NTN

RRC Parameters (NR)

RRC parameters for 5G NTN describe the detailed configuration framework that enables smooth operation of NR systems over satellites and high-altitude platforms. Each parameter is designed to handle the unique physical conditions of NTN, such as long signal travel time, Doppler frequency variation, and continuously changing satellite positions. These settings are defined in 3GPP specifications to provide a common structure for implementation across devices and networks.

The parameters include essential NTN-specific configurations such as reference location data, timing adjustment values, and satellite ephemeris information. These allow the UE to accurately calculate delay, compensate frequency offset, and align with the moving satellite. Configuration procedures also cover neighbor cell relations, synchronization validity, and polarization handling, ensuring the UE can maintain stable connectivity even as the satellite orbits or handover events occur.

Additional elements define the scheduling and feedback behavior of both uplink and downlink links. HARQ timing, PDCCH monitoring, and slot allocation mechanisms are optimized for long round-trip times to preserve efficiency. The framework also includes enhancements for random access, beam management, and measurement reporting to cope with dynamic link conditions.

Together, these RRC configurations enable the UE to operate seamlessly across terrestrial and non-terrestrial layers, maintaining service continuity and efficient resource use. They form the functional bridge that allows 5G to extend beyond Earth-based infrastructure into global satellite coverage.

Highlights

NTN Configuration: Provides the foundational parameters for configuring non-terrestrial networks (NTN). It includes synchronization validity to ensure time alignment between satellite and terrestrial systems, polarization settings (RHCP, LHCP, linear) for signal integrity, and ephemeris data to track satellite positions.
- ntn-Config-r17
Neighbor Cell Configurations: Specifies the setup for neighboring NTN cells, including parameters such as carrier frequencies and physical cell IDs, to ensure seamless handover and connectivity between cells in the NTN network.
- ntn-NeighCellConfigList-r17
Timing Adjustments: Introduces K_mac as a scheduling offset for aligning downlink and uplink frame timings. The TAInfo-r17 provides details for timing advance, accounting for the large distances inherent in NTN communication.
- TAInfo-r17
- n-TimingAdvanceOffset
Ephemeris Information: Supports tracking of satellite positions and movements, including orbital parameters and position-velocity data. This enables dynamic adjustment of communication paths and ensures reliable network operation.
- EphemerisInfo-r17
Distance Thresholds: Defines the maximum allowable distance for effective communication within NTN. This ensures the network can manage link budgets and latency effectively over vast distances.
- distanceThresh-r17
HARQ Feedback: Implements configurable downlink HARQ feedback mechanisms. This includes specific parameters to control and disable HARQ processes, supporting efficient error correction and retransmission handling.
- downlinkHARQ-FeedbackDisabled-r17
- nrofHARQ-ProcessesForPDSCH
- nrofHARQ-ProcessesForPDSCH-v1700
- DL-DataToUL-ACK-r17
- DL-DataToUL-ACK-v1700
- DL-DataToUL-ACK-DCI-1-2-r17
Adaptability for Diverse Scenarios: Ensures robust connectivity across various network domains. Includes parameters for NTN configuration, polarization, and ephemeris information to support diverse NTN deployment scenarios.
- ntn-Config-r17
- ntn-PolarizationDL-r17
- ntn-PolarizationUL-r17
- ephemerisInfo-r17
Advanced Resource Utilization: Facilitates efficient use of network resources through features like code block group transmission, ensuring optimal handling of transport blocks and resource allocation.
- PDSCH-CodeBlockGroupTransmission
- PDSCH-CodeBlockGroupTransmissionList-r16
- codeBlockGroupFlushIndicator

RRC Parameters

SIB19-r17 ::= SEQUENCE {

ntn-Config-r17 NTN-Config-r17 OPTIONAL, -- Need R

t-Service-r17 INTEGER (0..549755813887) OPTIONAL, -- Need R

referenceLocation-r17 ReferenceLocation-r17 OPTIONAL, -- Need R

distanceThresh-r17 INTEGER(0..65525) OPTIONAL, -- Need R

ntn-NeighCellConfigList-r17 NTN-NeighCellConfigList-r17 OPTIONAL, -- Need R

lateNonCriticalExtension OCTET STRING OPTIONAL,

...

