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While reading 3gpp 38.211, Chapter 6.3.1.5 I noticed

For non-codebook-based transmission, the precoding matrix equals the identity matrix.

So, I guess, non-codebook-based precoding shall be implemented somewhere else but I couldn’t find where. No page in the 3gpp spec has information about this. Where could I find implementation details?

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  • $\begingroup$ ok, it means bypass mode. Where precoding by a non-codebook matrix shall take place? $\endgroup$
    – Dmitriy
    Commented Nov 22, 2021 at 16:47
  • $\begingroup$ The values of such matric are arbitrary numeric values. There is no sense using identity matrix. Sorry, I don't understand your point. $\endgroup$
    – Dmitriy
    Commented Nov 22, 2021 at 16:51
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    $\begingroup$ The idea behind non-codebook precoding is that precoding matrix is not selected from a set (codebook) but is evaluated using DL/UL channel reciprocity. The 3GPP implicitly defines the place where codebook precoding takes place, but says nothing about non-codebook. $\endgroup$
    – Dmitriy
    Commented Nov 22, 2021 at 16:58
  • $\begingroup$ Read 38.214 6.1.1.2 and see youtu.be/lI0TSXb9sq0?t=602 $\endgroup$
    – AlexTP
    Commented Nov 22, 2021 at 17:24
  • $\begingroup$ I still don't get the idea where the multiplication by non-codebook matrix takes place. What I got is that SRS should be affected by it, so it happens after SRS multiplexing. $\endgroup$
    – Dmitriy
    Commented Nov 23, 2021 at 14:16

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See the book entitled "5G NR The next generation of wireless access technology" by Erik Dahlman. On page 165, Chapter 9, says "There is also a possibility for the network to operate with non-codebook-based precoding. In this case W is equal to the identity matrix and precoding is handled solely by the spatial filter F based on recommendations from the device."

"Note that the spatial filter F selected by the device also can be seen as a precoding operation, although not explicitly controlled by the network. The network can however restrict the freedom in the choice of F through the SRS resource indicator (SRI) provided as part of the DCI."

For more details on spatial filters read Chapter 8 of the book.

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