While wireless products such as cell phones are increasingly being used to transmit large amounts of data over long distances, often at the expense of battery life, another class of devices is emerging that transmits data slowly and over a short range. Examples include wearable or implanted medical sensors that form a ‘body-area network’ over which they communicate; and a network of communicating sensors, spread over an area of land, that can effectively monitor enemy troop movement or environmental conditions. Because these sensors can be hard to reach, however, they need to be able to operate for weeks or more on a single battery charge.
Key to the development of this technology are ultra-wideband (UWB) radios, which can communicate over a very large range of radio frequencies, allowing them to avoid interfering with existing radio channels and with each other. Ideally, these radios should be highly energy-efficient, and have the ability to measure distances to their neighboring radios so that they can optimize the network connecting them. Now, Yuanjin Zheng and co-workers from the A*STAR Institute of Microelectronics in Singapore have demonstrated a complete and efficient UWB radio with distance measurement capability for short-range, low-power wireless networks1.
The team’s radio has a power efficiency of 25.4%, placing it among the most efficient radios of this kind. It uses only a few nanojoules of energy for every bit that it receives or transmits. This efficiency is achieved by synchronizing the ‘transmit and receive’ processes, and powering down portions of the circuit when they are not in use. In addition to its efficiency, the radio can provide location information to an accuracy of 15 centimeters by measuring the time delay between transmitted and received pulses. The radio bandwidth is 1 gigahertz, compared to 1–20 megahertz for a traditional wireless radio. A high level of integration allows the entire system to be placed onto a single chip only 17 square millimeters in size, which can then be used inside a sensor or other device.
Zheng says the team plans to further reduce the power consumption of their chip, and improve the ranging accuracy for short- to mid-range distances. However, even their current radio should have ready applications, says Zheng: “The efficiency of this radio makes it useful for continuous vital signal monitoring of multiple sensor signals for both hospital and home healthcare applications.”
The A*STAR affiliated researchers mentioned in this highlight are from the Institute of Microelectronics