}

NTN-NeighCellConfigList-r17 ::= SEQUENCE (SIZE(1..maxCellNTN-r17)) OF NTN-NeighCellConfig-r17

NTN-NeighCellConfig-r17 ::= SEQUENCE {

ntn-Config-r17 NTN-Config-r17 OPTIONAL, -- Need R

carrierFreq-r17 ARFCN-ValueNR OPTIONAL, -- Need R

physCellId-r17 PhysCellId OPTIONAL -- Need R

}

DownlinkConfigCommon ::= SEQUENCE {

frequencyInfoDL FrequencyInfoDL OPTIONAL, -- Cond InterFreqHOAndServCellAdd

initialDownlinkBWP BWP-DownlinkCommon OPTIONAL, -- Cond ServCellAdd

...,

[[

ntn-Config-r17 NTN-Config-r17 OPTIONAL, -- Need R

initialDownlinkBWP-RedCap-r17 BWP-DownlinkCommon OPTIONAL -- Need R

]]

}

NTN-Config-r17 ::= SEQUENCE {

epochTime-r17 EpochTime-r17 OPTIONAL, -- Need R

ntn-UlSyncValidityDuration-r17 ENUMERATED{ s5, s10, s15, s20, s25, s30, s35,

s40, s45, s50, s55, s60, s120, s180, s240} OPTIONAL, -- Need R

cellSpecificKoffset-r17 INTEGER(0..1023) OPTIONAL, -- Need R

kmac-r17 INTEGER(0..512) OPTIONAL, -- Need R

ta-Info-r17 TAInfo-r17 OPTIONAL, -- Need R

ntn-PolarizationDL-r17 ENUMERATED {rhcp,lhcp,linear} OPTIONAL, -- Need R

ntn-PolarizationUL-r17 ENUMERATED {rhcp,lhcp,linear} OPTIONAL, -- Need R

ephemerisInfo-r17 EphemerisInfo-r17 OPTIONAL, -- Need R

...

}

kmac :K_mac is a scheduling offset provided by network if downlink and uplink frame timing are not aligned at gNB. It is needed for UE action and assumption on downlink configuration indicated by a MAC-CE command in PDSCH [see TS 38.2xy]. If the field is absent UE assumes value 0. For the reference subcarrier spacing value for the unit of K_mac in FR1, a value of 15 kHz is used. The unit of K_mac is number of slots for a given subcarrier spacing.

EpochTime-r17 ::= SEQUENCE {

sfn-r17 INTEGER(0..1023),

subFrameNR-r17 INTEGER(0..9)

}

TAInfo-r17 ::= SEQUENCE {

ta-Common-r17 INTEGER(0..66485757),

ta-CommonDrift-r17 INTEGER(-261935..261935) OPTIONAL, -- Need R

ta-CommonDriftVariant-r17 INTEGER(0..29470) OPTIONAL -- Need R

}

EphemerisInfo-r17 ::= CHOICE {

positionVelocity-r17 PositionVelocity-r17,

orbital-r17 Orbital-r17

}

PositionVelocity-r17 ::= SEQUENCE {

positionX-r17 PositionStateVector-r17,

positionY-r17 PositionStateVector-r17,

positionZ-r17 PositionStateVector-r17,

velocityVX-r17 VelocityStateVector-r17,

velocityVY-r17 VelocityStateVector-r17,

velocityVZ-r17 VelocityStateVector-r17

}

Orbital-r17 ::= SEQUENCE {

semiMajorAxis-r17 INTEGER (0..8589934591),

eccentricityE-r17 INTEGER (0..524287),

periapsis-r17 INTEGER (0..16777215),

longitude-r17 INTEGER (0..2097151),

inclinationI-r17 INTEGER (-524288..524287),

meanAnomalyM-r17 INTEGER (0..16777215)

}

PositionStateVector-r17 ::= INTEGER (-3355432..33554431)

VelocityStateVector-r17 ::= INTEGER (-131072..131071)

PUCCH-Config ::= SEQUENCE {

...

secondTPCFieldDCI-1-1-r17 ENUMERATED {enabled} OPTIONAL, -- Need R

secondTPCFieldDCI-1-2-r17 ENUMERATED {enabled} OPTIONAL, -- Need R

dl-DataToUL-ACK-r17 SetupRelease { DL-DataToUL-ACK-r17 } OPTIONAL, -- Need M

dl-DataToUL-ACK-DCI-1-2-r17 SetupRelease { DL-DataToUL-ACK-DCI-1-2-r17} OPTIONAL,--Need M

ul-AccessConfigListDCI-1-1-r17 SetupRelease { UL-AccessConfigListDCI-1-1-r17 } OPTIONAL,

--Need M

...

schedulingRequestResourceToAddModListExt-v1700 SEQUENCE (SIZE (1..maxNrofSR-Resources))

