NR Type II CSI Report High Rank Downlink Transmission
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Solution Overview
Problem
The 3GPP Release 15 type II codebook is limited to up to 2-layer transmissions, which is insufficient for the 4-layer SU-MIMO transmissions commonly required in NR FDD systems, and configuring an additional type I CSI report is not always feasible due to compatibility issues with commercial UEs.
Innovation Solution
Methods to construct rank 3 and rank 4 precoders based on a rank 2 precoder of a type II CSI report, estimate downlink PDSCH post-equalization SNR, and select downlink transmission rank, enabling high rank transmissions without needing an additional type I CSI report.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If 3GPP Release 15 type II codebook is used for SU-MIMO transmissions, then MU-MIMO performance is improved, but transmission rank is limited to 2 layers
Solution Approach 1:
The type II CSI report is designed to serve multiple functions: it provides accurate channel state information for MU-MIMO transmissions while also enabling SU-MIMO transmissions up to rank 4. The precoder structure with 2 base beams and 2 polarization ports is configured to support both MU-MIMO null forming and high-rank SU-MIMO transmissions through appropriate weight selection and combination.
Solution Approach 2:
The invention changes the interpretation and usage parameters of the type II CSI report. Instead of limiting it to rank 2 only, the system uses the reported precoders to construct higher-rank precoders for SU-MIMO by selecting and combining multiple precoder columns, effectively changing the rank parameter from 2 to up to 4 while maintaining compatibility with the existing type II report structure.
2Adaptability or versatility
If type I CSI report is configured for high rank SU-MIMO transmissions, then transmission rank support is improved, but device compatibility deteriorates
Solution Approach 1:
The type II CSI report structure is utilized for dual purposes: maintaining its original function for MU-MIMO channel state feedback while simultaneously enabling high-rank SU-MIMO transmissions. This eliminates the need for separate type I CSI report configuration, ensuring compatibility with commercial UEs that may not support type I reports while still achieving rank 4 SU-MIMO performance.
3Device complexity
If type II CSI report is used for both MU-MIMO and SU-MIMO, then system complexity is reduced, but transmission performance may deteriorate
Solution Approach 1:
The precoder construction uses local optimization by selecting specific columns from the type II reported precoder matrix that are most suitable for the current transmission scenario. For SU-MIMO, the system locally adapts the precoder by choosing the best 3 or 4 columns out of the available 2 base beams with 2 polarizations, optimizing performance for the specific rank and channel conditions while maintaining the unified type II report structure.
Data Source
AI summary
Systems and methods for enabling high rank transmissions for downlink Physical Downlink Shared Channel (PDSCH) transmissions based on a Channel State Information (CSI) report are provided. In some embodiments, a method performed by a Radio Access Network (RAN) node in a RAN of a cellular communications system comprises receiving a CSI report from a wireless communication device. The CSI report comprises a rank indicator that indicates a rank value of 2. The method further comprises selecting, based on the CSI report, a rank γ(>2) for downlink transmission to the wireless communication device, generating a rank γ precoder based on the CSI report, precoding a downlink signal to be transmitted to the wireless communication device based on the rank γ precoder to provide a precoded downlink signal, and transmitting the precoded downlink signal to the wireless communication device.