What is CPE?
CPE (Common Phase Error) is a measurement of phase noise degradation in OFDM-based systems. It represents the average of the phase noise sequence spanning an OFDM symbol, causing a uniform phase rotation of all subcarriers within that symbol. CPE is the dominant phase noise impairment in 5G NR systems and directly impacts EVM and demodulation performance, particularly at higher frequency bands (FR2/mmWave) where oscillator phase noise is inherently worse.
How Does CPE Work?
In an OFDM system, local oscillator phase noise has two effects: CPE and Inter-Carrier Interference (ICI). CPE is the common (average) phase rotation applied equally to all subcarriers within one OFDM symbol — it shifts the entire constellation by the same angle. This component can be estimated and compensated using phase tracking reference signals (PT-RS), which 5G NR specifically introduced for this purpose. ICI, by contrast, is the residual random component that causes crosstalk between subcarriers and is harder to correct. CPE magnitude increases with oscillator free-running linewidth and OFDM symbol duration.
Use Cases
5G NR receiver design and phase noise compensation, mmWave transceiver performance validation, PT-RS configuration optimization, EVM budget analysis for high-order modulation (256-QAM), and local oscillator specification for 5G base station and UE.
3GPP / Standards Reference
3GPP TS 38.211 (NR physical channels and modulation — PT-RS), 3GPP TS 38.104 (NR BS radio transmission)
Related Terms
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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.
