Russian scientists propose data encoding method for 6G standard

Russian scientists propose data encoding method for 6G standard

Researchers around the world are working on ways to transmit data in the terahertz (THz) range, which would make it possible to send and receive information much faster than today's technology. But encoding data in the THz range is much more difficult than in the gigahertz (GHz) range used by current 5G technology.

Terahertz is an electromagnetic wave with a frequency of 0.3 to 3 THz. It is a new band with many unique advantages. It is the frequency between the high-frequency edge of the millimeter wave band of electromagnetic radiation (300 GHz) and the low-frequency edge of the far-infrared spectrum band (3000 GHz). The corresponding wavelength of radiation in this band ranges from 1mm to 0.1mm (or 100μm), so it is also called the "submillimeter band".

Scientists from ITMO University in Russia have demonstrated the possibility of modifying terahertz pulses for use in data transmission.

Telecommunications companies in developed economies are beginning to adopt the new 5G standard, which will deliver faster wireless data speeds, while scientists are already working on its successor.

“We are working on 6G technology, which will increase data transmission speeds by 100 to 1,000 times, but implementing 6G requires us to switch to the terahertz range,” said Igor Oparin, a staff member at the Femtosecond Optics and Femtosecond Technologies Laboratory at ITMO University in Russia.

Now, a technology for transmitting multiple data channels simultaneously over a single physical channel has been successfully implemented in the infrared (IR) range. The technology is based on the interaction between two broadband infrared pulses, with a bandwidth measured in tens of nanometers. In the terahertz range, the bandwidth of such pulses would be much larger.

But scientists and engineers will need to find solutions to a number of key problems. One of them is ensuring that the two pulses interfere.

"In the terahertz range, pulses tend to contain a small number of field oscillations. Literally, one or two per pulse, and they are so short that they look like thin peaks on the graph," Oparin said. "It is quite challenging to achieve this kind of interference between pulses because they hardly overlap."

A team of ITMO scientists has suggested stretching the pulses so that their duration is several times longer, but still measured in picoseconds. In this case, the frequencies within one pulse will not appear simultaneously, but will follow one another. In scientific terms, this is called linear frequency modulation. However, this poses another challenge: while linear frequency modulation technology is already quite developed in the infrared range, its application in the terahertz range is still understudied.

"We have turned to a technique used in the microwave range," Oparin said. "With metallic waveguides, these waveguides tend to have high dispersion, which means that different transmitted frequencies propagate at different speeds there. But in the microwave range, these waveguides are used in single mode. In other words, the field is distributed in one configuration, a specific, narrow frequency band, and usually one wavelength. We took a similar waveguide with dimensions suitable for the terahertz range and passed a broadband signal through it, causing it to propagate in a different configuration. As a result, the duration of the pulse became longer, from 2 picoseconds to around 7 picoseconds, which is 3.5 times longer. This was our solution."

By using a waveguide, the researchers have been able to increase the length of the pulse to the theoretically necessary duration. This makes it possible to achieve interference between two linear frequency modulations.

"The great thing about this linear frequency modulation is that it shows the dependence between the structure of the pulse in time and the spectrum," Oparin said. "So we have the temporal form, or simply put, the field oscillations in time, and the spectral form, which represents these oscillations in the frequency domain. Let's say we have three peaks, three substructures in the temporal form, and three corresponding substructures in the spectral form. By removing part of the spectral form using a special filter, we can get flashes in the temporal form, and vice versa. This could be the basis for encoding data in the terahertz band."

The research results were published in the journal Scientific Reports.