Choir Brings Harmony to Internet of Things

Carnegie Mellon University researchers have a proposed a new platform, called Choir, to harmonize the billions of devices found in the Internet of Things (IoT).

"We want all of our devices to be smart, everything around us, from the chairs we sit on, to the phones we use to communicate, to the bags we lug around everywhere," said Swarun Kumar, an assistant professor of electrical and computer engineering (ECE). "To achieve this vision, the fundamental question that needs to be addressed is, 'How are we going to network these devices?' All of today's technologies, like cellular, Wi-Fi, and internet don't make the cut. The last link between your handbag and the internet does not yet exist."

Sensors and chips have been embedded in physical items such as coffee machines, thermostats, garage doors and traffic cameras to communicate with, and transmit information to, the IoT platform, which gathers and analyzes data and then shares it with relevant applications. This data-sharing has improved systems such as transportation and health care.

Choir uses urban Low-Power Wide Area Networks (LP-WANs), which help low-cost devices transmit information at low data rates (kilobits per second) over long distances. Kumar said the networks are ideal networks for low-cost, low-power IoT devices that have batteries with limited life spans. Although LP-WANs have been used successfully in open, rural settings, Kumar said implementing LP-WANs on a city-scale comes with several challenges.

"What really changes the game is when these radios are brought from rural environments to cities because first, there are going to be millions of radios in a relatively small area," Kumar said, "which can cause transmission collisions and drain the power of IoT devices."

He said a second challenge is the range of systems changes. In rural areas signals can potentially reach towers and base stations several miles away. In cities, buildings, concrete and other objects can absorb and weaken signals.

Kumar said Choir exploits the imperfections of low-cost LP-WAN radio components to help disentangle collisions at base stations, which allow devices to communicate with each other at greater distances.

"You can think about it this way: an ideal radio should be able to transmit and receive signals at 900 megahertz," Kumar said. "But in practice, because these radios are imperfect, there will be small differences. If you ask five or six different radios to transmit at 900 megahertz, they will all transmit at slightly different sets of frequencies. Some might transmit at 900.01. Others might transmit at 900.05. Our system, Choir, exploits these differences and filters out the received signal."

With the ability to untangle radio transmissions and the capacity to exploit other hardware imperfections, Choir improves the throughput, latency and battery life of LP-WAN nodes while increasing the range at which they can communicate. With this new technology, future LP-WAN towers could potentially gather sensor data from millions of low-power devices within a single city. These devices also could then communicate with each other.

Kumar said his team is continuing to refine Choir because they want to answer fundamental questions related to today's networking technologies.

"How do you ensure that this new age of the Internet of Things doesn't collapse under its own weight?" he asked. "If everything in the world is attached to the Internet, what are the new applications that can be enabled? And how do we ensure security and privacy of our information in a world where every object is inter-connected?

"The technology is starting to emerge — first-generation radio chips have just been rolled out, and LP-WAN standards are starting to be developed. As researchers at CMU, we really get to define the so-called Internet of Things. We get to define the future of the Internet that the public will use 10 years from now."

Along with Kumar, the team included ECE Ph.D. students Rashad Eletreby and Diana Zhang, and ECE Professor Osman Yagan. The researchers presented their paper, "Empowering Low-Power Wide Area Networks in Urban Settings," at SIGCOMM 2017, the annual conference for the ACM Special Interest Group on Data Communication in August in Los Angeles.