Cognitive Radio

FCC Adopts Rules to Allow Wireless Medical Devices

By Stanley Jungleib

Imagine a world where severed nerves could be repaired, the blind could regain sight and the deaf could again hear. If images of The 6 Million Dollar Man or the bionic woman spring to mind, you're right on target. Future and present merged into reality when the FCC recently adopted rules to allow wireless medical devices, bionics, to utilize a small portion of the mobile broadband spectrum. Medical devices have become miniaturized to the point where they can communicate within the body using certain radio frequencies (RF).

The FCC's report said this will create "a new generation of wireless medical devices that could be used to restore functions to paralyzed limbs. Medical Micropower Networks (MMNs) are ultra-low power wideband networks consisting of multiple transmitters implanted in the body that use electric currents to activate and monitor nerves and muscles."

MicrostimulatorImplantable Microstimulator

MMNs can be used to transmit movement commands from a sensor on a patient's spinal cord, through a wearable master control unit, to implants that electrically stimulate nerves. The same wireless technology might be used in devices to restore sight or hearing.

Many of our modern conveniences, such as television and radio occupy the RF spectrum that ranges from about 300 kHz to 300 GHz. The FCC's main job is to prevent interference between wireless operations throughout the spectrum. To do so, radio use is divided into "services." A secondary service, in most cases, must defer to signals from a primary service, and to the extent it creates any disruption there, a secondary service must cease transmission. The new FCC rules classify the range to be used by medical devices as a secondary service and allow for use of four blocks of the 400 MHz range of the RF spectrum.

So why is such a small allocation newsworthy? Because the regulations under which the new MMNs will operate signals an entirely new paradigm for radio. The FCC's action was politically bold, technically profound and its significance can not be overlooked.

Opposition raised concern that classifying medical devices as secondary could be dangerous. Nobody wants a situation where a radio disrupts a medical device network system. Realizing this, MMN developers thought far enough ahead to create an intelligent radio system robust enough to, in principle, withstand any interference. The technology employed is in fact called Cognitive Radio (CR), a movement quietly developed within academics that now seems ready for prime time.

Let's take a closer look at a general review of the technical evolution which makes CR possible. These subjects are very broad with as many variations as there are products – but here, I am focusing on how the MMN control system evolved.

Transceiver Diagram
Fig. 1: Conventional Transceiver Design
Click to enlarge

Fig. 1 shows a typical superheterodyne transceiver, the basic radio model for most of the 20th century. On the receive side you mix a local oscillator with the receive frequency to produce an Intermediate Frequency (IF) where predictable filtering creates your audio. The transmission process is reciprocal. The essential point is that all of the hardware is committed to operating on specific frequency ranges with a few modulation types (e.g. AM, FM, SSB).

Basic SDR DiagramFig. 2: Basic Software-Defined Radio (SDR)
Click to enlarge

Fig. 2 shows the transition underway for a decade or so as a result of solid-state miniaturization that is basically a cell phone, Software Defined Radio (SDR). Here, the transceiver components-often integrated hardware subsystems have become programmable for wider frequency ranges and different modulation methods especially involving digital data packets. A computer listens to its receiver via an analog to digital converter (ADC) and sends transmitter waveforms from its digital to analog converter (DAC). The SDR can be largely repurposed by downloadable applications.

SDR Transitions Cognitive RadioFig. 3: SDR Transitions Cognitive Radio
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Fig. 3 shows what is needed to add to SDR to create CR. Their design supersets both the traditional radio model and the SDR. Unlike cell phones, CR goes even further, essentially containing knowledge of their user's habits, operational purpose, context and applicable regulations (which can vary radically internationally), in addition to wide sensitivity to their electromagnetic and physical environment.

CR stands the 1934 Communications Act paradigm on its head: instead of blocks of spectrum and disparate radios built specifically for them, we'll have one general-purpose radio constantly redefined in real-time with its privileges and limits according to the needs of higher-priority services. The 10 or so "radios" we now have – cell phones wi-fi, remote controls, security systems, garage-door openers or Citizen's Band – can be replaced by one device that implements whatever RF that is needed through software and may be optimized to only emit the minimum radiation required to do its job.

Citizen's Band RadioCitizen's Band Radio

To experienced radio operators, especially hams, the concept of a CR that offers different features depending on when and where you are, may be unsettling. In 10 years it could also well be the only feasible solution to the problem of constantly increasing spectrum demand. But, challenging questions will arise. For example, what happens to short-wave listening and radio distance operating skills if the radios are regulated to use the most reliable routes at the least power? And when all radios (that is, phones) have adaptive emergency response capability will the traditional social justification for amateur radio even remain or be allowed? Finally, while dynamically inter-filling the spectrum may give more users better service through fewer, lower-power transmitters, the technique can potentially raise the population's aggregate daily radiation exposure as it is adopted by more services.

The importance of CR to the future of communications cannot be underestimated. It is the only current strategy by which regulators can quickly respond to the dynamic needs of this wireless world, as well as to be able to efficiently allocate the spectrum available for maximum advantage. Rather than protracted Service-FCC debates arising for every desired change (which can often take industry-killing years), operational responsibility can be largely attributed to the autonomous intelligence in the CR to do the right thing – as it can be in real-time re-programmed to serve in new contexts or under different national regulations, for example.

The American Radio Relay League (ARRL) appropriately emphasizes that much more experimentation remains to ensure the safety of MMNs under secondary status. Both the developers and the FCC seem willing to address those challenges. That they are now willing to subject their concept to the acid-test of intimately serving life itself speaks enormously of both their commitment to an urgent new vision for radio in general and the performance promised by CR specifically. I wish the entire effort good luck. Its success will profoundly affect and advance radio communications policy for the rest of the century.

Reading about CR scenarios, one is reminded of The Jetsons or The Six Million Dollar Man. Personally, I'm still waiting for Rosie, the robot maid. Thus far, CR's biggest vulnerability has been Artificial Intelligence, which has basically failed. When you try to design an intelligent robotic maid, you have the problem of defining the limits of her duties in the house; that algorithm is enormous. But when you limit your project to just making a radio do the right things with prescribed inputs, your chances of success increase enormously.

Without a doubt, without this ruling, implanted neurostimulator technology would not advance in the new direction it now can. Patients with brain, spinal cord injuries or strokes may not quite achieve Steve Austin's powers, but they well might be able to walk away from their wheelchairs and beds.

The full ARRL story, containing details and implications for all radio operations.

Details of the FCC adoption of rules for Cognitive Radio.


Stanley Jungleib (WA6LVC) began his technical career as a consultant at the U.S. Army Intelligence School in radar instruction and joined Sequential Circuits in 1979, beginning more than 30 years of leadership in music synthesis, including MIDI (1983) and General MIDI (1990). Founder of Seer Systems, Stanley holds multiple patents and is a life-long multi-instrumentalist. He has released music CDs and books, and written hundreds of manuals and technical articles. Stanley has been a Jameco cusomer for over 30 years.

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