Description
In the GSM system, 'FR' has two primary, interrelated meanings. First, it denotes the Full Rate traffic channel (TCH/FS), which is a physical radio resource allocation. This is a dedicated channel carrying user speech data at a gross bit rate of approximately 22.8 kbps, which includes speech coding, channel coding for error protection, and other overhead. The channel structure involves dividing the 200 kHz carrier into 8 time slots (TDMA), with a TCH occupying one time slot in a repeating frame structure. This channel is used for the actual bidirectional voice conversation.
Second, and more specifically, FR refers to the GSM Full Rate speech codec itself. This was the first digital speech codec standardized for GSM (specified in GSM 06.10, later 3GPP TS 06.10/TS 46.010). It is a Linear Predictive Coding (LPC) based codec with Regular Pulse Excitation (RPE), often called the RPE-LTP (Long-Term Prediction) codec. The codec operates by analyzing 20 ms segments (160 samples) of the input speech signal. It extracts parameters representing the vocal tract filter (LPC coefficients), the long-term pitch correlation (LTP), and the short-term residual signal (RPE). These parameters are encoded into a 260-bit block every 20 ms, resulting in a net bit rate of 13 kbps. Before transmission, this 260-bit block undergoes channel coding, where error-protection bits are added, increasing the transmitted bit rate to 22.8 kbps for the TCH/FS.
The role of the FR codec and channel was foundational. It defined the voice quality benchmark for early digital cellular networks, offering significant improvements in clarity and noise immunity compared to analog systems. However, its voice quality, often described as 'synthetic' or 'robotic,' was a known limitation. This led to the development of enhanced codecs like the Enhanced Full Rate (EFR) and later the Adaptive Multi-Rate (AMR) codec. In network operation, the FR channel remains a fallback option for compatibility, especially when a mobile station roams into a network that only supports the basic codec or when radio conditions are too poor to support more advanced, efficient codecs that require higher channel quality.
Purpose & Motivation
The GSM Full Rate codec and channel were created to solve the core problem of enabling efficient, secure, and higher-capacity digital voice communication for the first mass-market cellular standard. Prior to GSM, analog systems like NMT and AMPS were susceptible to eavesdropping, offered poor voice quality in noisy environments, and had limited capacity. The transition to digital was revolutionary. The FR codec's purpose was to digitize and compress the human voice into a low enough bit rate (13 kbps) to allow multiple users to share the same radio frequency through TDMA, dramatically increasing network capacity compared to analog FDMA systems.
Its development was driven by the need for a compromise between voice quality, complexity (and thus cost and power consumption of early digital signal processors), and spectral efficiency. The RPE-LTP algorithm was chosen as it provided acceptable quality within the severe computational constraints of late-1980s technology. While its quality was later surpassed, the FR codec successfully proved the viability of digital cellular voice, established the fundamental channel structure (TCH/FS), and laid the groundwork for all subsequent speech codec evolution in 3GPP standards. It addressed the initial business and technical requirement: to provide a commercially viable, standardized voice service that could be deployed globally.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (109 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-5, normative work from Rel-16.
In Release 16, the "FR" function was not directly modified; instead, the release focused on expanding New Radio (NR) channel bandwidths and carrier aggregation channel spacing. Specifically, it introduced wider channel bandwidths for multiple frequency bands, including n1, n7, n28, n38, n50, n66, n77, and n78, and defined new channel spacing requirements between E-UTRA and NR carriers. These changes were documented in updates to the core RF specification TS 38.104 and the multi-radio coexistence specification TS 37.104.
- Addition channel bandwidth of 30MHz for n50 in TS 38.104 TS 38.104CR0031
- CR for TS 38.104: adding wider channel bandwidths in Band n7 TS 38.104CR0037
- CR for TS 38.104: adding wider channel bandwidths in Band n77/n78 TS 38.104CR0105
- CR for TS 38.104: Addition channel bandwidth of 40MHz for n38 TS 38.104CR0106
- Introducing new channel bandwidth for band n28 TS 38.104CR0131
- CR for TS 38.104: adding wider channel bandwidths for n66 TS 38.104CR0139
+ 21 more changes
In Release 17, the primary update for the "FR" (Frequency Range) function was a correction to its defined range, specifically aligning it to FR2-1 as detailed in the RF performance specifications. This technical adjustment was implemented through Change Requests to the core TS 38.114 and TS 38.175 documents. No new channel bandwidths or modifications to the GSM Full Rate codec itself were introduced under the FR function in this release.
