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Bluetooth Low Energy: Chips, Use Profiles and Development Tools Coming Online Fast



The adoption of Bluetooth low energy (Bluetooth Core Specification Version 4.0) in July 2010 and the likely approval In April 2011 of the first four application profiles will put a powerful new technology into the hands of engineers who design ultra-low-power (ULP) wireless products.

Four semiconductor companies are already fielding chips and modules that conform to the Bluetooth low energy specification, and new development tools are coming to market quickly. Also – for the first time in its history – the Bluetooth SIG will conduct training courses in its newest technology. Considering that work on the spec began more than three years ago, it is finally practical to consider it for ULP applications that operate in the 2.4-GHz band.

Bluetooth low energy opens a wide range of applications to standards-based designs that need to operate for months or even years on coin-cell batteries. This vast application space has already been successfully pioneered by proprietary technologies and includes:
  • Health and fitness
  • Short-range medical monitoring
  • Remote-controlled entertainment devices and toys
  • Proximity applications, such as automatically unlocking doors and keeping tabs on small children, pets, and objects such as umbrellas or laptop computers
Bluetooth low energy may not always outperform the proprietary technologies in power consumption, range and other criteria. It does, however, deliver a competitive level of performance and has one other big advantage: earlier versions of Bluetooth technology are already integrated into hundreds of millions of mobile phones.

Although ULP technologies are often talked about, mobile phones are just as useful in many applications and the Bluetooth SIG has taken advantage of this installed base. It has paved the way for dual-mode chips that can communicate with both the Bluetooth V3 and V4.0 core specs.

What is Bluetooth low energy?
Previous versions of the Bluetooth spec – now known as Classic Bluetooth – were not created with personal area networks (PANs) in mind and therefore had a serious disadvantage in ULP applications. They could not run for months on coin cell batteries such as the 3-V lithium CR2032. Even larger batteries could not provide competitive lifecycles for products such as wireless keyboards and mice.

Classic Bluetooth (V3) owns the wireless mono headset market, however, in part because it operates with a synchronous protocol and essentially is “always on.” Data is exchanged every 600 μs just to maintain the communications link. But when the link is broken, the Classic Bluetooth link-up algorithm requires about a second to be re-established, which is too long for some PAN applications.

Although Bluetooth low energy still uses a synchronous protocol, it can compete with proprietary technologies in ULP markets because its duty cycle can be adjusted from 5 ms up to several seconds. The V4.0 spec also implements a number of other energy-conserving strategies, such as maximized standby time, faster connections, and reduced peak transmit/receive power.

To take advantage of the fact that packing lots of data into a long packet is more energy efficient than sending multiple packets, Bluetooth low energy’s message length is also adjustable. Plus, it includes other features pioneered by proprietary ULP technologies, such as maximized standby time, faster connections, and reduced peak transmit/receive power. Figure 1 illustrates the simplicity of the new, low-energy architecture.


Bluetooth Core Specification 4.0 low-energy (single-mode) architecture.

The key feature of the low-energy stack is a lightweight Link Layer (LL) that provides ultra-low power idle mode operation, simple device discovery and reliable point-to-multipoint data transfer with advanced power-save and encryption functionalities. Figure 2 shows the LL packet format.

Preamble
(1 octet)
Access Address
(4 octets)
PDU
(2 to 39 octets)
CRC
(3 octets)
Bluetooth low-energy link layer (LL) packet format

The packet includes a preamble for radio synchronization, an access address for physical link identification, a protocol data unit (PDU) to carry the payload data and the PDU header information, and a cyclic redundancy code (CRC) to ensure correctness of the data in the PDU. The payload data length is variable from two to 39 packets. The low-energy implementation obtains significant power savings by omitting unnecessary information (already known by the receiving device) when possible.

Single-mode chips are highly integrated, inexpensive devices. When operating in Bluetooth low energy mode, dual-mode chips will consume about 75 to 80 percent of conventional Bluetooth chips and cost just dimes more. Dual-mode chips will share much of Bluetooth technology’s existing functionality and radio in a single die.

To leverage the millions of Bluetooth sockets in cell phone and other devices, the Bluetooth SIG included dual-mode operation in its Core Specification 4.0 dual-mode chips. The generalized use scenario is for multiple single-mode devices operating at transmit power of <15 ma to communicate with dual-mode chips in cell phones and other devices. Dual mode chips execute a protocol that mediates between the Classic Bluetooth protocol and the low-energy protocol.

Low-energy profiles
The Bluetooth SIG is expected to adopt the first set of profiles for the low-energy, V4 core specification sometime this month. The profiles will include a generic health-and-fitness-device profile that identifies where and how a device is located on the body, as well as necessary documentation about the device. A thermometer profile also was approved. The next set, which might arrive as early as April, will include a heart rate monitor. The first profiles for proximity applications are also expected. They would cover applications such as a low-energy chip on a key fob that will inform the cell phone if it is separated by more than a few meters.

Recently introduced low-energy products include:
  • CSR Ltd’s µEnergy platform, which consists of two chips, the CSR1001, for keyboards and remote controls, and the CSR1000, which offers a smaller package for fitness products, watches, mice and other sensors
  • Texas Instruments’ CC2540 single mode chip and WiLink 6.0 support for dual-mode operation
  • Nordic Semiconductor’s μBlue solution that includes the nRF8000 family of chips and chipsets combined with µBlue software stacks and device profiles
  • EM Microelectronic’s EM9301, a fully integrated single-chip Bluetooth Low Energy (BLE) controller
With certified silicon and development tools available and profiles on the verge of being adopted, the timing is right for serious consideration of Bluetooth low-energy designs.

Resources:
  1. CSR PLC
    • Bluetooth RF Transceivers
    • Bluetooth Development Kits
  2. Laird Technologies
    • Bluetooth Antennas
    • Bluetooth Development Kits
    • Bluetooth Modules
  3. connectBlue
    • Bluetooth Modules
    • Bluetooth Development Kits:

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