Description
Forward Error Correction (FEC) is a fundamental digital signal processing technique used to control errors in data transmission over unreliable or noisy communication channels. In 3GPP systems, FEC operates by the transmitter encoding the message in a redundant way using an error-correcting code (ECC). This redundancy allows the receiver to detect a limited number of errors that may occur anywhere in the message and often to correct these errors without needing a retransmission request. The process involves the sender adding parity bits or using more complex algebraic structures to the original data bits before transmission. Upon reception, the decoder uses these extra bits to identify and correct bit errors caused by channel impairments like interference, fading, or noise.
The architecture of FEC in 3GPP spans multiple layers and radio access technologies (GSM, UMTS, LTE, NR). At the physical layer, convolutional codes, Turbo codes (introduced in UMTS), and Low-Density Parity-Check (LDPC) codes (for NR data channels) and Polar codes (for NR control channels) are specified. These codes are applied to transport channels after processes like channel coding, rate matching, and interleaving. The specific code and coding rate are selected based on the channel conditions and required reliability, often as part of link adaptation. The performance is characterized by the coding gain, which is the reduction in required signal-to-noise ratio for a given bit error rate compared to uncoded transmission.
FEC's role is critical for achieving the quality of service (QoS) targets for various services. For voice, it ensures intelligibility; for packet data, it maintains throughput and reduces latency by avoiding higher-layer retransmissions like those from the Radio Link Control (RLC) layer. In evolved systems, Hybrid Automatic Repeat Request (HARQ) is combined with FEC, where the initial transmission uses a weak FEC code, and subsequent retransmissions provide incremental redundancy for the decoder to combine, enhancing efficiency. The specifications detail code structures, encoding/decoding algorithms, and performance requirements for different channels (e.g., PDSCH, PUSCH, PBCH) across all 3GPP releases, ensuring interoperability and robust communication.
Purpose & Motivation
FEC was created to address the inherent unreliability of wireless communication channels. Unlike wired mediums, radio channels are susceptible to time-varying impairments like multipath fading, interference, and additive white Gaussian noise, which cause bit errors. Without FEC, systems would rely solely on retransmission protocols (ARQ), which introduce significant latency and reduce spectral efficiency, especially for real-time services like voice or video. The primary purpose of FEC is to proactively combat these errors at the physical layer, improving the raw bit error rate (BER) before data is passed to higher layers.
Historically, simple parity checks and block codes were used in early digital communications. 3GPP's GSM initially employed convolutional coding. The motivation evolved with UMTS and the need for higher data rates, leading to the adoption of Turbo codes, which offered performance near the Shannon limit. The continuous evolution through LTE to 5G NR is driven by demands for ultra-reliable low-latency communication (URLLC), enhanced mobile broadband (eMBB), and massive machine-type communication (mMTC). Each new service class has distinct reliability and latency requirements, necessitating more advanced FEC schemes like LDPC and Polar codes to provide higher coding gains, lower complexity, and better adaptability than previous generations.
FEC solves the problem of maintaining a target block error rate (BLER) under challenging signal conditions without excessive transmit power. It is a key enabler for spectral efficiency, allowing networks to operate at higher modulation orders (e.g., 256-QAM, 1024-QAM) by providing the necessary error resilience. By reducing the number of required retransmissions, FEC directly contributes to lower latency and higher throughput, which are critical performance indicators for modern cellular networks. It is a foundational technology without which reliable digital mobile communication would not be feasible.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (278 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the FEC function was newly introduced to support mission critical services, specifically over MBMS bearers. This included the capability for a GCS AS to request the application of FEC (and/or RoHC) to an MBMS bearer via the MB2 interface, with corresponding format definitions for the FEC framework configuration information. These enhancements were defined alongside several corrections to the related MBMS bearer activation and MB2 signaling procedures.
- FEC for mission critical services TS 23.280CR0043
- FEC and ROHC for mission critical services over MBMS TS 29.116CR0021
- FEC and ROHC for mission critical services over MBMS TS 29.468CR0047
- Correction of "Group creation confirmation response" TS 23.280CR0108
- Correction of interconnection configuration enforcement figure TS 23.280CR0130
- Correction of MC service system TS 23.280CR0143
+ 22 more changes
In Release 16, the FEC function saw no new, forward-looking enhancements described in the provided materials. The changes documented were limited to corrections, such as fixes to the EVS Alternative Fixed-Point Source Code implementation and miscellaneous corrections to LPP (LTE Positioning Protocol) field descriptions and message handling. The focus was on rectifying existing specifications rather than introducing new FEC capabilities or procedures.
