Wireless body area networks: What engineers need to know

The challenges of designing BANs include:

 • Form factor. Size and weight are very important for BAN sensors, as they directly affect the comfort of the patient. The smaller the area and mass of a node, the fewer restrictions it will introduce on the patient’s activities. However, this must be balanced against the requirements for sensor signal-to-noise ratio, noise immunity and efficiency of the antenna for the wireless communications link. As companies look at targeting BANs toward consumer applications, user-friendliness and reliability are both important factors for increased adoption.

• Power and current consumption. Battery life is a critical challenge in BAN node design. The need for frequent replacement or recharging of batteries is undesirable for wearable nodes and unacceptable for many implantable nodes. Several techniques, such as sensor and communication duty cycling and the use of super-regenerative radio receivers, are making strides toward longer operational times and battery autonomy. Some designers are looking toward new developments in energy harvesting techniques to extend the lifetime of their BAN products.

• Reliability. When dealing with medical devices and applications, it is imperative to have a system that provides sufficient data accuracy and unquestioned data reliability. Patient safety depends on the repeatability, accuracy and reliability of a BAN system at the sensing and wireless transmission levels.

• Security. To protect patient privacy and prevent hacking into the network, BAN nodes must implement adequate security measures.

• Intelligence. The level of local-signal processing capability determines how much power is available, the flexibility needed in the signal processing algorithm, how many nodes are in the network and the bandwidth of the signals of interest. Thanks to continued progress in lowering the power consumption of embedded microprocessors, nodes are becoming more and more intelligent.

Today, a BAN can be implemented using several wireless connectivity standards, such as Bluetooth, ZigBee, Wi-Fi, ANT or Bluetooth Low Energy. Those wireless connectivity standards were not originally developed for BAN applications, however.

The accompanying table depicts the original target applications for certain standards. While several standards carry additional overhead and therefore don’t generally meet the peak power (current) consumption requirements of less than 3 mA for wearable BAN devices, standards bodies and industry groups have implemented health-care-specific initiatives to meet BAN requirements.

Click on image to enlarge.

BAN systems can also be implemented using proprietary solutions from various vendors. Such systems often use different operating frequencies (depending on the country of operation) and aren’t interoperable. On the other hand, proprietary solutions allow BANs to be tailored to specific needs and may offer better characteristics—for example, lower power consumption—than public wireless standards provide.

To develop a communication standard optimized for low-power devices that is suitable for BAN applications, the IEEE launched IEEE 802.15 Task Group 6 (BAN) to develop the IEEE 802.15.6 standard in 2007. IEEE 802.15.6 offers several advantages over existing standards. It focuses on short distances, reduced cost and power consumption, and lower implementation complexity. The IEEE 802.15.6 standard defines the physical (PHY) layer as well as the media access control (MAC) protocol and the security layers.

Architectural details

Figure 2 describes the IEEE 802.15.6 architecture. It is comprised of a PHY layer and a common MAC and security layer.

The PHY layer is divided into three frequency bands in order to address the diverse data rate requirements imposed by medical and consumer applications: narrowband, ultrawideband and human body communications band. It targets a distance of three meters while supporting data rates varying between 100 kbits/second and 1 Mbit/s, with a peak power consumption of 3 mA. The MAC protocol controls access to the channel.

The standard has also defined three levels of security: level zero, for unsecured communication; level one, for authentication only; and level two, for both authentication and encryption.

Figure 2. High level overview of the IEEE 802.15.6 architecture. Click on image to enlarge.

Wireless BAN technology is gaining momentum thanks to several factors, among them the emergence of the IEEE 802.15.6 standard. Given continued trends in the development of low-power and low-cost CMOS radios and the drive for more information, the BAN market is expected to grow significantly.

Patient and consumer health applications will remain key drivers for BANs. But expect other applications, such as industrial and agricultural monitoring, to emerge as the technology evolves.

About the author

Iboun Taimiya Sylla manages business development in the Americas for low-power RF products at Texas Instruments. He received his bachelor’s degree in telecom engineering from Ecole Supérieure des Postes et des Télécommunications (Tunis, Tunisia), and his master’s and PhD degrees in electrical engineering from Ecole Polytechnique de Montréal. He also holds an MBA from the University of Texas at Dallas, with a focus on corporate finance and strategic leadership.