FREF

RF Reference Frequency

Physical Layer →
Introduced in Rel-15 Also in: User Equipment

FREF is the fundamental, highly stable master clock frequency source used to generate all other radio frequencies within a User Equipment or base station.

Category
Physical Layer
Introduced
Rel-15
Where
Radio Access Network › NG-RAN (5G)
Also touches
1 segments
Specifications
9 specs
FREF Description Purpose Related Classification Detected Changes Specifications

Description

The RF Reference Frequency (FREF) is the cornerstone frequency generation element in any 3GPP radio device, whether a UE or a gNB. It is typically derived from a temperature-compensated crystal oscillator (TCXO) or, in higher-end equipment, an oven-controlled crystal oscillator (OCXO). The FREF serves as the primary reference for the device's frequency synthesizer, which generates the local oscillator (LO) signals used for upconversion (transmission) and downconversion (reception). In the transmitter chain, the digital baseband signal is converted to analog and then mixed with the LO signal, which is a multiple of the FREF, to shift it to the desired RF carrier frequency. Any error or drift in the FREF causes a proportional error in the final transmitted carrier frequency, leading to out-of-channel emissions and interference with adjacent cells. In the receiver, the incoming RF signal is mixed down to baseband using an LO also derived from the FREF. An inaccurate FREF here causes the receiver to be mis-tuned, potentially placing the desired signal outside the passband of the channel filters and degrading demodulation performance. The 3GPP specifications (e.g., TS 38.101, 38.104) define stringent requirements for FREF accuracy, often in terms of parts per million (ppm), for different device categories and operating conditions. For example, a typical UE requirement might be ±0.1 ppm for normal conditions and ±0.25 ppm under extreme temperatures. The network relies on the aggregate accuracy of all devices' FREF to maintain orthogonality in OFDM systems and to enable successful handovers.

Purpose & Motivation

The FREF exists to ensure all radios in a cellular network operate on precisely defined frequencies. Without a stable and accurate common frequency reference, coherent communication would be impossible. The problems it solves are frequency drift, which causes interference and dropped calls, and the inability of receivers to lock onto transmitted signals. Historically, as channel bandwidths increased and modulation schemes became more complex (e.g., OFDM with closely spaced subcarriers), the tolerance for frequency error became exceedingly tight. The creation of standardized FREF requirements in 3GPP was motivated by the need for mass-produced, low-cost devices to maintain network-level frequency synchronization without requiring constant correction from the network. It addresses the limitations of cheaper, less stable oscillators by defining the minimum performance needed for reliable operation, ensuring that even a low-cost UE can meet the system's spectral purity and receiver sensitivity needs.

Classification

Part ofOFDM

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (25 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Rel-15 2 changes

In Release 15, the FREF (RF Reference Frequency) function was newly introduced to define the frequency error requirements for advanced uplink configurations. Specifically, it established the performance criteria for intra-band and inter-band uplink Carrier Aggregation (CA) when operating with uplink MIMO or transmit diversity. This provided the necessary foundation for the stringent RF synchronization needed in these multi-carrier and multi-antenna transmission schemes.

