Full-duplex wireless transmission holds great promise for the spectrum-starved wireless industry, but the technology did not make it into the first version of the 5G standard. Like LTE, the first 5G networks will use frequency division multiplexing (FDD) or time division multiplexing (TDD) to enable radios to send and receive on the same channel.

 

The technology could someday obviate the need for FDD and TDD because it will enable radios to send and receive on the same frequency at the same time. It works by filtering out the interference between the two signals. 

 

"Transmit and receive at the same time has not been possible prior to Kumu," said Joel Brand, VP of product management at Kumu Networks. Kumu has raised $45 million to develop the RF filtering technology that it says will enable full-duplex. Investors include Verizon Ventures, Deutsche Telekom and Swisscom. After five years of tests and trials, Kumu brought an RF integrated circuit to market this year.

 

"We've had systems in a variety of trials in the U.S., in Europe, in Asia and we've proven that the technology works," said Brand. Brand said one reason it took several years to get a chip to market was the complexity of shrinking Kumu's technology onto a single, affordable chip.

 

"Our technology is a combination of analog and digital," he explained. "When the radio is overloaded by its own transmission it first needs to be resolved in the analog domain before digital can kick in." Brand said the process of "miniaturizing" technology is better understood in the digital domain than in the analog domain.

 

Kumu finally launched its chip around the same time that the 3GPP approved the first 5G standard in Release 15. Since full-duplex is not part of the initial 5G spec, it will probably not become part of a 5G standard until the next release at the earliest.

 

"It's kind of late to get something as fundamental as full-duplex into the 5G standard," said analyst Linley Gwennap of The Linley Group. "MIMO already allows you to send two or more signals through the same channel ... and MIMO is already standard in every LTE phone and base station."

 

But full-duplex may have a role to play in wireless backhaul. Brand said Kumu's technology performs as well as fiber, and has been deployed in both the U.S. and Europe. 

 

Nonetheless, cellular is not Kumu's biggest opportunity in the short term. Brand believes that full-duplex will be adopted first for Wi-Fi, then in cable networks, and finally in 5G. He hopes that as smart homes connect more and more devices to their Wi-Fi routers, the need to cancel interference and maximize bandwidth will become clear.

 

Kumu appears to be ahead of its one major competitor, a Texas startup called
GenXComm. GenXComm, which is also developing full-duplex technology, has not yet released a chip. Late last year, GenXComm raised $7 million in a funding round led by Intel Capital, which also seems to see full-duplex impacting Wi-Fi before it makes its way to other technologies.

 

“Full-duplex technology has the potential to have a tremendous impact in a number of areas that are important to Intel, including Wi-Fi, Broadband Access, and 5G,” said Dan Artusi of Intel's connected home division in a press release announcing the GenXComm funding. GenXComm's other investors include Azure Capital Partners, Bandgap Ventures, Capital Factory, FAM Capital Partners, Lip-Bu Tan, UT Horizon Fund and WS Investment Co. 

 

Kumu's investors include Cisco, Singtel Innov8, New Enterprise Associates, Third Point and Khosla Ventures in addition to Deutsche Telekom, Swisscom and Verizon Ventures. Verizon Ventures invested in early 2016, and at this time is not commenting on Kumu.

 

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