Curved Light Beams May Boost 6G and WiFi Wireless Network Speeds

Future wireless broadband and home networks, using technologies such as 6G or WiFi in the higher frequency mmW and sub-TeraHertz (THz) bands (i.e. between around 24GHz and 300GHz), could be set for a significant speed boost after researchers discovered a way to curve light beams around objects.

The 6G standard is currently still in the early R&D phase, and the first commercial builds aren’t due until around 2028/30. But it is roughly aiming for theoretical peak data rates of up to 1Tbps (Terabits per second) – or 1000Gbps if you prefer – and may be able to harness radio spectrum up to the TeraHertz (THz) bands, while also using AI optimisations, new antenna designs and other changes to improve network efficiency.

NOTE: Terahertz (THz) radiation is more widely defined as the region of the electromagnetic spectrum (EM) in the range of 100GHz (3 mm) to 10THz (30 μm) – between the millimetre and infrared frequencies. By comparison, 5G was designed to work between 450MHz and 52GHz, with top theoretical speeds of up to 20Gbps.

At present, most mobile networks tend to work within the lower and mid-frequency mobile bands, such as between 700MHz and 3.8GHz, which enables their signals to travel further (more cost-effective). But this sacrifices some data speed due to limitations on the available spectrum amounts. One way around that is to push mobile and WiFi networks to harness much higher frequency bands, where there’s plenty of extra spectrum frequency.

The problem is that much higher mobile frequencies, like the 24-60GHz range for 5G (Ofcom has yet to auction off any of this in the UK for mobile) or 100GHz+ (THz) for future 6G networks, make for extremely weak signals that don’t travel very far and are very easily disrupted (i.e. weather, buildings, trees and device choice etc. all impact signal quality).

Consequently, mobile operators typically only deploy such solutions within the busiest urban areas (e.g. shopping centres) or for fixed-wireless links (e.g. to served individual homes/businesses), but even this would be a challenge once we get into the extremely challenging THz bands.

A New Approach

One possible solution to the aforementioned problem may now have come from a team of researchers at Brown University and Rice University in the USA, which published a report in Nature that, in simple terms, found a way of “curving” light beams mid-air to help them get around physical obstacles (e.g. buildings) – reducing the need for a line-of-sight connection.

Light in the THz band normally prefers to travel in straight lines, unless warped by the curvature of spacetime (e.g. around the edges of stars or black holes), but the team found a rather more accessible approach to achieve a similar sort of outcome.

Extract from the Research Paper

A key challenge in millimetre-wave and terahertz wireless networks is blockage of the line-of-sight path between a base station and a user. User and environmental mobility can lead to blockage of highly directional beams by intervening people or objects, yielding link disruptions and poor quality of service. Here, we propose a solution to this problem which leverages the fact that, in such scenarios, users are likely to be located within the electromagnetic near field of the base station, which opens the possibility to engineer wave fronts for link maintenance.

We show that curved beams, carrying data at high bit rates, can realize a link by curving around an intervening obstacle. We develop a model to analyse and experimentally evaluate the bandwidth limitations imposed by the use of self-accelerating beams. We also demonstrate that such links employ the full aperture of the transmitter, even those portions which have no direct line of sight to the receiver, emphasizing that ray optics fails to capture the behaviour of these near-field wave fronts.

This approach, which is ideally suited for use at millimetre-wave and terahertz frequencies, opens vast new possibilities for wave front management in directional wireless networks.

In the study, the team introduce the concept of self-accelerating beams. The beams are special configurations of electromagnetic waves that naturally bend or curve to one side as they move through space. The beams have been studied at optical frequencies but are now explored for terahertz communication. So, the actual photons still travel in a straight line, but the THz signal effectively bends around the object.

Fig. 5: Communicating around a semi-infinite obstacle

Naturally, there are some caveats with this, such as the fact that you’re going to suffer a fair bit of performance loss for receivers positioned behind the object. Not to mention that the lab test was conducted over very short distances inside a single room, while 6G signals in the wild would need to go much further. At present, the team still hasn’t fully quantified how much it will be possible to curve a signal and how far away it will work.

Curving a beam doesn’t solve all possible blockage problems, but what it does is solve some of them and it solves them in a way that’s better than what others have tried,” said Hichem Guerboukha, who led the study as a postdoctoral researcher at Brown and is now an assistant professor at the University of Missouri – Kansas City.

The development follows shortly after a separate team of Japanese researchers demonstrated a prototype 6G technology reaching a mobile broadband speed of 100Gbps (Gigabits per second) over a distance of 328 feet or 100 meters (here). The indoor test harnessed spectrum in the 100GHz band, while the outdoor test used the 300GHz band. The distance is impressive, given the bands being harnessed.

A different team of scientists in Japan similarly demonstrated (here) 6G speeds of up to 240Gbps, albeit over a shorter distance of only 66 feet (20 metres) – using 64 quadrature amplitude modulation (64QAM) at a single carrier frequency of 275GHz. We should point out that 6G, much like 4G and 5G before it, will also be able to harness all the existing mobile bands – at lower or mid-band frequencies.

As a side note, Ofcom are due to auction off their first 26GHz and 40GHz bands for mobile network operators in the near future (here), although the exact timeline remains somewhat dependent upon the outcome of Three UK and Vodafone’s proposed mega-merger. This is because that deal, if approved, would change the competitive landscape of UK spectrum ownership and thus needs to be settled before any auction can proceed (estimated for late 2024 or early 2025).

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