PORTLAND, Ore. — Today 2G, 3G, 4G, LTE, WiFi, Bluetooth, Zigbee and the rest all have a basic flaw that halve their potential bandwidth — they have to use multiplexing (either frequency, time or both) to carry on a two-way communication. Why? Because the transmitter signal is typically much much louder than the receiver signal, swamping it out and making it nearly impossible for both to use the same band without multiplexing. Now Kumu Networks Inc. (Sunnyvale, Calif.) claims to have perfected two-way full-duplex communications over the same band with a combination of hardware modules and software algorithms using ultra-precise step attenuators and phase shifters.
"Our claim to fame are interference-cancellation algorithms that control our full-duplex transceiver," Joel Brand, vice president of product management at Kumu Networks told EE Times. "At the end of day, hardware is only a part of solution."
Others have tackled the problem before, such as Columbia University which recently described a chip that works in the lab. However, Kumu claims that the secret sauce is the algorithms that drive a system in order to make it work under real-world conditions, where environmental factors have to be cancelled-out too — and in real time.
Kumuís self-interference cancellation technology isolates the receiver from the transmitter permitting full duplex operation on same frequency at same time.
"To get reliable full-duplex communications, you have to develop algorithms that control system interference from environment changes too, such as reflections off nearby buildings. The signal has to adapt in real time to any changes the environment too," Brand told us.
The basic principle behind full-duplex without multiplexing is similar to the concept of noise cancellation in headphones. A sample of the transmitted signal is taken, phase inversed, and used to cancel out the interference with the receiver's signal, which is a mixture of the quiet incoming message and loud outgoing message. This can be set-up to work perfectly in a sound-proofed anechoic chamber, but in the real world their will be out-of-phase reflections which are particularly troublesome when the reflections are changing, such as in a high-speed train or off-of cars driving by a building.
With Kumu modules on each end, major carriers have demonstrated that it works to double bandwidth without interference.
That's where Kumu's 30 filed and five granted patents come in, plus those it has a 15-year exclusive license from the four Stanford University students who got the ball rolling three years ago with two of their professors. The students have since returned to Stanford.
How's it work
The biggest problem the algorithms had to overcome is that the received signal is usually just above the noise floor which can be as much as low as -130dB, requiring that the transmitted signal be cancelled out with an accuracy of 90-to-100 parts-per-million (PPM).
"Our system uses hardware, under algorithmic control, to recreate the signal to be cancelled with pristine accuracy," Brand told us.
So far, Telefonica (Barcelona), SK Telecom (South Korea) and Deutsche Telecom (Germany) have demonstrated full-duplex systems using Kumu's system for applications as diverse as LTE backhaul and 5G robotics.
Kumu claims self-backhauled small cell removes all the barriers for successful small cell deployment.
Kumu predicts that its first commercial applications will be deployed in 2016, the same year it will also introduce miniaturized versions of its technology that work with mesh networks, WiFi and LTE across their diverse frequency bands worldwide.
Full-duplex wireless links may be answer to densification of wireless links making them ideal for control plane due to low latency and direct communications.
Besides Spanish, South Korean and German telecom giants, Kumu is also working with other unnamed European and one of the top three U.S. carriers, according to Brand. The company has also approached 5G standards groups in hopes of incorporating full-duplex into all aspects of the next-generation communications technology.
Kumu also claims its technology has military applications, such as jamming the cell phone signals used today to detonate improvised explosive devices (IEDs) without disrupting communications among troops.
— R. Colin Johnson, Advanced Technology Editor, EE Times
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