Bluetooth v4.0’s Smart start

The Bluetooth Special Interest Group (SIG) has been criticised for many things, but it’s difficult to level a complaint at its success in implanting the Bluetooth brand in the consumer’s mind. Back in 2008, an independent survey found that 85 percent of consumers ‘recognised the wireless technology’, and there’s a good chance the number is even greater now.

But with the launch of Bluetooth v4.0, the SIG faces a renewed challenge to explain exactly what its technology does. That’s because the new version isn’t like previous iterations; now, Bluetooth v4.0 architecture encompasses two very different types of radios and protocols. And while one type can communicate with previous versions, the other can’t.

For a buying public brought up on the promise of Bluetooth technology’s interoperability, not to mention an engineering community expected to deal with complex compliance issues to get their Bluetooth-equipped products to market, that’s confusing.

The SIG’s answer is new branding to help the consumer pick the product they need off the store shelf. Called Bluetooth Smart and Bluetooth Smart Ready, the new identity has come not a minute too early because Bluetooth v4.0, the technology behind the branding is now shipping in volume. For example, Apple’s iPhone 4S and new iPad (see figure 1) fulfil the requirements for Bluetooth Smart Ready, Microsoft has announced support for it in Windows version 8 and Motorola has also announced handsets with Bluetooth Smart Ready capability.

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Figure 1: Apple’s latest iPad fulfils the requirements for a Bluetooth Smart Ready device

But what does the Bluetooth Smart and Bluetooth Smart Ready branding really signify and how does Bluetooth v4.0 differ from previous versions of the technology? Read on to be enlightened - but first, a little bit of historical perspective.

Bluetooth vs. proprietary ultra low power

Once upon a time there were two types of ‘low power’ wireless technology. There was Bluetooth, a 2.4GHz short range technology bequeathed to the world by Ericsson, powered by relatively large capacity batteries (for example AA or bigger), offering a bandwidth of around 1Mbit/s (later much increased) and capable of such applications as streaming from cell phones to wireless headsets.

And then there was an even lower power technology wireless technology - pioneered by companies such as Nordic Semiconductor which coined the term ‘ultra low power’ to describe the technology - also operating in the 2.4GHz band and offering 1Mbit/s bandwidth. This latter technology was characterised by very low duty cycle operation (0.1 or even lower), average currents in the microampere range and months or years of operation from a coin cell battery. Applications included heart rate belts communicating with sports watches and wireless mice and keyboards.

These two technologies suited different market niches (with some small overlap) and never talked to each other because they spoke different languages. (Bluetooth used an open standard protocol to ensure interoperability, while ultra low power wireless technology used highly efficient proprietary protocols to keep power consumption down.)

But then an innovative team of engineers at handset maker Nokia realised that a huge new market for the company’s products would open up if they could communicate with the millions of ultra low power radios in the world. Instead of a keen jogger buying a relatively expensive heart rate belt and matching sportswatch to track their activity, for example, they would be able to buy a cheap heart rate belt and link it to the cell phone that they already owned.

From the engineer’s idea an alliance between Nokia, ultra low power radio specialist Nordic Semiconductor and some other like-minded firms was born. But Nokia was understandably reticent to add another radio chip to a cell phone that already boasted three or four RF devices, instead opting to leverage the Bluetooth chip already fitted to most of its handsets to do the job.

A couple of years into the project - when a lot of the chip architecture had been mapped out - good logic prevailed, and the alliance merged with the Bluetooth SIG, with the technology becoming known as 'ultra low power Bluetooth'.

Six years – and a lot of effort from Nordic’s engineers and those from other SIG members to complete the specification - after the initiative started, Bluetooth v4.0 (which incorporates ‘Bluetooth low energy’ as a hallmark feature) finally arrived.

A tale of two chips

The fundamental difference between previous versions of Bluetooth technology (for example, v2.1 and v3.0) and v4.0 is that the latest version uses two protocols.

