Composite IQ Offset (1xEV-DO)

Composite IQ Offset (also called I/Q origin offset) indicates the magnitude of the carrier feedthrough signal. When there is no carrier feedthrough, IQ offset is zero (-infinity dB).

You can select to not include the Composite IQ Offset error in 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. error results with the Include IQ Offset in EVM demodulation property (MeasSetup > 1xEV-DO Demodulation Properties > Advanced tab)

IQ origin offset is easily seen in the constellation diagram, as shown below:

$image\IQoffset_wmf.jpg$

In the above illustration, "x" is the center of the constellation diagram. When "x" occurs at the origin, the IQ offset is zero. When "x" is not at the origin, the IQ offset is the magnitude of the vector (in dB) between "x" and the origin.

The carrier feedthrough shown in the symbol table is computed only at the symbol times (the instant in time when symbols are detected).