  • CR to TS 38.104 on Combined updates from RAN4 #90 This document combines the proposed changes in the following Draft CRs from RAN4 #90: - R4-1900284, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1900763, "Draft CR to TS 38.104: Update of performance requirement numbers for DFT-s-OFDM based PUSCH" - R4-1900876, "Draft CR to TS 38.104: On RX spurious emissions requirement" - R4-1900968, "Draft CR for 38.104: Performance requirements for NR PUCCH format 1" - R4-1901329, "Draft CR to 38.104: Annex C.6 correction" - R4-1901330, "Draft CR to 38.104: Abbreviations addition" - R4-1901387, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1901474, "Draft CR to TS 38.104: Corrections on transmitter co-existence and co-location requirements" - R4-1901483, "Draft CR to TS 38.104: Corrections on general intermodulation requirement" - R4-1902239, "Draft CR to TS 38.104: Addition of missing EIRP/EIS definitions in terminology in clause 3.1" - R4-1902241, "Draft CR to 38.104; clarification of BS power limits" - R4-1902245, "Draft CR to 38.104: Correction to FR2 OTA Interfering signal mean power units" - R4-1902246, "Draft CR to 38.104; Correction to definition of OTA reference sensitivity" - R4-1902260, "draft CR to TS 38.104 - update emissions scaling" - R4-1902338, "Draft CR: Update on FR1 range extension for TS38.104" - R4-1902389, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1902394, "Draft CR to TS 38.104 – PUSCH requirements with CP-OFDM for FR2" - R4-1902396, "CR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1902444, "Draft CR to TS 38.104: Editorial CR for BS demodulation requirements" - R4-1902561, "Draft CR for updating PRACH performance requirements in TS38.104" - R4-1902571, "Corrections to 38.104 Delay profile calculation" - R4-1902642, "Draft CR to TS 38.104: Correction on multi-band operation related requirements" TS 38.104CR0019
  • CR to TS 38.104 Combined updates from RAN4 #90bis and RAN4#91 From RAN4 #90bis: - R4-1903105, "Draft CR to TS 38.104: Corrections on terminologies and editorial errors" - R4-1903319, "Draft CR to TS 38.104: removal of unused definition: "minimum EIRP level under extreme condition"" - R4-1903320, "Draft CR to TS 38.104: OSDD information correction" - R4-1903457, "Draft CR to TS 38.104: Removal of FFS for FR2 TDD OFF power level requirement in clause 9.5" - R4-1903499, "Draft CR to 38.104: Correction to unwanted emissions mask for bands n7 and n38" - R4-1903836, "Draft CR to TS 38.104: Correction on description on multi-band operation in section 4.8" - R4-1904024, "Draft CR to TS 38.104 Applicability rules for BS demodulation" - R4-1904234, "draftCR: Correlation matrix for 8Rx in TS 38.104" - R4-1904723, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1904726, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1904729, "Draft CR on PRACH performance requirements in TS38.104" - R4-1904734, "Draft CR on TS 38.104 Performance requirement for PUCCH format 1" - R4-1904735, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1904739, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1904745, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1904799, "Draft CR to TS 38.104: FRC update for PUSCH FR1 mapping type B and FR2 DMRS 1+1" - R4-1904816, "Draft CR : Clarification on step 5 and step 6 for delay profiles calculation (38.104)" - R4-1904842, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1905126, "draft CR to 38.104 for TAE requirements" - R4-1905139, "draft CR to TS 38.104 on EVM measurement (Annex B and C)" - R4-1905140, "Draft CR: editorial correction on FR1 spurious emission requirement in TS38.104" - R4-1905143, "Draft CR for TS 38.104: Addition of NOTE for transmitter intermodulation requirements in certain regions" - R4-1905144, "Draft CR to TS 38.104: FRC reference corrections for the Rx requirements" - R4-1905145, "Draft CR to TS 38.104: Clarification on application of interfering signal offsets for ACS, blocking and intermodulation requirements" - R4-1905148, "Draft CR to TS 38.104: Corrections on out-of-band blocking requirement" From RAN4 #91: - R4-1906002, "Draft CR to 38.104: Subclause 6.7 and 9.8 transmitter intermodulation – correction of interfering signal type" - R4-1906096, "Draft CR to 38.104: Correction of frequency range for OTA spurious emissions" - R4-1906311, "Draft CR to 38.104: Correction on FRC (Annex A)" - R4-1906346, "Removal of n65 in Rel-15 38.104" - R4-1906915, "Draft CR to TS 38.104: Clarification on application of interfering signal offsets for OTA ACS, blocking and intermodulation requirements" - R4-1906918, "Draft CR to TS 38.104: Clarification on type of interfering signal for ACS, in-band blocking and ICS requirements" - R4-1907110, "Draft CR to TS 38.104: correction of the fundamental frequency limit of 2.55GHz for the spurious emissions" - R4-1907246, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1907249, "Draft CR to TS 38.104: Correction on the terminology in PUSCH FRC tables" - R4-1907252, "Draft CR to TS38.104: Updates of PRACH performance requirements" - R4-1907255, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1907258, "Draft CR on NR UCI on PUSCH performance requirements for TS 38.104" - R4-1907261, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1907266, "Draft CR on TS 38.104 Performance requirement for PUCCH format 1" - R4-1907267, "Draft CR on TS 38.104 Performance requirement for multi-slot PUCCH format 1" - R4-1907272, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1907275, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1907277, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1907629, "Draft CR to 38.104: Term “reference signal” replacing by term “ideal signal” in EVM context" - R4-1907634, "Draft CR to 38.104: corrections to the EVM annex" - R4-1907659, "Draft CR to TS 38.104 on Spurious emission Category B in FR2" - R4-1907661, "Draft CR to 38.104 Definition of contiguous transmission bandwidth" - R4-1907662, "Draft CR to 38.104: BS TAE requirements" - R4-1907664, "Draft CR to 38.104: Clarification of interferer RB frequency for narrowband blocking" - R4-1907672, "Draft CR for TS 38.104: Correction on EVM" - R4-1907689, "Correction to CA carrier spacing" TS 38.104CR0029
Rel-16 9 changes

