By Thomas Embla Bonnerud, Nordic Semiconductor
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Figure 1. Proprietary solutions currently dominate the ultra-lower power wireless connectivitiy niche.
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 2.4 GHz 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.)
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Figure 2. Bluetooth low energy wireless technology features dual-mode and stand-alone implementations.
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 initiative 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 9,000 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 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 and the Wibree Alliance announced in June of last year 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
The lack of such an open standard has left a lucrative market for proprietary solutions to fill the ultra-low power (less than 15 mA 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 12 mA when transmitting or receiving at 0 dBm and 2 Mb/s) 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 organization to nurture the fledgling low energy wireless 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 cellphones allows a handset to communicate with other devices, such as PCs and headsets, with ease. But the Bluetooth SIG has realized 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 cellphone support? An 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 cellphone-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 cellphone that already has three or four. But if the wireless cellphone 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 in the summer of 2009.
Like its big sister, Bluetooth low energy wireless technology will operate in the 2.4 GHz 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 short-range 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 “stand-alone”. 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.)
Stand-alone 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.)
Ultra-low power consumption is critical to Bluetooth low energy wireless technology’s success. Stand-alone devices will be expected to run for many months or even years on standard coin-cell batteries (for example, CR2032, 3 V lithium devices). Stand-alone 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 stand-alone 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 2 µA when in standby mode and 900 nA in sleep mode.
Dual-mode chips are targeted at handsets, multimedia computers and PCs. The dual-mode specification is also advanced and its envisaged chips will feature power consumptions of around 75% to 80% 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.
Editor's Note: Look for the second part of this article in the November issue of Wireless Design & Development. Thomas will go on to define the huge potential and promising future Bluetooth low energy wireless technology can offer the industry. The complete article will be posted online at www.wirelessdesignmag.com.
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.Ultra-low power consumption is critical to Bluetooth low energy wireless technology’s success.
Thomas Embla Bonnerud is product manager ultra-low power wireless with Nordic Semiconductor, www.nordicsemi.com.