- CR to 37.104: Introduction of requirements for 35 and 45MHz channel bandwidths TS 37.104CR0949
- CR for TS 37.141: introduction of channel bandwidths 35MHz and 45MHz TS 37.141CR0990
- Big CR to 38.104 - Additional Channel BW TS 38.104CR0258
- Big CR to 38.104 - Additional Channel BW TS 38.104CR0291
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0319
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0343
+ 16 more changes
In Release 18, the primary new development for the "FR" function was the introduction of a 3 MHz channel bandwidth for NR operation, a new capability not defined in previous releases. This was supported by updates to the channel raster definition and the addition of this bandwidth option to existing NR frequency bands. Furthermore, the release specified the necessary RF requirements, such as Adjacent Channel Leakage power Ratio (ACLR), for equipment operating with this new 3 MHz channel bandwidth.
- CR to TS 37.141 - Consideration of NR 3 MHz channel bandwidth TS 37.141CR1068
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0450
- Big CR to TS 38.104 on introduction of 3 MHz channel bandwidth TS 38.104CR0500
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0512
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0538
- CR to TS38.104: Introduction of an enhanced channel raster TS 38.104CR0536
+ 25 more changes
In Release 19, the primary update for the FR function was the introduction of a new 7 MHz channel bandwidth for NR FR1, alongside clarifications and performance requirement corrections for this and the existing 3 MHz channel bandwidth. This involved updating multiple technical specifications (TS) to define the new bandwidth's transmitter and receiver RF requirements, including parameters for Adjacent Channel Leakage power Ratio (ACLR) and in-channel selectivity. The changes ensured the new channel bandwidth could be properly supported within the defined channel edge and carrier frequency framework for relevant operating bands.
- CR to TS37.104 Introduction of 7 MHz NR FR1 channel bandwidth TS 37.104CR1028
- CR to TS 37113 - Introduction of 7 MHz channel BW TS 37.113CR0142
- CR to TS37.141 Introduction of 7 MHz NR FR1 channel bandwidth TS 37.141CR1098
- Big CR to TS 38.104: Adding channel BW support in existing NR bands TS 38.104CR0685
- CR to 38.104 on adding new UL channel bandwidth to band n48 TS 38.104CR0698
- Running CR to TS 38.104 - Introduction of 7 MHz channel BW TS 38.104CR0725
+ 23 more changes
Explore further
Broader topics and technologies where FR plays a role.
Defining Specifications
3GPP specifications that define or reference FR, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TR 22.804 vg30 | 5G Automation in Vertical Domains Study | Rel-16 |
| TS 26.077 vj00 | AMR Noise Suppression Minimum Performance Requirements | Rel-19 |
| TS 26.231 vj00 | CTM Minimum Performance Requirements Testing | Rel-19 |
| TS 26.267 vj00 | eCall In-band Modem Specification | Rel-19 |
| TS 26.269 vj00 | eCall In-band Modem Conformance Testing | Rel-19 |
| TR 26.967 vj00 | eCall via CTM Suitability Analysis | Rel-19 |
| TR 26.969 vj00 | eCall In-band Modem Performance Characterization | Rel-19 |
| TR 26.975 vj00 | AMR Speech Codec Performance Background | Rel-19 |
| TR 26.978 vj00 | AMR Noise Suppression Selection Phase Technical Report | Rel-19 |
