Signal Processing Algorithms Improve Free-Space Communication

Researchers have developed a way to transmit data through free space by eliminating the need for fiber optic cables for light.

The use of light as a medium of communication seems to be a faster and more advanced technology. But while we are using light, what about the transmission medium? The present modern technology uses fiber cables as their transmission medium, but what if this light-carrying information could be transmitted as normal light? What development might lead to that?

New signal-processing algorithms have been shown to reduce the effect of noise in free-space optical experiments, potentially bringing the “free space” of the internet one step closer to reality. A team of researchers, from Aston University’s Aston Institute of Photonic Technologies and Glasgow University, used a commercially available photonic lantern, a commercial transponder, and a spatial light modulator to simulate the disturbance. By applying a sequential interference cancellation digital signal processing algorithm, they achieved record results.

Researchers simultaneously transmit multiple data signals using different spatially shaped beams of light using a so-called photonic lantern. Confusion changes the shape of the beams, often losing the signal if only a simple shape is transmitted and detected, but by detecting the light of these shapes with a second lantern, more light is detected. can be collected by the receiver, and the original data can be unscrambled. This greatly reduces the effect of the atmosphere on the quality of the data received, in a technique known as Multiple-input multiple-output (MIMO) digital signal processing.

According to professor Andrew Ellis of Aston University said, “Using a beam, when a beam is transmitted, the turbulence similar to a hot sunny day destroys the signal 50% of the time. Through sending multiple beams of different shapes through the same telescopes and identifying different shapes, not only have we increased the availability to more than 99%, we have increased the capacity to more than 500 Gbit/s, or more than 500 ultra-fast Pure -Fiber broadband links.”

This project aims to provide internet performance with a Pure-Fiber connection without the need to install cables. It uses a free space optical communication system that can link remote sites using a wireless optical line of site signal to link to nearby fiber sources in more affluent suburbs.

Reference: Yiming Li et al, Enhanced Atmospheric Turbulence Resiliency With Sequential Interference Cancellation DSP in Mode Division Multiplexing Free-Space Optical Links, Journal of Lightwave Technology (2022). DOI: 10.1109/JLT.2022.3209092