3GPP RF Conformance: TS 36.521 and 38.521 for LTE and 5G NR
Guide · 3GPP RF Conformance
The TS 36.521 (LTE) and TS 38.521 (5G NR) specifications form the 3GPP single reference for cellular terminal radio conformance. They set the RF thresholds, the test sequences and the application format that all downstream cellular certification schemes adopt: PTCRB in North America, GCF outside North America, and the full set of tier-1 carrier acceptance programmes (AT&T NAFI, Verizon OPC, Deutsche Telekom, NTT Docomo, China Mobile). This page describes the three-part architecture of the TS xx.521 specifications, their relationship with TS xx.523 and TS xx.508, the TX and RX scope, the FR1 versus FR2 split in 5G NR, the architecture of test benches built around a callbox, and the recurring pitfalls observed on early submissions.
A layered 3GPP documentation architecture
Section titled “A layered 3GPP documentation architecture”3GPP does not publish a monolithic UE conformance specification. It is decomposed into five documents that chain together and cross-reference one another. The same architecture is mirrored for LTE (series 36) and for 5G NR (series 38).
| Specification | Short title | Scope | LTE family | NR family |
|---|---|---|---|---|
| TS xx.521-1 | RF | UE RF transmitter and receiver | TS 36.521-1 | TS 38.521-1 (FR1) / TS 38.521-2 (FR2) |
| TS xx.521-2 | RRM | Radio Resource Management, mobility | TS 36.521-2 | TS 38.521-2 (NR RRM) |
| TS xx.521-3 | RF and Demod conditional | Carrier aggregation, MIMO, advanced modes | TS 36.521-3 | TS 38.521-3 |
| TS xx.523 | Signalling | Layer-3 sequences RRC and NAS | TS 36.523 | TS 38.523 |
| TS xx.508 | Application format | Formal test case structure | TS 36.508 | TS 38.508 |
Practical reading: a test case cited in TS 36.521-1 (for instance "Maximum Output Power for QPSK in Band 2") does not stand alone. The lab makes it executable by relying on TS 36.508 for the format, on TS 36.523 for the upstream signalling sequence with the callbox, and possibly on TS 36.521-3 for the aggregation variants. Ignoring this document stack leads to interpreting a test case in isolation and to running a non-compliant test.
TS xx.521-1, the RF core
Section titled “TS xx.521-1, the RF core”TS 36.521-1 and TS 38.521-1 carry the bulk of the radio conformance of a cellular terminal. The content splits into two blocks: transmitter characteristics and receiver characteristics.
Transmitter characteristics
Section titled “Transmitter characteristics”Each test is measured per band, per channel bandwidth, per duplex mode (FDD or TDD) and per modulation configuration. The matrix expands quickly when the product declares multiple bands.
- UE Maximum Output Power. Maximum transmit power by UE class, within the tolerance specified by TS 36.521-1 or TS 38.521-1. The threshold depends on the power class and on the band.
- EVM (Error Vector Magnitude). Measures modulation quality. Expressed as a percentage, capped per modulation (QPSK, 16-QAM, 64-QAM, 256-QAM). Excessive EVM points to a saturated PA or to weak RF filtering.
- ACLR (Adjacent Channel Leakage Ratio). Measures leakage into adjacent channels. Critical for multi-band coexistence and for inter-operator coexistence.
- OBW (Occupied Bandwidth). Measures the bandwidth effectively occupied by the signal, to remain within a regulatory width.
- Spectrum Emission Mask (SEM). Out-of-channel emission mask to respect point by point across frequency.
- Spurious Emissions. Out-of-band parasitic emissions and harmonics.
Receiver characteristics
Section titled “Receiver characteristics”- Reference Sensitivity (REFSENS). Reference receiver sensitivity, the dBm floor that must be met to reach a target block error rate (BLER). It is the most familiar and the most watched receiver test in design.
- ACS (Adjacent Channel Selectivity). Ability to receive a wanted signal in the presence of an interferer on the adjacent channel.
