Terahertz Receiver for 6G

Future mobile network: Small radio cells are connected by wireless high-speed terahertz links. (Source: IPQ, KIT / NPG)

Future wireless networks of the 6th generation (6G) will consist of a multitude of small radio cells that need to be connected by broadband communi­cation links. In this context, wireless trans­mission at THz frequencies represents a parti­cularly attrac­tive and flexible solution. Researchers at Karlsruhe Institute of Technology KIT have now developed a novel concept for low-cost terahertz receivers that consist of a single diode in combi­nation with a dedicated signal processing technique. In a proof-of-concept experiment, the team demonstrated trans­mission at a data rate of 115 Gbit/s and a carrier frequency of 0.3 THz over a distance of 110 meters.

The 6th generation of mobile communi­cations promises even higher data rates than 5G, shorter latency, and strongly increased densities of terminal devices, while exploiting Artificial Intelligence (AI) to control devices or auto­nomous vehicles in the Internet-of-Things era. “To simul­taneously serve as many users as possible and to transmit data at utmost speed, future wireless networks will consist of a large number of small radio cells,” explains Christian Koos, who works on 6G techno­logies together with his colleague Sebastian Randel. In these radio cells, distances are short such that high data rates can be transmitted with minimum energy consumption and low electro­magnetic immission. The associated base stations will be compact and can easily be mounted to building facades or street lights.

To form a powerful and flexible network, these base stations need to be connected by high-speed wireless links that offer data rates of tens or even hundreds of gigabits per second. This may be accomplished by terahertz carrier waves, which occupy the frequency range between microwaves and infrared light waves. However, terahertz receivers are still rather complex and expensive and often represent the bandwidht bottle­neck of the entire link. In cooperation with Virginia Diodes (VDI) in Charlottes­ville, USA, researchers of KIT’s Institute of Photonics and Quantum Elec­tronics (IPQ), Institute of Micro­structure Technology (IMT), and Institute for Beam Physics and Techno­logy (IBPT) have now demonstrated a parti­cularly simple inexpensive receiver for terahertz signals.

“At its core, the receiver consists a single diode, which rec­tifies the terahertz signal,” says Tobias Harter, who carried out the demons­tration together with his colleague Christoph Füllner in the framework of his doctoral thesis. The diode is a Schottky barrier diode, that offers large bandwidth and that is used as an envelope detector to recover the amplitude of the terahertz signal. Correct decoding of the data, however, addi­tionally requires the time-dependent phase of the terahertz wave that is usually lost during recti­fication. To overcome this problem, researchers use digital signal processing techniques in combi­nation with a special class of data signals, for which the phase can be reconstructed from the amplitude via the Kramers-Kronig relations.

The Kramers-Kronig relation describe a mathematical relationship between the real part and the imaginary part of an analytic signal. Using their receiver concept, the scientists achieved a trans­mission rate of 115 Gbit/s at a carrier frequency of 0.3 THz over a distance of 110 m. “This is the highest data rate so far demons­trated for wireless terahertz trans­mission over more than 100 m,” Füllner says. The terahertz receiver developed by KIT stands out due to its technical simplicity and lends itself to cost-efficient mass produc­tion. (Source: KIT)

Reference: T. Harter et al.: Generalized Kramers–Kronig receiver for coherent terahertz communications, Nat. Phot., online 9 September 2020; DOI: 10.1038/s41566-020-0675-0

Link: KIT Center Information – Systems – Technologies (KCIST), Karlsruhe Institute of Technology, Karlsruhe, Germany

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