FCC’s Best-Kept Secret on Medical Wireless Frequencies

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Ultrawideband frequencies offer a treasure trove of many gigahertz of available FCC spectrum.

A great deal has been written over the past few years bemoaning the lack of dedicated frequency bands for new wireless medical devices. Likewise, with the most recent initiative between the FDA and FCC in exploring the use of a variety of narrowband frequencies for a body area network, there has been great anticipation that a dedicated FCC-approved frequency band may be made available in the near future.

This would augur exiting new wireless medical sensor products some years from now, once the appropriate wireless chips have been developed. The purpose of this article is to explore the FCC’s best-kept secret when it comes to medical frequency bands. In particular, this article explores the use of ultrawideband frequencies, which were approved by the FCC in 2002.

Few practitioners are familiar with ultrawideband (UWB). On February 14, 2002, the FCC approved the use of a broad set of frequencies, from 3.1 to 10.6 GHz, at a transmit power level equivalent to the maximum permitted energy of miscellaneous unintentional radio emissions as outline in FCC part 15 – often called the class B limits, as an unlicensed band to spur the development of new innovative products. A further restriction on the use of this spectrum is that any given radio channel must be a minimum of 500 MHz wide.

Due to the physics involved with using such a large portion of the spectrum at such infinitesimal transmit power levels, ultrawideband radios tend to come in one of two varieties. One class is characterized by relatively low data rates, extremely low power consumption, and very modest transmit range. Within this class there are industry standard radios such as IEEE 802.15.4a or the newly emerging UWB variant of the IEEE 802.15.6 body area network, as well as some proprietary radios. Nearly all of these low data rate radios tend to use some form of pulse-based modulation to encode the data. Most of the low data rate radios currently operating in the ultrawideband frequencies were not developed for medical applications, but rather for use in position-location and tracking applications.

The second class of ultrawideband radios, which will be the focus of this article, are high-speed, highly energy-efficient radios that are characterized by short range (typically 3 meters to as much as 13 meters). A good example of this type of radio is the ISO-approved international ultrawideband radio standard developed by the ECMA standards body as ECMA 368 and ECMA 369.

Originally, this standard was developed by a consortium of companies headed by Intel for the purpose of replacing USB cables in the vicinity of PCs. Many of the factors that drove the design of this initial standard for use in short range high speed cable replacement applications makes ultrawideband radios ideal candidates for a variety of wireless medical applications. Though Intel abandoned the ultrawideband standard in September 2008, during the beginning of the financial crises and the recession, a number of smaller semiconductor companies, such as Alereon and veebeam, have completed the development of the ultrawideband standard and subsequently had their customers ship a variety of consumer-oriented end products to the market. A recent example is the Samsung Central Station wireless monitor powered by chips from Alereon. Within the medical industry, the most prominent company to announce a product that uses ultrawideband frequencies was GE Healthcare, with its FlashPad mobile x-ray system. Likewise, NDS Surgical Imaging is selling a wireless video product it calls ZeroWire for use in operating room theaters for connecting video cameras to large screen displays. Most recently, a small company in Asia has begun selling a wireless dental camera that uses ultrawideband.

UWB radios are essentially unknown to most of the wireless medical community. Some of the salient characteristics of UWB include the following:

  • UWB radios are orthogonal frequency-division multiplexing radios. First generation products are capable of transmission rates from 53.3 Mbps up to 480 Mbps. Second-generation products are capable of transmission rates up to 1.024 Gbps, with higher rates likely in the next few years. The corresponding delivered data throughput ranges from about 28 Mbps up to as much as 800 Mbps.
  • UWB radios operate using a synchronous time-slotted protocol, not a collision-based protocol like WiFi. This makes UWB ideally suited for streaming video traffic as well as data traffic.
  • UWB radios operate at such tiny transmit power that they don’t cause interference with electronic devices or other types of radios. Importantly, commercial UWB products don’t operate in the 5 GHz or 2.4 GHz frequency bands. Thus, it is impossible for a UWB radio to cause inference with Wi-Fi systems or infrastructure. Likewise, WiFi systems can’t cause interference with a UWB-based product.
  • UWB radios are highly energy efficient when measured from the perspective of milliwatts of power consumed versus the megabytes of data transferred. The high-speed UWB standard typically consumes about 500 mw of peak power, even when transmitting 480 Mbps. This combination is ideal for applications that require a high data rate, such as video cable replacements, transducer cables, and the like. For very low data rate sensor networks, the low-speed variant of UWB, which is characterized by miniscule power consumption numbers, typically 10 times more power efficient than even the newest Bluetooth low-energy standard, is more suitable.
  • UWB has more than 20 different channels available.
  • UWB radios form very tight pico-nets, thus enabling the reuse of channels when properly designed end units are separated by relatively short distances.
  • UWB radios are encrypted by a 128-bit AES key, so they are highly secure.
  • For a variety of radio physics reasons, UWB radios are extremely difficult to detect and very difficult to intercept, independent of the fact that they are secured by the 128-bit AES encryption key. Therefore, from a HIPAA requirements perspective, a UWB radio is far more secure than any form of WiFi radio.
  • From a regulatory perspective, UWB frequencies are authorized in the United States from 3.1 to 10.6 GHz at a transmit power of –41.3dBm/MHz. This is the equivalent of the FCC class 15B limit. A UWB radio must occupy a minimum of 500 MHz of bandwidth
  • Outside the United States, UWB is authorized and is an unlicensed radio band in the European Union, China, Japan, Korea, Russia, Canada, the UK, and many other countries that follow FCC or ISO standards. For simplicity, most countries outside the United States authorize UWB radios at the same transmit power levels as the FCC but restrict the frequencies to the 6–9 GHz bands.

