IQ Ref Time (802.11b/g DSSS/CCK/PBCC)

Menu Path: Trace > Data > Channel X > IQ Ref Time where X is the selected input channel.

When 802.11b/g DSSS Direct sequence spread spectrum. The data transmission scheme (sometimes referred to as a "'modulation" scheme) used in 802.11b WLANs. DSSS uses a radio transmitter operating at a fixed centre frequency, but using a relatively broad range of frequencies, to spread data transmissions over a fixed range of the frequency band. 802.11a and 802.11g (when not operating in 802.11b mode) use Orthogonal Frequency Division Multiplexing (OFDM)./CCK complementary code keying/PBCC packet binary convolutional code Demodulation is enabled, the IQ Ref Time trace is the demodulated time data results sampled at the chip times. This topic provides the following information:

• I-Q Ref Time trace data description

• Compensation information

• Time-Domain Trace Data Display information

• Parameter Interaction information

I-Q Ref Time

This is reference time data generated by the VSA from data acquired from the measured signal. This is an ideal representation of the measured input signal (IQ Meas Time). The resultant IQ reference signal is used for computing data analysis results and can be viewed simultaneously with the IQ measured signal for data comparisons.

Compensation

I/Q origin offset and burst amplitude-droop

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 digital demodulator produces time-domain data. If IQ RefTime is selected, the VSA displays the I/Q reference signal in the time domain. The data can be displayed in many formats including IQ Polar diagrams, Constellation diagrams, Eye diagrams and more (see Selecting a Trace Format)

If normalization is OFF, the VSA displays the instantaneous magnitude. If normalization is ON, the VSA scales the IQ reference trace to map it onto the unit circle, which yields a unitless y-axis.

Parameter Interaction

The following parameters affect how the VSA displays the I/Q reference signal:

• The Result Length parameters (Automatic and Manual) determine the measurement acquisition time, which in turn, determines the length of the displayed trace data.

• The Measurement Offset/Interval parameters limit the displayed trace data.

See Also

Available Trace Data (802.11b/g DSSS/CCK/PBCC)

IQ Meas Time (802.11b/g DSSS/CCK/PBCC)