OF SchedulingRequestResourceConfigExt-v1700

OPTIONAL, -- Need N

dmrs-BundlingPUCCH-Config-r17 SetupRelease { DMRS-BundlingPUCCH-Config-r17 }

OPTIONAL, -- Need M

dl-DataToUL-ACK-v1700 SetupRelease { DL-DataToUL-ACK-v1700 } OPTIONAL, -- Need M

dl-DataToUL-ACK-MulticastDCI-Format4-1-r17 SetupRelease

{ DL-DataToUL-ACK-MulticastDCI-Format4-1-r17 }

}

DL-DataToUL-ACK-r17 ::= SEQUENCE (SIZE (1..8)) OF INTEGER (-1..127)

DL-DataToUL-ACK-v1700 ::= SEQUENCE (SIZE (1..8)) OF INTEGER (16..31)

DL-DataToUL-ACK-DCI-1-2-r17 ::= SEQUENCE (SIZE (1..8)) OF INTEGER (0..127)

UL-AccessConfigListDCI-1-2-r17 ::= SEQUENCE (SIZE (1..16)) OF INTEGER (0..15)

NOTE : (Based on 38.331)

DL-DataToUL-ACK-r17, DL-DataToUL-ACK-v1700, DL-DataToUL-ACK-DCI-1-2-r17, UL-AccessConfigListDCI-1-2-r17

List of timing for given PDSCH to the DL ACK (see TS 38.213, clause 9.1.2). The field dl-DataToUL-ACK applies to DCI format 1_1 and the field dl-DataToUL-ACK-DCI-1-2 applies to DCI format 1_2 (see TS 38.212 clause 7.3.1 and TS 38.213 clause 9.2.3). The dl-DataToUL-ACK-v1700 is applicable for NTN and dl-DataToUL-ACKr17 is applicable for up to 71 GHz. If dl-DataToUL-ACK-r16 or dl DataToUL-ACK-r17 or dl-DataToUL-ACK-v1700 is signalled, UE shall ignore the dl-DataToUL-ACK (withoutsuffix). The value -1 corresponds to "inapplicable value" for the case where the A/N feedback timing is not explicitly included at the time of scheduling PDSCH. The fields dl-DataToUL-ACK-r17 and dl-DataToUL-ACK-DCI-1-2-r17 are only applicable for SCS of 480 kHz or 960 kHz.

ServingCellConfigCommon ::= SEQUENCE {

...

n-TimingAdvanceOffset ENUMERATED { n0, n25600, n39936 } OPTIONAL, -- Need S

...

ntn-Config-r17 NTN-Config-r17 OPTIONAL -- Need R

]],

[[

....,

[[

ra-ChannelAccess-r17 ENUMERATED {enabled} OPTIONAL -- Cond SharedSpectrum2

]]

}

n-TimingAdvanceOffset ; The N_TA-Offset to be applied for all uplink transmissions on this serving cell. If the field is absent, the UE applies the value defined for the duplex mode and frequency range of this serving cell. See TS 38.133-table 7.1.2-2.

PDSCH-ServingCellConfig ::= SEQUENCE {

codeBlockGroupTransmission SetupRelease { PDSCH-CodeBlockGroupTransmission }

OPTIONAL, -- Need M

xOverhead ENUMERATED { xOh6, xOh12, xOh18 } OPTIONAL, -- Need S

nrofHARQ-ProcessesForPDSCH ENUMERATED {n2, n4, n6, n10, n12, n16} OPTIONAL, -- Need S

pucch-Cell ServCellIndex OPTIONAL, -- Cond SCellAddOnly

...,

[[

maxMIMO-Layers INTEGER (1..8) OPTIONAL, -- Need M

processingType2Enabled BOOLEAN OPTIONAL -- Need M

]],

[[

pdsch-CodeBlockGroupTransmissionList-r16 SetupRelease {

PDSCH-CodeBlockGroupTransmissionList-r16 }

OPTIONAL -- Need M

]],

[[

downlinkHARQ-FeedbackDisabled-r17 SetupRelease { DownlinkHARQ-FeedbackDisabled-r17 }

OPTIONAL, -- Need M

nrofHARQ-ProcessesForPDSCH-v1700 ENUMERATED {n32} OPTIONAL -- Need R

]]

}

PDSCH-CodeBlockGroupTransmission ::= SEQUENCE {

maxCodeBlockGroupsPerTransportBlock ENUMERATED {n2, n4, n6, n8},

codeBlockGroupFlushIndicator BOOLEAN,

...

