Monitoring systems based on medical body area networks (MBAN) are among the innovations changing the way patients receive care. There’s no shortage of sensors and monitoring equipment today, but most patients currently are severely limited in their freedom of motion.
As explained in the FCC’s 2012 MBAN Report, “The MBAN technology will provide a flexible platform for the wireless networking of multiple body transmitters used for the purpose of measuring and recording physiological parameters and other patient information or for performing diagnostic or therapeutic functions, primarily in healthcare facilities. This platform will enhance patient safety, care, and comfort by reducing the need to physically connect sensors to essential monitoring equipment by cables and wires.”1
Using relatively low-power wireless technology in this way appears to be a straightforward solution to an important problem. However, as often happens in complex applications, the details make all the difference. The MBAN topic began to receive greater attention near the end of 2007 when GE Healthcare proposed secondary use of the 2,360- to 2,400-MHz spectrum already assigned for primary use in aeronautical mobile telemetry (AMT). The aerospace and flight test radio coordinating council (AFTRCC) opposed the proposal.
Actually, the MBAN story is a good example of how solutions were found through cooperation and consultation even though obstacles at first appeared insurmountable. In response to GE’s proposal, in April 2008, the FCC asked for comments from interested groups. Based on this input, a Notice of Proposed Rulemaking (NPRM) was issued in June 2009. As an example of comments the NPRM elicited, the American Telemedicine Association stated, “MBAN technology has the potential of freeing up millions of homebound patients suffering from chronic diseases such as congestive heart failure, diabetes, and chronic obstructive pulmonary disease.”1
Courtesy of Philips Healthcare
In January 2011, GE, Philips Healthcare Systems, and AFTRCC submitted a joint proposal that showed basic agreement on secondary use of the spectrum. It represented “the culmination of 15 months of discussion, analysis, and negotiation among and between the named parties.” The FCC’s First Report and Order and Further Notice of Proposed Rulemaking issued in May 2012, was greatly influenced by this proposal and ruled in favor of establishing MBANs on a secondary user basis.1
MBAN Conditions of Use
As enumerated and explained in the 2012 MBAN Report:1
- Frequencies from 2,360 to 2,390 already are used for AMT, so “MBAN devices may not operate outside the confines of a healthcare facility…. MBAN devices that operate in the 2,360- to 2,390-MHz band must comply with registration and coordination requirements….”
- The registration requirement will ensure that the locations of all MBAN operations in the 2,360- to 2,390-MHz band are recorded in a database….
- If the MBAN transmitter is within line-of-sight of an AMT receive site, the MBAN and AMT coordinators will work cooperatively to assess the risk of interference between the two operations and determine the measures that may be needed to mitigate interference risk.” Under some circumstances, the MBAN device may not be able to operate in that band.
- “We are requiring that an MBAN transmitter not operate in the 2,360- to 2,390-MHz band unless it is able to receive and comply with a control message that notifies the device to limit or cease operation in the band.”
- “MBAN transmitters [must] comply with the [existing] MedRadio rules and maintain a frequency stability of ±100 ppm of the operating frequency over the ambient environmental temperature range: 1) 25°C to 45°C in the case of MBAN transmitters and 2) 0°C to 55°C in the case of MBAN control transmitters.”
- A maximum 5-MHz bandwidth is set.
- Individual MBAN devices are limited to a maximum 1-mW EIRP transmit power measured in a 1-MHz bandwidth for the 2,360- to 2,390-MHz band. For the 2,390- to 2,400-MHz band, a maximum 20-mW power is allowed measured over a 5-MHz bandwidth.
Power and Location Limitations
Comments from a study performed by NIST to determine how radio waves propagated into and out of 12 large buildings help to explain why MBAN transmitters must only be used within a healthcare facility if operating in the 2,360- to 2,390-MHz band. According to the authors of the study, “A fundamental challenge to communications into and out of large buildings is the strong attenuation of radio signals caused by losses and scattering in the building materials and structure.”2
Clearly, because interference with existing AMT use is a concern, operating MBAN transmitters within a building helps mitigate the risk by attenuating the signal. For the NIST study, specially modified 1-W test transmitters operating on several government-controlled frequencies were carried throughout a variety of buildings while receivers at fixed locations outside the buildings measured the emissions.
The 2.445-GHz test frequency corresponded to the MBAN 2,360- to 2,400-MHz band but was used for only three of the buildings. One was an 11-story apartment building constructed of reinforced concrete, steel, and brick with standard interior-finish materials. It was fully furnished and occupied during the experiments. Another facility was an oil refinery, basically an outdoor facility with several intricate piping systems. Measurements were performed during daytime hours and, as a result, people were moving throughout the refinery. The main building at the NIST laboratories in Boulder, CO, also was investigated. It is a four-story building constructed of reinforced concrete, but because the building is built on a hillside, some locations are below ground level.
The position of the receiving antenna made a great deal of difference in the test results although it was just one of many variables. The 12 buildings had significantly different shapes ranging from a large round sports stadium to an 11-story apartment building. Nevertheless, as might be expected, when the antenna was set up close to the end of the long, narrow NIST building, signal attenuation was high until the transmitter approached that end of the building.
The study results are directly applicable to MBAN interference, but to appreciate the wide variation in the NIST data, it’s important to remember the purpose of the study. As the authors stated, “The data in these reports gives first responders and system designers a better understanding of what to expect from the radio-propagation environment in disaster situations. The goal of this work is to create a large, public-domain data set describing the attenuation of radio signals in various building types in the public safety and cellular telephone bands.”2
Figures 1 and 2 display relative signal strength vs. the number of times that value was received, regardless of the transmitter position within the buildings. As the figures show, the signal attenuation associated with the Bolder apartment building has a totally different characteristic than that for the NIST building. This is because the transmitter-building-receiver system behaviors are being compared, not just those of the buildings.
