Bluetooth low energy wireless technology backgrounder · PDF fileBluetooth low energy wireless technology backgrounder ... Examples include devices such as sensors, PC mice, ... (actually

Bluetooth low energy wireless technology backgrounder

Version 4: Updated 22 March 2011

Sections: 1. Introduction to Bluetooth low energy wireless technology 2. Specification 3. Characteristics 4. Applications 5. Comparison with Bluetooth wireless technology 6. Availability

(Note: Blue font indicates text reproduced on website.)

1. Introduction to Bluetooth low energy wireless technology

Bluetooth low energy wireless technology is an ultra-low power (ULP) 2.4GHz RF technology designed to bring wireless links to products that currently use: proprietary wireless that is unable to communicate with other wireless protocols; wired connections; or have (at present) no wireless communication provision but would benefit from one.

Examples include devices such as sensors, PC mice, or sports watches that have to run from low capacity batteries for periods of months or years without recharge or replacement. While there are proprietary solutions available (such as Nordic Semiconductor’s nRF24L Series – For more information on this technology please see Nordic’s “Proprietary transceiver technical backgrounder”), these are not interoperable with other manufacturers’ transceivers.

In addition, proprietary technology is unable to communicate with Bluetooth wireless technology, a standards-based wireless technology embedded into millions of handsets and PCs. Figure 1 illustrates a Personal Area Network (PAN) centred on a mobile phone communicating with a range of low battery capacity peripheral devices illustrative of those that would or could be targeted by Bluetooth low energy wireless technology.

Figure 1: Bluetooth low energy wireless technology-enabled PAN centred on a mobile phone.

Bluetooth low energy wireless technology will encourage rapid deployment of ULP wireless by providing a technology that is interoperable and able to communicate with handsets and PCs

featuring modified Bluetooth wireless technology transceivers (see later). The technology will usher in the next generation of RF communications by opening up many new opportunities for wireless data links that to date have been ruled out on the basis of either power or cost.

Bluetooth low energy wireless technology is a ULP wireless solution featuring:

• Ultra-low peak, average and idle mode power consumption; • Ultra-low cost plus small size for accessories and human interface devices (HID); • Minimal cost and size addition to handsets and PCs; • Global, intuitive and secure multi-vendor interoperability.

2. Specification

In June 2010, the Bluetooth Special Interest Group (SIG) announced it had adopted Bluetooth low energy wireless technology as a hallmark feature of the Bluetooth Core Specification Version 4.0 (“Bluetooth v4.0”). The specification details a short-range RF communication technology featuring ultra-low power consumption, a lightweight protocol stack and integration with Bluetooth wireless technology.

Bluetooth low energy wireless technology has much in common with Bluetooth Version 2.1 + EDR and Version 3.0 + HS (commonly referred to as “Classic Bluetooth wireless technology”). All three technologies are low cost, short range, interoperable, robust wireless technologies operating in the license-free 2.4GHz Industrial, Scientific and Medical (ISM) RF band.

But there is one critical difference: Bluetooth low energy wireless technology was designed from the outset to be a ULP technology whereas Classic Bluetooth technology is a “low power” wireless technology.

This difference dictates that the operational characteristics of Bluetooth low energy wireless technology and Classic Bluetooth wireless technology are opposites. Classic Bluetooth wireless technology is a “connection oriented” radio with a fixed connection interval ideal for high activity links like mobile phones communicating with wireless headsets. Among several measures to reduce the power consumption (see below) Bluetooth low energy wireless technology employs a variable connection interval that can be set from a few milliseconds to several seconds depending on the application. In addition, because it features a very rapid connection, Bluetooth low energy wireless technology can normally be in a “not connected” state (saving power) where the two ends of a link are aware of each other, but only link up when necessary and then for as short a time as possible.

The “Profiles” part of the technology’s layered architecture – that customize the “stack” for a specific application – will be introduced over the coming months. The specification does do is define the layers of Bluetooth low energy architecture, starting with the Physical Layer (PHY) (which transmits bits), Link Layer (LL) (which defines packet structure and control) and Host Controller Interface (HCI). Collectively, these three layers are known as the Bluetooth low energy Link Controller (or “Controller”). (See figure 2.)

Figure 2: The Bluetooth Core Specification Version 4.0 defines the Link Controller and Host part of Bluetooth low energy. Profiles will be ratified over the coming months.

Above the Controller, the Host layer incorporates the Logical Link Control and Adaptation Protocol (L2CAP) that provides a channel-based abstraction to applications and services. It carries out fragmentation and de-fragmentation of application data and multiplexing and de-multiplexing of multiple channels over a shared logical link.

In addition to L2CAP, the Host layer includes the Security Manager Protocol (SMP) and Attribute protocol (ATT). SMP uses a fixed L2CAP channel to implement the security functions between devices. ATT provides a method to communicate small amounts of data over a fixed L2CAP channel. Devices to determine the services and capabilities of other devices also use the Attribute protocol. The Generic Attribute (GATT) Profile specifies the structure in which profile data is exchanged. This structure defines basic elements such as services and characteristics, used in a profile. Finally, the Generic Access Profile (GAP) defines the basic requirements of a Bluetooth device.

