5G WiFi

Three carriers and Cisco invest in full duplex pioneer Kumu

Kumu Networks has raised a further $25m round of funding to support its particular take on full duplex technology, which is gaining rising levels of acceptance as a way to improve capacity in WiFi, cellular and backhaul networks – and a likely component of 5G.

Several vendors and universities are working on different approaches to full duplex, but Kumu is the most prominent of these, and its latest financing round boasts big name industry investors along with the venture capitalists – its major trial partner Deutsche Telekom, plus Swisscom, Verizon and Cisco.

Full duplex allows radios to transmit and receive on the same frequency, effectively doubling spectral efficiency, by cancelling out the self-inteference noise of transmission.

“Full duplex offers significant advantages and removes roadblocks from wireless endeavors as diverse as LTE-Advanced, general radio frequency planning and future standards and protocols,” said Rachid El Hattachi, Deutsche Telekom’s SVP of architecture and blueprints, commenting on the funding.

The company previously raised a $5.4m A round from New Enterprise Associates in September 2012, and, then a $15m B round featuring NEA, Vinod Khosla and Third Point Ventures. All those investors were also part of the new C round.

In October, Deutsche Telekom conducted the world’s first public operator trial of self-interference cancellation (SIC), a technology which has been defined as a Technology Building Block for 5G by the NGMN Alliance. Some carriers are interested in using it before that, especially for backhaul. DT said SIC technology could be used in existing networks and potentially solve small cell issues by using the same spectrum for access and backhaul.

The operator’s 5G:haus research arm conducted the tests in Prague, Czech Republic, with Kumu Networks. The aim was to determine whether SIC could enable full-duplex communication, and whether that would remain robust and stable in real world conditions.

Bruno Jacobfeuerborn, CTO at Deutsche Telekom, said in a statement: “I’m delighted to see the first experimental results of a potential 5G technology in DT’s real network environment. We use field trials to get a better understanding of a technology’s potential and that helps us to identify use cases and applications in the context of 5G.”

Kumu Networks CEO David Cutrer added: “We are encouraged to accelerate the commercialization of the technology for near term applications within the goal of realising the full potential of the technology in a 5G framework.”

Kumu came to the world’s attention in 2014 when it first demonstrated incoming and outgoing signals using the same frequency without interference, effectively doing away with the FDD/TDD difference. Then it found a way to incorporate its technology relatively easily into existing base stations, potentially paving the way for near term market adoption, rather than having to wait for the next wave of wireless systems.

Kumu’s Steven Hong said last year: “There is no DD anymore – not FDD or TDD”.

As well as the DT project, Kumu has been working on proof of concept tests with other carriers, notably Telefonica and SK Telecom – which demonstrated the system on their stands at Mobile World Congress in March 2015.

The company addresses the interference issue by connecting a smart echo-canceller in place of the usual RF rx/tx combiner/splitter in a standard base station. The Kumu radio generates an additional signal that cancels out the interference – a different approach to established interference cancellation techniques, and one which could be applied to cellular networks or to WiFi.

According to Kumu, the system is constantly scanning the radio environment, gauging the state of the airwaves at any given time, as well as the way the transmission is changing the signal environment at the receiver. Its algorithms then compensate for those changes as the signals arrive from the opposite direction, in effect applying echo cancellation to radio waves.

As well as improving speeds, Kumu says spare macrocell capacity created via this approach could be harnessed for backhauling nearby small cells, dividing the full 100Mbps of capacity in the macro sector between several metrocells, which would not need their own backhaul, and could also act as relays. In this scenario, the small cell would need to implement the special receiver but no special handsets or macrocells would be required. Another potential, and topical, application is to combine WiFi and LTE-U or LAA (LTE using 5GHz carriers for supplemental capacity) in one box while avoiding the usual interference issues.

Another full-duplex specialist, MIMOtech, is focusing on backhaul first. The company says it can double backhaul throughput in microwave bands using its Air Division Duplexing (ADD) technique, which combines full-duplex with MIMO. At MWC, the company launched its Janus AirDuplex range of microwave backhaul radios based on this technology, claiming data rates of up to 1Gbps in a single 28MHz channel, and 2Gbps in 56MHz.

CEO Buks Fouche said the system is more cost-effective than using millimeter wave spectrum above 42GHz for backhaul – an approach which many are testing for small cells because of the plentiful capacity available. He said: “The wireless industry is facing a crisis in its ability to keep up with the demand for backhaul capacity, and Janus AirDuplex provides a way to achieve higher throughput without resorting to using the millimeter wave frequency bands above 42GHz, which offer broader bandwidths but suffer atmospheric attenuation and also often attract higher licensing fees.”

ADD uses spatial multiplexing to double the capacity and spectral efficiency of conventional microwave platforms. With an antenna separation of about 100 millimeters, it can be considered as, in effect, a single-aperture antenna from the point of view of licensing, site rental cost and implementation, says its inventor, reducing capex and opex costs.

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