| TS 28.062 vj00 | Tandem Free Operation (TFO) Service Description | Rel-19 |
| TS 36.108 vj10 | Satellite Access Node RF Requirements | Rel-19 |
| TS 36.181 vj30 | E-UTRA RF Test Methods for Satellite Access Node | Rel-19 |
| TS 37.104 vj10 | MSR Base Station RF Characteristics | Rel-19 |
| TS 37.113 vj00 | EMC Requirements for Multi-Standard Radio Base Stations | Rel-19 |
| TS 37.141 vj10 | RF Test Methods for Multi-Standard Radio Base Stations | Rel-19 |
| TS 37.717 | 3GPP TR 37.717 | Rel-5 |
| TS 37.718 | 3GPP TR 37.718 | Rel-5 |
| TS 37.719 vj00 | 3GPP TR 37.719: Dual Connectivity Band Combinations | Rel-19 |
| TS 37.825 vg00 | High Power UE (PC2) for EN-DC TDD-TDD | Rel-16 |
| TR 37.941 vj20 | RF Conformance Testing Background for Radiated BS Requirements | Rel-19 |
| TS 38.101 vj31 | NR User Equipment Radio Transmissions | Rel-19 |
| TS 38.104 vj20 | NR Base Station RF Requirements | Rel-19 |
| TS 38.106 vj20 | NR Repeater Radio Transmission and Reception | Rel-19 |
| TS 38.108 vj20 | NTN NR Satellite Access Node RF Requirements | Rel-19 |
| TS 38.113 vj00 | NR Base Station EMC Specification | Rel-19 |
| TS 38.114 vj00 | EMC Requirements for NR Repeaters and NCR | Rel-19 |
| TS 38.115 vj20 | NR Repeater RF Conformance Testing Part 1 | Rel-19 |
| TS 38.124 vj00 | NR UE EMC Requirements | Rel-19 |
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | Rel-19 |
| TS 38.141 vj20 | NR Base Station RF Conformance Testing Part 1 | Rel-19 |
| TS 38.174 vj10 | NR Integrated Access and Backhaul Radio Spec | Rel-19 |
| TS 38.175 vj00 | EMC for NR IAB Nodes | Rel-19 |
| TS 38.176 vj20 | IAB Conformance Testing Specification | Rel-19 |
| TS 38.181 vj10 | NR Satellite Access Node RF Testing | 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 |
| TS 38.755 vj10 | NR FR1 DL Fragmented Carriers Study | Rel-19 |
| TS 38.769 vk00 | Ambient IoT Solutions in NR | Rel-20 |
| TS 38.793 vj00 | Simultaneous Rx/Tx Band Combinations TR | Rel-19 |
| TR 38.815 vf10 | NR Frequency Range 24.25-29.5 GHz Study | Rel-15 |
| TS 38.817 | 3GPP TR 38.817 | Rel-5 |
| TR 38.820 vg10 | NR; 7-24 GHz Frequency Range Study | Rel-16 |
| TS 38.826 vg00 | NR Vehicle UE 2Rx Exception Study | Rel-16 |
| TR 38.828 vg10 | CLI and RIM for NR | Rel-16 |
| TR 38.839 vh00 | Simultaneous Rx/Tx band combinations | Rel-17 |
| TR 38.847 vh20 | NR 47.2-48.2 GHz Frequency Range | Rel-17 |
| TR 38.849 vi50 | Technical Report | Rel-18 |
| TS 38.863 vj10 | NR NTN RF and Co-existence Spec | Rel-19 |
| TR 38.864 vi10 | Technical Report on Network Energy Savings for NR | Rel-18 |
| TR 38.877 vi10 | Technical Report | Rel-18 |
| TR 38.881 vi00 | Technical Report on Lower MSD for Inter-band CA/EN-DC/DC | Rel-18 |
| TS 38.887 vg00 | NR Band n259 Specification (39.5-43.5 GHz) | Rel-16 |
| TR 38.889 vg00 | NR-based access to unlicensed spectrum study | Rel-16 |
| TR 38.894 vi00 | Technical Report | Rel-18 |
| TR 38.921 vj00 | IMT Parameters Study for 6.4-7.1 & 10-10.5 GHz | Rel-19 |
| TR 38.922 vj20 | Study on IMT Parameters for NR in Higher Bands | Rel-19 |
| TR 45.903 vj00 | SAIC Feasibility Study for GSM Networks | Rel-19 |
| TR 45.914 vj00 | MUROS Feasibility Study for Voice Capacity | Rel-19 |
| TS 46.055 vj00 | GSM Enhanced Full Rate Speech Codec Performance | Rel-19 |
| TS 46.085 vj00 | GSM Speech Codec Interoperability Test Report | Rel-19 |
| TS 48.016 vj00 | Gb Interface Network Service Specification | Rel-19 |