In part 1 of this two-part series, we examined near-field communication. In part 2, we turn our attention to another tiny area network in healthcare called body area networks (BANs). BAN technology uses sensors that can be located on or in the body. These wearable or implantable sensors communicate with a controller within near-vicinity of the body. The biosensors are very small, needing so little power that they can harvest available kinetic body energy for their power supply. (In other words, no batteries are needed.) This also makes them suitable for long-term in vivo applications.1 In this installment of “Networking,” we will look at the technical side of BANs and how they’re being used in healthcare.
There are several types of BANs. The Federal Communications Commission (FCC) calls them medical body area networks (MBANs), dictating their broadcast frequency ranges and maximum RF power limits.2 As long as the vendors that make the MBAN devices stay within the FCC limits, they won’t need a specific license for each network installation. The two frequency ranges used are in the Industry Science and Medical (ISM) bands of 2,360 to 2,390 MHz and 2,390 to 2,400 MHz. These ranges are part of the so-called “quiet ISM band,” as opposed to the noisy and jam-packed 2,400 to 2,483.5 MHz range, where Wi-Fi and other wireless technologies operate.
In the 2,360 to 2,390 MHz band, maximum output is limited to 1 mW. BANs in this range are also limited to indoor use to help ensure they do not interfere with aeronautical mobile telemetry and radio telescopes, which use the same quiet band range. The 2,390 to 2,400 MHz band can be used anywhere, and is allowed a bit higher output of 20 mW. (For comparison, note that 802.11 wireless networks like Wi-Fi typically use 100 mW radios for communication.)
The IEEE has the additional specifications for MBANs, but refers to them as wireless body area networks in the IEEE 802.15.6 standard.1 The standard specifies all the other aspects and configurations of MBANs, including media access control (MAC), frame formats, security services, and a choice of narrow band, ultra-wide band, or human body communications (physical layer specs).
The basic BAN is set up as a star network, with a hub in the middle of the star and nodes connecting to the hub. There is only one hub in a BAN, but it can coexist with other BANs, up to two to four networks per square meter. Each BAN can support up to 100 nodes with ranges up to approximately 6.5 feet.3 In some cases, nodes are built with the ability to forward data from another node to the hub—but no deeper. Figure 1 depicts a BAN where the green node has the ability to connect another node to the hub in the middle of the network.
Typically, the nodes will contain body-connected sensors, and the hub would be a worn device. Examples of hub locations would be in a necklace, on a belt, on the wrist like a watch, or in the sole of a shoe (where it would also be a likely place to absorb and reuse the kinetic energy of walking). Alternatively, the hub may be placed away from the body as part of the bedside.4
Three Physical Layers
Published in 2012, the IEEE standard defines a common MAC layer with three possible physical layers, in addition to security levels and methods. The three physical layers are narrow-band (NB), ultra-wide band (UWB) and human body communication (HBC).
The NIST Approach
The National Institute of Standards and Technology (NIST) has several research projects under way with regard to what it calls pervasive IT, as noted on the NIST website:
Radio Frequency (RF) Propagation from Wearable and Implantable Medical Sensors: NIST is working to better understand RF propagation within and on the human body surface.
Modeling and Characterization of Harvestable Kinetic Energy for Wearable Medical Sensors: NIST is studying the statistical characteristics of harvestable kinetic energy generated from human motion. The result of this study can facilitate the development of efficient energy-management protocols for low-power wearable medical sensors.
Interference Analysis and Mitigation for Body Area Networks: NIST researchers are developing software tools that can help to study the interference on wearable and implantable wireless medical devices.
Smart Autonomous Sensors and Environments: NIST is conducting research to examine the optimal deployment of sensor devices (with controlled mobility) and the relevant possible trade-offs between coverage (ie, connectivity) and information sensing.
NB was designed for use in medical applications as wearable or implantable devices. NB supports data rates from 120 Kbps to nearly 1 Mbps, depending on location and power levels. NB also uses less of the available power for general operation (approximately 33%) than a comparable communication method like Bluetooth Low Energy, which uses about 80%. This means that NB has more power available for sensors and local processing.4
UWB in MBAN use comes in two flavors—impulse radio (IR-UWB) or wideband FM (FM-UWB). The impulse radio uses either a single pulse or a burst of pulses to represent the digital symbols of 1 and 0. UWB in general provides lots of implementation methods to generate high performance, low complexity to be robust with ultra-low-power operation. Low-power UWB radios that can handle up to 20 Mbps are already available5—technology marches on! Another main reason that MBANs often use UWB is that UWB signal power levels are in line with the medical implant communications service band, providing safe power levels for the human body and very low interference to other devices. UWB can be used in its default mode as defined in the standard, where IR-UWB transceivers are mandatory and FM-UWB transceivers are optional for medical and nonmedical use. UWB can also be used in a high quality of service mode (QoS), in which IR-UWB transceivers are mandatory. (There are no FM-UWB transceivers in QoS.) QoS traffic can trump other, less urgent traffic in high-priority medical applications,1 as in: “Here comes the ambulance. Better pull over and let it by!”
