Gain Imb (TD-SCDMA)
Gain Imb (Gain Imbalance) compares the gain of the I signal with the gain of the Q signal, as follows:
The effects of Gain Imbalance are best viewed in constellation diagrams, where the width of the constellation diagram is different than its height.
Because Gain Imbalance detection requires absolute phase information, this result is questionable when the DwPTS phase coding is not known, i.e. displayed as "unknown" in the . Because uplink traffic timeslots are not phase related to DwPTS, this applies at all times in the uplink case.
Detection of the DwPTS Phase Coding, and hence accuracy of Gain Imbalance, depends on low phase noise input data. Because of this, it may be necessary to lock frequency references, between the input hardware and the device under test, in order to achieve good results for these measurements.
See Also
IQ Gain Imbalance and Quadrature Skew Parameter Interaction