- Blocking (in-band, out-of-band, narrow-band). Robustness against a strong off-channel interfering signal.
- Intermodulation. Response to two simultaneous interferers that generate an intermodulation product inside the wanted band.
- Spurious Response. Measurement of the receiver's parasitic response lines.
- In-band Selectivity. Selectivity inside the active band.
Each receiver test is run at a target BLER (typically 5% or 10% depending on the case), at the minimum required input level, with a characterised interfering signal. The bench uses an interference signal generator in addition to the callbox.
TS xx.521-2, RRM
Section titled “TS xx.521-2, RRM”TS 36.521-2 and TS 38.521-2 verify the Radio Resource Management of the UE: what the terminal does as the network evolves around it. The tests do not measure a raw RF quantity, but a protocol behaviour with a reaction-time requirement.
- Cell selection and reselection. Initial cell choice, switch to another cell in idle mode when signal-to-noise dictates.
- Handover. Connected-mode switch to a neighbouring cell, intra-frequency, inter-frequency, inter-RAT (for instance LTE to NR), inter-band.
- Power Control. UE transmit power adjustment under network commands, with specified accuracy and dynamic range.
- Discontinuous Reception (DRX). Behaviour under discontinuous listening cycles, which drives IoT product battery life in stable coverage.
- Timing Advance. UE transmit timing adjustment in TDD to align bursts within the frame.
RRM campaign duration in the lab remains a heavy line item: multi-cell handover sequences, inter-RAT transitions and assisted-mobility tests demand many bench hours per band combination. The RRM part is also where many cellular IoT products diverge from smartphone-class behaviour: a tracker or a meter spends most of its life in idle DRX, so its cell reselection logic and PSM (Power Saving Mode) interaction are tested more aggressively than the corresponding mobility cases on a handset. A product whose firmware shortcuts the DRX cycle to save current may pass TS xx.521-1 cleanly and fail TS xx.521-2.
TS xx.521-3, conditional and advanced modes
Section titled “TS xx.521-3, conditional and advanced modes”TS 36.521-3 and TS 38.521-3 isolate the conditional tests: they apply only if the product declares the relevant feature. The part is heavy because the combinatorial diversity explodes in 4G LTE-Advanced and even more in 5G NR.
- Carrier Aggregation (CA). Aggregation of several carriers, intra-band contiguous, intra-band non-contiguous, inter-band. Each declared band combo opens a subset of cases.
- MIMO. Multiple-Input Multiple-Output, 2x2, 4x4, sometimes 8x8 in NR. Demodulation conditional on the antenna configuration.
- Higher-order modulation. 256-QAM, 1024-QAM on the downlink, conditional on declared UE capability.
- EN-DC (E-UTRA NR Dual Connectivity). Simultaneous combination of anchor LTE and NR for 5G NSA. Specific test cases on simultaneous LTE plus NR transmission coexistence on the same UE.
- Demodulation performance. Demodulation performance under degraded conditions (fading channels), with minimum throughput requirements.
The PTCRB or GCF test plan in scope only runs the conditional tests declared by the manufacturer through the capability matrix. Over-declaring drives unnecessary test volume; under-declaring causes a later audit to fail.
TS xx.523 and TS xx.508, the execution fabric
Section titled “TS xx.523 and TS xx.508, the execution fabric”TS 36.523 and TS 38.523 contain the signalling of the test cases, i.e. the message sequences exchanged between the UE and the callbox-emulated network: RRC (Radio Resource Control) messages, NAS (Non-Access Stratum) messages, broadcast system parameters, initial attaches. Each case in TS xx.521-1 or TS xx.521-2 references an upstream signalling procedure defined in TS xx.523.
TS 36.508 and TS 38.508 define the application format of the test cases, i.e. the formal structure used by all other documents. A lab that automates the tests relies on TS xx.508 to write the callbox driver consistently, and TS xx.508 also serves as the reference to validate that a test automation engine (TTCN-3 or proprietary tooling) faithfully reproduces the 3GPP case.
