What is SEM?
SEM (Spectrum Emission Mask) is a regulatory and standards-defined limit on the maximum permissible out-of-channel RF emissions from a transmitter, specified as a function of frequency offset from the assigned channel. SEM measurements ensure that a 5G NR transmitter does not radiate excessive energy outside its allocated bandwidth, protecting adjacent channels and other systems from interference. SEM compliance is mandatory for both base station and UE type approval.
How Does SEM Work?
SEM defines a maximum power spectral density envelope at various frequency offsets from the channel edge. The transmitter’s actual emissions must fall below this mask at every point. The measurement is performed using a spectrum analyser or signal analyser that captures the transmitted signal’s power spectrum and compares it against the defined mask. 3GPP defines SEM requirements in TS 38.104 (base stations) and TS 38.101 (UE), with the mask shape depending on channel bandwidth, frequency band, and device class. SEM is complementary to ACLR — while ACLR provides a single-number figure for the adjacent channel, SEM provides a frequency-dependent emissions profile. Transmitters that meet SEM requirements generally also meet ACLR requirements, but both are tested independently.
Use Cases
5G NR transmitter conformance testing, regulatory spectrum emission compliance, RF filter design specification, multi-operator coexistence analysis, and spectrum sharing interference assessment.
3GPP / Standards Reference
3GPP TS 38.104 (NR BS radio — SEM), 3GPP TS 38.101 (NR UE radio — SEM), ITU-R SM.329 (Spurious emissions)
Related Terms
ACLR | ACP | OBW | EVM | Harmonic
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
