Category Archives: Medical Body Area Networks

Still in shock by the post below? Don’t be. As always there’s hope on the horizon. The slides of the Hermes Partnership Workshop "Visions Towards ICT Supported Health" of last week have been posted online. If you want to find out more about one or more of the topics below, don’t hesitate to click here or on the links below.

“E-health in practice, business opportunities”, prof. dr. Felix Hampe, University of Koblenz, Germany

“Present experiences and future perspectives of Telerehabilitation”, prof. dr. ir. Hermie Hermens, University of Twente, The Netherlands

"Moving diagnostic, monitoring and therapeutic wireless medical devices into the homes and into the body",  dr. ir. Wouter Serdijn, Delft University of Technology

"Nanoscale smart communication components and systems”, a research proposal of Hermes partners, dr. Jean Benoit Pierrot, CEA LETI France  

"Status e-health and  telehealth in Poland”, prof. dr. Łukasz Januszkiewicz, University of Lodz, Poland

"e-health systems developments and business opportunities at SME-companies”, dr.ir. Piet Verhoeve, Televic, Belgium

"Energy harvesting in e-health applications”, dr. Paul Mitcheson, Imperial College, UK

Wouter

While enjoying lunch, the Biomedical Electronics Group gathered in the Davidse room (named after the former head of the Electronics Research Lab and also my "promotor", Jan Davidse) to listen to three presentations. The first one was by Duan Zhao, on an interesting new way of bridging the gap to low-power software radios by means of subsampling. After an introduction on the operation of a subsampling receiver, he explained to us a technique to remove the jitter originating from the sampling clock by using a harmonically related reference. Currently Duan is working hard on a manuscript to be submitted to GlobeCom.

The second presentation was by Neil Yongjia (as we call Yongjia because he will perform a song by Neil Young at the ELCA festival) on the correspondence and differences of successive approximation (SA) analog-to-digital converters (ADCs) and level-crossing ADCs. There is an interesting paradigm shift involved in the latter and many issues, such as DC sampling, bandwidth and slope limitations need to be investigated still. Nevertheless, it looks like the level-crossing ADC is a natural candidate for the conversion of physiological signals such as those that are generated by the body.

The third presentation was by Yours Truly, and was about how to turn your profession into the best job in the world. We touched upon cultural aspects, organizational aspects, academic aspects and personal aspects and things like procrastination, drive, bosses and the fun-factor. Probably in June, I will give a similar presentation to my colleagues of our faculty. 

Tomorrow will be the ELCA festical. Don’t miss it, as the world will never be the same…

Wouter

This little image on the left shows a rat carrying a wireless system, partly mounted on his head, partly realized as a kind of a backpack. It has been developed by researchers at Harvard University in close collaboration with colleagues at California Institute of Technology and is being used for neurological research on rats in the wild. According to Nature (Febr. 25, online) the entire systems comprises "a tetrode microdrive, for chronic positioning of electrodes in the brain; an integrated circuit for high channel-count neural recordings; and a radio-frequency wireless transmitter. The device takes up to 64 analog voltage signals from neurons in the brain and muliplexes them into one signal that appears in a temporally interleaved fashion, one after the other. Then that signal is transmitted by analog FM radio to a receiver."

The article further reports that good old FM (frequency modulation) transmission has been used as it outperforms digital wireless communication on weight, power drain, throughput and distance.

So why does analog FM outperform its digital counterparts, such as FSK, QPSK, QAM and OFDM? Before answering this question it is important to realize that from a channel-capacity perspective (as defined by Shannon) there is no preference for analog modulation over digital modulation. The answer thus has to follow from practical considerations. Digital modulation implies that the information is transmitted over the wireless radio channel in a digital fashion. As all information in nature, also neural signals are analog in nature and thus, in order to prepare the neural signals for their wireless journey, they have to be converted to the digital domain by analog-to-digital conversion (ADC). This thus requires at least one ADC. Often, depending on the digital modulation type used, channel coding is performed prior to the digital modulation. As a consequence, with these additional blocks, the entire transmitter becomes more complex, which, in turn, entails a larger power consumption and, when battery-operated, a larger battery and thus a larger weight on the head or back of the rat.

Another reason why analog FM may outperform its digital counterparts lies in the frequency spectrum of the transmitted radio signal. FM produces an almost flat frequency spectrum. As a consequence, it is relatively immune to frequency-selective fading, which is good for radio communication over relative long distances. Also, FM transmission does not require a highly linear power amplifier. This is good for its power efficiency and thus for the overall energy efficiency of the transmitter.

One final remark. From the picture it looks like the rat is loaded with a transmitter that has been implemented using discrete components, rather than with a single chip (or integrated circuit, IC). Many of the blocks needed for digital transmission could be implemented with a much smaller form factor and consuming less power when realized on-chip, rendering the antenna the largest component and the largest power consumer. In such a case the choice for either analog or digital could have just as well turned upside down.

Wouter