Posted in | Signal Processing

New Data Encoding Technique Proposed for 6G Standard

Globally, scientists are looking for ways to convey information in the terahertz (THz) range, as this would allow sending and receiving data relatively faster than what is enabled by present-day technology.

ITMO University’s Laboratory of Femtosecond Optics and Femtotechnologies Team. Image Credit: Faculty of Photonics and Optical Information.

However, the problem currently faced by the researchers is that the THz range makes it relatively difficult to encode data when compared to the GHz range, which is presently used by 5G technology.

ITMO University researchers have demonstrated that terahertz pulses could be modified and used for data transmission. A study on this topic was published in the Scientific Reports journal.

Telecommunications firms in sophisticated economies are starting to implement the latest 5G trend. This standard will provide users with wireless data transfer speeds that were never seen before. In the meantime, as the world is on the verge of migrating to this next-generation data networks, researchers are already working on its successor.

We’re talking about 6G technologies. They will increase data transfer speeds by anywhere from 100 to 1,000 times, but implementing them will require us to switch to the terahertz range.

Egor Oparin, Study Co-Author and Staff Member, Laboratory of Femtosecond Optics and Femtotechnologies, ITMO University

A technology intended for concurrent transfer of numerous data channels across a single physical channel has been effectively applied to the infrared (IR) range. Such a technology is based on the communication between a pair of broadband IR pulses with a bandwidth quantified in tens of nanometers.

The bandwidth of such pulses in the terahertz range would be relatively larger, which means their capacity to transfer data would also be larger.

However, before starting to account for 6G technology, engineers and researchers will need to identify solutions to various crucial problems. One of the problems to be addressed is to ensure the interference of a couple of pulses, which would lead to a supposed frequency comb or pulse train used for data encoding.

In the terahertz range, pulses tend to contain a small number of field oscillations; literally one or two per pulse,” added Egor Oparin. “They are very short and look like thin peaks on a graph. It is quite challenging to achieve interference between such pulses, as they are difficult to overlap.”

Researchers from ITMO University have now recommended that the pulse can be extended in time so that it can last many times longer and still be quantified in picoseconds. In this example, the varying frequencies inside a pulse would not take place concurrently, but rather follow one another sequentially. This is known as chirping or linear-frequency modulation in the scientific context.

But this approach presents another difficulty: even though chirping technologies have been considerably improved with respect to the infrared range, no research has been conducted on applying the technique in the terahertz range.

We’ve turned to the technologies used in the microwave range,” added Egor Oparin.

They actively employ metal waveguides, which tend to have high dispersion, meaning that different emission frequencies propagate at different speeds there. But in the microwave range, these waveguides are used in single mode, or, to put it differently, the field is distributed in one configuration, in a specific, narrow frequency band, and, as a rule, in one wavelength.

Egor Oparin, Study Co-Author and Staff Member, Laboratory of Femtosecond Optics and Femtotechnologies, ITMO University

Oparin continued, “We took a similar waveguide of a size suitable for the terahertz range and passed a broadband signal through it so that it would propagate in different configurations; because of this, the pulse became longer in duration, changing from two to about seven picoseconds, which is three and a half times more. This became our solution.”

With the help of a waveguide, the scientists were able to boost the length of the pulses to a duration required from a theoretical perspective. This allowed the researchers to achieve interference between a pair of chirped pulses that collectively produce a pulse train.

What’s great about this pulse train is that it exhibits a dependence between a pulse’s structure in time and the spectrum. So we have temporal form, or simply put field oscillations in time, and spectral form, which represents those oscillations in the frequency domain. Let’s say we’ve got three peaks, three substructures in the temporal form, and three corresponding substructures in the spectral form.

Egor Oparin, Study Co-Author and Staff Member, Laboratory of Femtosecond Optics and Femtotechnologies, ITMO University

By using a special filter to remove parts of the spectral form, we can ‘blink’ in the temporal form and the other way around. This could be the basis for data encoding in the terahertz band,” Oparin concluded.

Journal Reference:

Liu, X., et al. (2020) Formation of gigahertz pulse train by chirped terahertz pulses interference. Scientific Reports.


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