5G phones will get channel feedback within milliseconds of connecting

Huawei and Samsung wanted 5G Advanced phones to transmit with deliberately noisier signals — up to 6% Error Vector Magnitude instead of today's tighter limits — in exchange for higher uplink power and better cell-edge coverage, with base stations cleaning up the distortion using Digital Pre-Distortion receivers. Nokia, Ericsson, Qualcomm, ZTE and Vodafone blocked it for this release, pointing to simulated gains swinging wildly from -0.8 dB to 4.2 dB and unresolved questions about testing multiple phone models at once. The feature now moves into 6G study instead, delaying any commercial deployment by years unless a compatible design later gets back-ported to 5G.

The bigger, quieter change is how fast a phone gets useful channel feedback after it first connects. Instead of waiting for a full RRC setup, the network will now broadcast measurement configurations in system information, let the phone declare which ones it supports in message 3 of random access, and trigger the actual sounding and CSI reporting through a MAC control element in message 4. Companies agreed the report's computation clock starts at a slot boundary exactly 3 milliseconds after the phone acknowledges that message, giving chipset makers one predictable number to design around instead of a moving target.

A parallel fight was about where the timing command lives. Ofinno, Huawei, ZTE, Xiaomi, vivo, Qualcomm and seven others won a dedicated MAC-CE field for the slot offset, with the phone ignoring the standard K2 timing in the uplink grant; the new field does the same job as K2. CATT, MediaTek, Samsung, LG, Panasonic and Sharp argued for deriving the offset from existing delay values or a configured list instead. The network gets more direct control over exactly when the first channel report lands — useful for scheduling, at the cost of one more timing path for implementers to test.

For networks running massive MIMO with 48 to 128 antenna ports, 3GPP agreed to let CSI reference signals be spread thinly across frequency — as sparse as one-eighth of resource elements per port — with RRC signaling telling the phone exactly which resource blocks carry them. New CSI subband sizes (6, 12, or 24 PRBs depending on channel bandwidth) were tailored to these low-density signals. This cuts reference-signal overhead on large arrays, freeing resource elements for actual user data, though the underlying resource-block group sizing was left untouched.

Two fights stayed open. Retransmission handling for MSG4-triggered measurements got no rule at all — a 15-company bloc including Samsung, Qualcomm, Nokia and vivo blocked new mechanisms proposed by Huawei, ZTE, NTT DOCOMO and Sony, so phones will simply re-measure on any retransmission, redundant or not. And Samsung's proposal to trigger channel feedback with a single shared state across all newly activated secondary cells still faces resistance from Nokia, Ofinno and NTT DOCOMO, who want per-cell flexibility — a question that determines how much signaling overhead SCell activation carries once it reaches specification.