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How BLE enables new medical apps

Posted: 12 Dec 2011     Print Version  Bookmark and Share

Keywords:ambulatory patient monitors  low energy  power consumption 

As wireless technology replaces cables, patient mobility also increases through ambulatory patient monitors. Portable patient monitors, infusion pumps, surgical foot switches, and dozens of other medical devices currently use wireless connectivity to maintain a connection to monitoring and information systems.

One of the toughest issues facing portable medical devices today is power consumption. Power requirements for wireless connections constrain architecture and limit applications.

That could all change, thanks to the introduction of Bluetooth low energy technology specified in Bluetooth v4.0, which is making its way to designers and consumers today. Recent announcements by Microsoft and Apple supporting this new technology show its wide-ranging deployment in standard computing and communications platforms. The stage is set to deploy truly low-power wireless medical applications that have relied on custom components and platforms until now.

Bluetooth low energy technology is different from other wireless technologies because it combines a standardised technology designed from the very beginning for ultra-low-power batteries and a new sensor-based data collection framework. Bluetooth low energy technology will also be integrated in most handheld devices.

Bluetooth Special Interest Group (SIG) working groups have already released several profiles for health, fitness, and medical device use, and others are in progress. While these devices are not directly compatible with IEEE 11073, a whitepaper detailing the data conversion and compatibility mapping is also being developed to make data available to systems using the IEEE 11073 standard.

Bluetooth low energy technology is the key feature of the Bluetooth Core Specification 4.0 (Bluetooth v4.0) and has inherited several technical features from Classic Bluetooth technology that provide for robust, reliable connections. New features allow for event-driven data acquisition, proximity sensing, and time synchronisation. But in many ways, Bluetooth low energy technology is a very new wireless technology. Bluetooth v4.0 is fundamentally different in that it is designed for transmission of small amounts of data instead of periodic data streaming connections featured in Classic Bluetooth technology. For example, Classic Bluetooth technology provides support for headset and streaming audio data, a feature fundamentally absent from the Bluetooth low energy technology model. The technology features efficient discovery and connection set-up, short packages, and asymmetric design for small devices.

The lowest possible power consumption. Everything from physical design to use models is designed to keep the power consumption at a minimum. In order to reduce the power consumption, a Bluetooth low energy device is kept in sleep mode for most of the time. When an event occurs, the device wakes up and a short message is transferred to a gateway, PC or a smart phone. Maximum/peak power consumption is less than 15mA and the average power consumption is about 1µA. The active power consumption is reduced to a tenth of the energy consumption of Classic Bluetooth technology. In low duty cycle applications, a button cell battery CR2032 could last for 5–10 years of operation.

Cost efficient and compatible. In order to offer compatibility with Classic Bluetooth technology and cost efficiency for small battery-operated devices, there are two chipset types:

 • Dual-mode technology including both Bluetooth low energy and Classic Bluetooth functionality.
 • Stand-alone Bluetooth low energy technology optimised for small battery-operated devices with low cost and low power consumption in focus.

Robustness, security and reliability. Bluetooth low energy technology uses the same adaptive frequency hopping (AFH) technology as Classic Bluetooth technology to achieve a robust transmission in noisy RF environments found in the home, industrial, and medical applications. To minimise the cost and energy consumption, Bluetooth low energy technology has reduced the number of channels to 40 2MHz wide channels instead of the 79 1MHz wide channels in Classic Bluetooth technology.

Wireless co-existence. Bluetooth technology, Wireless LAN, IEEE 802.15.4/ZigBee, and several proprietary radios use the licence-free 2.4GHz industrial, scientific, and medical (ISM) bands. With so many technologies in the same radio space, interference can decrease the wireless performance (latency and throughput) due to the need for error correction and retransmission. In demanding applications, interference can be reduced through frequency planning and special antenna solutions. Both Classic Bluetooth technology and Bluetooth low energy technology utilise AFH, making the Bluetooth transmission robust and reliable. AFH also minimises interference from Bluetooth technology to other wireless ISM band radio technologies.

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