- Correction and addition of reference to Alt_FX_EVS implementation TS 26.444CR0025
- Corrections to affiliation procedures TS 23.280CR0190
- Corrections to the emergency alert procedures TS 23.280CR0210
- Corrections to clauses in 10.9 Location Management (on-network) TS 23.280CR0211
- Correction on Subcarrier Spacing in USD for ROM Service Delivery TS 26.346CR0635
- Correction of xMB Guidelines TS 26.348CR0005
+ 38 more changes
In Release 17, the FEC function itself is not explicitly mentioned in the provided materials. The listed Change Requests and grounding context focus on corrections and clarifications for other features, primarily Multicast Broadcast Service (MBS) procedures and Location Services (LCS) flows, involving entities like the MB-SMF, PCF, GMLC, and BSC. Therefore, based solely on the given information, no new forward erasure or error correction capabilities for FEC can be specifically identified for this release.
- Correction of IMC definition for terminals accessing IMS via SNPN TS 21.905CR0122
- Miscellaneous corrections TS 23.247CR0026
- PCC related MBS corrections TS 23.247CR0050
- Corrections to MBS Broadcast Session Establishment TS 23.247CR0051
- Corrections for Location dependent MBS session TS 23.247CR0078
- Resolving ENs, cleanup and corrections TS 23.247CR0081
+ 64 more changes
In Release 18, the FEC (Forward Erasure Correction) function was expanded with a new **RTP-based Application Layer FEC** capability, specifically developed to meet the traffic characteristics defined for **XR (Extended Reality)** services. This enhancement introduces a dedicated framework for applying FEC at the application layer to improve reliability for time-sensitive XR media streams.
- Adding ISAR track-a split rendering feature to TS 26.258 and Corrections to the IVAS C-Code and corresponding specification text TS 26.258CR0002
- [FS_XRTraffic] Application Layer FEC Traffic characteristics TS 26.925CR0004
- [FS_XRTraffic] Application Layer FEC Traffic characteristics TS 26.926CR0001
- Defining the missing 5MBS error handling procedures TS 29.580CR0048
- Resolve ENs on Group Message Delivery and corrections TS 23.247CR0161
- [FS_XRTraffic] RTP-based Application Layer FEC TS 26.926CR0002
+ 86 more changes
In Release 19, the FEC function saw no new technical developments or enhancements. The provided Change Requests and grounding specification text contain only corrections to other areas, such as Multicast Service emergency alerts, location reporting procedures, and API definitions, with no mention of Forward Erasure Correction or Forward Error Correction. Therefore, there were no updates to the FEC function in this release.
- Corrections to MC service emergency alert cancel request information flow TS 23.280CR0469
- Corrections on modifying the criteria during an ad hoc group alert (single MC system) TS 23.280CR0474
- Minor corrections in clause 10.11 TS 23.280CR0521
- Correction of Information Flow 10.17.2.5 - Group membership update response TS 23.280CR0549
- MCShAC - corrections to clause numbers TS 23.280CR0576
- Correction to client-triggered one-time location information report for shared functional alias procedure TS 23.280CR0593
+ 32 more changes
In Release 20, the FEC function introduced no new technical capabilities or procedures, as the approved Change Requests for this release consisted exclusively of editorial corrections and fixes to existing figures, messages, and location management clauses.
Explore further
Broader topics and technologies where FEC plays a role.