The operational mode of Bluetooth low energy wireless technology ideally suits transmission of data from compact wireless sensors (exchanging data every half second) or other peripherals like remote controls where fully asynchronous communication can be used. These devices send low volumes of data (i.e. a few bytes) infrequently (for example, a few times per second to once every minute or more seldom).

Bluetooth low energy wireless technology utilises two types of transceiver – a Bluetooth low energy chip (actually called a “peripheral” device in the specification) and a Bluetooth v4.0 chip. The Bluetooth low energy chip is brand new to the Bluetooth specification – it’s the part of the technology optimised for ULP operation. Bluetooth low energy chips can communicate with other Bluetooth low energy chips and Bluetooth v4.0 chips when the latter are using the Bluetooth low energy wireless technology part of their architecture to transmit and receive. (See figure 3.) Bluetooth v4.0 chips will also have the capability of communication with Classic Bluetooth wireless technology and other Bluetooth v4.0 chips using their conventional Bluetooth architecture.

Figure 3: Bluetooth v4.0 chips will use the Bluetooth low energy part of their architecture to communicate with Bluetooth low energy devices

Bluetooth low energy chips are likely to be used in applications such as Personal User Interface Devices (PUID) (such as watches), remote controls, proximity alarms, battery status indicators and heart rate monitors. Other health and fitness monitoring devices such as blood-glucose and -pressure, cycle cadence and cycle crank power will follow. Bluetooth v4.0 chips will be used anywhere a Classic Bluetooth chip is used today. The consequence is that cell phones, PCs, Personal Navigation Devices (PNDs) or other applications fitted with Bluetooth v4.0 chips will be capable of communicating with all the legacy Classic Bluetooth devices already on the market as well as all future Bluetooth low energy devices. (See figures 4a and 4b.) However, because they are required to perform Classic Bluetooth and Bluetooth low energy duties, Bluetooth v4.0 chips are not optimised for ULP operation to the same degree as Bluetooth low energy devices.

Figure 4a and b: Examples of target devices for Bluetooth v4.0 (left) and Bluetooth low energy wireless technology (right) implementations

3. Characteristics

There are three characteristics of Bluetooth low energy technology that underlie its ULP performance: maximised standby time, fast connection and low peak transmit/receive power. Bluetooth low energy technology uses just three “advertising” channels to search for other devices or promote its own presence to devices that might be looking to make a connection. In comparison, Classic Bluetooth wireless technology uses 32 channels. This means Bluetooth low energy wireless technology has to switch “on” for just 0.6 to 1.2ms to scan for other devices, while Classic Bluetooth wireless technology requires 22.5ms to scan its 32 channels. Consequently, Bluetooth low energy wireless technology uses 10 to 20 times less power than Classic Bluetooth wireless technology to locate other radios. Once connected, Bluetooth low energy wireless technology switches to one of its 37 data channels. (See figure 5.) During the short data transmission period the radio switches between channels in a pseudo-

random pattern using the Adaptive Frequency Hopping (AFH) technology pioneered by Classic Bluetooth wireless technology (although Classic Bluetooth wireless technology uses 79 data channels).

Figure 5: Bluetooth low energy wireless technology’s advertising channels have been carefully chosen to avoid clashes with Wi-Fi

Bluetooth low energy wireless technology features a raw data bandwidth of 1Mbps – greater bandwidth allows more information to be sent in less time. A competing technology that features a bandwidth of 250kbps, for example, has to be “on” for eight times as long (using more battery energy) to send the same amount of information.

Bluetooth low energy wireless technology can “complete” a connection (i.e. scan for other devices, link, send data, authenticate and “gracefully” terminate) in just 3ms. With Classic Bluetooth wireless technology, a similar connection cycle is measured in hundreds of milliseconds; more time on air requires more energy from the battery.

Bluetooth low energy wireless technology also keeps a lid on peak power in two other ways: by employing more “relaxed” RF parameters than Classic Bluetooth wireless technology, and by sending very short packets. Both technologies use a Gaussian Frequency Shift Keying (GFSK) modulation, however, Bluetooth low energy wireless technology uses a modulation index of 0.5 compared to Classic Bluetooth wireless technology’s 0.35. An index of 0.5 is close to a Gaussian Minimum Shift Keying (GMSK) scheme and lowers the radio’s power requirements. Two beneficial side effects of the lower modulation index are increased range and enhanced robustness.

Classic Bluetooth wireless technology uses a long packet length. When these longer packets are transmitted the radio has to remain in a relatively high power state for a longer duration, heating the silicon. This changes the material’s physical characteristics and would alter the transmission frequency (breaking the link) unless the radio was constantly recalibrated. Recalibration costs power (and requires a closed-loop architecture, making the radio more complex and pushing up the device’s price). In contrast, Bluetooth low energy wireless technology uses very short packets - which keeps the silicon cool. Consequently, a Bluetooth low energy transceiver doesn’t require power consuming recalibration and a closed-loop architecture.

