IQ Meas Time (GSM/EDGE/EDGE Evolution)

IQ Meas Time shows the time data results for the measured input signal.

Concepts

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

Measured I/Q signal

The measured IQ 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 optional amplitude droop compensation, system gain normalization, and filtering to the input signal.

Reference I/Q 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 Reference I/Q can be overlaid or compared side-by-side with the Measured I/Q signal.

Filtering

The GSM/EDGE/EDGE Evolution demodulator selects the appropriate filters to use depending on the burst format.

A wide or narrow pulse shape filter for HSR bursts can be specified as well.

Compensation

Compensation removes the effects of an error on the Measured I/Q signal.

All demodulation schemes are performed with carrier lock, symbol lock, and filtering. In addition, all schemes compensate for IQ origin offset and burst amplitude-droop.

Time-Domain Displays

The demodulator produces time-domain data. IQ Meas Time shows the Measured I/Q signal in the time domain. Likewise, IQ Ref Time shows the IQ reference signal in the time domain.

The time 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)).

The following parameters affect how the VSA displays the data in the IQ Meas Time and IQ Ref Time:

IQ Constellation Type: determines whether IQ time data is filtered and derotated before being displayed.
Normalize IQ Traces: When Normalize IQ Traces is cleared, the VSA displays the absolute magnitude. When Normalize IQ Traces is selected, the VSA scales the IQ data onto the unit circle, which yields a unitless y-axis.

Unlike Digital Demod, the IQ traces for the GSM/EDGE/EDGE Evolution demodulator are always displayed with one point per symbol, except for GMSK Gaussian Minimum Shift Keying, which is displayed with 10 points per symbol.