The Bluetooth low energy protocol is the new part of the Bluetooth specification – it’s the technology that’s designed for the ultra low power applications that traditionally used proprietary technology. (This is not to suggest that proprietary technology is about to disappear; many applications in this sector don’t need the interoperability Bluetooth low energy offers, and instead can benefit from the lower cost and performance optimisation proprietary technology offers.)

The specification calls for radios that are specifically designed to solely run the Bluetooth low energy protocol and are consequently referred to as ‘single mode’ devices.

Bluetooth v4.0 also features silicon radios that can support the 'traditional' Bluetooth protocol (for example BR/EDR) but have some extra circuitry - added at minimal cost and with little addition to the device’s real estate – to enable them to communicate with Bluetooth low energy (single mode) chips. Because these chips can handle both protocols, they are referred to as 'dual mode' devices.

Dual mode chips will be used anywhere traditional Bluetooth chip were previously used. Think cellphones, tablets, PCs, Personal Navigation Devices (PNDs), games consoles and ‘smart’ TVs among dozens of other applications.

Bluetooth branding

A Bluetooth Smart brand qualified product must meet three requirements: Incorporate Bluetooth Core Specification Version 4.0 (or higher) with Generic Attribute (GATT)-based architecture; feature a single mode radio, and use the GATT-based architecture to enable particular functionality of the device.

A Bluetooth Smart Ready qualified product must meet three similar requirements: Incorporate Bluetooth Core Specification Version 4.0 (or higher) with GATT-based architecture; feature a dual mode radio (BR/EDR + Bluetooth low energy) where both radio modes may be activated, individually or simultaneously, and provide a means by which the end user can choose to update functionality for a Bluetooth Smart device on the Bluetooth Smart Ready device.

Manufacturers of Bluetooth Smart Ready products should also provide a way for third parties to create and distribute applications that receive data from Bluetooth Smart devices.

For the consumer, Bluetooth Smart Ready products provide a mechanism for the end user to update the functionality of a Bluetooth Smart product. The user can download and install new profiles (optimised application-specific software) to support the new devices they purchase rather than depending on the hub device being supplied with support preinstalled.

The Bluetooth SIG’s new branding is designed to manage the public’s expectations. After many years of promoting Bluetooth technology’s interoperability and compatibility with legacy devices it now has to get the message over that things have changed.

The Bluetooth SIG’s new branding is designed to manage the public’s expectations. After many years of promoting Bluetooth technology’s interoperability and compatibility with legacy devices it now has to get the message over that things have changed.

The new branding is important for the consumer because it will help them choose the correct product for their activities. For example, it’s not possible to buy a Bluetooth Smart heart rate belt and expect it to talk to any Bluetooth-chipped cell phone. Rather the handset has to be Bluetooth Smart Ready because that means it has a Bluetooth v4.0 chip – and the other infrastructure and support required for Bluetooth Smart Ready - rather than a non-Bluetooth low energy compatible one (such as a v2.1 or v3.0 device). Table 1 summarises the interoperability.

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Table 1: Bluetooth Smart and Bluetooth Smart Ready compatibility

What’s new about v4.0?

The Bluetooth SIG doesn’t waste time bringing out new versions unless they offer something fundamentally new. But what exactly is it that design engineers and, ultimately, consumers gain from Bluetooth v4.0? To answer that question we need to take a closer look at the technology.

Traditional Bluetooth technology features a 'connection oriented' radio with a fixed connection interval ideal for high activity communication. Dual mode chips will continue to perform that role.

It’s important to understand that the power consumption of a dual mode chip when operating in BR/EDR mode is no different to previous versions of the technology. There is some power saving when the device is using its low energy capability, but the chips aren’t ultra low power devices. The functionality of the chip, its size, cost and compliance regime is close to the previous version.

In other words, if an engineer is designing a product that requires a high-duty cycle, short range, interoperable 2.4GHz radio technology, he’ll select a Bluetooth v4.0 dual mode chip from the favoured supplier in much the same way as they’d previously chosen a v2.1 or v3.0 chip. But the engineer does gain one significant advantage, which we’ll discuss below.