4. Applications

Bluetooth low energy wireless technology was designed for applications where Classic Bluetooth wireless technology is not viable because of severe power restraints. All of these applications will have one thing in common: they incorporate sensors (or other peripheral devices) powered by coin cell batteries sending small amounts of data infrequently. This is the first time a ULP wireless technology with guaranteed interoperability has been available to electronics designers and promises to kick start hundreds of new applications. Two of the earliest potential applications are Proximity Alarm and Indoor Location (sometimes referred to as “Indoor GPS”).

For example, by utilising a Bluetooth v4.0 chip in their handhelds, cell phone makers could offer a security device comprising a Bluetooth low energy powered watch that periodically communicates with the cell phone. If the cell phone moves out of range - and hence can’t contact the watch worn by the user – it would automatically lock and the watch would emit an alarm. This would prevent the cell phone being accidentally left behind and prove a major deterrent for any would-be thief.

The proximity alarm application could be extended to a portable PC that locks when the user moves out of range (and perhaps unlocks to be ready for use when the approaching user presses a button on their watch). The application could also be used as a child safety device where the child’s watch communicates with a parent’s while they remain in range with an alarm sounding if the child wanders away.

The low cost and low maintenance (because batteries require only infrequent changes) of Bluetooth low energy sensors will encourage widespread use in public places. One key application could be indoor location (where there is no GPS signal) whereby sensors around a large public building (such as an airport or rail station) constantly broadcast information about their location. A Bluetooth low energy equipped cell phone passing within range could then display that information to its owner. Sensors could also transmit other information such as flight times and gates, location of amenities, or special offers from nearby shops. (See figure 6.)

Figure 6: Bluetooth low energy equipped sensors around an airport terminal could constantly broadcast information about their location. A cell phone passing within range could then display that information

Bluetooth low energy wireless technology is also likely to be embraced by the sports and fitness sectors. So, for example, a person taking a workout could use their smart phone equipped with a Bluetooth v4.0 chip as the centre of a PAN comprising Bluetooth low energy wireless technology-equipped running shoes, heart rate belt and sports watch. Alternatively, the sports watch could communicate with a Bluetooth low energy chip in the gym’s rowing machine, and pass on the data to the smart phone.

Bluetooth low energy wireless technology could also be used to monitor heart rate and blood pressure at home or connect over-the-air to a doctor while a patient is rehabilitating out of hospital.

In the entertainment sector, Bluetooth low energy wireless technology will allow a user to steer a toy racing car clear of obstacles with their mobile phone, watch a little robot interact with that of a friend when they come close and turn up the volume on their MP3 player remote control.

5. Comparison with Bluetooth wireless technology

With well over a billion (1000 million) Bluetooth wireless technology chips shipped to date, it makes a lot of sense to build on its success by extending short-range wireless links to equipment with low capacity batteries. However, Bluetooth low energy wireless technology is certainly not designed to challenge Classic Bluetooth wireless technology. As a rule of thumb, as data rate increases the power consumption advantages of Bluetooth low energy wireless technology diminish. For this reason, there are some use cases that Classic Bluetooth wireless technology is better equipped to serve, and some that will benefit most from Bluetooth low energy wireless technology. There is room for both technologies in the marketplace.

Bluetooth low energy wireless technology is specifically designed for applications where Classic Bluetooth wireless technology’s power consumption means it’s not viable. A Bluetooth low energy chip will typically use one-tenth the power of Classic Bluetooth wireless technology. For example, Nordic has designed a Bluetooth low energy silicon radio (see below) that features peak currents below 12.5mA. Much depends on the application of course, but for a typical Bluetooth low energy sensor application such as a sports watch linking to heart rate belt (used for, say, 1.2 hours per day), the average current drawn from a Nordic single mode chip would be about 12µA, giving up to two years of life from the CR2032 battery.

Even a Bluetooth v4.0 device has the potential to use just 75 to 80 percent of the power consumption compared to Classic Bluetooth wireless technology alone. However, because Bluetooth v4.0 devices will use parts of Classic Bluetooth wireless technology’s hardware, power consumption is ultimately dependant upon the Bluetooth technology implementation. Consequently, Bluetooth v4.0 devices will not enjoy all of the benefits and possibilities outlined in the Bluetooth low energy wireless technology specification.

6. Availability

Although not many Profiles are available, semiconductor vendors are now shipping Bluetooth low energy chips.

Nordic, for example, recently announced the first in its µBlue™ Series of Bluetooth low energy chips. The first product in the µBlue family is the nRF8001 – a complete Bluetooth low energy solution in a 32-pin 5 by 5mm QFN package incorporating a fully embedded radio, link controller, and host subsystem - suitable for watches, sensors and remote controls among other applications. (See figure 7.)

Figure 7: Nordic Semiconductor’s µBlue™ nRF8001 – a complete Bluetooth low energy solution suitable for watches, sensors and remote controls among other applications

Bluetooth v4.0 chips are also becoming available. Devices such as cell phones should start to incorporate these devices towards the end of 2011. Once that happens, the full potential of this exciting new technology will start to be realized.

DOCUMENT ENDS

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