Hi Jake,
I understand that you want to know the reason behind different ways of selecting PMI for wideband and subband cases in MATLAB's 5g Toolbox.
This is done due to varying channel conditions:
- Wideband PMI Selection: Aims to maximize total throughput across the entire Bandwidth Part (BWP). It sums the SINRs across all Resource Blocks (RBs) for all layers to find the best PMI for the entire BWP.
- Subband PMI Selection: Accounts for channel variability across different subbands within the BWP. It averages the SINR per Resource Element (RE) within each subband to select the most suitable PMI for each specific subband.
The sum is used in the wideband case to optimize overall performance, while the average is used in the subband case for a more detailed adaptation to local channel conditions.I could not find the exact rationale explicitly documented, but it is consistent with the principles of link adaptation and precoding in the context of 5G communications. I think the choice of using sum or average is ultimately a design decision that reflects the different optimization goals for wideband and subband PMI selection.