Without TS xx.508 and TS xx.523, TS xx.521-1 tests are not executable, and reports are not traceable to a precise 3GPP case.
4G LTE and 5G NR, two parallel families
Section titled “4G LTE and 5G NR, two parallel families”The document structure is identical, the RF content differs. Below is the correspondence grid used by PTCRB and GCF test plans to cite the references.
| Generation | Frequency range | Main RF specification | Dominant mode |
|---|---|---|---|
| LTE (4G) | Bands 1 to ~88 (FDD), 33 to ~53 (TDD) | 3GPP TS 36.521-1 | Conducted (cable), OTA if UE without port |
| 5G NR FR1 | n1 to ~n107 sub-6 GHz | 3GPP TS 38.521-1 | Conducted, OTA in integrated design |
| 5G NR FR2 | n257, n258, n260, n261, n262 mmWave | 3GPP TS 38.521-2 | OTA mandatory |
| 5G NR NSA | LTE anchor + NR | Combined TS 36.521-1 + TS 38.521-1 | Dedicated EN-DC cases |
| GSM (2G) | 850, 900, 1800, 1900 MHz | TS 51.010 | In sunset, withdrawn from many test plans |
For a 5G NSA product, conformance is built by citing both families of specifications, because 5G NSA relies on an active LTE anchor. For a pure 5G SA product, only the 38.521 family is mobilised, but the reality of the market in 2026 remains largely NSA.
FR1 and FR2, two measurement methods
Section titled “FR1 and FR2, two measurement methods”5G NR introduces a methodological split with strong instrumentation impact.
FR1 (Frequency Range 1, sub-6 GHz). Classical methodology inherited from LTE. Conducted (cable) measurement when the UE exposes an antenna port (industrial cellular modules), OTA measurement in an anechoic chamber otherwise (products with integrated antennas, compact terminals).
FR2 (Frequency Range 2, mmWave above 24 GHz). TS 38.521-2 mandates OTA measurement exclusively, because mmWave antennas are integrated within the RFIC module and no realistically accessible external antenna port exists at those frequencies. This requires a dedicated OTA chamber, precise UE angular positioning, mmWave RF calibration, and a significant instrument budget. The OTA FR2 fleet remains small in Europe and North America, which becomes a calendar driver as soon as an mmWave product enters the scope.
A 5G FR1-only product avoids this constraint. An FR1 plus FR2 product cumulates both instrument types and both measurement campaigns.
Architecture of a TS xx.521-1 test bench
Section titled “Architecture of a TS xx.521-1 test bench”Whatever the target certification scheme, the TS xx.521-1 bench shares the same architecture: a network emulator (callbox), an RF coupling device with the UE, measurement instruments and an automation controller.
| Element | Role | Typical platforms |
|---|---|---|
| Signalling callbox | Emulates eNB (LTE) and gNB (NR), runs RRC, NAS, attach, scheduling | Anritsu MT8000A, R&S CMX500, Keysight UXM 5G |
| RF link | Couples UE to callbox in conducted or OTA | Calibrated RF cables or CTIA / 3GPP OTA chamber |
| Interferer generator | Provides interfering signals for ACS, blocking, intermodulation | Dedicated vector generators |
| Spectrum analyser | Measures ACLR, SEM, spurious | RF analysers covering the band of interest (sub-6 or mmWave) |
| OTA chamber | Measures TRP, TIS, beam, FR2 | 3GPP or CTIA anechoic chambers |
| Test controller | Sequences TS xx.521-1 cases automatically, compliant with TS xx.508 | Callbox software + TTCN-3 automation |
The signalling callbox is the central element. Without signalling capability, the UE cannot be driven into the network state required by each test case (RRC_CONNECTED in a given configuration). Spectrum analysers alone are not sufficient and cannot certify TS xx.521-1.
