Kumu Networks: Full Duplex on One Channel

Well-funded startup offers self-interference cancellation tech for single-frequency transmit and receive.


Kumu Networks is in an enviable position fitting today’s requirements for radio-frequency system designs. The Sunnyvale, Calif., startup, incorporated in 2011 and coming together the following year, has developed self-interference cancellation technology, enabling radios to send and receive signals at the same time on the same channel or on an adjacent channel. This full-duplex technology has applications in wireless and wireline communications.

With this patented technology, crafted by Stanford professors and graduate students, Kumu is able to address a variety of markets—cable networks, LTE and 5G cellular communications, microwave, military/aerospace, satellite and Wi-Fi.

Kumu touts its technology for doubling spectral efficiency and addressing spectrum scarcity, especially for frequencies lower than 6 GHz. Self-interference cancellation can work with full-duplex systems and multiple radios in the same location on the same or nearby frequencies, while improving the performance of traditional filters or replacing fixed filters with tunable filters, according to the company.

Mesh networks are the hot topic when it comes to wireless communications, whether they are LTE relay nodes, mobile ad-hoc networks, modern Wi-Fi extenders or old-fashioned repeaters. Self-interference cancellation tech can also help sort things out in the area of unlicensed frequency bands, which involve the Bluetooth, LTE-Unlicensed, Wi-Fi, ZigBee and Z-Wave protocols.

The startup is well-funded, raising $65 million in three rounds, the last of which was in early 2016. The private company’s financial backers include Cisco Investments, Deutsche Telekom, Khosla Ventures, New Enterprise Associates (NEA), Singtel Innovat8, Swisscom, Third Point and Verizon Ventures.

“We were originally funded by NEA and Khosla,” said Joel Brand, vice president of product management at Kumu Networks, “We were founded by a group that came out of Stanford, out of the research they were doing at Stanford in the context of full duplex.” He noted that nearly all wireless devices are using frequency-division duplexing or time-division duplexing. “The cellular phone that you’re using is typically using two separate frequencies—one to receive from the tower and a different one to send from your phone to the tower. They are not mixing, the up and the down. We came up with a very creative concept that said, we can change that.”

To address spectral scarcity, Brand said they wanted to “make the radio transmit and receive on the same frequency at the same time.” He compared the current state of communications with someone who is shouting and can only hear themselves. “If we stick a kind of a noise-canceling concept onto the radio, the noise canceling basically cancels your shout, and quiets down the shout, then the radio can listen to everything else on the outside. And if we can do that, then the radio can transmit and receive on the same frequency at the same time. Which doubles spectrum accumulation, which in the communications business is like finding a gold mine.”

Kumu has full-duplex technology systems deployed by the U.S. military and by two U.S. carriers, installed along with their small-cell infrastructure, said Brand. “They’re using it in order to backhaul their small cells, using the same frequency on which the small cell operates. They use their own frequencies for backhaul without giving it up,” he says. “This is a fairly expensive technology. It’s not especially cheap. In the process of developing this technology, we found that we can make this technology cheaper. And we are doing it in stages.”

Kumu’s management is stocked with veteran executives, Brand notes, offering “an interesting combination of personalities.”

  • CEO David Cutrer previously served as a co-founder of NextG Networks, which was sold to Crown Castle International in 2012 for about $1 billion in cash, and as a co-founder of LGC Wireless, which was acquired by ADC Telecommunications.
  • Steffen Hahn, vice president of engineering, has worked at Scintera Networks, Quellan, Airgo Networks and Philips Semiconductors (now NXP Semiconductors).
  • Brand himself has held executive positions at ConteXtream, Bytemobile and Ruckus Wireless.
  • Kumu’s co-founder and chief technology officer, Mayank Jain, was a graduate student at Stanford. He has worked at Nvidia, Qualcomm and Texas Instruments.
  • Jung Il-Choi, chief system architect and co-founder, created full-duplex radios, with his colleagues, while completing his Ph.D. in electrical engineering at Stanford.
  • Jeff Mehlman, another Kumu co-founder, serves as the startup’s director of engineering. He previously founded an Internet of Things home sensor startup. He has also worked in the automotive industry and had a brief stint at Apple. Mehlman put his Ph.D. on hold to help start Kumu Networks.

Brand takes the industry transition to 5G cellular communications in stride. “It’s a normal cycle in every technology, that every few years, there is the next version, whether it’s Wi-Fi or whether it’s cellular technology,” he said. “So, 5G is the next thing, the next improvement in the cellular technology. We learn from mistakes that we made in the definition of LTE, and we are fixing those. There has also been improvement in processing power, all kinds of other good things that enable new things that were not possible when LTE was designed. Most of the discussion around 5G is related to the protocol—for us, the protocol, whether the protocol happens to be LTE or 5G, whether it happens to be Wi-Fi or anything else—is totally irrelevant to us. We are operating below that level.”

He added, “Having said that, we are involved heavily in 5G in the context of massive MIMO. Massive MIMO is an RF technology.”

Kumu Networks seems to be in a sweet spot for communications in this moment.

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