What is OQAM?
OQAM (Offset QAM) is a digital modulation technique that staggers the in-phase (I) and quadrature (Q) components of a QAM signal by half a symbol period. This offset eliminates 180° phase transitions in the constellation, reducing the peak-to-average power ratio (PAPR) of the signal and enabling compatibility with per-subcarrier filtering in multicarrier systems like FBMC. OQAM is fundamental to FBMC-OQAM, which was studied as an alternative waveform for 5G.
How Does OQAM Work?
In standard QAM, the I and Q components transition simultaneously, creating large amplitude excursions when both components change at the same time (e.g., a transition through the constellation’s origin). In OQAM, the Q component is delayed by half a symbol period relative to the I component, ensuring that only one component changes at any given transition. This produces a smoother envelope with lower PAPR. In FBMC-OQAM, each subcarrier carries real-valued OQAM symbols rather than complex QAM symbols, with the filtering applied per-subcarrier. The staggering ensures that adjacent subcarrier signals remain orthogonal in the real field despite the use of non-orthogonal prototype filters.
Use Cases
FBMC-based multicarrier systems, cognitive radio and dynamic spectrum access, low-PAPR transmission for power-efficient devices, research into 6G waveform candidates, and satellite communication systems requiring spectral efficiency.
3GPP / Standards Reference
3GPP TR 38.802 (NR waveform study), IEEE literature on FBMC-OQAM, relevant ITU-R studies on waveform alternatives
Related Terms
FBMC | QAM | OFDM | PAPR | CP-OFDM
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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.
