More Spectrum Sought for Body Sensor Networks

by George Lawton

Healthcare costs are rising in many countries, and they've become a topic of considerable discussion in the US, as Congress mulls policies to lower costs. Meanwhile, vendors are moving forward on networking technology as a way to lower costs by improving patient monitoring in hospitals and at home. The technology could also help reduce the need for scarce labor, while increasing the accuracy and timeliness of vital patient data.

One recent survey reported that 40 percent of the labor spent on critical-care patients is spent manually recording patient information. Wired sensors are one approach to improve monitoring, but they take time to set up and must be disconnected and reconnected when patients are moved. They also pose an infection risk.

To help solve these problems, GE Healthcare has asked the US Federal Communications Commission (FCC) to allocate 40 MHz between 2360 and 2400 MHz for the Medical Body Area Network Service (MBANS). The MBANS spectrum would support wireless communications between noninvasive sensors in a body-sensor network (BSN) and stationary data-gathering terminals. If a patient is in a medical facility, the data would remain local, where doctors or nurses could process it. If the patient is remote, the data could be transmitted to a hospital, doctor's office, or other monitoring station. 

"GE's vision for the systems would enable wireless monitoring from anywhere in the hospital — or even remotely from home," said David Freeman, general manager of parameters for GE Healthcare. "BSNs have the potential to enable delivery of patient information earlier and to support informed clinical decision-making. Wireless BSNs would eliminate the need for wires, and could replace the traditional tangle of bedside cables used to capture a patient’s vital signs."

The market research firm, On World, predicts that the global wireless sensor network market for all healthcare applications will reach $3.6 billion in 2012. The most common BSN applications are monitoring of vital signs such as heart rate, blood glucose and oxygen levels, blood pressure, pulse, temperature, and respiration.

Connecting Inside

MBANS complements work within the IEEE 802.15.6 task group for body-area networks. There have been over 30 different proposals for the 802.15.6 standard, said Arthur Astrin, CEO of Astrin Radio and chair of 802.15.6 task group. The group hopes to merge the proposals into a baseline draft standard by November. The standard will support devices that operate around and inside the human body.

Implanted devices pose RF challenges because human bodies are a difficult radio environment — for example, changing batteries becomes more complicated and much riskier. In addition, the accepted limit for RF absorption rates inside the body is 25 microwatts, which is several orders of magnitude less than technologies such as Wi-Fi, which transmits at 20 milliwatts. "You also have the compound issue of having to reliably transmit at low power through fat, bone, and blood," said Astrin. 

The IEEE task group is looking at using existing spectrum available worldwide between 402–405 MHz, devices for implanted devices. The 40 MHz proposed by MBANS would support communications between the body and remote terminals. Astrin said the 802.15.6 group is looking to support communications both within the body and with external monitoring stations.

Navigating Interference

In its petition to the FCC, GE Healthcare argued that the existing 2400 MHz band set aside for unlicensed industrial, scientific, and medical applications faces too much interference to be suitable for critical medical applications. However, because the GE proposed spectrum is adjacent to the widely used 2400 MHz band, the company expects to leverage the economies of commercial RF components already developed for the 2400 MHz range.

The main concern about the proposal has come from existing users of the 2360 to 2400 MHz band, which include airline flight-testing applications. FCC Spokesperson Bruce Romano said that the MBANS proposal could go through much quicker if the MBANS and flight testing communities can agree on how to share the spectrum.

Standards Could Drive Interoperability

Standardization of medical sensor technology is important to create the infrastructure for a coherent data-gathering system. Mareca Hatler, director of research at On World, said that most wireless sensors use proprietary, noninteroperable protocols. "While individual wireless devices are relatively common in healthcare, body sensor networks today are rare due to concerns about data reliability, interference, FDA regulatory design issues, and litigation concerns. Interoperability standards are important for BSNs that feature multiple devices per patient or gateway."

External medical devices have made limited use of standard wireless protocols. Hatler pointed to Bluetooth's Medical Device Profile, which is used in hospital settings as well as in at-home health devices. Bluetooth offers a relatively large bandwidth for applications requiring continuous transmissions. ZigBee and its IEEE 802.15.4 radio standard are best for devices that require ultra low power and long duty cycles, and it's been used for certain types of BSN devices such as glucose meters.

Hospitals pose challenges for BSNs. For example, monitoring multiple sensors per patient increases the likelihood of interference from the hundreds of other wireless devices in this setting.

Hatler noted, "While we have not studied the FCC proposal in depth, allocating dedicated spectrum and defining a new type of device such as 802.15.6 could be a solution to minimize interference and support multiple wireless sensing devices. The challenges could be that this is a very recent development, and other technologies such as Bluetooth and ZigBee are more mature with commercial products used today in many markets."

George Lawton is a freelance technology writer based in Monte Rio, California. Contact him at glawton@glawton.com.