Researchers are implementing RIS technology in a wireless communications system to analyze the effects of channel aging in next-generation wireless communications.

In wireless communications, channels can not only change, but also become obsolete. For modern systems, the links between transmitter and receiver, user movement and power dissipation can break down over time. According to international collaboration of researchers studying preconfigurable smart surface (RIS) systems, understanding how channels are aging in future systems and how to mitigate such problems is crucial to developing the next generation of wireless communications.

RIS technology is highly anticipated for its potentially transformative role in future wireless communication systems. RIS-assisted systems include individually programmable and controlled circuits that can dynamically reflect signals and have the potential to achieve 6G wireless communications, according to the first author, Yang Zhang, at the School of Electronics and Information Engineering. Jiaotong University of Beijing.

RIS-assisted communication systems

“The study of the performance of RIS-assisted communication systems in the aging of the channel can examine whether the implementation of RIS in a wireless communication system can reduce the adverse effects of channel aging on system performance and how much performance gains can bring. Zhang explained. “This is useful to provide a theoretical basis for the design to optimize the RIS-assisted communication systems system.”

All three components of the communication system can move: RIS can be a satellite, the base station can move while the Earth rotates, and users are unpredictably mobile. Add modifications to the communication environment, such as physical barriers or weather disturbances, and communication channels will constantly change over time.

“These factors lead to the so-called channel aging phenomenon, in which channels vary over time with correlated channel variables in the transmission,” Zhang added. “The aging of the channel leads to a mismatch between the current and the forecast channels, which worsens the performance of the system. However, as far as we know, there are no studies on the impact of channel aging on RIS-assisted communication systems. As RIS will help develop wireless communication, it is important to analyze how RIS can improve channel quality with user mobility.

Next generation wireless communications

The researchers studied how the implementation of RIS technology in a wireless communication system affects the adverse effects of channel aging on system performance. They modeled a system in which a base station simultaneously sends signals to RIS and directly to individual mobile phone users. RIS reflects the signal to the same users, duplicating and amplifying the signal. In this model, RIS and the base station remain stationary while users move in the same direction at the same speed.

The system mathematically evaluates the best channel to send a signal based on location, traffic and potential barriers. The channel varies from the time it is evaluated to the time it is used to send or detect the signal – this is the phenomenon of aging.

A multi-user MISO communication system is considered, in which a BS equipped with Nt antennas serves K (K

Chanel’s aging

“Due to the additional end-to-end signal propagation path established by RIS, we found that RIS can reduce the adverse effects of channel aging on the communication system, as well as improve overall system performance compared to non-RIS systems. RIS, “Zhang explained. “In addition, the performance of the system has improved as the total transmission power and the number of antennas in the base station, the number of RIS reflectors and the time correlation coefficient have increased.

However, while RIS can increase transmission capacity by adding reflective elements, it does not have infinite capacity, as it will eventually become saturated.

“This analysis is useful in providing a theoretical basis for designing system optimization of RIS-assisted communication systems,” Zhang said. “The study can be further summarized along with several promising future directions. For example, we can apply this approach to the study of spatially correlated attenuations and more efficient channel estimation methods.

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Improving the ageing of next-generation wireless communications

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