IQ Meas Time and IQ Ref Time (Flex Frame)

There are two types of traces in the Trace > Data > Demod menu that display component carrier data: CCn (component carrier is fixed), and Display CC (component carrier is dynamically selected using the Carrier Aggregation > Selected CC for Trace Display parameter). See About Demod Per-Carrier Trace Types for more information.

The IQ Meas Time and IQ Ref Time trace data are the time data results of Flex Frame demodulation. IQ Meas Time is the data result for the measured input signal. IQ Ref Time trace data is the data result that would be derived from an ideal input signal (reference signal).

Concepts

The Flex Frame demodulator produces two signals: I/Q Measured and I/Q Reference.

I-Q measured signal

The IQ measured signal is the result of resampling the data to an integer number of points per symbol and applying carrier/symbol locking, IQ origin offset and amplitude droop compensation, system gain normalization, and filtering to the input signal. The filtering is user-selectable.

I-Q reference signal

A powerful analysis technique involves comparing a demodulated signal with an ideal signal generated from detected 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 a reference filter selected by the user. The resultant IQ reference can be overlaid or compared side-by-side with the IQ measured signal.

The reference filter can be selected independently from the measured signal (although the alpha/BT Bandwidth Time Product is the same for both filters). Therefore, different filters can be applied to the measured and reference signals to accommodate special test requirements.

Filtering

Different filters can be selected for the I/Q measured and I/Q reference signals. To do this, display the Flex Frame Properties dialog box and choose a filter under Measurement Filter for the I/Q measured signal; choose a filter under Reference Filter for the I/Q reference signal.

Compensation

All demodulation schemes are performed with carrier lock, symbol lock, and filtering (if filtering is selected). In addition, all schemes compensate for I/Q origin offset and burst amplitude-droop.

Time-Domain Displays

The VSA's digital demodulator produces time-domain data. If IQ Meas Time is selected, the VSA displays the I/Q measured signal in the time domain. Likewise, if IQ Ref Time, the VSA displays 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).

The following parameters affect how the VSA displays the I/Q measured and I/Q reference signals:

Result Length determines the number of symbols, which determines the length of the displayed trace.
Points per Symbol determines the number of points between symbols. Increase Points per Symbol to increase the resolution; decrease it to decrease the resolution.

Marker Coupling

When marker coupling is used, markers on applicable Demod traces (e.g., Err Vect Time, IQ Meas Time, IQ Ref Time, Mag Error, Phase Error) will couple to the corresponding point on the Time, Search Time and Raw Main Time traces. For Demod traces, frame start (symbol 0) = 0 sec on the x-axis.