Courtesy of NIST
Courtesy of NIST
In the extreme case of the NIST building, a first responder in the same location as the test antenna would experience very difficult radio communications conditions. Judging from the results achieved in testing other structures, moving from the end to the side of the building would significantly improve signal strength.
For MBAN applications, the NIST results show that the orientation of a healthcare facility relative to a nearby AMT receiver makes a difference. For example, a long, narrow building with its axis along a line of sight to the receiver affords the possibility of much greater attenuation than if it were situated broadside to the line of sight.
However, the larger take-away from the NIST report is the tremendous amount of attenuation that occurs for most locations within most types of buildings. For all 12 sites, there was a great deal of variation in the fixed receiver-to-building distance in addition to the variation that occurred as the transmitter was walked through the sites. The color-highlighted columns in Table 1 recalculate the mean and average received signal powers as absolute levels by taking into account the reference powers used for each of the 2.445-GHz tests. Looked at this way, and ignoring the extremes at each end of the range, receive signal power is -71.6 to -91.5 dBm, representing an overall attenuation of about 100 to 120 dB assuming a 1-W transmitted power level.
Data Source: NIST
MBAN in Practice
GE Healthcare
A number of wireless monitoring devices are available from GE, the ApexPro® FH Telemetry Transceiver being one that addresses ECG signal acquisition and transmission. It operates within the existing wireless medical telemetry service (WMTS) using TDMA and frequency hopping spread spectrum (FHSS) across 39 channels in the 608-614-MHz band.
GE’s DINAMAP® Pro Series monitors can interface to the ApexPro and deliver its data along with those from third-party vital-sign sensors to GE’s CARESCAPE™ network. All the data is available for viewing at the CIC Pro central station, part of the company’s CARESCAPE system.
Philips Healthcare Systems
The Philips IntelliVue Telemetry System is similar to GE’s ApexPro to the degree that both target ambulatory cardiac patients and both use a frequency hopping technology. IntelliVue incorporates a smart-hopping feature so it changes frequencies only to dodge interference or if it senses a stronger signal. This approach is linked to the system’s large 1,028-transceiver or wireless bedside monitor capacity.
Interestingly, this product is available in the United States as well as other countries. Here, it operates at 1.4-GHz, within the WMTS band. Like GE, Philips offers the broader infrastructure associated with a monitoring network that is separate from a hospital’s enterprise network traffic. Systems sold abroad operate on the 2.4-GHz frequency but otherwise have similar characteristics and capabilities.
Toumaz
Toumaz, one of the 24 parties that filed comments in response to the 2009 NPRM, has received 510(k) approval from the U.S. Food and Drug Administration for the company’s Sensium™ Digital Plaster, a small, ultra-low-power wireless body-worn monitor. According to the company, “[it] continuously and unobtrusively acquires high-quality vital signs data, including temperature, heart rate, and respiration rate. The current Sensium Digital Plaster is targeted for use in hospital general-ward environments. It also has the potential to be extended into telecare, chronic disease monitoring, community care settings, and the home where continuous or extended monitoring of patients is important.”3
A recent press release4 stated, “Our professional healthcare offering continues to be a key focus for the group with clear market needs to be addressed. Up to 87% of hospitals in the United States have stated an interest in installing wireless monitoring technology in the next two to five years, and our healthcare product aims to be a key driver in the evolution of healthcare monitoring. The Toumaz Sensium Vitals monitoring solution has FDA approval and shortly will start pilots in the United States.”
The release continued, “By 2016, the global market for wireless sports and fitness monitoring devices is forecast at 120 M units, and the opportunity to leverage our healthcare capabilities into the consumer arena is significant.”
Zarlink Semiconductor
Recently acquired by Microsemi, Zarlink also responded to the FCC’s 2009 NPRM. According to the company’s website, “Microsemi’s highly integrated medical-grade ultra-low-power radios are used to wirelessly connect implanted medical devices with programming and monitoring equipment and in ingested and sensor applications requiring ultra-low-power streaming data performance.”
The company’s interest in MBAN deliberations is understandable given its involvement in the implanted medical device market. For example, the website stated, “the Zarlink ZL70250 ultra-low-power RF transceiver provides a wireless link in applications where power consumption is of primary importance. The transceiver’s ultra-low-power requirement allows the use of a miniature button cell battery or energy-harvesting methods, enabling devices with extremely small form factor…. This device operates in unlicensed frequency bands between 795 and 965 MHz.”
Conclusion
The FCC’s 2012 Report establishes a shared frequency band for MBAN operation. This isn’t the first or only wireless medical spectrum assignment, but it appears to be a popular one. There already are products available to enter the market and, according to the report, “We are also persuaded that the ready availability of chipsets and technology that can be applied to this band will promote quick development of low-cost MBAN equipment.”
References
1. First Report and Order and Further Notice of Proposed Rulemaking, ET Docket No. 08-59, Amendment of the Commission’s Rules to Provide Spectrum for the Operation of Medical Body Area Networks, FCC, May, 2012.
2. Holloway, C. L., et al, Attenuation of Radio Wave Signals Coupled Into Twelve Large Building Structures, NIST, Technical Note 1545, August 2008.
3. “Toumaz Limited Announces Joint Venture for Newly Approved Sensium™ ‘Digital Plaster,’” Toumaz, News Release, July 8, 2011.
4. “Toumaz Limited Completes Acquisition of Frontier Silicon,” Toumaz, News Release, Aug. 20, 2012.