Realization of communication in the 6G/IOWN era: World first method developed by NTT and TDUs

NTT and Tokyo Denki University (TDU) have developed the world's first method (algorithm) for realizing radio propagation simulation that is both ultra-high speed and high accuracy. It has demonstrated its effectiveness on an actual quantum annealing machine. This technology is expected to be extremely useful in realizing wireless communication services that will keep all terminals connected, which is required in the 6G/IOWN (Innovative Optical and Wireless Network) era, including future automated driving. The results were showcased and presented at the 'NTT R&D Forum — IOWN ACCELERATION' from November 14 to 17.

A typical simulation method for estimating wireless communication quality is the ray trace method performed on a Von Neumann-type computer. However, this method required a substantial amount of computation time due to the complexity of calculating radio wave paths and accounting for actions such as reflection and diffraction of radio waves.

In response to this, NTT and TDU have devised the world's first propagation Quadratic Unconstrained Binary. Optimization (QUBO) model that runs on an annealing machine, a computer specialized for determining approximations to optimization problems, and established a technology that can reduce computation time to less than one-millionth of the conventional ray trace method, which was announced in December 2022. The method uses a perfect diffuse reflection model in which radio waves are scattered uniformly in all directions, allowing for ultra-fast estimation of wireless communication areas with spatial extents in cyberspace, where the actual environment is reproduced.

However, in the future 6G/IOWN era, when cyberspace and physical space will be highly integrated, a system will be necessary to realize radio communication quality estimation with a high accuracy of only a few dB while maintaining a high speed on the order of milliseconds (one-thousandth of a second). Therefore, it was necessary to incorporate into this propagation QUBO model the relationship between the angle of incidence and the angle of emission of radio wave scattering in a real environment, such as a wall surface.

The two parties have currently succeeded in incorporating the Fraunhofer approximation into the QUBO model, which can simulate the scattering of radio waves on building walls and other surfaces. This has significantly improved the accuracy of radio quality estimation in cyberspace, where the real environment is reproduced while maintaining high speed. It was also vital to reduce qubit usage to a feasible level, given the limitations of current quantum annealing machines for extensive computations in the QUBO model. By considering the properties of radio waves concerning the building structure, they established a method to suppress the explosion of the number of combinations in the path of radio waves and maintain it within the number of quantum bits provided by the current annealing machine.

Through this, both parties have now devised a novel propagation QUBO model that can be run on an annealing machine and have succeeded in achieving both real-time performance and high accuracy in estimating wireless communication quality for pinpoint locations. They also verified the operation by pseudo-quantum annealing and succeeded in operating the devised propagating QUBO model on a loosely coupled 5640-qubit quantum annealing machine, thereby confirming the effectiveness of the method on actual devices.

This achievement allows for real-time and highly accurate wireless communication quality estimation on current annealing machines. It also lays the groundwork for optimizing wireless resources (frequency, time, and space) for each wireless terminal, aligned with the quantum bit provision of actual products. The two parties will continue to develop technologies to achieve the 99.99999% reliability level targeted for 6G and will incorporate this method into wireless communication networks to demonstrate a wireless system with high-speed, high-capacity, and low-latency connections, aiming to establish the technology by 2030.