While Zarlink and Cambridge Consultants have focused on in-body communications for body networking, UK's Toumaz Technology Ltd. is developing solutions for on-body communications to improve healthcare and lifestyle management. Toward that goal, Toumaz has readied an ultralow-power wireless body monitoring system-on-chip called Sensium. Using Sensium, it has developed a body-worn sensor that is labeled digital plaster. When worn by the patient, this digital plaster (Figure 2) can continuously monitor multiple health signs, such as heart rate, body temperature, pulse rate and respiration and transfer that data to a base station where a medical record is kept.

In short, the Sensium is an ultralow-power-sensor interface and transceiver platform that includes a reconfigurable sensor interface, a digital block with 8051 processor and an RF transceiver block, along with a temperature sensor on-chip. In addition, on-chip program and data memory permits local processing of signals. One or more Sensium-enabled digital plasters continuously monitor key physiological parameters on the body and report to a base station Sensium plugged into a PDA or a smartphone. The data can be further filtered and processed by application software. According to the developer, a single Sensium can operate for a year on a single 30 mAhr battery.

In such an application, the system architecture can be split into three units: target station, base station and web server/central data-base. The wearable sensor nodes (target stations) support a range of sensors generating data at rates up to 50 kbps. Very low-level analog signals from the sensors are pre-processed by the chip before being transmitted as an RF signal to the base station. The base station can be linked to up to eight target stations, each monitoring multiple physiological signals on the body.

Based on its patented advanced mixed-signal (AMx) technology, this highly integrated medical chip, labeled TZ1030, was taped-out on Infineon's advanced 130 nm RF CMOS process. In fact, this chip leverages advances made at Imperial College London in ultralow-power RF circuits and signal processing (Figure 3). It has met all the targeted accuracy and performance parameters in initial functional testing, stated Toumaz's COO and co-founder Keith Errey. This ultralow-power 1 V SoC is now ready for mass production, noted Errey.

Concurrently, the developer has also inked a strategic development and distribution deal with a major U.S. healthcare service provider. Although its OEM partner was not identified, Toumaz said that the U.S. partner will help in gaining regulatory approvals, manufacturing, marketing and distribution.

Presently, the chip consumes about 3 mA at 1 V. The developer is looking to cut that power consumption significantly in the future. For that, it is exploring new radio architectures and other modulation techniques. Currently, the chip is using frequency-shift keying (FSK) with a carrier frequency of 868/915 MHz and is encased in an 80-pin BGA package. In addition, efforts are under way to increase the data rate from 50 kbps to more than 150 kbps without sacrificing power.

Meanwhile, the supplier continues to improve its digital plaster, which is still under development, according to Errey. Issues being addressed include flexible materials that are bio-compatible and water and air permeable, as well as low-cost manufacturing.

Spurred by advances in ultralow-power implantable and on-body RF devices and sensors, body area networking (BAN) is emerging as a high-speed, short-range wireless technology to wirelessly connect implanted medical devices and on-body sensors with monitoring tools to provide patient health data in real time. In fact, toward that goal, IEEE 802 in December 2007 approved the formation of a working task group 6 (TG6) for IEEE 802.15. Arthur W.Astrin was named the chairman of this task group. Astrin is also CEO of Astrin Radio in Palo Alto, Calif.

This group will further define a standard for short-range, wireless communication in the vicinity of, or inside the human body, and will use the frequency bands approved by national medical and regulatory authorities. In fact, in a paper presented by Astrin at last year's second International Symposium on Medical Information and Communications Technology (ISMICT 07) in Oulu, Finland, he showed the following bands as candidates for the application.

• MICS band: 402-405 MHz: USA, EU, Korea, Japan (FCC 47 CFR 95.601-95.673 subpart E);
• medical radio FCC proposed band: 401-402 MHz and 405-406 MHz;
• wireless medical telemetry service (WMTS) band: 608-614 MHz (TV ch. 37), 1395-1400 MHz, 1427-1432 MHz;
• idustrial, scientific and medical (ISM) band: 868/915 MHz, 2.4 GHz, 5.8 GHz;
• UWB band;
• RFID links: 135 kHz, 6.78 MHz, 13.56 MHz (ERC Rec. 70-03);
• inductive link band: 9 kHz-315 kHz (ECC Report 12); and
• capacitive carrierless baseband transmission.

The paper also presented a draft of initial requirements for BAN. As per the paper, the distance coverage for BAN is 2 to 5 m with a power consumption of about 1 mW/Mbps at a distance of 1 m. For powering BAN nodes, Astrin's paper identified recharge-able Lithium, inductive recharging and energy scavenging as power sources for in-body devices. Likewise, for on-body sensors, power technologies to be considered include temperature difference, non-rechargeable (Zinc-air, Lithium and silver-oxide) and Lithium-ion rechargable.

To get the process moving, IEEE 802.15.6 task group had its first meeting in January in Taipei, Taiwan. In essence, with a coverage of 2-5 m, 802.15.6 is being targeted at three major markets: medical healthcare service, assistance to people with disabilities, and body interaction and entertainment. However, there is no official timeline for ironing out the standard.

Meanwhile, researchers Marco Hernandez and Ryuji Kohno of Medical Information and Communications Technology Group, National Institute of Communications and Information Technologies, Kanagawa, Japan have developed a novel physical layer (PHY) for BAN and have proposed it to the IEEE standardization working group 802.11.6.

As BANs require very low power consumption, the researchers have developed a theory of signaling in the very low-power regime from an information theory perspective. For a practical implementation, Hernandez and Kohno have worked out a lower bound on the energy consumed by a practical system, including power consumption at transmitter and receiver. As transceivers operate close to the human body, and, in some cases, implemented onto a human body, the level of radiation absorbed by human tissues is a special concern, stated Hernandez. Keeping those factors in mind, the researchers have proposed a simple, energy efficient and low-risk tissue-heating UWB signal design for BAN. For that, they have developed energy-efficiency metrics that include the effect of practical transceivers and information theoretic results as the starting point for low-power system design. Also, a safety metric based on the SAR in the near and far fields of dipole antennas is also estimated.

In essence, based on the results achieved, Marco and Kohno have proposed on-off signaling with non-coherent detection, which employs a truncated-triangular-modulated sine function as pulse waveform for PHY. To demonstrate its feasibility, the researchers have implemented the low-power UWB transceiver design in CMOS. The results of this research were presented at ISMICT07 in a paper titled, “Ultralow-power UWB signal design for body area networks.”

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