Compensate IQ Mismatch (802.11n/ac/ax/be)
enables demodulation measurements to be made that exclude the IQ impairments (IQ Gain Imbalance, IQ Quadrature Error, and IQ Time Skew errors) from the EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. and RCE Relative Constellation Error is the RMS level of the Error Vector Magnitude, averaged over all subcarriers and all detected OFDM symbols. measurement results. The I/Q Compensation algorithm uses the measured Gain Imb, Quad Err, and Time Skew error estimates shown in the Syms/Errs Summary Table. This feature is useful for determining what the EVM/RCE metric results would be for a DUT Device under Test: An acronym used to describe some type of electrical apparatus connected to test instrumentation. The apparatus can range from a single component to a complex subsystem such as a mobile phone, base station or MSC. in which the IQ mismatch impairments are the dominant factor in EVM/RCE degradation, but could be removed by a later calibration process or redesign.
When IQ compensation is disabled, the IQ impairments shown in the summary table are estimated using the SIG subfields. When IQ compensation is enabled, the IQ impairments are estimated using the Data subcarriers.
IQ impairments are removed from the EVM/RCE metrics and demodulation measurement results. IQ impairments are estimated using the Data subcarriers.
(Default) IQ impairments are not removed from the EVM/RCE metrics and demodulation measurement results. IQ impairments shown in the summary table are estimated using the SIG subfields.
Using the Compensate I/Q mismatch feature
The performance and effectiveness of the feature is completely determined by the accuracy of the VSA's measured I/Q mismatch impairment estimates. The accuracy of the I/Q error estimates may be degraded in the following measurement situations:
- The VSA is using an incorrect modulation format to demodulate/analyze the signal (This problem may be due to large signal impairments causing the VSA Automatic Data Subcarrier Modulation Format feature to wrongly detect the modulation format).
- There is not enough subcarriers or symbols included in the measurement result length (This problem may be indicated with "***" characters shown as the Summary Table data result values).
- The DUT Impairments are so large that the VSA cannot correctly demodulate the signal.
See Also
