Kumu Networks has been an early proponent of full duplex technology to boost capacity in wireless applications, including 5G, wireless and backhaul, but it has struggled to hit the commercial mainstream. Now it has secured a $5m award from the US Department of Defense (DoD) to prototype a 5G full duplex system for integrated access and backhaul (IAB), an important aspect of the 5G Release 16 standards. This will make heavy use of Kumu’s signature IP in self-interference cancellation (SIC).
IAB can extend coverage by using spectrum from a cell site both for backhaul and for access to surrounding sites, essentially setting up a mesh network.
Full duplex allows the same channel to be used for transmit and receive, potentially doubling the capacity of a piece of spectrum. Several companies have worked on 5G and WiFi implementations, and Kumu has patented several approaches to minimizing interference. Although its most revolutionary impact would be on access network capacity in constrained bands, it is simpler to deploy in backhaul scenarios and these were the focus of several early trials.
Of course, there is a natural fit with IAB, since full duplex would not only allow the same spectrum and connection to be used either for access and backhaul, depending on changing requirements, but potentially the same channels. The DoD project is to scale and test an IAB systems at the Hill Air Force Base in Utah as part of a 5G testbed that is running there, supported by vendors including Nokia and Ericsson.
The DoD has recently revived some of its old prominent role in developing new technologies that have military application but can also be released for commercial businesses too. The USA’s focus on becoming a 5G and 6G powerhouse is stimulating R&D in many quarters, and the DoD is expected to play a significant part, so being part of one of its testbeds is not just a niche activity for a start-up like Kumu, but potentially a way to boost recognition and commercial credibility.
Kumu’s VP of product, Joel Brand, said the engagement will open the opportunity both to sell to the military, and to fund and accelerate development of its technology for the wider market. In particular, Kumu is promoting its self-interference cancellation technology, which is critical to make full duplex viable.
Kumu is adapting this technology for the recently standardized IAB to address some of its trade-offs in terms of spectrum capacity. By allowing transmit and receive in the same channel, these are greatly reduced because all the spectrum can be used all the time – by contrast, time division duplex or frequency division duplex schemes avoid interference by forcing different signals to take turns, or to live in different channels, so that some spectrum is wasted.
While IAB trials in the USA – whether the DoD’s, or commercial tests by Verizon – are tied into the release of C-band spectrum, another recent area of focus for Kumu was on another source of new US airwaves, 6 GHz for WiFi. Kumu has developed a chipset in which its self-interference cancellation is focused on supporting all three WiFi bands – 2.4 GHz, 5 GHz and 6 GHz – in the same device, avoiding interference despite narrow guard bands between the two higher frequencies. This guard band is too small for conventional RF filters to handle, Brand said, so the Kumu chip can be used instead, or to enhance a filter’s performance.
Kumu gained prominence with full duplex trials with some high profile names like Deutsche Telekom and NTT Docomo. But a chip technology that, however innovative, currently remains in a niche, needs to ride any wave that comes its way – hence the moves to adapt the core technology for WiFi and backhaul.
Other applications where self-interference threatens to be a big issue could include WiFi and IoT radios like Bluetooth in the 2.4 GHz band. As well as its original use case of full duplex spectral efficiency, the Kumu technology is being tested with a view to reducing size, weight and isolation requirements for mobile base station filters and for the antennas which go into repeaters, relay nodes and RFID readers.
Kumu 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.
Kumu has investment from Deutsche Telekom, Swisscom, Verizon and Cisco, among others. In October 2016, DT conducted the world’s first public operator trial of self-interference cancellation, a technology which has been defined as a Technology Building Block for 5G by the NGMN Alliance.
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. 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.