It is known that for optimal RIS control, perfect CSI of all the links between BS and MS through the RIS is required. Therefore, channel estimation and corresponding message feedback methods will be needed at the BS/MS.
Few studies suggest a two-stage channel estimation approach for RIS-aided MIMO channels, using iterative re-weighted method for estimating channel parameters sequentially.
Will this be a good way to go about it, or there is/are better methods.
If there is no specific channel structure, then you will have to transmit pilots using N different RIS configurations, in order to excite all dimensions of the channel.
However, if there is some channel structure (e.g., spatial sparsity) one might be able to reduce the pilot signaling.
Thank you for your response Prof. Emil. It will be great if you could recommend few articles from where I can build on.
I summarized the basics of channel estimation on Page 24 and 25 of the following paper:
https://arxiv.org/pdf/2102.00742.pdf
Some more references and details on LMMSE estimation is provided in the following paper: https://arxiv.org/pdf/2109.03663
Emil Björnson What you have mentioned in P24 and P25, the techniques are universal in both near-field and far-field cases? Would channel estimation be different in the near field of the RIS.
Our team recently discovered that
- it is possible to obtain the CSI by low-cost power sensors attached to RIS elements
- the CSI acquisition could be realized in a dimension-independent manner, i.e., the overhead is independent of the number of RIS elements
The mechanism is quite similar to the "double slit interference experiment".
https://arxiv.org/pdf/2204.13505
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