Given this treasure trove of many gigahertz of secret FCC spectrum available, the question remains: What wireless medical applications are most suitable to be addressed using UWB? With the breadth of equipment in the market, and the innovation driving new diagnostic products, we will examine this question from the perspective of physical and cable characteristics as opposed to attempting to guess which medical applications may benefit most from UWB’s unique properties. From this perspective, UWB is generally best suited to the following uses for medical applications:

  • Portable or battery-powered equipment with the need for replacing a cable that is of modest to high data rates and operates at relatively short distances within a room.
  • Cart-based equipment, often used at bedside or in an operating theater, where portability and frequent movement are important and removing a cable would be of benefit—whether for convenience, sterile field considerations, maneuverability, superior usability, or other factors.
  • Products that currently use a cable to transmit electrical signals from some form of real-time transducer head to a piece of base equipment or that transmit various forms of real-time imaging or video data.
  • Any product that uses a USB cable, Ethernet cable, parallel cable, VGA cable, HDMI cable, or some other form of video cable is generally an application where UWB can be useful.
  • Any product that needs to display data on an LCD monitor.
  • Any product that connects to a PC-, Mac-, Linux, or Android-based platform.

It is also worthwhile to discuss sensor networks and body area networks and the potential for UWB to address these applications. As mentioned, UWB radios are typically characterized by ultra-low power, low data rates, high speed, and short range. For networks that must be continuously active over extended periods of time, or most networks that are implantable, the class of ultra-low power and low-speed UWB radios is undoubtedly the most appropriate solution. This class of UWB radios was specially designed for the power and data-rate characteristics of this application. Conversely, there is an ever-increasing class of sensor-oriented products that collect data over extended periods of time but only transfer this data for processing on relatively rare occasions. This class of applications is well suited for using high-speed UWB, which can quickly and efficiently transfer large amounts of data. This unique property has the potential to change the way medical sensor designers think about and, thus, architect the solutions to their design challenges.

For instance, today, due to power and data-rate constraints, an engineer may design an extremely smart sensor that limits the amount of data captured by applying large amounts of advanced signal processing to the raw sensor data captured. Conversely, the sensor may only capture events with specific signatures. Some design challenges may be better suited to an approach that captures large amounts of essentially raw sensor data in flash memory, then transfers the data at speed from 50 MBps to up to 200 MBps on some periodic basis to a home-based receiver or a receiver in the patient’s hospital room or that is collected by medical staff.

In summary, much of the clamor in the medical industry for wireless spectrum has been focused on the desire for a dedicated frequency band authorized by the FCC suitable for a specific class of sensor networks or body area networks. To date, however, few companies have availed themselves of the gigahertz worth of UWB frequencies available from the FCC. These frequencies can address a broad class of wireless applications for cable replacement and also be applied to a number of classes of sensor applications. Moreover, UWB semiconductors that implement the high speed UWB standard are available on the market today. Therefore, product design doesn’t have to wait for the 5 years it will take for new spectrum and new chips to become available. Further, UWB radios have many properties that can prove highly valuable to a variety of medical-cable-replacement and sensor applications. UWB radios are highly secure and encrypted, and UWB doesn’t interfere with other forms of electronic equipment or WiFi infrastructure, is eight times more power efficient per megabyte of data transferred than standard wireless technology, and is authorized in the United States as well as most major economic zones around the world. Finally, UWB is suitable for many portable, battery-powered, and cart-based applications, as well as any medical applications that currently have a USB, Ethernet, or video cable; utilizes a PC-, Mac-, or Linux-based system; or displays data on an LCD screen.

Eric Broockman is CEO of Alereon (Austin, TX).

Eric Broockman
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