Ted Rappaport's paper, Millimeter wave mobile communications for 5G cellular: It will work! inspired 5G. The new Wireless Communications and Applications Above 100 GHz: Opportunities and Challenges for 6G and Beyond points the way forward in wireless above 100 GHz. Ted and colleagues believe, "The mobile industry will be able to work well up to 800 GHz in the future using the small-cell architectures envisioned for 5G."
The reach of millimetre wave 5G is a major issue, due to signal loss. The paper discusses several ways to compensate for the increased loss in even higher frequencies. The key is that the antenna size goes down as frequencies go up. At 28 GHz, a 256 antenna module is the size of a chip. The beam will be pencil sized and hard to detect.
"THz will enable new sensing applications such as miniaturized radars for gesture detection and touchless smartphones, spectrometers for explosive detection and gas sensing , THz security body scanning, air quality detection , personal health monitoring systems , precision time/frequency transfer, and wireless synchronization , , ."
Ted emails, "There might be tens of thousands of antenna elements at the THz frequency range. Hybrid beamforming most likely will be needed since the physical spacing between elements will be smaller than the physical size of RF transistors, but our paper has some exciting and potentially fruitful ideas about how to implement arrays with that magnitude of antenna elements for phased arrays of the future."
This is not easy work. For example, "This paper also presents approaches and results that reduce the computational complexity and simplify the signal processing used in adaptive antenna arrays, by exploiting the Special Theory of Relativity to create a 'cone of silence' in over-sampled antenna arrays that improves performance for digital phased array antennas." Faraday would be amazed.
Much of the content is reviewing the work the authors are doing to understand the beam properties. What kind of walls can the beams go through? What's the effect of rain and fog? What are the right approaches to channel models? An enormous amount of research is being done at high frequencies. The paper has 178 footnotes. A great deal is still unknown.
It will often be possible to see around corners.
Wireless Communications and Applications Above 100 GHz: Opportunities and Challenges for 6G and Beyond
Frequencies from 100 GHz to 3 THz are promising bands for the next generation of wireless communication systems because of the wide swaths of unused and unexplored spectrum. These frequencies also offer the potential for revolutionary applications that will be made possible by new thinking, and advances in devices, circuits, software, signal processing, applications, and systems. This paper describes many of the technical challenges and opportunities for wireless communication and sensing applications above 100 GHz, and presents a number of promising discoveries, novel approaches, and recent results that will aid in the development and implementation of the sixth generation (6G) of wireless networks, and beyond. This work shows recent regulatory and standard body rulings that are anticipating wireless products and services above 100 GHz, and illustrates the viability of wireless cognition, hyper-accurate position location, sensing and imaging. This paper also presents approaches and results that reduce the computational complexity and simplify the signal processing used in adaptive antenna arrays, by exploiting the Special Theory of Relativity to create a “cone of silence” in over-sampled antenna arrays that improves performance for digital phased array antennas. Also, new results that give insights into power efficient beam steering algorithms, and new propagation and partition loss models above 100 GHz are given, and promising imaging, array processing, and position location results are presented. The implementation of spatial consistency at THz frequencies, an important component of channel modeling that considers minute changes and correlations over space, is also discussed. This paper offers the first indepth look at the vast applications of THz wireless products and applications, and provides approaches for how to reduce power and increase performance across several problem domains, giving early evidence that THz techniques are compelling and available for future wireless communications.