Conducted (cable) versus OTA
Section titled “Conducted (cable) versus OTA”Two RF coupling configurations coexist.
Conducted (cable). The UE is connected to the callbox by an RF cable plugged into its antenna port. Preferred method when an accessible antenna port exists (industrial modules, debug evaluations). Provides reproducible results with minimal measurement uncertainty.
OTA (Over-The-Air). The UE is placed in an anechoic chamber, the integrated antenna is used as-is. Mandatory for products without an external antenna port and for FR2 mmWave. More realistic measurement with respect to user experience, but higher measurement uncertainty and stringent chamber calibration requirement.
PTCRB and GCF schemes accept both methods within the framework defined by TS 36.521-1 and TS 38.521-1. A cellular IoT product without an accessible antenna port (compact gateway, tracker, medical terminal) will be tested in OTA, with chamber options matched to the UE class.
CA and EN-DC, the matrix multipliers
Section titled “CA and EN-DC, the matrix multipliers”Carrier Aggregation and EN-DC are the main drivers of test matrix inflation.
Carrier Aggregation. Each band combination declares a subset of cases. A "B2+B4" declaration in LTE opens tests that "B2" alone and "B4" alone do not include. The 3GPP band combination tables list hundreds of options for LTE and several hundred for NR.
EN-DC. For 5G NSA, each "LTE-band + NR-band" combination forms an EN-DC combo declared separately, with its own test cases in TS 36.521-1 (anchor LTE side) and TS 38.521-1 (NR side). A product declaring LTE B2, B4, B5, B12, B30, B66 plus NR n5, n66, n77 expands the matrix very quickly.
Declaration scope is therefore a structural project decision, with material impact on campaign calendar and budget. See PTCRB tests for the breakdown of test families inside a PTCRB test plan.
Where PTCRB and GCF layer on top
Section titled “Where PTCRB and GCF layer on top”PTCRB and GCF do not rewrite 3GPP. They rely on TS 36.521 and TS 38.521 as the technical reference, and add on top a governance (PVG on the PTCRB side, CAG on the GCF side), a list of priority bands, a list of recognised labs, a certificate format (EPC on the PTCRB side, declaration on the GCF side) and administrative sequences.
| Layer | Technical reference | Governance | Dominant geography |
|---|---|---|---|
| 3GPP | TS 36.521, TS 38.521, TS xx.523, TS xx.508 | 3GPP TSG RAN WG5 | Worldwide (specifications) |
| PTCRB | Test plans based on TS 36.521 and TS 38.521 | PTCRB Validation Group | North America |
| GCF | Test plans based on TS 36.521 and TS 38.521 | Certification Agreement Group | Europe, Asia, MENA |
| Carrier acceptance | PTCRB / GCF superset plus network interop | Operator (AT&T NAFI, etc.) | Operator's network |
Carrier schemes (AT&T NAFI, Verizon OPC, Deutsche Telekom IoT, NTT Docomo, China Mobile / Telecom / Unicom) rest on PTCRB or GCF as the baseline and add network interoperability tests (throughput, attach behaviour, IMS, eSIM). See PTCRB test plans for the detailed list of PTCRB test plans and their 3GPP mapping.
The 3GPP Release question
Section titled “The 3GPP Release question”A TS 36.521 or TS 38.521 specification has no meaning without its version number, which corresponds to a 3GPP Release.
- Release 15. First NR Release (NSA then SA). Reference for the first commercial 5G deployments.
- Release 16. Additions for NR-Light, V2X, positioning, NR-U (NR on unlicensed spectrum).
- Release 17. RedCap (Reduced Capability), NR-Light for industrial IoT and wearables, extended FR2 additions.
- Release 18. First 5G-Advanced Release, improved MIMO, AI/ML in RAN.
A PTCRB or GCF test plan cites the Release and version of TS xx.521 it takes as reference. The same band may have an adjusted RF threshold, a test case added, modified or removed between two Releases. Version tracking is non-negotiable: a "compliant with TS 38.521-1" file without version may be rejected by a lab or by an operator. See PTCRB pitfalls for the list of version errors observed on submission.
