New transmitter could make wireless devices more energy-efficient

Researchers from MIT and elsewhere have designed a novel transmitter chip that significantly improves the energy efficiency of wireless communications, which could boost the range and battery life of a connected device.Their approach employs a unique modulation scheme to encode digital data into a wireless signal, which reduces the amount of error in the transmission and leads to more reliable communications.The compact, flexible system could be incorporated into existing internet-of-things devices to provide immediate gains, while also meeting the more stringent efficiency requirements of future 6G technologies.The versatility of the chip could make it well-suited for a range of applications that require careful management of energy for communications, such as industrial sensors that continuously monitor factory conditions and smart appliances that provide real-time notifications.“By thinking outside the box, we created a more efficient, intelligent circuit for next-generation devices that is also even better than the state-of-the-art for legacy architectures. This is just one example of how adopting a modular approach to allow for adaptability can drive innovation at every level,” says Muriel Médard, the School of Science NEC Professor of Software Science and Engineering, a professor in the MIT Department of Electrical Engineering and Computer Science (EECS), and co-author of a paper on the new transmitter.Médard’s co-authors include Timur Zirtiloglu, the lead author and a graduate student at Boston University; Arman Tan, a graduate student at BU; Basak Ozaydin, an MIT graduate student in EECS; Ken Duffy, a professor at Northeastern University; and Rabia Tugce Yazicigil, associate professor of electrical and computer engineering at BU. The research was recently presented at the IEEE Radio Frequency Circuits Symposium.Optimizing transmissionsIn wireless devices, a transmitter converts digital data into an electromagnetic signal that is sent over the airwaves to a receiver. The transmitter does this by mapping digital bits to symbols that represent the amplitude and phase of the electromagnetic signal, which is a process called modulation.Traditional systems transmit signals that are evenly spaced by creating a uniform pattern of symbols, which helps avoid interference. But this uniform structure lacks adaptability and can be inefficient, since wireless channel conditions are dynamic and often change rapidly.As an alternative, optimal modulation schemes follow a non-uniform pattern that can adapt to changing channel conditions, maximizing the amount of data transmitted while minimizing energy usage.But while optimal modulation can be more energy efficient, it is also more susceptible to errors, especially in crowded wireless environments. When the signals aren’t uniform in length, it can be harder for the receiver to distinguish between symbols and noise that squeezed into the transmission.To overcome this problem, the MIT transmitter adds a small amount of padding, in the form of extra bits between symbols, so that every transmission is the same length.This helps the receiver identify the beginning and end of each transmission, preventing misinterpretation of the message. However, the device enjoys the energy efficiency gains of using a non-uniform, optimal modulation scheme.This approach works because of a technique the researchers previously developed known as GRAND, which is a universal decoding algorithm that crack any code by guessing the noise that affected the transmission.Here, they employ a GRAND-inspired algorithm to adjust the length of the received transmission by guessing the extra bits that have been added. In this way, the receiver can effectively reconstruct the original message.“Now, thanks to GRAND, we can have a transmitter that is capable of doing these more efficient transmissions with non-uniform constellations of data, and we can see the gains,” Médard says.A flexible circuitThe new chip, which has a compact architecture that allows the researchers to integrate additional efficiency-boosting methods, enabled transmissions with only about one-quarter the amount of signal error of methods that use optimal modulation.Surprisingly, the device also achieved significantly lower error rates than transmitters that use traditional modulation.“The traditional approach has become so ingrained that it was challenging to not get lured back to the status quo, especially since we were changing things that we often take for granted and concepts we’ve been teaching for decades,” Médard says.This innovative architecture could be used to improve the energy efficiency and reliability of current wireless communication devices, while also offering the flexibility to be incorporated into future devices that employ optimal modulation.Next, the researchers want to adapt their approach to leverage additional techniques that could boost efficiency and reduce the error rates in wireless transmissions.“This optimal modulation transmitter radio frequency integrated circuit is a game-changing innovation over the traditional RF signal modulation. It’s set to play a major role for the next generation of wireless connectivity such as 6G and Wi-Fi,” says Rocco Tam, NXP Fellow for Wireless Connectivity SoC Research and Development at NXP Semiconductors, who was not involved with this research.This work is supported, in part, by the U.S. Defense Advanced Research Projects Agency (DARPA), the National Science Foundation (NSF), and the Texas Analog Center for Excellence.