Nordic Semiconductor (Nordic Semiconductor editorial contact: Steven Keeping, e-mail: steven.keeping@nordicsemi.no, Tel: +61 (0)403 810827) TITLE: The (peripheral) value of Bluetooth low energy wireless technology STANDFIRST: What s behind the Bluetooth low energy initiative and what does it offer that other wireless technologies don t? Thomas Embla Bonnerud describes the developments so far and maps out the technology s future TEXT: By the end of 2007 (the last year for which official figures are available), cumulative shipments of Bluetooth technology reached around 1.75 billion with 800 million shipping in that year alone. And according to US analysts IC Insights, the short-range 2.4GHz wireless technology s growth is going to do anything but slow. The company predicts that between 2006 and 2010, unit shipment growth will average 33 percent per year and revenues will rise from US$1.47 billion in 2006 to more than US$3.2 billion in 2010. By any measure, it would seem that Bluetooth technology has attained a practically unassailable position in short-range, low power wireless. Yet, if this is the case, why are a number of non-bluetooth 2.4GHz solutions also doing extremely well? This is because Bluetooth technology s applications are limited when power and cost are major constraints. For example, Bluetooth technology is unable to run on ultra-low power coin cells because they lack capacity and the ability to deliver the peak current demanded by a transmitting or receiving Bluetooth chip. (See figure 1.) Figure 1: Proprietary solutions currently dominate the ultra-low power wireless connectivity niche The downside of these non-bluetooth ultra-low power wireless products (examples include wireless desktops with one year battery lifetimes in the keyboard, mouse and remote control, and sports watches with tiny coin cell heart rate and distance sensors) is a lack of interoperability between products from different vendors. Without a viable Bluetooth-based ultra-low power solution, interoperable wireless gadgets and devices remain a dream. Handset giant Nokia saw the need for an interoperable ultra-low power wireless technology earlier than most and started working on a solution back in 2001 with a view to introducing it as an open industry initiative. The Finnish company took a major step forward in October 2006 when it joined with a group of like-minded companies, including Nordic Semiconductor, to form the Wibree imitative, in order to encourage the development of a specification and then hardware.
Meanwhile, the Bluetooth Special Interest Group (SIG) a not-for-profit trade association comprising 9000 member companies including such industry heavyweights as Ericsson, Intel, Lenovo, Microsoft, Motorola, Nokia and Toshiba faced pressure from its members for an alternative to the base technology (see sidebar Bluetooth technology today ) that wasn t limited to applications with relatively large (rechargeable or AA-sized at best) batteries. The SIG s members were keen to extend wireless connectivity to everything from biomedical monitors, watches, toys, sports goods and thousands of other consumer products, removing inconvenient wires and connectors, and opening up entire new product categories. Then, in one of the industry s worst kept secrets, the Bluetooth SIG s and the Wibree Alliance announced in June of 2007 a decision to merge the fledgling Wibree specification into the Bluetooth specification to become ultra low power Bluetooth technology (recently renamed Bluetooth low energy wireless technology). So much for the history, what designers are now interested in is what the Bluetooth low energy wireless technology specification will look like, what challenges the technology will solve and when it will be available. Bluetooth low energy wireless technology fills the gap Even before Bluetooth low energy wireless technology was a gleam in a researcher s eye, design engineers seeking to add wireless connectivity faced a bewildering choice of options. Just considering the technologies based on open standards there were WiMAX (based on IEEE802.16d), Wi-Fi (IEEE802.11b, g and soon n), Bluetooth technology (IEEE802.11.15.1) and ZigBee (IEEE802.15.4). At first glance, these various technologies appear to cover the entire wireless communications spectrum from long-range, high-bandwidth to short-range, low-power consumption (suitable for batterypowered portable devices). (See sidebar The wireless zoo ). However, with a little imagination and study of the various specs many engineers realised there was a pressing need for an additional RF technology to ensure interoperable wireless connectivity between small personal portable products with extremely limited battery power if reasonable battery life was to be achieved (for example, several months to a year). The lack of such an open standard has left a lucrative market for proprietary solutions to fill the ultralow power (less than 15mA when transmitting or receiving and an average current in the microamp range), short-range (tens of metres) wireless connectivity niche for consumer applications. For example, the company I work for, Nordic Semiconductor, has been very successful with its nrf24xxx family of 2.4 GHz transceivers in millions of wireless mice, keyboards, health sensors and sports watches across the globe. Proprietary solutions are endowed with bandwidth, interference immunity, a good price and enviable battery life. For example, Nordic s nrf24l01 transceiver (which consumes around 12mA when transmitting or receiving at 0dBm and 2Mbps) running the company s nrf2601 Wireless Desktop Protocol (WDP) provides a wireless mouse with a battery life of a year on two AA batteries (under normal usage) compared to a month for an equivalent Bluetooth-equipped mouse. However, the downside of proprietary products is that they re not interoperable. While that s hardly a concern for manufacturers making both ends of a peer-to-peer link (who seek to benefit from a proprietary solution s superior price/performance ratio) it does prevent use by manufacturers intending to wirelessly connect to other company s products, or those looking for a second source of transceivers. These latter groups are the target customers for Bluetooth low energy wireless technology. Extending wireless connectivity While not everyone is a supporter of open standards many say they add cumbersome bureaucracy and stifle innovation without the formation of the not-for-profit Bluetooth SIG in 1998 it is quite possible Bluetooth technology would not have thrived. The early years would have required an enormous investment in the technology s technical specification, marketing and promotion - with no guarantee of success - by only a handful of sponsors. Furthermore, this limited support could have deterred companies from specifying it into their products for fear of obsolescence.