Common pitfalls in TS xx.521
Section titled “Common pitfalls in TS xx.521”Spec without cited version. The file mentions "TS 38.521-1" without version number or Release. For a real campaign, the version number (for instance V17.x.y) must be cited. Without it, the lab picks, which triggers a validation loop at audit.
Capability under-declaration. The manufacturer omits an EN-DC band combination or a CA combination actually supported by the module. The product works in deployment, but a later operator audit reveals the missing test case and the product is removed from the active IMEI list.
FR1 versus FR2 confusion. A product declared as 5G NR FR1 only is tested with TS 38.521-1, without resorting to TS 38.521-2. If the module is in fact FR1 plus FR2 (which happens with chipset derivatives), part of the RF content is not covered.
REFSENS at the floor. Reference sensitivity sits right at the threshold. Any thermal drift, antenna aging or production variation drags a portion of products below the limit, with a production failure rate that grows. Good design targets a comfortable margin on REFSENS rather than equality with the threshold.
ACLR crushed by an aggressive PA. PA (Power Amplifier) optimisation to reach maximum power compresses the signal and violates the ACLR threshold. Typical symptom of an undersized PA, usually recovered through PA back-off at the cost of reduced useful power.
Bench without signalling. Equipped with a spectrum analyser alone, the lab measures spurious but cannot execute a TS 36.521-1 test case in full. The real scope requires a signalling callbox (Anritsu, R&S, Keysight). Useful as pre-tests, not valid for PTCRB or GCF.
Wrong-class OTA chamber. An FR2 mmWave product tested in an FR1 sub-6 GHz chamber: unacceptable measurement uncertainty, calibration outside range, invalid results. The OTA chamber must cover the exact frequency range of the product.
Reference to TS xx.521-1 without TS xx.508 / TS xx.523. The report cites only TS xx.521-1 with no reference to TS xx.508 or TS xx.523, hence with no traceability of the execution sequence. A serious audit raises the gap.
Version tracking missing in lifecycle. The product passed TS 38.521-1 V16.x.y, then a module stack update introduces behaviour modified by TS 38.521-1 V17.x.y. Without a re-evaluation plan, the product drifts from the reference without triggering re-certification.
Connection with other schemes
Section titled “Connection with other schemes”3GPP TS 36.521 and TS 38.521 serve as the baseline for the three cellular certification families a cellular IoT product encounters:
- PTCRB, in North America, via PTCRB scope and PTCRB tests.
- GCF, outside North America, which shares the 3GPP technical base.
- Carrier acceptance: AT&T NAFI, Verizon OPC, Deutsche Telekom IoT, China Mobile / Telecom / Unicom, NTT Docomo, etc.
The regularity of the architecture (five parts TS xx.521-1, TS xx.521-2, TS xx.521-3, TS xx.523, TS xx.508) makes transposition between 4G LTE and 5G NR FR1 / FR2 families straightforward. For vocabulary (UE, eNB, gNB, RRC, NAS, RRM, EVM, ACLR, REFSENS, CA, EN-DC, FR1, FR2, NSA, SA), see the spilma glossary.
Sources & references
- 3GPP TS 36.521-1, LTE UE conformance specification, Part 1: RF , 3GPP www.3gpp.org/dynareport/36521-1.htm
- 3GPP TS 38.521-1, NR UE conformance specification, FR1 standalone , 3GPP www.3gpp.org/dynareport/38521-1.htm
- PTCRB Certification Program , PTCRB www.ptcrb.com/
- GCF, Global Certification Forum , GCF www.globalcertificationforum.org/
- 3GPP Specifications by series , 3GPP www.3gpp.org/specifications-technologies/specifications-by-series
- 3GPP TS 38.521-2, NR UE conformance specification, FR2 standalone , 3GPP www.3gpp.org/dynareport/38521-2.htm