Full duplex: A fundamental radio tech breakthrough

It is generally accepted that we’re fast approaching the limits of what is possible with radio waves, due to numerous technical constraints that have plagued RF-based wireless networks since their inception over 100 years ago. But what if one of those constraints — perhaps the biggest — was blown away?

The constraint of the duplex

One of the most well-known constraints in RF that it is generally impossible to transmit and receive at the same time on the same frequencies because the act of transmission creates a massive amount of interference for the receiver, preventing the receiver from “hearing” the desired signal coming from the environment.

This principle is the reason why most radio technologies that involve transmission and reception use some sort of half-duplex scheme, where various techniques are used to split the channel in two. With FDD (frequency division duplex), transmission and reception are separated into separate frequencies, far enough away in frequency space that any emissions bleeding over from the transmitter to the receiver would be firmly rejected. With TDD (time division duplex), transmission and reception share the same frequencies, but the operations of transmission and reception are separated by time. That is, transmission occurs for a period of time, then reception occurs for a period of time, and continues to alternate as such.

According to Joel Brand, Vice President of Product Management at Kumu Networks, the way Kumu enables full duplex operation is somewhat similar to how echo cancellation works. The receiver “listens” to determine the RF environment and uses algorithms to predict how the transmission will be altered by the environment and cancel it out from data received from the receiver. By doing so, the problem of self-interference goes away, and the receiver can “hear” the signal it is supposed to hear while the transmitter is active.