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Content for  TS 38.300  Word version:  16.3.0

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5.4  Carrier aggregation

5.4.1  Carrier aggregation

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. The maximum number of configured CCs for a UE is 16 for DL and 16 for UL.
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5.4.2  Supplementary Uplink

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.

5.5  Transport Channels

The physical layer offers information transfer services to MAC and higher layers. The physical layer transport services are described by how and with what characteristics data are transferred over the radio interface. An adequate term for this is "Transport Channel". This should be clearly separated from the classification of what is transported, which relates to the concept of logical channels at MAC sublayer.
Downlink transport channel types are:
  1. Broadcast Channel (BCH) characterised by:
    • fixed, pre-defined transport format;
    • requirement to be broadcast in the entire coverage area of the cell, either as a single message or by beamforming different BCH instances.
  2. Downlink Shared Channel (DL-SCH) characterised by:
    • support for HARQ;
    • support for dynamic link adaptation by varying the modulation, coding and transmit power;
    • possibility to be broadcast in the entire cell;
    • possibility to use beamforming;
    • support for both dynamic and semi-static resource allocation;
    • support for UE discontinuous reception (DRX) to enable UE power saving.
  3. Paging Channel (PCH) characterised by:
    • support for UE discontinuous reception (DRX) to enable UE power saving (DRX cycle is indicated by the network to the UE);
    • requirement to be broadcast in the entire coverage area of the cell, either as a single message or by beamforming different BCH instances;
    • mapped to physical resources which can be used dynamically also for traffic/other control channels.
Uplink transport channel types are:
  1. Uplink Shared Channel (UL-SCH) characterised by:
    • possibility to use beamforming;
    • support for dynamic link adaptation by varying the transmit power and potentially modulation and coding;
    • support for HARQ;
    • support for both dynamic and semi-static resource allocation.
  2. Random Access Channel(s) (RACH) characterised by:
    • limited control information;
    • collision risk.
Sidelink transport channel types are:
  1. Sidelink broadcast channel (SL-BCH) characterised by:
    • pre-defined transport format.
  2. Sidelink shared channel (SL-SCH) characterised by:
    • support for unicast transmission, groupcast transmission and broadcast transmission;
    • support for both UE autonomous resource selection and scheduled resource allocation by NG-RAN;
    • support for both dynamic and semi-static resource allocation when UE is allocated resources by the NG-RAN;
    • support for HARQ;
    • support for dynamic link adaptation by varying the transmit power, modulation and coding.
Association of transport channels to physical channels is described in TS 38.202.
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5.6  Access to Shared Spectrum |R16|Word‑p. 36

5.6.1  Overview

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 operates in either dynamic or semi-static channel access mode as described in TS 37.213. In both channel access modes, the gNB and 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.
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5.6.2  Channel Access Priority ClassesWord‑p. 37
The Channel Access Priority Classes (CAPC) of radio bearers and MAC CEs are either fixed or configurable:
  • 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.
CAPC
5QI

1
1, 3, 5, 65, 66, 67, 69, 70, 79, 80, 82, 83, 84, 85
2
2, 7, 71
3
4, 6, 8, 9, 72, 73, 74, 76
4
-

When performing Type 1 LBT for the transmission of an uplink TB (see TS 37.213, clause 4.2.1.1) and when the CAPC is not indicated in the DCI, the UE shall select the CAPC as follows:
  • If only MAC CE(s) are included in the TB, the highest priority CAPC of those MAC CE(s) is used; or
  • If CCCH SDU(s) are included in the TB, the highest priority CAPC is used; or
  • If DCCH SDU(s) are included in the TB, the highest priority CAPC of the DCCH(s) is used; or
  • The lowest priority CAPC of the logical channel(s) with MAC SDU multiplexed in the TB is used otherwise.
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5.7  Sidelink |R16|

5.7.1  General

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

5.7.2  Sidelink resource allocation modesWord‑p. 38
Two sidelink resource allocation modes are supported: mode 1 and mode 2. In mode 1, the sidelink resource allocation is provided by the network. In mode 2, UE decides the SL transmission resources in the resource pool(s).

5.7.3  Physical sidelink channels and signals

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 5 symbols for normal and extended cyclic prefix cases respectively, including the associated DM-RS.
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5.7.4  Physical layer procedures for sidelink

5.7.4.1  HARQ feedback

Sidelink HARQ feedback uses PSFCH and can be operated in one of two options. In one option, which can be configured for unicast and groupcast, PSFCH transmits either ACK or NACK using a resource dedicated to a single PSFCH transmitting UE. In another option, which can be configured for groupcast, PSFCH transmits NACK, or no PSFCH signal is transmitted, on a resource that can be shared by multiple PSFCH transmitting UEs.
In sidelink resource allocation mode 1, a UE which received PSFCH can report sidelink HARQ feedback to gNB via PUCCH or PUSCH.
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5.7.4.2  Power Control

For in-coverage operation, the power spectral density of the sidelink transmissions can be adjusted based on the pathloss from the gNB.
For unicast, the power spectral density of some sidelink transmissions can be adjusted based on the pathloss between the two communicating UEs.

5.7.4.3  CSI report

For unicast, channel state information reference signal (CSI-RS) is supported for CSI measurement and reporting in sidelink. A CSI report is carried in a sidelink MAC CE.

5.7.5  Physical layer measurement definition

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).

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