In contrast, as an open standard, Bluetooth technology encourages healthy competition between silicon vendors and stimulates a broad array of competitive yet interoperable products and services for end users. This gives manufacturers who may have previously never considered wireless connectivity the confidence to introduce it into their next generation products. At the same time, the specification s development and marketing costs are shared by pooling the resources of member companies. Bluetooth technology is now one of the strongest brands in wireless connectivity with exceptionally high consumer awareness. It is by far the most widely adopted short-range wireless technology and is a key technology in mobile phones and PCs. Taking all this into consideration it becomes clear that the natural organisation to nurture the fledgling Wibree technology is the Bluetooth SIG. In addition, Nokia s original vision for Wibree using a handset as the centre of a wireless Body Area Network co-ordinating wireless peripherals sits comfortably with the Bluetooth SIG. Currently, the Bluetooth chip embedded in all but the most basic mobile phones allows a handset to communicate with other devices such as PCs and headsets with ease. But the Bluetooth SIG has realised how useful it would be if this communication could extend to sensors or other devices fitted with ultra-low power wireless connectivity. How many new or enhanced standalone devices could the mobile phone support? Intelligent sports watch with heart rate, foot pod or cycle cadence sensors; RF remote control functionality; health and wellness sensors. The list is endless. Current Bluetooth technology doesn t allow such connectivity because any mobile phone-based peripheral device would have to be small and lightweight and therefore coin cell-powered. Moreover, the handset makers aren t about to add yet another radio to a mobile phone that already has three or four. But if the wireless mobile phone peripherals employed Bluetooth low energy wireless technology, and handsets were equipped with suitably modified Bluetooth chips that integrated the ultra-low power functionality into an existing Bluetooth die then everything becomes possible. Inside Bluetooth low energy wireless technology* The Bluetooth low energy wireless technology draft specification details a short-range RF communication technology featuring ultra-low power consumption, a lightweight protocol stack and integration with Bluetooth technology. According to the current estimate, the first commercial version of the interoperability specification will be available during the second half of 2009. Like its big sister, Bluetooth low energy wireless technology will operate in the 2.4GHz Industrial, Scientific and Medical (ISM) band. It features a physical layer bit rate of 1 Mbit/s with a range of up to 15 metres. This may seem over-engineered for sending relatively little information across a shortrange wireless link, but this bandwidth has been carefully chosen because years of field experience with proprietary technology such as that gained with Nordic Semiconductor s nrf24xxx transceivers has shown that 1 Mbit/s is the optimal tradeoff in exactly the kind of wireless applications Bluetooth low energy wireless technology will target. The tradeoff is between transmit power which increases with increasing bandwidth and duty cycle which decreases with increasing bandwidth for a given amount of data. The Bluetooth low energy wireless technology specification will feature two implementations, namely dual-mode and single-mode. In the dual-mode implementation Bluetooth low energy functionality is integrated into traditional Bluetooth circuitry. The resulting architecture shares much of Bluetooth technology s existing functionality and radio and results in a minimal cost increase compared to contemporary chips. (See figure 2.)
