LG’s much publicized exit from the global smartphone market was swiftly followed by a less prominent reiteration of its commitment to cellular research and particularly 6G.
The Korean technology player has struck a new partnership with US-based test and measurement group Keysight Technologies and the Korea Advanced Institute of Science & Technology (KAIST), to pursue research on future 6G technologies around transmission in the so called terahertz frequencies between millimeter wave and infrared light.
This is one of several recently announced collaborations around 6G at a time when even its predecessor – 5G transmission in the mmWave frequencies between 6 GHz and 300 GHz – itself still lies in the future for the vast majority of countries and operators, as was underlined in the latest RAN Research report on the future of spectrum. But this itself provides one clue why 6G research is already being conducted in earnest.
The underlying point is that while the ascent into mmWave frequencies under 5G represents quite a fundamental shift for mobile communications, the further extension into THz frequencies can be regarded as more of an evolutionary step since it will exploit many of the same technological innovations, such as beamforming and massive MIMO. Furthermore, mmWave communication is being expedited through small cells and repeaters that extend line of sight (LOS) or near line of sight (NLOS) links to overcome signal degradation resulting from multipath fading and other sources of RF attenuation.
Then although rate of attenuation through the air generally increases with frequency the changes are not that sharp. There have been various measurements of propagation loss, including one by Aalto University at a US shopping mall, reporting similar profiles of path loss at 28 GHz and 140 GHz.
Now 28 GHz is one of the earlier bands for mmWave, while 140 GHz is regarded as being in the THz category. That is admittedly confusing since at 140 GHz frequencies the wavelength is just over 2mm, so well above the mmWave threshold. In fact, frequencies in the 100-fold range from 100 GHz to 10 THz are usually defined as being in the THz category and therefore under consideration for 6G, even though strictly they overlap with the mmWave bands.
This wide band was once referred to as the ‘Terahertz Gap’, because it appeared to be virtually useless for human exploitation as a result of the high attenuation through the air, falling between mmWave and infrared, which both have plenty of applications. But now the THz band is already being exploited for near field communications for applications sometimes described as ‘whisper radio’, including wiring harnesses in circuit boards and wireless personal area networks (PANs).
Future recruitment of THz frequencies for cellular communications now looks increasingly likely, despite some significant challenges to overcome. These include blockage, resulting from the great losses to signal reflection and scattering at frequencies above 300 GHz.
Another problem is beam squint resulting from changes in direction of signals caused by variable delays across wavefronts at THz levels that cause beams to arrive out of focus or ‘blurred’. The latter can be overcome by inserting true time delays to correct the aberrations, but these are technical challenges that are the focus of research by various agencies, such as Germany’s Fraunhofer Institute.
Under 6G, terahertz signals would only be transmitted via beamforming, which is already featuring for mmWave. This could then liberate the huge bandwidth available at these higher frequencies for putative future applications generating vast amounts of data, such as holographic projection.
This would exploit the one saving grace of high frequency radio waves from the transmission perspective, the ability to condense antenna arrays to ever greater densities as wavelengths get shorter below 1mm. So to overcome the short transmission distance over the resulting from huge propagation loss, ultra-massive (UM) MIMO systems would have to be developed incorporating sub-millimeter wavelength antennas array to achieve sufficient compensating gain.
Another reason for investing in 6G could be said to be political, in the wake of the schisms opening up as a result of the actions against China and Huawei in particular, as well as other geopolitical factors. There are moves in the US for example to turn Open RAN and cloud-based 5G into a crusade to tilt the balance of mobile standards development and supply chains back towards its own industries away from China in particular, but also from the Far East and Nordics generally where they have become focused, under the banner of America First.
Such sentiments lie behind the Next G Alliance, set up to manage progress to 6G. That does involve Ericsson with the thinking being perhaps that the two big Nordic players can be kept onside, even if the ultimate ambition is to make the USA a major power in 6G.
South Korea and Japan, two big drivers of 5G, are also jostling for position as early leaders in 6G. South Korea has penciled in 2026 as the year to launch its first 6G pilot and 2029 for the first commercial services in the country. Its government has laid out a strategy around pre-emptive development of technologies under the 6G banner and earmarked KRW200bn ( about $180m) between 2021 and 2026 period to develop basic 6G technology.
The government selected five major use cases for the pilot project: digital healthcare immersive content, self-driving cars, smart cities and smart factories.
The Japanese government is similarly boosting public-private cooperation in 6G R&D and is establishing a comparable ¥30bn ($270m) fund for that over the coming few years. Various factors then are conspiring to propel early 6G R&D.