Defining Specifications
3GPP specifications that define or reference FEC, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 03.071 v7b0 | Location Services (LCS) Stage 2 Description | Rel-7 |
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.247 vj30 | 5G Multicast/Broadcast Service Architecture | Rel-19 |
| TS 23.280 vk10 | Common Architecture for Mission Critical Services | Rel-20 |
| TS 23.468 vj00 | Group Communication System Enablers for LTE | Rel-19 |
| TS 23.479 vj00 | MBMS API for Mission Critical Services | Rel-19 |
| TR 23.780 ve00 | MBMS for Mission Critical Communication Services | Rel-14 |
| TS 23.792 vg00 | MBMS API for Mission Critical Services | Rel-16 |
| TS 25.201 vj00 | UTRA Physical Layer General Description | Rel-19 |
| TS 25.221 vj00 | UTRA TDD Physical Layer Specification | Rel-19 |
| TS 25.222 vj00 | UTRA TDD Multiplexing & Channel Coding | Rel-19 |
| TS 26.110 vj00 | 3G-324M Multimedia Codecs for Circuit Switched Networks | Rel-19 |
| TS 26.226 vj00 | Cellular Text Telephone Modem (CTM) | Rel-19 |
| TS 26.230 vj00 | CTM C Code Implementation for Text Transmission | Rel-19 |
| TS 26.253 vj00 | IVAS Codec Algorithmic Description | Rel-19 |
| TS 26.258 vj10 | IVAS Codec Floating-Point C Code Specification | Rel-19 |
| TS 26.267 vj00 | eCall In-band Modem Specification | Rel-19 |
| TS 26.268 vj00 | eCall In-band Modem ANSI-C Code | Rel-19 |
| TS 26.269 vj00 | eCall In-band Modem Conformance Testing | Rel-19 |
| TS 26.346 vj20 | MBMS User Services Media Codecs & Protocols | Rel-19 |
| TS 26.348 vj00 | xMB Interface Specification | Rel-19 |
| TS 26.441 vj00 | EVS Audio Processing Introduction | Rel-19 |
| TS 26.442 vj00 | EVS Codec Fixed Point ANSI-C Code | Rel-19 |
| TS 26.443 vj00 | EVS Codec Floating-Point C Code | Rel-19 |
| TS 26.444 vj00 | EVS Codec Conformance Test Sequences | Rel-19 |
| TS 26.450 vj00 | EVS Codec DTX System Level Aspects | Rel-19 |
| TS 26.451 vj00 | EVS Codec Voice Activity Detector (VAD) Specification | Rel-19 |
| TS 26.452 vj00 | EVS Codec Fixed-Point C Code Implementation | Rel-19 |
| TS 26.502 vj30 | 5G Multicast-Broadcast User Services Architecture | Rel-19 |
| TS 26.802 vj20 | Multicast Enhancements for 5G Media Streaming | Rel-19 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TR 26.805 vh01 | Study on Media Production over 5G NPN Systems | Rel-17 |
| TS 26.851 vb20 | Enhancements to Multimedia (EMM) for PSS, MMS, MBMS | Rel-11 |
| TS 26.880 ve00 | MBMS Enhancements for Mission Critical Video | Rel-14 |
| TS 26.881 vf00 | MBMS FEC for Mission Critical Services Study | Rel-15 |
| TS 26.891 vg00 | Media Distribution Services in 5G System | Rel-16 |
| TR 26.925 vj00 | Media Traffic Characteristics for 3GPP Networks | Rel-19 |
| TR 26.926 vj00 | Traffic Models & Quality Evaluation for Media/XR in 5G | Rel-19 |
| TR 26.936 vj00 | Audio Codec Characterization Technical Report | Rel-19 |
| TR 26.946 vj00 | MBMS User Services Overview | Rel-19 |
| TR 26.947 vj00 | FEC Evaluation for MBMS Enhancement | Rel-19 |
| TR 26.952 vj00 | EVS Codec Selection, Verification & Characterization | Rel-19 |
| TR 26.997 vj00 | IVAS Codec Specification | Rel-19 |
| TS 29.116 vj00 | REST-based protocol for xMB reference point | Rel-19 |
| TS 29.333 vj00 | MRFC-MRFP Mp Interface Protocol | Rel-19 |
| TS 29.468 vj00 | MB2 Reference Point Protocol Definition | Rel-19 |
| TS 29.580 vj30 | 5G MBSF Service Interface Stage 3 Specification | Rel-19 |
| TS 36.355 vj00 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 37.355 vj20 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 38.191 vj00 | NR Ambient IoT RF Characteristics | Rel-19 |
| TS 38.201 vj00 | NR Physical Layer General Description | Rel-19 |
| TS 38.202 vj00 | 5G NR Physical Layer Services | Rel-19 |
| TS 38.769 vk00 | Ambient IoT Solutions in NR | Rel-20 |
| TR 38.835 vi01 | Technical Report on XR Enhancements for NR | Rel-18 |
| TS 44.031 vj00 | Radio Resource LCS Protocol (RRLP) | Rel-19 |
| TS 44.318 vj00 | Generic Access Network (GAN) Interface Procedures | Rel-19 |
| TS 46.041 vj00 | GSM Half Rate Speech DTX Operation | Rel-19 |