Understanding and Improving Error Vector Magnitude (EVM) with IQ-NC and ccEVM Technologies

Error Vector Magnitude (EVM) is a critical indicator of signal quality in modern digital communication systems. As technologies evolve towards higher bandwidths and more complex modulation schemes, the accuracy of EVM measurements becomes increasingly challenging due to the limitations of measurement equipment, particularly the noise introduced by the receiver. To address these challenges, advanced techniques like Cross-Correlated EVM (ccEVM) and IQ Noise Correction (IQ-NC) have been developed. ccEVM employs two or more receivers to simultaneously capture the signal under test. By cross-correlating the error vectors from these receivers, the uncorrelated noise components are canceled out, providing a more accurate assessment of the DUT's intrinsic EVM performance. This technique is particularly beneficial for characterizing high-performance devices with very low error, as it effectively isolates DUT’s impairments from the noise of the measurement system.

IQ-NC utilizes the coherent averaging of repetitive waveforms with a single receiver to reduce random noise, thereby improving the EVM floor. It is a valuable tool when dealing with low-power signals or high-order modulations where receiver noise can significantly impact the measurement. Keysight Technologies offers both IQ-NC and ccEVM capabilities within its PathWave Vector Signal Analysis (VSA) software and X-Series Measurement Applications (X-apps), supported by a range of high-performance signal analyzers, oscilliscopes and modular instruments. These advanced techniques empower engineers to overcome the limitations of traditional EVM measurements, enabling more accurate and reliable characterization of next-generation wireless communication systems like 5G NR/5G-Advanced, WLAN, Digital Demod, Custom OFDM, DVB-S2/S2X ultimately facilitating the development and deployment of higher-quality wireless technologies.