5G phones will get MIMO channel data faster, using the simplest signaling path

No agreements reached on several CSI enhancements for 5G Advanced in RAN1#122

The physical layer working group (RAN1) discussed several detailed technical enhancements for 5G Advanced's MIMO capabilities, specifically related to Channel State Information (CSI) reporting for up to 128 antenna ports. These discussions, documented in a moderator summary, did not result in any final agreements. Several proposals from companies were noted but not approved, meaning they will be revisited at future meetings. The key disagreements centered on how to precisely define the behavior of new CSI codebooks and reporting mechanisms for larger antenna arrays.

One major point of contention was a proposal (Proposal 1.B) to define how a 'soft scaling' feature interacts with an existing CSI feature (SD+PD NES). The proposal, led by Google, Fujitsu, Lenovo, and ZTE/Sanechips, was opposed by a large group including Samsung, Ericsson, Apple, Qualcomm, and Nokia. The moderator noted that the interaction between these features has not been explicitly agreed upon and requires more discussion. No reason for the opposition was recorded in the meeting documents.

Similarly, a proposal (Proposal 1.D) on antenna port mapping for a Doppler-based CSI codebook (Type-II) was presented by vivo, Apple, CATT, Xiaomi, and NEC. It faced opposition from another large group including Google, Samsung, Ericsson, and Qualcomm, who argued it would impact network implementation. The moderator deemed the proposal technically sound but noted the significant opposition. No reason for the opposition was recorded in the meeting documents.

A clarifying proposal (Proposal 1.F) regarding a bitmap used in CSI reporting for large arrays received support from Fraunhofer, Samsung, Ericsson, Apple, and others, but was opposed by NTT DOCOMO, Google, ETRI, ZTE/Sanechips, and Huawei/HiSi. The moderator called the proposal technically sound, but the meeting did not adopt it. No reason for the opposition was recorded in the meeting documents.

Another unresolved topic was a rule (Proposal 2.A) for associating interference measurement resources with channel measurement resources in a specific reporting mode. This proposal, supported by Huawei/HiSi, Google, and NTT DOCOMO, was opposed by Samsung, Ericsson, Apple, Qualcomm, and others. The moderator questioned the need for the rule. No reason for the opposition was recorded in the meeting documents.

A proposal (Proposal 1.G) to clarify the text for Sounding Reference Signal (SRS) port grouping was supported by Huawei/HiSi, NTT DOCOMO, vivo, Qualcomm, Samsung, and others, but was opposed by Google, Spreadtrum, and Nokia who saw no ambiguity in the current text. The moderator considered the proposal valid. No reason for the opposition was recorded in the meeting documents.

Conversely, one proposal (Proposal 3.A) for defining an equation for Coordinated Joint Transmission (CJT) calibration reporting received broad support from almost all listed companies, with only Nokia opposing it on the grounds that the standard is already clear. Despite this widespread support, the meeting did not adopt the proposal, and it was marked 'TO BE REVISED' for the next meeting.

Proposal adds equation for CQI calculation with linked delay reports

A coalition including Huawei, ZTE, and Google proposed adding a specific mathematical equation to the 5G standard to describe how a device should calculate Channel Quality Indicator (CQI) when a Coordinated Joint Transmission (CJT) report is linked with a separate delay calibration report. This scenario involves compensating for timing misalignment between different transmission points.

The 'Reason for change' stated is: 'It was agreed that CJTC Dd report can be linked with Rel-18 Type-II CJT... Analogous to Rel-19 Type-II CJT mode-1, this can be reflected in the CQI/PMI calculation equation. However, the current description in TS38.214 already captures the necessary behaviour albeit without equation.' Most companies supported the addition for clarity, though Nokia argued the specs were already clear without it. The moderator revised the proposal based on feedback from several companies.

The meeting did not make a decision on this proposal; it was noted and the text was revised for future discussion.