Probably the most interesting of the three communication methods is HBC.6 The MBAN standard for HBC as the physical layer uses electric field communication technology. As in the other methods, the HBC standard covers the entire physical-layer protocol for MBANs, such as packet structure, modulation, and preamble. The band of operation is centered at 21 MHz.6
Information is exchanged among electronic on-the-body devices by capacitive coupling pico-amp currents through the body. HBC does not require traditional antennas, which means HBC-based systems need less power than others, often less than 1 mW.
Power is distributed via the body’s conductive medium like a bus. Likewise, data and control information are also distributed over the human body. The power source can use DC or AC signals. Devices can also be selectively powered using different AC power signal frequencies. In an example from a Microsoft patent related to BANs, for instance, a 100-Hz signal powers one device, while a 150-Hz signal powers another.6 Digital data modulate the power signal using frequency and/or amplitude modulation techniques (FM or AM).
The patent sums it up pretty well: “The power source and peripheral devices can interact to form a complete computer network where the body serves as the bus coupling the devices together.”6 Kinetic power converters can be used in the MBAN to provide the network’s power and signaling needs. For example, there can be a kinetic power converter in the sole of a shoe, or in a wristwatch getting kinetic power from arm movement.
BANs provide communication between ultra-small and ultra-low-power intelligent sensors that are on or in the body. The radio-enabled sensors can continuously transmit physiological data. Implantable medical devices can also deliver medication called “smart pills” for precision drug delivery. There are also smart endoscope capsules, glucose monitors, and eye pressure sensors. There are wearable sensors that provide electrocardiogram, temperature, respiration, heart rate, and blood pressure information.
One example of a BAN application is a sensor that also controls an insulin reservoir and pump. The system can sense glucose levels and deliver just the right amount of insulin at the right time for the diabetic patient.7
Another example is the MobiHealth cardiac monitoring system, which integrates an ECG system with a GPS for serious or high-risk cardiovascular patients. When the ECG system alarms, patients can be easily found with their GPS data. The complete system is embedded into a shirt made from a “smart fabric” that is comfortable and washable. The MobiHealth system is considered an autonomous system, in that it looks for anomalies using the configured alarm levels and makes the call to the medical team dispatcher based on its ECG analysis.3
It is systems like these that make smart sensors and BANs a key element in the ongoing transformation of healthcare by technology.7
1. IEEE. (2012, Feb 29). IEEE Std 802.15.6-2012. IEEE Std 802.15.6-2012 IEEE Standard for Local and metropolitan area networks Part 15.6: Wireless Body Area Networks. New York, New York, USA: IEEE Standards Association. Available at: http:// http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber=6161600. Accessed October 20, 2014.
2. Federal Communications Commission. (2013). Small Entity Compliance Guide. FCC. Washington DC: US Gov’t. doi: FCC 12-54 ET Docket No. 08-59. Available at: https://apps.fcc.gov/edocs_public/attachmatch/DA-13-1086A1.pdf. Accessed October 20, 2014.
3. Karulf E. Body area networks survey paper. St Louis; Washington University in St Louis; 2008.
4. Davenport D. (2011). IEEE 802.15.6 Tutorial. Project Meeting: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs). 2011; 4, 8-15, 17-20, 23-26. IEEE. Available at: https://mentor.ieee.org/802.15/dcn/08/15-08-0491-00-0006-fcc-public-notice-2360-to-2400-mhz-mbans-proposal-update.pdf. Accessed October 20, 2014.
5. Imec International. (2012, Oct 30). Ultra-Low Power Circuits for Small Connected Devices. Belgium: Imec International.
6. Williams L. (2000). United States of America Patent No. US6754472 B1 – Method and apparatus for transmitting power and data using the human body. Available at: http://www.google.com/patents/US6754472. Accessed October 20, 2014.
7. NIST. (2014). Body Area Networks & Pervasive Health Monitoring Fact Sheet. Retrieved from NIST Healthcare: http://www.nist.gov/healthcare/emerging/ban.cfm. Accessed October 20, 2014. 24×7
Jeff Kabachinski is the director of technical development for Aramark Healthcare Technologies in Charlotte, NC. For more information, contact [email protected].