}

PDSCH-CodeBlockGroupTransmissionList-r16 ::= SEQUENCE (SIZE (1..2))

OF PDSCH-CodeBlockGroupTransmission

DownlinkHARQ-FeedbackDisabled-r17 ::= BIT STRING (SIZE (32))

downlinkHARQ-FeedbackDisabled ; Used to disable the DL HARQ feedback, sent in the uplink, per HARQ process ID. The first/leftmost bit corresponds to HARQ process ID 0, the next bit to HARQ process ID 1 and so on. Bits corresponding to HARQ process IDs that are not configured shall be ignored. The bit(s) set to one identify HARQ processes with disabled DL HARQ feedback and the bit(s) set to zero identify HARQ processes with enabled DL HARQ feedback.

UE Capability

For 5G NR operating over Non-Terrestrial Networks (NTN), a dedicated set of UE capability information elements is defined to ensure reliable operation under long propagation delays, high Doppler shifts, and moving satellite platforms. These capability fields allow the network to identify whether a UE supports NTN-specific procedures such as uplink pre-compensation, extended timers across protocol layers, and satellite-based timing alignment. They also define support for features like RRC_INACTIVE operation over NTN, Random Access and Signalling Data Transmission (RA-SDT/CG-SDT), and the ability to maintain connectivity across geostationary (GSO) and non-geostationary (NGSO) scenarios. Additional items cover CQI reporting, multicast slot repetition, and scenario-specific configurations. Together, these parameters describe how an NTN-enabled UE adapts timing, frequency, access, and signalling behavior to cope with satellite dynamics and ensure seamless integration with terrestrial 5G systems.

NOTE : for formal description of these parameters, refer to 38.306

nonTerrestrialNetwork-r17 Indicates whether the UE supports NR NTN access.
- Extends timers in MAC, RLC, and PDCP layers to handle long RTT.
- Adapts RACH procedure to large propagation delay.
- Receives NTN-specific System Information Blocks (SIBs).
- Supports multiple TACs per PLMN broadcast within one cell.
uplinkPreCompensation-r17 Indicates support for uplink time/frequency pre-compensation and timing relationship enhancements.
- UE-specific Timing Advance (TA) calculation using GNSS position and satellite ephemeris.
- Common TA calculation based on network parameters (defaults to 0 if not provided).
- Combination of open-loop (autonomous/common TA) and closed-loop (command-based) control in RRC_CONNECTED.
- Applies calculated TA to uplink transmissions.
- Estimates UE-gNB RTT and delays Random Access Response (RAR) window accordingly.
- Performs frequency pre-compensation to counter Doppler shift on the service link.
- Determines correct timing for:
  - PUSCH, PUCCH, and PDCCH-ordered PRACH scheduling.
  - CSI reference and aperiodic SRS activation.
  - TA command and CG Type-2 PUSCH transmission.
- Handles timing for MAC CE actions using K_mac and K_offset values.
- Monitors PDCCH in recovery search space using K_mac during beam failure recovery.
- Receives cell-specific K_offset and K_mac in system information.
- Mandatory for UE supporting nonTerrestrialNetwork-r17.
- Applies to NTN bands in TS 38.101-5 (Table 5.2.2-1) and HAPS bands in TS 38.104 (Clause 5.2).
inactiveStateNTN-r17 Indicates UE support for RRC_INACTIVE in NTN as specified in TS 38.331.
- Mandatory if nonTerrestrialNetwork-r17 is supported.
ra-SDT-NTN-r17 Indicates UE support for RA-SDT (data/signalling via Random Access) in RRC_INACTIVE state.
- Supports 4-step RA type.
- If twoStepRACH-r16 is supported for NTN, supports 2-step RA type as well.
- Defined in TS 38.331.
- Requires nonTerrestrialNetwork-r17 support.
srb-SDT-NTN-r17 Indicates support for using SRB2 over RA-SDT or CG-SDT in NTN.
- Defined in TS 38.331.
- Requires ra-SDT-NTN-r17 or cg-SDT-r17 support in NTN bands.
- Requires nonTerrestrialNetwork-r17 support.
ntn-ScenarioSupport-r17 Indicates whether the UE supports NTN features in GSO or NGSO scenario.
- If not present but nonTerrestrialNetwork-r17 is supported:
  - UE supports both GSO and NGSO.
  - UE supports mobility between GSO and NGSO.
cqi-4-BitsSubbandNTN-SharedSpectrumChAccess-r17 Indicates support for 4-bit per-subband CQI reporting for NTN and shared spectrum channel access.
dynamicSlotRepetitionMulticastNTN-SharedSpectrumChAccess-r17 Indicates maximum number of supported dynamic slot-level repetitions for group-common PDSCH (multicast) for NTN and shared spectrum access.
- Value n8 = 8 repetitions.
- Value n16 = 16 repetitions.
- Requires support for dynamicMulticastPCell-r17.