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 terahertz (THz) frequencies represents a particularly attractive and flexible solution.
The 6G mobile communications promise even higher data rates, 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. In these radio cells, distances are short so that high data rates can be transmitted with minimum energy consumption and low electromagnetic emission. The associated base stations will be compact and can easily be mounted to building facades or streetlights.
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 (Gbit/s). This may be accomplished by THz carrier waves that occupy the frequency range between microwaves and infrared light waves; however, THz receivers are still rather complex and expensive and often represent the bandwidth bottleneck of the entire link.
Researchers have developed a novel concept for low-cost THz receivers that consists 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 receiver consists of a single diode that rectifies the THz signal. The Schottky barrier diode offers large bandwidth and is used as an envelope detector to recover the amplitude of the THz signal. Correct decoding of the data, however, additionally requires the time-dependent phase of the THz 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 relation. The Kramers-Kronig relation describes a mathematical relationship between the real part and the imaginary part of an analytic signal.