“Where the Wi-Fi sucks” is where a new wireless protocol does its magic

“Where the Wi-Fi sucks” is where a new wireless protocol does its magic

1bps ought to be enough for anybody —

ONPC won’t help you browse the Internet, but it’s a good way to monitor devices.

A man operates an elaborate computer interface.

Enlarge / BYU assistant professor of computer engineering Phil Lundrigan is looking at an ONPC heartbeat on an RF signal analyzer.

Researchers at Brigham Young University have created a new RF protocol that runs on top of existing consumer Wi-Fi at significantly greater range. But before you get too excited, the protocol’s bandwidth is extremely low—so much so that it makes LoRa look like an OC-24. The protocol, called ONPC—short for On-Off Noise Power Communication—currently only specifies a single bit per second.

Although ONPC only conveys one bit per second of data, its range is 60m or more beyond Wi-Fi—and it runs in software alone, on unmodified Wi-Fi hardware. An ONPC device can connect to standard Wi-Fi when range permits, fall back to ONPC mode if the connection drops, and then re-connect to the Wi-Fi when it becomes available again.

Disconnected versus unpowered

BYU Associate Professor of Computer Engineering Phil Lundrigan told Ars that ONPC was inspired by problems in an otherwise unrelated health care research project he’d worked on. The project required placing IoT sensors in the homes of study participants so that BYU’s control over the environment was minimal to nonexistent. The project also required the sensors to report back to the researchers over the Internet, using whatever Wi-Fi the study participants had in place.

Unsurprisingly, participants’ home Wi-Fi tended to have problems. The sensors didn’t need much of a connection, since they only needed to report small amounts of data over a time series—so placing them at the dubious edges of coverage was basically OK. The problem the researchers ran into was that at the edge of coverage, their sensors would frequently drop off the Wi-Fi for hours or even days at a time.

Dropping off the Wi-Fi wasn’t necessarily a big problem. The sensors were perfectly capable of continuing to store data locally, and they would send all the collected data in a batch whenever they managed to reconnect to the Wi-Fi again. But if the sensor was truly powered off or broken—and thus not collecting data—this posed real problems for the study.

This left researchers balancing the need to make sure sensors worked against the likelihood of annoying participants badly enough that they might drop out of the study. In one memorable case, a basket of laundry in front of a sensor was all that kept it from transmitting its data to the researchers. When the laundry basket was moved, the device almost immediately reconnected to the house’s Wi-Fi and began transmitting its stored data.

Shave and a haircut, two bits

The desire to know whether their sensors were working, even if they weren’t connected, led the researchers to the idea of ONPC. 802.11 Wi-Fi requires a bi-directional signal strong and clean enough to establish a 1Mbps PHY rate, and if such a signal can’t be established, the client device and Wi-Fi infrastructure are effectively invisible to one another.

Although a Wi-Fi AP (Access Point) can’t actually receive frames sent by a STA (Station, or Wi-Fi client device) outside its range, it’s still possible for it to detect them by looking for changes in the RF noise floor. When a STA outside the AP’s range transmits a frame, the noise floor increases. When the STA stops transmitting, the noise floor decreases.

  • This is an overview of an ONPC-capable Wi-Fi network. Whenever possible, the devices just use normal Wi-Fi. When the network isn’t available, they transmit ONPC frames instead.

  • By looking for patterns in the RF noise floor, an ONPC receiver can detect the presence of individual ONPC devices.

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