In Release 16, the FREF (RF Reference Frequency) function was updated to specify performance requirements for new NR features including DFT-s-OFDM based PUSCH and CP-OFDM PUSCH in FR2, and to refine requirements for various PUCCH formats. Furthermore, the release introduced explicit channel arrangement and performance specifications for Carrier Aggregation (CA) scenarios, such as intra-band contiguous CA with UL MIMO, and added new reference measurement channels for these configurations. These enhancements also included corrections to interferer frequency offsets for ACS and EVM window length to improve measurement accuracy.

  • Introduction of LTE/NR spectrum sharing in band 48/n48 frequency range TS 38.104CR0220
  • CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements TS 38.104CR0102
  • CR to T 38.104: Implementation of endorsed draft CRs from RAN4#92 (Rel-16) (Mirrors changes in R4-1908440 for Rel-15 TS 38.104) - R4-1907940, "Draft CR to TS 38.104: Correction on the terminology in FRC tables in A.1 and A.2" - R4-1908307, "Draft CR to TS 38.104: Clarification on application of OTA receiver requirements for BS supporting polarization" - R4-1908387, "Draft CR for TS38.104: editorial correction for reference meausrement channel" - R4-1908619, "Draft CR to TS38.104: Correction on interferer frequency offset values for ACS" - R4-1908629, "Draft CR to TS38.104: Corrections on EVM window length (Annex B.5.2, C.5.2)" - R4-1908774, "DraftCR to 38.104: Editorial Corrections to redudant units in clause 10.8.3" - R4-1908805, "Draft CR to 38.104: Limits in FCC title 47 for OTA operating band unwanted emissions (9.7)" - R4-1909270, "Draft CR to TS 38.104: Receiver spurious emissions frequency correction" - R4-1909309, "DraftCR to TS 38.104: text corrections, Rel-15" - R4-1909310, "DraftCR to 38.104: correction of TAB connectors mapping to TAB connector TX min cell group, Rel-15" - R4-1909416, "draft CR 38.104 - correct reference to annex F" - R4-1910066, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1910069, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1910072, "Draft CR on NR UCI on PUSCH performance requirements for TS 38.104" - R4-1910075, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1910078, "Draft CR to TS38.104: Updates to NR PRACH performance requirements" - R4-1910081, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1910084, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1910088, "Draft CR for 38.104: Performance requirements for NR PUCCH format 1" - R4-1910089, "Draft CR for 38.104: Performance requirements for NR multi-slot PUCCH" - R4-1910094, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1910431, "Corrections to EVM calculations in 38.141-1 annex B" - R4-1910462, "Draft CR to 38.104: Correction on regional requirements (4.5)" - R4-1910493, "Draft CR to TS 38.104 correction to Annex C.7" - R4-1910606, "Draft CR for TS 38.104: Channel spacing for adjacent NR carriers" TS 38.104CR0034
  • CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH (Rel-16) TS 38.104CR0049
  • CR for 38.104 on PUSCH requirements with CP-OFDM and FR1 TS 38.104CR0063
  • CR to TS 38.104: Finalization of interfering RB centre frequency offsets in receiver narrowband blocking requirement TS 38.104CR0083

+ 3 more changes

Rel-17 2 changes

In Release 17, the FREF (RF Reference Frequency) function was updated with corrections to the frequency offset symbols used for the spectrum emission mask for non-transmitted channels. This change, detailed in a CR to TS 38.104, ensured accurate measurement of out-of-band emissions in scenarios involving carrier aggregation and other multi-carrier operations. The revision specifically refined the technical parameters for assessing unwanted emissions from adjacent, non-active frequencies.

