Kumu Networks let one radio send and receive at once, doubling capacity in carrier trials

MIT Technology Review reported in September 2015 that Kumu Networks, spun out of Stanford in 2012, had shown in real cellular tests that its trick could double the capacity of a wireless link. The company grew from research refuting the assumption that radios cannot transmit and receive simultaneously, which rests on the fact that a radio's outgoing signal is billions of times stronger than incoming ones. Radios therefore use separate channels or take turns.

Kumu's founders built hardware and software that filters the outgoing signal out of the receiver, giving a 'full duplex' connection, which doubles effective capacity of a channel or lets one channel replace two. In September, Deutsche Telekom installed a small LTE tower with Kumu's technology on a Prague rooftop, with devices on cars playing phones, moving or blocked by buildings. An unnamed large US carrier ran similar, smaller tests on its network near Sunnyvale. Kumu's Steven Hong said the doubling of spectral efficiency held in all conditions tested.

Filter the radio's own transmission out of its receiver, so it can send and receive at once on one channel.

Cancelling self-interference at the receiver removes the reason radios could not do both at once.

Doubling use of a channel adds capacity without needing more spectrum.

The result held for moving devices and blocked line of sight in a live LTE setup.

A long-held limit may be an engineering assumption; test it before designing around it.

The detailed results were not public. A Columbia professor called it the first hint of a realistic demonstration. Kumu said close-together test devices sometimes interfered and the system did not always adapt fast, for instance when a car passed. Its first product, a cable-free small cell using full duplex for backhaul, was due for field tests in 2016, and the team hoped to shrink the unit from a hardback book to a credit-card size chip.