Figure 2: Bluetooth low energy wireless technology features dual-mode and single-mode implementations Single-mode chips will be highly integrated and compact devices. The simplified Bluetooth low energy wireless technology protocol stack features a lightweight Link Layer (LL) providing ultra-low power idle mode operation, simple device discovery and reliable point-to-multipoint data transfer with advanced power-save and encryption functionalities. The LL provides a means to schedule Bluetooth low energy wireless technology traffic between Bluetooth transmissions. Profiles will include support for HIDs, sensors and sports watches. (See figure 3.) Figure 3: Sports watches are a prime target for Bluetooth low energy wireless technology
Ultra-low power consumption is critical to Bluetooth low energy wireless technology s success. Singlemode devices will be expected to run for many months or even years on standard coin-cell batteries (for example, CR2032, 3 V lithium devices). Single-mode chips will typically operate with low duty cycles, entering ultra-low power idle and sleep modes, to wake up periodically for a communication burst. In typical single-mode Bluetooth low energy wireless technology operations such as a sports watch communicating with a heart rate monitor, for example the chip s peak current consumption will be less than 15mA when transmitting or receiving, dropping to around 2µA when in standby mode, and 900nA in sleep mode. Dual-modes chips are targeted at handsets, multimedia computers and PCs. The dual-mode specification is also advanced and it is envisaged chips will feature power consumptions of around 75 to 80 percent of conventional Bluetooth chips when operating in Bluetooth low energy wireless technology mode and cost just tens of cents more. These next generation dual-mode Bluetooth chips will share much of Bluetooth technology s existing functionality and radio in a single die. However, because dual-mode devices will use parts of Bluetooth technology s hardware, power consumption is ultimately dependant upon the Bluetooth implementation. Consequently, dual-mode devices will not enjoy all of the benefits and possibilities outlined in the Bluetooth low energy wireless technology specification. Huge potential Initial applications for Bluetooth low energy wireless technology include leisure, healthcare, entertainment and office. So, for example, a person taking a workout could use their smartphone equipped with a Bluetooth dual mode chip as the centre of a Personal Area Network (PAN) comprising Bluetooth low energy wireless technology-equipped running shoes, Bluetooth low energy wireless technology-equipped heart rate belt and Bluetooth low energy wireless technology-equipped sportswatch. It s also possible that this data could be sent to a suitably equipped GPS unit that could then make predictions about where the user will be in the future based on their current rate of progress. Alternatively, the sportswatch could communicate with a Bluetooth low energy wireless technology chip in a gym s rowing machine, and pass on the data to the smartphone. Bluetooth low energy wireless technology could also be used to monitor heart rate and blood pressure and then wirelessly connect to a mobile phone that could then send an SMS message to the hospital doctor periodically. Or a runner could log heart rate, distance and speed and send it to friends mobile phones for them to beat on their own runs. Or a winemaker could record temperature and humidity from sensors in a vineyard as he strolls around inspecting plants. 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. But these are just the obvious examples; with a dual-mode Bluetooth chip in a mobile phone being able to communicate with both other Bluetooth-equipped devices and single-mode Bluetooth low energy wireless technology-equipped products the opportunities are vast. (See figure 4.) Single-mode chips will also be able to talk directly to other single-mode chips.
Figure 4: Bluetooth low energy wireless technology extends wireless connectivity beyond the capabilities of traditional Bluetooth technology As Nordic Semiconductor s CEO, Svenn-Tore Larsen puts it: Once you ve got a really cheap way to add an interoperable wireless link to anything that s battery powered the potential is huge. Designers will come up with thousands of ways to use that link, especially if the information can be transmitted to a mobile phone and stored. A promising future The Bluetooth low energy wireless technology specification is still at the draft stage and engineers are often cynical about how long it takes standards-based specifications to be ratified and reach massmarket use. In the case of Bluetooth technology, this is said to have taken seven years. But Bluetooth low energy wireless technology should proceed more quickly because it is already at an advanced stage and the Bluetooth SIG is much more experienced group now than it was back in the 90 s. In addition, Nordic Semiconductor is developing the hardware and software for single-mode chips right now, and Bluetooth chip suppliers are busy working on the dual-mode chips. Probably the only major impediment to the rapid uptake of Bluetooth low energy wireless technology is fear among non-rf designers about designing-in the technology. Nordic Semiconductor works with these types of customer all the time and overcomes such fears by offering silicon solutions in the form of highly integrated RF silicon, Bluetooth low energy wireless technology software and development tools, and reference designs to lower the learning curve and speed time-to-market. Estimated availability of Bluetooth low energy wireless technology sample devices is aligned with the standard s ratification. The envisaged market for Bluetooth low energy wireless technology is clear. It is targeted at those manufacturers who want to add a low cost, ultra-low power, robust 2.4GHz wireless link to their product in order to transmit small volumes of data to another single-mode chip equipped device or a central resource such as a mobile phone or PC. Because Bluetooth low energy wireless technology can run from coin cell batteries, it can be integrated into thousands of low-power items to form PANs with dual-mode Bluetooth chip-equipped devices. By the first anniversary of the Beijing 2008 Olympic Games, we could see Bluetooth low energy wireless technology-enabled mobile handsets on the market. Given that intelligent sports sensors and performance monitoring will be a prime market for Bluetooth low energy wireless technology, the anniversary of the Games will be a fitting occasion for the first product rollout of this exciting new wireless technology. *Note: Technical information is provisional and subject to change prior to the publication of the industry open standard.
