Comp IQ Meas Time and IQ Ref Time (TD-SCDMA)
When TD-SCDMA Demodulation is enabled, the Comp and Comp trace data are the time data results of TD-SCDMA demodulation for the composite signal. Comp is the data results for the measured input signal. Comp trace data is the data results that would be derived from an ideal input signal (reference signal).
IQ measured and IQ reference signals
The VSA's demodulator produces two signals: I/Q Measured and I/Q Reference.
The IQ measured signal is the result of resampling the data to one point per chip and applying carrier locking, symbol locking, IQ origin offset compensation, filtering and system gain normalization to the incoming signal.
IQ reference signal is the ideal signal that the VSA generates from the IQ measured signal demodulated data bits. The VSA detects bits from the measured IQ signal and reconstructs a sequence of ideal I and Q states. These are then treated as ideal impulses and are baseband filtered according to the reference filter and added together to form the IQ reference signal. The resultant IQ reference signal is then used compare and analyze against the IQ measured signal.
Online help for Digital Demodulation includes a block diagram that shows how I/Q measured and I/Q reference data are generated.
Time-Domain Displays
The VSA's demodulator produces time-domain data. If Comp is selected, the VSA shows the composite IQ measured signal in the time domain. Likewise, if Comp is selected, the VSA shows the composite IQ reference signal in the time domain.
The Midamble field of the traffic timeslot is included in the data analysis. The shading in the trace display indicates the location of the midamble. The demodulation algorithm cannot deal with more than one midamble shift (k). If more than one midamble shift exists, the data is invalid and an error message appears.
For filter settling reasons, 4 chips at the start and end of the timeslot are ignored, resulting in data results that are 8 chips shorter than the full traffic timeslot length (not including the GP).
The data can be displayed in a variety of trace data formats, including I-Q, Constellation, Q-Eye, I-Eye, and Trellis-Eye formats (see Selecting a Trace Format)).
If normalization is OFF, the VSA shows the instantaneous magnitude. If normalization is ON, the VSA scales the composite IQ measured and composite IQ reference traces so that the RMS level is one, which produces a unitless y-axis.
For further details about normalization, see Normalize IQ Traces.
Composite Ref Time Display
The 89600 TD-SCDMA demodulation software uses an advanced multi-parameter estimator to synthesize the reference waveform. This algorithm adjusts reference code domain timing and phase dynamically. As a result, the magnitude of the Composite Reference Time waveform is not absolutely flat. If the y-axis annotation is LinMag, the trace will not be perfectly flat and the marker readout Chip Magnitude values will not be identical.
See Also