  • CR to TS 38.104 on reference to FRCs TS 38.104CR0411
  • CR to TS 38.104: Corrections on frequency offset symbols for spectrum emission mask for non-transmitted channels TS 38.104CR0307
Rel-18 6 changes

In Release 18, the FREF function saw updates to RF reference frequency tables and regulatory references, including corrections for the NR-ARFCN table for band n263 and for extending NR operation to 71GHz. It also involved adjustments to reference sensitivity (PREFSENS) for band n104 and incorporated necessary international regulatory information for operations in the 1610-1626.5 MHz range and references to specific FCC orders.

  • (NR_NTN_LSband-Core) Additional information on the international regulations and WRC provisions for a UE operating in 1610-1626.5 MHz frequency range TS 38.741CR0007
  • CR to TS 38.104 on table references for OTA operating band unwanted emission limits TS 38.104CR0437
  • CR to TS 38.104: NR-ARFCN table reference correction for band n263, Rel-18 TS 38.104CR0460
  • CR to TS 38.104 on corrections of table references for extending current NR operation to 71GHz TS 38.104CR0468
  • CR for TR 38.104, Correction on reference of PREFSENS for in-band blocking and out-of-band blocking for band n104 TS 38.104CR0472
  • (NR_SUL_UL_n24-Core) Missing reference to FCC Order DA 20-48 TS 38.104CR0659
Rel-19 6 changes

In Release 19, the FREF (RF Reference Frequency) function was updated with specific corrections for Non-Terrestrial Network (NTN) operations, particularly addressing the NR L-band NS (Network Synchronization) flag references. Additionally, corrections were made to the NS_02N and NS_24N flag references to ensure accurate frequency and synchronization signaling. These refinements were part of a broader set of maintenance changes that also included corrections to test case annex references and requirements for NB-IoT in-band operation.

  • Corrections for the NTN NR L-band NS flag references TS 38.863CR0050
  • Corrections for the NS_02N and NS_24N flag references TS 38.863CR0051
  • Corrections for the NTN NR L-band NS flag references TS 38.863CR0049
  • (NR_FR1_lessthan_5MHz_BW-Core)CR for TS38.104, Correction on reference sensitivity levels requirement apply to BS that supports NB-IoT operation in NR in-band for 3 MHz channel bandwidth TS 38.104CR0739
  • Correct Annex references in TC 8.2.6 TS 38.141CR0695
  • Correct Annex references in TC 8.2.14 TS 38.141CR0697

Explore further

Broader topics and technologies where FREF plays a role.

Topics
Service Based ArchitectureLTE / LTE-AdvancedLawful InterceptRadio Access Network
Technologies
LTE

Defining Specifications

3GPP specifications that define or reference FREF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.

SpecificationTitleRelease
TS 38.101 vj31 NR User Equipment Radio Transmissions Rel-19
TS 38.104 vj20 NR Base Station RF Requirements Rel-19
TS 38.141 vj20 NR Base Station RF Conformance Testing Part 1 Rel-19
TS 38.191 vj00 NR Ambient IoT RF Characteristics Rel-19
TS 38.194 vj00 Ambient IoT Base Station RF Spec Rel-19
TS 38.521 vj20 NR Physical Layer UE Conformance Testing Rel-19
TS 38.741 vj00 NTN L-/S-band for NR Technical Specification Rel-19
TR 38.785 vh00 UE radio transmission for enhanced NR sidelink Rel-17
TS 38.863 vj10 NR NTN RF and Co-existence Spec Rel-19