In contrast, Bluetooth low energy 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 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 absolutely necessary and then for as short a time as possible.

Bluetooth low energy chips can operate for long periods (months or even years) from a coin cell battery such as a 3V, 220mAh CR2032. The trade off is that these devices can only support very low duty cycle operation.

If the designer’s looking for an interoperable 2.4GHz radio technology for fully asynchronous transmission from a device that needs to 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) then Bluetooth low energy is the best choice. Compact wireless sensors such as heart rate monitors, cycle speed and distance pods, or blood glucose monitors are typical examples of such devices.

Bluetooth low energy uses some interesting tricks to reduce its power consumption. The technology minimises time on air by employing only 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, conventional Bluetooth technology uses 32 channels.

This means Bluetooth low energy technology has to switch 'on' for just 0.6 to 1.2ms to scan for other devices, while conventional Bluetooth technology requires 22.5ms to scan its 32 channels. Consequently, Bluetooth low energy technology uses 10 to 20 times less power to locate other radios.

Once connected, Bluetooth low energy technology switches to one of its 37 data channels and then hops in a pseudo-random pattern using the Adaptive Frequency Hopping (AFH) technology pioneered by conventional Bluetooth technology (although the latter uses 79 data channels).

Bluetooth low energy technology features a raw data bandwidth of 1Mbit/s allowing information to be sent rapidly so the radio can quickly return to an ultra low power sleep state. A connection (i.e. scan for other devices, link, send data, authenticate, and 'gracefully' terminate) takes just 3ms. With conventional Bluetooth technology, a similar connection cycle is measured in hundreds of milliseconds. Remember, more time on air requires more energy from the battery.

Bluetooth low energy technology also keeps a lid on peak power in two other ways: by employing more 'relaxed' RF parameters than its big brother, and by sending very short packets. Shorter packets further minimise the time on air and also keep the silicon cooler, eliminating the need for power-consuming recalibration and a closed-loop architecture.

Extending the Bluetooth ecosystem

Bluetooth low energy technology was designed for applications where conventional Bluetooth technology is not viable because of severe power restraints. 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.

But exactly what sort of applications? A clue to some of these is provided by the Bluetooth SIG’s release of a family of profiles in the forthcoming months: these profiles optimise a generic Bluetooth low energy chip for a specific application such as Personal User Interface Devices (PUID) (for example, watches), Remote Control, Proximity Alarm, Battery Status and Heart Rate Monitor. Other health and fitness monitoring profiles such as blood-glucose and -pressure, cycle cadence, and cycle crank power will follow.

Nordic Semiconductor, as a specialist ultra low power wireless connectivity company, is among a group of silicon vendors that have released Bluetooth low energy solutions. A quick look at the company’s offerings serves to demonstrate some of the early applications and how those designers who have included a Bluetooth v4.0 in their product have also extended its connectivity to more products than they may have realised.

There are two chips in the company’s µBlue Bluetooth low energy family so far, the nRF8001 and the recently released nRF8002. Both include fully-qualified Bluetooth v4.0 low energy protocol stacks.

The first device in Nordic’s µBlue Bluetooth low energy chip family, the nRF8001 (plus a µBlue prototype kit and Software Development Kit) was released in January 2011. By delivering sub 12.5mA peak currents and connected mode average currents as low as sub 12µA (for 1s connection intervals), Nordic claims the nRF8001represents the industry’s lowest power Bluetooth low energy solution. The chip combines Radio, Link Layer and Host Stack into one End Product Listing (EPL), enabling designers to easily create new Bluetooth end products without any additional listing fees.

The nRF8002 System-on-Chip (SoC) is a good alternative for designers wanting to quickly develop a Bluetooth Smart product without needing to spend a lot of time learning how to use the technology. The chip is an easy to design-in single solution for wireless tags and other accessories such as bracelets, pendants, keychains, small toys, and armbands (see figure 2).

