Tuning Body-to-Body Networks with RF Modeling
by George Lawton
Understanding the human body's radio characteristics is in its infancy. The dynamics of human tissue capacitive, absorptive, and resistive properties pose unique challenges to wireless networking. Apple’s latest iPhone was unexpectedly crippled by the capacitive effects of an errant finger.
Researchers at the Wireless Communications Research Group (WCRG) at Queen's University in Belfast hope to improve on this field with better RF modeling of the human body in different types of environments. The results could lead to new antennas, better RF channel designs, and improved networking protocols. A recent US$800,000, 5-year grant from the Royal Academy of Engineering and the Engineering and Physical Research Council is jumpstarting their research.
The new antennas promise wireless devices with more robust connectivity and less radiation directed back at the wearers. The new protocols could lead to new types of mesh networks that could prove valuable in medical body area networks (BANs), sports team equipment, or collaborative gaming devices. The WCRG plans to leverage all the project findings to develop disruption-tolerant and mesh networking protocols.
Off-Body Transmission Errors
The research focuses on how to bridge the communication gap between the many devices expected to be worn on (or in) peoples' bodies as well as the communications with base stations in the house, office, or cell phone towers. Simon Cotton, WCRG research fellow said, "Much of the previous and current research on what we call body-centric communications has dealt with wireless devices situated on the body communicating with other wireless devices colocated on the body." He cited medical BANs as an example.
Cotton said that our understanding of how to effectively transmit the information collected in such networks in an off-body direction to a wireless base station or other nearby wireless devices hasn’t kept pace with the technology to implement the networks. "The aim of this research," he explained, "is build a fundamental understanding of signal propagation between human bodies forming body-to-body networks and to build new statistical and analytical models which describe this process."
Under the guidance of William Scanlon, professor of wireless communications at Queen's University, the WCRF has cultivated extensive expertise in antenna design, wireless channels, and networking. The research in this study will let the group create new antennas designed specifically for body-to-body network use and develop novel protocols that are tailored to the dynamics of this new type of mobile ad hoc network.
Human RFs
The antenna is one of the most significant elements in any RF system. It couples the electromagnetic signal to the air, and human bodies complicate both on- and off-site communications. Local communications on a single body require low power and an antenna that spreads the signal out across the body’s surface, whereas communication with other devices requires an antenna that sends the signal away from the body. The WCRF researchers are looking at how to create wearable antenna patches that can support both modes of communication using separate antenna elements.
The antenna designs will require a better understanding of the human body as an operating environment, Cotton said. Placing antennas on the human body introduces new design challenges: "These include antenna-body electromagnetic interaction, radiation pattern distortion that may lead to nonisotropic signal reception and time-varying shifts in resonant frequency." Cotton expects the research to generate understanding and models to support antennas specifically developed for effective body-to-body communications.
Patch antennas should be more flexible and compact than traditional monopole antennas. They can also embed a ground plane that directs most of the radiation away from the body's surface, unlike the omnidirectional radiation pattern associated with the monopole. This will make it easier to transmit to a wireless device on another body.
The researchers will look at popular ISM frequencies, such as the 868 MHz and 2.45 GHz as used in ZigBee and Wi-Fi. They will also study future high-bandwidth body-to-body communications using new antenna array designs at 60 GHz.
Mind the Gap
When gaps occur in traditional cellular networks, communication is impossible. Several research groups have developed disruption-tolerant and mesh network protocols that let peers pass information between each other in a way that bridges these gaps. These new human RF models will help to improve these types of protocols.
These protocols will let networks pass information along via a kind of sneakernet among people who move into physical proximity of each other. For example, a group of friends could exchange high-definition videos between body computers when pairs of people are physically proximate via BitTorrent-like protocols. Firefighters might relay video or vital signs information to others in the team or to a command center.
"With the possibility of widespread use of body-to-body networks in densely populated areas," Cotton said, "this type of technology will be used in everything from medical applications to recreational activities such as mobile gaming and truly mobile cloud computing. Cellular companies would be in an ideal position to capitalize on this research."
George Lawton is a freelance technology journalist. Contact him via his website at http://www.glawton.com.
