Compensate I/Q Mismatch (802.16 OFDMA)

Menu Path: MeasSetup > IEEE 802.16 OFDMA Demod Properties > Advanced tab > Compensation

Default: Cleared (See OFDMA Standard Presets Table)

Compensate I/Q Mismatch removes IQ impairments, including IQ Gain Imbalance, IQ Quadrature Error, and IQ Timing 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. metrics and demodulation measurement results. The I/Q Compensation algorithm uses the measured Gain Imb, Quad Err, and Timing Skew error estimates shown in Syms/Err 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.

Cleared:  IQ impairments are not removed from the EVM/RCE metrics and demodulation measurement results.

Selected:  IQ impairments are removed from the EVM/RCE metrics and demodulation measurement results.

The performance and effectiveness of the Compensate I/Q Mismatch feature is completely determined by the accuracy of the VSAs measured I/Q mismatch impairment estimates.

NOTE:

When "Compensate IQ mismatch" (Advanced demod property) is enabled, Data-and-Pilot aided channel estimation method will be used, regardless of the selected “Equalizer Training” method.

Using Compensate I/Q Mismatch

The performance and effectiveness of Compensate I/Q Mismatchis completely determined by the accuracy of the VSAs measured I/Q mismatch impairment estimates. The accuracy of the I/Q error estimates may be degraded in the following measurement situations:

  1. The VSA is using an incorrect modulation format to demodulate/analyze the signal. (This problem may be due to large signal impairments causing the Data Tone Modulation feature to wrongly detect the modulation format.)
  2. 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.)
  3. The DUT Impairments are so large that the VSA cannot correctly demodulate the signal.
  4. Composite IQ Mismatchrequires generating a valid reference signal for the entire measurement interval. If any portion of the zone geometry is not interpreted accurately, the compensation algorithm will not work correctly. The following cases could cause inaccurate compensation of IQ mismatch:
    • Active Data bursts incorrectly specified as inactive in a Manual Definition Source or Map file. If data bursts are present in the signal, but marked inactive in the zone definition, this will lead to incorrect IQ mismatch compensation.
    •  Incorrect or incomplete DLMAP decoding (when using Downlink Auto-detect Definition mode). If portions of the zone are not fully defined in the decoded DLMAP, but are present in the signal, this will lead to incorrect IQ mismatch compensation.

Example: Effects of Large IQ Gain Imbalance Impariment

The table below shows the difference in the maximum allowable measured Gain Imbalance impairment before the data results become inaccurate for the Auto and Manual Data Tone Modulation modes of operation. This example uses a Downlink signal in which the major contributor to signal degradation is due to IQ mismatch impairments.


FCH DL-MAP downlink map: A MAC message that defines burst start time for both time division multiplex and time division multiple access (TDMA) by a subscriber station (SS) on the downlink. Burst format 		Auto
Data Tone Modulation
(IQ Gain Imbalance)

Manual
Data Tone Modulation

(IQ Gain Imbalance)
2 sym QPSK Quadrature phase shift keying 1.5 dB* 8 dB*
10 sym QPSK 1.5 dB* 8 dB*
10 sym 16QAM 1.6 dB* 3 dB*
10 sym 64QAM n/a 1.2 dB*

Legend: * Maximum measured IQ Gain Imbalance to insure accurate data results.

See Also

Advanced Tab (802.16 OFDMA)

Data Tone Modulation (802.16 OFDMA)