3 GPP TSG RAN WG 1 NR3 Nagoya

Background (1/3) – Agreement from RAN 1#90 • In RAN#90 it has been agreed

Background (2/3) • In RAN 1 adhoc#2, several options about the relationship between TB

Background (3/3) • Observations: • CBGs are an important tool to ensure the e.

Proposals for discussion • When CBG-based retransmission is configured, the UE can be configured

Slides: 5

3 GPP TSG RAN WG 1 NR#3 Nagoya, Japan, 6. 3. 3. 3 R 1 -171 xxxx Discussion on TB-ack/CBG-Nack for initial transmissions ZTE, Sanechips, [Media. Tek, AT&T, Sequans, Interdigital, KT, Wilus, HTC], …

Background (1/3) – Agreement from RAN 1#90 • In RAN#90 it has been agreed for a CBG based retransmisison, that CBG ack is reported when the same CBG has been decoded correctly • It remained FFS how to handle the case when TB CRC check is not passed while all CBG´CRC check have passed • It also remained unspecified how to handle the feedback for the initial transmission when CBGs are configured Agreements: • For single CW case with CBG based retransmission for the semi-static codebook with HARQ-ACK multiplexing, at least following is supported for the HARQ-ACK composition and mapping per TB • HARQ-ACK codebook includes HARQ-ACK corresponding to all the CBGs (including the nonscheduled CBG(s)) • At least followings are supported • HARQ-ACK payload size is the same with the configured number of CBGs • Each HARQ-ACK bit corresponds to each CBG • FFS payload size reduction • ACK is reported for a CBG if the same CBG has been successfully decoded • FFS how to handle the case if TB CRC check is not passed while CB CRC check is passed for all the CBs

Background (2/3) • In RAN 1 adhoc#2, several options about the relationship between TB -ack/nack and CBG ack/nack were up for email agreement until July 13 th • From Chairman notes RAN 1_NRAH 2_final, for email agreement • When CBG-based retransmission is configured, TB-level HARQ-A/N is supported and at least following options can be considered for downselection in RAN 1#90. • Option 1. Add 1 bit upon CBG-level HARQ-ACK bits • Option 2. Use all NACK of CBG-level HARQ-ACK bits • Option 3. Use different PUCCH format or PUCCH resource • No progress was made on the above topic, it needs to be discussed again

Background (3/3) • Observations: • CBGs are an important tool to ensure the e. MBB performance • RAN 1 should ensure that CBG transmission can be used effiently • We need to specify the UE behavior when TB CRC has failed but all CB CRC checks have been correct • For assumed BLER with 10% it would be inefficient to report CBG-acks évery thime the initial transmission has succesful • A TB-ack is sufficient in these cases. • TB-level A/N can use 1 -2 bits payload with low power, leading to UE power savings and uplink interference reduction

Proposals for discussion • When CBG-based retransmission is configured, the UE can be configured to support TB-level HARQ-A/N • When both TB and CBG level HARQ A/N are configured 1. In case TB CRC check failed but all CB CRC checks passed, the UE uses TB-level A/N for feedback (solves FFS from previous agreement) 2. In case TB CRC check passed but some CB CRC failed, the UE uses CBG-level HARQ A/N 3. In case TB CRC check failed and one/some CB CRC checks passed, the UE uses CBGlevel A/N for feedback 4. In case of TB CRC check passed and all CB CRC checks passed, the UE uses TB-HARQ A/N • Decide upon how to resolve the TB and CBG-level HARQ A/N format and resource allocation. • E. g. down-select between options 1 -3 from slid “Background 2/3”