Full duplex wireless, which allows radios to transmit and receive on the same channel by cancelling out Self Interference, will be “a reality very soon” and could be deployed in multiple applications across the market, revolutionising some aspects of the wireless network, according to one of the key players trying to commercialise the technology.
Sachin Katti, Chief Scientist and Co-Founder of Kumu Networks, and also a Professor at Stanford University where the technology that Kumu Networks is marketing was developed, said that operators are right now evaluating full duplex as an option.
“We have units that show working in-band Full Duplex radios being tested and verified by Tier One operators. Full Duplex radios are going to be a reality very soon,” he said.
“Almost every carrier has mentioned 5G as a candidate for 5G technology,” Katti said, but he doesn’t think we will be waiting 5-10 years for commercialisation. “We will see commercialisation of this technology next year, probably,” he claimed.
Full Duplex works by isolating the receive path from interference leaking from the transmitter, allowing the receiver to “hear” received signal at the same time as its transmitter is transmitting. Katti likened trying to “listen” to an incoming signal whilst also transmitting as akin to trying to hear a whisper while you yourself are shouting. Transmitted interference can be “billions” of times more powerful than received signal, he said.
Full Duplex, Katti said, has a number of applications, from device, to cellular and WiFi access to backhaul.
Kumu’s interference cancellation technology could be applied as a “building block” that sits in front of the radio in a variety of products and devices, with Katti describing a “simple front end to any radio” that would create a “tunable radio head” allowing a wide variety of applications.
The cancellation technology can work for any frequency and air interface, including any potential new waveforms, Katti said, providing a tunable radio head that could be used to:
– Create universal roaming phones that work on all bands – by allowing phones to be tuned to the available frequency band in the market instead of relying on static filters to handle cross-band interference.
– Double the capacity on LTE access networks by sending and receiving on the same channel.
– Double the capacity on wireless backhaul links
– Enable small cells to “self-backhaul” by using the same frequencies at the same time for backhaul and access.
– Enable tight HetNet coordination by creating enhanced interference coordination, enabling what in effect is a very low latency control plane by receiving control channel data at the same time as transmitting, thereby mititgating the need for high capacity fronthaul to carry co-ordination.
– Allow increased use of under-utilised spectrum, for example by allowing LTE-U (LTE in unlicensed bands such as 2.4GHz and 5GHz) and WiFi to co-exist by avoiding LTE signals “leaking” to WiFi channels.
– Although not stated by Katti in this talk (to LTE World Summit in Amsterdam) Full Duplex would also render invalid the distinction between TDD and FDD, by effectively allowing uplink and downlink in the same spectrum, without the need for unpaired spectrum technology.
What Self Interference Cancellation has to do is compensate for both this additional “noise” and the introduction of non-linear harmonic components at the receiver.
How Does Full Duplex Work?
The Stanford developed technology relies on algorithms that track Self-Interference and can cancel it in real time by cancelling out interference introduced to the original transmitted signal.
In a radio the original “clean” digital signal transmitted from the baseband is converted to analogue and converted to the right carrier frequency. This leads to analogue components along the TX (transmitter) chain distorting the signal and adding “noise”. This might include an analogue circuit adding cubic and higher-order harmonic components of signal, or a power amplifier adding transmitter “noise”.
What Self Interference Cancellation has to do is compensate, at the receiver, for both this additional “noise” and the introduction of non-linear harmonic components. This requires both the cancellation of the interfering signal in analog at RF and cancellation algorithms working between the digital baseband and the baseband modem.
Katti described this architecture as “tunable mixed signal processing from RF chips and DSPs that sits in front of the radio”.