Further information: Thomas Embla Bonnerud is Product Manager ultra low power Wireless, with Nordic Semiconductor. For more information on Nordic Semiconductor s nrf24xxx and Bluetooth low energy wireless technology products please visit www.nordicsemi.com SIDEBARS Bluetooth technology today Officially introduced in 1998, Bluetooth technology s intended purpose was as a short-range communications protocol intended to replace cables connecting portable and fixed devices while maintaining high levels of security. The technology s key features are robustness, low power and low cost. Bluetooth technology operates in the unlicensed 2.4GHz Industrial, Scientific and Medical (ISM) band. The raw data rate is 1Mbps or 3Mbps with EDR. Class 2 radios most commonly found in mobile devices have a range of 10m. The latest version in volume production is Bluetooth Version 2.0 + EDR (Enhanced Data Rate) (Version 2.1 + EDR is nearing commercialisation). Many features of the core specification are optional, allowing product differentiation; there are a family of profiles, such as the Advanced Audio Distribution Profile (A2DP) that optimises performance for a particular application. Bluetooth technology uses a Frequency Hopping Spread Spectrum (FHSS) scheme to modulate the carrier signal. This scheme splits the 2.4GHz ISM band into 79 x 1MHz channels (with a 1MHz guard channel at the lower end of the band and a 2MHz guard channel at the higher end). Transmitting and receiving Bluetooth devices then hop between the 79 channels 1600 times per second in a pseudorandom pattern. From Version 1.2 on, the scheme was revised to include adaptive frequency hopping (AFH). This algorithm allows Bluetooth devices to mark channels as good, bad, or unknown. Bad channels in the frequency-hopping pattern are then replaced with good channels via a look-up table. During typical operation, a channel is shared by a group of devices synchronised to a common clock and frequency-hopping pattern. The master provides the synchronisation reference for the slaves. A group of devices synchronised in this fashion form a piconet or PAN. Bluetooth technology s strength is its interoperability. While Version 1.0 struggled in this respect, from Version 1.2 onwards, interoperability with other Bluetooth-equipped devices is virtually assured. Bluetooth s power consumption varies depending on operational mode but rises to around 35 to 45mA when using the full transmission capability between a single master and slave for a contemporary Bluetooth Version 2.0 + EDR device*. This drops back to 5 to 10mA when simply maintaining synchronisation and down to microamp levels when in a quiescent mode. In a streaming audio application, for example, MP3 player to headphones, the rechargeable Li-ion battery is discharged in around ten hours, while two AA batteries in a wireless mouse last around 100 hours. Note that Bluetooth can t run from a CR2032 3V coin cell the battery of choice for many ultra-low power application because of its limited capacity of around 220mAh and maximum current draw of around 20mA. *Average figure, check manufacturers specifications for details of a specific device The wireless zoo Described by its promoters as a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL, WiMAX can operate in the range from 2 to 66GHz over a range of several kilometres and offers useable bandwidths up to 12Mbps. It is designed to provide portable computer users with Internet access and requires devices with highcapacity batteries. Wi-Fi is a proven solution for wireless LANs (WLANs). Its high-speed (up to 200Mbps in the draft IEEE802.11n version) enables sufficient bandwidth for web browsing, file transfer and even data streaming between computers. Latterly, improvements in battery technology have seen Wi-Fi increasingly adopted on portable devices like PDAs and mobile phones (primarily for web surfing and e-mailing when near a Wi-Fi hotspot ). Nonetheless, Wi-Fi s power consumption does drain batteries quickly if used frequently.
Offering up to 3 Mbit/s bandwidth in its latest 2.0+EDR version, Bluetooth technology is a reasonable compromise between speed and power consumption for applications such as transferring photo files from a mobile phone to a printer, or relaying voice from a mobile phone to wireless headset. Bluetooth technology can be used frequently while still allowing the Li-ion batteries typical of portable devices to last for tens of hours between recharges. ZigBee has been designed as a low-power technology and can be powered from small AAA cells but is targeted as specific very low duty cycle applications. ZigBee is the basis of inexpensive, selforganizing mesh networks for industrial control, building- and home-automation. The addition of complex network features necessary to guarantee smooth operation impact costs and link latency. In addition, because it is designed for static networks, ZigBee is ill-suited to the ad hoc nature of networks typical of consumer implementations. NORDIC SEMICONDUCTOR 2009, www.nordicsemi.com May be reproduced with permission from Nordic Semiconductor