What is TT?
TT (Test Tolerance) represents the allowable margin of error applied to 3GPP conformance test limits to account for measurement uncertainty in the test system. TT ensures that pass/fail decisions are fair — a device is not failed simply because the test equipment introduced a measurement error that pushed the result beyond the specification limit. TT values are defined by 3GPP for each conformance test based on a detailed analysis of the test system’s measurement uncertainty budget.
How Does TT Work?
3GPP derives TT values through a rigorous process: first, the maximum permissible measurement uncertainty (Test System Uncertainty, TSU) is defined for each test. Then, the TT is calculated such that the probability of a false fail (a good device incorrectly failing) and false pass (a bad device incorrectly passing) are balanced. For most tests, the TT expands the specification limit by an amount related to the TSU. For example, if the TX power specification is +/- 2 dB and the TT is 0.7 dB, the conformance test limits become +2.7 dB / -2.7 dB. Test laboratories must demonstrate that their measurement uncertainty is within the TSU to use the standard TT values; otherwise, they must apply their own uncertainty and may have tighter effective limits.
Use Cases
5G NR UE and base station conformance testing, test laboratory accreditation (ISO 17025), production test guardbanding, measurement system qualification, and regulatory compliance verification.
3GPP / Standards Reference
3GPP TS 38.521 (NR UE conformance — test tolerances), 3GPP TR 38.903 (Derivation of test tolerances for NR), 3GPP TS 38.141 (NR BS conformance — test tolerances)
Related Terms
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