Content for  TS 38.300  Word version:  18.4.0

In Carrier Aggregation (CA), two or more Component Carriers (CCs) are aggregated. A UE may simultaneously receive or transmit on one or multiple CCs depending on its capabilities:

• A UE with single timing advance capability for CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells sharing the same timing advance (multiple serving cells grouped in one TAG);
• A UE with multiple timing advance capability for CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells with different timing advances (multiple serving cells grouped in multiple TAGs). NG-RAN ensures that each TAG contains at least one serving cell;
• A non-CA capable UE can receive on a single CC and transmit on a single CC corresponding to one serving cell only (one serving cell in one TAG).

CA is supported for both contiguous and non-contiguous CCs. When CA is deployed frame timing and SFN are aligned across cells that can be aggregated, or an offset in multiples of slots between the PCell/PSCell and an SCell is configured to the UE.

In conjunction with a UL/DL carrier pair (FDD band) or a bidirectional carrier (TDD band), a UE may be configured with additional, Supplementary Uplink (SUL). SUL differs from the aggregated uplink in that the UE may be scheduled to transmit either on the supplementary uplink or on the uplink of the carrier being supplemented, but not on both at the same time.

In uplink CA or SUL, a UE configured with uplink Tx switching can have Tx chain(s) dynamically switched from one uplink band or two uplink bands to another uplink band or two uplink bands for enabling up to 2Tx UL transmission in one uplink band or simultaneous UL transmissions in two uplink bands at a time.

NR Radio Access operating with shared spectrum channel access can operate in different modes where either PCell, PSCell, or SCells can be in shared spectrum and an SCell may or may not be configured with uplink. The applicable deployment scenarios are described in Annex B.3. The gNB performs channel access mode procedures as described in TS 37.213. The gNB and the UE may apply Listen-Before-Talk (LBT) before performing a transmission on a cell configured with shared spectrum channel access. When LBT is applied, the transmitter listens to/senses the channel to determine whether the channel is free or busy and performs transmission only if the channel is sensed free. When the UE detects consistent uplink LBT failures, it takes actions as specified in TS 38.321. The detection is per Bandwidth Part (BWP) and based on all uplink transmissions within this BWP. When consistent uplink LBT failures are detected on SCell(s), the UE reports this to the corresponding gNB (MN for MCG, SN for SCG) via MAC CE on a different serving cell than the SCell(s) where the failures were detected. If no resources are available to transmit the MAC CE, a Scheduling Request (SR) can be transmitted by the UE. When consistent uplink LBT failures are detected on SpCell, the UE switches to another UL BWP with configured RACH resources on that cell, initiates RACH, and reports the failure via MAC CE. When multiple UL BWPs are available for switching, it is up to the UE implementation which one to select. For PSCell, if consistent uplink LBT failures are detected on all the UL BWPs with configured RACH resources, the UE declares SCG RLF and reports the failure to the MN via SCGFailureInformation. For PCell, if the uplink LBT failures are detected on all the UL BWP(s) with configured RACH resources, the UE declares RLF.

The Channel Access Priority Classes (CAPC) of radio bearers and MAC CEs are either fixed or configurable for operation in FR1:

• Fixed to the lowest priority for the padding BSR and recommended bit rate MAC CEs;
• Fixed to the highest priority for SRB0, SRB1, SRB3 and other MAC CEs;
• Configured by the gNB for SRB2 and DRB.

When choosing the CAPC of a DRB, the gNB takes into account the 5QIs of all the QoS flows multiplexed in that DRB while considering fairness between different traffic types and transmissions. Table 5.6.2-1 below shows which CAPC should be used for which standardized 5QIs i.e. which CAPC to use for a given QoS flow.

Sidelink supports UE-to-UE direct communication using the sidelink resource allocation modes, physical-layer signals/channels, and physical layer procedures below.

Two sidelink resource allocation modes are supported for sidelink communication: mode 1 and mode 2. Two sidelink resource allocation schemes are supported for SL-PRS transmission: scheme 1 and scheme 2. In mode 1/scheme 1, the sidelink resource allocation is provided by the network. In mode 2/scheme 2, UE decides the SL transmission resources in the resource pool(s).

Physical Sidelink Control Channel (PSCCH) indicates resource and other transmission parameters used by a UE for PSSCH. PSCCH transmission is associated with a DM-RS. Physical Sidelink Shared Channel (PSSCH) transmits the TBs of data themselves, and control information for HARQ procedures and CSI feedback triggers, etc. At least 6 OFDM symbols within a slot are used for PSSCH transmission. PSSCH transmission is associated with a DM-RS and may be associated with a PT-RS. Physical Sidelink Feedback Channel (PSFCH) carries HARQ feedback over the sidelink from a UE which is an intended recipient of a PSSCH transmission to the UE which performed the transmission. PSFCH sequence is transmitted in one PRB repeated over two OFDM symbols near the end of the sidelink resource in a slot. The Sidelink synchronization signal consists of sidelink primary and sidelink secondary synchronization signals (S-PSS, S-SSS), each occupying 2 symbols and 127 subcarriers. Physical Sidelink Broadcast Channel (PSBCH) occupies 9 and 7 symbols for normal and extended CP cases respectively, including the associated DM-RS.

For measurement on the sidelink, the following UE measurement quantities are supported:

• PSBCH reference signal received power (PSBCH RSRP);
• PSSCH reference signal received power (PSSCH-RSRP);
• PSCCH reference signal received power (PSCCH-RSRP);
• Sidelink received signal strength indicator (SL RSSI);
• Sidelink channel occupancy ratio (SL CR);
• Sidelink channel busy ratio (SL CBR).

The Sidelink Positioning Reference Signal (SL-PRS) is defined to facilitate Ranging/Sidelink positioning methods, such as SL-TOA, SL-TDOA, SL-RTT, SL-AoA, through the following set of measurements SL-PRS RSRP, RSRPP, RTOA, RSTD, Rx-Tx timing difference and AoA as described in TS 38.305.