19-01-2013, 03:15 PM
Ubiquitous computing (UC)
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INTRODUCTION
Ubiquitous computing (UC) has come a long way since its incep¬tion by Marc Weiser. Making computers intuitively blend into the environment has been a major area of research during the past twenty years. Many advances have been made in ubiquitous com¬puting. One of them is the recent development of body sensor networks, but currently these networks are neither intuitive nor do they blend seamlessly into environment. Body coupled com¬munications (BCC) is a new technology that might make body sensor networks more intuitive and more seamless.
Operating principles of Body coupled com¬munications
Body coupled communications is a physical layer technology where the signals travels "on" and "in" the body instead of through and off the body as with radio. This can be seen in figure 1 citekaist:low. The electric field of the body is subtly modified so that a mes¬sage can be sent and received. This gives a workable channel for communications that "sticks" to the body. The receiver and the transmitter are connected to this channel leading to an ethernet like network on the body. Body coupled communications in theory has a number of advan¬tages compared to wired and radio communication. The first ad¬vantage is that wires are not needed to connect different devices. Secondly, because the signal sticks to the body the signal is in¬herently difficult to eavesdrop. Another advantage is that less power is needed to send data, because the data is not broadcast to everywhere, it is just send around the body. Another factor why this technology could be less power hungry in theory, is that changing an electric field consumes less power than generating electromagnetic waves[1].
Current problems with communication in body sensor networks
While wireless sensor networks are gradually becoming main¬stream, the smaller related body sensor networks are still in their infancy.
Body sensor networks consists of number of intercom¬municating sensors that can be worn and that monitor the body.
These devices communicate to each other and possibly send data to an off body location for further processing. While related to wireless sensor networks the challenges are different. Body sen¬sor networks have to deal with more dynamic environment than wireless sensor nodes because humans rarely sit still. This causes problems with the communication between the nodes with the ra¬dio techniques currently used. To overcome problems with trans¬mission such as interference and disconnects the power of the transmission is increased.
This allows the signal to be re¬ceived from a greater distance, leading to privacy concerns. In¬terference is a major problem with radio based technologies be¬cause most radio based techniques use frequencies that are near to each other and that are also used for other purposes like tele¬phony. Because the signal strength is increased to mini¬mize interference the power usage increases leading to batteries running out of power sooner. In table 3 the bandwidth requirements of multiple sensors are given, combining this with table 1 shows that it is feasible to build body sensor networks with radio today.
But the energy usage of such a network is too large to keep such a network running with¬out constantly needing to recharge the nodes.
Other uses of body coupled communica¬tions
While body sensor networks are interesting for body coupled communications, it is not the sole area of interest for body cou¬pled communications. Body coupled communications can also be used for more mundane tasks where the fact that a network is made is completely oblivious to the user. Examples of this would be streaming music to headphones and unlocking doors by touch¬ing them when carrying a body coupled key. The only thing that the user would know is that the data travels through his or her body.
Previous work
Body coupled communications was discovered in the middle of the nineties. At MIT Zimmerman discovered body cou¬pled communications by accident while doing human interface research on position sensors. Simultaneously at the Sony Labs a similar technology was developed that resulted in the wearable key prototype. These discoveries led to an initial media frenzy. But soon afterwards interest was lost in body coupled communications because of what was then thought were fun¬damental limitations of the technology (Zimmerman thesis mis¬takenly stated that the technology had fundamental limit of 852 Kb/s). During the initial stages there was also research done at powering devices via the body. But this did not lead to much.