Bluetooth Low Energy Technology and Healthcare
Wireless technology has been replacing cables and allowing increased patient mobility for decades using Ambulatory Patient Monitors. Portable patient monitors, infusion pumps, surgical foot switches and dozens of other medical devices currently use wireless connectivity to maintain the connection to monitoring and information systems.
One of the toughest issues facing portable medical devices, especially as they make their way from the hospital to the home, is power consumption. Power needs for the wireless connections constrain architecture and limit applications to those capable of the battery needs of the technology.
That is all about to change with the introduction of Bluetooth low energy technology specified in Bluetooth v4.0 that 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.
What makes Bluetooth low energy technology different is the unique combination of a standardized technology designed from the very beginning for ultra-low power batteries, a new sensor-based data collection framework, and the fact that Bluetooth low energy technology will be integrated in most handheld devices.
Bluetooth SIG working groups have already released several profiles for health, fitness and medical device use; and others are in process. While these devices are not directly compatible with IEEE 11073, a whitepaper detailing the data conversion and compatibility mapping is also being developed in order to make data available to systems utilizing the IEEE 11073 standard.
The Bluetooth SIG forecasts that Bluetooth low energy technology will be implemented in billions of products within just a few years:
- Phone Accessories > 10 billions
- Smart Energy (counters and displays) ~ 1 billions
- Home Automation > 5 billions
- Health, Wellness, Sports & Fitness > 10 billions
- Assisted Living > 5 billions
- Animal Tagging ~ billions
- P2P Intelligent Transport Systems > 1 billion
- Industrial Automation/M2M > 10 billions
2 Bluetooth Low Energy Technology Features
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 synchronization. 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 provides support for headset and streaming audio data, a feature that is fundamentally absent from the Bluetooth low energy technology model. The technology features very efficient discovery and connection set-up, short packages and asymmetric design for small devices.
2.1 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.
2.2 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 optimized for small battery-operated devices with low cost and low power consumption in focus.
Figure 1: Bluetooth low energy chipsets are available in two versions
2.3 Robustness, Security and Reliability
Bluetooth low energy technology uses the same Adaptive Frequency Hopping (AFH) technology as Classic Bluetooth technology in order to achieve a robust transmission in ‘noisy’ RF environments found in the home, industrial and medical applications. In order to minimize 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.
Figure 2: Bluetooth low energy technology uses 40 instead of the Classic Bluetooth technology’s 79 channels.
2.4 Wireless Co-existence
Bluetooth technology, Wireless LAN, IEEE 802.15.4/ZigBee and several proprietary radios use the license-free 2.4GHz Industrial Scientific Medical (ISM) band. 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 utilize AFH, making the Bluetooth transmission robust and reliable. AFH also minimizes interference from Bluetooth technology to other wireless ISM band radio technologies.
Figure 3: This illustration demonstrates AFH operation in the presence of three channels of 802.11b/g (Wireless LAN). The three advertising channels as well as nine data channels out of the 37 data channels are located in-between the channels that are used by Wireless LAN.
2.5 Connection Range
Bluetooth low energy technology has a slightly different modulation than Classic Bluetooth technology. This modulation differentiation offers a range of up to 300 meters with a 10dBm radio chipset (Bluetooth low energy maximum).
3 Ease of Use and Integration
A Bluetooth low energy solution is typically based on a master connected to a number of slaves. A device is either a master or a slave, but never both; there is no scatternet topology for Bluetooth low energy technology. The master controls how often the slaves are allowed to communicate and the slave only communicates by request from the master.
A new Bluetooth low energy feature compared to Classic Bluetooth technology is the “advertising” functionality. A device (acting as a slave) can in this way announce that it has something to transmit to the master. An advertisement message can also include an event or a measurement value. This feature could be used, for example, to implement a fall detector that would advertise its need for help while transmitting the location of the person who fell – all without completing a connection.
Figure 4: An advertiser periodically sends messages and will always be a slave once the connection is established. A scanner is ready to receive an advertisement message and a connection request and will always be a master once the connection is established.
3.1 Software Structure
All parameters in Bluetooth low energy technology have a state that is accessed using what is called the Attribute Protocol. All attributes are represented as characteristics that describe signal value, presentation format, client configuration, etc. A battery, for example, could have the following characteristics:
- Level: 0 -100%
- State: NOT_USED, CHARGING, RECHARGE_COMPLETE, DISCHARGING, CRITICAL_REPLACE_NOW, RECHARGE_NOW
In the Generic Attribute Profile (GATT) service groups, features and declarations are brought together to specify the standard set of features available in all devices. In the Generic Access Profile (GAP) connections, discoverability, connectability and bonding are described. Through these attributes, it is possible to build numerous basic services and profiles. Some examples of basic services and profiles include the following:
- Find Me
- Automation I/O
- Building Automation (Temperatures, Thermostat, Humidity)
- Lighting (On/Off Switch, Dimmer)
- Remote Controllers
- Fitness (Step Counter/Activity monitor, Heart rate monitor)
- Medical Devices (Glucose Meter, Weight Scale, etc.)
3.2 Example Use Models
The reduced power and cost of Bluetooth low energy technology enable many medical use models from the home to the hospital. The example model in the home could be used to log data and establish trends for a Congestive Heart Failure (CHF) patient using several types of sensors and the patient’s mobile phone.
Figure 5: Example home medical Bluetooth low energy use model.
A similar architecture is shown below for use as an in-hospital vital signs monitor, utilizing Bluetooth low energy technology and Classic Bluetooth technology where appropriate based on the technologies’ strengths.
Figure 6: Example of a hospital medical Bluetooth low energy use model.
Bluetooth low energy technology is a powerful application enabler that will change the way we today experience wireless applications. Its low power and cost, as well as its robust communication technology make it ideal for low power home and hospital medical applications.
As the technology is being implemented in almost all mobile devices, there is an opportunity to utilize off-the-shelf handheld devices and enable new use models that leverage off of the rich user interface and communication features of those platforms.
About the Authors
Rolf Nilsson is the CEO and founder of connectBlue with over 30 years of thorough insight and know-how from industrial automation and communication. Before founding connectBlue, Rolf was the President of Eurotherm Scandinavia and before that he was in leading positions at Alfa Laval Automation/ABB Automation Products.
Bill Saltzstein is the President of connectBlue Inc., and the Medical Business Development Manager with over 25 years of experience in medical device development and wireless technology.
Prior to joining connectBlue, Bill worked as a wireless medical expert through his own company Code Blue Communications, and product management and development positions at Medtronic Physio-Control, Instromedix and Hewlett-Packard.
connectBlue™ is a leading provider of robust Industrial and Medical wireless solutions, designed and tested for the most demanding applications and environments. Based on Bluetooth technology, Wireless LAN (WLAN) and IEEE 802.15.4 / ZigBee, connectBlue provides ready-to-use products and modules as well as custom design solutions. connectBlue has its head office in Sweden and local offices in Germany and USA. For more information, please visit www.connectblue.com
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