Kumu Networks Reveals First Analog Finite Impulse Response Filter on a Chip

December 31, 2019 by Gary Elinoff

The KU1500 is designed to allow radios to send and receive signals at the same time on the same or adjacent channels.

Kumu Networks has announced KU1500, a completely analog IC said to be the first analog finite impulse response (FIR) filter on a chip. 



The KU1500. Screen capture used courtesy of Kumu Networks

Kumu Networks claims that the IC eliminates the unavoidable latency introduced by digital filtering: as such, it cancels the time to convert the analog signal to digital, perform filtering, and reconvert the result to analog.


Full-duplex Communication

Kumu Networks claims that its self-interference cancellation technology, which this new IC facilitates, makes it possible "to transform a half-duplex radio into a full-duplex radio operating in the same spectrum with twice the throughput."


Full-duplex communication

KU1500, combined with other Kumu Networks technology, is said to allow radios to "talk" and "listen" on the same channel at the same time. Image used courtesy of Kumu Networks

While half-duplex radios refer to devices like walkie-talkies that only allows one user to speak at a time, a full-duplex radio refers to communication in which both parties can both speak and listen at the same time (for example, telephone correspondence).

Radio communications require two frequency bands: one for the first transceiver’s transmitter to address the other’s receiver; the other for the second transceiver’s transmitter to address its target’s receiver. However, because transmitters emit slightly beyond their designated bands, filtering is necessary.


Guard band

Usually, a guard band is necessary to separate the transmitter and the receiver. Self-interference cancellation is said to eliminate the need for guard bands and filters. Screen capture used courtesy of Kumu Networks


Even with filtering, a guard band must exist between the two frequency bands for separation. Because of the growing population of radio devices, the spectrum is becoming increasingly scarce. 


Self-interference Cancellation Technology

Analog self-interference technology eliminates the need for digital filters as well as guard bands. Kumu Networks' cancellation technology, as implemented in the KU1500, is software-generated. Unlike digital filters, the KU1500 can immediately adjust its range to follow as the transmit/receive frequency channels change.


Self-interference Cancellation Technology

Kumu Networks claims that its technology cancels out the main signal that overloads the receiver’s front end and the noise that leaks into the receive channel. Image from Kumu Networks


As illustrated above, self-interference cancellation allows Radio 1 to speak to Radio 2, and for Radio 2 to talk to Radio 1 simultaneously. This is possible even with little to no guard band.


More Radios in the Same Space

With Kumu Networks’ technology, Tri-band Wi-Fi routers with dual 5GHz radios, for example, can use any two available channels. Because self-interference cancellation doesn't require a guard band, users don't need to hunt for free channels on opposite ends of the allotted spectrum. 


KU1500 acts as a self-interference canceller

When paired with Kumu Networks tuning logic (for FPGA platforms), the KU1500 acts as a self-interference canceller. Screen capture used courtesy of Kumu Networks

The result is that more radios can operate in the same space. The long stretches of essentially empty spectrum, eaten up by guard bands, are eliminated. 

Spectrum Sharing

Radios that can transmit and receive at the same time make better use of the shared spectrum. Modalities such as Wi-Fi, LTE-Unlicensed, Bluetooth, Z-wave, and Zigbee, must all coexist in unlicensed portions of the radio spectrum. Accordingly, in some regions of the globe, the use of “listen-before-talk” protocols have been put in place to maintain order.

Kumu Networks' “listen-while-talking” radio devices are designed to share the spectrum more efficiently. Additionally, networks can more effectively collaborate to share an increasingly scarce radio spectrum. 


Markets and Applications

The most obvious markets that will benefit from Kumu Networks' self-interference cancellation technology include communications (through mobile networks, Wi-Fi, Bluetooth, cable networks, and LTE and 5G).

In a broad sense, KU1500 will be useful in adaptive filtering, equalization, cancellation, and predictive modeling. This makes it a candidate for use in medical imaging, automotive and industrial sensors, high-end audio, military communication, first responder communication.


Evaluation and Support Tools

Kumu Networks has released the KU1500 evaluation board in an effort to smooth the path toward development.


KU1500 evaluation board

The KU1500 evaluation board. Image from Kumu Networks

With the evaluation board, the filter can be configured, for example, as a bandpass filter, a band-stop filter, or as a 3-notch filter.


KU1500 FIR filter response examples

KU1500 FIR filter response examples. Screen capture used courtesy of Kumu Networks 


Kumu Networks expresses confidence that the analog finite impulse response filter IC will "empower RF system designers to manage and even eliminate the self-interference produced by local transmitters."



If you've worked with RF systems, what is your experience with self-interference? Share your thoughts in the comments below.

1 Comment
  • J
    jeffl_2 January 07, 2020

    How well does that cancellation scheme work when there’s multipath interference in the far field?

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