Researchers at Korea Maritime and Ocean University have proposed a novel signal design for simultaneous wireless information and power transfer (SWIPT). SWIPT, a promising radio frequency-based technology to connect and energize low-power devices wirelessly over a long distance, could enable the Internet of Things in the future.
However, state-of-the-art low-power SWIPT receivers still consume much more energy for communication than the amount they can harvest, which hinders further development and growth of the Internet-of-Things (IoT) ecosystem. Currently such systems typically use receiver architectures based on time-switching and power-splitting schemes.
While these designs can be implemented using conventional energy and information modules, say the researchers, they do not tap the potential benefits of an integrated system. Therefore, researchers have also suggested an integrated receiver architecture (IntRx).
The new design is based on this latter approach.
“Our motivation was to design a suitable signal to be used in an integrated type receiver for the SWIPT system,” says Dr. Junghoon Kim. “The signal can bring information and power together and be decoded and harvested by a single integrated type receiver.”
To begin with, the researchers modified a conventional pulse position modulation scheme (M-PPM) to make it suitable for SWIPT IntRx. It encodes information on the pulse position and transmits high-amplitude pulses for short periods.
Consequently, the high peak-to-average-power ratio of this new signal leads to higher harvesting power at the receiver compared to the conventional signals, which continuously deliver the same level of average power. This improvement is based on a higher instantaneous power conversion (RF to DC) efficiency owing to the high peak-to-average power ratio (PAPR) signal design that takes advantage of the nonlinearity of the energy harvester’s rectifier.
Simultaneously, the receiver can extract the information from the rectified signal by finding the position of the pulse in a specific duration. Therefore, the non-coherent modulation method allows decoding without power-consuming radio frequency components such as low noise amplifier (LNA) and mixer, making it suitable for low-power IntRx SWIPT systems.
The researchers also implemented a SWIPT testbed in an indoor environment and verified the benefit of their new signal design in a real-world setting. The experiments showed the IntRx system and PPM signal pair to have more than 200% gain over conventional methods in WPT perspective.
Also, the experiment confirmed that a low-power consuming information decoding scheme works well in reality. Moreover, say the researchers, the findings were consistent with theoretical and numerical calculations.
“Our technique will lead to small battery-less devices with low power consumption and small form factor,” says Kim. “It shall catalyze the explosive growth of the Internet of Things ecosystem.”