On Channel Reciprocity in Reconfigurable Intelligent Surface Assisted Wireless Network
Abstract
Channel reciprocity greatly facilitates downlink precoding in time-division duplexing (TDD) multiple-input multiple-output (MIMO) communications without the need for channel state information (CSI) feedback. Recently, reconfigurable intelligent surfaces (RISs) emerge as a promising technology to enhance the performance of future wireless networks. However, since the artificial electromagnetic characteristics of RISs do not strictly follow the normal laws of nature, it brings up a question: does the channel reciprocity hold in RIS-assisted TDD wireless networks? After briefly reviewing the reciprocity theorem, in this article, we show that there still exists channel reciprocity for RIS-assisted wireless networks satisfying certain conditions. We also experimentally demonstrate the reciprocity at the sub-6 GHz and the millimeter-wave frequency bands by using two fabricated RISs. Furthermore, we introduce several RIS-assisted approaches to realizing nonreciprocal channels. Finally, potential opportunities brought by reciprocal/nonreciprocal RISs and future research directions are outlined.
Cite
@article{arxiv.2103.03753,
title = {On Channel Reciprocity in Reconfigurable Intelligent Surface Assisted Wireless Network},
author = {Wankai Tang and Xiangyu Chen and Ming Zheng Chen and Jun Yan Dai and Yu Han and Shi Jin and Qiang Cheng and Geoffrey Ye Li and Tie Jun Cui},
journal= {arXiv preprint arXiv:2103.03753},
year = {2022}
}
Comments
In general, when the control signals applied to the unit cells remain unchanged, commonly designed and fabricated RISs inherently obey the reciprocity theorem. Nevertheless, there are several RIS-assisted approaches to realizing nonreciprocal channels. Potential opportunities brought by reciprocal/nonreciprocal RISs and future research directions are outlined