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Figure 2: The nRF8002 is an easy to design-in single solution for wireless tags and other accessories

Incorporating the nRF8002 into a product demands no specialist understanding of Bluetooth low energy technology or any embedded firmware development. By using a Nordic nRF8002 Development Kit, developers can design Bluetooth Smart tags and accessories using a simple graphical user interface that allows them to go no deeper than configuring the built-in application layer and mapping inputs and outputs to external components such as buttons, LEDs and buzzers. The nRF8002 incorporates built-in support for a range of Bluetooth v4.0 profiles including: Find Me, Proximity, Alert Notifications and Battery Status.

It’s been a long time coming, but Bluetooth v4.0 and Bluetooth low energy chips, protocol, profiles and support are now in place - representing the culmination of over six years of hard work. Many pioneering companies are already incorporating the chips into their products and it’s safe to expect a tsunami of Bluetooth Smart- and Bluetooth Smart Ready-qualified products to follow. For example, analyst IMS estimates that from next year, a billion Bluetooth low energy devices will be sold every year. That represents the fastest adoption of any wireless technology by far.

Interoperability assured

Several major companies have already incorporated the nRF8001 into products. Japanese consumer electronics company Casio, for example, has developed its G-SHOCK Bluetooth Low Energy Watch which can communicate with compatible cell phones (see figure 3).

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Figure 3: G-SHOCK Bluetooth Low Energy Watch can communicate with any Bluetooth Smart Ready cell phone

The watch includes functionality such as stopping cell phone ring alerts and a Finder Function that enables users to locate a misplaced handset by activating its alarm and vibration functions from the watch.

Dayton Industrial, an OEM/ODM of wireless monitors, employed the nRF8001 in what it claims is the world’s first production-ready Bluetooth low energy heart rate belt that’s ready to go into volume production. A person that owns a cell phone into which the designer has thoughtfully incorporated a Bluetooth v4.0 chip will be able to set-up and use the heart rate belt within seconds and take advantage of a range of health and fitness apps that offer new ways of collecting, interpreting and displaying training data.

To show how this works to inquisitive engineers, Nordic supplies an iOS Demo App that works with a wide range of the most popular Bluetooth Smart (and ANT+) accessories such as wireless heart rate straps, foot pods, bike speed-distance, cadence, and power sensors, temperature, proximity tags, weight scales, and blood pressure monitors (see figure 4).

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Figure 4: Nordic’s iOS Demo App works with a wide range of the most popular Bluetooth Smart (and ANT+) accessories

The most recent development using an nRF8001 perhaps best demonstrates how Bluetooth low energy will dramatically extend the already huge Bluetooth ecosystem.

Hong Kong-based IDT has just released a Bluetooth low energy blood pressure monitor for home use (see figure 5). The monitor is the first such device in the world to utilise Bluetooth low energy and the recently adopted Blood Pressure profile. The monitor can communicate with a Bluetooth Smart Ready cell phone, and then the handset can send the data to a remote server in the medical facility. Such ultra low power wireless-enabled technology allows a patient to stay in the comfort of their own home, limits the time they need to spend with a physician, and enables medical staff to make well-informed decisions about when to prescribe drugs - saving health authorities a fortune.

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Figure 5: IDT’s blood pressure monitor is the first such device in the world to utilise Bluetooth low energy and the recently adopted Blood Pressure profile

Many of these applications do rely on assured interoperability. The SIG arranges regular 'unplugfests' to make sure that devices from different manufacturers communicate as promised. Nordic and Broadcom, a leading manufacturer of Bluetooth chips, have also worked together to make sure that the promise of Bluetooth v4.0 interoperability works in practice.

In August last year, Nordic announced successful wireless communication tests between a prototype design for a Bluetooth low energy proximity fob and Broadcom’s BCM4330, the industry’s first combo chip solution certified to the Bluetooth v4.0 standard.

Although Nordic never doubted the outcome of the interoperability testing between its chip and that from another manufacturer, it was still gratifying – and a testament to the Bluetooth specification – that the wireless link was established without problem and operated seamlessly.