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The Peripheral Value of Bluetooth Low Energy Wireless Technology (Part 2 of 2)

Thu, 12/04/2008 - 5:11am
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.

By Thomas Embla Bonnerud, Nordic Semiconductor

Initial applications for Bluetooth low energy wireless technology include leisure, healthcare, entertainment and office. So, for example, a person working out could use their smartphone, equipped with a Bluetooth dual mode chip, as the center 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 cellphone 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' cellphones 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. With a dual-mode Bluetooth chip in a cellphone, being able to communicate with both other Bluetooth-equipped devices and stand-alone Bluetooth low energy wireless technology-equipped products the opportunities are vast. (See Figure 4.) Stand-alone chips will also be able to talk directly to other stand-alone chips.

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."

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 mass-market 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 a much more experienced group now than it was back in the 90's. In addition, Nordic Semiconductor is developing the hardware and software for stand-alone 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

click to enlarge

Figure 4: Bluetooth low energy wireless technology extends wireless connectivity beyond the capabilities of traditional Bluetooth technology.
technology. Nordic Semiconductor works with these types of customers 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 2.4 GHz wireless link to their product in order to transmit small volumes of data to another stand-alone chip equipped device or a central resource such as a cellphone 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.

Editor's Note: To read Part 1 of this article, go to www.wirelessdesignmag.com.

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

Bluetooth Technology Today
Officially introduced in 98, 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 2.4 GHz Industrial, Scientific and Medical (ISM) band. The raw data rate is 1 Mb/s or 3 Mb/s with EDR. Class 2 radios — most commonly found in mobile devices — have a range of 10 m.

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 optimizes performance for a particular application.

Bluetooth technology uses a Frequency Hopping Spread Spectrum (FHSS) scheme to modulate the carrier signal. This scheme splits the 2.4 GHz ISM band into 79 x 1 MHz channels (with a 1 MHz guard channel at the lower end of the band and a 2 MHz guard channel at the higher end). Transmitting and receiving Bluetooth devices then hop between the 79 channels 1600 times per second in a pseudo-random 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 synchronized to a common clock and frequency-hopping pattern. The master provides the synchronization reference for the slaves. A group of devices synchronized 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 45 mA 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 10 mA when simply maintaining synchronization 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 220 mAh and maximum current draw of around 20 mA. *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 66 GHz over a range of several kilometers and offers useable bandwidths up to 12 Mb/s. It is designed to provide portable computer users with Internet access and requires devices with high-capacity batteries.

Wi-Fi is a proven solution for wireless LANs (WLANs). Its high-speed (up to 200 Mb/s in the draft IEEE802.11n version) enables sufficient bandwidth for web browsing, file transfer and even data streaming between computers. Lately, improvements in battery technology have seen Wi-Fi increasingly adopted on portable devices like PDAs and cellphones (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 cellphone to a printer, or relaying voice from a cellphone 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, self-organizing 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.


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