As explained earlier, the fact that only 3 channels are used for reconnection means that reconnection is much faster than "classic" Bluetooth, on the order of milliseconds rather than seconds.

The industry is moving to ICs that can implement all the functionality in a sensor-type device except the sensing element itself. The CC2541 from TI is an example of a single-mode Bluetooth low energy SoC solution containing the radio, an MCU and peripherals, as well as on-chip reprogrammable flash memory.

Other factors may also play a role. For example, if you want your device to be able to communicate with iOS-based devices, then Bluetooth low energy may be an easier way to achieve that. Apple currently requires any BR/EDR devices that support anything other than a set of pre-defined profiles to be certified under the MFI program. For Bluetooth low energy devices there are no such restrictions, and an iOS app running on an iPhone 4S, iPhone 5, iPod touch (5th generation) or iPad 3 (using iOS 5 or newer) can use a GATT-based API to communicate with BLE devices.

When it comes to other operating systems, some Android phones already support Bluetooth v4.0 and we expect more to come. Windows 8 will ship with full Bluetooth v4.0 support, and APIs have already been revealed at Microsoft developer events.

Another factor to consider is the ease of development and availability of development tools and documentation. Some single-mode Bluetooth low energy vendors provide royalty-free software stacks and all documentation openly available from a web site. In the "classic" Bluetooth space, it is more common to charge royalties for the protocol stack and keep datasheets and other technical documentation under NDA.

Conclusion
With Bluetooth v4.0, designers of Bluetooth devices have another tool in their tool-box, one known variously under the monikers Bluetooth Smart, Bluetooth Smart Ready or Bluetooth low energy. Regardless of what you call it, this new technology builds on the massive success of Bluetooth in the short-range wireless market and enables new applications to make use of Bluetooth technology through lower power consumption, lower complexity and lower cost.

About the author
Karl Helmer Torvmark has been working for Texas Instruments since 2006 and Chipcon since 2001 (Chipcon was acquired by TI in 2006). During this time, he has had several roles, including Field Application Engineer, Product Marketing Engineer and Strategic Marketing. He has been involved with Bluetooth low energy (Bluetooth Smart) since it was still called Wibree. Currently, he is responsible for product strategy in TI's Low Power RF group. In his spare time, Karl enjoys electronic music, electronics DIY as well as repairing and playing old arcade games.

To download the PDF version of this article, click here.


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