Despread IQ Meas Time and IQ Ref Time (W-CDMA(3GPP)/HSPA)
When Demodulation is enabled, the and traces are the demodulated time data results, sampled at the chip times, for the specified Code Channel (Code Channel) and code layer (Spread Code Length). is the data results for the measured input signal. trace data is the data results that would be derived from an ideal input signal (reference signal).
Concepts
The VSA's demodulator produces two signals: I/Q Measured and I/Q Reference.
IQ measured signal
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 and burst amplitude droop compensation, filtering and system gain normalization to the incoming signal.
IQ reference 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.
The Digital Demodulation topic includes a block diagram that shows how I/Q measured and I/Q reference data are generated.
Compensation
Demodulation is performed with carrier lock and chip lock. In addition, the VSA compensates for I/Q origin offset and burst amplitude droop.
Time Domain Displays
The VSA's demodulator produces time domain data. Select and the VSA shows the I/Q measured signal in the time domain. Likewise, select and the VSA shows the I/Q reference signal in the time domain.
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 Trace Formats (Digital Demodulation)).
If normalization is off, the VSA shows the instantaneous magnitude. If normalization is on, the VSA scales the IQ measured and IQ reference traces to map them onto the unit circle, which yields a unitless y-axis.
For 16-QAM Quadrature Amplitude Modulation Code Channels (HSPA HS-PDSCH High Speed Physical Downlink Shared Channel signals), if normalization is on, the VSA scales the channel IQ measured and channel IQ reference traces so that the RMS level is one.
For further details about normalization, see Normalize IQ Traces.
Parameter Interaction
The following parameters affect how the VSA shows the I/Q measured and I/Q reference signals:
- Result Length determines the number of slots in the measurement.
- Measurement Interval and Measurement Offset determine which slots will be displayed
How to Make a HSPA+MIMO Despread (x) Trace Data measurement
To learn how to use the Despread Traces parameter to make a Despread (x) Channel Trace Data measurement, see HSPA+ MIMO Overview - Despread (x) Trace Data.
See Also
