Making a Channel Quality Measurement

This topic describes how to configure the VSA to make a channel quality measurement.

Overview

You must manually configure the VSA Channel Quality Measurement feature to measure your signal. To do so, configure the parameters in the Channel Quality Properties dialog (Stimulus Definition, Analysis, and Compensation tabs).

Signal Setup

Before selecting the Channel Quality measurement mode, make sure that the input signal is correctly captured by the analyzer. Specify the VSA basic signal measurement setup parameters so that the input signal is fully captured including; the center frequency, span, input range, etc.. You can use the Spectrum and Time traces to verify that the signal of interest is properly captured.

Demo Signals

To use a demo signal, click File > Recall > Recall Demo >, navigate to the "%PROGRAMFILES%\Keysight\89600 Software <ReleaseVersion>\89600 VSA Software\Help\Signals\CQM" folder and select a Demo File.

Configuring the Measurement

Step 1 - Specify the signal parameters

To begin, select the Channel Quality measurement type, click MeasSetup > Measurement Type > General Purpose > Channel Quality. Then open the Channel Quality Properties dialog by clicking MeasSetup > Channel Quality Properties... .

Loading a demo signal file like"cqm-mpath.htm" will auto-select the Channel Quality measurement type.

A multitone stimulus signal is required to use the Channel Quality measurement. If a different type of stimulus signal is required, use a different measurement technique. For example:

Single carrier modulated signal (QPSK Quadrature phase shift keying, etc.): use Digital Modulation analysis or Custom IQ analysis, and adaptive equalization.
OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. modulated signal: use a standard-specific measurement (like WLAN WLAN - Wireless Local Area Network: A system that includes the distribution system (DS), access points (APs), and portal entities. It is also the logical location of distribution and integration service functions of an extended service set (ESS). A WLAN system contains one or more APs and zero or more portals in addition to the DS. modulation analysis), or Custom OFDM analysis, and look at the channel frequency response results.
Noise or other arbitrary waveform stimulus: use vector mode measurements with multi-channel hardware, math functions, or stimulus/response graphing.

Step 2 – Configure the measurement parameters

Set up the measurement parameters in the Channel Quality Properties dialog.

Stimulus Definition Tab

Create a stimulus definition (usually to match your multitone input signal).

Recall from File.../Save to File... selects an existing stimulus definition or save the current stimulus definition.
Tone Spacing sets the spacing between tones (kHz kiloHertz: A radio frequency measurement (one kilohertz = one thousand cycles per second).).
Number of Tones sets the number of tones in the stimulus.
Update updates the stimulus tones from the current measurement. The Active/Inactive, Magnitude, Phase, and Active Tone Threshold properties determine what properties of the tone definitions are updated.

Analysis Tab:

Configure the channel response analysis.

Copy Response to copies the channel response for the selected Data Registers.
- Ch[N] selects the Data Register path (Dx) for the channel response to be copied for each measurement channel. Setting this to "None" implies no copy will be performed for the associated measurement channel.
Analysis Interval sets the amount of time (in seconds) to process for each channel quality measurement.

More data will be acquired than this to account for settling and for the compensation smoothing interval.

Compensation Tab:

Configure the channel response measurement to adjust the analysis based on anticipated or discovered differences between the stimulus signal definition and the measured response waveforms.

Timing Adjust sets the difference (in ppm) between the sample clock of the measured signal and the sample clock expected from the stimulus definition.
Coarse Frequency Estimation attempts to do a frequency offset compensation prior to the channel quality measurement.
Frequency Offset corrects the acquired time data for frequency offset before calculating the channel response.
Phase Drift corrects the acquired time data for phase drift within the Analysis Interval before calculating the channel response.
Gain Drift corrects the acquired time data for gain drift within the Analysis Interval before calculating the channel response.
Smoothing Interval sets the drift (phase/gain) compensation smoothing interval.

Step 3 – Configure the trace data

Configure the trace data to measure the performance of your signal. Available traces include (but not limited to):

Spectrum - Displays the averaged Instantaneous Spectrum.
Ch Frequency Response - Frequency-domain complex-valued trace for channel quality measurements. Includes analysis results like group delay, phase linearity, and magnitude linearity.
Stimulus Definition - Frequency-domain trace showing the currently active multitone definition, including the phase and magnitude of tones in the multitone definition.
Summary - Scalar metrics from the channel quality measurement analysis.
Tracking Response - Complex-valued time trace to identify variation in gain and phase drift through the analysis interval. Useful to identify impairments such as AM Amplitude Modulation - CW modulation using amplitude variation in proportion to the amplitude of the modulating signal. Usually taken as DSB-LC for commercial broadcast transmissions and DSB-SC for multiplexed systems./PM/FM Frequency Modulation.

Step 4 – Make adjustments

Adjust the measurement parameters in the Channel Quality Properties dialog. Adjust the analysis based on anticipated or discovered differences between the stimulus signal definition, and the measured response waveforms.